Narrative Review of the Literature on Adherence to Disease-Modifying Therapies Among Patients with Multiple Sclerosis

While no curative treatment exists for multiple sclerosis (MS), several disease-modifying therapies (DMTs) have been developed to reduce relapse rates, slow disability progression, and modify the overall disease course. However, because of the chronic nature of the disease, long-term therapy adherence can be challenging for some patients with MS. Low adherence to DMTs has been shown to be associated with higher rates of disease relapses and progression as well as with an increase in medical resource utilization. As new MS treatments are developed, a comprehensive understanding of current adherence rates and the impact of adherence on clinical and economic outcomes is of particular interest. Our objective was to conduct a review of the published literature to evaluate rates of adherence to DMTs in MS and the impact of adherence on both clinical and economic outcomes from the patient and payer perspectives. Systematic literature searches were conducted using MEDLINE, EMBASE, and the Cochrane Central Register for Controlled Trials. Studies were limited to those completed on human subjects, written in the English language, and published between May 1, 2001, and May 1, 2011. Additional inclusion criteria required that studies involve a population of patients with MS, utilize the administration of DMTs, and report a measurement of adherence. Studies reporting persistence measures (e.g., treatment discontinuation rates) or rates of switching between DMTs (with no other measure of adherence reported) were excluded if they did not also assess adherence. Among the 24 studies meeting inclusion criteria, adherence to DMTs ranged from 41% to 88%. Weighted mean adherence rates were higher for intramuscular (IM) interferon beta-1a (IFNβ-1a) administered once a week (69.4%), and subcutaneous (SC) IFNβ-1b administered every other day (63.8%) than for SC IFNβ-1a administered 3 times a week (58.4%) and glatiramer acetate administered daily (56.8%). There was a numerically greater risk of MS relapse or disease progression among patients nonadherent to therapy versus adherent patients, with findings statistically significant in 2 of 4 studies. Additionally, 2 studies showed statistically significant reductions in inpatient or emergency room utilization and total MS-related medical costs among patients adherent to therapy compared with nonadherent patients. Higher patient out-of-pocket copayments and coinsurance were significantly associated with lower adherence to DMTs, while the use of interventional or disease therapy management programs were associated with improved adherence. Lack of medication adherence remains a problem among patients with MS. Improvements in adherence have the potential to improve patient and payer burden in terms of improved clinical outcomes and lower nonpharmacy medical resource utilization.