Studies on the absorption, distribution, and elimination of amiquinsin hydrochloride, a hypotensive drug

EUROPEAN JOURNAL OF PHARMACOLOGY 10 (1970) 360-368. NORTH-HOLLAND PUBLISHING COMPANY

STUDIES ON THE ABSORPTION, OF AMIQUINSIN

DISTRIBUTION,

HYDROCHLORIDE,

AND ELIMINATION

A HYPOTENSIVE

DRUG

John D. CONKLIN and R.D. HOLLIFIELD Drug Distribution Unit, Eaton Laboratories, The Norwich Pharmacal Company, Norwich, New York 13815, USA

Accepted 24 Febraury 1970

Received 23 September 1969

J.D. CONKLIN and R.D. HOLLIFIELD, Studies on the absorption, distribution, and elimination of amiquinsin hydrochloride, a hypotensive drug, European J. Pharmacol. 10 (1970) 360-368. A sensitive and specific spectrophotofluorometric procedure is described for the determination of amiquinsin hydrochloride, a hypotensive drug, in biologic materials. Results are presented which show that either oral or parenteral dosage of amiquinsin HC1 to dogs yields blood drug levels which are dose related and linear urinary drug dose responses. At least 1/5 of the dose usually is recovered in urine under these conditions. Intravenous administration of amiquinsin HCI to dogs results in a biphasic drug disappearance curve in blood. Only low concentrations of amiquinsin HCI were detectable in the bile, aqueous humor, and cerebrospinal fluid of the dog. Although no major specific tissue binding sites were apparent for amiquinsin HCI in the dog, the drug was found in most tissues at levels greater than those currently present in blood. Evidence is also presented which indicates that there is placental transfer of amiquinsin HCI in the guinea pig, rabbit, dog, and sheep. Drug analysis

Biphasic drug disappearance

Drug dose response

1. INTRODUCTION Amiquinsin hydrochloride, 4-amino-6,7-dimethoxquinoline hydrochloride hydrate, is a drug which exhibits hypotensive activity (Jandhyala, Grega and Buckiey, 1967). The structural formula m a y be represented as follows:

NH2 C H 3 0 ~ CH30 ~ , ~ N ~ j

HC1-H20

Amiquinsin hydrochloride Results are presented in this paper concerning the absorption, distribution, and elimination o f amiquinsin HC1 in the dog. The relationship between these parameters and the pharmacologic properties of the drug are discussed. Data also are reported regarding a

Drug transfer

sensitive and specific spectrophotofluorometric procedure for the determination o f this drug in biologic materials.

2. MATERIALS AND METHODS 2.1. Drug characteristics

Amiquinsin HC1, a white crystalline powder with a molecular weight o f 258.70 and a decomposition point of 2 6 6 - 2 6 7 °, has a solubility in water of at least 50 g/l, with a pH o f 5.3 at saturation. It is well established that protein binding, degree o f ionization, and lipid solubility are major factors regulating drug transfer (Brodie, 1964). Information on these characteristics for amiquinsin HC1 are presented in table 1. The partition coefficient for amiquinsin HCI in selected solvents versus buffer (phosphate 0.154 M, pH 7.4) was determined as an index

J.D.Conklin, R.D.Hollifield, Absorption, distribution, and elimination of amiquinsin hydrochloride Table 1 Factors regulating drug transfer. pKa a) 9.05

Partition coefficient b) solvent-buffer Chloroform 0.144 Benzene 0.004 Heptane 0.009

