Interferon-beta therapy did not slow the long-term progression of disability in adults with relapsing-remitting multiple sclerosis in a retrospective cohort study based on prospectively collected data.

Patients who took interferon-beta (IFN-beta) experienced rates of disease progression that were similar to a group of contemporaneous peers who did not take IFN-beta and a historical cohort of MS patients studied before IFN-beta therapy became available, Dr. Afsaneh Shirani of the Brain Research Centre at Vancouver (B.C.) Coastal Health Research Institute and her associates reported July 18 in JAMA.

These findings are consistent with those of the longer-term clinical trials that have examined IFN-beta’s efficacy in MS. They call into question the routine use of the drug to prevent or delay disability, the researchers noted.

Previous postmarketing studies have suggested that IFN-beta is beneficial in slowing the progression of MS, but many of those studies had methodologic flaws. For their study, Dr. Shirani and her colleagues used information from a province-wide database that is thought to cover 80% of the MS patients in British Columbia.

The investigators compared outcomes in 868 patients who took IFN-beta in 1995-2004 with 829 contemporaneous control patients who were eligible to take the drug during the same period but chose not to. They also assessed outcomes in a historical control group of 959 unexposed patients who were studied in 1985-1995 before IFN-beta was approved for use in Canada.

At baseline, the study subjects in all three groups had median scores of 2.0 on the 10-point Expanded Disability Status Scale (EDSS), in which higher scores indicate more-severe disability.

Most (76%) of the study subjects were women, and the mean age at onset of MS was 32 years. Median length of follow-up was 5 years for the group receiving IFN-beta, 4 years for their contemporaries who did not receive IFN-beta, and 11 years for the historical controls.

There was no evidence of an association between IFN-beta therapy and MS progression. A total of 94 patients in the treated group (11%), 44 (5%) in the contemporaneous control group, and 222 (23%) in the historical control group reached the main outcome of a sustained, irreversible EDSS score of 6. That score indicates “intermittent or unilateral constant assistance (cane, crutch, or brace) required to walk about 100 meters, with or without resting,” according to the investigators, who said that the differences between the groups were not significant (JAMA 2012;308:247-56).

These results did not change appreciably when the data were adjusted to account for differences among the study groups in comorbidity and socioeconomic status, nor did they change in any of several sensitivity analyses.

The results were also similar for a secondary outcome measure, the attainment of an EDSS score of 4 (indicating “fully ambulatory without aid, up and about 12 hours a day despite relatively severe disability; able to walk without aid for 500 meters”). A total of 156 (18%) patients in the treated group, 68 (8%) in the contemporaneous control group, and 268 (28%) in the historical control group reached this end point. These differences also were not statistically significant.

The study is limited by the fact that factors other than IFN-beta treatment may have changed over time, which could bias the comparison with the historical control group. In addition, the decision to forgo IFN-beta therapy may have been related to several factors that could not be accounted for in this observational study, which could bias the comparison with the contemporaneous control group. For example, patients may have decided against IFN-beta therapy because they were in a stable phase of disease, had a needle phobia, were unable or unwilling to adhere to a noncurative treatment, wanted to become pregnant, or had personal or religious objections to using a drug that contains human albumin, Dr. Shirani and her associates said.

It is possible that a subgroup of relapsing-remitting MS patients may benefit from IFN-beta. “Further work is needed to identify these potential patients; perhaps through pharmacogenomic or biomarker studies, paving the way for a tailored, personalized medicine approach,” they added.

This study was supported by the Canadian Institutes of Health Research, the National Multiple Sclerosis Society, the Multiple Sclerosis Society of Canada, the Michael Smith Foundation for Health Research, the Christopher Foundation, the University of British Columbia, the Medical Services Commission of British Columbia, the Natural Sciences and Engineering Research Council of Canada, and the United Kingdom Multiple Sclerosis Trust. Dr. Shirani’s associates reported numerous ties to industry sources.