Azathioprine

Combination therapy, the association of an anti-Tumor Necrosis Factor (TNF) to an immunosuppressant, is recognized as the most effective treatment during Crohn's disease (CD). Several mechanisms have been proposed to explain the superiority of combination therapy over monotherapy, the additive effect of two effective drugs or the prevention of anti-TNF immunogenicity. As the best combination therapy is unknown, both azathioprine (AZA) and methotrexate (MTX) are used. Some retrospective studies suggest a higher effectiveness of AZA. MTX may have an advantage in terms of safety. The investigators hypothesize that AZA is more effective than MTX as combination therapy with adalimumab to improve short-term endoscopic, clinical and pharmacological outcomes in CD patients.