In vivo sensitivity monitoring of chloroquine for the treatment of uncomplicated vivax malaria in four bordered provinces of Thailand during 2009-2010.

Background & objectives: Chloroquine (CQ), followed by 14-day primaquine, is the recommended regimen for the treatment of Plasmodium vivax infection in Thailand. CQ resistant P vivax (CRPv) has not yet challenged the efficacy of the drug. The present study was conducted to assess the current response of P. vivax to CQ alone in Thailand. Methods: A 28-day in vivo therapeutic efficacy study was conducted from June 2009 to December 2010 in 4 sentinel sites. Recurrence of parasitaemia and the clinical condition of patients were assessed on each visit during follow-up. The drug levels in recurrent patients' blood were measured using HPLC. Data were analyzed using the WHO 2008 program for the analysis of in vivo tests. Results: Of the total 212 patients included in the study, 201 completed the 28-days follow-up, while 11 were excluded. In five patients (2.5%), parasitaemia reappeared within the 28-days follow-up. On the day of recurrent parasitaemia, the level of chloroquine/desethylchloroquine (CQ-DCQ) was above the minimum effective concentration (>= 100 ng/ml) in one patient, but lower in four patients. Conclusion: Reappearance of the parasite within 28 days of follow-up in one of five patients was due to parasite resistance to CQ. The 2.5% prevalence of CQ treatment failure for P vivax malaria in the study areas signals the need to launch monitoring activities for CQ resistant P. vivax in malaria endemic areas in order to detect further development of parasite resistance and to estimate the level of burden across the country.