The relationship of serum infliximab concentrations to clinical improvement in rheumatoid arthritis: results from ATTRACT, a multicenter, randomized, double-blind, placebo-controlled trial.
OBJECTIVE
To investigate the relationship between serum concentrations of infliximab, a monoclonal anti-tumor necrosis factor alpha antibody, and clinical improvement from infliximab therapy for rheumatoid arthritis (RA).


METHODS
Multiple blood samples were obtained from each of 428 subjects with active RA who were enrolled in a multicenter, randomized, double-blind, placebo-controlled trial (ATTRACT [Anti-Tumor Necrosis Factor Trial in Rheumatoid Arthritis with Concomitant Therapy]) evaluating the clinical efficacy and safety of infliximab therapy. Serum levels of infliximab were measured by enzyme-linked immunosorbent assay. Dose-response trends were analyzed using generalized logistic regression techniques. Pharmacokinetic modeling was used to predict the serum concentrations of infliximab after simulated infusions using doses and dosing intervals not evaluated in the trial.


RESULTS
At week 54, 26% of the subjects receiving 3 mg/kg infliximab every 8 weeks had undetectable trough serum levels of infliximab, a significantly greater proportion than in the other 3 treatment groups (P < 0.001). Increased magnitude of American College of Rheumatology (ACR) response (measured by the ACR-N, a continuous measure of clinical improvement derived from the ACR 20% response criteria) and greater reduction from baseline in serum C-reactive protein level were both associated with higher trough serum concentrations of infliximab (P < 0.001), as was less progression of radiographic joint damage (P = 0.004), providing support for a dose-response relationship. Pharmacokinetic models predicted that decreasing the dosing interval from 8 weeks to 6 weeks would yield higher trough serum levels of infliximab than increasing the dose by 100 mg.


CONCLUSIONS
These results suggest that some patients with RA may benefit from infliximab given at higher doses than 3 mg/kg or more frequently than every 8 weeks.
St Clair
E William
EW
Duke University Medical Center, Durham, NC 27710, USA. stcla003@mc.duke.edu
Wagner
Carrie L
CL
Fasanmade
Adedigbo A
AA
Wang
Benjamin
B
Schaible
Thomas
T
Kavanaugh
Arthur
A
Keystone
Edward C
EC
D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000097:blood* / Q000493:pharmacokinetics*; D018501:Antirheumatic Agents / Q000008:administration & dosage / Q000097:blood* / Q000493:pharmacokinetics*; D001172:Arthritis, Rheumatoid / Q000000981:diagnostic imaging / Q000628:therapy*; D004311:Double-Blind Method; D006801:Humans; D000069285:Infliximab; D016015:Logistic Models; D011859:Radiography; D016896:Treatment Outcome
D000911:Antibodies, Monoclonal; D018501:Antirheumatic Agents; D000069285:Infliximab