In Vitro Activity of Antimalarials Against Clinical Isolates of Plasmodium falciparum in Yaounde, Cameroon

The in vitro activity of nine antimalarials was determined against 119 fresh clinical isolates of Plasmodium falciparum obtained from symptomatic indigenous patients in Yaounde, Cameroon. using the isotopic semimicrotest. Seventy-four parasites were resistant to chloroquine (mean 50% inhibitory concentration [IC50] 337 nM); 45 were chloroquine-sensitive (mean IC50 35.6 nM). Twenty-five of 58 chloroquine-resistant parasites were resistant to monodesethylamodiaquine, the biologically active metabolite of amodiaquine. None of the chloroquine-sensitive isolates was resistant to monodesethylamodiaquine (IC50 17.3 nM). Pyronaridine, quinine, mefloquine, halofantrine, and artemether were highly active against the chloroquine-sensitive and the chloroquine-resistant isolates. Of the 43 isolates tested, 25 were sensitive to both pyrimethamine and cycloguanil, the biologically active metabolite of proguanil. The in vitro responses of chloroquine and monodesethylamodiaquine, chloroquine and quinine, quinine and mefloquine, mefloquine and halofantrine, artemether and mefloquine or halofantrine, and pyrimethamine and cycloguanil were significantly correlated. The present study suggests that chloroquine resistance is highly prevalent in vitro in Yaounde and that the alternative drugs are generally highly active against the chloroquine-resistant parasites.