Drug utilization and medication adherence for the treatment of psoriatic arthritis: an Italian study.

Introduction: This study aims to evaluate the persistence, treatment adherence and drug cost associated with biologic and targeted synthetic disease-modifying antirheumatic drugs (b/tsDMARDs) in the management of psoriatic arthritis (PsA) in Italy, with a focus on biosimilar drugs.

Methods: This was a retrospective observational study involving eight hospital pharmacies, between January 2017 and December 2020, on naïve patients with at least one b/tsDMARD dispensation indicated for PsA. Patients were followed up for 12 months and persistence and adherence were evaluated by proportion of days covered (PDC). The originator and biosimilar for adalimumab and etanercept were compared. Furthermore, the real annual cost per patient based on adherence to therapy was calculated.

Results: Patients initiating b/tsDMARDs for PsA had a mean persistence of 263 days and 48.6% remained persistent for 1 year. Adherent patients (PDC ≥ 0.8) were 47.6% for the overall population. Similar persistence and adherence were observed between patients treated with the adalimumab originator and its biosimilar, while patients treated with the etanercept originator showed lower persistence and adherence compared to those treated with its biosimilar (mean persistence: 222 vs. 267 days, patient persistent at 1 year: 29.4% vs. 51.5%, mean PDC: 0.53 vs. 0.70, adherent patients: 23.5% vs. 51.5%). The average annual drug cost ranged from €8,724 (etanercept) to €14,783 (ustekinumab), with an annual saving of more than €2,500 by using biosimilars.

Conclusion: Poor adherence to medications contributes to suboptimal clinical outcomes. The comparison between biosimilar and originator offers further evidence in support of the biosimilar to optimizing resources in healthcare.