XYREM
Clinical safety rating: caution
Comprehensive clinical and safety monograph for XYREM (XYREM).
Gamma-hydroxybutyrate (GHB) agonist at GABA-B and GHB receptors, modulating dopamine and serotonin activity.
| Metabolism | Primarily via the enzyme GHB dehydrogenase (unidentified) and to a lesser extent via beta-oxidation (Krebs cycle). Minor metabolism by CYP450 isoenzymes (not major). |
| Excretion | Primarily renal (≥95% as metabolites, mainly as CO2 and succinate via Krebs cycle); negligible biliary/fecal excretion. |
| Half-life | 0.5–1 hour; clinical context: requires twice-nightly dosing for sustained effects in narcolepsy. |
| Protein binding | ~1%; negligible binding to plasma proteins. |
| Volume of Distribution | 0.8–1.0 L/kg; consistent with total body water distribution. |
| Bioavailability | Oral: ~88% (fasted); reduced by high-fat meal. |
| Onset of Action | Oral: 15–45 minutes (sleep onset); may be delayed with food. |
| Duration of Action | 2–4 hours per dose; clinical note: divided dose (first at bedtime, second 2.5–4 hours later) to maintain overnight sleep. |
9 g orally per night divided into two doses: first dose of 4.5 g at bedtime, second dose of 4.5 g given 2.5 to 4 hours later. Titrate based on efficacy and tolerability; range 6 to 9 g per night.
| Dosage form | SOLUTION |
| Renal impairment | For GFR 30-59 mL/min: reduce total nightly dose by 50%. For GFR <30 mL/min or on dialysis: contraindicated. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B or C: reduce initial dose by 50% (e.g., 4.5 g total nightly dose) and titrate cautiously. |
| Pediatric use | For narcolepsy with cataplexy in children ≥7 years: weight-based dosing. Body weight <20 kg: no data. 20-30 kg: 4 g total nightly dose divided; 30-45 kg: 6 g total; ≥45 kg: 9 g total; titrate in 1.5 g increments per night weekly. |
| Geriatric use | Start at lower end of dosing range (e.g., 6 g total nightly dose) due to potential age-related renal impairment; monitor for confusion, falls, and nocturnal wandering. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for XYREM (XYREM).
| Breastfeeding | Unknown if excreted in human milk. No M/P ratio available. Caution advised; consider discontinuing nursing or drug based on importance to mother. |
| Teratogenic Risk | Pregnancy Category B. No evidence of fetal harm in animal studies; no adequate human studies in first trimester. Avoid use during pregnancy unless benefit outweighs risk. |
| Fetal Monitoring | Anticipated weight gain, blood pressure, and signs of CNS depression in neonate if used near term. No specific fetal monitoring required. |
■ FDA Black Box Warning
Central nervous system (CNS) depression: Risk of respiratory depression, coma, and death. Concomitant use with alcohol or other CNS depressants is contraindicated. Abuse potential: Schedule III controlled substance; misuse can lead to dependence and withdrawal.
| Serious Effects |
Concomitant use with alcohol or other CNS depressants, succinic semialdehyde dehydrogenase deficiency, and MAO inhibitor use (due to potential interaction).
| Precautions | CNS depression (including respiratory depression), abuse and dependence, sleep-related behaviors (e.g., sleepwalking), depression/suicidality, hypertension, and nocturnal hypoventilation. Monitor for respiratory impairment in patients with compromised respiratory function. |
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| Fertility Effects | No human data; animal studies show no impairment of fertility at clinically relevant doses. |