P290. Infliximab drug levels in Crohn's disease responding to the treatment
J. Morgenstern1, E. Baestlein2, L. Leifeld1, P. Nguyen3, J. Stein4, W. Kruis1
1ev. KH Köln Kalk, Cologne, Germany; 2Gastroenterologische Gemeinschaftspraxis, Cologne, Germany; 3Florence-Nightingale-KH, Duesseldorf, Germany; 4St. Marienkrankenhaus, Frankfurt, Germany
Background: Though many studies have investigated antibody formation against Infliximab (IFX) demonstrating poor association to therapeutic effects less, is known about IFX serum levels in successfully treated patients with Crohn's disease (CD).
Methods: Consecutive patients (n = 22) with CD under a scheduled (infusions every 8 weeks) treatment with IFX (5 mg/kg body weight) were recruited. Inclusion criterion was known clinical response to IFX. During the 8 weeks treatment interval IFX serum levels, CRP and HarveyBradshaw-Index (HBI) were repeatedly determined. IFX serum levels were measured by using an immuno-competitive assay (Immundiagnostik AG, Bensheim, Germany).
Results: Serum levels of IFX between before and one week after infusion showed a dramatic increase (13.13±9.87 µg/ml trough level and 101.62±47.54 µg/ml one week later; mean ±SD). Despite all patients were clinical responders the range of IFX peak levels varied widely (27.6201 µg/ml). As figure 1 depicts there exists an apparent association between courses of IFX drug levels, CRP and HBI.
Mean CRP levels increased beyond 5 mg/l between week 5 and 6 while HBI increased during the same time from 3 to 4. In contrast, at week 4 mean serum levels of IFX decreased below 31 µg/ml, which may be a critical serum level for the clinical response.
Conclusions: IFX serum levels in clinically responding patients with CD increase after IFX infusions significantly but show high interindividual variance in peak concentrations and decay. There is apparent association between the drop of serum IFX levels and increase of CRP, and HBI, where a level of 31 µg/ml may be critical. Worsening of clinical symptoms and CRP is associated to ineffective IFX serum levels and should lead to an adaption of the individual IFX treatment.
Measurements of infliximab drug levels were sponsored by Immundiagnostik AG, Bensheim, Germany.