Global assessment of partial artemisinin resistance: Multicenter trial across Kenya, Peru, and Thailand in patients with uncomplicated Plasmodium falciparum malaria.

Introduction: 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_1/2) 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_1/2 was higher in the Thai (4.1 hours) than Peruvian (2h) or Kenyan cohorts (2.2h) (p<0.0001). Higher PC_1/2 was partially explained by K13 mutations in 13 (28%) of 46 Thai subjects, including WHO validated and candidate mutations. Twelve (26%) Thai cohort subjects had PC_1/2≥5h 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 that satisfied WHO criteria for drug resistance establishes this area as endemic. Longer PC_1/2 found in wildtype and candidate K13 mutant infections within the Thai cohort require further investigation to identify alternative mechanisms of resistance.