Prostaglandin derivates as ocular hypotensive agents

PII: S1350-9462(97)00003-7

Prostaglandin Derivates as Ocular Hypotensive Agents Albert Alm

Department of Ophthalmology, University Hospital, Uppsala University, S-701 85 Uppsala, Sweden CONTENTS Abstract

292

1. Background 292 1.1. A brief prostaglandin history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 1.1.1. Discovery of prostaglandins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 1.1.2. Prostaglandin receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 1.1.3. Prostaglandins and the eye . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 1.2. Animal experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 1.2.1. E€ects on prostaglandins on intraocular pressure in experimental animals . . . . . . . . . . . 294 1.2.2. Mechanism of action. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 2. Early clinical experience with natural prostaglandins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 2.1. PGF2a-isopropyl ester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 2.2. PGD2 and PGE2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 3. Latanoprost 296 3.1. Preclinical studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 3.1.1. Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 3.1.2. Receptor anity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 3.1.3. E€ects on blood ¯ow and vascular permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 3.1.4. Mechanism of action. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 3.2. Clinical studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 3.2.1. Short-term studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 3.2.1.1. Pharmacokinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 3.2.1.2. E€ect/side-e€ect separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 3.2.1.3. Mechanism of action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 3.2.1.4. Dose and dose regimen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 3.2.1.5. Combination with other drugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 3.2.1.5.1. Beta-adrenergic-receptor blockers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 3.2.1.5.2. Cholinergic agonist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 3.2.1.5.3. Adrenergic agonists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 3.2.1.5.4. Carbonic anhydrase inhibitors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 3.2.2. Long-term studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 3.2.2.1. Ecacy compared to timolol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 3.2.2.2. Ocular side-e€ects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 3.2.2.2.1. Ocular irritation and conjunctival vasodilatation . . . . . . . . . . . . . . . . . 304 3.2.2.2.2. Blood±ocular barrier permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 3.2.2.2.3. Iris pigmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 3.2.2.2.4. Other ocular side-e€ects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 3.2.2.3. Systemic side-e€ects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 Progress in Retinal and Eye Research Vol. 17, No. 3, pp. 291 to 312, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 1350-9462/98/$19.00 + 0.00

292

A. Alm

3.2.2.3.1. Pulmonary e€ects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 3.2.2.3.2. Cardiovascular e€ects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 3.2.2.3.3. Laboratory values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 4. Unoprostone

308

5. Future directions References

308 309

AbstractÐLow doses of naturally occurring prostaglandins reduce the intraocular pressure (IOP) in many species. Species di€erences do occur both in terms of eciency and mechanism of action, and also among the di€erent prostaglandins. Among the prostaglandins mainly PGF2a has been tested in human eyes. Although it is an e€ective ocular hypotensive drug it is not clinically useful due to pronounced ocular side-e€ects, mainly conjunctival hyperemia and irritation, at doses that produce a maximal e€ect on IOP. Modi®cation of the drug has resulted in two analogues that are now in clinical use, latanoprost and unoprostone. In long-term studies latanoprost, when applied as a once-daily dose of a 0.005% concentration, reduces IOP at least as e€ectively as adrenergic beta-receptor blockers. The reduction of IOP is due to increased out¯ow. This takes place mainly, or exclusively, through the uveoscleral routes, thus introducing a new pharmacological principle for the treatment of glaucoma. The drug reaches systemic concentrations that are below the level expected to stimulate FP-receptors outside the eye and it is rapidly eliminated with a half-life in plasma of 17 minutes, which explains why the clinical trials have not revealed any systemic side-e€ects with latanoprost. The most frequent sidee€ect observed with latanoprost is an increased pigmentation of the iris mainly in eyes with irides that are already partly brown. This e€ect is seen with several naturally occurring prostaglandins and is due to stimulation of melanin production in the melanocytes of the iridial stroma. No structural changes of the melanocytes have been observed in studies performed both in vivo and in vitro. The mechanism of action for unoprostone is the same as for latanoprost. No e€ect on iris colour has been reported for unoprostone but so far there is limited experience with the drug in eyes with a mixed iris colour. # 1998 Elsevier Science Ltd. All rights reserved

1. BACKGROUND 1.1. A Brief Prostaglandin History 1.1.1. Discovery of prostaglandins

The main purpose of this review is to report present clinical experience with prostaglandin analogues. A brief introduction to these new candidates for the treatment of glaucoma may serve as a useful background. The prostaglandins (PGs) belong to a group of local hormones, the eicosanoids, named after their common 20-carbon skeleton. There are a number of naturally occurring PGs synthesised from arachidonic acid. The ®rst indication that these local hormones existed was reported by Kurzrok and Lieb (1930) who found that human seminal ¯uid contracted uterine muscles. The presence of a substance in human seminal ¯uid that could contract smooth muscles was later veri®ed by Goldblatt (1933, 1935) and von Euler (1934). von Euler (1934) described the presence of two lipidic substances in human seminal ¯uid, one water-soluble and one lipid-soluble. The substances were given the

names prostaglandin E (PGE) and prostaglandin F (PGF) based on the assumption that they were produced by the prostate gland and on their solubility in ether and phosphate ("fosfat" in Swedish) respectively. It has later been found that the two PGs were not produced by the prostate gland but by the seminal vesicles and that PGs are released in many tissues where they act as local hormones with a wide range of biological activities. They are not metabolized locally but released into the circulation and then rapidly inactivated mainly during their passage through the lung (Ferreira and Vane, 1967). The PGs constitute a family of substances and the naturally occurring PGs include PGF2a, PGE2, PGD2, and PGI2 (prostacyclin). TXA2 (thromboxane) is usually included among the PGs although it has a slightly di€erent ring structure. The last letter in the abbreviation of the naturally occurring prostaglandins (D, E, and F) refer to the ring structure and the number, e.g. PGE2, to the number of unsaturated double bonds in the side-chains. The various PGs have strikingly di€erent e€ects among themselves and in di€erent tissues. In the eye the PGs have tra-

Prostaglandin derivates as ocular hypotensive agents

ditionally been regarded as potent miotics and as key players in the in¯ammatory process but it is now known that they are miotics only in some species and that the full in¯ammatory response involves a large number of substances, including the leukotrienes and other lipoxygenase products of arachidonic acid metabolism, several chemically unrelated peptides, and sensory nerves. 1.1.2. Prostaglandin receptors

The di€erent naturally occurring PGs act on a corresponding family of prostanoid receptors. All natural PGs have anity to more than one of the prostanoid receptors which means that selective agonists or antagonists are needed to clarify the biological activity of the respective receptor in di€erent tissues. At present there are only a few such selective drugs but those that have been developed and tested in the eye for their ocular hypotensive e€ect have demonstrated the importance of selectivity. Compounds based on PGF2a, but more selective for the FP-receptor, have a better therapeutic pro®le than the mother compound while some compounds based on other naturally occurring PGs have produced mainly ocular irritation and even increased IOP. The accepted classi®cation of PG-receptors (Coleman et al., 1994) and the rank of anities for some naturally occurring PGs are shown in Table 1. 1.1.3. Prostaglandins and the eye

The rabbit eye is unusually prone to an in¯ammatory response. Even comparatively mild trauma will elicit hyperemia, break down of the blood± ocular barrier with protein leakage into the anterior chamber, and an increased intraocular pressure (IOP). In the mid-®fties Ambache (1955, 1957) could demonstrate that an extract from the rabbit iris contracted smooth muscles and induced miosis in the cat eye. It was assumed that the extract included a substance, irin, that was responsible for the smooth muscle contraction. It was later shown that this crude extract from the iris included, among other things, at least two di€erent natural PGs, PGF2a (AÊnggaÊrd and

293

Table 1. Relative binding anities for naturally occuring prostaglandins to receptors of the DP, EP, and FP subtypes Receptor:

Relative binding anities

DP EP1 EP2 EP3 FP

PGD2 >> PGE2, PGF2a PGE2 > PGE1 > PGF2a > PGD2 PGE1 = PGE2 >> PGF2a PGD2 PGE1 = PGE2 > PGE2a > PGD2 PGF2a > PGF1a > PGD2 > PGE2

Samuelsson, 1964) and PGE2 (Ambache et al., 1966; Ambache and Brummer, 1968). It is now known that PGs are potent miotics only in some species. In fact, there is a large species variety of the miotic e€ect of endogenous substances. Thus PGs are potent miotics in cats (Waitzman and King, 1967; Eakins, 1970) and dogs (Bito et al., 1989). In rabbits substance P (Bill et al., 1979; Mandahl and Bill, 1981) and the C-terminal calcitonin gene-related peptide fragment CGRP(8±37) (Andersson and AlmegaÊrd, 1993) contract the iris sphincter and in primates cholecystokinin is a miotic agent (Bill et al., 1990). Thus, it is not surprising that non-steroidal anti-in¯ammatory agents failed to prevent surgical miosis in vitreoretinal (Smiddy et al., 1990) and cataract surgery (Kervick and Johnston, 1990). PGs are not metabolised in the eye due to lack of the enzyme responsible for the ®rst step of PG inactivation, PG dehydrogenase (Eakins, 1976). Instead, inactivation of intraocular PG activity is achieved by removal of PGs from the eye by outward-directed active transport systems for inorganic anions in the blood±ocular barriers (Bito and Salvador, 1972). During in¯ammation of the anterior segment of the eye the eciency of this transport system is reduced (Bito, 1974). It has been suggested that this characteristic of the transport system may explain the cystoid macular edema (CME) in aphakic eyes (Miyake et al., 1989). An inhibition of PG removal due to a lowgrade post-operative in¯ammation might then permit PGs to di€use through the vitreous body and reach the retina and induce vascular changes resulting in an edema. This hypothesis has been supported by studies on the e€ect of ketorolac tromethamine 0.5% ophthalmic solution on the e€ect of chronic aphakic or pseudophakic cystoid

294

A. Alm

macular edema, where visual acuity was signi®cantly improved in treated eyes compared to placebo-treated eyes (Flach et al., 1991). Thus it seems likely that PGs play a role in CME but it is not clear whether CME is a direct e€ect of the PGs, which PGs or prostanoid receptors that are involved, or why this e€ect is concentrated to the macular area without similar e€ects in the remaining part of the retina. 1.2. Animal Experiments 1.2.1. E€ects on prostaglandins on intraocular pressure in experimental animals

