Clinical response and susceptibility in vitro of Plasmodium vivax to the standard regimen of chloroquine in Thailand

Abstract

The clinical effectiveness of the standard regimen of chloroquine (CQ) (a total dose of 1500 mg, given over 48 h at 0, 6, 24 and 48 h) for the treatment of Plasmodium vivax malaria in Thailand was investigated in 57 patients in an endemic area of Thailand (Chantaburi Province, eastern Thailand). For radical treatment, an additional course of a tissue schizontocidal agent, primaquine, was given following the complete course of CQ. With this regimen, satisfactory whole blood concentration-time profiles of CQ and its major metabolite desethylchloroquine (DECQ) were achieved. Mean whole blood levels of CQ and DECQ always much exceeded the reported therapeutic level of CQ (90 ng/mL) during the first 7 d of treatment. All patients responded well to the treatment; in most cases, complete and rapid clearance of parasitaemia was observed within the first 48 h. No reappearance of the parasitaemia was detected in peripheral blood films of any patient within 14 d of the evaluation period. In 6 patients, however, reappearance of P. vivax parasitaemia was observed after 30 d; 2 of them had not completed the course of primaquine. There was no difference in whole blood concentrations of CQ and DECQ, admission parasitaemia, susceptibility of the isolates to chloroquine in vitro, and parasite clearance time between patients with or without reappearance of parasitaemia. A prominent trend of deteriorating sensitivity of the parasite to the drug was, however, suggested.