Mercaptopurine and inflammatory bowel disease: the other thiopurine

Background: Data about use and effectiveness of mercaptopurine in inflammatory bowel disease are relatively limited. Aims: To assess the possible therapeutic indications, efficacy and safety of mercaptopurine as an alternative to azathioprine in inflammatory bowel disease. Methods: Retrospective observational study in patients treated with mercaptopurine in a total cohort of 1,574 patients with inflammatory bowel disease. Results: One hundred and fifty-two patients received mercaptopurine, 15.7% of these patients as an initial thiopurine, 5.3% after azathioprine failure, and 79% after azathioprine intolerance. In 52.6% of patients (n = 80), adverse effects of mercaptopurine occurred, resulting in withdrawal in 49 of them. Mercaptopurine was effective in 39% of cases (95% CI 31-48%). In the remaining patients, failure was due mainly to withdrawal due to side effects (55.1%) and therapeutic step-up (33.7%). The average total time of mercaptopurine exposure was 36 months (IQR: 2-60). Myelotoxicity with mercaptopurine was more common in patients with intermediate TPMT activity than in those with normal activity (p = 0.046). Conclusions: In our setting, mercaptopurine is primarily used as a rescue therapy in patients with azathioprine adverse effects. This could explain its modest efficacy and the high rate of adverse effects. However, this drug is still an alternative in this group of patients, before a therapeutic step-up to biologics is considered.