Pharmacokinetic Features and Presence of Antidrug Antibodies Associate With Response to Infliximab Induction Therapy in Patients With Moderate to Severe Ulcerative Colitis

BACKGROUND & AIMS: The pharmacokinetics of infliximab during induction treatment for ulcerative colitis (UC) have not been studied. We investigated serum concentrations of infliximab and the early appearance of antibodies to infliximab (ATI) during induction treatment in patients with moderate-to-severe UC. METHODS: We performed a prospective analysis of 19 consecutive patients with moderate-severe UC (endoscopic Mayo >= 2) receiving induction therapy with infliximab (5 mg/kg at weeks 0, 2, and 6) at 2 centers in Amsterdam, The Netherlands, from July 2012 through March 2014. Serial serum and fecal samples were collected for 6 weeks and concentrations of infliximab, ATI, c-reactive protein (CRP), albumin, and fecal calprotectin were measured. Treatment success was defined as endoscopic response (>= 1 point reduction in the endoscopic Mayo score) at week 8. RESULTS: Eleven patients (58%) had an endoscopic response. The median serum concentrations of infliximab at week 6 were 8.1 mu g/mL in responders (interquartile range, 3.0-13.7 mg/mL) and 2.9 mu g/mL in nonresponders (interquartile range, 0.01-5.8 mu g/mL) (P = .03). ATIs were detected in 7 patients as early as day 18 (median, 28 d; interquartile range, 18-42 d). Six of the 8 nonresponders tested positive for ATIs vs 1 of 11 responders (P <.01; odds ratio, 30.0; 95% CI, 2.2-406.2). Patients with a baseline concentration of CRP greater than 50 mg/L had lower drug exposure from weeks 0 to 6 (587 mg/L/d in patients with high levels of CRP vs 1361 mg/L/day in patients with low CRP; P = .001). The median area under the curve for serum concentration of infliximab during induction therapy was 1230 mg/L/d in nonresponders vs 1352 mg/L/d in responders (P = .65). CONCLUSIONS: There is a significant difference in serum concentration of infliximab at week 6 of treatment between responders and nonresponders. Early development of ATIs during induction therapy reduces the serum concentration of infliximab and is associated with nonresponse to treatment. Patients with high baseline serum levels of CRP had lower serum concentrations of infliximab. Clinical trial number: NL39626.018.12.