Mercaptopurine treatment should be considered in azathioprine intolerant patients with inflammatory bowel disease

Background  Adverse drug reactions are a significant reason for therapeutic failure during thiopurine treatment of inflammatory bowel disease. Some smaller series in this patient population have shown that a switch to mercaptopurine may be successful in many cases of azathioprine intolerance.
Aim  To assess the long-term outcome of mercaptopurine treatment in a large patient population with azathioprine intolerance.
Methods  We identified 135 patients (74 women; median age 40 years) with Crohn's disease ( n  = 88) or ulcerative colitis ( n  = 47) and reviewed their medical records.
Results  A total of 70 patients (52%) tolerated mercaptopurine and were followed up for 736 (362–1080) days; 65 patients discontinued mercaptopurine due to adverse events after 25 (8–92) days. Mercaptopurine was tolerated in 71% (12/17) with hepatotoxicity and in 68% (13/19) with arthralgia/myalgia during azathioprine treatment. Previous abdominal surgery was more common in mercaptopurine intolerant patients 39/65 (60%) vs. 27/70 (39%); P  = 0.02] and thiopurine methyltransferase activity was higher in mercaptopurine tolerant patients than in mercaptopurine intolerant patients 13.2 (11.4–15.3) vs. 11.8 (9.6–14.2) U/mL red blood cells; P  = 0.04; n  = 81].
Conclusions  A trial of mercaptopurine should be considered in azathioprine intolerance, as half of the patients tolerate a switch to mercaptopurine. Patients with hepatotoxicity or arthralgia/myalgia during azathioprine treatment might benefit more often than those with other types of adverse events.