Natalizumab (Tysabri) Re-Initiation of Dosing

Study 101-MS-322 (NCT00306592) was conducted to evaluate the safety of natalizumab monotherapy following re-exposure to natalizumab in former clinical trial participants in Studies C-1801 (NCT00027300), C-1802 (NCT00030966), and C-1803 (NCT00097760) and included subjects in North America. In parallel with the conduct of that study, this study (101-MS-321 \[NCT00297232\]) was initiated for participants in Europe and the rest of the world. In addition, after 48 weeks, participants from 101-MS-322 (NCT00306592) could enter study 101-MS-321 (NCT 00297232), which was considered the Long-Term Treatment Period of 101-MS-322 (NCT00306592). The primary purpose and primary outcome for both studies are identical; therefore, the combined long-term data from both studies are presented. (Combined Week 48 data from both studies are presented in the 101-MS-322 \[NCT00306592\] record.)