Differential glatiramer acetate treatment persistence in treatment-naive patients compared to patients previously treated with interferon

BACKGROUND: In the treatment of multiple sclerosis, a change of therapy is considered after treatment failure or adverse events. Although disease modifying drugs’ (DMD) efficacy and side effects have been fully analysed in clinical trials, the effects of previous therapy use are less well studied. We aimed to study medication persistence with glatiramer acetate in treatment-naive patients and in patients previously treated with interferon. METHODS: A retrospective study of relapsing-remitting multiple sclerosis patients treated with glatiramer acetate in an MS Unit of a Spanish University Hospital (January 2004 – September 2013). Treatment time on glatiramer acetate was studied. Reasons for treatment discontinuation were considered as follows: lack of efficacy, serious adverse event, injection-related side effect, pregnancy and lost to follow-up. Use of prior DMD was registered and analysed. Homogeneity of groups was analysed using Fisher's and Mann-Whitney’s tests. The Kaplan Meier method and Cox regression model were used to estimate time to and risk of treatment discontinuation. RESULTS: In total, 155 relapsing-remitting multiple sclerosis patients were treated with glatiramer acetate: 100 treatment-naive patients and 55 treated previously with interferon. At the end of the study, 76 patients (49.0 %) continued on glatiramer acetate (with an average treatment time (ATT) of 50.4 months, s.d.32.8) and 50 patients (32.3 %) had switched therapy: 27 patients (17.4 %) for inefficacy (ATT 29.2 months, s.d.17.5), 20 patients (12.9 %) for injection site reactions (ATT 16.5 months, s.d.20.3) and 3 patients (1.9 %) after serious adverse events (ATT 15.7 months, s.d.15.1). ATT in our cohort was 39 months (s.d.30.0), median follow-up 34 months. Six months after glatiramer acetate initiation, probability of persisting on GA was 91.4 %, 82.5 % after 12 months and 72.5 % after 2 years. The risk of glatiramer acetate treatment discontinuation was 2.8 [1.7 – 4.8] times greater for treatment-naive patients than for patients treated previously with interferon and this was hardly modified after adjusting for sex and age. CONCLUSIONS: Glatiramer acetate was safe and useful with low rates of serious adverse events and low rates of break-through disease. Injection intolerance proved a major limitation to glatiramer acetate use. Patients who had been previously treated with interferons presented a lower probability of glatiramer acetate discontinuation than treatment-naive patients.