In vitro activity of artemether against African isolates (Senegal) of Plasmodium falciparum in comparison with standard antimalarial drugs

The in vitro activity of artemether against 56 African isolates of Plasmodium falciparum from Senegal was evaluated using an isotope-based drug susceptibility semi-microtest. The 50% inhibitory concentration (IC50) values for artemether were in a narrow range from 0.8 to 15.2 nM (mean IC50 = 3.43 nM) and the 95% confidence interval (CI) was 2.50-4.36 nM. Artemether was equally effective on chloroquine-sensitive and chloroquine-resistant isolates (mean IC50 = 346 nM, 95% CI = 2.08-4.84 nM versus mean IC50 = 2.80 nM, 95% CI = 2.00-3.60 nM). There was a significant positive correlation between responses to artemether and mefloquine (r(2) = 0.36, P < 0.001), artemether and quinine (r(2) = 0.085, P < 0.05), artemether and halofantrine (r(2) = 0.075, P < 0.05), quinine and mefloquine (r(2) = 0.205, P < 0.01), quinine and halofantrine (r(2) = 0.124, P < 0.05), and mefloquine and halofantrine (r(2) = 0.801, P < 0.001). A positive correlation between these drugs suggests in vitro cross-resistance or at least in vitro cross-susceptibility.