Mephobarbital

Pronunciation

(me foe BAR bi tal)

U.S. Brand Names

Mebaral®

Synonyms

Methylphenobarbital

Generic Available

Canadian Brand Names

Mebaral®

Use

Sedative; treatment of grand mal and petit mal epilepsy

Restrictions

C-IV

Pregnancy Risk Factor

Contraindications

Hypersensitivity to mephobarbital, other barbiturates, or any component of the formulation; pre-existing CNS depression; respiratory depression; severe uncontrolled pain; history of porphyria; pregnancy

Adverse Reactions

>10%: Central nervous system: Dizziness, lightheadedness, drowsiness, "hangover" effect

1% to 10%:

Central nervous system: Confusion, mental depression, unusual excitement, nervousness, faint feeling, headache, insomnia, nightmares

Gastrointestinal: Constipation, nausea, vomiting

Drug Interactions

Substrate of CYP2B6 (minor), 2C8/9 (minor), 2C19 (major); Inhibits CYP2C19 (weak); Induces CYP2A6 (weak)

Acetaminophen: Barbiturates may enhance the hepatotoxic potential of acetaminophen overdoses

CNS depressants: Sedative effects and/or respiratory depression with barbiturates may be additive with other CNS depressants; monitor for increased effect; includes ethanol, sedatives, antidepressants, narcotic analgesics, and benzodiazepines

Cyclosporine: Levels may be decreased by barbiturates; monitor

CYP2C19 inducers: May decrease the levels/effects of mephobarbital. Example inducers include aminoglutethimide, carbamazepine, phenytoin, and rifampin.

CYP2C19 inhibitors: May increase the levels/effects of mephobarbital. Example inhibitors include delavirdine, fluconazole, fluvoxamine, gemfibrozil, isoniazid, omeprazole, and ticlopidine.

Griseofulvin: Barbiturates may impair the absorption of griseofulvin, and griseofulvin metabolism may be increased by barbiturates, decreasing clinical effect

Guanfacine: Effect may be decreased by barbiturates

MAO inhibitors: Metabolism of barbiturates may be inhibited, increasing clinical effect or toxicity of the barbiturates

Methoxyflurane: Barbiturates may enhance the nephrotoxic effects of methoxyflurane

Valproic acid: Metabolism of barbiturates may be inhibited by valproic acid; monitor for excessive sedation; a dose reduction may be needed

Mechanism of Action

Increases seizure threshold in the motor cortex; depresses monosynaptic and polysynaptic transmission in the CNS

Pharmacodynamics/Kinetics

Onset of action: 20-60 minutes

Duration: 6-8 hours

Absorption: ~50%

Half-life elimination, serum: 34 hours

Dosage

Oral:

Epilepsy:

Children: 6-12 mg/kg/day in 2-4 divided doses

Adults: 200-600 mg/day in 2-4 divided doses

Sedation:

Children:

<5 years: 16-32 mg 3-4 times/day

>5 years: 32-64 mg 3-4 times/day

Adults: 32-100 mg 3-4 times/day

Dosing adjustment in renal or hepatic impairment: Use with caution and reduce dosages

Dietary Considerations

High doses of pyridoxine may decrease drug effect; barbiturates may increase the metabolism of vitamin D & K; dietary requirements of vitamin D, K, C, B12, folate and calcium may be increased with long-term use.

Patient Education

May cause drowsiness, may impair coordination and judgment; do not discontinue abruptly; notify physician of dark urine, pale stools, jaundice, abdominal pain, persistent nausea, and vomiting; do not skip doses

Nursing Implications

High doses of pyridoxine may decrease drug effect

Dental Health: Effects on Dental Treatment

No significant effects or complications reported

Dental Health: Vasoconstrictor/Local Anesthetic Precautions

No information available to require special precautions

Mental Health: Effects on Mental Status

Dizziness and drowsiness are common; may cause confusion, nervousness, depression, nightmares, or insomnia; may rarely cause hallucinations

Mental Health: Effects on Psychiatric Treatment

May rarely cause agranulocytosis; use caution with clozapine and carbamazepine; may induce hepatic enzymes resulting in an increase or decrease effect of concurrent psychotropic; monitor to altered response

Dosage Forms

Tablet: 32 mg, 50 mg, 100 mg

References

Pond SM, Olson KR, Osterloh JD, et al, "Randomized Study of the Treatment of Phenobarbital Overdose With Repeated Doses of Activated Charcoal," JAMA , 1984, 251(23):3104-8.

Zawada ET, Nappi J, Done G, et al, "Advances in the Hemodialysis Management of Phenobarbital Overdose," South Med J , 1983, 76(1):6-8.

International Brand Names

Mebaral® (CA); Methylphenobarbital® (IL); Phemiton® (HR, SI); Prominal® (AU)

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