DRUG-SENSITIVITY OF PLASMODIUM-FALCIPARUM IN GABON - ACTIVITY CORRELATIONS BETWEEN VARIOUS ANTIMALARIALS

The sensitivity of Plasmodium falciparum to chloroquine, mefloquine, q uinine, halofantrine, and sulfadoxine/pyrimethamine has been investiga ted at Lambarene, in the Gabonese rain forest, between April and Septe mber 1992. WHO standard micro in vitro tests were performed. Of 43 iso lates tested for response to chloroquine all were resistant to the dru g with mean EC 50 and EC 90 values of 1.86 and 4.18 mu mol/l blood, re spectively, indicating the highest degree of resistance ever reported from Central Africa. With sulfadoxine/pyrimethamine 19 out of 27 isola tes showed 90% inhibition of schizont maturation at a pyrimethamine co ncentration of at least 75 nmol/l blood medium mixture, indicating 30% of resistance to sulfadoxine/pyrimethamine. In contrast all isolates tested were fully inhibited by mefloquine at 3.2 mu mol/l blood (40 is olates), quinine at 5.12 mu mol/l blood medium mixture (41 isolates) a nd halofantrine at 3 nmol/l blood medium mixture (40 isolates) indicat ing full sensitivity to these drugs. A significant positive correlatio n was found between responses to quinine and mefloquine. The response to halofantrine was positively correlated with the responses to quinin e and mefloquine, in the case of chloroquine and halofantrine an inver se relationship was observed. Compared with previous data from Gabon, the findings suggest a substantial increase of chloroquine resistance, in contrast to reports from neighbouring countries, which show stabil ising or even declining chloroquine resistance patterns.