Chloroquine resistance of Plasmodium falciparum in Brazil detected by a simple in vitro method.

The sensitivity of Plasmodium falciparum to antimalarial drugs is primarily determined by observing changes in the level of parasitaemia after administration of drugs to man. Performance of such a study and interpretation of its results may present certain difficulties, especially when conducted among persons living in malarious areas. The present study was conducted to evaluate the usefulness of a simple in vitro method for detecting chloroquine-resistant strains among infected residents of Mato Grosso, Brazil. The findings indicated the participants were infected with chloroquine-resistant P. falciparum. Subsequent administration of a standard regimen of chloroquine (25 mg/kg) to these subjects confirmed the findings observed in vitro by failing to cure 28 out of 30 infections. This in vitro technique seems to provide a useful method of determining the presence or prevalence of chloroquine-resistant strains in a given area.