- Email: [email protected]
Long-acting methods for fertility regulation
Journal of Controlled
Release, 6 (1987)
Elsevier Science Publishers
LONG-ACTING
METHODS
387
387-394
B.V.. Amsterdam
-
Printed
in The Netherlands
FOR FERTILITY
REGULATION*
Henry L. Gabelnick** Contraceptive
Research and Development
Program,
16 11 North Kent Street, Suite 806, Arlington,
Virginia 22209
(U.S.A.)
and Peter E. Hall Special Programme of Research, Development 12 11 Geneva 2 7 (Switzerland)
and Research Training in Human Reproduction,
World Health Organization,
The development of sophisticated technology for the zero-order delivery of contraceptive steroids has been the goal of several public-sector organizations and some pharmaceutical companies for nearly a generation. In fact, a nondegradable implant which delivers the progestogen, levonorgestrel, from silicone rubber (NORPLANT@) has already been approved in six countries and will be submitted for approval by the FDA shortly. Several approaches to biodegradable implants have been attempted with more or less success. The biodegradable implants still require a minor surgical procedure for insertion so it has been argued that the use of injectable preparations, although irreversible for the duration of action, would be preferable. For this purpose, a number of polymeric systems, either microspheres or approximations of true microcapsules, have been developed. However, for most of them, the performance has been no better than that of simple esters. Data are included which indicate that simple esterification may be superior to polymeric drug-delivery systems.
INTRODUCTION
The development of delivery systems to optimize the dosage of contraceptive steroids has been an objective of several public-sector programs such as the Contraceptive Development Branch (CDB) of the National Institutes of Health, the Special Programme in Human Reproduction ( HRP) of the World Health Organization, the Population Council, the Program of Applied Research on Fertility Regulation (PARFR) and now the Contraceptive Research and Development Program (CONRAD) sponsored by the U.S. Agency for Inter*Paper presented at the Third International Symposium on Recent Advances in Drug Delivery Systems, February 24-27,1987, Salt Lake City, UT, U.S.A. **To whom correspondence should be addressed.
0168-3659/87/$03.50
0 1987 Elsevier Science Publishers
national Development. In addition, many pharmaceutical companies have explored the utility of long-acting contraceptives. There are many reasons for this interest, but the most important are to increase efficacy and to reduce the body burden with a concomitant increase in the margin of safety. Since the early sixties, synthetic steroids have been used for fertility regulation in oral dosage forms usually consisting of a fixed ratio combination of a progestogen and an estrogen. Because of the short half-lives of these drugs, blood levels in excess of those required to achieve the desiredpharmacodynamic effect, i.e. blockage of ovulation or at least alteration of cervical mucus to block sperm penetration, are required. Recent changes in formulations to biphasic or triphasic dosages have attempted to
B.V.
388
lower the total dose by having two or three ratios of progestogen to estrogen during the menstrual cycle but still require a greater drug level than is required if the dose could be administered in a zero-order delivery system. Low dose “mini-pills” have also been tried but have not been very successful due to a much higher pregnancy rate which probably can be attributed to the increased sensitivity to missed doses. The first attempt at a long-acting contraceptive steroid came shortly after the introduction of oral contraceptives in the form of an intramuscular injection of a microcrystalline suspension of the synthetic steroid depot medroxyprogesterone acetate (DMPA) , known by the trade-name of Depo-Provera@. This progestogen-only dosage accomplishes one of the objectives of a long-acting contraceptive, i.e. increases efficacy due to ease of compliance with the once-every-three-months dosage schedule, but at 150 mg per injection the total dose remains high and very high initial peaks in blood levels are obtained. In addition, this approach leads to significant disruptions of bleeding patterns. This drug has also had a difficult history with the Food and Drug Administration. Although approved for the treatment of endometrial carcinoma and renal carcinoma more than 25 years ago, when its use for contraception was requested, the application was not approved. Adverse findings in toxicity studies in beagle dogs and monkeys have been cited as reasons not to grant approval. This application has been in dispute now for at least 20 years and its resolution remains uncertain. Because the findings in dogs and monkeys have not been observed in humans, the drug is now approved in over 80 countries. In fact, in the four years between 1981 and 1985, it is estimated that the use for contraception worldwide has increased from 2,000,OOO to 4,000,OOO women although negative publicity ensuing from proceedings in the U.S. was at its height during that time. Another long-acting preparation on the market outside of the U.S. is norethindrone enanthate which ideally should be administered every 60
days and is estimated to be used by about l,OOO,OOOwomen. Thus, it would appear that a substantial market for long-acting delivery systems for contraceptive drugs exists.
BIODEGRADABLE
IMPLANTS
The diffusion of steroids through silicone rubber was first described in 1966 [ 1 ] and since then a promising, long-acting delivery system based on this technology has been developed by the Population Council [ 21. It is called NORPLANT@), is currently approved in several countries, and is now in an introductory phase in most parts of the world. Its major drawback is the need for 6 devices which is partially offset by its &year lifetime. An improved version requiring only two implants is currently being tested. Both of these systems require a surgical procedure to remove them, so programs to develop biodegradable implants have long been considered important [ 31. Because these approaches have often been described, it is not necessary to dwell on their characteristics other than to say that polymer classes such as polyesters, poly (ortho esters) and poly (amino acids) have frequently been used because their breakdown products are likely to be nontoxic. Although all of these approaches have made progress, not many have been tested in the clinic because reproducible delivery of the required amount of drug has not yet been demonstrated. One system which has advanced to clinical testing is based on poly (e-caprolactone) tubing filled with levonorgestrel suspended in ethyl oleate [ 41. The first clinical study of this delivery system which is called CAPRONOR@ was successful although only a 30-day exposure was tested [ 51. Subsequently WHO expanded the evaluation of this system by conducting studies in Bangkok and London (Figs. 1 and 2 ) . The size of the standard error seen in the plasma levels is in large part due to variations between individuals. In all of the studies no adverse reactions were noticed either systematically or
389
00I
5
10
15
20
25
30
35
40
45
W
Fig. 1. Mean levonorgestrel levels ( & s.e.) in the serum of subjects in London during treatment with one or two 2.5 cm Capronor devices.
