Side effect profile of interferon beta-1b in MS: results of an open label trial.

To determine which patients are prone to side effects from interferon beta-1b and which side effects are most troublesome, we studied 72 patients with clinically definite MS who were started on interferon beta-1b after its release and found that the side effects significantly associated with treatment included skin reactions, flu-like symptoms, fatigue, leukopenia, new or worsened depression, and new or worsened headache. Of these, only fatigue and depression were significantly associated with discontinuance of therapy. Moreover, the course of disease before initiation of treatment also had a significant impact on the likelihood of discontinuing medication. Thus, despite an apparently similar therapeutic benefit (as judged by the similarly reduced attack rate in each group), patients with a secondary chronic progressive course were more likely to discontinue treatment (63%) than patients with either a relapsing/progressive course (18%) or a remitting/relapsing course (7%). Indeed, in the final regression equation, the only factors significantly related (r = 0.875) to the discontinuance of therapy were fatigue (p < 0.0001), a fatigue-depression interaction (p < 0.0001), and a chronic progressive course of disease (p<0.0001). Thus, if future clinical trials are to provide useful information on the value of interferon beta-1b in progressive MS, the side effects of fatigue and depression will need to be ameliorated to limit the drop-out rate from such trials.