Plasmaprotein binding In vitro c) In vim c) 2 hr 53.8% 6 hr 17.8% 24 hr 6.2%

45.8% 15.2% 7.3%

a) pKa of the free base of amiquinsin HC1. b) Determined as described by Conklin, Buzard, and Heotis (1965), using phosphate buffer 0.154 M, pH 7.4. c) Determined as described by Buzard, Conklin, and Buller (1961), with the exception that 100 ml of phosphate buffer 0.154 M, pH 7.4 was used as a bath. In vitro-Drug added to control dog plasma. In vim-Plasma collected from dogs dosed with drug. of lipid solubility (Conklin, Buzard, and Heotis, 1965). Plasma-protein binding was measured by dialysis at pH 7.4 as described in an earlier report (Buzard, Conklin, and Buller, 1961), using either samples of freshly collected control dog plasma to which the drug was added (in vitro) or samples obtained from dogs following an intravenous infusion of the drug (in vivo). These studies were conducted at drug concentrations representative of those encountered during experimental investigation. 2.2. Drug administration Amiquinsin HC1 was administered orally to dogs as crystalline material in gelatin capsules. The drug was also administered parenterally (intravenously or intramuscularly) to dogs as a solution in 5% dextrose, pH 4.4 to 4.8. Drug solutions were infused intravenously at a rate of 1.91 ml/min and at doses ranging from 1.25 to 10.00 mg/kg per hr using a Harvard pump. 2.3. Collection o f biologic materials Sodium pentobarbital, administered either intravenously or intraperitoneally, served as an anesthetic. Blood samples usually were collected concurrently with samples of biologic fluids and tissues, by venipuncture or cardiac puncture, using heparin as an anticoagulant. Urine was obtained as a voided sample or by catheterization. Unless otherwise indicated, healthy, adult male Beagle dogs were used throughout the study.

361

Amiquinsin HC1 was infused intravenously in dogs for 1 to 5 hr and aqueous humor (AH) and cerebrospinal fluid (CSF) obtained as described by Buzard and Conklin (1965). For bile collection the common bile duct was cannulated just cephalad to the entrance into the duodenum, the gall bladder emptied of bile, and the cystic duct then ligated at the juncture with the common bile duct. Both ureters were cannulated and the urine was pooled during collection. The drug was infused intravenously in these dogs for 1 hr. In the investigation of the tissue disposition of amiquinsin HC1 in the dog, the drug was administered intravenously as a single injection and a blood sample collected at a specified time after dosage. The animal was then anesthetized, immediately sacrificed by exsanguination, and samples of tissues were rapidly removed, washed, and frozen. This procedure also was repeated with 2 pregnant Beagles (last period of gestation) which had received the drug orally for 14 days. The placental transfer of amiquinsin HC1 was investigated in guinea pigs, rabbits, dogs, and sheep in the last period of gestation using methods reported earlier (Conklin, Buzard, and Heotis, 1965). Solutions of the drug were infused intravenously into the femoral vein at doses ranging from 1.25 to 5.00 mg/kg per hr for 2 hr and at the following rates (ml/min): guinea pig 0.51, rabbit 0.764, dog 1.91, and sheep 3.82. Degradation studies with amiquinsin HC1 were conducted with maternal and fetal kidney and liver slices from the guinea pig and dog using the procedure of Buzard and Conklin (1964). 2.4. Drug analysis The reagents used include crystalline amiquinsin HC1 from Eaton laboratories; 0.2 M glycine buffer, pH 10.6 (prepared with ammonia-free glycine and sodium hydroxide); 0.1 N hydrochloric acid; 1-hexanol (practical grade); and heptane (practical grade). A Baird-Atomic Fluorispec (Model SF-1) with the following instrumental parameters was used to measure fluorescence: slit arrangement for both excitation and fluorescence was no. 3; the light path was adjusted with a no. 3 spacer; sensitivity was no. 8; the excitation wavelength was 330 nm and the fluorescence wavelength 360 nm. Exactly 50 mg of amiquinsin HCI are dissolved in

362

J.D.Conklin, R.D.Hollifield, Absorption. distribution, and elimination of amiquinsin hydrochloride

50 ml of water. Ten ml of this solution are diluted with water to obtain a final drug concentration of 100 gg/ml. This solution is then diluted with water to obtain standards in the range of 0.10 to lOpg per sample. Aqueous standards are prepared using 0.5 ml of water and 1.0 ml of a standard solution. The reference standards are prepared using 0.5 ml of biologic fluid or 0.5 g of biologic tissue and 1.0 ml of a standard solution. Water and the respective biologic fluid or tissue, used to prepare the reference standards, serve as control samples. Dilute 0.5 ml of the biologic fluid with 1.0 ml of water, add 1.5 ml of the 0.2 M glycine buffer, and mix. Five ml of the hexanol and heptane admixture (4:1) are then added and the contents mixed vigorously for 2 rain and centrifuged for 10 min. Four ml of the alcohol admixture (top layer) are removed and placed in another test tube. Five ml of 0.1 N HC1 are added and the contents mixed vigorously for 1 min and centrifuged for 5 min. Three ml of the aqueous phase (bottom layer) are removed and the fluorescence is measured in accordance with the instrumental parameters described previously. The procedure is modified slightly for the analysis of drug in tissue. The tissue (0.5 g) is homogenized (Potter-Elvehjem apparatus) in 2.0 ml of the 0.2 M glycine buffer and the homogenate placed in another test tube. The homogenizer tube is then rinsed with an additional 1.5 ml of the glycine buffer and the wash added to the homogenate. One ml of water is added, followed by 10.0 ml of the admixture, and the contents mixed vigorously. Following centrifugation, 8.0 ml of the admixture are removed and treated as described previously. A .standard curve for amiquinsin HC1 is constructed by plotting fluorescence as a function of the amount of drug present. The fluorescence of the control is subtracted from the fluorescence of the unknown sample and the amount of amiquinsin HCI present determined from the standard curve.

