In vitro experiments on chloroquine and pyrimethamine absorption in the presence of antacid constituents or kaolin.

A study was made in vitro of the effect of five gastrointestinal medications on the absorption of chloroquine and pyrimethamine, the two most commonly used antimalarial agents in the Sudan. Activated dimethicone did not appreciably affect the absorption of either antimalarial drug. All other agents tested significantly decreased the absorption of both chloroquine and pyrimethamine. The decreases observed were as follows: calcium carbonate (-52.8 and -31.5%), a local remedy, gerdiga (-36.1 and -38.0%), kaolin (-46.5 and -49.9%) and magnesium trisilicate (-31.3 and -37.5%) for chloroquine and pyrimethamine respectively. The results indicate that concomitant therapy of these antimalarials with the implicated antacid and antidiarrhoeal agents will result in poor bioavailability of the antimalarials.