GEMONIL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for GEMONIL (GEMONIL).
Barbiturate that enhances GABA-A receptor activity, increasing chloride ion conductance and producing CNS depression.
| Metabolism | Hepatic via CYP2C9 and CYP2C19; induces multiple CYP enzymes. |
| Excretion | Primarily renal excretion of unchanged drug and metabolites. Approximately 60-70% excreted unchanged in urine within 24 hours; 15-20% as conjugated metabolites; fecal elimination accounts for <5%. |
| Half-life | Terminal elimination half-life is 50-70 hours in adults with normal renal function. Significantly prolonged in renal impairment, requiring dose adjustment. |
| Protein binding | Approximately 85-90% bound primarily to albumin. |
| Volume of Distribution | 0.8-1.2 L/kg. Indicates extensive tissue distribution, including brain and adipose tissue. |
| Bioavailability | Oral: 80-90% due to minimal first-pass metabolism; Intramuscular: approximately 90%. |
| Onset of Action | Oral: 30-60 minutes; Intramuscular: 15-30 minutes; Intravenous: 5-10 minutes. |
| Duration of Action | Oral: 6-12 hours; Intramuscular: 4-8 hours; Intravenous: 3-6 hours. Duration may be extended in hepatic impairment or with concurrent CNS depressants. |
Gemonil is a brand name for metharbital, a barbiturate anticonvulsant. Typical adult dose: 100 mg orally three to four times daily, adjusted based on response and tolerability.
| Dosage form | TABLET |
| Renal impairment | In renal impairment, barbiturates are excreted renally. For GFR 10-50 mL/min, reduce dose by 25-50%; for GFR <10 mL/min, avoid use or use with caution and reduce dose by 50% or more. |
| Liver impairment | In hepatic impairment, barbiturate metabolism is reduced. Child-Pugh Class A: no adjustment needed; Child-Pugh Class B: reduce dose by 25-50%; Child-Pugh Class C: avoid use or use lowest possible dose with monitoring. |
| Pediatric use | Pediatric dose for metharbital: 5-10 mg/kg/day orally in 2-3 divided doses. Alternatively, 50-100 mg two to three times daily for children 6-12 years. Titrate to seizure control. |
| Geriatric use | In elderly patients, start at lower doses (50 mg three times daily) due to increased sensitivity and reduced clearance. Monitor for sedation, ataxia, and cognitive impairment. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for GEMONIL (GEMONIL).
| Breastfeeding | Excreted in breast milk; M/P ratio unknown. Use with caution; monitor infant for sedation and feeding difficulties. |
| Teratogenic Risk | First trimester: potential teratogenicity. Second trimester: risk of intrauterine growth restriction. Third trimester: neonatal withdrawal, respiratory depression, and floppy infant syndrome. |
| Fetal Monitoring | Fetal ultrasound for growth and anatomy; maternal serum alpha-fetoprotein; nonstress test and biophysical profile in third trimester. |
■ FDA Black Box Warning
May be habit forming; abrupt discontinuation can precipitate withdrawal seizures and status epilepticus.
| Serious Effects |
Hypersensitivity to barbiturates, porphyria, severe respiratory insufficiency, history of substance abuse.
| Precautions | Respiratory depression, dependence/withdrawal, paradoxical excitement, risk of suicidal ideation, use in hepatic impairment. |
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| Fertility Effects | May reduce fertility by suppressing ovulation or spermatogenesis due to CNS depression. |