Although there is a marked species variation for the ocular e€ects of di€erent PGs, a reduction of the IOP is a common e€ect for many of them. The PG-analogues used for glaucoma treatment today are based on PGF2a and they reduce IOP by increasing uveoscleral ¯ow (see below). Studies in experimental animals indicate that some prostaglandins have other e€ects on aqueous humor dynamics than the PGF2a-derivates now used. Thus some insight into the studies performed on experimental animals is valuable since they demonstrate that present PG-analogues may not exploit the full potential of PGs as ocular hypotensive agents. In the seventies the rabbit was the main animal model for studies of the e€ect of PGs on IOP. The initial studies showed little promise. Thus topical application of 0.5±50 mg PGE1 to the rabbit eye caused a dose-dependent increase in IOP, with the expected hyperemia and break down of the blood±aqueous barrier (Kass et al., 1972). However, Camras et al. (1977) managed to show that a low dose, 5 mg, of PGF2a reduced IOP in the rabbit eye for several hours. Subsequent studies have con®rmed that PGF2a (Lee et al., 1984) as well as PGE2, PGD2 (Woodward et al., 1989a), PGE3, and PGD3 (Kulkarni and Sririvasan, 1985) reduce IOP in the rabbit eye. PGF2a and PGE2 also reduce IOP in normotensive cats, dogs, and monkeys (Stern and Bito, 1982; Lee et al., 1984; Camras et al., 1987; Crawford et al., 1987; Groeneboer et al., 1989), as well as in glaucomatous eyes of experimental

animals (Camras and Bito, 1981; Wang et al., 1990; Gum et al., 1991). Considerable species di€erences have become apparent both with respect to the mechanism of action of PGs on aqueous humor dynamics in experimental animals (see below) and with respect to the overall e€ect on IOP. Thus the e€ect of PGF2a in rabbits lasts for only a few days and then the e€ect on IOP is gradually lost while the e€ect on IOP is maintained in cats and monkeys (Bito et al., 1983). In rabbits and monkeys, but not in cats, PGF2a produces a biphasic response with an initial hypertensive phase followed by a prolonged reduction of the IOP (Lee et al., 1984; Crawford et al., 1987). An initial ocular hypertensive phase is also seen in rabbits with PGE2 and seems to be mediated by platelet activating factor (Jager et al., 1993). Such e€ects, and the species di€erences reported below, entail an obvious problem when screening various PGs or PG-analogues for their potential use as glaucoma drugs. The species di€erences observed are as rule not absolute and in order to obtain a drug with minimal sidee€ects several animal models will be required.

1.2.2. Mechanism of action

The mechanism by which prostaglandins reduce IOP is not the same among di€erent species, perhaps due to a combination of di€erent prostaglandin e€ects and di€erences in the anatomy of the out¯ow routes. Neither PGE1, PGE2, nor PGF2a has any e€ect on out¯ow through the trabecular meshwork in monkeys (Kaufman, 1986). This is important information on the mechanism of action of PGs since the various parts of the out¯ow can be determined with precision in the monkey eye, unlike the human eye. The lack of e€ect of PGF2a on conventional out¯ow in the monkey eye has been con®rmed in several studies which have also shown that PGF2a does not reduce aqueous humor ¯ow which strongly suggests that PGF2a reduces IOP mainly if not exclusively by increasing the uveoscleral out¯ow (Crawford et al., 1987; Crawford and Kaufman, 1987; Nilsson et al., 1989; Gabelt and Kaufman, 1989; Gabelt and Kaufman, 1990).

Prostaglandin derivates as ocular hypotensive agents

In other species other mechanisms of action and other prostanoid receptors are involved. Increased facility of out¯ow through the conventional trabecular route has been observed for PGF2a in rabbits (Poyer et al., 1992) and for PGA2 in cats (Toris et al., 1995). In rabbits stimulation of the EP3-receptor is more e€ective than stimulation of the EP2, FP, or TP-receptor in reducing IOP (Waterbury et al., 1990), and the e€ect of PGF2a-analogues on IOP was even reported to be negatively correlated to FP-receptor stimulation (Woodward et al., 1989b). Also reduction of aqueous ¯ow has been reported for PG-analogues. Thus the main e€ect on IOP induced by PGD2 in rabbits is due to reduced aqueous ¯ow (Goh et al., 1989). In monkeys, on the other hand, the DP-receptor agonist SQ27986 induced an initial ocular hypertensive phase without any following reduction of IOP (Crawford et al., 1992), and the experience with PGD2-analogues in human eyes has also been disappointing (see below).

2. EARLY CLINICAL EXPERIENCE WITH NATURAL PROSTAGLANDINS 2.1. PGF2a-Isopropyl Ester

The ®rst study of the e€ect on PGs on the human eye was reported by Giu€re (1985). He used 200 mg of the tromethamine salt of PGF2a which reduced IOP in normotensive eyes signi®cantly. The e€ect lasted from 4 to 24 hr after application of the drug with a maximum of about 4 mm Hg after 7 hr. However, the drug caused marked super®cial irritation with conjunctival hyperemia, ocular pain and even headache and Giu€re concluded that these side-e€ects constituted a "serious handicap" that "could discourage their use in chronic therapy" (1985). It would soon become apparent that this evaluation was correct. Lee et al. (1988) reported similar experience with the tromethamine salt of PGF2ain the dose range 62.5±250 mg, and experience with the pro-drug, PGF2a-isopropyl ester, which can be used in much lower doses (see below) has not changed Giu€reÂ's assessment.

295

The lipid solubility of the tromethamine salt is low and a high dose must be used to ensure adequate penetration into the eye. Esteri®cation of the carboxyl group of PGF2a increases the lipid solubility and the penetration into the eye (Bito and Baroody, 1987) and PGF2a-isopropyl ester (PGF2a-IE) was found to be a much more potent drug in cat and primate eyes (Bito, 1984). The ester is hydrolyzed to PGF2a during its passage through the corneal epithelium by butyryl-cholinesterase and carboxyl esterase (Camber et al., 1986; Cheng-Bennett et al., 1994). Concomitant use with a cholinesterase inhibitor such as physostigmine does not signi®cantly a€ect this de-esteri®cation (unpubl. obs.). The potency of this new pro-drug was con®rmed in the ®rst study on normal human eyes (Villumsen and Alm, 1989). 2.5± 10 mg reduced IOP signi®cantly. With 10 mg the e€ect lasted for 24 hr with a maximal reduction of almost 6 mm Hg 8 hr after dosing. However, this ®rst study also showed that esteri®cation of the drug was not enough to cause a clinically useful separation between e€ect and side-e€ects. The nature of the ocular side-e€ects was the same as with the tromethamine salt and the degree of ocular irritation with the 10-mg dose was de®nitely clinically unacceptable. In a subsequent study 0.5 mg of PGF2a-IE was applied twice daily to previously untreated glaucoma patients (Villumsen et al., 1989). It reduced IOP with about 20% with modest side-e€ects. Similar e€ects on the IOP and side-e€ects were found in two other studies on PGF2a-IE, one in normal eyes (Kerstetter et al., 1988), and one in patients (Camras et al., 1989). Although these studies showed that a clinically desirable e€ect on IOP with only modest side-e€ects could be achieved with PGF2a-IE it was obviously unsatisfactory to use a dose at the lower range of the dose±response curve. Esteri®cation of the drug made it possible to reach a good e€ect on the IOP at much lower doses than the tromethamine salt, but to what extent the e€ect/side-e€ect ratio was reduced has never been tested in a comparative study. However, it seemed reasonable to continue in this direction and a di-ester of PGF2a with a second ester at C-15, 15-propionate-PGF2a-IE, was also tested in normal eyes (Villumsen and Alm, 1990a). The idea was that a second ester

296

A. Alm

would slow down the hydrolysis and reduce the side-e€ects presumably induced by receptors located on the surface of the eye. However, we could not ®nd any di€erence in the e€ect/sidee€ect pro®le between the two esters and this approach was abandoned in favor of an attempt to modify the molecule in order to obtain a more selective FP-agonist than PGF2a. This seemed a reasonable approach since most of the side-e€ects (vasodilatation and break down of the barrier) are not mediated by the FP-receptor. 2.2. PGD2 and PGE2

Since PGD2 as well as PGE2 reduced IOP in experimental animals (see above) these drugs, or analogues, have also been tested in human eyes. The response of the human eye to these prostanoids were very similar. At 50 mg PGD2, as well as the analogue BW245C at 2.5 mg, caused an initial increase in the IOP of normal eyes of almost 4 mm Hg and the following ocular hypotensive phase was modest, 1±2 mm Hg (Nakajima et al., 1991). Flach and Eliason (1988) reported a similar experience with a PGE2-analogue. Both drugs also caused marked ocular irritation. 3. LATANOPROST 3.1. Preclinical Studies

Fig. 1. Chemical structures of PGF2a, PGF2a-IE, latanoprost and unoprostone.

3.1.1. Structure

3.1.2. Receptor anity

Latanoprost(codenamePhXA41;13,14-dihydro17-phenyl-18,19,20-trinor-PGF2a-isopropyl ester) is a PGF2a-isopropyl ester-analogue with a phenyl ring substituted for carbons 18-20 in the omega chain (Stjernschantz and Resul, 1992). The double bond between carbons 13 and 14 has been saturated. Its structure is shown in Fig. 1. Latanoprost is the result of an extensive search for a suitable potent and selective FP-agonists. Phenyl-substituted analogues with shorter or longer omega chains were found to be less active and less selective for the FP-receptor than the 17phenyl substituted analogue (Stjernschantz and Resul, 1992).

Latanoprost is a more selective agonist for the FP-receptor than PGF2a, and it has only marginal e€ect on most of the other PG-receptors (Stjernschantz et al., 1995). The receptor pro®les of PGF2a and latanoprost are presented in Table 2. In order to stimulate other PG-receptors, mainly the EP1-receptor, latanoprost has to be given in a concentration that is at least a thousand fold compared to that which is needed to stimulate the FP-receptor. The search for a more selective FP-agonist turned out to be the right approach and the selectivity for the FP-receptor is the most likely explanation for the e€ective sep-

297

Prostaglandin derivates as ocular hypotensive agents Table 2. Receptor pro®le of PGF2a and latanoprost. EC50 values in moles/l. 6.7*10 3.8*10-7 1.4*10-5 1.1*10-7 3.1*10-3 2.9*10-5

Latanoprost 3.6*10-9 6.9*10-6 3.6*10-4 1.7*10-5 >1.0*10-2 1.1*10-4

8 7 2

6 5 4

1

3

Reprinted with permission from Stjernschantz et al., 1995

2

aration between e€ect and side-e€ects obtained with latanoprost (see also Fig. 2).

0

Hypermia

FP EP1 EP2 EP3 DP/IP TP

-9

3

9

IOP reduction mm Hg

PGF2a

10

1 0 Placebo

0.3 µg

1.0 µg

3.0 µg

10.0 µg

log (dose + 1)

3.1.3. E€ects on blood ¯ow and vascular permeability

Topical application of PGF2a-IE caused a marked vasodilatation in the conjunctiva. It also induced a short initial ocular hypertension (Villumsen and Alm, 1989). The probable reason for the initial hypertensive phase is a dilatation of intraocular vessels. Determination of ocular blood ¯ow with labelled microspheres in monkeys have shown that PGF2a causes a marked increase in blood ¯ow through the anterior uvea (Stjernschantz et al., 1989). The e€ect of latanoprost on ocular blood ¯ow has also been determined in monkeys with labelled microspheres. 6 mg applied topically as a single doseÐcorresponding to about 4 times the clinical doseÐhad no e€ect on blood ¯ow through any of the intraocular tissues (Stjernschantz et al., 1995). Another important aspect on the clinical use of prostaglandins is their possible e€ect on vascular permeability. In cynomolgus monkeys the same dose, 6 mg as a single topical dose, had no e€ect on the permeability to albumin of the vessels of the anterior uvea (Stjernschantz et al., 1995). These studies con®rm the clinical experience that the increased selectivity has indeed markedly improved the e€ect/side-e€ect pro®le of the drug compared to PGF2a and justi®ed the assumption that most of the side-e€ects are mediated by other prostanoid receptors than the FP-receptor.

