Observations during an elective interruption of natalizumab treatment: a post-marketing study.

In this prospective post-marketing study, 21 patients with multiple sclerosis treated with natalizumab for 24 consecutive months elected a trial of treatment interruption (90-180 days). During a mean duration of treatment interruption of 111.5 days 4 patients (19.0%) experienced a relapse and 9 out of 19 (47.4%) had MRI activity. Number of contrast-enhancing lesions at baseline was lower than during treatment interruption, but the difference was not significant. These findings suggest that disease activity may return after the last infusion of natalizumab. Patients should have regular MRI assessment during treatment interruption to rapidly identify any return of disease activity. The aim of this study was to determine the optimal duration for temporary interruption of natalizumab therapy in patients who have received continuous therapy with natalizumab for 24 months.