Background Several firstline disease modifying therapies (DMTs) have shown significant benefit in preventing relapses and slowing disease progression among multiple sclerosis (MS) patients. Lower adherence may be associated with lower efficacy and thus with a higher risk of relapse. Adherence to DMTs was also associated with a lower likelihood of hospitalisation and relapse, and lower medical costs.

Purpose The objective of this study was to analyse adherence to parenteral firstline treatments in MS patients and related factors.

Material and methods This was an observational, retrospective, longitudinal study. All MS adult patients starting firstline treatment with intramuscular(IM) interferon(IFN)-beta-1-a, subcutaneous(SC) IFN-beta 1-a, SC IFN-beta 1-b and glatiramer acetate from 1 September 2005 to 31 August 2015 were included. Data were collected from the pharmacy department electronic records. DMT adherence was measured using the medication possession ratio (MPR) calculated as the number of days of any DMT medication over the study period (MPR had a maximum value of 100%). Patients with MPR ≥90% were classified as adherent. Patient characteristics compared between adherent and non-adherent patients included demographics (age, gender), treatment and route of administration. Categorical variables were compared using the χ² or Fisher’s exact tests; continuous variables were compared using the non-parametric Wilcoxon rank sum test. One way analysis of variance (ANOVA) was performed to explore treatment influence. A logistic regression model was used to estimate the risk adjusted rate of non-adherence. A p value ≤0.05 was considered to indicate a statistically significant difference.

Results 176 patients were included, 67.6% women and 32.4% men. Mean age (±SD) was 36.27±11 years. Treatment distribution: 36.4% SC IFN-beta 1-a, 10.2% SC IFN-beta 1-b, 39.2% IM IFN-beta-1-a, 14.2% glatiramer acetate. 84.1% of patients were adherent. Mean (±SD) adherence was 93.6%±16.5%. In univariate analysis no difference was observed regarding gender (OR 1.2, 95% CI 0.5–2.8; p=0.85) and route of administration (OR 0.7, 95% CI 0.3–1.6; p=0.533). Adherent patients were older (mean age difference=2.2 years, 95% CI 9.4–0.6; p=0.04). No difference was observed between treatments in ANOVA analysis (p=0.52). In multivariate analysis, age was the only associated variable (OR 1.05, 95% CI 1.01–1.10; p=0.02).

Conclusion Firstline adherence was high among MS treated patients although nearly one sixth of patients were non-adherent. Younger patients were more likely to be non-adherent.

No conflict of interest