Disease-Modifying Therapies and Adherence in Multiple Sclerosis: Comparing Patient Self-Report with Pharmacy Records

BACKGROUND: Self-report and pharmacy records are often used to measure adherence rates to disease-modifying therapies (DMTs) in multiple sclerosis (MS), but little is known about how the sources compare. OBJECTIVE: Compare self-report and pharmacy records for assessing DMT use and adherence rates. METHODS: Demographic information, self-reported DMT use, and missed DMT doses in the previous 30 days were obtained from consecutive MS patients attending an MS clinic and linked to pharmacy records. A medication possession ratio (MPR) was calculated using pharmacy records for the year before and after the visit; MPR <80% defined nonadherence. Agreement between self-report and pharmacy records was assessed using Cohen's kappa (κ). RESULTS: Of 326 participants, 135 reported using an injectable DMT. There was near-perfect and perfect agreement between self-report and pharmacy records for DMT use (κ = 0.95; 95% CI 0.91-0.98) and DMT agent (κ = 1.00). Nonadherence was estimated at 13% (17/128) from the 30-days self-report compared to 30% (34/113) and 43% (53/123) in the year pre- and post-clinic visit from pharmacy records, indicating moderate to fair agreement (year prior: κ = 0.41; 95% CI 0.22-0.59; year post: κ = 0.22; 95% CI 0.09-0.36). CONCLUSIONS: Patients self-reports closely reflected pharmacy records when assessing DMT use and product. Moderate to fair agreement was found when comparing adherence rates between sources.