Fig. 2. The e€ect on IOP and conjunctival hyperemia of four single doses of PhXA34 and placebo. IOP reduction is presetned as the IOP before treatment less the IOP during treatment. Conjunctival hyperemia was estimated from standard photographs and is presented as the maximal hyperemia score during treatment less the hyperemia score before treatment. Reprinted with permission from Villumsen, J. and Alm, A. (1992) PhXA34 prostaglandin analogue. E€ect on intraocular pressure in patients with ocular hypertension. Br. J. Ophthalmol. 76, 214-217.

3.1.4. Mechanism of action

The fact that latanoprost retained the hypotensive e€ect on the eye is of course a strong indication that it has the same e€ect on uveoscleral out¯ow as PGF2a. That this is the case has also been veri®ed in studies on monkeys where uveoscleral ¯ow was determined by the technique described by Bill (1965). These studies showed that latanoprost, like PGF2a, has a marked e€ect on uveoscleral out¯ow in monkeys. Topical application of 3 mg daily for 5 days almost doubled uveoscleral out¯ow whereas it had no e€ect on conventional trabecular out¯ow (Stjernschantz et al., 1995). The results are presented in Table 3.

3.2. Clinical Studies 3.2.1. Short-Term studies

Short-term studies are performed mainly to evaluate pharmaco-kinetics, to decide the dose and the dose-regimen, to con®rm previous information on

298

A. Alm Table 3. E€ect of latanoprost on aqueous humor out¯ow in monkeys after topical administration of 3 mg once daily for 5 days. (Mean + SEM, n =6) Variable Trabecular out¯ow (ml/min) Uveoscleral out¯ow (ml/min) Total out¯ow (ml/min) Out¯ow facility (ml/min/mm Hg)

Exp eye

Control eye

0.43 2 0.11 0.59 2 0.14** 1.02 2 0.16 0.13 2 0.02

0.48 2 0.07 0.37 2 0.12 0.86 2 0.15 0.12 2 0.02

** p <0.01 Reprinted with permission from Stjernschantz et al., 1995

mechanism of action, and to detect any alarming side-e€ects. Such information is needed to design the long-term studies necessary to get information on the usefulness of the drug compared to existing therapeutic alternatives. In the following the term short-term studies is used for single-dose studies and studies with repeated application for up to at the most 2 weeks. 3.2.1.1. Pharmacokinetics In healthy volunteers the fate of 3 mg 3H-labelled latanoprost applied topically as an eye drop provided the following information: 77±88% is absorbed systemically, 90% is bound to plasma proteins within 3 min. A maximum plasma concentration of 64 pg/ml is reached within 40 min, and the drug and/or its metabolites is rapidly eliminated with a half-life of 17 minutes in plasma. 88% is eliminated by the kidneys, essentially all of it within 24 hr, and 15% through faeces with a more prolonged elimination time indicating some biliary excretion of drug or metabolites (<0.09% 144±168 hr post-dose). Relevant corresponding ®gures for an i.v. infusion were similar (SjoÈquist et al., 1994). Peak plasma levels 5±60 min post-dose in 10 patients treated in one or both eyes with latanoprost for at least one year were very low, below 70 pg/ml (unpubl. obs.), and no latanoprost activity could be detected with radio-immunoassay in plasma samples taken before applying the drug, that is 12±24 hr after the previous dose con®rming that there is no accumulation of the drug during longterm treatment. Analysis of aqueous concentrations of latanoprost applied at various times before cataract surgery have shown that latanoprost reaches a peak in aqueous about 2±3 hr after application

(SjoÈquist et al., 1997). The peak concentration was about 55 ng/ml. These ®gures can be compared to the anity of various prostanoid receptors presented in Table 2. The concentration of latanoprost in the bottle, 0.005%, is about 10ÿ4 M. The peak concentration in aqueous is about 10ÿ7 M, that is well within the range for stimulation of FP-receptors but below the range for stimulation of other prostanoid receptors. The peak concentration in plasma, around 10ÿ10 M, is below even the range for stimulation of FP-receptors. 3.2.1.2. E€ect/Side-E€ect separation In the ®rst studies the epimeric mixture, code name PhXA34, was used. In doses corresponding to 0.5±5 mg latanoprost it reduced IOP with 2± 4 mm Hg in normal human eyes 6±10 hr after a single dose (Alm and Villumsen, 1991) with only a slight conjunctival hyperemia after the highest dose. With repeated administration of the highest dose once daily for 7 days mean IOP was below 9 mm Hg 12 hr post dose, and a signi®cant e€ect on IOP was observed up to 144 hr after the last dose (Alm and Villumsen, 1991). This study, as well as two other studies (Ziai et al., 1993; Toris et al., 1993), con®rmed that neither latanoprost nor PhXA34 reduces aqueous ¯ow. A small but statistically signi®cant increase in out¯ow facility was found, but not large enough to explain the reduction in IOP. As out¯ow through the uveoscleral route may in¯uence clinical tonography the observed increase of out¯ow facility may at least partly be due to increased facility of the uveoscleral out¯ow routes. A dose response study of the e€ect of PhXA34 on patients with ocular hypertension (Villumsen and Alm, 1992) showed a good separation of the

Prostaglandin derivates as ocular hypotensive agents

Fig. 3. IOP (Mean and SEM) at 4 pm on baseline and at 2 week intervals during treatment for 12 weeks. Both groups received 0.5% timolol twice daily at baseline and througout the study. After the baseline measurements 0.006% latanoprost was added once daily (square) or twice daily (triangle). Reprinted with permission from Alm et al. (1995) Latanoprost administered once daily caused a maintained reduction of intraocular pressure in glaucoma patinets treated concomitantly with timolol. Br. J. Ophthalmol. 79, 12-16.

dose±response curves for e€ect on IOP and conjunctival hyperemia (Fig. 3). A maximal reduction of IOP (32% from baseline) was obtained with 3 mg of PhXA34. This dose corresponds to a 30-ml drop of the 0.005% solution of latanoprost used clinically. A signi®cant conjunctival hyperemia was seen only at a dose of 10 mg. A dosedependent IOP reduction lasting at least 12 hr after application of PhXA34 to normal eyes or eyes with ocular hypertension was con®rmed in two other studies (Camras et al., 1992; Hotehama and Mishima, 1993). In another study Racz et al. (1996) showed that latanoprost is e€ective also at night, which may be an important advantage considering the known lack of e€ect on aqueous ¯ow by adrenergic beta-receptor blockers at night (McCannel et al., 1992). 3.2.1.3. Mechanism of action There is no clinical technique for direct determination of uveoscleral ¯ow, but from one study uveoscleral out¯ow was calculated from measurements of other parameters of aqueous humor dynamics at two pressure levels (Toris et al., 1993). The results support the assumption that increased uveoscleral out¯ow is the main mechanism of action also in the human eye. The exact

299

mechanism behind the increased uveoscleral ¯ow is not known. The ciliary muscle of cynomolgus monkeys contains FP-receptor mRNA and protein (Ocklind et al., 1996), and binding sites for EP2- and FP-receptors exist in human ciliary muscles (Matsuo and Cynader, 1992), although the dominant prostanoid receptor was found to be of the EP2 subclass (Matsuo and Cynader, 1993). The fact that latanoprost is almost twice as e€ective as the epimeric mixture PhXA34 also argues for a receptor-mediated e€ect. Two mechanisms have been proposed; relaxation of the ciliary muscle or changes in the extracellular matrix of the ciliary muscle. PGF2a relaxes ciliary muscle of the rhesus monkey (Poyer et al., 1995), and short-term treatment with large doses of PGF2a causes a dilatation of the intramuscular spaces of the ciliary muscle of cynomolgus monkeys (LuÈtjen-Drecoll and Tamm, 1988), but such changes have not been observed with latanoprost (Svedbergh and Forsberg, 1993). To what extent there is a structural change of the ciliary muscle in the human eye is not clear but it is known that the e€ect on IOP is reversible. Withdrawing latanoprost after 1 year's treatment will cause the IOP to reach pre-treatment levels within 3 weeks (unpubl. obs.) 3.2.1.4. Dose and dose regimen In the Phase III clinical trials 0.005% latanoprost has been applied once daily, as a rule in the evening. The choice of this dose regimen is based on the results of several studies. As a rule the ecacy of the drug has been based on the "diurnal IOP", a term used to indicate the mean of three measurements made at 4-hr intervals during the day. In the single-dose studies reported above (Villumsen and Alm, 1992; Hotehama and Mishima, 1993) a concentration corresponding to about 0.005% latanoprost produced a maximal e€ect with little side-e€ects, while lower concentrations were less e€ective. The maximal e€ect on IOP did not appear until 6±10 hr after application of the drug and a signi®cant e€ect was retained for at least 12 hr. The dose±response relationship for repeated doses was tested in a study where patients with ocular hypertension were treated for one month with three concentrations of latano-

300

A. Alm

prost; 0.0035, 0.006, or 0.0115% (Alm et al., 1993). The eye drops were administered twice daily. The e€ect was evaluated by comparing the diurnal IOP at baseline and after 2 and 28 days of treatment. All three doses reduced IOP signi®cantly better than placebo but the di€erence between the three doses was small. Thus this study did not give clear-cut information about the optimal concentration of latanoprost, but an evaluation of all dose±response studies performed with latanoprost has provided information that gives strong support to the conclusion that 0.005% is just at the top of the dose±response curves for single as well as repeated administration. However, the one-month study (Alm et al., 1993) showed that there was a short-term partial loss of the e€ect during the ®rst two weeks of treatment. Thus on day 2 the reductions of the IOP were 32±38% for the three concentrations of latanoprost, and 19±22% on day 28. From another study it was clear that the escape observed in the above study might be due to the dose regimen; twice-daily applications of latanoprost. Nagasubramanian et al. (1993) compared the e€ect of 0.006% latanoprost applied once or twice daily (in the evening). On the second day of treatment mean diurnal IOP was reduced from an untreated level of about 25 mm Hg, by 30, and 36% with once- and twice-daily latanoprost respectively. After two weeks of treatment the ecacy was reversed. Once daily caused a 36% reduction compared to 28% with twice daily. Thus given once daily the e€ect was slightly improved from day 2 to day 14, while the reverse was seen with twice-daily applications. This observation was con®rmed in a study where 0.006% latanoprost was added to timolol in glaucoma patients (Alm et al., 1995a). Latanoprost was applied once or twice daily for 3 months. Throughout the study latanoprost once daily reduced IOP more eciently than latanoprost twice daily at all time points from the ®rst measurement 2 weeks after treatment start. The mean diurnal IOP at the last examination was signi®cantly lower in the once-daily group compared to the twice-daily group, 15.7 and 18.0 mm Hg respectively, although they started at almost identical IOP levels, 24.8 and 24.9 mm Hg (Fig. 3).

