Mephobarbital

Pronunciation: meh-foe-BAR-bih-tahl
Class: Sedative and hypnotic, barbiturate

Trade Names

Mebaral
- Tablets 32 mg
- Tablets 50 mg
- Tablets 100 mg

Pharmacology

Depresses sensory cortex, decreases motor activity, alters cerebellar function, and produces drowsiness, sedation, and hypnosis.

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Pharmacokinetics

Absorption

Approximately 50% of an oral dose is absorbed from the GI tract.

Metabolism

Metabolized in the liver to phenobarbital. About 75% of the oral dose is converted to phenobarbital in 24 h.

Elimination

The metabolite, phenobarbital, may be excreted unchanged in the urine or further metabolized and excreted in the urine as glucuronide or sulfate conjugates.

Onset

30 to 60 min after an oral dose.

Duration

10 to 16 h.

Indications and Usage

As a sedative for relief of anxiety, tension, and apprehension; as an anticonvulsant for the treatment of grand mal and petit mal epilepsy.

Contraindications

Manifest or latent porphyria; hypersensitivity to any barbiturate.

Dosage and Administration

Epilepsy
Adults

PO 400 to 600 mg/day.

Children older than 5 yr of age

PO 32 to 64 mg 3 or 4 times daily.

Children younger than 5 yr of age

PO 16 to 32 mg 3 or 4 times daily.

Storage/Stability

Store tablets at controlled room temperature (less than 77°F).

Drug Interactions

Alcohol, CNS depressants

May enhance CNS depressant effects.

Anticoagulants (eg, warfarin), beta-blockers (eg, metoprolol), doxycycline, felodipine, griseofulvin, methadone, metronidazole, nifedipine, quinidine, theophyllines, verapamil

Activity of these drugs may be reduced by mephobarbital.

Anticonvulsants

Serum levels of carbamazepine, valproic acid, and succinimides may be reduced. Valproic acid may increase mephobarbital levels.

Estrogens, estrogen-containing oral contraceptives

May reduce contraceptive effectiveness.

MAOIs

The effects of mephobarbital may be prolonged.

Methoxyflurane

Risk of renal toxicity may be increased.

Phenytoin

May increase mephobarbital levels while phenytoin levels may increase or decrease.

Laboratory Test Interactions

Decreased serum bilirubin; false-positive phentolamine test results; decreased response to metyrapone.

Adverse Reactions

Cardiovascular

Bradycardia; hypotension; syncope.

CNS

Agitation; confusion; hyperkinesia; ataxia; CNS depression; nightmares; nervousness; psychiatric disturbance; hallucinations; insomnia; anxiety; dizziness; thinking abnormality; headache.

GI

Nausea; vomiting; constipation.

Hematologic

Megaloblastic anemia.

Hepatic

Liver damage.

Respiratory

Hypoventilation; apnea.

Miscellaneous

Hypersensitivity reactions including angioedema, skin rashes, exfoliative dermatitis; fever.

Precautions

Pregnancy

Category D .

Lactation

Excreted in breast milk.

Children

See Route/Dosage section.

Elderly

More sensitive to drug effects; dosage should be reduced.

Renal Function

Use with caution and in reduced dosage.

Hepatic Function

Use with caution and in reduced dosage.

Special Risk Patients

Use with caution in patients with a history of drug abuse who are mentally depressed or have suicidal tendencies, and those with myasthenia gravis, myxedema, or impaired cardiac or respiratory function.

Abrupt discontinuation

Status epilepticus may result from the abrupt discontinuation of mephobarbital, even when administered in small daily doses in the treatment of epilepsy.

Acute or chronic pain

Because paradoxical excitement may be induced, use with caution.

Debilitated patients

Increased sensitivity to drug effects; dosage should be reduced.

Dependence

May be habit forming; tolerance or psychological and physical dependence may occur with continued use.

Vitamin D deficiency

Mephobarbital may increase vitamin D requirements. Rarely, rickets and osteomalacia have been reported following prolonged use.

Vitamin K

Bleeding in the early neonatal period caused by coagulation defects may follow exposure to anticonvulsant drugs in utero; therefore, vitamin K should be given to the mother before delivery or to the child at birth.

Overdosage

Symptoms

CNS and respiratory depression, Cheyne-Stokes respiration, areflexia, constriction of pupils, oliguria, tachycardia, hypotension, lowered body temperature, coma, shock syndrome (including apnea, circulatory collapse, respiratory arrest, and death).

Patient Information

  • Advise patient or caregiver to read the patient information leaflet before starting therapy and with each refill.
  • Instruct patient with seizures to continue to take other medications for the condition unless advised otherwise by health care provider.
  • Advise patient with anxiety to take as needed and to seek alternative methods for controlling or preventing anxiety (eg, stress reduction, counseling).
  • Advise patient that medication is usually started at a low dose and then gradually increased as tolerated until max benefit is obtained.
  • Advise patient that medication may be habit forming, to take as prescribed, and not to stop taking or change the dose unless advised by health care provider.
  • Advise patient to take each dose without regard to meals but to take with food if stomach upset occurs.
  • Advise patient that if a dose is missed to skip that dose and take the next dose at the regularly scheduled time. Caution patient to never take 2 doses at the same time.
  • Advise patient that if medication needs to be discontinued, it will usually be slowly withdrawn over 2 wk or more unless safety concerns (eg, rash) require a more rapid withdrawal.
  • Instruct patient to avoid alcoholic beverages and other depressants while taking this medication.
  • Instruct patient with seizures to contact health care provider if seizures get worse, new types of seizures occur, or bothersome adverse reactions (eg, drowsiness, indigestion) occur.
  • Advise patient that drug may impair judgment, thinking, or motor skills, or cause drowsiness and to use caution while driving or performing other tasks requiring mental alertness until tolerance is determined.

Copyright © 2009 Wolters Kluwer Health.

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