3. RESULTS

3.1. Analyt& procedure A standard curve for amiquinsin HC1 as determined by the described procedure exhibits linearity from 0 to lO/ag (fig. 1). Since quenching occurs with

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Fig. 1. Standard curve for amiquinsin HC1. samples containing amounts greater than 10 pg of the drug, dilutions are made with 0.1 N HCI so that the amount of drug present is accurately determined from a linear portion of the standard curve. With the exception of bile, recoveries of added drug from dog biologic materials (table 2) showed agreement between the control-corrected aqueous and reference standards with each set of determinations. Similar results (recovery range 93-99%) were obtained with dog AH, CSF, brain, heart, lung, muscle, and fat tissue. A bile reference standard curve was used to determine biliary drug concentrations. The method in its described form has a sensitivity of 0.20/~g/ml or per g. When 2.5 ml of 0.1 N HC1 are used instead of the recommended 5.0ml to extract the drug from the alcohol admixture, the method sensitivity is increased to 0.02 gg/ml, with a standard curve which is linear from 0 to 0.2/lg. To provide information on the specificity of the method, chromatography was conducted according to a method reported previously (Hollifield and Conklin, 1968). Samples of biologic materials collected from dogs following the administration of amiquinsin HC1 were subjected to the analytic procedure; the acid extracts then were spotted on Whatman No. 1 paper and subjected to ascending paper chromatography in a system of 95% ethanol: n-butanol: 0.5 N acetic acid or ammonium hydroxide (1:4:1) for 16hr. Under ultraviolet light a purple fluorescent spot was visible under acid conditions (R f 0 . 7 0 ) and under base conditions (RfO.60) with blood, bile, and urine, and with heart, lung, spleen, liver, and kidney tissues. Similar R f values for this spot were obtained with corre-

J.D.Conklin, R.D.Hollifield, Absorption, distribution, and elimination of amiquinsin hydrochloride

363

Table 2 Recoveries of amiquinsin HC1 from dog biologic materials. Excitation 330 n m - fluorescence 360 n m Fluorescence units a), amiquinsin HC1 (ug)

Recovery b)

Material

Control

0.1

0.5

1.0

5.0

10.0

Mean -+ S.D. c)

Water Blood Plasma Bile Urine

0.19 0.19 0.20 0.24 0.39

1.01 1.01 1.00 0.71 1.02

4.73 4.80 4.86 3.68 4.43

9.23 9.20 9.13 7.51 9.03

47.80 47.80 47.80 38.75 46.60

91.10 91.10 91.46 77.41 88.23

100.2% 100.2% 79.1% 97.3%

Water Liver Kidney Spleen

0.19 0.25 0.30 0.30

0.90 0.91 0.93 0.90

91.80 91.75 91.70 91.03

99.7% 100.47t 99.1%

9.13 8.98 8.96 8.96

0.7 1.5

5.5 2.6

1.4 2.6 0.9

a) Control corrected data based on a m e a n from at least 3 samples. b) Based on amiquinsin HCI concentrations in water. c) Standard deviation.

