Changing response to chloroquine of Plasmodium falciparum in Saradidi, Kenya, from 1981 to 1984

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Abstract
From 1981 through 1984, the response of Plasmodium falciparum to chloroquine was monitored in Saradidi, Kenya, as a part of a community-based health programme to provide treatment for malaria in each village. Before 1983, all 71 infections treated with chloroquine were sensitive in vivo; parasitaemia cleared by day 3 and remained absent to day 7. In June 1983, 23.1% of 26 infections treated with chloroquine base 10 mg kg−1either recrudesced in seven days (RI resistance, five infections) or decreased but failed to clear (RII resistance, one infection). In September 1983, 16.2% of 68 and in February 1984, 13.2% of 53 infections were resistant in vivo after treatment with chloroquine base 10 mg kg−1. A course of chloroquine base 25 mg kg−1over three days remained effective; only two (1.6%) of 129 infections examined were resistant in vivo; in both, parasitaemia cleared then recurred (RI). In September 1984, however, nine (10.2%) infections were resistant after treatment with chloroquine base 25 mg kg−1; in four of these parasitaemia decreased but never cleared (RII). Similar results were observed in vitro. In the Rieckmann macro in vitro test, 63.3% of 30 P. falciparum isolates tested were resistant to chloroquine (minimal inhibitory concentration (MIC) ≥l.25x 10−6mol l−1blood) in June 1983, as were 61.8% of 34 isolates in the Rieckmann micro test (MIC ≥1.14 × 10−6mol l−1blood). The effective drug concentrations to chloroquine for 99% inhibition (EC50) increased in the macro in vitro test from 0.617 × 10−6mol 1−1blood in May 1981 to 1.917 × 10−6mol 1−1in june 1983 and in the micro test from 0.929 × 10−6mol l−1blood in May 1982 to 3.458 × 10−6mol l−1in September 1984. It was not possible to associate increased drug pressure with the development of resistance since resistance occurred in areas with varying degrees of drug use. The results demonstrate a changing pattern of the response of IP. falciparum to chloroquine in Saradidi.

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