Optimised infliximab monotherapy is as effective as optimised combination therapy, but is associated with higher drug consumption in inflammatory bowel disease.

Background Combination treatment with azathioprine for 6-12 months is the preferred strategy for starting infliximab due to improved pharmacokinetics. However, optimised infliximab monotherapy with proactive dose escalations in case of low trough levels is a safer but under-studied alternative. Aim To compare the clinical success and infliximab consumption of combination vs optimised monotherapy strategies. Methods We studied the clinical success and infliximab consumption of both strategies in 149 patients (94 Crohn's disease; 55 ulcerative colitis) starting infliximab and undergoing intensive drug monitoring assisted treatment optimisation. Results The drug retention rates were similar for optimised monotherapy and combination treatment after induction (96% vs 97%, P = 0.73), after the first year (90% vs 83%, P = 0.23) and at the end of follow-up (74% vs 75%, P = 0.968). Similarly, no differences were observed for steroid use at year 1 (5% vs 14%, P = 0.08) or mucosal healing at the end of follow-up (64% vs 67%, P = 0.8). Higher infliximab consumption (7.6 mg/kg q8 weeks [interquartile range (IQR): 5.9-10.3] vs 6.4 mg/kg q8 weeks [IQR: 5.2-8.0], P = 0.019) combined with lower trough levels (1.7 mu g/mL [IQR: 0.3-6.6] vs 5.0 mu g/mL [2.5-8.7], P = 0.012) resulted in almost 3-fold higher drug-to-trough ratio (3.9 vs 1.5) in monotherapy compared to combination strategy at year 1. At the end of follow-up, when azathioprine had been discontinued for a median of 14 [IQR: 3-33] months, these differences disappeared. Conclusions In this study, optimised infliximab monotherapy was as clinically effective as combination therapy but was associated with significantly higher infliximab consumption. The infliximab-sparing effect disappeared after azathioprine withdrawal.