Late onset interstitial nephritis associated with mesalazine treatment

Patients taking mesalazine should have renal function monitored regularly to avoid nephrotoxicity Mesalazine is widely prescribed for the treatment of inflammatory bowel disease. It is a single molecule of 5-aminosalicylic acid (5-ASA), and is structurally similar to phenacetin and aspirin. Occasionally, treatment with mesalazine may lead to a severe indolent interstitial nephritis causing appreciable morbidity. Unless detected and treated early this may progress to end stage renal failure despite withdrawal of the drug.1 It is obvious from the increasing number of reports of nephritis and renal failure occurring after treatment with mesalazine that the premise that “there is no need for routine monitoring of renal function”2 needs to be reviewed; the need for a review has been suggested by a number of recent reports. 1 3–9 We report two cases of late onset interstitial nephritis induced by mesalazine (Asacol); the first presented after at least 5 years of continuous treatment with the drug and the second after 1 year. ### Case 1 A 38 year old laboratory technician began taking mesalazine for ulcerative colitis. After 2 years of continuous treatment he remained well with normal renal function (serum creatinine concentration 76 μmol/l; normal range 71-133 μmol/l) and negative results on urinalysis. He had an exacerbation of his colitis during the third and fourth years of treatment. On each occasion he responded to a combination of oral prednisolone treatment and an increase in the dose of mesalazine to 1.2 g twice a day. Each time, steroid treatment lasted for 3 months and began with 40 mg a day of prednisolone which was rapidly tapered down to a maintenance dose of 10 mg a day. Repeat serum creatinine concentration measured after 3 years of mesalazine treatment was 79 μmol/l. Thereafter the dose of mesalazine fluctuated between 800 …