0632 Design Elements for a Switch Study from High- to Low-Sodium Oxybate Evaluating Blood Pressure in Narcolepsy (XYLO)

Abstract Introduction High sodium intake can increase blood pressure (BP) and future cardiovascular risk. Individuals with narcolepsy have an elevated cardiovascular comorbidity burden before considering medication-specific risks. Low-sodium oxybate (LXB; Xywav®) is approved by the US Food and Drug Administration (FDA) to treat excessive daytime sleepiness or cataplexy in patients ≥7 years of age with narcolepsy and idiopathic hypersomnia in adults. LXB has the same active moiety as high-sodium oxybates (sodium oxybate [SXB, Xyrem®] and fixed-dose SXB [Lumryz™]) but contains 92% less sodium. The objective of XYLO is to measure ambulatory and in-clinic systolic BP (SBP) changes after switching to LXB from a high-sodium oxybate in participants with narcolepsy (NCT05869773). Methods This 6-week, open-label, multicenter, switch study is enrolling participants 18–70 years of age with narcolepsy (type 1 or 2) taking 6–9 g/night of high-sodium oxybate for ≥6 weeks. Hybrid enrollment supports both on-site and decentralized (monitored at the participant’s home by mobile health professionals) participation, and may broaden the pool of eligible participants. After ≥2 weeks on stable high-sodium oxybate dose/regimens (screening period), participants switch to the same dose/regimen of LXB for 6 weeks (intervention period). The primary endpoint is the change in 24-hour SBP from baseline (the most recent screening measurement prior to switching) to the end-of-treatment visit (approximately 6 weeks after switching) measured via 24-hour ambulatory BP monitoring (ABPM). Secondary endpoints evaluate change from baseline to end-of-treatment visit in-clinic SBP, as well as daytime average SBP and nighttime average SBP measured via 24-hour ABPM. Results Recruitment began in June 2023. This study uses a group sequential design with an adaptive sample size target of 57–77 participants completing the 6-week intervention period. This design provides 90% power to detect a mean difference of 3.5 mmHg (a clinically relevant change) in 24-hour SBP (assuming a standard deviation of the differences in 24-hour SBP of 8 mmHg). Conclusion XYLO will enable the assessment of 24-hour BP changes following transition from a high-sodium oxybate to LXB. Planned hybrid enrollment with a decentralized option may increase study access leading to a more diverse clinical trial population. Support (if any) Jazz Pharmaceuticals