Background: Risdiplam (RIS) and nusinersen (NUS) are disease-modifying therapies for spinal muscular atrophy (SMA) that require ongoing administration. However, evidence on adherence/persistence with these therapies beyond 12-months remains limited, despite their critical role in maintaining therapeutic benefit.
Objective: To describe persistence and adherence to RIS and NUS over a 36-month period.
Methods: A retrospective cohort study using HealthVerity® claims data (9/2015–6/2025) included patients initiating RIS from 8/2020 or NUS from 7/2017 (index = first claim), with ≥1 SMA diagnosis before or on index and continuous enrollment ≥12 months prior (or overlapping if <1 yr old) and ≥36 months after index or until death. Onasemnogene abeparvovec was excluded from the comparison due to its one-time administration. Persistence: time from index to discontinuation or switch, assessed by Kaplan-Meier. Discontinuation: gap ≥31 days for RIS; ≥2 consecutive missed doses for NUS. Adherence: proportion of days covered (PDC) ≥0.9. Days supply obtained from pharmacy claims for RIS; and minimum of labeled interval or observed time to next dose for NUS. Persistence and adherence were described at 12, 24, and 36 months; median persistence and mean PDC at 36 months were reported.
Results: 350 patients were included in RIS cohort (mean age [range]: 20 yr [1-62]; female: 53%) and 600 in NUS cohort (18 yr [0-61]; 51%). Persistence at 12, 24, and 36 months was 70%, 51%, and 40% for RIS (median: 26 months) and 66%, 52%, and 34% for NUS (median: 25 months). Adherence at 12, 24, and 36-months was 64%, 51%, and 45% for RIS (mean PDC: 0.73) and 53%, 41%, and 27% for NUS (mean PDC: 0.66).
Conclusion: Persistence and adherence to RIS and NUS declined over 36 months, with 40% and 34% of patients remaining persistent and 45% and 27% adherent, respectively, highlighting potential challenges in sustaining long-term SMA treatments.