Xyrem - Drug Monograph

Introduction

Xyrem (sodium oxybate) is the oral sodium salt of gamma-hydroxybutyrate (GHB), a central nervous system depressant. It is FDA-approved for the treatment of cataplexy and excessive daytime sleepiness in patients with narcolepsy, and more recently for idiopathic hypersomnia in adults. Its unique mechanism of action on GABA-B receptors distinguishes it from traditional stimulants used for narcolepsy, and its restricted distribution program reflects its serious abuse potential.

Drug Class and Overview

Xyrem belongs to the class of CNS depressants acting as GABA-B receptor agonists, structurally related to the neurotransmitter gamma-aminobutyric acid (GABA). Unlike benzodiazepines or barbiturates that target GABA-A receptors, sodium oxybate produces its effects primarily through GABA-B receptor modulation. It is the only FDA-approved medication specifically for cataplexy, and its restricted distribution under a Risk Evaluation and Mitigation Strategy (REMS) program distinguishes it from other narcolepsy therapies.

Mechanism of Action

Sodium oxybate is a GABA-B receptor agonist with additional activity at GHB-specific receptors in the brain. The mechanism underlying its clinical benefit in narcolepsy is not fully understood but is thought to involve consolidation of sleep architecture—particularly increasing slow-wave (deep) sleep during nighttime—and modulation of dopaminergic signaling. Its sedative effects are mediated through hyperpolarization of neurons via increased potassium conductance and decreased calcium influx at presynaptic terminals.

Indications

• Treatment of cataplexy in patients with narcolepsy
• Treatment of excessive daytime sleepiness in patients with narcolepsy
• Treatment of idiopathic hypersomnia in adults (FDA-approved indication)

Dosage and Administration

Xyrem is administered orally as a solution, taken as two divided doses at bedtime and again 2.5 to 4 hours later due to its short half-life.

• Adults (narcolepsy): Initiate at 2.25 g per night, divided as 1.125 g at bedtime and 1.125 g 2.5–4 hours later. Titrate weekly by 1.5 g/day increments to a recommended range of 6–9 g per night.
• Adults (idiopathic hypersomnia): Dosing typically initiated at 1.5 g per night, titrated upward as tolerated.
• Pediatric patients (≥7 years, narcolepsy): Weight-based dosing, generally starting at 0.025 g/kg/dose at bedtime.
• Hepatic impairment: Dose reduction is recommended; avoid in patients with severe hepatic impairment.
• Renal impairment: Use with caution; sodium load may be clinically relevant.

Pharmacokinetics

• Absorption: Rapidly absorbed orally, with peak plasma concentrations within 30–60 minutes.
• Distribution: Low protein binding (<10%); crosses the blood-brain barrier readily.
• Metabolism: Undergoes minimal hepatic metabolism via the citric acid cycle; not significantly metabolized by CYP enzymes.
• Elimination: Primarily eliminated as carbon dioxide via expiration; small amounts excreted unchanged in urine.
• Half-life: Approximately 30–60 minutes (short), necessitating the twice-nightly dosing regimen.

Contraindications

• Concomitant use with sedative-hypnotics or CNS depressants (including alcohol)
• Patients with succinic semialdehyde dehydrogenase deficiency (rare inborn error of metabolism)
• Known hypersensitivity to sodium oxybate

Warnings and Precautions

• CNS depression and respiratory depression: Significant risk, particularly when combined with alcohol or other CNS depressants.
• Abuse and dependence: GHB has a well-documented history as a drug of abuse (date rape drug); Xyrem is subject to strict REMS requirements with restricted distribution.
• Sodium load: Each gram contains approximately 110–130 mg of sodium; caution in patients with heart failure, hypertension, or renal impairment.
• Confusion, depression, and suicidality: Monitor for mood changes, particularly in patients with a history of psychiatric disorders.
• Sleepwalking and sleep-related behaviors: Patients may engage in activities while not fully awake with no memory of the event.