sponding control biologic materials to which amiquinsin HC1 was added. Following chromatography, this spot was eluted with 0.1 N HC1 and the excitation and fluorescence scans recorded. Each eluate exhibited an excitation peak at 330 nm and a fluorescence peak at 360 nm, characteristic of amiquinsin HC1. No spots were visible under either white or ultraviolet light with samples of control biologic fluids or tissues. In addition, a light blue fluorescent spot was observed in both systems (acid R f 0 . 5 6 , base R f 0 . 3 6 ) with urine collected from dogs dosed with the drug. This spot when eluted did not exhibit either excitation or fluorescence from 250 to 600 nm. It is assumed that this material does not contribute significantly to the concentration of amiquinsin HC1 in urine as determined by the analytic procedure. This blue spot was also noted with dog bile obtained after drug dosage (acid R f 0 . 5 7 , base R f 0 . 3 8 ) , in addition to 2 other purple fluorescent spots which were only observed in the acid system (Rf0.30, 0.49). Each of these eluted spots yielded excitation and fluorescence curves similar to those obtained with amiquinsin HC1. Based on the amount of fluorescence obtained with these eluted spots, it is estimated that approximately 50% of the fluorescence observed in a bile sample as determined by the analytic procedure may be attributed to amiquinsin HC1.

3.2. Absorption Intravenous, intramuscular, or oral administration of amiquinsin HC1 to dogs produced blood drug levels which were dose related (figs. 2 - 4 ) . In agreement with this, linear drug dose responses, were also

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Fig. 2. Disappearance o f amiquinsin HCI from dog blood after intravenous injection. Results are based on a m e a n from 3 dogs for each dose. (© 2.5 mg/kg, X 5.0 mg/kg, • 10.0 mg/kg, S.D.).

J.D. Conklin, R.D.Hollifield, Absorption, distribution, and elimination of amiquinsin hydrochlorMe

364

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Fig. 3. Appearance of amiquinsin HCI in dog blood after oral dosage. Results are based on a mean from 3 dogs for each dose. (© 10 mg/kg, X 20 mg/kg, • 40 mg/kg, ~ S.D.).

Fig. 4. Appearance of amiquinsin HCI in dog blood after intramuscular dosage. Results are based on a mean from 3 dogs for each dose. (© 2.5 mg/kg, X 5.0 mg/kg, • 10.0 mg/kg,

+ s.D.). apparent in urine for each route o f drug administration studied (table 3). This direct relationship indicates that urinary drug e x c r e t i o n is a reliable indic a t o ; for the in vivo absorption o f amiquinsin HC1. On the basis o f urinary drug recoveries acquired following intravenous administration (table 3), the urinary drug recoveries e n c o u n t e r e d after either oral

or intramuscular dosage (table 3) showed that b o t h dosage forms were well absorbed. A m i q u i n s i n HC1 was not detectable in b l o o d samples collected over a 6 hr period following oral drug dosage at 20 m g / k g to a dog in which the pylorus was ligated. It appears that the absorption o f amiquinsin HCI f r o m the dog gastrointestinal tract is p r e d o m i n a n t l y intestinal.

Table 3 Urinary drug excretion in dogs following administration of amiquinsin HC1 by different routes.

a) b) c) d)

Route of administration

Dose (mg/kg)

Intravenous a)

2.5 5.0 10.0

9.2 17.6 33.1

28.7% 28.8% 25.4%

5.5 3.7 2.7

Oral b)

10.0 20.0 40.0

32.0 59.8 117.3

21.1% 22.1% 22.3%

3.3 2.9 3.0

Intramuscular c)

2.5 5.0 10.0

7.4 15.1 28.9

27.2% 22.9% 24.3%

2.4 8.4 4.0

Urinary excretion d), 0 24 hr Mean total (mg)

Mean recovery + S.D.

Amiquinsin HCI as a solution in 5% dextrose was administered as a single injection (10 ml) into the cephalic vein. Amiquinsin HCI as crystalline material in a gelatin capsule was administered orally as a single dose. Amiquinsin HCI as a solution in 5% dextrose was administered as a single injection (2 ml) into the vastus lateralis muscle. Data are based on a mean from at least 3 dogs for each dose.

