Lack of in vitro effect of ivermectin on Plasmodium falciparum.

Abstract. The in vitro activity of ivermectin was assessed against the K1 isolate of Plasmodiumfalciparum. The mean IC 50 and IC 90 of ivermectin were 8.0 and 35.0 ∝g/ml, respectively. These resultsindicate that ivermectin has a very low activity against P. falciparum in vitro. The aim of this study was to determine ifivermectin has an antiparasitic effect on P.falciparum in vitro.The in vitro activity of ivermectin was as-sessed against the K1 isolate of P. falciparium bythe radioisotopic method of Desjardins et al(1979), with minor modification. Serial dilutionsof ivermectin, dissolved in 100% methanol wereadded to the wells of microtiter plates and driedovernight. The wells were subsequently inocu-lated with 90 ∝l of a 2.2% suspension of parasit-ized cells (0.5% parasitemia and 90% rings) and10 ∝l of [ 3 H] hypoxanthine. The final ivermectinconcentrations in the RPMI 1640 culture mediumvaried between 0.01 and 1,000 ∝g/ml. The mi-croculture plates were incubated for 48 hours at37oC in a 5% O