Azathioprine and 6-mercaptopurine for maintenance of remission in ulcerative colitis.

Background: Maintenance of remission is essential in inflammatory bowel disease (IBD) in terms of disease course and long-term prognosis. The thiopurines azathioprine and 6-mercaptopurine have longstanding merit in ulcerative colitis, but more therapeutic options have been developed. This review is an update and extension of a review last published in 2016.

Objectives: To assess the effectiveness and safety of azathioprine and 6-mercaptopurine in monotherapy or combined therapy regimens compared to placebo or active controls for the maintenance of remission in ulcerative colitis.

Search methods: We searched Cochrane Central Register of Controlled Trials (until May 2023), ClinicalTrials.gov (until May 2023), Embase (until August 2022), MEDLINE (until May 2023), and WHO ICTRP (until May 2023). We checked reference lists of the included studies and, if needed, contacted the authors to request more data or information.

Selection criteria: Randomized controlled trials (RCTs) of at least 24 weeks' duration comparing azathioprine or 6-mercaptopurine with placebo or any other medication, or comparing different treatment modalities of azathioprine or 6-mercaptopurine, in persons of any age with quiescent ulcerative colitis were eligible. We only considered studies with mixed IBD populations or with a preceding induction period if separate results on participants with ulcerative colitis in remission were available or could be calculated. The primary outcome was failure to maintain clinical or endoscopic remission (relapse). Secondary outcomes included change in disease activity, quality of life, hospitalization, need for surgery, days off work, adverse events, and withdrawal due to adverse events.

Data collection and analysis: Two authors independently extracted data using standard forms, resolved any disagreements by consensus, and assessed study quality using the Cochrane risk of bias tool (RoB 2). We conducted separate analyses by type of control, calculated pooled risk ratios (RRs) or risk differences (RDs) using the fixed-effect model unless heterogeneity was likely, and assessed the certainty of evidence using the GRADE approach.

Main results: We included 10 studies in the review, including 468 adult participants with ulcerative colitis. The risk of bias across these was low for most outcomes, but we considered some outcomes to have some concerns or high risk of bias due to insufficient information on concealment of allocation and outcome measurement. Based on five placebo-controlled studies, azathioprine or 6-mercaptopurine may reduce the risk of failing to maintain remission. In the thiopurine group, 45% (64/143) of participants failed to maintain remission compared to 67% (96/143) of participants receiving placebo (RR 0.66, 95% confidence interval (CI) 0.54 to 0.82; 5 studies, 286 participants; low-certainty evidence). Three studies reported withdrawals due to adverse events. Among participants on azathioprine, 4% (3/80) withdrew due to adverse events compared to 0% (0/82) of placebo participants (RD 0.04, 95% CI -0.02 to 0.09; 3 studies, 162 participants; low-certainty evidence). The evidence is of low certainty when comparing 6-mercaptopurine to 5-aminosalicylate. Based on one three-armed trial, 27% (3/11) of 6-mercaptopurine participants failed to maintain remission compared to 100% (2/2) of 5-aminosalicylate participants (RR 0.35, 95% CI 0.13 to 0.97; 1 study, 13 participants; low-certainty evidence). This trial also involved an induction phase; we only included the results for participants in remission. The single trial comparing 6-mercaptopurine to 5-aminosalicylate did not report separate data on adverse events and withdrawals due to adverse events for the subgroup with successful induction of remission, so we could not analyze these outcomes for this comparison.

Authors' conclusions: Low-certainty evidence suggests that azathioprine or 6-mercaptopurine therapy may be more effective than placebo for the maintenance of remission in ulcerative colitis. More research is needed to evaluate the value of therapeutic drug monitoring and the effects of various treatment modalities on long-term safety.