Home Drug Guide Metharbital

Drug Guide

Generic Name

Metharbital

Brand Names Gemonil

Classification

Therapeutic: Anticonvulsant, Antiepileptic

Pharmacological: Barbiturate

FDA Approved Indications

Epilepsy

Mechanism of Action

Enhances GABA-mediated inhibitory neurotransmission by increasing the duration of chloride channel opening at GABA-A receptors, producing sedative and anticonvulsant effects.

Dosage and Administration

Adult: Initial dose: 100-150 mg daily, divided into 2-4 doses. Adjust based on response and tolerability.

Pediatric: Doses vary; typically started with 5-8 mg/kg/day, divided into 2-4 doses, titrated based on clinical response.

Geriatric: Begin at lower end of dosing range, monitor closely for sedation and respiratory depression.

Renal Impairment: Use with caution; dose adjustments may be necessary.

Hepatic Impairment: Use with caution; hepatic metabolism may be impaired, affecting dosing.

Pharmacokinetics

Absorption: Well absorbed orally.

Distribution: Widely distributed, crosses the blood-brain barrier.

Metabolism: Metabolized in the liver via hepatic enzymes.

Excretion: Excreted primarily in urine.

Half Life: Approximately 6-12 hours, variable depending on individual factors.

Contraindications

Hypersensitivity to barbiturates.
Porphyria.

Precautions

Use with caution in respiratory insufficiency, hepatic impairment, and in pregnancy (category D).
Risk of dependence and abuse.

Adverse Reactions - Common

Sedation, drowsiness (Common)
Impaired cognition, ataxia (Common)

Adverse Reactions - Serious

Respiratory depression (Rare)
CNS depression leading to coma (Rare)
Hypersensitivity reactions (Rare)

Drug-Drug Interactions

Other CNS depressants (additive sedative effects).
Bone marrow suppressants.

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Assessment: Monitor anticonvulsant effectiveness, signs of toxicity, liver function, respiratory function.

Diagnoses:

Risk for injury due to sedation or ataxia.
Impaired breathing.

Implementation: Administer with meals if GI upset occurs; monitor serum levels if applicable.

Evaluation: Assess for seizure control, adverse reactions, and toxicity.

Patient/Family Teaching

Take medication exactly as prescribed.
Avoid alcohol and CNS depressants.
Report signs of toxicity or allergic reactions.
Use caution to prevent falls and injuries.

Special Considerations

Black Box Warnings:

Potential for respiratory depression, dependence, and abuse.

Genetic Factors: Poor metabolism in some populations may affect drug levels.

Lab Test Interference: May alter liver function tests.

Overdose Management

Signs/Symptoms: Confusion, coma, respiratory depression, pin-point pupils.

Treatment: Supportive care, airway management, activated charcoal if recent ingestion, and potentially dialysis in severe cases.

Storage and Handling

Storage: Store at room temperature away from moisture and heat.

Stability: Stable for 2-3 years under proper conditions.