High dose of primaquine in primaquine resistant vivax malaria

The efficacy of low dose chloroquine, characteristic pattern of relapse and the relapse rate in vivax malaria after high dose primaquine were investigated in 167 Thai patients. 87 patients were allocated at random to receive 300 mg, and 80 received 450 mg of chloroquine on the first day of admission. All patients in both groups showed a rapid response with comparable fever clearance times (27.3 vs. 26.1 h) and parasite clearance times (67.1 vs. 58.1 h). After recovery and clearance of parasitaemia, the patients were allocated at random (double blind) to receive 2 dosage regimens of primaquine, a daily dose of 15 mg or 22.5 mg for 14 d. Relapses in both groups occurred within 6 months; no patient relapsed beyond that period. The relapse rate in the primaquine 15 mg group was significantly higher than that in the 22.5 mg group (17.5% vs. 2.4%).