Participants who complete study SD-809-C-18 (NCT02195700), SD-809-C-23 (NCT02291861), or any other SD-809 study will be enrolled in this study. This study include a screening period (Part A), a titration period (Part A), a long-term treatment period (Part A), a double-blind, randomized withdrawal period (Part B), treatment after completion of the randomized withdrawal period (Part B), and a post-treatment safety follow-up period (Part A and Part B). EU participants who complete Part B will be invited to participate in Part C.