Drug Interactions

• Alcohol and CNS depressants: Additive CNS and respiratory depression; absolute contraindication.
• Sedative hypnotics: Concomitant use increases risk of severe respiratory depression.
• Divalproex and valproic acid: May increase sodium oxybate plasma concentrations by approximately 25%; dose reduction may be warranted.
• Antidepressants: Caution with tricyclics, SSRIs, and SNRIs due to potential additive CNS effects.
• Topiramate: Concurrent use has been associated with coma; avoid combination.

Adverse Effects

Common (≥10%): Nausea, dizziness, vomiting, somnolence, headache, and enuresis (bedwetting), particularly in pediatric populations.

Serious but less common: Respiratory depression, severe confusion, depression, suicidal ideation, sleepwalking, and seizures upon abrupt discontinuation.

Monitoring Parameters

• Respiratory status, particularly during initiation and titration
• Mental status and mood changes (depression, suicidality)
• Signs of misuse, abuse, or diversion
• Electrolytes and fluid status in patients sensitive to sodium load
• Sleep patterns and cataplexy frequency

Patient Education

• Take only as prescribed; never share medication with others.
• Do not mix with alcohol or other sedatives.
• Prepare doses using the provided dosing syringe and water only.
• Allow at least 2 hours after eating before taking the first dose.
• Remain in bed after taking each dose due to rapid onset of sleep.
• Do not drive or operate machinery for at least 6 hours after the second dose.
• Report any unusual sleep behaviors, mood changes, or breathing problems immediately.

Clinical Pearls

1. Xyrem's REMS program requires prescribers, pharmacies, and patients to enroll; it cannot be dispensed from a regular pharmacy.
2. The twice-nightly dosing schedule is pharmacokinetically driven—Xyrem has a half-life of only ~40 minutes, making it a poor candidate for single bedtime dosing.
3. Sodium content is clinically significant (~1,000 mg sodium at 9 g dose); consider in heart failure and hypertension.
4. Abrupt discontinuation can precipitate severe withdrawal, including anxiety, insomnia, tremor, and rebound cataplexy.
5. Despite GHB's reputation as a "party drug," pharmaceutical sodium oxybate has a well-established safety profile when used as prescribed under REMS oversight.
6. Combining with modafinil or other wakefulness-promoting agents allows complementary management of daytime symptoms.

References

1. Jazz Pharmaceuticals. Xyrem (sodium oxybate) oral solution prescribing information. U.S. Food and Drug Administration. Updated 2023.
2. American Academy of Sleep Medicine. Clinical Practice Guidelines for the Treatment of Narcolepsy and Other Hypersomnias. Journal of Clinical Sleep Medicine. 2021.
3. Bogan R, et al. Idiopathic Hypersomnia: Current and Emerging Treatment Options. CNS Drugs. 2020.
4. Xywav (calcium, magnesium, potassium, and sodium oxybates) prescribing information, Jazz Pharmaceuticals. FDA. 2021.
5. Robinson DM, Keating GM. Sodium Oxybate: A Review of Its Use in the Management of Narcolepsy. CNS Drugs. 2007.
6. Nishino S, Mignot E. Pharmacological Aspects of Human and Canine Narcolepsy. Progress in Neurobiology. 1997.
7. Fuller DE, et al. GHB: A Drug of Abuse and a Therapeutic Agent. International Journal of Neuropsychopharmacology. 2004.
8. U.S. Drug Enforcement Administration. Gamma-Hydroxybutyric Acid (GHB). DEA Diversion Control Division. 2020.
9. Benbadis SR, et al. Sodium Oxybate in the Treatment of Idiopathic Hypersomnia: A Retrospective Study. Sleep Medicine. 2020.
10. Thorpy MJ. Recently Approved and Investigational Drugs for Narcolepsy. Neurology. 2019.
11. Dauvilliers Y, et al. Safety and Efficacy of Sodium Oxybate in Pediatric Narcolepsy. Sleep. 2021.
12. Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th Edition. McGraw-Hill. 2018.