From the above studies it is clear that once-daily application of a concentration of 0.005% latanoprost is the optimal dose regimen. There are at least two possible explanations for the observation that twice-daily applications are less e€ective. In the above studies latanoprost was applied in the evening, and the e€ect was determined from determinations of IOP during the day (between 8 am and 5 pm). One can speculate that latanoprost has a dual e€ect on aqueous humor dynamics. A small increase in aqueous ¯ow lasting e.g. 6±8 hr would blunt some of the early e€ect of latanoprost on IOP and explain why applying a drop also in the morning would cause a less e€ective pressure reduction during the day. In monkeys Crawford et al. (1987) and Nilsson et al. (1989) found a small but statistically signi®cant increase in aqueous ¯ow with PGF2. Studies in humans have not shown a signi®cant e€ect on aqueous ¯ow but the tendency in those studies has been towards a small increase in ¯ow (Alm and Villumsen, 1991; Ziai et al., 1993; Toris et al., 1993). An increase in aqueous ¯ow of about 15% would have been enough to explain the di€erence in diurnal IOP reduction between once- and twice-daily applications of latanoprost in the above studies (Nagasubramanian et al., 1993; Alm et al., 1995a). Still, this explanation is an unlikely one. In a recent study (unpubl. obs.) we found no di€erence in aqueous ¯ow during the day between evening and twice-daily applications of latanoprost. Thus a true reduction of the ecacy of latanoprost by a partial receptor adaptation at twice daily, but not once daily, applications is the most likely explanation. The clinical implication is clear; latanoprost should be applied once daily only. A second dose will not augment the e€ect but more likely reduce it. One of the long-term studies compared the ecacy of latanoprost applied in the morning with latanoprost applied in the evening (Alm et al., 1995b). When diurnal IOP (between 8 am an 4 pm) was used as the ecacy parameter applying latanoprost in the evening was superior. Evening application reduced IOP during the day with 1± 2 mm Hg more than morning application. However, this is only a consequence of the time curve for the e€ect of latanoprost. The peak e€ect does not appear until 6±10 hr after application of

301

Prostaglandin derivates as ocular hypotensive agents

the drug and the e€ect remains at this level for up to 20 hr post dose. Measuring IOP at 8 am, noon, and 4 pm means that at least the two ®rst measurements will be made during the peak e€ect of latanoprost applied in the evening, compared to only one of three measurements if latanoprost is applied in the morning. If IOP had been determined during the night it seems likely that morning application would have been superior.

3.2.1.5. Combination with other drugs Combined treatment is common in glaucoma. A drug that increases out¯ow, as latanoprost, is usually combined with a drug that reduces in¯ow, such as adrenergic beta-receptor blockers or carbonic anhydrase inhibitors. A combination of more than two drugs is not uncommon, and it is obviously important to obtain information on possible interaction between drugs that may be combined clinically. Such studies have been reported for latanoprost in combination with commonly used glaucoma drugs, but most of these studies were made before it became clear that latanoprost should be given only once daily. Thus most of the information on the combination of latanoprost with other drugs has been obtained with twice-daily applications of latanoprost, which is a suboptimal dose regimen for latanoprost. These studies have also been short-term studies, but it seems likely that unexpected interaction might have been detected. However, longterm experience on e€ect and side-e€ects of latanoprost in combination with other drugs is still lacking.

3.2.1.5.1. Beta-adrenergic-receptor blockers. One would expect latanoprost and a drug that reduces aqueous ¯ow to be an ideal combination, Moreover, early studies demonstrated that the e€ect on IOP of PGF2a-isopropyl ester was additive to that of timolol (Villumsen and Alm, 1990b; Lee et al., 1991). A marked additional e€ect of latanoprost added to timolol was also seen in a study reported above (Alm et al., 1995a) where latanoprost applied once or twice daily was added to timolol (Fig. 3). In this study the e€ect of timolol was not known; patients were recruited that had been on timolol for various length of time but were no longer regulated on timolol alone. Rulo et al. (1994) evaluated the e€ect of 0.006% latanoprost and 0.5% timolol given alone or combined. Each drug was applied twice daily. The drugs were given as monotherapy for one week and then the two drugs were combined for another week. Latanoprost alone reduced IOP with 31%, timolol with 24%. Combined the two drugs reduced IOP with 35-40% (Table 4) con®rming that the e€ect of the two drugs is additive. 3.2.1.5.2. Cholinergic agonist. In another study with the same design as the one above a combination of 0.006% latanoprost twice daily and 2% pilocarpine given three times a day was investigated (FristroÈm and Nilsson, 1993). A small additive e€ect was observed. Latanoprost alone reduced IOP with 23%, pilocarpine alone with 14%. The combined e€ect of the two drugs was 27±29% (Table 4). The additive e€ect of latanoprost to pilocarpine is somewhat unexpected since pilocarpine contracts the ciliary

Table 4. Percentual reduction of intraocular pressure in four latanoprost combination studies Treatment Latanoprost Timolol Latanoprost Pilocarpine Latanoprost Dipivefrin 1 2 3

Baseline IOPmm Hg

Reduction on monotherapy

Added e€ect of second drugcombined therapy

28.5 24.2 25.1 23.8 19.3 22.3

8.9 5.9 6.0 3.5 4.5 3.9

2.61 2.61 1.52 3.02 2.43 3.53

0.006% latanoprost was applied twice daily. From Rulo et al. (1994) 0.006% Latanoprost was applied twice daily. From FristroÈm and Nilsson (1993) 0.005% latanoprost was appled once daily. Unpubl obs

302

A. Alm

muscle and inhibits the e€ect of prostaglandins in monkeys (Crawford and Kaufman, 1987). The probable reason is that in human eyes the e€ect of pilocarpine on the ciliary muscle is shortlasting with return of normal accommodative range within 2 hr (Berggren, 1985). This observation was con®rmed in a recent study where the e€ect of 0.005% latanoprost on IOP in young volunteers with a healthy ciliary muscle was studied (unpubl. obs.). In order to cause a maximal contraction of the ciliary muscle 0.8% physostigmine, a potent contractor of the ciliary muscle, was applied every second hour for 14 hr. Latanoprost was applied as a single dose. Despite the intense, but short-lasting contraction of the ciliary muscle the e€ect on IOP of the two drugs was mainly additive. 3.2.1.5.3. Adrenergic agonists. Camras et al. (1985) reported that systemic indomethacin reduced the epinephrine-induced reduction of intraocular pressure concluding that part of the epinephrine e€ect was mediated by prostaglandins. One could then speculate that adding latanoprost to epinephrine would have little e€ect on the IOP. Another reason for investigating the combination epinephrine and prostaglandins is a possible additive e€ect on the blood±aqueous barrier. Chronic stimulation of the sympathetic nerves in rabbits causes a break down of the blood±aqueous barrier that seems to be mediated by prostaglandins (Bartels and Pawlowski, 1990). A small, prostaglandin-mediated increase in the blood±aqueous barrier permeability to sodium ¯uorescein was reported after treatment with epinephrine for 2 months or more in human eyes (Miyake et al., 1987), and Araie et al. (1992) reported a biphasic response of the blood± aqueous barrier in human eyes to a single dose of phenylephrine; an initial marked increase in aqueous ¯are followed by a decrease. Thus the e€ects of the combination latanoprost and dipivefrin on IOP and aqueous ¯are, as determined with a laser ¯are meter, were followed in one study. 0.005% latanoprost once daily or 0.1% dipivefrin twice daily was applied for 2 weeks followed by another 2 weeks of combined treatment. The e€ects on the IOP are summarized in Table 4. There was a marked

additivity of the e€ect on IOP for the two drugs. The results of the ¯are measurements are discussed in Section 3.2.2.2.2. 3.2.1.5.4. Carbonic anhydrase inhibitors. The combination carbonic anhydrase inhibitors and latanoprost is another combination where there is no theoretical ground to expect an interaction. To date the additivity of latanoprost to carbonic anhydrase inhibitors has only been tested with an oral inhibitor, diamox (unpubl. obs.) In this study acetazolamide was administered as Diamox Depot 250 mg twice daily for 4 days after a baseline IOP-curve. On the 4th day a new diurnal IOP curve was made and then half of the patients received latanoprost, 0.005%, and the other half placebo every evening for 2 weeks before a ®nal diurnal IOP curve. Latanoprost was signi®cantly better than placebo when added to acetazolamide. Acetazolamide alone reduced IOP from 25.5 to 19.5 mm Hg (23%) in the group that received latanoprost and from 26.2 to 21.5 mm Hg (18%) in the placebo-group. Latanoprost caused a signi®cant further reduction of 2.9 mm Hg (15%) while IOP increased with 1.3 mm Hg in the placebo group.

3.2.2. Long-Term studies

The Phase III-trials are long-term studies designed to compare the treatment under study with that of an established and accepted standard both in terms of ecacy and safety. Timolol is generally accepted as the drug of choice for treatment of glaucoma and in the Phase-III trials latanoprost was compared to timolol. 3.2.2.1. Ecacy compared to timolol Three large Phase III trials have been reported, one performed in Scandinavia (Alm et al., 1995b), one in Great Britain (Watson et al., 1996), and one in USA (Camras et al., 1996a). These are obviously the basic studies for evaluation of the ecacy of latanoprost as well as safety. All three studies included patients with open angle glaucoma or ocular hypertension. They were treated for 6 months with either timolol 0.5% twice daily or latanoprost 0.005% once daily in randomized,

303

Prostaglandin derivates as ocular hypotensive agents Table 5. Baseline IOP and reduction in mm Hg after 6 month's treatment with 0.005% latanoprost (Lat) once daily or 0.5% timolol (Tim) twice daily. The IOP is the average of three measurements with an interval of 4 hrs during the day starting at 8 or 9 am Scandinavia

