Therapeutics of Narcolepsy

Development of a lower-sodium oxybate formulation for the treatment of patients with narcolepsy and idiopathic hypersomnia

INTRODUCTION

Sodium oxybate (SXB) is a standard of care for cataplexy, excessive daytime sleepiness, and disrupted nighttime sleep in narcolepsy. At recommended dosages in adults (6-9 g/night), SXB increases daily dietary intake of sodium by 1100-1640 mg. Because excess sodium intake is associated with increased blood pressure and cardiovascular risk, an oxybate formulation containing 92% less sodium than SXB (lower-sodium oxybate; LXB) was developed to provide an alternative oxybate treatment option. In 2020, LXB was approved for treatment of cataplexy or excessive daytime sleepiness in patients 7 years of age and older with narcolepsy, and in 2021, for treatment of idiopathic hypersomnia in adults.

AREAS COVERED

Development of LXB from initial concept to regulatory approval is described, including formulation development and preclinical and clinical studies. Pharmacokinetic parameters and bioequivalence evaluations from phase 1 clinical trials are detailed. Efficacy and safety results from phase 3 clinical trials of LXB in patients with narcolepsy or idiopathic hypersomnia are presented and discussed.

EXPERT OPINION

Reducing sodium from high sodium‒containing medications is an important step to offset cardiovascular risks associated with high sodium consumption. The development of LXB exemplifies the importance of a collaborative approach to drug development, with patient needs paramount.

PLAIN LANGUAGE SUMMARY

Sodium oxybate (Xyrem®) is a medication for people with narcolepsy aged 7 years and older. Xyrem treats symptoms of excessive daytime sleepiness (EDS) or cataplexy (attacks of muscle weakness caused by emotion) in narcolepsy. At the recommended dosages in adults, Xyrem adds a large amount of sodium to daily dietary intake. Too much sodium in the diet is associated with increased blood pressure and risks of damage to the heart and blood vessels. Researchers used calcium, magnesium, and potassium ions in addition to a small amount of sodium to make a new oxybate medication, called Xywav®, that has 92% less sodium than Xyrem. Xywav and Xyrem were similar in laboratory and animal studies. In people, the body absorbs and processes Xywav slightly differently than Xyrem, but Xywav treatment has been shown to work the same to reduce symptoms of cataplexy and EDS in people with narcolepsy and is approved by the US Food and Drug Administration. Another neurological disorder with EDS is called idiopathic hypersomnia. Based on a clinical study, Xywav also reduced EDS and other symptoms in people with idiopathic hypersomnia. Side effects with Xywav are similar to those seen in previous studies with Xyrem.

The ICSD-3 and DSM-5 guidelines for diagnosing narcolepsy: clinical relevance and practicality

Narcolepsy is a chronic neurological disease manifesting as difficulty with maintaining continuous wake and sleep. Clinical presentation varies but requires excessive daytime sleepiness (EDS) occurring alone or together with features of rapid-eye movement (REM) sleep dissociation (e.g., cataplexy, hypnagogic/hypnopompic hallucinations, sleep paralysis), and disrupted nighttime sleep. Narcolepsy with cataplexy is associated with reductions of cerebrospinal fluid (CSF) hypocretin due to destruction of hypocretin peptide-producing neurons in the hypothalamus in individuals with a specific genetic predisposition. Updated diagnostic criteria include the Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5) and International Classification of Sleep Disorders Third Edition (ICSD-3). DSM-5 criteria require EDS in association with any one of the following: (1) cataplexy; (2) CSF hypocretin deficiency; (3) REM sleep latency ≤15 minutes on nocturnal polysomnography (PSG); or (4) mean sleep latency ≤8 minutes on multiple sleep latency testing (MSLT) with ≥2 sleep-onset REM-sleep periods (SOREMPs). ICSD-3 relies more upon objective data in addition to EDS, somewhat complicating the diagnostic criteria: 1) cataplexy and either positive MSLT/PSG findings or CSF hypocretin deficiency; (2) MSLT criteria similar to DSM-5 except that a SOREMP on PSG may count as one of the SOREMPs required on MSLT; and (3) distinct division of narcolepsy into type 1, which requires the presence of cataplexy or documented CSF hypocretin deficiency, and type 2, where cataplexy is absent, and CSF hypocretin levels are either normal or undocumented. We discuss limitations of these criteria such as variability in clinical presentation of cataplexy, particularly when cataplexy may be ambiguous, as well as by age; multiple and/or invasive CSF diagnostic test requirements; and lack of normative diagnostic test data (e.g., MSLT) in certain populations. While ICSD-3 criteria reflect narcolepsy pathophysiology, DSM-5 criteria have greater clinical practicality, suggesting that valid and reliable biomarkers to help standardize narcolepsy diagnosis would be welcomed.

Effect of oral JZP-110 (ADX-N05) treatment on wakefulness and sleepiness in adults with narcolepsy

BACKGROUND

JZP-110 is a wake-promoting agent with dopaminergic and noradrenergic activity.

METHODS

This double-blind, crossover study, randomized adults with narcolepsy with or without cataplexy (N = 33) to placebo or JZP-110 at 150 mg/day (weeks 1 and 3) increased to 300 mg/day (weeks 2 and 4). Patients had to have baseline Epworth Sleepiness Scale (ESS) scores ≥10 and mean sleep latencies ≤10 min on the Maintenance of Wakefulness Test (MWT). Efficacy end points included MWT sleep latency and ESS, and the percentage of patients improved on the Clinical Global Impression of Change.

RESULTS

Patients were primarily male (57.6%) and white (69.7%), with a mean (standard deviation) age of 37.1 (12.4) years. At two weeks, the change in the mean MWT sleep latency was 11.8 min longer with JZP-110 than with placebo (P = 0.0002); JZP-110 resulted in greater changes in sleep latency on each MWT trial (P <0.001). For ESS, JZP-110 was more efficacious relative to placebo after 1 (P <0.0001) and two weeks (P = 0.0002); final ESS scores were 10.8 with JZP-110 and 15.2 with placebo, changes of -6.7 and -2.4, respectively. JZP-110 was generally well tolerated; the most common adverse events with JZP-110 were nausea (12%), noncardiac chest discomfort (9.1%), and headache (9.1%).

CONCLUSIONS

The efficacy of JZP-110 for impaired wakefulness and excessive sleepiness was observed at 150-300 mg/day and as early as one week after initiating treatment (Clinicaltrials.gov identifier NCT01485770).