Evidence of Plasmodium falciparum Malaria Multidrug Resistance to Artemisinin and Piperaquine in Western Cambodia: Dihydroartemisinin-Piperaquine Open-Label Multicenter Clinical Assessment

Abstract

Western Cambodia is recognized as the epicenter of Plasmodium falciparum multidrug resistance. Recent reports of the efficacy of dihydroartemisinin (DHA)-piperaquine (PP), the latest of the artemisinin-based combination therapies (ACTs) recommended by the WHO, have prompted further investigations. The clinical efficacy of dihydroartemisinin-piperaquine in uncomplicated falciparum malaria was assessed in western and eastern Cambodia over 42 days. Day 7 plasma piperaquine concentrations were measured and day 0 isolates tested for in vitro susceptibilities to piperaquine and mefloquine, polymorphisms in the K13 gene, and the copy number of the Pfmdr-1 gene. A total of 425 patients were recruited in 2011 to 2013. The proportion of patients with recrudescent infections was significantly higher in western (15.4%) than in eastern (2.5%) Cambodia (P <10(-3)). Day 7 plasma PP concentrations and median 50% inhibitory concentrations (IC50) of PP were independent of treatment outcomes, in contrast to median mefloquine IC50, which were found to be lower for isolates from patients with recrudescent infections (18.7 versus 39.7 nM; P = 0.005). The most significant risk factor associated with DHA-PP treatment failure was infection by parasites carrying the K13 mutant allele (odds ratio [OR], 17.5; 95% confidence interval [CI], 1 to 308; P = 0.04). Our data show evidence of P. falciparum resistance to PP in western Cambodia, an area of widespread artemisinin resistance. New therapeutic strategies, such as the use of triple ACTs, are urgently needed and must be tested. (This study has been registered at the Australian New Zealand Clinical Trials Registry under registration no. ACTRN12614000344695.).

FIG 1

Map of Cambodia showing study sites and other provinces where DHA-PP has been tested. Western and eastern provinces are shown in red and green, respectively. Black dots mark the study sites (city and province names).

FIG 2

Cumulative risk at day 42 of patients with P. falciparum failing DHA-PP treatment. Shown is the overall difference between patients from western (red) and eastern (green) sites (P = 0.01). The hazard ratio (for western Cambodia versus eastern Cambodia) is 6.5 (95% CI, 2.9 to 14.1).

FIG 3

Plasma PP concentrations at day 7 as a function of clinical outcome. The gray dashed line indicates the PP concentration that defines adequate PP absorption (≥30 ng/ml). Red dots represent patients from western Cambodia sites, and green dots represent those from eastern Cambodia sites. ACPR, adequate clinical and parasitological response; TF, treatment failures.