Effectiveness of amodiaquine as treatment for chloroquine-resistant Plasmodium falciparum infections in Kenya.

Studies were conducted in Malindi, Kenya, to assess the response of Plasmodium falciparum to chloroquine and amodiaquine in vivo (by an extended 14-day test) and in vitro (with the Rieckmann micro test). In-vivo resistance was demonstrated in 19 of 69 (28%) infections treated with chloroquine, but in only 2 of 60 (3.3%) of those treated with amodiaquine (p less than 0.001). In-vitro resistance to chloroquine was demonstrated in 15 of 23 (65%) tests. In contrast, 22 of the same 23 isolates were sensitive to amodiaquine in vitro. Effective concentrations by probit analysis for 50% and 99% (EC50 and EC99) inhibition, respectively, were 180.7 and 4319.6 nmol/l for chloroquine and 12.2 and 147.0 nmol/l for amodiaquine. The results suggest that amodiaquine is effective for the treatment of chloroquine-resistant falciparum malaria in Kenya.