Background & aims: The effect of different treatment regimens on antibody responses to infliximab and their clinical significance was examined by using data from ACCENT I.

Methods: Patients with Crohn's disease (n = 573) received 5 mg/kg infliximab (week 0) and then were randomly assigned to blinded infusions at weeks 2 and 6 and every 8 weeks until week 46 of placebo (group I), 5 mg/kg infliximab (group II), or 5 mg/kg infliximab at weeks 2 and 6, followed by 10 mg/kg thereafter (group III). At week 14 or later, patients losing response could cross over to episodic infliximab treatment increased by 5 mg/kg. Samples for antibody determination were collected before the first infusion and at weeks 14, 22, 54, 62, 72, and, if applicable, before and after crossover.

Results: Through week 72, antibodies to infliximab were detected in 30%, 10%, and 7% of groups I, II, and III, respectively (P < 0.0001). Patients receiving immunomodulators had a lower incidence of antibodies compared with patients receiving infliximab alone (10% and 18%, respectively; P = 0.02). Antibodies were associated with a 12% absolute increase in infusion reactions but no increase in serious infusion reactions or serum sickness-like reactions. In the overall population, similar proportions of antibody-positive and antibody-negative patients achieved clinical response (64% and 62%, respectively; P = NS) or clinical remission (41% and 39%, respectively; P = NS) at week 54. Notably, 86% of patients responded to retreatment, and 63% were in clinical response at week 54; however, fewer antibody-positive group I patients attained clinical remission (31%) compared with those who were antibody negative (37%) or antibody inconclusive (54%) (P = NS).

Conclusions: Reduced antibody formation and greater clinical benefit were observed with an induction regimen followed by maintenance treatment compared with a single dose followed by episodic retreatment in Crohn's disease patients treated with infliximab.