-one Implant(2.5 cm, * TWO Implants (2.5 cm)
Fig. 2. Mean levonorgestrel levels ( f s.e.) in the serum of subjects in Bangkok during treatment with one or two 2.5 cm Capronor devices.
the site of the implants. Two-year toxicological evaluations in rats and monkeys were sponsored by NIH and again no adverse findings were reported. Therefore, NIH, WHO and the Indian Council of Medical Research are now starting a l-year Phase II clinical study in which the safety and efficacy of CAPRONOR@ will be ascertained.
at
INJECTABLE
MICROCAPSULES
Numerous investigators have published on the use of the polymers poly (lactic acid) and
poly ( glycolic acid) for drug delivery since the mid-1970’s and, in particular, for the release of contraceptive steroids [ 6-101. Poly (lactic acid) and poly (glycolic acid) and their copolymers have been used in implants and as injectable microcapsules or microspheres. Microcapsules represent a polymeric envelope through which the enclosed drug diffuses and microspheres, a polymer-drug matrix from which the drug is usually released by means of a combination of diffusion and erosion. The development of microspheres for releasing contraceptive steroids is discussed by Beck and Tice [ 111. Several approaches have been taken by different investigators but a significant part of the work on contraceptive steroids has been funded in recent years by PARFR, and systems for the release of norethindrone, levonorgestrel, progesterone, ethinyl estradiol and testosterone have been developed. Microsphere systems have the advantages that they can be administered by injection; the rate and duration of drug release in uiuo can be determined by selection of microsphere size and the degree of loading of the steroid in the microspheres; they are completely biodegradable; and do not cause irritation at the injection site. The only preparations on which there have been extensive clinical trials are those releasing norethindrone [ 121. As yet, only preliminary investigations have been undertaken with microsphere preparations of the other steroids. Studies are being undertaken on several of the norethindrone preparations to optimize the formulations and dosages needed for go-day contraceptive coverage.
LONG-ACTING
PRODRUGS
In 1975, WHO convened a meeting to assess the feasibility of synthesizing new long-acting progestogens and androgens, the former to be used in the development of new injectable fertility regulating agents in women and the lat-
terin conjunction with methods being developed inhibit spermatogenesis in the male [ 131. It was concluded that WHO would proceed with a chemical synthesis program in order to: a. obtain a long-acting agent that would be more potent than the two existing preparations, depot-medroxyprogesterone acetate (DMPA) and norethindrone enanthate, in that it would exert contraceptive activity for a period of up to 6 months and allow a decrease in the overall steroid load given to the body; b. obtain steroids with a different pharmacological profile, which would reduce progestogen-induced side effects, particularly intermenstrual bleeding; and c. allow a significant reduction of costs of the eventual products to the public sector. Rather than attempting to synthesize new steroid moieties, the approach taken was to use well-studied synthetic progestogens, initially norethindrone and later levonorgestrel, and prepare derivatives that would act as prodrugs. The prodrug would be inactive or at least have limited intrinsic progestagenic properties until hydrolyzed in the body to the active parent steroid. To achieve this aim, it was decided to synthesize esters at the tertiary hydroxyl group at position C-17 of the 19-nortestosterone compounds [ 14 1. A group of chemists from laboratories in Australia, Brazil, Bulgaria, People’s Republic of China, Democratic Republic of Germany, Iran, Mexico, Nigeria, Poland, Singapore, Spain, and Sri Lanka synthesized the agreed esters. In Several cases, the appropriate carboxylic acid was not available and had to be synthesized by the group. A system for the quality control of each ester and, if necessary, further purification was established. After formulation, the compounds were screened by CDB/NIH in a rat estrus suppression test. More than 230 esters, ester oximes and ethers of norethindrone and levonorgestrel were prepared of which 94 norethindrone esters and 45 levonorgestrel esters were evaluated. Three
Fig. 3. Levonorgestrel level in the cynomolgus monkey after a single dose of 10 mg, 20 mg or 40 mg of HRP003.
esters, the cyclobutylcarboxylate, the cyclopropylcarboxylate and the butanoate of levonorgestrel, all formulated as microcrystalline had considerably longer-acting suspensions, properties than did medroxyprogesterone acetate when assessed in this test system [ 151. Pharmacokinetic/pharmacodynamic studies were then undertaken by CDB in sub-human primates, mainly the cynomolgus monkey. While the rat estrus suppression test proved to be a most valuable screening tool, some caution must be exerted in totally relying on such a model since it did give rise to some anomalies. A study was undertaken by CDB of several levonorgestrel derivatives in the cynomolgus monkey including the cyclopentyl carboxylate as a “negative” control since it has shown little inhibition of estrus in the rat screening test. This ester gave a pharmacokinetic profile of levonorgestrel close to that which might be generated by an implant or other delivery system with levonorgestrel remaining detectable for 15 months (see Fig. 3). Based on the results of the monkey pharmacokinetic studies, there are four compounds arising from WHO’s Chemical Synthesis Programs which are presently under study as part of a joint WHO/NIH collaborative project to develop a new long-acting injectable contraceptive. These are:
391
cyclobutyl levonorgestrel HRPOOl carboxylate, HRPOO2 - levonorgestrel butanoate, HRP003 levonorgestrel cyciopentyl carboxylate, HRPOll. - levonorgestrel cyclopentyl carboxylate-3-oxime. Following assessment of toxicological data, and pharmacodynamic a pharmacokinetic study was begun with HRPOOl and HRPOOZ in humans, Data obtained from the rhesus monkey (Fig. 4) indicated that the two esters had quite different pharmacokinetic profiles, HRPOOB giving rise to a considerably smaller peak than HRPOOl. HRPOOB gave rise to measurable levels of levonorgestrel in the circulation for more than 100 days, while with HRPOOl levonorgestrel became unmeasurable at around 60 days. The monkey data indicated that, on a weight.-by-weight basis, a dose of 50 mg would be appropriate for study in the human. A study was then undertaken in 5 women on each compound in London and Mexico City and it was concluded that: a. unlike in the rhesus monkey, it is difficult to differentiate between the pharmacokinetic profiles of the two esters in the human; b. the peak levels of levonorgestrel are high (5-27 nmol/l) and levonorgestrel is still measurable in the plasma of most subjects up to 9 months after injection; and c. no subjects showed ovulatory levels of progesterone prior to 6 months. Thus the study has been repeated at dose levels of 12.5mg and 25 mg at the same two centers, London and Mexico City. Both centers have studied 5 subjects at each dosage, 12.5 mg and 25 mg, of both compounds. The data show that at a dose of 12.5mg ovulation returns during the third month post-injection. Analysis will shortly be undertaken on all the data from the study; however, preliminary assessment of the results would indicate that a dosage in the order of 15-20 mg of both these compounds assures inhibition of ovulation for a 3-month period. With regard to HRP003, the compound which
