Chloroquine (CQ) resistance is associated with decreased accumulation of CQ in the parasite digestive vacuole of P. falciparum, but its mechanism in P. vivax is unknown.
CQ uptake and efflux was quantified in ring and trophozoite stages of P. falciparum and P. vivax field isolates, and the effect of CQ resistance reversal agents (CQRRA) on CQ uptake and efflux was assessed in both species.
CQ resistance in P. falciparum was associated with reduced CQ accumulation, but not an increase in CQ efflux. In contrast, CQ accumulation occurred faster and CQ efflux slower in P. vivax, although CQ uptake was not associated with CQ susceptibility in P. vivax. CQ uptake was modified by CQRRAs in P. falciparum, but not in P. vivax. The results add to a growing body of evidence that the mechanism of CQ resistance and possibly the mode of CQ action are different between these two species.