Etanercept Dose, Not Methotrexate Use, Affects Serum Etanercept Concentration in JIA

Concomitant methotrexate did not appear to have a significant effect on serum etanercept concentration or clinical response in patients with JIA.

Serum concentrations of etanercept in juvenile idiopathic arthritis (JIA) may not affected by concomitant use of methotrexate (MTX), according to study results published in Pediatric Rheumatology.

Patients with JIA with an inadequate response traditional synthetic disease-modifying antirheumatic drugs (DMARDs) may receive etanercept. Many of these patients also receive concomitant MTX; however, there are insufficient data regarding the effects of MTX use on serum levels of etanercept.

Patient records were retrospectively reviewed from 8 pediatric rheumatology centers in Finland. Patients with JIA who received regular treatment with etanercept between 2014 and 2017 were evaluated with regard to etanercept dose, serum concentration, and concomitant medication use.

A total of 180 patients (61% girls; mean age, 8.0 years) with JIA were included in the study, of whom 97 (54%) received concomitant MTX and 83 (46%) received etanercept monotherapy or other synthetic disease-modifying antirheumatic drugs (DMARDs).

[W]e observed that MTX did not affect serum ETN concentration, but increase of the ETN dose increased its serum concentration.

Researchers observed that MTX nonusers vs users had higher rates of concomitant leflunomide (28% vs 1%; P <.0001) and sulfasalazine (10% vs 2%; P =.046).

The median time of etanercept concentration assessment was 12 months after initiation during which the median dose was 0.75 mg/kg/week (range, 0.49-1.47 mg/kg/week) and the median MTX dose was 13.0 mg/m2 (range, 5.5-24.2 mg/m2). The median concentrations of etanercept among the MTX users and nonusers were 1.60 mg/mL (range, 0.40-6.30 mg/mL) and 1.70 mg/mL (range, 0.60-4.90 mg/mL), respectively.

Researchers did not observe a correlation between MTX dose and etanercept concentration (r=0.01). In both groups, the concentration of etanercept was not significantly related to erythrocyte sedimentation rate, C-reactive protein, 10-point Juvenile Arthritis Disease Activity Score (JADAS10), or patient’s or physician’s global assessment wellbeing scores.

The only significant correlations observed in this study were between etanercept dose and concentration among both the MTX users (r=0.35; P =.03) and nonusers (r=0.54; P =.03).

The study may have been limited by the significant differences at baseline observed between the groups.

The study authors concluded, “[M]TX did not affect serum [etanercept] concentration, but increase of the [etanercept] dose increased its serum concentration.”