Fig. 4. Levonorgestrel levels in the rhesus monkey after a single dose of 5 mg WRPOOl, 5 mg HRPOOZ or 20 mg of DMPA
showed the long duration of action in the cynomolgus monkey, a pharmacokinetic/pharmacodynamic study was designed to see whether a similar pharmacokinetic profile could be obtained in the human. Although the expected dose is likely to be 40-50 mg, it was decided that because of the compound’s apparent long-acting properties, the study should begin with a dosage of 10 mg and 20 mg. Preliminary results from the study indicate no inhibition of ovulation during the first treatment month with either 10 mg or 20 mg. Finally, a pharmacokinetic/pharmacodynamic study of HRPOll, a levonorgestrel ester with the addition of an oxime group at C-3, has been started recently in the human. There is biological evidence that levonorgestrel acetate oxime and other oximes have a different hormonal profile to levonorgestrel which includes intrinsic estrogenic activity. This appears to manifest itself, in limited studies in the baboon and the human, as giving a less disruptive effect on the endometrium and thus fewer incidences of spotting and bleeding. Thus, WHO in collaboration with NIH has been looking closely at alternative oximes with long-acting properties. One compound which appears to have a better duration of activity than others synthesized is HRPOll. Hence a study of the pharmacokinetits of this compound was undertaken in the cynomolgus monkey which lead to the selection
392
of doses of 20 mg and 40 mg for the human pharmacokinetic study. A two-year toxicological study of HRPOll in rats and monkeys was recently completed in which HRPOll was given at doses of either 3, 30 or 150 mg/kg every 60 days in both species. On a weight basis, the doses used are probably more than 1 X, 10x and 50x the expected human dose. No adverse effects were observed and thus plans are currently being made to undertake a Phase II clinical trial to ascertain whether the oxime really does cause less disruption of endometrial bleeding compared with the existing injectable contraceptive steroids. Furthermore, the oxime, because of its intrinsic estrogenic properties, would be expected to have less effect on lipid and lipoprotein metabolism, hence a study to assess its effects on these parameters is also being planned. Long-acting dosage forms for males are also of great interest for fertility regulation. Although the administration of androgens alone has not been completely successful in the suppression of spermatogenesis, it is anticipated that in combination with agents such as GnRH antagonists, it will be necessary to supplement testosterone to maintain libido. Since the available esters of testosterone were too short in duration, e.g. testosterone enanthate needs to be given every 2 to 3 weeks, WHO and NIH explored many esters in their synthesis and screening program described above. In this instance, the best compound appears to be testosterone trans-4-n-butyl cyclohexyl carboxylate. After intramuscular injection in monkeys plasma levels were maintained at a constant level for almost 2 months as shown in Fig. 5 [ 161. The improvement in comparison to testosterone enanthate is quite significant. Although microcapsular approaches to delivery of testosterone are also underway, the large daily dose of approximately 5 mg makes it rather difficult. It is anticipated that both esters and microcapsules will be tested extensively in men in the near future [ 171.
Fig. 5. Testosterone levels in ovariectomized rhesus monkeys after a single intra-muscular
injection
on day zero.
DISCUSSION
In all of the approaches to achieving longacting delivery systems, difficulties have existed with reproducibility. Batch-to-batch variation in the preparation of microcapsules has plagued the investigators in this field, and on more than one occasion planned clinical trials have had to be cancelled due to release rates not meeting specifications. This difficulty has also occurred with implants, and in those systems where the dose is designed to be low the pregnancy rate is likely to skyrocket since there is little margin for error. On the other hand, the nominally simpler systems like DMPA can also be problematic. In fact, because it is illustrative of the problems one can encounter when developing dosage forms it is worth considering this example in some detail. DMPA is formulated as an aqueous microcrystalline suspension which can have differences in the particle size distribution despite their being micronized. The steroid can exist in several polymorphic forms which can influence the structure and hence the hardness of the crystals being micronized. Furthermore, the micronization process can be undertaken in several ways. Thus very different particle size distribution can be obtained, as shown in the examples in Fig. 6, whereas it can be claimed that both preparations are micronized. Differences in particle size can almost cer-
393
----
93% 35%
WT WT.
below below
10” IOU
s,7_e l”rni
Fig. 6. Particle size distribution of two formulations of DMPA.
tainly contribute to the efficacy of preparations in different populations. It is becoming clearer that there are significant differences between the pharmacokinetics and pharmacodynamics of a depot steroid in different populations. While there are several studies describing population differences, it is most clearly illustrated in studies on Thai and Mexican women. The Thai women adsorb and clear MPA faster than their Mexican counterparts [ 18,191. A schematic representation of differences in pharmacokinetic profiles is shown in Fig. 7. In addition, after DMPA use, ovulation returns more quickly in Thai women that in Mexican women [ 181. It is probable that diet, body mass or fat distribution are playing a role in the phar-
__---
Human,
Thai
Human,
Mexican
150 mg
macological differences observed in these two populations. These inherent population differences coupled with formulation differences may give rise to the type of situation found recently in Northern Thailand. McDaniel et al. [ 201 reported an increase in method failures with DMPA when certain family planning clinics changed from DMPA produced by one manufacturer to that produced by another. Since at that time about 110,000 women had received DMPA injections from that clinic and approximately 300,000 women-years of experience had been accumulated, an increase of pregnancy rate from 0.1 to 0.4% was considered unacceptable. It transpired that the pregnancies were associated with batches of the new brand of DMPA which had a small particle size (formulation 1 in Fig. 6). It is therefore postulated that in a population which absorbs and clears the drug rapidly, a formulation difference such as smaller particle size can exacerbate a situation in which women give rise to a pharmacokinetic profile close to the minimum required for go-day contraceptive coverage. A shorter period of coverage will ensue and hence a situation where there is risk of pregnancy prior to the next injection. To test this hypothesis WHO will shortly undertake a multicentered pharmacokinetic and pharmacodynamic study using DMPA formulated in three particle sizes: 3-10 pm, 10 - 20 pm and 20 - 40 pm. Centers in Mexico and Thailand will be included in the study.
