Persistence and adherence to interferon and glatiramer acetate in patients with multiple sclerosis.

Objectives: To analyse persistence and adherence in patients with multiple sclerosis receiving first-line treatment with subcutaneous glatiramer acetate 20 mg (GA), subcutaneous interferon β1a (IFNβ1a-sc), intramuscular interferon β1a (IFNβ1a-im) and subcutaneous interferon β1b (IFNβ1b-sc) and to identify associated factors and reasons for discontinuation.

Methods: An observational retrospective study was performed between January 1999 and November 2014. Persistence was defined as the time from treatment initiation until discontinuation, and adherence as the number of units dispensed since treatment initiation until its interruption divided by the theoretical number of units needed to cover said period as a percentage. A patient was considered adherent if ≥95%. Persistence was measured using the Kaplan-Meier method and univariate Cox regression; adherence was measured using a univariate binary logistical regression model.

Results: The study included 224 patients. The median persistence was 1349 days (95% CI 1017.4 to 1680.6). Patients receiving IFNβ1a-im continued treatment for a longer time (1720 days; 95% CI 1196.8 to 2243.2), while patients treated with IFNβ1a-sc had the lowest persistence (771 days; 95% CI 377.4 to 1164.6) (HR=1.7; 95% CI 1.02 to 2.72). Patients with Expanded Disability Status Scale (EDSS) 1.5-6 discontinued treatment earlier than those with EDSS 0-1 (HR 1.5; 95% CI 1.01 to 2.25); 94.4% of patients discontinued treatment due to medical decision, primarily due to lack of efficacy (24.6%) and adverse effects (17.4%), while 80.8% of patients had good adherence. GA had the highest adherence, with no major difference from IFNβ1a-im, while IFNβ1b-sc showed the highest non-adherence (OR 3.5; 95% CI 1.29 to 9.28).

Conclusions: The persistence levels obtained were lower than in similar studies. EDSS was identified as an independent predictor of treatment interruption. Acceptable adherence was achieved among the population, comparable to other studies and influenced by the drug.