In vivo and in vitro susceptibility to chloroquine of Plasmodium falciparum in Kinshasa and Mbuji-Mayi, Zaire

From April to June 1983, combined in vivo and in vitro studies were conducted to assess the response to chloroquine of Plasmodium falciparum in Kinshasa and Mbuji-Mayi, Zaire. A total of 109 patients were treated with chloroquine, either as a single dose of 10 mg/kg or as a full dose of 25 mg/kg. All patients rapidly cleared their asexual parasitaemia, no recurrence being noted during the subsequent 3 weeks of follow-up. In the fourth week, recurrences were noted in 3 out of 66 patients treated with the full dose of chloroquine and in 10 out of 43 patients treated with the single dose. A total of 101 in vitro tests (30 macro tests, 39 micro tests, and 32 48-hour tests) were successfully performed with blood samples collected from 51 of these patients. Full sensitivity to chloroquine was demonstrated in all but 3 of the successful in vitro tests, the results from these 3 tests being contradicted either by alternative in vitro tests or by the corresponding in vivo findings. These investigations thus failed to detect chloroquine resistance at the level reported in East Africa or eastern Zaire (in Kivu).