Pharmacokinetics and tissue distribution of 14C-5-aminosalicylic acid (14C-5-ASA) in rats

5-Aminosalicylic acid (5-ASA) is effective in the treatment of ulcerative colitis and Crohn's disease. As part of a preclinical metabolism profile with 5-ASA, we evaluated the tissue level and distribution of 14C-5-ASA in rats. Biodistribution of 14C-radioactivity was determined in the major organs of rats after a single oral dose (34 mg/kg; 15 uci/rat). Data from tissue area under the curve (AUC 0-72) indicated that the highest amounts of radioactivity were retained in cecum (481.1 hr.ug.equ/gm), colon-rectum (178.5 hr.ug.equ/gm), ileum (166.7 hr.ug.equ/gm), jejunum (65.5 hr.ug.equ/gm), followed by kidneys (58.0 hr.ug.equ/gm) and liver (14.8 hr.ug.equ/gm). The radioactivity retained in tissues at 72 hours postdose was wither nondetectable or less than 0.1 ppm. The radioactivity concentration in blood was highest at 0.5 hr (tmax) postdose and the terminal half-life (t1/2) of 14C-radioactivity (5-ASA + metabolite) was 2.7 hours. 14C-5-ASA is absorbed and distributed in the body. The greatest amount of 14C-radioactivity was found in the stomach and GI tract. 14C-5-ASA was eliminated completely (44.9% in the urine, 51.7% in the feces) 72 hours after administration without significant tissue retention