Non-adherence and discontinuation rate for oral and parenteral methotrexate: A retrospective-cohort study in 8,952 patients with psoriatic arthritis

Background and aims: Treatment options for PsA, following non-steroidal anti-inflammatory drugs (NSAIDs), include conventional synthetic disease modifying anti-rheumatic drugs (csDMARDS), particularly methotrexate (MTX). The present study was performed to determine the non-adherence and discontinuation rates of different methotrexate (MTX) formulations in psoriatic arthritis (PsA). Approach and results: We performed a retrospective-cohort study on patients with PsA identified by disease-specific code in the administrative-health-databases of a Northern Italian region (Lombardy) between 2004 and 2015. Subjects were defined as non-adherent if less than 80% of the prescribed MTX dose was taken based on the time between each prescription. Discontinuation rates were calculated using the time between the first and the last MTX prescription over an observation period of 120 months. Among 8952 patients with PsA, 33% were treated with MTX (mean dosage 10 mg/week ± 2.5 mg standard deviation), more frequently (59%) in its parenteral formulation at a 10 mg weekly dosage (35%). Oral glucocorticoids were prescribed to 21% of patients, while non-steroidal anti-inflammatory drugs to 45%. Approximately 37% of patients with PsA were defined as non-adherent to MTX, with the oral formulation associated with an increased risk of non-adherence (hazard ratio 2.08, 95% confidence interval 1.84–2.35, p