150 mg
CONCLUSION
-. : ..\_
r
-._
--._
---__
---___ ------________
-----_-
-Mm
10
20
30
40
50
60
70
80
90
Days
Fig. 7. MPA levels in the circulation of Mexican and Thai women after a single dose of 150 mg of DMPA.
Although the results from the comparison study just described will take some time to obtain, the lesson has already been learned once more. In the past when simple formulations and oral dosage was the rule, the issue of bioavailability was not in the forefront. There is often not much that can be done about differences in metabolism and drug binding that can occur from one ethnic group to the next, other than
394
being constantly vigilant in the planning and analysis of clinical trials so that these differences are determined. However, for those of us who are in involved in the development of new dosage forms, particularly those which are now often disparagingly referred to as “high-tech”, there is an overwhelming need to concentrate more on the characterization and understanding of the physical-chemical properties of these systems so that lack of reproducibility no longer plagues us. REFERENCES P.J. Dziuk and B. Cook, Passage of steroids through silicone rubber, Endocrinolo~, 78 (1966) 208-211. I. Sivin, Clinical effects of NORPLANT~~ subdermal implants for contraception, in: D.R. Mishell, Jr. (Ed.), Long-Acting Steroid Contraception, Raven Press, New York, (1983), pp. 89-116. H.L. Mishell, Jr. (Ed.), Long-Acting Steroid Contraception, Raven Press, New York, (1983)) pp. 149-173. C.G. Pitt and A. Schindler, CAPRONOR@ - A biodegradable delivery system for levonorgestrel, in: G.L. Zatuchni, A. Goldsmith, J.D. Shelton and J.J. Sciarra (Eds.) , Long-Acting Contraceptive Delivery Systems, Harper and Row, Publishers, Philadelphia, (1984) pp. 48-63. S.J. Ory, C.B. Hammond, S.G. Yancy, R.W. Hendren, The effect, of a biodegradable contraceptive capsule (CAPRONOR@ ) containing levonorgestrel gonadotropin, estrogen and progesterone levels, Am. J. Obstet. Gynec., 145 (1983) 600-605. L.R. Beck, D.R. Gowsar, D.H. Lewis, J.W. Gibson, and C.E. Flowers, New long-acting injectable microcapsule contraceptive system, Am. J. Obstet. Gynecol., 135 (1979) 419-426. G.A. Boswell, Jr., and R.M. Scribner, Polylactide drug mixtures, US. Patent. 3,773,199, (1973). D.L. Gardner, A.J. Patanus, and D.J. Fink, Steroid release from microcapsules, in: Drug Delivery Systems, H.L. Gabelnick (Ed.), Department of Health, Education and Welfare, Washin~n, D.C., DHEW Publ. No. (NIH) 77-1238, (1977), pp. 265-278.
R. Gurney, N.A. Peppas, D.D. Harrington and G.S. Banks, Development of biodegradable and injectable latices for controlled release of potent drugs, Drug Devel. Industr. Pharm., 7 (1981) I-25. 10 T.M. Jackanicz, H.A. Nash, D.L. Wise and J.B. Gregory, Poly (lactic acid) as a biodegradable carrier for contraceptive steroids, Contraception, 8 (1973) 227.-233. 11 L.R. Beck and T.R. Tice, Poly (lactic acid) and poly (lactic acid-co-glycolic acid) contraceptive delivery systems, in: D.R. Mishell (Ed. ) , Long-Acting Steroid contraception, Raven Press. New York, (1983), pp. 175-199. 12 L.R. Beck, V.Z. Pope, Long-acting injectable northisterone contraceptive system: Review of clinical studies, Research Frontiers in Fertility Regulation, 3 (2 ) (1984) 1. 13 P. Crabbe, E. Diczfalusy and C. Djerassi, Injectable contraceptive synthesis, an example of international cooperation, Science, 209 (1980) 992-994. 14 P. Crabbk, S. Archer, G. Benagiano, E. Diczfalusy, C. Djerassi, J. Fried and T. Higuchi, Long-acting contraceptive agents, design of the WHO chemical synthesis programme, Steroids, 41 (1983) 243-253. 15 P.E. Hall, G. Bialy, R.P. Blye and P. Crabbe, Development of certain levonorgestrel esters as long-acting injectable contraceptives, in: G.I. Zatuchni, A. Goldsmith, J.D. Shelton and J.J. Sciarra (Eds.), LongActing Contraceptive Delivery Systems, Harper and Row, Philadelphia, (1984), pp. 190-200. 16 G.M.H. Waites, Methods for the regulation of male fertility, in: S.-Z. Qian and G.M.H. Waites (Eds.) , Advances im Fertility Regulation in the Male, The People’s Medical Publishing House, Beijing, (1985), pp. 1-9. 17 A. Goldsmith, personal communication, 1986. 18 S. Basso], J. Garza-Flores, M.C. Cravioto, V. DiazSanchez, K. Fotherby, R. Lichtenburg and G. PerezPalacios, Ovarian function following a single administration of depo-medroxyprogesterone acetate (DMPA) at different doses, Fertil. Steril. 42 (1984) 216-222. 19 K. Fotherby, S. Koertswang and M.A. Mathrubutham, A pharmacokinetic study of different doses of Depo-Provers, Contraception, 22 (1980) 527-536. 20 E.B. McDaniel, R.H. Gray, and T. Pardthisong, Method failure pregnancy rates with Depo-Provera and local substitute. Lancet (1984) 1293. 9
Release, 6 (1987)
Elsevier Science Publishers
LONG-ACTING
METHODS
387
387-394
B.V.. Amsterdam
-
Printed
in The Netherlands
FOR FERTILITY
REGULATION*
Henry L. Gabelnick** Contraceptive
Research and Development
Program,
16 11 North Kent Street, Suite 806, Arlington,
Virginia 22209
(U.S.A.)
