This is a Phase 2b, multicenter, open-label extension, one-year, safety, tolerability, and efficacy study in adults who previously completed an applicable double-blind SPN-817 clinical study. This study will include a double-blind Dose Titration/Bridging Period of 8-10 weeks in which SPN-817 will be titrated to the participant's maximum tolerated dose based on response. Following the Dose Titration/Bridging Period, participants will enter an Open Label Extension (OLE) Period of 42-44 weeks. When participants finish the OLE Period, they will initiate a Tapering Period (up to 4 weeks) followed by an End-of-Tapering Period video contact (VC) after the last dose of study drug. The duration of study treatment before starting the 4-week Tapering Period will be one year (52 weeks).