Baseline Reduction

Great Britain

USA

Lat

Tim

Lat

Tim

Lat

Tim

25.1 8.0

24.6 6.4

25.2 8.5

25.4 8.4

24.4 6.7

24.1 4.9

Reprinted with permission from Alm et al., 1997

double-masked, parallel group studies. The US study included 268 patients, the GB study 294, and the Scandinavian study 267, that is in all 829 patients. Of these 460 were treated with latanoprost and 369 with timolol. These studies were designed to demonstrate if latanoprost was within 1.5 mm Hg of the IOP reducing e€ect of timolol. There were minor di€erences in the three studies. In the US study patients previously treated with timolol were allowed to be included after washout of the timolol e€ect for 3 weeks. In the other two studies patients previously treated with adrenergic beta-receptor blockers within the last 6 months or for a period of more than 3 months at any time were excluded. In the GB and US study latanoprost was applied in the evening, in the Scandinavian study a cross-over design was used with application of latanoprost either in the evening or the morning with a switch after 3 months. In all three studies the ecacy of the two drugs was based on the di€erence in mean diurnal IOP after 6 months of treatment. The main ecacy parameter, reduction of mean diurnal IOP at the end of 6 months, is presented in Table 5. In the three studies latanoprost reduced mean diurnal IOP signi®cantly by 27±34% from the untreated baseline level of 24.4±25.2 mm Hg, and timolol by 20±33% from 24.1 to 25.4 mm Hg. The two drugs were equally ecient in the GB study. In the Scandinavian study latanoprost was signi®cantly better than timolol, but within the accepted 1.5 mm Hg limit, while in the US study latanoprost was signi®cantly better than timolol, even considering the 1.5 mm Hg limit. There were some di€erences in patient demography (Table 6) but to what extent they have contributed to the di€erent e€ects of IOP is not clear. The mean di€erence between the e€ect on IOP of the two

drugs is small and the clinical signi®cance of this di€erence is not clear. The chance to reach a predetermined "target pressure" may be regarded as a clinically more relevant ecacy parameter. This was calculated for the combined results from the three studies. Table 7 presents a comparison between the two drugs for various "target pressures". Such a comparison indicates that latanoprost is consistently more e€ective than timolol, when mean diurnal IOP is used as the ecacy parameter, and that the di€erence becomes more marked if the goal is to reach IOP:s well within the normal range of IOP. However, it should be pointed out that using the mean diurnal IOP as the ecacy parameter does not take into consideration the peak e€ects and whether there is a di€erence in peak e€ect between the two drugs is not known. The fact that treatment with oral beta-adrenergic blockers was permitted in the inclusion criteria may also have contributed to the di€erence between the two drugs. Oral beta-adrenergic blockers will reduce the e€ect of timolol, Table 6. Patient demographics (in %) of the three Phase III-studies Scandinavian

GB

US

Males Caucasians Heredity Ocular Hypertensives POAG Capsular glaucoma Pigmentary glaucoma Mixed glaucoma Bilateral glaucoma Prior treatment

47 99 35 46 34 16 1 3 64 7

65 97 29 50 41 2 1 6 86 6

43 69 35 63 31 2 1 2 85 74

Reprinted with permission from Alm et al., 1997

304

A. Alm

Table 7. Cumulative frequency of patients (%) reaching a "target IOP" at the end of 6 months of treatment in three Phase III studies Target pressure (mmHg)

Latanoprost (%)

Timolol (%)

p-value

<13.0 <15.0 <17.0 <19.0 <21.0

13.1 35.2 64.6 86.7 94.5

5.7 24.2 54.7 80.5 91.2

0.001 0.002 0.006 0.025 0.087

The table includes only patients that completed 6 months of treatment, 398 patients were treated with latanoprost and 318 with timolol. p-values were calculated by the Chi-2 test Reprinted with permission from Alm et al., 1997

but it is unlikely to explain more than part of the di€erence since less than 10% of the patients randomized to timolol were on oral beta-adrenergic blockers during the study. In the three studies an average of 15% of latanoprost-treated patients and 17% of timolol-treated patients were treated in one eye only. Timolol reduced IOP signi®cantly also in the untreated fellow eye by between 1.1 mm Hg (Alm et al., 1995b) and 3.0 mm Hg (Watson et al., 1996). The e€ect of latanoprost on the fellow eye ranged between 0.4 mm Hg (Alm et al., 1995b) and 1.2 mm Hg (Watson et al., 1996; Camras et al., 1996a). The di€erence between timolol and latanoprost in this respect may re¯ect the fact that timolol, unlike latanoprost, reaches e€ective plasma levels when applied as eye drops. In all three studies patients were invited to enter a follow-up extension for 6 months. In the Scandinavian and the UK study this extension was later prolonged with another 12 months. The ®rst 198 patients that completed one year's treatment with latanoprost have been reported (Camras et al., 1996b). In this follow-up IOP was reduced from 25.2 23.0 mm Hg to 17.4 22.7 mm Hg (32% reduction) with little tendency to drift over time, but 12 patients (6%) needed additional timolol to maintain adequate IOP control. Mishima et al. (1996) compared the e€ect of latanoprost, 0.005%, applied in the morning to timolol, 0.5%, applied twice daily. 89 patients were treated with latanoprost and 95 patients with timolol. IOP was determined at 9 am (trough for both treatments). Latanoprost reduced morning IOP statistically signi®cantly better than timolol,

6.2 mm Hg (27%) vs. 4,4 mm Hg (19%) at the end of the study. 3.2.2.2. Ocular side-E€ects PGF2a-IE caused two major ocular side-e€ects, conjunctival hyperaemia and ocular irritation/discomfort, mainly experienced as a foreign body sensation (Villumsen and Alm, 1989). Thus these side-e€ects were carefully followed in the studies on latanoprost. The fact that prostaglandins are released in the in¯ammatory response has also prompted regular slit-lamp examinations to detect any ¯are as a sign of increased permeability of the blood±aqueous barrier, and a few studies have also been made with non-invasive determinations of the aqueous protein concentration. There has been no consistent change in either visual acuity or refraction in the 3 large 6-month Phase III studies but an unexpected ocular sidee€ect has occurred; an increased pigmentation of the iris. 3.2.2.2.1. Ocular irritation and conjunctival vasodilatation. Ocular discomfort is a term including burning or stinging, itching, foreign body sensation, eye pain, tearing, photophobia and/or a feeling of dry eyes. It was reported as adverse event 44 times in 460 patients treated with latanoprost and 20 times in 369 patients treated with timolol (Alm et al., 1995b; Watson et al., 1996; Camras et al., 1996a). As a rule these reports concerned transient events for both drugs and it was concluded that ocular discomfort is unlikely to be a problem in most patients on either drug.

Prostaglandin derivates as ocular hypotensive agents

In most studies the degree of conjunctival hyperaemia was determined by comparison with a set of standard photographs. The set consisted of four photographs corresponding to no (0), mild (1), moderate (2) or marked (3) hyperaemia, and a scale of 0±3 including half-steps, was used. Some increase in conjunctival hyperaemia is unavoidable when eye drops containing a preservative are administered chronically to the eye, but the studies also show that latanoprost causes some increase in conjunctival hyperaemia not due to the preservative. Thus in the Phase III studies the increase in hyperaemia score from baseline was slightly more pronounced with latanoprost, from 0.10 to 0.20, compared with timolol from 0.01 to 0.07. These ®gures show that conjunctival hyperaemia during latanoprost treatment is as a rule not more than one would expect with most eye drops. A few eyes may show more pronounced hyperaemia and conjunctival hyperemia has been reported as an adverse event more than once in about 1% of patients on long-term treatment with latanoprost which suggests that it may become a clinical problem in some patients. 3.2.2.2.2. Blood±ocular barrier permeability. Slitlamp examination has been used in most studies to evaluate any sign of intraocular in¯ammation, either cells or ¯are in the aqueous humour. In the three 6-months phase III studies (Alm et al., 1995b; Watson et al., 1996; Camras et al., 1996a) a slight ¯are was reported at one or two occasions in 8 of 460 patients on latanoprost and 4 of 369 patients on timolol, and the frequency did not increase during the open label extension of these studies. Ziai et al. (1993) determined the aqueous protein concentration non-invasively in normal eyes and eyes with ocular hypertension. They used three di€erent techniques; polarization of cameral ¯uorescence, intensity of backscattered light from the anterior chamber (¯are) and cameral ¯uorescence after oral administration of sodium ¯uorescein. They found no di€erence between treated and non-treated eyes after 5 days of treatment with latanoprost 0.006% twice daily. The laser ¯are meter was used in a study on the combination of 0.005% latanoprost once daily and 0.1% dipivefrin twice daily (see 3.2.1.5.3.).

305

Neither drug increased ¯are whether given alone or in combination (unpubl. obs.). These studies were limited to treatment for up to 4 weeks. Sixteen patients in the Scandinavian Phase III study were followed with the laser ¯are meter during treatment with 0.005% latanoprost once daily for 6±12 months. The treatment had no e€ect on ¯are (unpubl. obs.). Thus in the clinical studies latanoprost has not a€ected the blood± ocular barriers. The lack of e€ect on the blood± aqueous barrier re¯ects the receptor pro®le of latanoprost. It has little anity to the EP2-receptors which are involved in break down of the blood±ocular barriers in rabbits (Protzman and Woodward, 1990). However, it should be stressed that clinical studies are performed on a selected group of patients, and separate studies or longterm clinical experience may be necessary to detect a possible latanoprost-induced activation of an in¯ammatory response in eyes pre-disposed to anterior segment in¯ammation. The same precaution should be taken for the use of latanoprost in aphakic eyes. Latanoprost did not induce CME in aphakic monkeys (unpubl. obs.) but very few aphakic patients have been involved in the clinical studies, and long-term experience is therefore lacking for this patient group. 3.2.2.2.3. Iris pigmentation. Among 460 patients treated for 6 months with latanoprost increased pigmentation of the iris was observed in 31 (6.7%) (Alm et al., 1995b; Watson et al., 1996; Camras et al., 1996a). With increased treatment time the frequency increased and during one year of treatment 8% showed a de®nite increase in iris pigmentation and another 7% a suspected increase (Camras et al., 1996b). Figure 4 shows an example of an eye with increased iris pigmentation after 6 months' treatment. The incidence di€ers between eyes with di€erently colored irides, so that green±brown, yellow± brown, and blue±brown eyes, in that order, show the highest incidence, whereas eyes with uniformly blue, grey or green irides were much less a€ected even after two years of treatment. About 60% of eyes with an initial green±brown iris will show an increased pigmentation within one year. The corresponding ®gure for initially blue±brown eyes is about 20%. All patients that have

306

A. Alm

Fig. 4. The left eye of one patient treated with latanoprost before (left) and after (right) 6 months' treatment with latanoprost 0.005% once daily. From Alm et al. (1995) E€ects on introcular pressure and side e€ects of 0.005% latanoprost applied once daily, evening or morning. A comparison with timolol. Ophthalmology 102, 1743-1752. Courtesy of Ophthalmology.

