In Vitro Susceptibility of Plasmodium falciparum to Chloroquine, Amodiaquine, Quinine, Mefloquine, and Sulfadoxine/Pyrimethamine in Equatorial Guinea

Between March 1990 and June 1992, a study was carried out in Equatorial Guinea on the in vitro response of Plasmodium falciparum to different antimalarial drugs. Field work for the study was conducted both in the country's island region as well as on the mainland, and resistant isolates were found to exhibit interregional differences. On the island of Bioko, 204 tests were performed with 16% (11 of 69) resistant to chloroquine, 9% (4 of 46) resistant to quinine, 14% (6 of 43) resistant to a combination of sulfadoxine/pyrimethamine, and 6.5% (3 of 46) resistant to amodiaquine. In the mainland area of Bata, the same antimalarial drugs and mefloquine were tested with the following results: 9% (5 of 58) resistant to chloroquine; 2% (1 of 58) resistant to amodiaquine, and 3% (2 of 58) resistant to a combination of sulfadoxine/pyrimethamine. No isolates resistant to quinine or mefloquine were found. Effective concentrations (EC50, EC90, and EC99) and regression lines (log dose/response) for each antimalarial drug were calculated to establish a surveillance system for antimalarial drug chemosensitivity in Equatorial Guinea. Finally, 12 isolates from 12 patients previously treated with chloroquine were studied to compare both tests (in vivo-in vitro) and obtain a correlation between the RII and RIII types of in vivo and in vitro resistances. No correlation for the RI type was found between the two methods.