Increased antimalarial activity of azithromycin during prolonged exposure of Plasmodium falciparum in vitro.

The minimum inhibitory concentration, MIC, of azithromycin was determined for 2 isolates of Plasmodium falciparum at 48 and 96 h. The MIC at 48 h for the K1 and FC isolates were 6.2 and 8.7 micrograms/ml, respectively. At 96 h, the MIC decreased to 0.08 microgram/ml for the K1 isolate and 0.04 microgram/ml for the FC isolate. The marked reduction in the MIC values between the first and second asexual erythrocytic cycles suggests that the drug acts slowly and that it may have to be used in combination with a faster acting drug.