OBJECTIVES

Artemisinin-resistant Plasmodium falciparum challenges the effectiveness of all artemisinin-based combination therapies.

METHODS

We conducted a clinical study in Peru, Kenya, and Thailand between June 2013 and November 2015 in subjects treated with three standard doses of artesunate followed by two doses of mefloquine. The primary endpoint was parasite clearance half-life (PC) during the 72-hour period of treatment. Secondary endpoints included clinical outcome at 42 days, detection of kelch13 (K13) mutations, pharmacokinetics, and pharmacodynamics.

RESULTS

The mean PC was higher in the Thai (4.1 hours) than Peruvian (2 hours) or Kenyan cohorts (2.2 hours) (P <0.0001). Higher PC was partially explained by K13 mutations in 13 (28%) of 46 Thai subjects, including World Health Organization (WHO) validated and candidate mutations. Twelve (26%) Thai cohort subjects had PC ≥5 hours with parasites from nine subjects carrying K13 mutations. There was an overall 42-day cure rate of 100% across all subjects.

CONCLUSIONS

This is the first concurrent evaluation of artemisinin resistance across three continents. The presence of 11% Thai subjects who satisfied WHO criteria for drug resistance establishes this area as endemic. Longer PC found in wild-type and candidate K13 mutant infections within the Thai cohort require further investigation to identify alternative mechanisms of resistance.