Long-term interferon-β treatment for multiple sclerosis

Abstract.

The aim of our study was to analyze the dropout rate in patients with relapsing-remitting multiple sclerosis (RRMS) under long-term treatment with the three commercially available interferon beta (IFNβ) preparations. According to the drug taken, we divided 122 RRMS patients into 4 groups: Betaferon group, 56 patients taking INFβ-1b (24 MIU weekly, subcutaneous injections); Avonex group, 38 patients taking IFNβ-1a (6 MIU weekly, intramuscularly); Rebif group, 18 patients taking INFβ-1b (18 MIU subcutaneously). Ten patients who shifted from Betaferon to Avonex were included in a fourth group. Dropouts were registered every trimester with the related cause. Data were evaluated using Kaplan-Meier survival analysis and log-rank test. During the observation period of five years, 48 patients (39.9%) dropped out: 48% of the patients in Betaferon group withdrew at a median of 758 days, 26% of the Avonex group at 356 days; 38% of the Rebif group at 421 days, and 40% of those who shifted from Betaferon to Avonex at 259 days. The differences between groups were not significant on survival analysis. Patients receiving higher dose treatment (Betaferon and Rebif groups) dropped out mainly for clinical adverse events; conversely, patients receiving lower dose therapy (Avonex group) dropped out most often for inefficacy. Patients who shifted to a lower dose treatment (fourth group) had a dropout rate similar to that of the initial treatment. Our data showed that one-third of the patients stopped the therapy, mostly for adverse events and then for inefficacy, while the remaining two-thirds were still on treatment without problems up to 5 years of follow-up. Compliance seems related to the dose of the drug, but further analysis is needed to confirm our data.