Eight healthy volunteers who had not taken chloroquine 2 to 12 months previously participated in a single dose study designed to evaluate the pharmacokinetics of chloroquine and some of its metabolites. Each subject received two tablets of chloroquine sulfate (300 mg base) only. Blood and urine samples were collected just before and periodically after chloroquine administration. These samples were assayed for chloroquine and its N-dealkylated metabolites (monodesethylchloroquine, didesethylchloroquine, 7-chloro-4-aminoquinoline), chloroquine side chain N-oxide and chloroquine di-N-oxide using a high performance liquid chromatographic method. Residual levels of chloroquine and its N-oxidation metabolites were found in all subjects. 7-chloro-4-aminoquinoline was eliminated more slowly (t1/2z = 126.48 +/- 20.13 h) than the other metabolites and the unchanged drug (t1/2z = 106.43 +/- 10.13 h). Also, 7-chloro-4-aminoquinoline had a significantly faster (Student's t-test, P less than 0.05) formation clearance when compared with the other metabolites. The plasma concentration of 7-chloro-4-aminoquinoline was about twice that of the unchanged drug while the plasma concentration of monodesethylchloroquine was about 46% that of the unchanged drug. In order to investigate whether the metabolites were produced from the same binding sites or closely related sites on the cytochrome P-450 system, their formation clearances were correlated. The best correlation (r2 = 0.83) was observed for didesethylchloroquine and monodesethylchloroquine, and a fair correlation (r2 = 0.59) was observed for monodesethylchloroquine and 7-chloro-4-aminoquinoline. Formation clearances of the other metabolites were poorly correlated.(ABSTRACT TRUNCATED AT 250 WORDS)

A controlled study was carried out in ten healthy, male volunteers (randomly distributed into control and test groups of five subjects each) to determine the effect of low-dose cimetidine on chloroquine elimination. The control group subjects received two tablets of chloroquine sulfate (300-mg base) only, while the test group subjects took 400-mg cimetidine at bedtime for four days prior to chloroquine (two tablets of chloroquine sulfate) administration and throughout the duration of the study. Blood samples, 5 mL, were collected periodically after chloroquine administration. The samples were assayed for chloroquine and monodesethylchloroquine using a combination of thin-layer chromatography and spectrophotometry. Wilcoxon's test for unpaired data at P less than .05 was used to determine if there was any significant difference in the elimination of chloroquine in the test group when compared with the control group. The apparent oral clearance rate of chloroquine was reduced from 0.49 +/- 0.04 L/d/kg in the control group to 0.23 +/- 0.02 L/d/kg in the test group, and the elimination half-life was prolonged from 3.11 days in the control group to 4.62 days in the test group. There was a 47.04% reduction in the AUC0-7d of monodesethylchloroquine, the major metabolite of chloroquine, in the test group when compared with the control group. The apparent volume of distribution at steady state was increased from 0.46 +/- 0.07 L/kg in the control group to 0.72 +/- 0.10 L/kg in the test group. All these changes were statistically significant. The conclusion is that cimetidine impairs the elimination of chloroquine in healthy subjects.

Twenty-one healthy Nigerian volunteers distributed into four groups participated in a study to determine the significance of chloroquine disposition in chloroquine-induced pruritus. It involved the administration of chloroquine with or without promethazine pre-administration to the subjects. Group I consisted of 8 chloroquine non-hypersensitive subjects receiving 2 tablets of chloroquine sulphate (300 mg base); Group II consisted of 5 chloroquine non-hypersensitive subjects receiving 2 tablets of chloroquine sulphate 30 minutes after 25 mg promethazine tablet pre-administration; Group III consisted of 5 chloroquine hypersensitive subjects treated as in Group II; Group IV consisted of 3 hypersensitive subjects treated as in Group I. Blood (5 ml) and urine samples were collected periodically for up to 6 days post-dose. The samples were analysed for chloroquine and some of its oxidation metabolites by a specific HPLC method. Probit plots of cumulative drug/metabolite ratios were done to determine if there is polymorphism in chloroquine metabolism. There was bimodality only in the distribution of chloroquine/monodesethylchloroquine ratios, suggesting polymorphism in the metabolic oxidation of chloroquine in these subjects. Higher levels of monodesethylchloroquine were obtained in Group IV subjects when compared with any of the other groups. The oral clearance rate, elimination half-life, and volume distribution at steady state of chloroquine in the study groups were not significantly different (P greater than 0.05). In the absence of promethazine there appears to be an extensive metabolism of chloroquine in hypersensitive individuals to produce monodesethylchloroquine which probably determines the degree of pruritus experienced by an individual.

Simultaneous milk and saliva samples were collected over a seven-day period from five lactating subjects after they had ingested two tablets of chloroquine sulfate (300 mg base). The samples were analyzed for chloroquine content by use of a combination of thin-layer chromatography and spectrophotometry. Regression analysis of two variables subject to error was used to determine the milk:saliva levels relationship. The Student's t test for paired data at .05 level of significance was used to evaluate the relationship between chloroquine levels in milk and saliva. The milk:saliva chloroquine concentrations ratio obtained by regression analysis was 0.89 +/- 0.08 (r = .93; P less than .05), and this compared favorably with the value of 0.99 +/- 0.07 obtained from the ratio of the AUC. There were no significant differences in the Tmax, Cmax, AUC, clearance, and elimination half-life values of chloroquine in milk and saliva (P greater than .05). Milk and saliva appear to be part of the central compartment. The amount of chloroquine estimated to be consumed by a nursling over a 24-hour period is about 0.55% of a 300-mg dose consumed by the mother. The data suggest that milk chloroquine levels can be estimated from saliva levels.

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