Susceptibility of African isolates of Plasmodium falciparum to artemisinin (qinghaosu).

We studied in vitro susceptibility of 79 African strains of Plasmodium falciparum to artemisinin, chloroquine, quinine, mefloquine and halofantrine and the potential cross-resistance among the drugs. Most strains presented an 50% inhibitory concentration (IC50) of artemisinin below 26 nmol/liter. A positive correlation between IC50S of artemisinin and those of quinine, mefloquine and halofantrine was observed. Cross resistance between artemisinin and other antimalarials may limit its use as a replacement drug.