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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.
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
EpilepsyAdults
PO 400 to 600 mg/day.
Children older than 5 yr of agePO 32 to 64 mg 3 or 4 times daily.
Children younger than 5 yr of agePO 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 depressantsMay enhance CNS depressant effects.
Anticoagulants (eg, warfarin), beta-blockers (eg, metoprolol), doxycycline, felodipine, griseofulvin, methadone, metronidazole, nifedipine, quinidine, theophyllines, verapamilActivity of these drugs may be reduced by mephobarbital.
AnticonvulsantsSerum levels of carbamazepine, valproic acid, and succinimides may be reduced. Valproic acid may increase mephobarbital levels.
Estrogens, estrogen-containing oral contraceptivesMay reduce contraceptive effectiveness.
MAOIsThe effects of mephobarbital may be prolonged.
MethoxyfluraneRisk of renal toxicity may be increased.
PhenytoinMay 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.
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Further information
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