Severe infusion reactions to infliximab: aetiology, immunogenicity and risk factors in patients with inflammatory bowel disease

Background Infliximab (IFX) elicits acute severe infusion reactions in about 5% of patients with inflammatory bowel disease (IBD). Aim To investigate the role of anti-IFX antibodies (Ab) and other risk factors. Methods The study included all IBD patients treated with IFX at a Danish university hospital until 2010 either continuously (IFX every 4-12 weeks) or episodically (reinitiation after >12 weeks). Anti-IFX Ab were measured using radioimmunoassay. Results Twenty-five (8%) of 315 patients experienced acute severe infusion reactions. Univariate analysis showed that patients who reacted were younger at the time of diagnosis (19 vs. 26 years, P = 0.013) and at first IFX infusion (28 vs. 35 years, P = 0.012). Furthermore, they more often received episodic therapy (72% vs. 31%, P < 0.001) and logistic regression revealed this as the only significant predictor of reactions (OR 5 [2-13]; P < 0.001). IFX reinitiation after 6 months intermission further increased the risk (OR 8 [3-20], P < 0.001). Most reactions (n = 14, 88%) occurred at 2nd infusion in the 2nd treatment series (P = 0.006). Anti-IFX IgG Ab were highly positive in 19 of 20 patients (95%) shortly after the reactions (median 84 U/mL). Anti-IFX IgG Ab measured prior to the retreatment series were negative in 7 of 11 patients tested (64%). Anti-IFX IgE Ab were negative in all patients with reactions. Conclusions Acute severe infusion reactions were strongly associated with development of anti-IFX IgG Ab, but not with anti-IFX IgE Ab. The risk was particularly high at the 2nd infusion in retreatment series. Negative anti-IFX Ab before reinitiation did not rule out reactions. Aliment Pharmacol Ther 2011; 34: 51-58