Long-term efficacy and safety of low-sodium oxybate in an open-label extension period of a placebo-controlled, double-blind, randomized withdrawal study in adults with idiopathic hypersomnia

Study Objectives: To evaluate 6-month efficacy and safety of low-sodium oxybate in people with idiopathic hypersomnia during an open-label extension period (OLE) of a phase 3 clinical trial. Methods: Efficacy measures included the Epworth Sleepiness Scale (ESS), Idiopathic Hypersomnia Severity Scale (IHSS), Patient Global Impression of Change (PGIc), Functional Outcomes of Sleep Questionnaire, short version (FOSQ-10), and Work Productivity and Activity Impairment Questionnaire: Specific Health Problem (WPAI:SHP). Treatment-emergent adverse events were collected throughout the OLE.Results: The OLE population included 106 participants. Most were female (71%) and White (83%), and the mean (SD) age was 41.0 (13.8) years. ESS scores decreased (improved) during the OLE (mean [SD], study baseline: 16.3 [2.8]; OLE week 2: 6.7 [4.7]; OLE end: 5.3 [3.7]), and IHSS total scores trended toward a decrease (study baseline: 32.6 [7.3]; OLE week 2: 16.2 [8.9]; OLE end: 14.8 [8.6]. Median (minimum, maximum) paired differences from OLE week 2 to OLE end were ESS,-1.0 (-20, 7; nominal P = .012); IHSS,-1.0 (-31, 19; nominal P = .086). The proportion of participants reporting PGIc ratings of "very much improved" increased from 36.7% at OLE week 2 to 53.8% at the OLE end. The FOSQ-10 and WPAI:SHP scores remained stable during OLE. The incidence of newly reported treatment-emergent adverse events decreased over the duration of the OLE.Conclusions: Efficacy and safety of low-sodium oxybate were maintained or improved during the 6-month OLE, supporting long-term treatment with low-sodium oxybate in adults with idiopathic hypersomnia.