Finding appropriate timing for the combination of azathioprine and infliximab: propensity score matching and inverse probability of treatment weighting analysis.

BACKGROUND: The combination of azathioprine (AZA) with infliximab (IFX) enhances clinical efficacy in treating Crohn's disease (CD), increasing the risk of adverse events. This study aims to identify the optimal timing for AZA administration in IFX combination therapy to maximize patient benefit. METHODS: This was a retrospective, single-center study, which analyzed patients with CD undergoing IFX treatment from January 2017 to December 2022. Baseline data were collected. To minimize potential confounding effects, we utilized two established propensity score methods: propensity score matching (PSM) and inverse probability of treatment weighting (IPTW). The primary efficacy outcome was defined as the proportion of patients achieving clinical remission at the 54-week follow-up. Safety outcomes were evaluated through comprehensive monitoring and systematic classification of adverse events. RESULTS: A total of 528 active CD patients were included. Of these, 146 received concomitant AZA (AZA group), while 382 did not (non-AZA group). Following PSM or IPTW, the AZA group demonstrated significantly higher clinical remission rates (PSM: P < 0.001, IPTW: P < 0.001) compared to the non-AZA group. Furthermore, 46 patients used AZA during induction (IP-AZA group) and 100 during maintenance (MP-AZA group). After PSM or IPTW, both groups showed similar remission rates at 54 weeks (PSM: P = 0.793, IPTW: P = 0.508), with comparable safety profiles. CONCLUSION: For CD patients treated with IFX, whether AZA was initiated in the induction phase or during the maintenance phase, the impact on clinical outcomes and occurrence of adverse events was similar.