Prostaglandin derivates as ocular hypotensive agents

developed increased pigmentation of the iris have been withdrawn from the studies. During followup of these patients for up to almost 3 years the change in iris pigmentation has been stable without signs of reversibility or further increase (unpubl. obs.). Slit lamp examinations and iris photographs have not revealed any structural changes apart from an increased amount of brown pigment. Naevi and freckles have not changed color or size. Apart from the change in color the iris looks normal and pigment dispersion has not been observed. Three iridectomy specimens from irides treated with latanoprost for 12±18 months have been evaluated histologically and by electron microscopy and were found to be normal (unpubl. obs.). Extensive pre-clinical research has been performed demonstrating that this e€ect is also seen with the naturally occurring prostaglandins PGE2 and PGF2a, (SeleÂn et al., 1997) that no cell proliferation is involved and that the change in color is due to melanogenesis (Stjernschantz et al., 1996). Thus it has been concluded that the change in iris pigmentation is unlikely to cause any longterm consequence besides the cosmetic one. The possibility of a late loss of pigment and induction of a pigmentary glaucoma also seem unlikely; iridial melanocytes are continent and do not release melanin (Prota, 1992). As pointed out above, the follow-up of eyes with increased iris pigmentation for almost 3 years have not indicated any loss of pigment or late complication due to the increased iris pigmentation. 3.2.2.2.4. Other ocular side-E€ects. The highest number of objective ocular side-e€ects have been found in the cornea. The most common corneal e€ect was punctate corneal erosions which were reported in 44 patients (9.6%) on latanoprost and 32 (8.7%) on timolol. Most of these punctate epithelial erosions were mild sporadic events, but repeated corneal erosions were also observed and four patients on latanoprost were withdrawn due to repeated corneal erosions in the three large 6month Phase III studies (Alm et al., 1995b; Watson et al., 1996; Camras et al., 1996a). The latanoprost eye drops, as well as the vehicle used as placebo, contain twice the amount of the

307

preservative benzalkonium chloride as timolol eye drops. This may have contributed to the epithelial erosions in patients on latanoprost in the masked study where patients on latanoprost received twice the clinical dose of benzalkonium chloride. During the extension of the Phase III studies, where no placebo eye drops were used, punctate erosions were less frequent (Camras et al., 1996b). 3.2.2.3. Systemic side-E€ects The low systemic dose of latanoprost when applied as one or two 0.005% eye drops once daily, and the short half-life of the drug in the systemic circulation suggests that drug-related systemic side-e€ects should be unlikely. The peak plasma concentration after topical application is around 10ÿ10 M, which is below the level needed for e€ective stimulation of the FP-receptor (see 3.2.1.1). 3.2.2.3.1. Pulmonary e€ects. Large doses of PGF2a act as bronchoconstrictors in the human lung (Newball et al., 1980). These e€ects are mediated by thromboxane (TP)-receptors (Featherstone et al., 1990). Latanoprost has little e€ect on the TP-receptor. Thus latanoprost applied as eye drops is not expected to have any e€ect on pulmonary function. This has been supported by studies in 12 healthy volunteers and 11 asthmatic patients who received latanoprost eye drops in each eye up to a concentration of 0.035% (unpubl. obs.). No negative e€ect was seen on any of the respiratory parameters tested in either test group. The number of adverse events of shortness of breath or wheezing in the masked part of the ®rst 3 Phase III-studies were lower with latanoprost than with timolol, 2 vs 6, in spite of the fact that patients were selected to tolerate timolol (routines for prescribing betaadrenergic antagonists were followed). This is in accordance with recent reports that timolol causes unrecognized bronchospasm in about 25% of patients above the age of 60 without a history or airway disease (Diggory et al., 1995). 3.2.2.3.2. Cardiovascular e€ects. Blood pressure and heart rate were determined 12 hr after the previous dose in the long-term studies (Alm et

308

A. Alm

al., 1995b; Watson et al., 1996; Camras et al., 1996a). Timolol caused a signi®cant reduction in heart rate in all three studies, latanoprost only in the Scandinavian study (Alm et al., 1995b). The e€ects on blood pressure were minor and of no clinical signi®cance with either drug. 3.2.2.3.3. Laboratory values. Blood samples were analyzed for hematocrit level, hemoglobin level, mean corpuscular volume, mean corpuscular hemoglobin concentration, erythrocyte count, leukocyte count, di€erential count, platelets, prothrombin, partial thromboplastin time, serum cholesterol level (total, high-density, and lowdensity lipoprotein), serum triglycerides, serum proteins, glucose value, creatine level, urea level, bilirubin level, alkaline phosphatase, SGOT, SGPT, sodium, potassium, calcium, and chloride. Urine analysis included assessment of protein and glucose. No signi®cant changes were seen for any laboratory value (Alm et al., 1995b; Watson et al., 1996; Camras et al., 1996a).

4. UNOPROSTONE Isopropyl 20-ethyl-9a,11a-dihydroxy-15-keto-cisD5-prostanoate (unoprostone, previous code name UF-021) is another PGF2a-related compound (Fig. 1). It has been on the market in Japan for more than one year, but there is little experience with the drug outside Japan. Sakurai et al. (1991) reported that 0.12% solution reduced IOP in normal eyes without any e€ect on aqueous ¯ow, out¯ow facility, or episcleral venous pressure. With twice-daily applications for 28 days the e€ect on IOP was too small to be detected on the last day of treatment, which may be due to a very low untreated level of IOP, less than 10 mm Hg. In a double-masked comparison with timolol, 0.12% unoprostone given twice daily to 158 patients for 12 weeks was found to be equally e€ective in reducing IOP as timolol (Azuma et al., 1993). Aoyama and Ueno (1996) reported the clinical experience of treating 96 patients with unoprostone for an average of 5.4 months. They used the drug in a number of patients not normally seen in the clinical trials and, as expected, some new information was obtained. Thus they

found little e€ect on IOP in patients with diabetes mellitus, and a high frequency of blepharoconjunctivitis in patients with a history of intraocular operation. Severe corneal defects were also seen in patients with diabetes mellitus. Some ¯uctuation of ¯are intensity that disappeared when unoprostone was discontinued was observed. It is reasonable to assume that the present wide-spread use of latanoprost will also unveil some e€ects not noted in the clinical trials. 5. FUTURE DIRECTIONS The clinical experience with latanoprost and unoprostone is limited to the clinical studies and at the most about one year of clinical experience in a limited group of patients. Unexpected sidee€ects may still appear but the present experience with PG-analogues as ocular hypotensive drugs suggests that they have come to stay. The increased pigmentation of the iris is a completely new side-e€ect and the long-term consequences need to be closely monitored. Attempts to avoid this side-e€ect by further modi®cation of the molecule is an obvious future goal. As it seems to be a class e€ect for prostanoids, or at least possible to induce with several di€erent naturally occurring prostanoids, it may, however, not be possible to separate iris pigmentation and e€ect on IOP. Still, modern molecular biology should make it possible to decide if it is possible by de®ning the receptors involved in melanogenesis and increased uveoscleral ¯ow respectively. The most obvious clinical studies to gain further information on this side-e€ect are studies aimed at determining the end point of the change in iris color, the possibility to better predict if a change in iris pigmentation is likely to occur or not, and more information on iris morphology in patients on long-term treatment with prostanoids. The wide variety of e€ects on aqueous humor dynamics observed with di€erent PGs in di€erent species suggests that neither latanoprost nor unoprostone utilizes the full capacity of prostanoids to reduce IOP. As pointed out above animal studies indicate that PGs are involved to some extent also in determining the rate of aqueous ¯ow and out¯ow facility through the trabecular meshwork.

Prostaglandin derivates as ocular hypotensive agents

Thus, we can expect an intensive search for alternatives as there is no obvious reason to believe that the ®rst generation will turn out to be the ultimate prostaglandin for the treatment of glaucoma. REFERENCES Alm, A. and Villumsen, J. (1991) PhXA34Ða potent ocular hypotensive drug. A study on e€ect±side-e€ect relationship and on aqueous humor dynamics in healthy volunteers. Arch. Ophthalmol. 109, 1564±1568. Alm, A., Villumsen, J., ToÈrnquist, P., Mandahl, A., Airaksinen, J., Tuulonen, A., Marsk, A., Resul, B. and Stjernschantz, J. (1993) Intraocular pressure reducing e€ect of PhXA41 in ocular hypertensive patientsÐa one month study. Ophthalmology 100, 1312±1317. Alm, A., WidengaÊrd, I., Kjellgren, D., SoÈderstroÈm, M., Nilsson, S. E., FristroÈm, B., Heijl, A. and Stjernschantz, J. (1995a) Latanoprost administered once daily caused a maintained reduction of intraocular pressure in glaucoma patients treated concomitantly with timolol. Br. J. Ophthalmol. 79, 12±16. Alm, A., Stjernschantz, J. and the Scandinavian Latanoprost Study Group (1995b) E€ects on intraocular pressure and side-e€ects of 0.005% latanoprost once daily, evening or morning. A comparison with timolol. Ophthalmology 102, 1743±1752. Ambache, N. (1955) Irin, a smooth-muscle contracting substance present in rabbit iris. J. Physiol. (London) 129, 65P±66P. Ambache, N. (1957) Properties of irin, a physiological constituent of the rabbit iris. J. Physiol. (London) 135, 114±132. Ambache, N. and Brummer, H. C. (1968) A simple chemical procedure for distinguishing E from F prostaglandins, with application to tissue extracts. Br. J. Pharmacol. 33, 162±170. Ambache, N., Kavanagh, L. and Whiting, J. (1966) Some di€erences in uveal reactions between cats and rabbits. J. Physiol. (London) 182, 110±130. Andersson, S. E. and AlmegaÊrd, B. (1993) CGRP(8±37) and CGRP(32±37) contract the iris sphincter in the rabbit eye: antagonism by spantide and GR82334. Regul. Pept. 49, 73±80. AÈnggaÊrd, E. and Samuelsson, B. (1964) Smooth muscle stimulating lipids in sheep iris, identi®cation of prostaglandin F2a, prostaglandins and related factors. Biochem. Pharmacol. 13, 281±283. Aoyama, Y. and Ueno, S. (1996) E€ect of UF-021 (Rescula registered), a prostaglandin-related compound, on intraocular pressure and anterior chamber ¯are counts. Folia Ophthalmol. Jpn. 47, 914±919. Araie, M., Mori, M. and Oshika, T. (1992) E€ect of topical phenylephrine on the permeability of the blood±aqueous barrier in man. Graefe's Arch. Clin. Exp. Ophthalmol. 230, 171±174. Azuma, I., Masuda, K., Kitazawa, Y., Takase, M. and Yamamura, H. (1993) Double-masked comparative study of UF-021 and timolol ophthalmic solutions in

