Artemisinin derivative-based combination therapy is expected to suppress the development of Plasmodium falciparum drug resistance in Africa. We have performed an artemether-lumefantrine (Coartem; Novartis) follow-up clinical trial in Zanzibar, in which pfcrt K76T and pfmdr1 N86Y frequencies were determined before drug administration and in all recurrent parasites during a follow-up period of 42 days. A significant increase in pfmdr1 86N was observed after exposure to the drug. This points to 86N as a potential marker of lumefantrine resistance in vivo, while suggesting that Coartem is not robust enough to avoid selection of resistance-associated mutations in some malarial settings.

Background Artemether-lumefantrine (AL) is a major and highly effective artemisinin-based combination therapy that is becoming increasingly important as a new first-line therapy against Plasmodium falciparum malaria. However, recrudescences occurring after AL treatment have been reported. Identification of drug-specific parasite determinants that contribute to treatment failures will provide important tools for the detection and surveillance of AL resistance. Method The findings from a 42-day follow-up efficacy trial in Tanzania that compared AL with sulfadoxine-pyrimethamine (SP) were analyzed to identify candidate markers for lumefantrine tolerance/resistance in the chloroquine resistance transporter gene (pfcrt) and multidrug resistance gene 1 (pfmdr1). The findings were corroborated in vitro with genetically modified isogenic P. falciparum parasite lines. Results Treatment with AL selected for the chloroquine-susceptible pfcrt K76 allele (P < .0001) and, to a lesser extent, the pfmdr1 N86 (P = .048) allele among recurrent infections. These genotypes were not selected during SP treatment. No pfmdr1 gene amplifications were observed. Isogenic pfcrt-modified parasite lines demonstrated a 2-fold increase in susceptibility to lumefantrine, which was directly attributable to the K76T mutation. Conclusions Our findings suggest that the pfcrt K76T mutation is a drug-specific contributor to enhanced P. falciparum susceptibility to lumefantrine in vivo and in vitro, and they highlight the benefit of using AL in areas affected by chloroquine-resistant P. falciparum malaria.

Summaryobjective Artemether-lumefantrine (AL), presently the most favoured combination therapy against uncomplicated Plasmodium falciparum malaria in Africa, has recently shown to select for the pfmdr1 86N allele. The objective of this study was to search for the selection of other mutations potentially involved in artemether-lumefantrine tolerance and/or resistance, i.e. pfmdr1 gene amplification, pfmdr1 Y184F, S1034C, N1042D, D1246Y, pfcrt S163R and PfATP6 S769N.methods The above mentioned SNPs were analysed by PCR-restriction fragment length polymorphism and pfmdr1 gene amplification by real-time PCR based protocols in parasites from 200 children treated with AL for uncomplicated P. falciparum malaria in Zanzibar.results A statistically significant selection of pfmdr1 184F mostly in combination with 86N was seen in reinfections after treatment. No pfmdr1 gene amplification was found.conclusion The results suggest that different pfmdr1 alleles are involved in the development of tolerance/resistance to lumefantrine.