Chloroquine sensitivity of Plasmodium falciparum in Ibadan, Nigeria: II. Correlation of in vitro with in vivo sensitivity.

Plasmodium falciparum malaria was treated in 82 children with 25 mg/kg chloroquine orally over three days. They were observed for 28 days during which blood films were examined periodically for malaria parasites. Asexual forms of P. falciparum, present in the blood films of all the patients before commencing treatment, disappeared rapidly and by the third day no parasites were seen in blood films from any of them. Among the patients observed for more than three days, blood films remained negative throughout the observation period. In vitro tests of sensitivity of blood samples from 10 patients showed chloroquine concentrations of 0.5 to 0.8 nmol/ml to inhibit completely maturation from ring forms to schizonts. This suggests that P. falciparum in the Ibadan area is probably still fully sensitive to chloroquine.