and Peter E. Hall Special Programme of Research, Development 12 11 Geneva 2 7 (Switzerland)
and Research Training in Human Reproduction,
World Health Organization,
The development of sophisticated technology for the zero-order delivery of contraceptive steroids has been the goal of several public-sector organizations and some pharmaceutical companies for nearly a generation. In fact, a nondegradable implant which delivers the progestogen, levonorgestrel, from silicone rubber (NORPLANT@) has already been approved in six countries and will be submitted for approval by the FDA shortly. Several approaches to biodegradable implants have been attempted with more or less success. The biodegradable implants still require a minor surgical procedure for insertion so it has been argued that the use of injectable preparations, although irreversible for the duration of action, would be preferable. For this purpose, a number of polymeric systems, either microspheres or approximations of true microcapsules, have been developed. However, for most of them, the performance has been no better than that of simple esters. Data are included which indicate that simple esterification may be superior to polymeric drug-delivery systems.
INTRODUCTION
The development of delivery systems to optimize the dosage of contraceptive steroids has been an objective of several public-sector programs such as the Contraceptive Development Branch (CDB) of the National Institutes of Health, the Special Programme in Human Reproduction ( HRP) of the World Health Organization, the Population Council, the Program of Applied Research on Fertility Regulation (PARFR) and now the Contraceptive Research and Development Program (CONRAD) sponsored by the U.S. Agency for Inter*Paper presented at the Third International Symposium on Recent Advances in Drug Delivery Systems, February 24-27,1987, Salt Lake City, UT, U.S.A. **To whom correspondence should be addressed.
0168-3659/87/$03.50
0 1987 Elsevier Science Publishers
national Development. In addition, many pharmaceutical companies have explored the utility of long-acting contraceptives. There are many reasons for this interest, but the most important are to increase efficacy and to reduce the body burden with a concomitant increase in the margin of safety. Since the early sixties, synthetic steroids have been used for fertility regulation in oral dosage forms usually consisting of a fixed ratio combination of a progestogen and an estrogen. Because of the short half-lives of these drugs, blood levels in excess of those required to achieve the desiredpharmacodynamic effect, i.e. blockage of ovulation or at least alteration of cervical mucus to block sperm penetration, are required. Recent changes in formulations to biphasic or triphasic dosages have attempted to
B.V.
388
lower the total dose by having two or three ratios of progestogen to estrogen during the menstrual cycle but still require a greater drug level than is required if the dose could be administered in a zero-order delivery system. Low dose “mini-pills” have also been tried but have not been very successful due to a much higher pregnancy rate which probably can be attributed to the increased sensitivity to missed doses. The first attempt at a long-acting contraceptive steroid came shortly after the introduction of oral contraceptives in the form of an intramuscular injection of a microcrystalline suspension of the synthetic steroid depot medroxyprogesterone acetate (DMPA) , known by the trade-name of Depo-Provera@. This progestogen-only dosage accomplishes one of the objectives of a long-acting contraceptive, i.e. increases efficacy due to ease of compliance with the once-every-three-months dosage schedule, but at 150 mg per injection the total dose remains high and very high initial peaks in blood levels are obtained. In addition, this approach leads to significant disruptions of bleeding patterns. This drug has also had a difficult history with the Food and Drug Administration. Although approved for the treatment of endometrial carcinoma and renal carcinoma more than 25 years ago, when its use for contraception was requested, the application was not approved. Adverse findings in toxicity studies in beagle dogs and monkeys have been cited as reasons not to grant approval. This application has been in dispute now for at least 20 years and its resolution remains uncertain. Because the findings in dogs and monkeys have not been observed in humans, the drug is now approved in over 80 countries. In fact, in the four years between 1981 and 1985, it is estimated that the use for contraception worldwide has increased from 2,000,OOO to 4,000,OOO women although negative publicity ensuing from proceedings in the U.S. was at its height during that time. Another long-acting preparation on the market outside of the U.S. is norethindrone enanthate which ideally should be administered every 60
days and is estimated to be used by about l,OOO,OOOwomen. Thus, it would appear that a substantial market for long-acting delivery systems for contraceptive drugs exists.
BIODEGRADABLE
IMPLANTS
The diffusion of steroids through silicone rubber was first described in 1966 [ 1 ] and since then a promising, long-acting delivery system based on this technology has been developed by the Population Council [ 21. It is called NORPLANT@), is currently approved in several countries, and is now in an introductory phase in most parts of the world. Its major drawback is the need for 6 devices which is partially offset by its &year lifetime. An improved version requiring only two implants is currently being tested. Both of these systems require a surgical procedure to remove them, so programs to develop biodegradable implants have long been considered important [ 31. Because these approaches have often been described, it is not necessary to dwell on their characteristics other than to say that polymer classes such as polyesters, poly (ortho esters) and poly (amino acids) have frequently been used because their breakdown products are likely to be nontoxic. Although all of these approaches have made progress, not many have been tested in the clinic because reproducible delivery of the required amount of drug has not yet been demonstrated. One system which has advanced to clinical testing is based on poly (e-caprolactone) tubing filled with levonorgestrel suspended in ethyl oleate [ 41. The first clinical study of this delivery system which is called CAPRONOR@ was successful although only a 30-day exposure was tested [ 51. Subsequently WHO expanded the evaluation of this system by conducting studies in Bangkok and London (Figs. 1 and 2 ) . The size of the standard error seen in the plasma levels is in large part due to variations between individuals. In all of the studies no adverse reactions were noticed either systematically or
389
00I
5
10
15
20
25
30
35
40
45
W
Fig. 1. Mean levonorgestrel levels ( & s.e.) in the serum of subjects in London during treatment with one or two 2.5 cm Capronor devices.
