Background: High incidence of chloroquine-resistant vivax malaria has led to increasing case fatality and incidence of complicated malaria with Plasmodium vivax contributing to morbidity and mortality. Current guidelines recommend the use of chloroquine along with tissue schizontcides like primaquine for the treatment of Plasmodium vivax malaria. There were reports of increasing resistance to chloroquine in Plasmodium vivax species especially from Asia during the period when this study was taken up. Methods: Present study is a one arm, 28 day follow up, hospital based prospective observational study including 150 children aged 1 to 12 years with smear positive isolated Plasmodium vivax infections. Chloroquine was administered at the standard dose of 25 mg base/kg body weight over three days. Recurrence of parasitaemia and clinical conditions of patients were assessed on days 1, 2, 3, 7, 14, and 28 during the 28-day follow-up period. Results: All 150 children included in the study, completed their 28 day follow up. Mean age for enrolment was 5.96±2.38 years. The mean parasite index (%) on enrolment was 1.22±0.46. Based on the per protocol analysis, chloroquine efficacy (adequate clinical and parasitological response) was 92.7%. Treatment was well tolerated. Early treatment failure was seen in 2.7% of study population, late clinical failure in 2% and late parasitological failure in 2.7% of study population, suggesting that response to chloroquine was good in the study population. Conclusions: In the present study the chloroquine therapy showed high therapeutic efficacy (92.7%) in the treatment of uncomplicated vivax malaria. It was also well tolerated and equally safe when used in therapeutic doses. Regular monitoring of the pattern of resistance to chloroquine is needed in vivax malaria endemic areas of the country and measures are taken rapidly and effectively to control spread of resistance.

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