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Mephobarbital


General


Pronunciation

(me foe BAR bi tal)


Brand Names: U.S.

  • Mebaral ‚ ® [DSC]

Indications


Use: Labeled Indications

Sedative; treatment of grand mal and petit mal epilepsy


Contraindications


Hypersensitivity to mephobarbital, other barbiturates, or any component of the formulation; history of porphyria


Dosing and Administration


Dosing: Adult

Epilepsy: Oral:

400-600 mg/day; Note: Initiate at low dose and gradually increase over 4-5 days. Taper other antiepileptics off as dose increases. When lowering or discontinuing dose, taper over 4-5 days.

Coadministration with phenobarbital: Average dose: 200-300 mg/day mephobarbital plus 50-100 mg/day of phenobarbital (doses should be approximately half the amount of those when used alone)

Coadministration with phenytoin: Use full dose of mephobarbital and reduce phenytoin dose (average dose: phenytoin 230 mg/day plus mephobarbital 600 mg/day)

Sedation: Oral: 32-100 mg 3-4 times/day


Dosing: Geriatric

Refer to adult dosing. Start at lowest recommended doses.


Dosing: Pediatric

Epilepsy: Oral:

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

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

Note: Initiate at low dose and gradually increase over 4-5 days. Taper other antiepileptics off as dose increases. When lowering or discontinuing dose, taper over 4-5 days.

Sedation: Oral: 16-32 mg 3-4 times/day


Dosing: Renal Impairment

Use with caution and reduce dose.


Dosing: Hepatic Impairment

Use with caution and reduce dose.


Administration

Administer at bedtime if seizures occur at night and during the day if seizures are diurnal.


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.


Dosage Forms/Strengths


Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product

Tablet, oral:

Mebaral ‚ ®: 32 mg [DSC] [scored]

Mebaral ‚ ®: 50 mg [DSC], 100 mg [DSC]


Drug Interactions

Acetaminophen: Barbiturates may increase the metabolism of Acetaminophen. This may 1) diminish the effect of acetaminophen; and 2) increase the risk of liver damage.

Alcohol (Ethyl): CNS Depressants may enhance the CNS depressant effect of Alcohol (Ethyl).

Beta-Blockers: Barbiturates may decrease the serum concentration of Beta-Blockers. Exceptions: Atenolol; Levobunolol; Metipranolol; Nadolol.

Calcium Channel Blockers: Barbiturates may increase the metabolism of Calcium Channel Blockers. Management: Monitor for decreased therapeutic effects of calcium channel blockers with concomitant barbiturate therapy. Calcium channel blocker dose adjustments may be necessary. Nimodipine Canadian labeling contraindicates concomitant use with phenobarbital. Exceptions: Clevidipine.

Chloramphenicol: Barbiturates may increase the metabolism of Chloramphenicol. Chloramphenicol may decrease the metabolism of Barbiturates.

CNS Depressants: May enhance the adverse/toxic effect of other CNS Depressants. Exceptions: Levocabastine (Nasal).

Contraceptives (Estrogens): Barbiturates may diminish the therapeutic effect of Contraceptives (Estrogens). Contraceptive failure is possible. Management: Use of a non-hormonal contraceptive is recommended.

Contraceptives (Progestins): Barbiturates may diminish the therapeutic effect of Contraceptives (Progestins). Contraceptive failure is possible. Management: Use of alternative, nonhormonal contraceptives is recommended.

Corticosteroids (Systemic): Barbiturates may decrease the serum concentration of Corticosteroids (Systemic).

CycloSPORINE: Barbiturates may increase the metabolism of CycloSPORINE.

CycloSPORINE (Systemic): Barbiturates may increase the metabolism of CycloSPORINE (Systemic).

CYP2C19 Inducers (Strong): May increase the metabolism of CYP2C19 Substrates.

CYP2C19 Inhibitors (Moderate): May decrease the metabolism of CYP2C19 Substrates.

CYP2C19 Inhibitors (Strong): May decrease the metabolism of CYP2C19 Substrates.

Disopyramide: Barbiturates may increase the metabolism of Disopyramide.

Divalproex: May decrease the metabolism of Barbiturates. Barbiturates may decrease the serum concentration of Divalproex.

Doxycycline: Barbiturates may decrease the serum concentration of Doxycycline.

Droperidol: May enhance the CNS depressant effect of CNS Depressants. Management: Consider dose reductions of droperidol or of other CNS agents (e.g., opioids, barbiturates) with concomitant use.

Etoposide: Barbiturates may decrease the serum concentration of Etoposide.

Etoposide Phosphate: Barbiturates may decrease the serum concentration of Etoposide Phosphate. Barbiturates may increase the metabolism, via CYP isoenzymes, of etoposide phosphate.

Felbamate: Barbiturates may decrease the serum concentration of Felbamate. Felbamate may increase the serum concentration of Barbiturates. Management: Monitor for elevated barbiturate concentrations/toxicity if felbamate is initiated/dose increased, or reduced concentrations/effects if felbamate is discontinued/dose decreased. Refer to phenobarbital dosing guidelines for patients receiving that agent.

Fosphenytoin: Barbiturates may enhance the CNS depressant effect of Fosphenytoin. Barbiturates may decrease the serum concentration of Fosphenytoin. Fosphenytoin may increase the serum concentration of Barbiturates.

