Nusinersen for Spinal Muscular Atrophy in the United States: Findings From a Retrospective Claims Database Analysis

Introduction: Spinal muscular atrophy (SMA) is a rare, genetic neuromuscular disorder caused by deletion/mutation of the survival motor neuron 1 gene, characterized by progressive loss of motor neurons, resulting in increasing muscular weakness, deteriorating motor function, and, in its most severe form, death before 2 years. Nusinersen, an antisense oligonucleotide that increases expression of the functional SMN protein, was approved for SMA by US and European regulatory agencies in 2016 and 2017, respectively. The indicated regimen requires intrathecal injections every 4 months, following the first four injections during the loading phase. Adherence is integral to treatment success. Adherence to nusinersen may pose particular challenges as most patients with SMA are young children who require complex multidisciplinary care (including ongoing intrathecal treatment administration and potential specialized anesthetic and surgical procedures) at specialized centers. However, real-world data on adherence to nusinersen are limited.

Methods: We conducted a retrospective claims database analysis from December 23, 2016, to November 20, 2019, to study nusinersen adherence and discontinuation/persistence in US patients with SMA types 1-3 who completed the loading phase, and to determine the impact of non-adherence or treatment discontinuation on SMA-related comorbidities, health care resource utilization (HCRU), and costs.

Results: We identified 23 patients with SMA type 1, 41 patients with SMA type 2, and 260 patients with SMA type 3 who had completed the loading phase. Deviations from the indicated nusinersen treatment schedule were frequent in real-world usage, with most patients receiving ≥1 dose outside the scheduled interval. Across SMA types, non-adherent patients were more likely to have had SMA-related comorbidities (e.g., feeding difficulties, dyspnea and respiratory anomalies, and muscle weakness) and greater HCRU. Persistence rates 12 months after treatment initiation for patients with SMA types 1, 2, and 3 were 55.2%, 42.4%, and 54.6%, respectively. Patients who discontinued nusinersen and those who did not had generally similar comorbidity profiles. Discontinuation was associated with greater health care costs across SMA types.

Conclusion: Our analysis of claims data indicated that discontinuation and non-adherence to nusinersen treatment were prevalent, and associated with greater frequency of comorbidities, greater HCRU, and increased costs for patients.