Polymorphisms in Plasmodium falciparum chloroquine resistance transporter and multidrug resistance 1 genes: parasite risk factors that affect treatment outcomes for P. falciparum malaria after artemether-lumefantrine and artesunate-amodiaquine

Abstract

Adequate clinical and parasitologic cure by artemisinin combination therapies relies on the artemisinin component and the partner drug. Polymorphisms in the Plasmodium falciparum chloroquine resistance transporter (pfcrt) and P. falciparum multidrug resistance 1 (pfmdr1) genes are associated with decreased sensitivity to amodiaquine and lumefantrine, but effects of these polymorphisms on therapeutic responses to artesunate-amodiaquine (ASAQ) and artemether-lumefantrine (AL) have not been clearly defined. Individual patient data from 31 clinical trials were harmonized and pooled by using standardized methods from the WorldWide Antimalarial Resistance Network. Data for more than 7,000 patients were analyzed to assess relationships between parasite polymorphisms in pfcrt and pfmdr1 and clinically relevant outcomes after treatment with AL or ASAQ. Presence of the pfmdr1 gene N86 (adjusted hazards ratio = 4.74, 95% confidence interval = 2.29 - 9.78, P < 0.001) and increased pfmdr1 copy number (adjusted hazards ratio = 6.52, 95% confidence interval = 2.36-17.97, P < 0.001 : were significant independent risk factors for recrudescence in patients treated with AL. AL and ASAQ exerted opposing selective effects on single-nucleotide polymorphisms in pfcrt and pfmdr1. Monitoring selection and responding to emerging signs of drug resistance are critical tools for preserving efficacy of artemisinin combination therapies; determination of the prevalence of at least pfcrt K76T and pfmdr1 N86Y should now be routine.

Figure 1.

Patient flow chart for study of parasite risk factors that affect treatment outcomes for Plasmodium falciparum malaria after treatment with artemether-lumefantrine (AL) or artesunate-amodiaquine (ASAQ).

Figure 2.

Polymerase chain reaction–adjusted efficacy as assessed by Kaplan-Meier survival estimates for artemether-lumefantrine (AL) by Plasmodium falciparum multidrug resistance 1 (pfmdr1) genotype of initial parasites. Dotted line indicates World Health Organization–recommended 90% efficacy cutoff value for antimalarial drugs. Clinical response of patients with parasites that carry A, pfmdr1 86Y (blue) versus 86N or N/Y (red); n = 2,543 patients at risk and B, pfmdr1 copy number > 1 (yellow) versus single copy (green); n = 808 patients.

Figure 3.

A, Cumulative (left panels) and relative (right panels) risks of polymerase chain reaction (PCR)–adjusted reinfection for baseline Plasmodium falciparum chloroquine resistance transporter (pfcrt) and P. falciparum multidrug resistance 1 (pfmdr1) genotypes after artemether-lumefantrine treatment, in which recrudescent and re-infections with other genotypes were treated as competing events. B, Cumulative (left panels) and relative (right panels) risks of PCR-adjusted re-infection for baseline pfcrt and pfmdr1 genotypes after artesunate-amodiaquine treatment, in which recrudescent and re-infections with other genotypes were treated as competing events.