-one Implant(2.5 cm, * TWO Implants (2.5 cm)
Fig. 2. Mean levonorgestrel levels ( f s.e.) in the serum of subjects in Bangkok during treatment with one or two 2.5 cm Capronor devices.
the site of the implants. Two-year toxicological evaluations in rats and monkeys were sponsored by NIH and again no adverse findings were reported. Therefore, NIH, WHO and the Indian Council of Medical Research are now starting a l-year Phase II clinical study in which the safety and efficacy of CAPRONOR@ will be ascertained.
at
INJECTABLE
MICROCAPSULES
Numerous investigators have published on the use of the polymers poly (lactic acid) and
poly ( glycolic acid) for drug delivery since the mid-1970’s and, in particular, for the release of contraceptive steroids [ 6-101. Poly (lactic acid) and poly (glycolic acid) and their copolymers have been used in implants and as injectable microcapsules or microspheres. Microcapsules represent a polymeric envelope through which the enclosed drug diffuses and microspheres, a polymer-drug matrix from which the drug is usually released by means of a combination of diffusion and erosion. The development of microspheres for releasing contraceptive steroids is discussed by Beck and Tice [ 111. Several approaches have been taken by different investigators but a significant part of the work on contraceptive steroids has been funded in recent years by PARFR, and systems for the release of norethindrone, levonorgestrel, progesterone, ethinyl estradiol and testosterone have been developed. Microsphere systems have the advantages that they can be administered by injection; the rate and duration of drug release in uiuo can be determined by selection of microsphere size and the degree of loading of the steroid in the microspheres; they are completely biodegradable; and do not cause irritation at the injection site. The only preparations on which there have been extensive clinical trials are those releasing norethindrone [ 121. As yet, only preliminary investigations have been undertaken with microsphere preparations of the other steroids. Studies are being undertaken on several of the norethindrone preparations to optimize the formulations and dosages needed for go-day contraceptive coverage.
LONG-ACTING
PRODRUGS
In 1975, WHO convened a meeting to assess the feasibility of synthesizing new long-acting progestogens and androgens, the former to be used in the development of new injectable fertility regulating agents in women and the lat-
terin conjunction with methods being developed inhibit spermatogenesis in the male [ 131. It was concluded that WHO would proceed with a chemical synthesis program in order to: a. obtain a long-acting agent that would be more potent than the two existing preparations, depot-medroxyprogesterone acetate (DMPA) and norethindrone enanthate, in that it would exert contraceptive activity for a period of up to 6 months and allow a decrease in the overall steroid load given to the body; b. obtain steroids with a different pharmacological profile, which would reduce progestogen-induced side effects, particularly intermenstrual bleeding; and c. allow a significant reduction of costs of the eventual products to the public sector. Rather than attempting to synthesize new steroid moieties, the approach taken was to use well-studied synthetic progestogens, initially norethindrone and later levonorgestrel, and prepare derivatives that would act as prodrugs. The prodrug would be inactive or at least have limited intrinsic progestagenic properties until hydrolyzed in the body to the active parent steroid. To achieve this aim, it was decided to synthesize esters at the tertiary hydroxyl group at position C-17 of the 19-nortestosterone compounds [ 14 1. A group of chemists from laboratories in Australia, Brazil, Bulgaria, People’s Republic of China, Democratic Republic of Germany, Iran, Mexico, Nigeria, Poland, Singapore, Spain, and Sri Lanka synthesized the agreed esters. In Several cases, the appropriate carboxylic acid was not available and had to be synthesized by the group. A system for the quality control of each ester and, if necessary, further purification was established. After formulation, the compounds were screened by CDB/NIH in a rat estrus suppression test. More than 230 esters, ester oximes and ethers of norethindrone and levonorgestrel were prepared of which 94 norethindrone esters and 45 levonorgestrel esters were evaluated. Three
Fig. 3. Levonorgestrel level in the cynomolgus monkey after a single dose of 10 mg, 20 mg or 40 mg of HRP003.
esters, the cyclobutylcarboxylate, the cyclopropylcarboxylate and the butanoate of levonorgestrel, all formulated as microcrystalline had considerably longer-acting suspensions, properties than did medroxyprogesterone acetate when assessed in this test system [ 151. Pharmacokinetic/pharmacodynamic studies were then undertaken by CDB in sub-human primates, mainly the cynomolgus monkey. While the rat estrus suppression test proved to be a most valuable screening tool, some caution must be exerted in totally relying on such a model since it did give rise to some anomalies. A study was undertaken by CDB of several levonorgestrel derivatives in the cynomolgus monkey including the cyclopentyl carboxylate as a “negative” control since it has shown little inhibition of estrus in the rat screening test. This ester gave a pharmacokinetic profile of levonorgestrel close to that which might be generated by an implant or other delivery system with levonorgestrel remaining detectable for 15 months (see Fig. 3). Based on the results of the monkey pharmacokinetic studies, there are four compounds arising from WHO’s Chemical Synthesis Programs which are presently under study as part of a joint WHO/NIH collaborative project to develop a new long-acting injectable contraceptive. These are:
391
cyclobutyl levonorgestrel HRPOOl carboxylate, HRPOO2 - levonorgestrel butanoate, HRP003 levonorgestrel cyciopentyl carboxylate, HRPOll. - levonorgestrel cyclopentyl carboxylate-3-oxime. Following assessment of toxicological data, and pharmacodynamic a pharmacokinetic study was begun with HRPOOl and HRPOOZ in humans, Data obtained from the rhesus monkey (Fig. 4) indicated that the two esters had quite different pharmacokinetic profiles, HRPOOB giving rise to a considerably smaller peak than HRPOOl. HRPOOB gave rise to measurable levels of levonorgestrel in the circulation for more than 100 days, while with HRPOOl levonorgestrel became unmeasurable at around 60 days. The monkey data indicated that, on a weight.-by-weight basis, a dose of 50 mg would be appropriate for study in the human. A study was then undertaken in 5 women on each compound in London and Mexico City and it was concluded that: a. unlike in the rhesus monkey, it is difficult to differentiate between the pharmacokinetic profiles of the two esters in the human; b. the peak levels of levonorgestrel are high (5-27 nmol/l) and levonorgestrel is still measurable in the plasma of most subjects up to 9 months after injection; and c. no subjects showed ovulatory levels of progesterone prior to 6 months. Thus the study has been repeated at dose levels of 12.5mg and 25 mg at the same two centers, London and Mexico City. Both centers have studied 5 subjects at each dosage, 12.5 mg and 25 mg, of both compounds. The data show that at a dose of 12.5mg ovulation returns during the third month post-injection. Analysis will shortly be undertaken on all the data from the study; however, preliminary assessment of the results would indicate that a dosage in the order of 15-20 mg of both these compounds assures inhibition of ovulation for a 3-month period. With regard to HRP003, the compound which
