SUMMARY 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 (pg/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 50ug/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-aminosalicylic acid.It has been established that salicylazosulphapyridine (sulphasalazine, salazopyrin, SASP) is of therapeutic benefit in the management of ulcerative colitis, both in the active and the quiescent phase (Svartz, 1942(Svartz, , 1948; Baron, Connell, Lennard-Jones, and Jones, 1962;Dick, Grayson, Carpenter, and Petrie, 1964;Misiewicz, Lennard-Jones, Connell, Baron, and Jones, 1965).The metabolism of SASP is better understood as a result of recent studies in the normal subject (Schr6der and Campbell, 1972). Similar information during its clinical use is scant. We have already reported our results in a preliminary communication (Das, Eastwood, McManus, and Sircus, 1972).It has been suggested that about one third of a given dose of SASP is absorbed from the small intestine, the remainder passes to the colon where SASP is split into its components, presumably by bacteria. Most of the sulphapyridine (SP) thus liberated is absorbed whereas about one third of the 5-aminosalicylic component is also absorbed at this level, the remainder being excreted in the stool. In TPresented as part of a PhD thesis, University of Edinburgh Present address:
