The metabolism of salicylazosulphapyridine in ulcerative colitis. I. The relationship between metabolites and the response to treatment in inpatients.

The metabolism of salicylazosulphapyridine was studied in 16 patients with ulcerative colitis admitted to hospital. The acetylator phenotype was determined on admission. The mean serum concentration (mug/ml) (at steady state eight +/- two days in patients responding to treatment) of SASP, total SP, and 5-ASA were 18.7 +/- 12.8; 53.7 +/- 23.1; and 1 +/- 0.9 for slow acetylators and 17.6 +/- 7.1; 31 +/- 9.0 and 1 +/- 0.9 for fast acetylators respectively. Twenty-four hour urinary excretion of SASP, total SP, and 5-ASA were 4.6% +/- 3.1; 52% +/- 9.6 and 22.3 +/- 6.7% of the administered dose respectively. Serum total SP concentration of 20 to 50 mug/ml appeared to coincide with clinical improvement in the absence of any side effects related to salicylazosulphapyridine. No such relationship could be shown with serum SASP, individual metabolites, or 5-aminosalicyclic acid.