Xywav - Drug Monograph

Introduction

Xywav (calcium, magnesium, potassium, and sodium oxybates) is a central nervous system (CNS) depressant approved for the treatment of cataplexy or excessive daytime sleepiness in patients ≥7 years with narcolepsy, and for idiopathic hypersomnia (IH) in adults. It is the low-sodium successor formulation to sodium oxybate (Xyrem), providing the same active moiety (γ-hydroxybutyrate, GHB) with substantially reduced sodium content per dose. Because it shares the abuse and dependence potential of GHB, Xywav is a Schedule III controlled substance available only through a restricted REMS program.

Drug Class and Overview

• Class: CNS depressant; sodium-oxybate analog; GABA-B receptor agonist.
• Active moiety: γ-hydroxybutyrate (GHB), delivered as a mixture of calcium, magnesium, potassium, and sodium oxybates (0.5 g total oxybate per mL of solution).
• Key distinguishing features: Provides the same pharmacologic activity as sodium oxybate but with ~92% less sodium per maximum nightly dose, a clinically meaningful consideration for patients with hypertension, heart failure, or chronic kidney disease. Available only through the XYWAV and XYREM REMS program.

Mechanism of Action

GHB is an endogenous metabolite of GABA that acts as a low-affinity agonist at GABA-B receptors and as an agonist at its own high-affinity GHB receptors. Activation of GABA-B receptors on thalamocortical and mesocorticolimbic circuits produces dose-dependent CNS depression, increases slow-wave (deep) sleep, stabilizes REM sleep architecture, and reduces cataplexy. The clinical effects in narcolepsy (consolidation of nighttime sleep, reduced cataplexy, improved daytime alertness) and in IH (improved sleep continuity and daytime function) are attributed to enhanced slow-wave sleep and reduced sleep fragmentation.

Indications

• Treatment of cataplexy or excessive daytime sleepiness in patients ≥7 years of age with narcolepsy (FDA-approved, 2020).
• Treatment of idiopathic hypersomnia in adults (FDA-approved, 2021).
• Off-label uses have been described (e.g., refractory alcohol withdrawal, fibromyalgia), but evidence is limited and not part of the labeled indication.

Dosage and Administration

General administration: Oral solution, diluted in approximately 60 mL of water in the pharmacy-provided dosing device. The first dose is taken at bedtime while the patient is in bed; the second dose is taken 2.5–4 hours later, again with the patient remaining in bed. Patients typically set an alarm to wake for the second dose.

Narcolepsy (cataplexy / EDS) — adults:

• Initial: 4.5 g nightly, divided as 2.25 g at bedtime and 2.25 g 2.5–4 hours later.
• Titrate in increments of 1.5 g/night (0.75 g per dose) at weekly intervals.
• Effective dose range: 6–9 g/night; maximum 9 g/night.

Narcolepsy — pediatric patients ≥7 years: Weight-based dosing; total nightly dose should be divided into two doses (with two exceptions for lighter patients at low doses, where a single dose may be given). Maximum recommended dose is 9 g/night. Titrate per adult schedule.

Idiopathic hypersomnia (adults):

• Initial: ≤3 g/night in one or two divided doses.
• Titrate by approximately 1.5 g/night every 1–2 weeks based on efficacy and tolerability.
• Effective dose range: 6–9 g/night; maximum 12 g/night.

Renal/hepatic adjustment: No formal dose adjustment is required for renal impairment; in patients with hepatic impairment, starting dose should be halved and titrated with caution because metabolism is hepatic. (Hepatic adjustment per FDA labeling; verify current label.)

Geriatric: Use with caution; consider lower starting doses.

Pregnancy/lactation: Use only if benefits outweigh risks; GHB is excreted in milk and is contraindicated per some international guidance. Limited data.

Pharmacokinetics

• Absorption: Rapid; Tmax ~30–75 minutes; oral bioavailability is dose-proportional but exhibits high interpatient variability.
• Distribution: Very low protein binding (<1%); apparent volume of distribution is moderate. GHB readily crosses the blood-brain barrier.
• Metabolism: Primarily via cytosolic GHB dehydrogenase (a β-oxidation pathway) to succinic acid, which enters the Krebs cycle to yield CO2 and water. A minor pathway involves β-ketoreductase. CYP450 enzymes play a negligible role, so pharmacokinetic drug interactions via CYP induction or inhibition are minimal.
• Elimination: Mostly exhaled as CO2; <5% excreted unchanged in urine.
• Half-life: Short, ~0.5–1 hour.

Contraindications

• Concomitant use with sedative-hypnotic agents (including benzodiazepines and barbiturates).
• Concomitant use with alcohol.
• Succinic semialdehyde dehydrogenase (SSADH) deficiency.

Warnings and Precautions

• Boxed warning: CNS depression and abuse/misuse. Serious respiratory depression, coma, and death have been reported with misuse or coadministration with other CNS depressants. Distribution restricted through the XYWAV and XYREM REMS program.
• Respiratory depression: Particularly at higher doses or with concomitant CNS depressants; caution in patients with sleep-disordered breathing (e.g., obstructive sleep apnea).
• Dependence and withdrawal: Chronic high-dose use can produce physical dependence; abrupt discontinuation may precipitate rebound cataplexy and withdrawal syndromes (insomnia, anxiety, tremor, autonomic instability).
• Depression and suicidality: Monitor mood; depression and suicidal ideation have been reported.
• Parasomnias and sleepwalking: Confusional arousals and complex sleep-related behaviors may occur.
• Sodium content: Although low (~131 mg Na+ at 9 g/night), still relevant for patients requiring strict sodium restriction.
• Special populations: Use caution in the elderly, hepatic impairment, and pregnancy.