309

patients with primary open-angle glaucoma or ocular hypertension. Jpn. J. Ophthalmol. 37, 514±525. Bartels, S. P. and Pawlowski, A. M. (1990) Chronic electrical stimulation of sympathetic nerves: e€ects on blood±aqueous barrier. Curr. Eye Res. 9, 927±934. Berggren, L. (1985) Individual responsiveness to topical pilocarpine and the e€ects of variations in application technique. Acta Ophthalmol. 63, 642±646. Bill, A. (1965) The aqueous humor drainage in the cynomolgus monkey (Macaca irus) with evidence for unconventional routes. Invest. Ophthalmol. 4, 911±919. Bill, A., Stjernschantz, J., Mandahl, A., Brodin, E. and Nilsson, G. (1979) Substance P: release on trigeminal nerve stimulation, e€ects in the eye. Acta Physiol. Scand. 106, 371±373. Bill, A., Andersson, S. E. and AlmegaÊrd, B. (1990) Cholecystokinin causes contraction of the pupillary sphincter in monkeys but not in cats, rabbits, rats and guinea-pigs: antagonism by lorglumide. Acta Physiol. Scand. 138, 479±485. Bito, L. Z. (1974) The e€ects of experimental uveitis on anterior uveal prostaglandin transport and aqueous humor composition. Invest. Ophthalmol. 13, 299±306. Bito, L. Z. (1984) Comparison of the ocular hypotensive e€ecacy of eicosanoids and related compounds. Exp. Eye Res. 38, 181±194. Bito, L. Z. and Baroody, R. A. (1987) The ocular pharmacokinetics of eicosanoids and their derivates. 1. Comparison of ocular eicosanoid penetration and distribution following the topical application of PGF2a, PGF2a-1-methyl ester, and PGF2a-1-isopropyl ester. Exp. Eye Res. 44, 217±226. Bito, L. Z. and Salvador, E. V. (1972) Intraocular ¯uid dynamics. III. The site and mechanism of prostaglandin transfer across the blood intraocular ¯uid barriers. Exp. Eye Res. 14, 233±241. Bito, L. Z., Draga, A., Blanco, D. J. and Camras, C. B. (1983) Long-term maintainance of reduced intraocular pressure by daily or twice daily topical application of prostaglandins to cat or rhesus monkey eyes. Invest. Ophthalmol. Vis. Sci. 24, 312±319. Bito, L. Z., Camras, C. B., Gum, G. G. and Resul, B. (1989) The ocular hypotensive e€ects and side-e€ects of prostaglandins on the eyes of experimental animals. In The Ocular E€ects of Prostaglandins and Other Eicosanoids, ed. L. Z. Bito and J. Stjernschantz, pp. 349±368. Alan R. Liss. Inc., New York. Camber, O., Edman, P. and Olsson, L.-I. (1986) Permeability of prostaglandin F2a and prostaglandin F2a esters across cornea in vitro. Int. J. Pharm. 29, 259±266. Camras, C. B. and Bito, L. Z. (1981) Reduction of intraocular pressure in normal and glaucomatous primate (Aotus trivirgatus) eyes by topically applied prostaglandin F2a. Curr. Eye Res. 1, 205±209. Camras, C. B., Bito, L. Z. and Eakins, K. E. (1977) Reduction of intraocular pressure by prostaglandins applied topically to the eyes of conscious rabbits. Invest. Ophthalmol. Vis. Sci. 16, 1125±1134. Camras, C. B., Feldman, S. G., Podos, S. M., Christensen, R. E., Gardner, S. K. and Fazio, D. T. (1985) Inhibitors of the epinephrine-induced reduction of intraocular pressure by systemic indomethacin in humans. Am. J. Ophthalmol. 100, 169±175. Camras, C. B., Podos, S. M., Rosenthal, J. S., Lee, P. Y. and Severin, C. (1987) Multiple dosing of prostaglandin F2a

310

A. Alm

or epinephrine on cynomolgus monkey eyes. I. Aqueous humour dynamics. Invest. Ophthalmol. Vis. Sci. 28, 463±469. Camras, C. B., Siebold, E. C., Lustgarten, J. S., Serle, J. B., Frisch, S. C., Podos, S. M. and Bito, L. Z. (1989) Maintained reduction of intraocular pressure by prostaglandin F2a-1-isopropyl ester applied in multiple doses in ocular hypertensive and glaucoma patients. Ophthalmology 96, 1329±1337. Camras, C. B., Schumer, R. A., Marsk, A., Lustgarten, J. S., Serle, J. B., Stjernschantz, J., Bito, L. Z. and Podos, S. M. (1992) Intraocular pressure reduction with PhXA34, a new prostaglandin analogue, in patients with ocular hypertension. Arch. Ophthalmol. 110, 1733±1738. Camras, C. B. and the United States Latanoprost Study Group (1996a) Comparison of latanoprost and timolol in patients with ocular hypertension and glaucoma: a six-month, masked, multicenter trial in the United States. Ophthalmology 103, 138±147. Camras, C. B., Alm, A., Watson, P., Stjernschantz, J. and the Latanoprost Study Groups (1996b) Latanoprost, a prostaglandin analog, for glaucoma treatment. Ecacy and safety after 1 year of treatment in 198 patients. Ophthalmology 103, 1916±1934. Cheng-Bennett, A., Chan, M. F., Chen, G., Gac, T., Garst, M. E., Gluchowski, C., Kaplan, L. J., Protzman, C. E., Roof, M. B., Sachs, G., Wheeler, L. A., Williams, L. S. and Woodward, D. F. (1994) Studies on a novel series of acyl ester prodrugs of prostaglandin F2a. Br. J. Ophthalmol. 78, 560±567. Coleman, R. A., Smith, W. L. and Narumiya, S. (1994) International union of pharmacology classi®cation of prostanoid receptors; properties, distribution, and structure of the receptors and their subtypes. Pharmacol. Rev. 46, 205±229. Crawford, K. and Kaufman, P. L. (1987) Pilocarpine antagonizes prostaglandin F2a-induced ocular hypotension in monkeys. Evidence for enhancement of uveoscleral out¯ow by prostaglandins F2a. Arch. Ophthalmol. 105, 1112±1116. Crawford, K., Kaufman, P. L. and Gabelt, B. T. (1987) E€ects of topical PGF2a on aqueous humour dynamics in cynomolgus monkeys. Curr. Eye Res. 6, 1035±1044. Crawford, K. S., Kaufman, P. L., Hubbard, W. C. and Woodward, D. F. (1992) The DP-receptor agonist SQ27986 raises but does not lower intraocular pressure in ocular normotensive monkeys. J. Glaucoma 1, 94±99. Diggory, P., Cassels-Brown, A., Vall, A., Abbey, L. M. and Hillman, J. S. (1995) Avoiding unsuspected respiratory side-e€ects of topical timolol with cardioselective or sympathomimetic agents. Lancet 345/8965, 1604±1606. Eakins, K. E. (1970) Increased intraocular pressure produced by prostaglandins E1 and E2 in the cat eye. Exp. Eye Res. 10, 87±92. Eakins, K. E. (1976) Prostaglandins and the eye. In Advances in Prostaglandin Research. Prostaglandins: Physiological, Pharmacological and Pathological Aspects, ed. S. M.M Karim, pp. 63±81. University Park Press, Baltimore. Featherstone, R. L., Robinson, C., Holgate, S. T. and Church, M. K. (1990) Evidence for thromboxane-receptor mediated contraction of guinea pig and human airways in vitro by prostaglandin (PG) D2, 9a,11b-PGF2 and PGF2a. Naunyn-Schmied. Arch. Pharmacol. 341, 439±443.

Ferreira, S. H. and Vane, J. R. (1967) Prostaglandines: their disappearance from and release into the circulation. Nature 216, 868±873. Flach, A. J. and Eliason, J. A. (1988) Topical prostaglandin E2 e€ects on normal human intraocular pressure. J. Ocular Pharmacol. 4, 13±18. Flach, A. J., Jampol, L. M., Weinberg, D., Kra€, M. C., Yannuzzi, L. A., Campo, R. V., Neumann, A. C., Cupples, H. P., Le¯er, W. H., Pulido, J. S. and Lavelle, C. (1991) Improvement in visual acuity in chronic aphakic and pseudophakic cystoid macular edema after treatment with topical 0.5% ketorolac tromethamine. Am. J. Ophthalmol. 112, 514±519. FristroÈm, B. and Nilsson, S. E. G. (1993) Interaction of PhXA41, a new prostaglandin F2a analogue, with pilocarpine. A study on patients with elevated intraocular pressure. Arch. Ophthalmol. 111, 662±665. Gabelt, B. T. and Kaufman, P. L. (1989) Prostaglandin F2a increases uveoscleral out¯ow in the cynomolgus monkey. Exp. Eye Res. 49, 389±402. Gabelt, B. T. and Kaufman, P. L. (1990) The e€ect of prostaglandin F2a on trabecular out¯ow facility in cynomolgus monkeys. Exp. Eye Res. 51, 87±91. Giu€reÂ, G. (1985) The e€ects of prostaglandin F2a in the human eye. Graefe's Arch. Clin. Exp. Ophthalmol. 222, 139±141. Goh, Y., Araie, M., Nakajima, M., Azuma, I. and Hayaishi, O. (1989) E€ect of topical prostaglandin D2 on the aqueous humor dynamics in rabbits. Graefe's Arch. Clin. Exp. Ophthalmol. 227, 467±481. Goldblatt, M. W. (1933) A depressor substance in seminal ¯uid. J. Soc. Chem. Industry 5, 1056±1057. Goldblatt, M. W. (1935) Properties of human seminal plasma. J. Physiol. (London) 84, 208±218. Groeneboer, M. C., Hoyng, P. F. J. and Kuizenga, A. (1989) Prostaglandin F2a isopropyl ester versus Iloprost phenacyl ester in rabbit and beagle eyes. Curr. Eye Res. 8, 131±138. Gum, G. G., Kingsbury, S., Whitley, R. D., Garcia, A. and Gelatt, K. N. (1991) E€ect of topical PGA2, PGA2 isopropylester, and PGF2a isopropylester on intraocular pressure in normotensive and glaucomatous canine eyes. J. Ocul. Pharmacol. 7, 107±116. Hotehama, Y. and Mishima, H. K. (1993) Clinical ecacy of PhXA34 and PhXA41, two novel prostaglandin F2aisopropyl ester analogues for glaucoma treatment. Jpn. J. Ophthalmol. 37, 259±269. Jager, G. V., Van-Delft, J. L., Van-Haeringen, N. J., Verbeij, N. L. J. and Braquet, P. (1993) Antagonist of plateletactivating factor prevents prostaglandin E2 induced ocular hypertension in rabbits. Prostaglandins 45, 97± 105. Kass, M. A., Podos, S. M., Moses, R. A. and Becker, B. (1972) Prostaglandin E1 and aqeuous humor dynamics. Invest. Ophthalmol. 11, 1022±1027. Kaufman, P. L. (1986) E€ects of intracamerally infused prostaglandins on out¯ow facility in cynomolgus monkey eyes with intact or retrodisplaced ciliary muscle. Exp. Eye Res. 43, 819±827. Kerstetter, J. R., Brubaker, R. F., Wilson, S. E. and Kullerstrand, L. J. (1988) Prostaglandin F2a-1-isopropylester lowers intraocular pressure without decreasing aqueous humor ¯ow. Am. J. Ophthalmol. 105, 30±34. Kervick, G. N. and Johnston, P. B. (1990) The e€ect of indomethacin 0.5% ophthalmic suspension in preventing