Fig. 4. Levonorgestrel levels in the rhesus monkey after a single dose of 5 mg WRPOOl, 5 mg HRPOOZ or 20 mg of DMPA
showed the long duration of action in the cynomolgus monkey, a pharmacokinetic/pharmacodynamic study was designed to see whether a similar pharmacokinetic profile could be obtained in the human. Although the expected dose is likely to be 40-50 mg, it was decided that because of the compound’s apparent long-acting properties, the study should begin with a dosage of 10 mg and 20 mg. Preliminary results from the study indicate no inhibition of ovulation during the first treatment month with either 10 mg or 20 mg. Finally, a pharmacokinetic/pharmacodynamic study of HRPOll, a levonorgestrel ester with the addition of an oxime group at C-3, has been started recently in the human. There is biological evidence that levonorgestrel acetate oxime and other oximes have a different hormonal profile to levonorgestrel which includes intrinsic estrogenic activity. This appears to manifest itself, in limited studies in the baboon and the human, as giving a less disruptive effect on the endometrium and thus fewer incidences of spotting and bleeding. Thus, WHO in collaboration with NIH has been looking closely at alternative oximes with long-acting properties. One compound which appears to have a better duration of activity than others synthesized is HRPOll. Hence a study of the pharmacokinetits of this compound was undertaken in the cynomolgus monkey which lead to the selection
392
of doses of 20 mg and 40 mg for the human pharmacokinetic study. A two-year toxicological study of HRPOll in rats and monkeys was recently completed in which HRPOll was given at doses of either 3, 30 or 150 mg/kg every 60 days in both species. On a weight basis, the doses used are probably more than 1 X, 10x and 50x the expected human dose. No adverse effects were observed and thus plans are currently being made to undertake a Phase II clinical trial to ascertain whether the oxime really does cause less disruption of endometrial bleeding compared with the existing injectable contraceptive steroids. Furthermore, the oxime, because of its intrinsic estrogenic properties, would be expected to have less effect on lipid and lipoprotein metabolism, hence a study to assess its effects on these parameters is also being planned. Long-acting dosage forms for males are also of great interest for fertility regulation. Although the administration of androgens alone has not been completely successful in the suppression of spermatogenesis, it is anticipated that in combination with agents such as GnRH antagonists, it will be necessary to supplement testosterone to maintain libido. Since the available esters of testosterone were too short in duration, e.g. testosterone enanthate needs to be given every 2 to 3 weeks, WHO and NIH explored many esters in their synthesis and screening program described above. In this instance, the best compound appears to be testosterone trans-4-n-butyl cyclohexyl carboxylate. After intramuscular injection in monkeys plasma levels were maintained at a constant level for almost 2 months as shown in Fig. 5 [ 161. The improvement in comparison to testosterone enanthate is quite significant. Although microcapsular approaches to delivery of testosterone are also underway, the large daily dose of approximately 5 mg makes it rather difficult. It is anticipated that both esters and microcapsules will be tested extensively in men in the near future [ 171.
Fig. 5. Testosterone levels in ovariectomized rhesus monkeys after a single intra-muscular
injection
on day zero.
DISCUSSION
In all of the approaches to achieving longacting delivery systems, difficulties have existed with reproducibility. Batch-to-batch variation in the preparation of microcapsules has plagued the investigators in this field, and on more than one occasion planned clinical trials have had to be cancelled due to release rates not meeting specifications. This difficulty has also occurred with implants, and in those systems where the dose is designed to be low the pregnancy rate is likely to skyrocket since there is little margin for error. On the other hand, the nominally simpler systems like DMPA can also be problematic. In fact, because it is illustrative of the problems one can encounter when developing dosage forms it is worth considering this example in some detail. DMPA is formulated as an aqueous microcrystalline suspension which can have differences in the particle size distribution despite their being micronized. The steroid can exist in several polymorphic forms which can influence the structure and hence the hardness of the crystals being micronized. Furthermore, the micronization process can be undertaken in several ways. Thus very different particle size distribution can be obtained, as shown in the examples in Fig. 6, whereas it can be claimed that both preparations are micronized. Differences in particle size can almost cer-
393
----
93% 35%
WT WT.
below below
10” IOU
s,7_e l”rni
Fig. 6. Particle size distribution of two formulations of DMPA.
tainly contribute to the efficacy of preparations in different populations. It is becoming clearer that there are significant differences between the pharmacokinetics and pharmacodynamics of a depot steroid in different populations. While there are several studies describing population differences, it is most clearly illustrated in studies on Thai and Mexican women. The Thai women adsorb and clear MPA faster than their Mexican counterparts [ 18,191. A schematic representation of differences in pharmacokinetic profiles is shown in Fig. 7. In addition, after DMPA use, ovulation returns more quickly in Thai women that in Mexican women [ 181. It is probable that diet, body mass or fat distribution are playing a role in the phar-
__---
Human,
Thai
Human,
Mexican
150 mg
macological differences observed in these two populations. These inherent population differences coupled with formulation differences may give rise to the type of situation found recently in Northern Thailand. McDaniel et al. [ 201 reported an increase in method failures with DMPA when certain family planning clinics changed from DMPA produced by one manufacturer to that produced by another. Since at that time about 110,000 women had received DMPA injections from that clinic and approximately 300,000 women-years of experience had been accumulated, an increase of pregnancy rate from 0.1 to 0.4% was considered unacceptable. It transpired that the pregnancies were associated with batches of the new brand of DMPA which had a small particle size (formulation 1 in Fig. 6). It is therefore postulated that in a population which absorbs and clears the drug rapidly, a formulation difference such as smaller particle size can exacerbate a situation in which women give rise to a pharmacokinetic profile close to the minimum required for go-day contraceptive coverage. A shorter period of coverage will ensue and hence a situation where there is risk of pregnancy prior to the next injection. To test this hypothesis WHO will shortly undertake a multicentered pharmacokinetic and pharmacodynamic study using DMPA formulated in three particle sizes: 3-10 pm, 10 - 20 pm and 20 - 40 pm. Centers in Mexico and Thailand will be included in the study.
