Additive effects of ciprofloxacin on the in-vitro activity of chloroquine against a clinical isolate of Plasmodium falciparum.

As chloroquine and ciprofloxacin each possess substantial inhibitory activity against the schizonts of Plasmodium falciparum, it seems possible that a combination of the two drugs may be clinically useful. The effects on the erythrocytic stages of P. falciparum of combined treatment with chloroquine and ciprofloxacin were therefore evaluated in vitro, using the World Health Organization's standardized micro test. When used alone, the median inhibitory concentration (IC(50)) of chloroquine against the schizonts in the assay mixtures was found to be 7.75 microg/ml, whereas the corresponding value for ciprofloxacin was markedly lower, at 3.35 microg/ml. When they were used together, however, there was marked and statistically significant mutual enhancement of schizont inhibition by the two drugs, indicating that a chloroquine-ciprofloxacin combination may be useful clinically, in the treatment and management of P. falciparum malaria.