In vitro response of Plasmodium falciparum to chloroquine in the Nandi district, Kenya.

Thirty-six isolates of Plasmodium falciparum from Nandi district, Kenya, which were tested for their sensitivity to chloroquine using the WHO in vitro macrotechnique, yielded a total of 29 successful tests, one of which showed overt resistance with schizont maturation at chloroquine levels of > 1.5 x 10(-6) mol/l. The majority of isolates showed reduced sensitivity to chloroquine, and the EC(99) was 1.7218 x 10(-6) mol/l. These findings are indicative of widespread in vitro resistance of a low degree which may remain largely unnoticed in immune individuals. However, in nonimmune subjects one may expect also in vivo resistance because the parasites will not be completely cleared after a normally curative dose of chloroquine.