J.D.Conklin, R.D.Hollifi'eld, Absorption, distribution, and elimination of amiquinsin hydrochloride 3.3. Distribution Investigation established that blood drug concentrations at least twice as great as those concurrently in plasma were consistently obtained in dogs following either oral or parenteral administration of amiquinsin HCI. Therefore, drug levels in blood rather than in plasma were measured during the present study. The disappearance of amiquinsin HC1 from the blood of dogs following a single intravenous dose o f the drug at 10 mg/kg yielded a biphasic curve (fig. 2). It is assumed that the initial phase of the curve is due to the rapid accumulation of the drug in tissues, while the second portion is attributed to the slow release of tissue-bound drug and its metabolic degradation and excretion. A drug half-life of 198 min -+ S.D. 15 was estimated for this second phase. Drug levels were measured simultaneously in the blood, AH, and CSF while amiquinsin HC1 was infused intravenously (1.91 ml/min) for 1 to 5 hr at doses ranging from 5 to 10 mg/kg per hr. Although slightly higher concentrations o f amiquinsin HC1 appeared in the AH than in the CSF, the drug levels

365

in both fluids were about 1/10 that of the concurrent blood level or less. The mean drug concentration ratios (fluid/blood) were 0.08 -+ S.D. 0.01 for AH and 0.06-+ S.D. 0.01 for CSF, when the blood levels ranged from 1 to 5/ag/ml. Drug tissue disposition was studied in the dog following a single intravenous dose of amiquinsin HC1 at 10 mg/kg. With the exception of fat and brain, tissue/blood drug ratios considerably greater than 1 were found for each of the tissues examined (table 4). The relatively low drug ratios (tissue/blood) encountered with fat agree with the partition coefficients provided earlier for the drug (table 1). Since little of the drug was detectable in the CSF, it is not unexpected that low brain/blood drug ratios were obtained. However, very similar drug concentrations were present in brain tissue at each of the sampling intervals, suggesting that a redistribution of the drug may occur. In comparison, data reported by Jandhyala, Grega, and Buckley (1967), suggest that the drug may lower blood pressure via a central mechanism. No preferential localization of the drug was noted between either the cerebrum, cerebellum, medulla, or

Table 4 Tissue disposition of amiquinsin HCI in dogs. Drug concentration ratio: tissue/blood a)

Kidney Liver Spleen Adrenal b) Lung Heart Skeletal muscle Kidney fat Brain Blood drug concn. #g/ml d)

A Concentration %/235 rain

Time after dosage

Tissue 5 rain

20 rain

60 min

120 min

240 min

13.6 5.5 6.4 6.3 4.4 3.8 1.8 0.1 0.1

28.4 8.3 10.0 8.2 6.5 3.2 2.8 0.2 0.3

25.2 9.2 6.5 11.0 4.4 2.4 1.7 0.1 0.5

13.3 7.2 6.6 9.7 4.2 2.6 2.0 0.1 0.7

14.0 8.6 6.3 9.7 4.9 2.5 1.8 0.1 0.8

85.7 69.2 76.2 69.5 86.6 88.6 82.2 78.0 No decrease c)

6.9, 7.8

3.6, 3.9

3.0, 3.6

2.0, 2.3

1.5, 1.5

79.6

Conditions: Amiquinsin HC1 as a solution in 5% dextrose was administered by a single intravenous injection at 10 mg/kg. a) Data are based on a mean from 2 dogs for each time period. Three samples were dissected from a different portion of the tissue at necropsy from each dog and analyzed. b) One dog used for each time interval. c) The brain drug concentrations increased slightly (0.9 ug/g at 5 rain to 1.4/~g/g at 240 min). d) Blood drug concentration for each dog used.

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J.D.Conklin, R.D.HollifieM, Absorption, distribution, and elimination o f amiquinsin hydrochlorMe

midbrain. Tissue/blood drug ratios of 1 to 2 were observed with selected blood vessels such as the aorta, vena cava, femoral artery and vein. The placental transfer of amiquinsin HC1 was investigated in 4 species, each representative of a different placental type. Drug appeared to some extent in the fetal circulation in all of the species studied following a 2 hr intravenous drug infusion (table 5). Increases in drug dose resulted in increased drug levels in both the maternal and fetal blood of each species. Fetal urinary drug concentrations were detectable in the dog and sheep providing additional evidence for the placental transfer of amiquinsin HCI. Oral administration of amiquinsin HC1 to 2 pregnant Beagles (last period of gestation) for 14 days at 10 mg/kg per day, resulted in mean blood drug ratios (fetal/maternal) of 0.62 +- S.D. 0.05 and 0.81 + S.D. 0.03, respectively, for the litters. Fetal and maternal urinary drug levels were also detectable. Drug ratios (fetal tissue/maternal blood) ranging from 2 to 5 were obtained for fetal kidney and liver tissue under these conditions. Degradation studies conducted with maternal and fetal kidney and liver slices from the guinea pig and dog established that in these tissues and species, fetal tissue degradation of amiquinsin HC1 was less than or about equivalent to that

