Monitoring of infliximab in clinical practice

Objective: To evaluate the applicability of a solid phase ELISA technique for monitoring infliximab (IFX) and anti-infliximab antibodies in the clinical practice. Method: A retrospective observational study was performed of the results of the determination of blood IFX concentrations and the presence of anti-IFX antibodies in treated patients with rheumatological or gastrointestinal disease. The blood samples were collected before administration of the drug. The determination of IFX and anti-IFX antibodies was carried out using two independent ELISA techniques. The pharmacoeconomic evaluation was based on a cost-benefit study. Results: Forty-one samples from 27 patients were processed: 19 corresponding to the Department of Rheumatology and eight to the Department of Digestive Diseases. Twenty-four percent of the IFX concentrations were within the therapeutic range, and 32% were undetectable. Anti-IFX antibody concentrations were found in six samples from five patients. All five had undetectable IFX levels. A linear monocompartmental model was used for the pharmacokinetic estimation and showed adequate internal validity. The pharmacokinetic parameters were: Cl 12.8 ±3.3 ml/h/70 kg, Vd 4.3 ±0.5 l/70 kg and t½ 259 ±113 h. The clinical decisions derived from the monitoring process were significantly related to the serum IFX concentrations. Conclusions: The evaluated technique allows the monitoring of IFX and anti-IFX antibodies in the clinical practice with optimum cost-benefit performance. The monitored patients showed a high percentage of subtherapeutic or undetectable concentrations. The presence of undetectable concentrations was significantly correlated to the recorded anti-IFX antibody levels (›2 IU/ml). Based on the results obtained, a linear monocompartmental model has been developed for the clinical monitoring of IFX that shows adequate internal validity. The model therefore can help to predict the concentrations of IFX and anti-IFX antibodies, and their correlation to clinical response