Tolerability and safety of mercaptopurine in azathioprine- intolerant patients with inflammatory bowel disease C. W. LEES, A. K. MAAN, B. HANSOTI, J. SATSANGI & I. D. R. ARNOTT GI Unit, University of Edinburgh, Edinburgh, UK Correspondence to: Dr C. W. Lees, Gastrointestinal Unit, Molecular Medicine Centre, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK. E-mail: charlie.lees@ed.ac.uk Publication data Submitted 24 September 2007 First decision 27 October 2007 Resubmitted 2 November 2007 Accepted 3 November 2007 SUMMARY Background Azathioprine intolerance is a common clinical problem, requiring drug withdrawal in up to 30% of patients. The successful use of mercaptopu- rine is described, but data to support this strategy are needed. Aims To assess the tolerability of mercaptopurine in inflammatory bowel dis- ease patients previously intolerant of azathioprine, and identify predic- tive factors. Methods Sixty-one azathioprine-intolerant patients (31 males, median age at diagnosis 32 years, 31 with Crohn’s disease, 30 with ulcerative colitis) who had been treated with mercaptopurine were identified. Intolerances included nausea and vomiting, flu-like illness, neutropenia, hepatotoxicity and pancreatitis. Results Mercaptopurine was tolerated by 59% (36 of 61) of azathioprine-intoler- ant patients (median dose 1.0 mg ⁄ kg), 61% (17 of 28) in patients with azathioprine-related nausea and vomiting, 61% (11 of 18) with flu-like illness, 33% (three of nine) with hepatotoxicity, 100% (one of one) with neutropenia, 100% (three of three) with rash and 0% (zero of one) with pancreatitis. Mercaptopurine intolerance was frequently for a different adverse event. Those intolerant of mercaptopurine were younger (28.4 years vs. 37.0 years; P = 0.014) and more frequently female (14 ⁄ 30 vs. 2 ⁄ 29, P = 0.027). Mercaptopurine tolerability was not affected by diagnosis, location, behaviour, surgery, smoking, family history or extra-intestinal manifestations. Conclusion Mercaptopurine may be tolerated in up to 60% of azathioprine-intoler- ant patients, and treatment should be considered, particularly if intoler- ance was due to nausea, vomiting, flu-like illness or rash. Aliment Pharmacol Ther 27, 220–227 Alimentary Pharmacology & Therapeutics 220 ª 2008 The Authors Journal compilation ª 2008 Blackwell Publishing Ltd doi:10.1111/j.1365-2036.2007.03570.x