Increased relapse activity for multiple sclerosis natalizumab users who become nonpersistent: a retrospective study.

BACKGROUND Natalizumab disease-modifying therapy for relapsing-remitting multiple sclerosis (MS) is efficacious in randomized controlled trials. Few studies have estimated the association between real-world natalizumab persistence behavior and relapse-related outcomes. OBJECTIVES To (a) examine the impact of using natalizumab consistently (i.e., persistent) on relapse-related outcomes as compared with transitioning to inconsistent natalizumab use (i.e., nonpersistent) and (b) examine the impact of other treatment patterns on relapse-related outcomes for those who initiated natalizumab. METHODS Using the IMS PharMetrics Plus claims database (years 2006-2012), we identified MS subjects who initiated natalizumab (no natalizumab claims in year prior) and had at least 2 years of follow-up. Persistence in annual follow-up periods was defined as no 90-day or greater gap in natalizumab therapy. Relapse was an MS-related hospitalization or outpatient visit with intravenous or oral steroid burst claim within 7 days. Analyses compared observations based on changes in natalizumab persistence and natalizumab nonpersistence status from 1 year to the next (e.g., transitioning from persistent to nonpersistent), estimating differences in mean annual relapses and mean annual relapse-related costs. RESULTS A total of 2,407 natalizumab initiators had at least 2 years of follow-up, yielding 4,770 year-to-year natalizumab treatment patterns where each subject contributed 1, 2, or 3 year-to-year treatment patterns. In the year prior, 3,187 treatment patterns were persistent; 731 (22.9%) of these transitioned to nonpersistence. The remaining 1,583 treatment patterns were nonpersistent in the year prior; 132 (8.3%) of these transitioned to persistence. Persistent to nonpersistent treatment patterns were associated with a mean relapse-rate increase of 0.23 (95% CI = 0.12, 0.35), and a mean increase in relapse-related costs of $1,346 (95% CI = $97, $2,595). Nonpersistent to persistent treatment patterns were associated with a mean relapse-rate decrease of -0.15 (95% CI = -0.32, 0.017) and a mean decrease in relapse-related costs of -$1,369 (95% CI = -$2,761, $23). CONCLUSIONS Findings suggest that real-world persistent natalizumab users who become nonpersistent have statistically significant increases in annual relapses and relapse-related costs. Those who transition from nonpersistent to persistent have nonsignificant reductions in relapses and their associated costs.