Adverse effects with oral 5-aminosalicyclic acid.

Two patients with ulcerative colitis and a past history of allergic reactions to sulfasalazine had similar reactions when treated with 5-aminosalicylic acid. This suggests that, at least in some patients, the adverse effects of sulfasalazine are due to 5-aminosalicylic acid rather than sulfapyridine. Desensitization to sulfasalazine was successfully carried out in one patient but was not attempted in a second.