The pharmacokinetics of chloroquine in healthy and Plasmodium chabaudi-infected mice: implications for chronotherapy.

The schizogony of malarial parasite is a typical cyclic phenomenon where the different stages of parasite development appear at regular time intervals. Each of the stages is specifically sensitive to different antimalarial drugs. Knowledge of the details of the cycle, drug susceptibility and the pharmacokinetics of drugs, could allow the improvement of drug action by the chronotherapeutic approach: treatment at the time of appearance of the drug sensitive stage with a drug that displays rapid pharmacokinetics. Since murine malarias serve as preferable models for in vivo drug testing, the pharmacokinetics of subcutaneously (sc) administered chloroquine (CQ) were tested in the whole blood of healthy mice and in animals slightly (1.5-3.5% parasitemia) or heavily infected (21-25% parasitemia) with Plasmodium chabaudi chabaudi. The half-time of absorption was around 5 min and almost independent of parasitemia. The apparent half-time of drug concentration decay was around 40 min in healthy animals, about 90 min at low parasitemia and about 410 min in heavy infection, indicating that the concentration of CQ is a typical spike, that is prolonged by asymptomatic disease, and considerably more by the active accumulation of CQ in infected cells. The latter is confirmed by the 3-fold higher peak blood [CQ] at the trophozoite stage and < 1.5-fold increase during schizogony. In conjunction with our previous experiments which showed that a single sc injection of 5 mg/kg CQ is sufficient to eliminate the drug susceptible mid-term trophozoite stage, the present results seem to justify to propose the chronotherapeutic approach for the treatment of malaria.