of maternal tissues; indicating that fetal blood drug levels may be used as an index of placental transfer for amiquinsin HC1. 3.4. Elimination The concentration of amiquinsin HC1 was determined simultaneously in the blood, bile, and urine of dogs following a l hr intravenous drug infusion. Although a substantial amount of drug (at least 20% of dose) was excreted in the urine, only a small amount (about 0.5% or less of dose) was recovered in the bile (table 6). An increase in drug dose was followed by a concurrent increase in blood, bile and urine drug concentrations. These urinary drug recoveries (table 6) are in agreement with those provided earlier (table 3) which established that at least 1/5 of an oral or parenteral dose of amiquinsin HC1 usually is recovered in dog urine. As shown previously (table 4), amiquinsin HCI was detectable in all of the dog tissues examined. With the possible exception of brain, the drug does not appear to be bound selectively by any of these tissues. The drug apparently disappears at comparable rates from these tissues (except brain) and these rates are correlated with the rate at which amiquinsin HCI disappears from blood (see table 4). Slices (0.5 ram)

Table 5 Placental transfer of anaiquinsin tiC1. Species

Dose (mg/kg/hr)

Maternal blood (ug/ml) a)

Blood drug concn, ratio fetal/maternal

drug concn,

Guinea Pig

1.25 2.50 5,00

1.12 2.16 2.65

0.15 0.24 0.36

Rabbit

1.25 2.50 5.00

1.08 2.30 4.42

0,5l 0.41 0.29

Dog

1.25 2.50 5.00

1.12 2.35 4.97

0.49 0.52 0.46

Sheep

1.25 2.50 5.00

1.50 2.26 4.49

0.16 0.14 0.20

Conditions: Solutions of amiquinsin HCI in 5% dextrose were infused intravenously for 2 hr at the following rates: guinea pig 0.51, rabbit 0.764, dog 1.91, and sheep 3.82 ml/min. a) Data for each dose are based on a mean from at least two animals in the last period of gestation.

J.D.Conklin, R.D.HollifieM, Absorption, distribution, and elimination o f amiquinsin hydrochlorMe

367

Table 6 Biliary and urinary drug excretion in dogs following administration of amiquinsin HC1. Dose

1.25 mg/kg/hr a)

Time (hr) 1 b) 2 3 4 5 6

Blood drug conch. (tag/ml) 0.78 0.28 0.22 0.18 0.16 0.14

Interval (hr) 0-1 b) 1-2 2-3 3-4 4-5 5-6

Drug conch. (~g/ml) Bile

Urine

1.56 7.56 5.70 3.88 2.56 2.02

290.50 400.00 129.00 50.00 28.00 24.00

0.45% c) 2.50 mg/kg/hr a)

1 b) 2 3 4 5 6

1.78 0.64 0.52 0.44 0.38 0.34

0-1 b) 1-2 2-3 3-4 4-5 5-6

2.36 15.14 12.00 9.40 7.56 5.60 0.25% c)

21.80% c) 387.20 1,300.00 328.00 182.00 130.00 94.00 26.67% c)

Conditions: A solution of amiquinsin HC1 in 5% dextrose was infused intravenously for 1 hr at 1.91 ml/min. a) One dog used for each dose. b) Drug infusion completed. c) Drug recovery for 6 hr. of adult-dog liver and kidney tissue exhibited degradation rates of about 160 t~g/g per hr for amiquinsin HC1 at a drug concentration of 600/ag/g under in vitro conditions. A 2-fold increase in the substrate (drug) concentration yielded a corresponding increase in the rate of destruction of the drug by either tissue. It appears that tissue degradation may be partially responsible for the elimination of amiquinsin HCI.

