Disposition of 5-aminosalicylic acid, the active metabolite of sulphasalazine, in man

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Abstract
The disposition of 5-aminosalicylic acid (5-AS), the therapeutically active metabolite of sulphasalazine (SZ), has been studied in patients with active inflammatory bowel disease, in patients with biliary tract disease and post-operative T-tube drainage, and in healthy volunteers. Subjects were treated 3 times a day either with 5-AS 0.5 g suppositories and a slow-release preparation or with SZ 1 g tid (equivalent to 5-AS 1.14 g/day). Plasma and urine concentrations of 5-AS and its acetylated major metabolite (AcAS) were monitored during one dosing interval. In a cross-over trial in 5 patients with ulcerative colitis no difference, was found in the dose-corrected mean (± SD) steady state plasma levels (Css) of 5-AS and AcAS between treatment with 5-AS suppositories (0.10±0.07 and 0.50±0.20 µg/ml, respectively) and SZ (0.12±0.14 and 0.67±0.14 µg/ml, respectively). Urinary excretion of total AS (5-AS+AcAS), too, was similar (192±70 and 179±79 mg/day) with both forms of treatment. The oral slow-release form of 5-AS produced slightly higher Css in 5 patients with Crohn's disease (5-AS 0.21±0.22 µg/ml; AcAS 0.83±0.40 µg/ml) and in 5 healthy volunteers (5-AS 0.28±0.14 µg/ml; AcAS 1.10±0.43 µg/ml). Urinary recovery of total AS averaged 20±6% (patients) and 27±10% (volunteers). The cross-over trial in 7 patients with a biliary T-tube revealed that after single doses of 5-AS 1 g and SZ 2 g between 0.01% and 0.75% could be recovered in collected bile (85–500 ml/day) as total AS (traces of free 5-AS, and acetylated and glucuronidated 5-AS), indicating some enterohepatic circulation.