Artemisinin Resistance in Cambodia: A Clinical Trial Designed to Address an Emerging Problem in Southeast Asia

Background. Increasing rates of failure of artemisinin-based combination therapy have highlighted the possibility of emerging artemisinin resistance along the Thai-Cambodian border. We used an integrated in vivo-in vitro approach to assess the presence of artemisinin resistance in western Cambodia. This article provides additional data from a clinical trial that has been published in The New England Journal of Medicine. Methods. Ninety-four adult patients from Battambang Province, western Cambodia, who presented with uncomplicated falciparum malaria were randomized to receive high-dose artesunate therapy (4 mg/kg/day orally for 7 days) or quinine-tetracycline. Plasma concentrations of dihydroartemisinin, in vitro drug susceptibility, and molecular markers were analyzed. Cases meeting all the following criteria were classified as artemisinin resistant: failure to clear parasites within 7 days of treatment or reemergence of parasites within 28 days of follow-up; adequate plasma concentrations of dihydroartemisinin; prolonged parasite clearance; and increased in vitro drug susceptibility levels for dihydroartemisinin. Results. Two (3.3%) of 60 artesunate-treated patients were classified as artemisinin resistant. Their parasite clearance times were prolonged (133 and 95 h, compared with a median of 52.2 h in patients who were cured). These patients had 50% inhibitory concentrations of dihydroartemisinin that were almost 10 times higher than the reference clone W2. Resistance did not appear to be mediated by the pfmdr1 copy number or selected PfATPase6 polymorphisms previously proposed to confer artemisinin resistance. Conclusion. Artemisinin resistance has emerged along the Thai-Cambodian border. The potentially devastating implications of spreading resistance to a drug that currently has no successor call for further studies of this emerging problem.