Background and Aims: The efficacy of azathioprine for Crohn's disease under adalimumab treatment remains obscure. Methods: In an open-labelled prospective study, we evaluated the efficacy of adalimumab with and without azathioprine in patients with active Crohn's disease, who were naïve to biologics and thiopurines. The patients were randomly assigned to subcutaneous administration of adalimumab [monotherapy group] or to exactly the same schedule of adalimumab with azathioprine [25- 100 mg daily] [combination group] for 52 Weeks. The primary endpoint was clinical remission at WWeek 26. We also evaluated the score for simple endoscopic severity of Crohn's disease before the therapy and at WWeeks 26 and 52. Results: A total of 176 patients were randomized to either the monotherapy group [n = 85] or to the combination group [n = 91]. Eighteen patients [21.2%] from the monotherapy group and 7 patients [7.7%] from the combination group withdrew owing to active disease, and 15 patients [16.5%] from the combination group and 1 patient [1.2%] from the monotherapy group withdrew due to side effects of the medications. Non-responder imputation analysis revealed that the remission rate at WWeek 26 did not differ between the monotherapy group and the combination group [71.8% vs 68.1%; OR 0.84, p = 0.63]. The rate of endoscopic improvement at WWeek 26 was significantly higher in the combination group [84.2%, n = 57] than in the monotherapy group [63.8%, n = 58] [p = 0.019]. Conclusion: The clinical efficacy of a combination of adalimumab and azathioprine at WWeek 26 did not differ from that of adalimumab monotherapy in patients with Crohn's disease naïve to both medications.
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