Regarding Side Effects Of Aminosalicylate Drugs Like Mesalazine (Used In treatment of Ulcerative Colitis)

A 36-year-old man is reviewed in clinic. He has recently been started on mesalazine 400mg tds for ulcerative colitis. Which one of the following adverse effects is least likely to be attributable to mesalazine?
A. Interstitial nephritis
B. Headaches
C. Acute pancreatitis
D. Agranulocytosis
E. Infertility

Answer:
E. Infertility

Discussion: Oligospermia is seen in patients taking sulphasalazine due to the sulphapyridine moiety, which is not present in mesalazine.

Aminosalicylate drugs :
5-aminosalicyclic acid (5-ASA) is released in the colon and is not absorbed. It acts locally as an anti-inflammatory. The mechanism of action is not fully understood but 5-ASA may inhibit prostaglandin synthesis

Sulphasalazine 
 a combination of sulphapyridine (a sulphonamide) and 5-ASA
 many side-effects are due to the sulphapyridine moiety: rashes, oligospermia, headache, Heinz body anaemia, megaloblastic anaemia
 other side-effects are common to 5-ASA drugs (see mesalazine)

Mesalazine
 a delayed release form of 5-ASA
 sulphapyridine side-effects seen in patients taking sulphasalazine are avoided
 mesalazine is still however associated with side-effects such as GI upset, headache, agranulocytosis, pancreatitis (pancreatitis is 7 times more common in patients taking mesalazine than sulfasalazine), interstitial nephritis

Olsalazine 
 two molecules of 5-ASA linked by a diazo bond, which is broken by colonic bacteria