Prolonged exposure of Plasmodium falciparum to ciprofloxacin increases anti-malarial activity

The minimum inhibitory concentration (MIC) of ciprofloxacin was determined for 2 isolates of Plasmodium falciparum at 48, 96, and 144 hr. The MIC decreased from mean values of 28.1 micrograms/ml for the FC isolate and 27.2 micrograms/ml for the K1 isolate at 48 hr to 2.8 micrograms/ml and 4.4 micrograms/ml, respectively, at 96 hr. Concentrations of 0.1-1.0 micrograms/ml were effective in suppressing parasite growth over 144 hr of incubation. These findings indicate that the multiplication of malaria parasites can be inhibited by clinically achievable concentrations of ciprofloxacin provided that exposure to the drug is prolonged over several asexual erythrocytic cycles. They also raise the possibility that this antibiotic could be used eventually, in combination with a rapidly acting but noncurative drug regimen, to treat patients with refractory falciparum infections.