Sulphasalazine is cleaved into 5-aminosalicylic acid and sulphapyridine by colonic bacteria. The bulk of evidence favours sulphapyridine rather than 5-aminosalicylic acid as the active moiety (as well as the main producer of side-effects) though a therapeutic action from the 30% of sulphasalazine that is absorbed unaltered also cannot be excluded.
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