- The absorption of captopril from aqueous solution and solid dosage form was compared in the jejunum and colon of the anesthetized rat, with and without a mixture of oleic acid and sodium oleate (OASO). Captopril was absorbed better in the jejunum than in the rat colon (32.5 ± 7.5% compared with 9.0 ± 4.6% of the administered dose, respectively). The addition of 1.0 or 2.5% of OASO significantly enhanced captopril colonic absorption, but did not affect captopril absorption from the rat jejunum. AUC 0–5 h values were increased two-fold after colonic administration of captopril-OASO solid formulations. The colonic absorption with or without OASO was characterized by flat drug plasma profiles. It is concluded that colonic delivery of captopril together with OASO could be used to sustain captopril input into the body for a prolonged period of time.