Pharmacokinetics of primaquine in man. II. Comparison of acute vs chronic dosage in Thai subjects.

We have investigated the pharmacokinetics of primaquine after acute and chronic administration of the drug to five healthy Thai volunteers. After acute dosage (15 mg p.o.) mean (+/- s.d.) peak plasma concentrations of 65.0 +/- 34.7 ng ml-1 were achieved within 2 +/- 1h. Thereafter plasma drug concentrations declined monoexponentially with a mean elimination half life of 4.4 +/- 1.4 h. The mean (+/- s.d.) oral clearance was 37.6 +/- 15.5 1 h-1. These values are in broad agreement with values obtained in healthy Caucasians after administration of an equivalent dose of primaquine. Repeated dosing with primaquine had no effect on the mean pharmacokinetic parameters calculated for this drug. In contrast, individual pharmacokinetic parameters for some subjects exhibited gross and unpredictable changes after chronic dosage. The carboxylic acid metabolite of primaquine accumulated in plasma after repeated dosing such that by day 14 of chronic dosing the mean AUC (0,24) for this metabolite was 74% greater than that obtained after acute administration of primaquine.