Plasmodium falciparum drug resistance phenotype as assessed by patient antimalarial drug levels and its association with pfmdr1 polymorphisms

Abstract

Background: Multidrug-resistant Plasmodium falciparum is a major threat to global malaria control. Parasites develop resistance by gradually acquiring genetic polymorphisms that decrease drug susceptibility. The aim of this study was to investigate the extent to which parasites with different genetic characteristics are able to withstand individual drug blood concentrations.

Methods: We analyzed 2 clinical trials that assessed the efficacy and effectiveness of artemether-lumefantrine. As a proof of concept, we used measured day 7 lumefantrine concentrations to estimate the concentrations at which reinfections multiplied. P. falciparum multidrug resistance gene 1 (pfmdr1) genotypes of these parasites were then correlated to drug susceptibility.

Results: Reinfecting parasites with the pfmdr1 N86/184F/D1246 haplotype were able to withstand lumefantrine blood concentrations 15-fold higher than those with the 86Y/Y184/1246Y haplotype.

Conclusions: By estimating drug concentrations, we were able to quantify the contribution of pfmdr1 single-nucleotide polymorphisms to reduced lumefantrine susceptibility. The method can be applied to all long-half-life antimalarial drugs, enables early detection of P. falciparum with reduced drug susceptibility in vivo, and represents a novel way for unveiling molecular markers of antimalarial drug resistance.

Figures

Figure 1.

Estimated lumefantrine (LUM) concentrations for reinfecting Plasmodium falciparum carrying different pfmdr1 single-nucleotide polymorphisms (SNPs) at codons 86, 184, and 1246. Each reinfection is represented 3 times, once for each SNP. Only pure infections (concerning the pfmdr1 SNPs) were included in the analysis. According to the Mann–Whitney rank sum test, there was a significant difference between N86 and 86Y (P < .001), 184F and Y184 (P < .001), and D1246 and 1246Y (P = .006; Table 2). Black lines, median values; grey lines, interquartile ranges.

Figure 2.

Estimated lumefantrine concentrations for reinfecting Plasmodium falciparum carrying different pfmdr1 haplotypes at codons 86, 184, and 1246. Each open circle represents a reinfection. Only haplotypes with ≥3 observations were considered for analysis. Median values were 31.4 nM (interquartile range [IQR], 10.5–76.1 nM) for NFD, 15.8 nM (IQR, 2.53–46.0 nM) for NYD, 2.16 nM (IQR, 0.293–3.77 nM) for YYY, and 0.678 nM (IQR, 0.108–3.87 nM) for YYD (Table 2). Black lines, median values; grey lines, interquartile ranges.