Drug Interactions

• Alcohol: Contraindicated — additive CNS/respiratory depression.
• Sedative-hypnotics (benzodiazepines, barbiturates, non-benzodiazepine Z-drugs): Contraindicated/combination should generally be avoided due to additive respiratory depression.
• Divalproex sodium: Increases GHB AUC by ~25%; consider reducing Xywav dose if clinically indicated.
• Topiramate: May modestly decrease GHB exposure; clinical significance uncertain.
• Other CNS depressants (opioids, sedating antihistamines, antipsychotics, TCAs): Additive sedation; monitor and minimize.
• CYP interactions: None of major clinical relevance because CYP450 metabolism is negligible.

Adverse Effects

• Very common (≥10%): Headache, nausea, dizziness, somnolence, vomiting, dry mouth, decreased appetite.
• Common (1–10%): Tremor, anxiety, insomnia, sleep paralysis, hyperhidrosis, dyspepsia, abdominal pain, fatigue, falls, peripheral edema.
• Serious (uncommon): Respiratory depression, profound CNS depression (especially with co-ingestants), depression/suicidal ideation, psychosis, seizures on withdrawal, dependence, complex sleep-related behaviors.
• Frequency language above reflects FDA labeling and standard references; exact incidence varies by dose and population.

Monitoring Parameters

• Clinical response: cataplexy frequency, daytime sleepiness (e.g., Epworth Sleepiness Scale), nighttime sleep quality, functional status.
• Vital signs and oxygen saturation when clinically indicated (sleep-disordered breathing risk).
• Mood and suicidality at each visit.
• Signs of misuse, diversion, or dependence.
• Renal and hepatic function when clinically warranted.
• Sodium intake and cardiovascular status in patients requiring sodium restriction.

Patient Education

• Take only as prescribed; never increase the dose or take an extra dose.
• Prepare both doses at bedtime; dilute each dose in ~60 mL of water using the supplied syringe.
• Remain in bed after each dose; do not drive, operate machinery, or perform tasks requiring alertness for at least 6 hours after dosing.
• Do not drink alcohol or use other sedatives (including benzodiazepines, opioids, or sleep aids).
• Do not share medication; keep locked and out of reach of others (serious risk if ingested by children or those without tolerance).
• Notify your prescriber immediately of worsening depression, suicidal thoughts, abnormal sleep behaviors, or excessive daytime sleepiness.
• Do not stop abruptly; taper under medical supervision if discontinuation is needed.

Clinical Pearls

1. Xywav is the same active moiety as sodium oxybate (Xyrem) but with markedly reduced sodium load — a preferred option in patients with hypertension, heart failure, or CKD who would otherwise require sodium restriction.
2. Both doses of the night must be taken; missing the second dose reduces efficacy, while overlapping doses (taking the second too soon) increases sedation risk.
3. Despite Schedule III status, GHB has well-documented abuse potential and serious withdrawal; institutional discharge planning should anticipate this for inpatient admissions.
4. Pharmacokinetic drug interactions are largely non-CYP; the most clinically relevant interactions are pharmacodynamic (alcohol and CNS depressants) and divalproex (mildly increases GHB exposure).
5. The short half-life (~30–60 min) means dose titration can occur as quickly as every 1–2 weeks, unlike most CNS depressants.
6. For pediatric patients ≥7 years, weight-based dosing and a maximum of 9 g/night apply; care should be coordinated with a pediatric sleep specialist.

References

1. Jazz Pharmaceuticals, Inc. XYWAV (calcium, magnesium, potassium, and sodium oxybates) oral solution. U.S. Prescribing Information.
2. U.S. Food and Drug Administration. FDA approves first treatment for idiopathic hypersomnia (Xywav). FDA News Release, August 12, 2021.
3. American Academy of Sleep Medicine. Practice Parameters for the Treatment of Narcolepsy and other Hypersomnias of Central Origin. Sleep, 2007 (and subsequent updates).
4. Morgenthaler TI, et al. Practice Parameters for the Treatment of Narcolepsy and other Hypersomnias of Central Origin. Sleep, 2007.
5. Maski K, et al. Treatment of Central Disorders of Hypersomnolence: An American Academy of Sleep Medicine Clinical Practice Guideline. Journal of Clinical Sleep Medicine, 2021.
6. Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th Edition. Chapter on sedative-hypnotic and anxiolytic drugs.
7. Katzung BG, Vanderah TW. Basic and Clinical Pharmacology, 15th Edition. Section on sedative-hypnotic drugs.
8. Black J, et al. Sodium oxybate in the treatment of narcolepsy. CNS Drugs (review article).
9. Dauvilliers Y, et al. Efficacy and safety of oxybate for idiopathic hypersomnia: clinical trial program summary. Sleep Medicine Reviews.
10. National Institute of Neurological Disorders and Stroke (NINDS). Narcolepsy fact sheet. U.S. National Institutes of Health.
11. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders (DSM-5-TR). Narcolepsy and hypersomnolence disorder criteria.
12. Lexicomp Online. Oxybates (calcium, magnesium, potassium, and sodium oxybates). Wolters Kluwer. (Subscription reference used for drug information summaries.)