5 ASAs, (Mesalazine amongst others)

Are a group of drugs which are used to treat relapse and maintain remission in inflammatory bowel diseases. They may be taken orally or by foam enema or suppository. The preferred route and formulation depends on the location and extent of the disease. For those with disease limited to the last few centimetres of large bowel (the rectum) a suppository may be the most effective way of getting high levels of drug to the desired location with the minimum risk of side effects. For those with small bowel disease an oral formulation that releases the 5ASA all the way through the gut, such as Pentasa tablets or granules may be preferred. For those with colonic disease a preparation that is preferentially released in the large bowel, such as octasa or asacol may be most fitting.

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In general 5 ASAs are more effective for maintenance of remission in ulcerative colitis than in Crohn’s disease. In Ulcerative colitis, where of a hundred patients on no treatment can expect that about 45 will relapse in a 12 month period, regular use of 5 ASAs would be expected to reduce that number to between 20 to 25 out of each hundred patients a year. Of course this does not predict what happens to an individual patient.

Side effects include nausea and occasionally worsening diarrhoea and kidney damage, but kidney damage is very rare. Nevertheless because of the risk of kidney damage it is appropriate for patients to have kidney function tests (a blood test) before starting these medicines and at interval thereafter.

https://www.crohnsandcolitis.org.uk/about-crohns-and-colitis/publications/aminosalicylates-5-asas