Interferon-beta-1a: A Review of its Pharmacological Properties and Therapeutic Potential in Multiple Sclerosis.

The presumed but as yet unspecified autoimmune-mediated basis for the pathogenesis of multiple sclerosis has led to attempts to modify the immune system of patients with this disease based on general and selective approaches. The rationale for using interferon-beta for the treatment of multiple sclerosis is based on its antiviral and complex immunoregulatory activities. Interferon-beta-1a (Avonex(R)) is a recombinant molecule which is indistinguishable from natural interferon-beta derived from human fibroblasts. Its precise mechanism of action is unknown, although effects on immune system processes which have been implicated in the pathogenesis of multiple sclerosis have been documented. T cell activation and migration into the CNS is a primary process in the pathogenesis of multiple sclerosis. In vitro and in vivo, interferon-beta-1a, compared with placebo or no treatment, significantly reduced expression of T cell surface activation markers, and significantly increased CNS levels of interleukin-10 - a potent inhibitor of cell-mediated immune responses. Pharmacokinetic studies indicate that intramuscular injection is the optimal route of administration for this formulation of interferon-beta-1a. In patients with relapsing-remitting multiple sclerosis who participated in a randomised double-blind trial, interferon-beta-1a 30mug (6 MIU) administered by intramuscular injection once weekly for 2 years (n = 158), compared with placebo (n = 143), significantly extended the time to onset of sustained neurological disability. Interferon-beta-1a also reduced the rate of disease relapse by approximately one-third compared with placebo, a finding which was supported by cranial magnetic resonance imaging (MRI) data showing significant reductions in lesion number and volume. Interferon-beta-1a was well tolerated, with influenza-like symptoms making up the majority of adverse reactions. The clinical significance of the beneficial effect of interferon-beta-1a on disease progression has been endorsed by the findings of a retrospective statistical analysis of the disability outcomes data obtained in the double-blind trial. In patients with relapsing multiple sclerosis, interferon-beta-1a is the only drug that has been demonstrated to significantly slow disease progression without excessive toxicity, in addition to significantly reducing the rate of relapse - measured clinically and by MRI. Notwithstanding the absence of long term tolerability data, and data from comparative trials with other agents, interferon-beta-1a represents a promising advance in drug therapy for relapsing multiple sclerosis.