The aim of the study was to assess the in vitro potentiating effects of atorvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, in combination with mefloquine, chloroquine or monodesethylamodiaquine against Plasmodium falciparum and to evaluate whether the effects of atorvastatin could be associated with mutations or gene copy number in multidrug resistance (MDR)-like protein genes.The susceptibilities of 21 parasite strains to combinations of atorvastatin with mefloquine, chloroquine or monodesethylamodiaquine were assessed using the in vitro isotopic microtest. Genotypes and gene copy number were assessed for pfmdr1, pfmdr2 and pfmrp genes.Atorvastatin demonstrated synergistic effects in combination with mefloquine. The mefloquine IC(50) (50% inhibitory concentration) was reduced by 7%, 24% and 37% in the presence of atorvastatin at concentrations of 0.1, 0.5 and 1.0 microM, respectively. The synergistic effect of atorvastatin on the response to mefloquine was significantly associated with pfmdr1 copy number. The concentration of atorvastatin that could reduce the IC(50) of mefloquine by 50% was 2.4 +/- 1.3 microM for the 12 strains that contained one copy of pfmdr1 and 5.8 +/- 2.1 microM for the 9 strains that contained two copies or more. The synergistic effect of atorvastatin in combination with mefloquine was found to be significantly unrelated to mutations in pfmdr1, pfmdr2 or pfmrp genes.The synergy of the effect of mefloquine at concentrations relevant to its achievable plasma concentrations in patients taking 80 mg of atorvastatin daily suggests that atorvastatin will be a good candidate in combination with mefloquine for malaria treatment.