In vitro susceptibility of Gabonese wild isolates of Plasmodium falciparumto artemether, and comparison with chloroquine, quinine, halofantrine and amodiaquine

The in vitro activity of artemether against 63 African isolates of Plasmodi um falciparum from Libreville, Gabon was evaluated using an isotopic drug s usceptibility semi-microtest. The 50 % inhibitory concentration (IC50) valu es for artemether were in a narrow range from 0.8 to 34.8 nM (mean IC50 5.0 nM) and the 95 % confidence interval (CI95 %) was 3.6-6.3 nM. In vitro dec reased susceptibility or resistance were observed with artemether (14 %), t o chloroquine (90 %), to quinine (32 %). Isolate susceptibility to amodiaqu ine and halofantrine was high i.e. 100 % and 98 %, respectively. There was a significant positive correlation between responses to artemether and amod iaquine (r(2) = 0.45, P < 0.001), artemether and chloroquine (r(2) = 0.36, P < 0.001), artemether and quinine (r(2) = 0.31, P < 0.001), and artemether and halofantrine (r(2) = 0.19, P < 0.01). Positive correlation between the se drugs suggests in vitro cross-resistance or at least common features in drug uptake and/or mode of action or resistance.