Abstract
Effect of plasma-protein binding displacement on the intestinal absorption of sulfonamides in rabbits was investigated by using salicylic acid and phenylbutazone as displacing drugs. Salicylic acid and phenylbutazone significantly reduced the in situ intestinal absorption of sulfadimethoxine that showed high binding to plasma proteins. These two displacing drugs also enhanced the in situ intestinal exsorption of sulfadimethoxine. However, salicylic acid and phenylbutazone showed no significant effect in the transport of sulfadimethoxine from mucosal to serosal side solution through the intestinal membrane or the uptake of sulfadimethoxine by the intestinal preparation in vitro. In addition, salicylic acid and phenylbutazone did not affect the in situ intestinal absorption and exsorption of sulfanilamide that showed little binding to plasma proteins. From these results, it is concluded that the displacement of one drug from its plasma-protein binding sites by another drug is an important determinant affecting drug absorption.
