Safety of azathioprine and 6-mercaptopurine in patients with inflammatory bowel disease naïve to thiopurine treatment
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OBJECTIVES: To determine if 6-mercaptopurine (MP) is better tolerated than azathioprine (AZA) as the initial thiopurine treatment in patients suffering from inflammatory bowel disease (IBD). Switching patients with IBD from AZA to MP is advocated in patients intolerant to AZA. However, no study has determined if MP is more suited than AZA as a first-line treatment for patients who are naïve to thiopurine treatment.

STUDY: The tolerance of AZA and MP treatments in clinical practice was retrospectively evaluated from start to 12 months after initiating treatment in 113 patients with IBD who were all naïve to thiopurines (82 patients treated with AZA and 31 patients with MP).

RESULTS: 65% of the patients treated with AZA and 61% of the patients treated with MP tolerated their treatment during 12 months (i.e., no group difference, p = 0.742). No difference in reported side effects between the two treatments was observed. The mean equivalent initial dose (0.92 vs. 0.61 mg/kg; p < 0.001) and the mean equivalent dose at 12 months (1.98 vs. 1.65 mg/kg; p = 0.014) was significantly higher in the MP group vs. the AZA group. The proportion of patients with ΔMCV ≥ 7 at 12 months was numerically higher in the MP group than in the AZA group (53% vs. 31%; p = 0.090).

CONCLUSIONS: In this retrospective observational study, no differences in tolerance or adherence between AZA and MP were observed in patients naïve to thiopurines. However, MP treatment was at a higher equivalent thiopurine dose than AZA treatment, which tended to be associated with better treatment response.
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