A comparison of serum concentrations of sulphasalazine and some of its metabolites after therapy by the oral or rectal route.

A study was carried out in 14 patients with quiescent ulcerative colitis to compare serum levels of sulphasalazine and some of its metabolites after 7-days' treatment orally with 1 g sulphasalazine 3-times daily followed by 7-days' treatment with a 3 g sulphasalazine enema daily. The results showed that, although there were wide individual variations in levels after oral and rectal administration, with the same dosage the levels were far higher when the drug was given orally. Dose-related side-effects such as nausea and headache have been shown previously to occur more commonly with high serum levels of sulphapyridine to which sulphasalazine is metabolized. Levels after rectal administration were below those normally associated with side-effects. In view of the finding that at least 70% of patients with mild to moderate ulcerative colitis respond to rectal treatment it is suggested that this route of administration should be considered for patients experiencing side-effects after oral sulphasalazine.