Abstract

Sulphasalazine (Salazopyrin) has been used in the treatment of inflammatory bowel disease for more than 40 years. The drug consists of two compounds - sulphapyridine and 5-amino salicylic acid (5-ASA, approved name mesalazine) - joined by a diazo bond. Sulphasalazine is poorly absorbed in the small bowel and so reaches the large bowel where bacteria split the diazo bond, releasing sulphapyridine and mesalazine. The mesalazine moiety is the active component of the drug,¹ and probably acts topically in the colon. Mesalazine is absorbed in the ileum, and so is unlikely to be effective in the treatment of ulcerative colitis when given by mouth.² The sulphapyridine acts as a carrier molecule which prevents absorption in the small bowel; it causes most of the unwanted effects of sulphasalazine. Several different oral preparations have been developed in an attempt to deliver mesalazine to the colon without the need for a toxic carrier. Asacol (Tillots) is the first to be marketed in the UK, and is licensed for use only in patients intolerant of sulphasalazine.