Long-term persistence with the immunomodulatory drugs for multiple sclerosis: a retrospective database study.

BACKGROUND

Immunomodulatory drugs (IMDs) for multiple sclerosis (MS) have been available in Canada since 1995 and are currently the most commonly prescribed treatment for MS. However, relatively little is known about the long-term persistence to these drugs.

OBJECTIVE

The purpose of this study was to describe patterns of, and factors associated with, long-term persistence to the first-line IMDs in an MS population in British Columbia, Canada.

METHODS

Study data were collected from the British Columbia MS database. Adults from British Columbia with definite MS who were prescribed a first-line IMD (interferon beta-1b, interferon beta-1a [subcutaneous and intramuscular], and glatiramer acetate) from January 1, 1995, through December 31, 2008, were eligible for the study. Time to discontinuation of use of all first-line IMDs (ie, switching among IMD therapies was allowed) and the initially prescribed IMD was assessed using Kaplan-Meier survival analysis and multivariate Cox regression.

RESULTS

A total of 1896 patients were included. Mean (SD) age was 40.2 (9.5) years, and 75.1% were female. Median time to discontinuation of all first-line IMD therapies was 6.3 years (95% CI, 5.8-6.7 years). Patients with a longer disease duration and higher level of disability were at higher risk for discontinuing use of the IMDs. Age, sex, and the initial IMD were not associated with discontinuation. Persistence appeared to have decreased over time (P = 0.01 for trend). Median time to discontinued use of, or switching from, the initially prescribed IMD was 2.9 years (95% CI, 2.5-3.2 years).

CONCLUSIONS

Approximately half of the MS patients discontinued use of their IMD within 6 years. It is unknown whether this persistence is adequate because uncertainties remain regarding the optimal level of persistence to the IMDs. Further investigation is needed to examine why some individuals are more at risk for discontinuation of IMD therapy and why, in contrast to other chronic diseases, persistence to IMDs in patients with MS has not improved over time.