0579 Long-Term Safety of Once-Nightly Oxybate for Narcolepsy: RESTORE Study Interim Analysis of Data

Introduction The pivotal phase 3 REST-ON trial (NCT02720744) evaluated the efficacy and safety of once-nightly sodium oxybate (ON-SXB; FT218), an investigational extended-release formulation for treatment of adults with narcolepsy. In REST-ON, ON-SXB met its 3 coprimary endpoints: improvement in mean sleep latency on the Maintenance of Wakefulness test, Clinical Global Impression-Improvement rating (% much/very much improved), and number of weekly cataplexy attacks at all doses tested (P< 0.001 vs placebo). The safety profile of ON-SXB was consistent with that of immediate-release (IR) SXB. The ongoing RESTORE trial (NCT04451668) is an open-label/switch study evaluating the safety and tolerability of ON-SXB. Methods Participants aged ≥16 years with narcolepsy type 1 or 2 who completed the REST-ON trial, were on stable-dose (≥1 month) IR oxybate, or were oxybate-naive are eligible for RESTORE. Initial doses were 4.5 g/night or equivalent/closest to the previous total IR oxybate dose/night for those switching; incremental adjustments (1.5 g/week; maximum dose, 9 g/night) were allowed. Safety data for participants receiving ≥1 dose of ON-SXB as of 01 July 2022 are reported here. Results This analysis includes interim data from 180 participants (REST-ON participants, n=15 [8.3%]; oxybate-naive, n=35 [19.4%]; switch, n=130 [72.2%]). Most participants are white (n=150 [83.3%]) and female (n=122 [67.8%]); mean age is 35 years [range, 16–84]). Most participants who reported an adverse event (AE; n=105 [58.3%]) had AEs that were mild (61.9%) or moderate (32.3%) in severity. Three participants had serious AEs (abscess, deep vein thrombosis, rib fracture and pneumothorax); all were deemed unrelated to ON-SXB and all 3 participants continued in the study. Adverse drug reactions (ADRs; ie, AEs related/possibly related to study drug) were reported by 76 (42.2%) participants with 6 (3.3%) participants discontinuing ON-SXB owing to ADRs. ADRs occurring in ≥3% of participants were nausea (11.7%), somnolence (6.7%), headache (5%), enuresis (5%), somnambulism (3.9%), dizziness (3.9%), tremor (3.9%), and vomiting (3.3%). Conclusion Interim data from the RESTORE study indicate that ON-SXB is generally well tolerated with a low rate of discontinuation owing to ADRs. If granted final FDA approval, ON-SXB will offer adults with narcolepsy a once-at-bedtime oxybate treatment option. Support (if any) Avadel Pharmaceuticals