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Class: Sedative and hypnotic, barbiturate
- Tablets 32 mg
- Tablets 50 mg
- Tablets 100 mg
Depresses sensory cortex, decreases motor activity, alters cerebellar function, and produces drowsiness, sedation, and hypnosis.
Approximately 50% of an oral dose is absorbed from the GI tract.
Metabolized in the liver to phenobarbital. About 75% of the oral dose is converted to phenobarbital in 24 h.
The metabolite, phenobarbital, may be excreted unchanged in the urine or further metabolized and excreted in the urine as glucuronide or sulfate conjugates.
30 to 60 min after an oral dose.
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.
Manifest or latent porphyria; hypersensitivity to any barbiturate.
Dosage and AdministrationEpilepsy
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.
Store tablets at controlled room temperature (less than 77°F).
Drug InteractionsAlcohol, 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.
Bradycardia; hypotension; syncope.
Agitation; confusion; hyperkinesia; ataxia; CNS depression; nightmares; nervousness; psychiatric disturbance; hallucinations; insomnia; anxiety; dizziness; thinking abnormality; headache.
Nausea; vomiting; constipation.
Hypersensitivity reactions including angioedema, skin rashes, exfoliative dermatitis; fever.
Category D .
Excreted in breast milk.
See Route/Dosage section.
More sensitive to drug effects; dosage should be reduced.
Use with caution and in reduced dosage.
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.
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.
Increased sensitivity to drug effects; dosage should be reduced.
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.
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.
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).
- 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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