How does formulary restrictions impact health outcomes for patients with multiple sclerosis (MS)? To answer this question, Blaylock, Van Nuys and Joyce (2025) use data 100% Medicare claims data from 2018-2022 covering patients with both prescription drug plans (PDPs) and Medicare Advantage Prescription Drug plans (MA-PDs). Individuals were categorized as above vs. below average formulary breadth depending on how many disease modifying therapies (DMTs) were covered. Outcomes of interest include the rate of MS relapse.
Using this approach, the authors found that:
Oral or injectable MS DMTs were frequently excluded from coverage (>50% excluded in 2022: PDPs, 11 of 15 DMTs; MA-PD, 9 of 15 DMTs). The MS relapse rate was greater for low- vs high-coverage PDPs (10.6% vs 9.5%; odds ratio [OR], 0.88 [95% CI, 0.84-0.92]) and MA-PDs (7.8% vs 6.9; OR, 0.88 [95% CI, 0.85-0.91]). In multivariable analyses, broader formulary coverage during baseline was associated with less MS relapse during follow-up (PDP: adjusted OR, 0.93 [95% CI, 0.90-0.96] for drugs and 0.94 [95% CI, 0.91-0.97] for classes; MA-PD: adjusted OR, 0.88 [95% CI, 0.83-0.94] for drugs and 0.92 [95% CI, 0.86-0.98] for classes).
You can read the full paper here.