Griseofulvin: Barbiturates may decrease the serum concentration of Griseofulvin.

HydrOXYzine: May enhance the CNS depressant effect of Barbiturates. Management: Consider a decrease in the barbiturate dose, as appropriate, when used together with hydroxyzine. With concurrent use, monitor patients closely for excessive response to the combination.

LamoTRIgine: Barbiturates may decrease the serum concentration of LamoTRIgine. Management: See lamotrigine prescribing information for specific age-dependent dosing guidelines regarding concurrent use with a barbiturate, as well as for adjusting lamotrigine dosing if concurrent barbiturate therapy is discontinued.

Meperidine: Barbiturates may enhance the CNS depressant effect of Meperidine. Barbiturates may increase serum concentrations of the active metabolite(s) of Meperidine.

Methadone: Barbiturates may decrease the serum concentration of Methadone.

Phenytoin: May enhance the CNS depressant effect of Barbiturates. Barbiturates may decrease the serum concentration of Phenytoin. Phenytoin may increase the serum concentration of Barbiturates.

Primidone: May enhance the adverse/toxic effect of Barbiturates. Primidone is converted to phenobarbital, and thus becomes additive with existing barbiturate therapy.

Propafenone: Barbiturates may decrease the serum concentration of Propafenone.

Pyridoxine: May increase the metabolism of Barbiturates. Apparent in high pyridoxine doses (eg, 200 mg/day)

QuiNIDine: Barbiturates may enhance the hepatotoxic effect of QuiNIDine. Barbiturates may decrease the serum concentration of QuiNIDine.

Rifamycin Derivatives: May increase the metabolism of Barbiturates.

Selective Serotonin Reuptake Inhibitors: CNS Depressants may enhance the adverse/toxic effect of Selective Serotonin Reuptake Inhibitors. Specifically, the risk of psychomotor impairment may be enhanced.

Teniposide: Barbiturates may decrease the serum concentration of Teniposide. Management: Consider alternatives to combined treatment with barbiturates and teniposide due to the potential for decreased teniposide concentrations. If the combination cannot be avoided, monitor teniposide response closely.

Theophylline Derivatives: Barbiturates may decrease the serum concentration of Theophylline Derivatives. Exceptions: Dyphylline.

Thiazide Diuretics: Barbiturates may enhance the orthostatic hypotensive effect of Thiazide Diuretics.

Tricyclic Antidepressants: Barbiturates may increase the metabolism of Tricyclic Antidepressants.

Valproic Acid: May decrease the metabolism of Barbiturates. Barbiturates may decrease the serum concentration of Valproic Acid.

Vitamin K Antagonists (eg, warfarin): Barbiturates may increase the metabolism of Vitamin K Antagonists.

Voriconazole: Barbiturates may decrease the serum concentration of Voriconazole.


Adverse Reactions


>1%: Central nervous system: Somnolence

<1% (Limited to important or life-threatening): Abnormal thinking, agitation, anxiety, apnea, ataxia, bradycardia, constipation, confusion, depression, dizziness, fever, hallucinations, headache, hyperkinesia, hypersensitivity reactions (including angioedema, exfoliative dermatitis, skin rash), hypotension, hypoventilation, insomnia, liver injury, nausea, nervousness, nightmares, psychiatric disturbances, unusual excitement, vomiting


Warnings/Precautions


Concern related to adverse effects:

- CNS depression: May cause CNS depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks which require mental alertness (eg, operating machinery or driving).

- Paradoxical responses: May cause paradoxical responses, including agitation and hyperactivity, particularly in acute pain, chronic pain, and elderly, debilitated, or pediatric patients.

Disease-related concerns:

- Cardiovascular disease: Use with caution in patients with cardiovascular disease.

- Depression: Use with caution in patients with depression or suicidal tendencies.

- Hepatic impairment: Use with caution in patients with hepatic impairment; dosage adjustment recommended.

- Myasthenia gravis: Use with caution in patients with myasthenia gravis.

- Myxedema: Use with caution in patients with myxedema.

- Renal impairment: Use with caution in patients with renal impairment; dosage adjustment recommended.

- Respiratory depression: Use with caution patients with respiratory disease.

- Substance abuse: Use with caution in patients with a history of drug abuse; potential for drug dependency exists. Tolerance, psychological and physical dependence may occur with prolonged use.

Concurrent drug therapy issues:

- Sedatives: Effects with other sedative drugs or ethanol may be potentiated.

Other warnings/precautions:

- Pain: Use with caution when administering to patients in acute or chronic pain.

- Withdrawal: Anticonvulsants should not be discontinued abruptly because of the possibility of increasing seizure frequency; therapy should be withdrawn gradually to minimize the potential of increased seizure frequency, unless safety concerns require a more rapid withdrawal.


Pregnancy Risk Factor

D


Pregnancy Considerations

Barbiturates cross the placenta and distribute in fetal tissue. Teratogenic effects have been reported with first trimester exposure. Exposure during the third trimester may lead to symptoms of acute withdrawal following delivery; symptoms may be delayed up to 14 days.


Actions


Pharmacology

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


Absorption

~50%


Onset of Action

20-60 minutes


Duration of Action

6-8 hours


Half-Life Elimination

Serum: 34 hours

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