Glatiramer acetate and interferon beta-1a for intramuscular administration: a study of outcomes among multiple sclerosis intent-to-treat and persistent-use cohorts.

OBJECTIVE: To study outcomes of multiple sclerosis (MS) patients treated with either glatiramer acetate (Copaxone) or interferon beta-1a for once-weekly, intramuscular administration (Avonex).

METHODS: An 'intent-to-treat' (ITT) cohort (n=1282) was established, consisting of patients diagnosed with MS who began therapy on either glatiramer acetate (GA) or intramuscular interferon beta-1a (IFN beta-1a-IM) and had continuous insurance coverage from 6 months before to 24 months after the date when they began taking the medication. A 'persistent use' (PU) cohort (n=639) was also constructed, consisting of individuals who, in addition to the criteria listed above, had a claim for GA or IFN beta-1a-IM within 28 days of the end of the 2-year post-period. Data were obtained from the i3 InVision Data Mart Database from July 2001 to June 2006. Multivariate regressions were used to examine both the 2-year total direct medical costs and the likelihood of relapse associated with the use of each of these alternative MS medications. A relapse was defined as either being hospitalized with a principal diagnosis of MS or having an outpatient visit with a MS diagnosis followed within 7 days by a claim for a corticosteroid. All regressions controlled a wide range of factors that may potentially affect outcomes.

RESULTS: In the ITT cohort, patients who started therapy on GA had a significantly lower 2-year risk of relapse (10.01 vs. 5.18%; p=0.0034) as well as significantly lower 2-year total medical costs ($44,201 vs. $41,121; p=0.0294). In the PU cohort, patients who used GA also had a significantly lower 2-year risk of relapse (7.25 vs. 2.16%; p=0.0048) as well as significantly lower total medical costs ($67,744 vs. 63,714; p=0.0445).

LIMITATIONS: The analyses relies on an administrative claims database of an insured population and hence, may not be generalizeable to other populations. In addition, such a database precludes measurement of lost work time, unemployment, caregiver burden or other costs associated with MS.

CONCLUSIONS: Results from this study indicate that the use of GA is associated with significantly lower probability of relapse as well as significantly lower 2-year total direct medical costs than IFN beta-1a-IM.