150 mg
CONCLUSION
-. : ..\_
r
-._
--._
---__
---___ ------________
-----_-
-Mm
10
20
30
40
50
60
70
80
90
Days
Fig. 7. MPA levels in the circulation of Mexican and Thai women after a single dose of 150 mg of DMPA.
Although the results from the comparison study just described will take some time to obtain, the lesson has already been learned once more. In the past when simple formulations and oral dosage was the rule, the issue of bioavailability was not in the forefront. There is often not much that can be done about differences in metabolism and drug binding that can occur from one ethnic group to the next, other than
394
being constantly vigilant in the planning and analysis of clinical trials so that these differences are determined. However, for those of us who are in involved in the development of new dosage forms, particularly those which are now often disparagingly referred to as “high-tech”, there is an overwhelming need to concentrate more on the characterization and understanding of the physical-chemical properties of these systems so that lack of reproducibility no longer plagues us. REFERENCES P.J. Dziuk and B. Cook, Passage of steroids through silicone rubber, Endocrinolo~, 78 (1966) 208-211. I. Sivin, Clinical effects of NORPLANT~~ subdermal implants for contraception, in: D.R. Mishell, Jr. (Ed.), Long-Acting Steroid Contraception, Raven Press, New York, (1983), pp. 89-116. H.L. Mishell, Jr. (Ed.), Long-Acting Steroid Contraception, Raven Press, New York, (1983)) pp. 149-173. C.G. Pitt and A. Schindler, CAPRONOR@ - A biodegradable delivery system for levonorgestrel, in: G.L. Zatuchni, A. Goldsmith, J.D. Shelton and J.J. Sciarra (Eds.) , Long-Acting Contraceptive Delivery Systems, Harper and Row, Publishers, Philadelphia, (1984) pp. 48-63. S.J. Ory, C.B. Hammond, S.G. Yancy, R.W. Hendren, The effect, of a biodegradable contraceptive capsule (CAPRONOR@ ) containing levonorgestrel gonadotropin, estrogen and progesterone levels, Am. J. Obstet. Gynec., 145 (1983) 600-605. L.R. Beck, D.R. Gowsar, D.H. Lewis, J.W. Gibson, and C.E. Flowers, New long-acting injectable microcapsule contraceptive system, Am. J. Obstet. Gynecol., 135 (1979) 419-426. G.A. Boswell, Jr., and R.M. Scribner, Polylactide drug mixtures, US. Patent. 3,773,199, (1973). D.L. Gardner, A.J. Patanus, and D.J. Fink, Steroid release from microcapsules, in: Drug Delivery Systems, H.L. Gabelnick (Ed.), Department of Health, Education and Welfare, Washin~n, D.C., DHEW Publ. No. (NIH) 77-1238, (1977), pp. 265-278.
R. Gurney, N.A. Peppas, D.D. Harrington and G.S. Banks, Development of biodegradable and injectable latices for controlled release of potent drugs, Drug Devel. Industr. Pharm., 7 (1981) I-25. 10 T.M. Jackanicz, H.A. Nash, D.L. Wise and J.B. Gregory, Poly (lactic acid) as a biodegradable carrier for contraceptive steroids, Contraception, 8 (1973) 227.-233. 11 L.R. Beck and T.R. Tice, Poly (lactic acid) and poly (lactic acid-co-glycolic acid) contraceptive delivery systems, in: D.R. Mishell (Ed. ) , Long-Acting Steroid contraception, Raven Press. New York, (1983), pp. 175-199. 12 L.R. Beck, V.Z. Pope, Long-acting injectable northisterone contraceptive system: Review of clinical studies, Research Frontiers in Fertility Regulation, 3 (2 ) (1984) 1. 13 P. Crabbe, E. Diczfalusy and C. Djerassi, Injectable contraceptive synthesis, an example of international cooperation, Science, 209 (1980) 992-994. 14 P. Crabbk, S. Archer, G. Benagiano, E. Diczfalusy, C. Djerassi, J. Fried and T. Higuchi, Long-acting contraceptive agents, design of the WHO chemical synthesis programme, Steroids, 41 (1983) 243-253. 15 P.E. Hall, G. Bialy, R.P. Blye and P. Crabbe, Development of certain levonorgestrel esters as long-acting injectable contraceptives, in: G.I. Zatuchni, A. Goldsmith, J.D. Shelton and J.J. Sciarra (Eds.), LongActing Contraceptive Delivery Systems, Harper and Row, Philadelphia, (1984), pp. 190-200. 16 G.M.H. Waites, Methods for the regulation of male fertility, in: S.-Z. Qian and G.M.H. Waites (Eds.) , Advances im Fertility Regulation in the Male, The People’s Medical Publishing House, Beijing, (1985), pp. 1-9. 17 A. Goldsmith, personal communication, 1986. 18 S. Basso], J. Garza-Flores, M.C. Cravioto, V. DiazSanchez, K. Fotherby, R. Lichtenburg and G. PerezPalacios, Ovarian function following a single administration of depo-medroxyprogesterone acetate (DMPA) at different doses, Fertil. Steril. 42 (1984) 216-222. 19 K. Fotherby, S. Koertswang and M.A. Mathrubutham, A pharmacokinetic study of different doses of Depo-Provers, Contraception, 22 (1980) 527-536. 20 E.B. McDaniel, R.H. Gray, and T. Pardthisong, Method failure pregnancy rates with Depo-Provera and local substitute. Lancet (1984) 1293. 9