Evaluation of the sensitivity in vivo and in vitro of Plasmodium falciparum malaria to quinine in an area of full sensitivity to chloroquine.

The sensitivity of Plasmodium falciparum to quinine in Nigeria was examined in vivo and in vitro prior to the re-introduction of the drug into malaria therapy in that country in the face of spreading chloroquine resistance in Africa. The parasites showed full sensitivity in vivo to quinine, with a mean parasite clearance time of 2.4 d and a mean fever clearance time of 1.4 d. Using the in vitro microculture technique, the Nigerian isolates were found to have a minimum inhibitory concentration (IC) of 1.28 mumol quinine/litre blood-medium mixture. The IC50 and IC99 were 0.25 mumol/litre and 0.8 mumol/litre respectively. The study afforded an opportunity to compare the sensitivity of P. falciparum to quinine and chloroquine in a population in which chloroquine resistance was not a problem and the results showed slower parasitological and clinical response to quinine than to chloroquine.