Seven RCTs (n=408) and 30 uncontrolled studies (n=1,632) were included. Six of the seven RCTs were higher quality studies (scored 3 or higher on Jadad scale). Mean follow-up period ranged from three to 18 months (controlled studies) and from three to 58 months (uncontrolled studies).
Controlled studies: Maintenance of clinical remission in ulcerative colitis was statistically significantly higher in patients treated with azathioprine/mercaptopurine compared to placebo (OR 2.59, 95% CI 1.26 to 5.3; three RCTs), but not compared to 5-aminosalicylates. Absolute risk reduction was 23% and the number needed to treat to prevent one recurrence was five (compared to placebo). There was statistically significant heterogeneity between studies that compared azathioprine/mercaptopurine versus 5-aminosalicylates.
There was little beneficial effect of azathioprine/mercaptopurine (OR 1.59, 95% CI 0.59 to 4.29; four RCTs) for induction of remission of ulcerative colitis. When only higher-quality studies were considered (studies that scored 3 or higher), azathioprine/mercaptopurine was beneficial for maintenance of remission (OR 2.44, 95% CI 1.42 to 4.17), but not for induction (OR 1.21, 95% CI 0.6 to 2.41). Subgroup analysis results for placebo-controlled trials were presented.
Uncontrolled studies: Mean efficacy of azathioprine/mercaptopurine in ulcerative colitis patients was 65% (95% CI 62% to 67%; 30 studies). Subgroup results on studies where azathioprine/mercaptopurine was prescribed for steroid resistance showed a mean efficacy rate of 66% (95% CI 59% to 73%). The mean efficacy rate for induction was 65% (95% CI 55% to 75%) and for maintenance was 76% (95% CI 71% to 81%).