4. DISCUSSION Amiquinsin HC1 should exist essentially in the ionized form at extracellular body pH (range 7 . 3 5 7.45). Data provided in this report indicate that this drug is lipid insoluble and essentially unbound to plasma proteins at pH 7.4. With the exception of urine, only relatively small amounts of this drug were found in dog body fluids (blood, bile, AH, and CSF). However, the drug readily enters most tissues, and reaches substantial tissue drug concentrations. Per-

haps the exceptional water solubility (50 g/l) of amiquinsin HCI facilitates the transfer of this drug across these membranes. Recognition of the relationship between the physicochemical properties of drugs and their biologic activities has received increased attention. Interest is now often devoted to investigating the structureactivity relationships of drug analogues in regard to efficacy and toxicity (AriOns. 1966; Goldstein, Aronow, and Kalman, 1968). Information concerning the cardiovascular effects and the in vivo disposition of another hypotensive quinoline (6,7-dimethoxy-4hydroxyquinoline HC1) was reported previously (Bickerton et al., 1964; Conklin, Buzard, and Heotis, 1965). Structurally the only difference between this quinoline derivative and amiquinsin HCI is that the hydroxyl group on the quinoline ring is replaced by an amino group in amiquinsin HC1. Despite the structural similarities, differences were noted in cardiovascular effects between these two drugs (Bickerton et al., 1964; Jandhyala, Grega and Buckley, 1967). In addition, some differences are also apparent

368

J.D.Conklin, R.D.Hollifi'eld, Absorption, distribution, and elim&ation o f amiquinsin hydrochloride

between these drugs in regard to hi vivo distribution (Conklin, Buzard, and Heotis, 1965). In particular, the intravenous injection of either drug at an equivalent dose to dogs resulted in a biphasic curve for each of the drugs in blood. The drug half-life for the second phase was 69 min -+ S.D. 16 for the hydroxyquinoline and 198 rain +- S.D. 15 for amiquinsin HC1. No major preferential tissue storage depots were apparent for either drug in the dog and the rate of disappearance for each drug from tissue correlated with its disappearance rate from blood. In agreement with the half-life observed for each drug from the second phase of the biphasic curves, much greater tissue/blood drug concentration ratios were noted with amiquinsin HC1 than with the hydroxyquinoline. These results agree with a report that amiquinsin HC1 has a more prolonged hypotensive effect than the hydroxyquinoline (Jandhyala, Grega, and Buckley, 1967). It appears that there is a correlation between the duration of hypotensive activity and drug half-life in blood and tissue for these two quinoline derivatives.

ACKNOWLEDGEMENTS The authors express their appreciation to J. Stevens for technical assistance and to J. Michels for some of the physical data.

REFERENCES Ari~ns, E.J., 1966, Molecular pharmacology, a basis for drug design, Progr. Drug Res. 10,429. Bickerton, R.K., R.F. Dailey, W.T. Rockhold and R.H. Buller, 1964, The cardiovascular effects of 6,7-dimethoxy-4-hydroxyquinoline hydrochloride (U-558), J. Pharmacol. Exptl. Therap. 144,218. Brodie, B.B., 1964, Physico-chemical factors in drug absorption, in: absorption and distribution of drugs, ed. T.B. Binns (Williamsand Wilkins, Baltimore) p. 16. Buzard, J.A., J.D. Conklin and R.H. BuUer, 1961, Lymphatic transport of selected nitrofuran derivatives in the dog, Am. J. Physiol. 201,492. Buzard, J.A. and J.D. Conklin, 1964, Placental transfer of nitrofurantoin and furaltadone, Am. J. Physiol. 206, 189. Buzard, J.A. and J.D. Conklin, 1965, A comparison of the concentrations of certain nitrofurans in the aqueous humor and cerebrospinal fluid of the dog, Brit. J. Pharmacol. 24,266. Conklin, J.D., J.A. Buzard and J.P.Heotis, 1965, Studies on the absorption, distribution and elimination of 6,7-dimethoxy-4-hydroxyquinoline hydrochloride (U-558), Arch. Int. Pharmacodyn. 155, 105. Goldstein, A., L. Aronow and S.M. Kalman, 1968, Principles of drug action, (Harper and Row, New York, Evanston. London) p. 30. Hollifield, R.D. and J.D. Conklin, 1968, A spectrophotofluorometric procedure for the determination of dantrolene in blood and urine, Arch. Int. Pharmacodyn. 174,333. Jandhyala, B.S., G.J. Grega and J.P. Bucklcy, 1967, Hypotensive activity of several quinoline derivatives, Arch. Int. Pharmacodyn, 167,217.