This is the first ever study depicting the expanse of Methotrexate (MTX) adherence in juvenile idiopathic arthritis (JIA) and juvenile dermatomyositis (JDM) paediatric patients. It has been efficiently estimated on the basis of Dried blood spot measurement of Individual methotrexate polyglutamates.

This is the first ever study depicting the expanse of Methotrexate (MTX) adherence in juvenile idiopathic arthritis (JIA) and juvenile dermatomyositis (JDM) paediatric patients. It has been efficiently estimated on the basis of Dried blood spot measurement of Individual methotrexate polyglutamates.

Data were collected prospectively from a cohort of 48 children (median age 11.5 years) who received oral or subcutaneous (SC) MTX therapy for JIA or JDM. Dried blood spot samples were obtained from children by finger pick at the clinic or via self- or parent-led sampling at home, and they were analysed to determine the variability in MTXPG concentrations and assess adherence to MTX therapy.

Wide fluctuations in MTXPG total concentrations (>2.0-fold variations) were found in 17 patients receiving stable weekly doses of MTX, which is indicative of nonadherence or partial adherence to MTX therapy. Age (P = 0.026) and route of administration (P = 0.005) were the most important predictors of nonadherence to MTX treatment. In addition, the study showed that MTX dose and route of administration were significantly associated with variations in the distribution of MTXPG subtypes. Higher doses and SC administration of MTX produced higher levels of total MTXPGs and selective accumulation of longer-chain MTXPGs (P < 0.001 and P < 0.0001, respectively).

Nonadherence to MTX therapy is a significant problem in children with JIA and JDM. The present study suggests that patients with inadequate adherence and/or intolerance to oral MTX may benefit from SC administration of the drug. The clinical utility of MTXPG levels to monitor and optimise adherence to MTX in children has been demonstrated.