Evidence of interferon beta-1a dose response in relapsing-remitting MS: the OWIMS Study. The Once Weekly Interferon for MS Study Group.

OBJECTIVE

To compare efficacy of interferon beta-1a, 22 microg or 44 microg weekly, with placebo in relapsing MS.

BACKGROUND

Uncertainty exists concerning the optimal dose regimen for interferon beta in relapsing-remitting MS. Many patients and physicians prefer the convenience and lesser side effects of an injection given once weekly (qw) as opposed to three times weekly. Pharmacokinetic data and information on biologic markers suggest that this frequency may be suboptimal.

METHODS

Randomized, double-blind study of interferon beta-1a 22 microg, 44 microg, or placebo administered by weekly subcutaneous injection for 48 weeks. Proton density (PD)/T2-weighted and T1-weighted-gadolinium MRI scans during 24 weeks of therapy were analyzed for the number of combined unique (CU) lesions (primary outcome). Biannual PD/T2 scans were analyzed for T2 activity and burden of disease (BOD).

RESULTS

CU lesions at 24 weeks had a median of 0.71/scan with placebo, 0.5/scan with 22 microg (not significant), and 0.33/scan with 44 microg (p = 0.002). T2 new lesion count/scan (mean/median) at 48 weeks was 3.2/1.5 for placebo, 2.4/1.0 for 22 microg (p = 0.03), and 1.5/1.0 for 44 microg (p = 0.0005). BOD at 48 weeks showed a median increase of 5.9% for placebo compared with a decrease of 1.4% in the 44 microg group (p = 0.0058) and 2% in the 22 microg group (p = 0.0018). No clinical variable, apart from steroid use in the 44 microg qw group (p = 0.014), showed significance.

CONCLUSIONS

These data confirm an MRI benefit of interferon beta-1a at low dose in MS, but highlight the limited clinical effect. Taken together with other studies, the data demonstrate a dose-effect relationship for both clinical and MRI variables.