Effectiveness and optimization of low-sodium oxybate in participants with narcolepsy switching from a high-sodium oxybate: data from the Substitution of Equal Grams of Uninterrupted Xyrem to Xywav study.

Study objectives: Low-sodium oxybate (LXB; calcium, magnesium, potassium, and sodium oxybates; Xywav) contains the same active moiety as high-sodium oxybates (SXBs; SXB [Xyrem] and fixed-dose SXB [Lumryz]), with 92% less sodium, and is approved in the United States for treatment of cataplexy or excessive daytime sleepiness in patients 7 years of age and older with narcolepsy, and idiopathic hypersomnia in adults. Patients with narcolepsy have increased cardiovascular risk relative to people without narcolepsy. LXB's lower sodium content is recognized by the United States Food and Drug Administration in the narcolepsy population as clinically meaningful in reducing cardiovascular morbidity compared with SXBs. The Substitution of Equal Grams of Uninterrupted Xyrem to Xywav study (NCT04794491) examined the transition experience of patients with narcolepsy switching from SXB to LXB.

Methods: Eligible participants were aged 18-80 years with narcolepsy type 1 or 2 on a stable SXB dose/regimen. After 2 weeks, participants transitioned gram-per-gram to LXB for 6 weeks, with opportunity for subsequent titration. Assessments included the Epworth Sleepiness Scale, Patient Global Impression of change, Ease of Switching Medication Scale, and Forced Preference Questionnaire.

Results: The study enrolled 62 participants at baseline; 60 transitioned to LXB and 54 completed the study. At baseline and end of the LXB intervention/early discontinuation, respectively, mean total doses were 8.0 and 8.0 g/night; mean Epworth Sleepiness Scale scores were 9.4 and 8.8. Most participants reported improvement (45%) or no change (48%) in narcolepsy symptoms on the Patient Global Impression of change, reported the transition to LXB was "easy" (easy, extremely easy, not difficult at all; 93%) on the Ease of Switching Medication Scale, and preferred LXB compared with SXB (79%) on the Forced Preference Questionnaire, most commonly due to the lower sodium content.

Conclusions: Most participants switched from SXB to LXB with minimal modifications of dose/regimen and reported the transition process was easy. Effectiveness of oxybate treatment was maintained on LXB, and most participants preferred LXB to SXB. No new safety or tolerability issues were identified.

Clinical trial registration: Registry: ClinicalTrials.gov; Name: An Interventional Safety Switch Study (Segue Study) of XYWAV in Narcolepsy; URL: https://classic.clinicaltrials.gov/ct2/show/NCT04794491; Identifier: NCT04794491.

Citation: Macfadden W, Leary EB, Fuller DS, Kirby MT, Roy A. Effectiveness and optimization of low-sodium oxybate in participants with narcolepsy switching from a high-sodium oxybate: data from the Substitution of Equal Grams of Uninterrupted Xyrem to Xywav study. J Clin Sleep Med. 2024;20(9):1467-1477.