Relationship between inflammation and infliximab pharmacokinetics in rheumatoid arthritis

Aims Infliximab, an anti‐tumour necrosis factor‐α monoclonal antibody, is indicated in rheumatoid arthritis ( RA ). Our objective was to evaluate the influence of the sources of infliximab pharmacokinetic variability in RA . Methods Eighty‐four patients treated with infliximab for RA were included in a prospective noncomparative study. They were analysed between two consecutive infliximab infusions. Infliximab concentrations were measured before the infusion, 2 h, 1 and 4 weeks after the infusion and immediately before the next infusion. Infliximab concentrations were described using a two‐compartment population pharmacokinetic model. Results The mean (interindividual standard deviation) estimated central volume of distribution was 2.3 l (36%) and systemic clearance was 0.019 l h −1 (37%). The central volume of distribution increased with bodyweight; it was doubled between 50 and 90 kg. Systemic clearance increased with pre‐infusion C ‐reactive protein concentration by 20%, varying from 3 to 14 mg l − 1, and was decreased by 30% when methotrexate was coadministered. Conclusions The influence of methotrexate and inflammation on infliximab clearance suggests that individual adjustment of infliximab doses according to disease activity may be useful in RA .