Comparative pharmacokinetics of sulphasalazine and sulphapyridine after rectal and oral administration to patients with ulcerative colitis.

Rectal administration of sulphasalazine to patients with ulcerative colitis has recently been shown to have similar therapeutic activity but fewer side effects than oral treatment. The present study is a comparison of the pharmacokinetics of sulphasalazine (SASP) and its metabolite sulphapyridine (SP) after rectal and oral administration of SASP to 6 patients with ulcerative colitis. The areas under the concentration-time curves (AUC) and the maximum concentrations (Cmax) of SASP and SP were significantly lower after rectal than oral administration of SASP (p less than 0.05). These findings support the view that the lower frequency of side effects after rectal administration of SASP may result from the lower plasma levels of SASP and SP.