Longitudinal Dosing Patterns and Treatment Costs Among Patients with Spinal Muscular Atrophy Initiating Nusinersen and Risdiplam.

INTRODUCTION: Spinal muscular atrophy (SMA) is a neuromuscular disorder historically associated with high morbidity, mortality, and healthcare costs. Disease-modifying therapies have improved outcomes, but their long-term economic burden remains uncertain. Nusinersen and risdiplam, both chronic therapies, differ from onasemnogene abeparvovec, a one-time gene therapy. Understanding real-world treatment costs of chronic SMA therapies is critical to inform therapeutic choice. METHODS: This retrospective cohort study used the Komodo Health Research Database (2016-2024). Patients with SMA aged ≥ 2 years who initiated nusinersen or risdiplam were followed up to 5 years. Dosing patterns and drug acquisition and administration costs (2024 USD) were assessed annually, overall and by age group and scoliosis status. RESULTS: Among 3864 eligible patients, 2743 initiated nusinersen and 1121 initiated risdiplam (mean age 21.4 vs. 25.3 years, respectively; 51.5% vs. 46.1% male). Median follow-up was 5.5 years for nusinersen and 1.1 years for risdiplam. Persistence declined over time, with 39.5% of patients treated with nusinersen and 63.7% of patients treated with risdiplam remaining on their index therapy at years 5 and 4. Patients treated with nusinersen received 3.6 injections on average in year 1 and 2.8-3.1 annually thereafter. Median annualized nusinersen treatment costs were $504,173 in year 1 and $438,788-548,608 in years 2-5. Patients treated with risdiplam had a median of 96 days of supply in year 1 (51.5% with > 90 days); median annualized drug costs were $143,331 overall in year 1 and $259,419 among those with > 90 days of supply, increasing to $264,701-289,340 in years 2-4. Costs were similar across subgroups. CONCLUSION: Nusinersen and risdiplam persistence declined over time. Among patients remaining on their index therapy, both treatments had high long-term costs, highlighting the substantial and ongoing financial burden of chronic SMA therapies and the need for real-world evidence to inform healthcare planning. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT07378943.