Biliary excretion of 2,4,5-trichlorophenoxyacetic acid in the rat.

Urethane-anesthetized, male Sprague-Dawley rats were administered 25 mg/kg 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) intravenously. 6 h after administration, 15.7% of the dose was recovered in the bile. Reversed-phase high-performance liquid chromatography (HPLC) analysis of bile indicated that more than 85% of compound excreted in bile was unchanged 2,4,5-T. Since renal function was apparently compromised by the urethane anesthesia, only 4% of the dose was recovered in urine in 6 h. These data demonstrate that biliary excretion can be a slow but significant route of elimination under conditions of impaired renal function. Since 2,4,5-T is eliminated largely as the unchanged acid, reabsorption and thus enterohepatic circulation may significantly prolong the half-life of 2,4,5-T in the body.