In vitro activities of antibiotics against Plasmodium falciparum are inhibited by iron

The in vitro activities of cyclines (tetracycline, doxycycline, minocycline , oxytetracycline, and rolitetracycline), macrolides (erythromycin, spiramy cin, roxithromycin, and lincomycin), quinolones (norfloxacin and ofloxacin) , rifampin, thiamphenicol, tobramycin, metronidazole, vancomycin, phosphomy cin, and cephalosporins (cephalexin, cefaclor, cefamandole, cefuroxime, cef triazone, cefotaxime, and cefoxitin) were evaluated on Plasmodium falciparu m clones, using an isotopic, micro-drug susceptibility test. Only tetracycl ines, macrolides, quinoIones, and rifampin demonstrated in vitro activity a gainst P. falciparum, which increased after a prolonged exposure (96 or 144 h). In the presence of iron (FeCl3), only the activities of tetracyclines and norfloxacin were decreased. Their in vitro activity against intraerythr ocytic stages of multidrug-resistant P. falciparum and their efficacy in vi vo favor the use of antibiotics as antimalarial drugs. However, due to thei r slow antimalarial action and to the fact that they act better after prolo nged contact, they probably need to be administered in conjunction with a r apidly acting antimalarial drug, such as a short course of chloroquine or q uinine.