Cost Sharing of Disease-Modifying Treatments (DMTs) as Policy Lever to Improve DMTs' Access in Multiple Sclerosis.

Objectives: To understand the nonlinear relationship between out-of-pocket (OOP) payments and disease-modifying treatment (DMT) use and adherence, primarily to pinpoint the threshold at which the use of DMTs becomes price sensitive.

Methods: Individuals with more than two multiple sclerosis (MS) diagnoses (International Classification of Diseases, Ninth Revision code 340) were identified from the MarketScan database (2006-2009). Heterogeneity in treatment was normalized by calculating an annual OOP payment as the average OOP payment for purchasing a fixed basket of DMTs at the insurance plan level. A local linear regression with a model-based recursive partitioning algorithm was applied to explore the relationship between OOP and consequently lower DMT use and adherence as measured by days covered by DMT.

Results: We identified the inflection points in annual OOP payments as $442 for DMT use and $890 for DMT adherence. For patients with annual OOP payments of more than $442, a $100-increase in OOP payment was associated with a decline of 0.6% in DMT use; for annual OOP payments of more than $890, a $100-increase in OOP payment was associated with two fewer days of DMT treatments.

Conclusions: Although the use of DMTs and DMT adherence appeared unassociated with OOP payment below $442 and $890, respectively, an excessive OOP payment was a barrier to DMT access. This information can inform maximum monthly and yearly payment caps when designing valued-based insurance plans.