Abstract

The blood schizontocidal chloroquine (CQ) and the tissue schizontocidal and gametocytocidal primaquine (PQ) remain the mainstay treatment of Plasmodium vivax and Plasmodium ovale infections for more than six decades. The review focuses on the clinical pharmacokinetic studies of both drugs in Thai population that have provided useful information for clinical application in the treatment of malaria.  There appears to be no major differences in the pharmacokinetics of both drugs with respect to the influences of ethinicity, acute phase malaria infection, and G6PD status. The increase in systemic exposure of CQ and/or its metabolite mono-desethylchlorooquine (DECQ) following oral administration could be due to change in the absorption kinetics during acute phase infection. The high clinical efficacy of CQ for treatment of P. vivax infection in Thailand supports this benefitial pharmacokinetic change. Transiently high and toxic plasma/whole blood concentrations of CQ following intravenous infusion at high rate is explained by the pharmacokinetic characteristics of CQ.  Pharmacokinetics of PQ following repeated dosing in most studies appears to be similar to that following a single dosing. This suggests that auto-inhibition of PQ metabolism during multiple dosing is unlikely. Co-administration of CQ, dihydroartemisinin-piperaquine (DHA-PIP), and pyronaridine-artesunate (PYR-ARS) significantly altered the pharmacokinetics of PQ. In the presence of these drugs, PQ exposure was significantly increased. The apparent volume of distribution of PQ was reduced when co-administered with PYR-ARS. In addition, plasma concentrations of CPQ were significantly increased in the presence of CQ.  Clinical relevance of these interactions needs to be confirmed.

Key words: Malaria, pharmacokinetics, chloroquine, primaquine, Thai population.