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

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Abstract
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 μmol quinine/litre blood-medium mixture. The IC50 and IC99 were 0·25 μmol/litre and 0·8 μmol/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.