Absorption of Sulphonamides and Antitubercular Drugs from the Rat Lung

Abstract

1. Pulmonary absorption half-times (min) in the rat for four sulphonamides and three antitubercular drugs were: sulphadimethoxine, <1.0; sulphamethoxypyridazine, 1.0; isoniazid, 1.9; sulphisoxazole, 3.3; p-aminosalicylate, 4.5; ethambutol, 40; and sulphaguanidine, 41.2. Absorption rates (first-order rate constants) generally ranked in the same order as the chloroform-to-water (pH 7.4) partition coefficients of the compounds.3. Concentration studies with isoniazid, p-aminosalicylic acid, and ethambutol failed to show evidence of a saturable carrier-type transport process for these drugs.4. The results suggested that these chemotherapeutic agents are absorbed from the respiratory tract mainly by a process of simple diffusion.