Prostaglandin derivates as ocular hypotensive agents surgically induced miosis during planned extracapsular cataract extraction. Int. Ophthalmol. 14, 77±79. Kulkarni, P. S. and Sririvasan, B. D. (1985) Prostaglandins E3 and D3 lower intraocular pressure. Invest. Ophthalmol. Vis. Sci. 26, 1178±1182. Kurzrok, C. and Lieb, C. (1930) Biochemical studies on human semen: action of semen on the human uterus. Proc. Soc. Exp. Biol. Med. 28, 268±272. Lee, P. Y., Podos, S. M. and Severin, C. (1984) E€ect of prostaglandin F2a on aqueous humor dynamics in rabbit, cat, and monkey. Invest. Ophthalmol. Vis. Sci. 25, 1087±1093. Lee, P.-Y., Shao, H., Xu, L. and Qu, C.-K. (1988) The e€ect of prostaglandin F2a on intraocular pressure in normotensive human subjects. Invest. Ophthalmol. Vis. Sci. 29, 1474±1477. Lee, P-Y., Shao, H., Camras, C. B. and Podos, S. M. (1991) Additivity of prostaglandin F2a-1-isopropyl ester to timolol in glaucoma patients. Ophthalmology 98, 1979± 1082. LuÈtjen-Drecoll, E. and Tamm, E. (1988) Morphological study of the anterior segment of cynomolgus monkey eyes following treatment with prostaglandin F2a. Exp. Eye Res. 47, 761±769. Mandahl, A. and Bill, A. (1981) Ocular responses to antidromic trigeminal stimulation, intracameral prostaglandin E1 and E2, capsaicin and substance P. Acta Physiol. Scand. 112, 331±338. Matsuo, T. and Cynader, M. S. (1992) Localisation of prostaglandin F2a and E2 binding sites in the human eye. Br. J. Ophthalmol. 76, 210±213. Matsuo, T. and Cynader, M. S. (1993) The EP2 receptor is the predominant prostanoid receptor in the human ciliary muscle. Br. J. Ophthalmol. 77, 110±114. McCannel, C. A., Heinrich, S. R. and Brubaker, R. F. (1992) Acetazolamide but not timolol lowers aqueous humor ¯ow in sleeping humans. Graefe's Arch. Clin. Exp. Ophthalmol. 230, 518±520. Mishima, H. K., Masuda, K., Kitazawa, Y., Azuma, I. and Araie, M. (1996) A comparison of latanoprost and timolol in primary open-angle glaucoma and ocular hypertension. A 12-week study. Arch. Ophthalmol. 114, 929±932. Miyake, K., Miyake, Y. and Kuratomi, R. (1987) Long-term e€ects of topically applied epinephrine on the blood±aqueous barrier in humans. Arch. Ophthalmol. 105, 1360±1363. Miyake, K., Shirasawa, E. and Hikita, M. (1989) Hypotheses on the role of prostaglandins in the pathogenesis of epinephrine maculopathy and aphakic cystoid macular edema. In The Ocular E€ects of Prostaglandins and Other Eicosanoids, ed. L. Z. Bito and J. Stjernschantz, pp. 265±276. Alan R. Liss. Inc., New York. Nagasubramanian, S., Sheth, G. P., Hitchings, R. A. and Stjernschantz, J. (1993) Intraocular pressure-reducing e€ect of PhXA41 in ocular hypertension. Comparison of dose regimens. Ophthalmology 100, 1305±1311. Nakajima, M., Goh, Y., Azuma, I. and Hayashi, O. (1991) E€etcs of prostaglandin D2 and its analogue, BW245C, on intraocular pressure in humans. Graefe's Arch. Clin. Exp. Ophthalmol. 229, 411±413. Newball, A. H., Keiser, H. R. and Lenfant, C. (1980) Prostaglandin F2a functions as a local hormone on human airways. Respir. Physiol. 41, 183±197.

311

Nilsson, S. F. E., Samuelsson, M., Bill, A. and Stjernschantz, J. (1989) Increased uveoscleral out¯ow as a possible mechanism of ocular hypotension caused by prostaglandin F2a-1-isopropylester in the cynomolgus monkey. Exp. Eye Res. 48, 707±716. Ocklind, A., Lake, S., Wentzel, P., NisteÂr, M. and Stjernschantz, J. (1996) Localization of the prostaglandin F2a receptor messenger RNA and protein in the cynomolgus monkey eye. Invest. Ophthalmol. Vis. Sci. 37, 716±726. Poyer, J. F., Gabelt, B. and Kaufman, P. L. (1992) The e€ect of topical PGF2a on uveoscleral out¯ow and out¯ow facility in the rabbit eye. Exp. Eye Res. 54, 277±283. Poyer, J. F., Millar, C. and Kaufman, P. L. (1995) Prostaglandin F2a e€ects on isolated rhesus monkey ciliary muscle. Invest. Ophthalmol. Vis. Sci. 36, 2461± 2465. Prota, G. (1992), In Melanins and Melanogenesis. Academic Press, San Diego. Protzman, C. E. and Woodward, D. F. (1990) Prostanoidinduced blood±aqueous barrier breakdown in rabbits involves the EP2 receptor subtype. Invest. Ophthalmol. Vis. Sci. 31, 2463±2466. Racz, P., Ruzsonyi, M. R., Nagy, Z. T., Gagyi, Z. and Bito, L. Z. (1996) Around-the-clock intraocular pressure reduction with once-daily application of latanoprost by itself or in combination with timolol. Arch. Ophthalmol. 114, 268±273. Rulo, A. H., Greve, E. L. and Hoyng, P. F. (1994) Additive e€ect of latanoprost, a prostaglandin F2a analogue, and timolol in patients with elevated intraocular pressure. Br. J. Ophthalmol. 78, 899±902. Sakurai, M., Araie, M., Oshika, T., Mori, M., Masuda, K., Ueno, R. and Takase, M. (1991) E€ects of topical application of UF-021, a novel prostaglandin derivative, on aqueous humor dynamics in normal human eyes. Jpn. J. Ophthalmol. 35, 156±165. SeleÂn, G., Stjernschantz, J. and Resul, B. (1997) Prostaglandin-induced iridial pigmentation in primates. Survey Ophthalmol. 41(Suppl), S125±S128. SjoÈquist, B., Byding, P., Resul, B. and Stjernschantz, J. (1994) The systemic pharmacokinetics of latanoprost in man after intravenous and topical administration. Invest. Ophthalmol. Vis. Sci. 35(ARVO), 2220. SjoÈquist, B., AlmegaÊrd, B., Khalifeh, V. and Alm A. (1997). The bioavailability of Xalatan in the human eye. Invest. Ophthalmol. Vis. Sci. 38 (ARVO). Smiddy, W. E., Glaser, B. M., Michels, R. G. and Vitale, S. (1990) Miosis during vitreoretinal surgery. Retina 10, 42±46. Stern, F. A. and Bito, L. Z. (1982) Comparison of the hypotensive and other ocular e€ects of prostaglandin E2 and F2a on cat and rhesus monkey eyes. Invest. Ophthalmol. Vis. Sci. 22, 588±598. Stjernschantz, J. and Resul, B. (1992) Phenylsubstituted prostaglandin analogs for glaucoma treatment. Drugs of the Future 17, 691±704. Stjernschantz, J., Nilsson, S. F. E. and Astin, M. (1989) Vasodynamic and angiogenic e€ects of eicosanoids in the eye. In The Ocular E€ects of Prostaglandins and Other Eicosanoids, ed. L. Z. Bito and J. Stjernschantz, pp. 155±170. Alan R. Liss, Inc., New York. Stjernschantz, J., SeleÂn, G., SjoÈquist, B. and Resul, B. (1995) Preclinical pharmacology of latanoprost, a phenylsubstituted PGF2a analogue. In Advances in Prostaglandin,

312

A. Alm

Tromboxane, and Leukotriene Research, ed. B. Samuelsson, Vol. 23, pp. 513±518. Raven Press, New York. Stjernschantz, J., SeleÂn, G., Ocklind, A., Wenzel, P., Resul, B. and Lake, S. (1996) Prostaglandin-induced increase of iridial pigmentation. Pigment Cell Res. Suppl 5, 19±20. Svedbergh, B. and Forsberg, I. (1993) A morphological study on the e€ects of chronic administration of latanoprost (LP) on the ciliary muscle and trabecular meshwork in monkeys. Invest. Ophthalmol. Vis. Sci. 34(ARVO), 932. Toris, C. B., Camras, C. B. and Yablonski, M. E. (1993) E€ects of PhXA41, a new prostaglandin F2a analog, on aqueous humor dynamics in human eyes. Ophthalmology 100, 1297±1304. Toris, C. B., Yablonski, M. E., Wang, Y.-L. and Hayashi, M. (1995) Prostaglandin A2 increases uveoscleral out¯ow and trabecular out¯ow facility in the cat. Exp. Eye Res. 61, 649±657. Villumsen, J. and Alm, A. (1989) Prostaglandin F2a-isopropylester eye drops. E€ects in normal human eyes. Br. J. Ophthalmol. 73, 419±426. Villumsen, J. and Alm, A. (1990a) Ocular e€ects of two di€erent prostaglandin F2a esters. A doublemasked crossover study on normotensive eyes. Acta Ophthalmol. 68, 341±343. Villumsen, J. and Alm, A. (1990b) The e€ect on intraocular pressure of adding prostaglandin F2a-isopropylester to timolol in patients with open angle glaucoma. A randomized, masked, placebo-controlled study. Arch. Ophthalmol. 108, 1102±1105. Villumsen, J. and Alm, A. (1992) PhXA34 prostaglandin analogue. E€ect on intraocular pressure in patients with ocular hypertension. Br. J. Ophthalmol. 76, 214±217. Villumsen, J., Alm, A. and SoÈderstroÈm, M. (1989) Prostaglandin F2a-isopropylester eye drops. E€ect on intraocular pressure in open angle glaucoma. Br. J. Ophthalmol. 73, 975±979.

von Euler, U. S. (1934) Zur Kenntnis der Pharmakologischen Wirkungen von Nativsekreten und Extrakten mannlicher accessorischer Geschlechtsdrusen. Nauyn Schmiedeberg's Arch. Exp. Pathol. Pharmacol. 175, 78± 84. Waitzman, M. B. and King, C. D. (1967) Prostaglandin in¯uences on intraocular pressure and pupil size. Am. J. Physiol. 212, 329±334. Wang, R. F., Camras, C. B., Lee, P. Y., Podos, S. M. and Bito, L. Z. (1990) E€ects of prostaglandin F2a, A2, and their esters in glaucomatous monkey eyes. Invest. Ophthalmol. Vis. Sci. 31, 2466±2470. Waterbury, L. D., Eglen, R. M., Fauror, G. F. and Cooper, G. F. (1990) EP3, but not EP2, FP, or TP prostanoidreceptor stimulation may reduce intraocular pressure. Invest. Ophthalmol. Vis. Sci. 31, 2560±2567. Watson, P., Stjernschantz, J. and the Latanoprost Study Group (1996) A six-month, randomized, doublemasked study comparing latanoprost with timolol in open-angle glaucoma and ocular hypertension. Ophthalmology 103, 126±137. Woodward, D. F., Williams, L. S. and Chen, J. (1989a) Marked di€erential e€ects of prostanoid metabolites on rabbit intraocular pressure. Ophthalmic Res. 21, 428± 435. Woodward, D. F., Burke, J. A., Williams, L. S., Palmer, B. P., Wheeler, L. A., Woldemussie, E., Ruiz, G. and Chen, J. (1989b) Prostaglandin F2a e€ects on intraocular pressure negatively correlate with FP-receptor stimulation. Invest. Ophthalmol. Vis. Sci 30, 1838±1842. Ziai, N., Dolan, J. W., Kacere, R. D. and Brubaker, R. F. (1993) The e€ect on aqueous dynamics of PhXA41, a new prostaglandin F2a analogue, after topical application in normal and ocular hypertensive human eyes. Arch. Ophthalmol. 111, 1351±1358.