Risdiplam utilization, adherence, and associated health care costs for patients with spinal muscular atrophy: a United States retrospective claims database analysis

Abstract

Background: Spinal muscular atrophy (SMA) is a genetic neuromuscular disease associated with progressive loss of motor function. Risdiplam, a daily oral therapy, was approved in the United States for the treatment of SMA. Risdiplam's effectiveness depends on patient adherence to the treatment regimen. This retrospective claims database analysis assessed real-world treatment adherence and persistence, and all-cause health care costs by adherence status, for patients with SMA receiving risdiplam. Outcomes were summarized by SMA types (1-4) and age groups (0-2, 3-5, 6-17, and ≥ 18 years).

Results: 86 patients with ≥ 1 SMA diagnosis, risdiplam treatment, and ≥ 6 months of continuous enrollment after the index date (SMA diagnosis) were identified in the IQVIA PharMetrics^® Plus database (01/01/2020-06/30/2022). One patient had SMA type 1 (a 1-year-old boy), 18 had type 2 (mean ± SD age: 7.9 ± 5.7 years; 61% female), 47 had type 3 (17.3 ± 10.2 years; 55% female), and 20 had type 4 (38.2 ± 11.6 years; 55% female). The mean proportion of days covered (PDC) with risdiplam was 0.89 overall, ranging from 0.88 for SMA type 4 to 0.97 for type 1. The majority (83.7%) of patients were adherent to risdiplam (PDC ≥0.80), ranging from 75.0% for type 4 to 100% for type 1. Adherence ranged from 76.5% among 6-12-year-olds to 100% among 0-2-year-olds. Compared with adherent patients, nonadherent patients had higher median total health care costs by $335,049 for type 2, $41,204 for type 3, and $12,223 for type 4. Among adherent patients, patients with PDC between 0.90 and 1.00 had lower costs compared with patients with PDC between 0.80 and 0.90.

Conclusions: Nonadherence to risdiplam was observed in the first year of treatment, especially for patients with SMA type 4 and patients aged 6-12 years. Nonadherence was associated with higher all-cause health care costs, with the most pronounced cost difference for SMA type 2. For adherent patients, those who were highly adherent incurred lower health care costs. These findings underscore the importance of treatment adherence and persistence for patients with SMA receiving risdiplam, particularly for younger children and those with greater disease severity.

Keywords: Adherence; Claims database analysis; Health care costs; Health care utilization; Persistence; Risdiplam; Spinal muscular atrophy; United States.

Fig. 1

Sample selection of patients with SMA who received risdiplam. FDA, Food and Drug Administration; SMA: spinal muscular atrophy. ^aThe index date was defined as initiation of risdiplam. ^bPatients with SMA were classified into four SMA types using the algorithm presented in Tables S1 and S2

Fig. 2

Kaplan Meier analysis of treatment persistence to risdiplam.^{a, b} IQR, interquartile range; NA, not applicable; NR, not reached; SD, standard deviation; SMA, spinal muscular atrophy. ^aRisdiplam discontinuation was defined as no claim for risdiplam within 30 days after the previous days of supply was exhausted or switching to nusinersen and/or onasemnogene abeparvovec. ^bPersistence was defined as the time from the index date (i.e., initiation of risdiplam) to the date of risdiplam discontinuation or end of study period

Fig. 3

Total health care costs among patients with SMA who were adherent vs. not adherent to risdiplam.^{a, b}Note: The figure displays the minimum, first quartile, median, third quartile, and maximum. The thick black line represents the median cost. The length of the box represents the 25th and 75th percentiles for costs (i.e., the interquartile range). The minimum and maximum health care cost, excluding outliers, is shown at the end of the whisker and at the start of the whisker, respectively. PDC, proportion of days covered; SMA, spinal muscular atrophy; USD, United States dollar. ^aAdherence was defined as PDC ≥ 0.80. ^bOne outlier patient with excessive health care costs (>$4 million) was excluded from the analysis. This patient underwent multiple procedures that were unrelated to SMA within a relatively short timeframe

Fig. 4

Total health care costs among SMA patients by level of PDC.^{a, b} PDC, proportion of days covered; PPPY, per-patient per-year; SMA, spinal muscular atrophy; USD, United States dollar. ^aOne outlier patient with excessive health care costs (>$4 million) was excluded from the analysis. This patient underwent multiple procedures that were unrelated to SMA within a relatively short timeframe. ^bPDC level 0.80–0.90 means patients had a PDC level of ≥ 0.80 and < 0.90