Combination of the antibiotics erythromycin and tetracycline with three standard antimalarials against Plasmodium falciparum in vitro.

Combinations of antibiotics and standard antimalarials have been assayed against P. falciparum in vitro, using incorporation of 14C isoleucine as an indicator of drug action. Chloroquine and erythromycin have been shown to act synergistically against a chloroquine-resistant strain and additively towards a chloroquine-sensitive strain, confirming their action against sensitive and resistant P. berghei in vivo, described elsewhere. Combinations of erythromycin with mefloquine or quinine acted anergically in 24 hour assays in which unphysiologically high concentrations of quinolinemethanol were necessary for demonstrable drug effect. In 48 hour assays, an additive effect was obtained with these combinations. Tetracycline is additive in combination with each of the standard antimalarials used in this study. The relevance of results obtained in vitro to parasite drug sensitivities in vivo is discussed.