Long-term safety and effectiveness of natalizumab redosing and treatment in the STRATA MS Study.

Objectives: Report long-term safety and effectiveness of natalizumab over 240 weeks in the prospective, observational, open-label Safety of TYSABRI Re-dosing and Treatment (STRATA) Study.

Methods: Patients (N = 1,094) previously enrolled in natalizumab multiple sclerosis clinical trials received natalizumab 300 mg IV every 4 weeks, up to 240 weeks. Serious adverse events, Expanded Disability Status Scale (EDSS) scores, and annualized relapse rates were analyzed.

Results: At data cutoff (February 9, 2012), natalizumab exposure was 3,460 patient-years; a median of 56 (range 1-70) infusions were received. Serious adverse events, including progressive multifocal leukoencephalopathy, were consistent with natalizumab's known profile. Upon natalizumab re-exposure, rates of anti-natalizumab antibodies and hypersensitivity reactions were 3% and 5% overall, and 40% and 24% among patients with 1 to 2 prior natalizumab doses. Patients originally randomized to placebo/another disease-modifying therapy vs natalizumab in previous studies had significantly higher EDSS scores at STRATA baseline; this difference persisted over 240 weeks. EDSS scores generally remained stable. Patients initially randomized to natalizumab had lower annualized relapse rates over 240 weeks.

Conclusions: Serious adverse events were consistent with natalizumab's known safety profile; short exposure with a gap before redosing was associated with higher incidences of anti-natalizumab antibodies and hypersensitivity reactions. Stability of EDSS scores and consistently low relapse rates over 5 years of natalizumab treatment are consistent with its known efficacy profile.

Classification Of Evidence: This study provides Class III evidence that in patients with relapsing-remitting multiple sclerosis, natalizumab stabilizes EDSS scores, decreases relapse rates, and is associated with an increased risk of progressive multifocal leukoencephalopathy.