MEPHOBARBITAL

MEPHOBARBITAL
(me-foe-bar'bi-tal)
Mebaral, Methylphenobarbital
Classifications: anticonvulsant; barbiturate; sedative-hypnotic;
Therapeutic: anticonvulsant; sedative-hypnotic

Prototype: Phenobarbital
Pregnancy Category: D
Controlled Substance: Schedule IV

Availability

32 mg, 50 mg, 100 mg tablets

Action

Long-acting barbiturate that limits the spread of seizure activity by increasing the threshold for motor cortex stimuli. Exerts strong sedative effect, but relatively mild hypnotic effect.

Therapeutic Effect

Reduces seizure activity by decreasing excitability in nerve cells. Depresses CNS producing drowiness, hypnosis, and sedation.

Uses

To control grand mal and petit mal epilepsy, alone or in combination with other anticonvulsant agents, and for sedative effect in management of delirium tremens and other acute agitation and anxiety states.

Contraindications

Hypersensitivity to barbiturates; coma; ethanol intoxication hepatic encephalopathy; porphyria; status epilepticus; pregnancy (category D).

Cautious Use

Fever, hyperthyroidism, alcoholism; respiratory disorders, COPD, sleep apnea; mental status changes, major depression; suicidal ideation; liver, kidney, or cardiac dysfunction; lactation.

Route & Dosage

Anticonvulsant
Adult: PO 400–600 mg/d in divided doses
Child: PO5 y, 16–32 mg t.i.d. or q.i.d.; ≥5 y, 32–64 mg t.i.d. or q.i.d.

Sedative
Adult: PO 32–100 mg t.i.d. or q.i.d.
Child: PO5 y, 16–32 mg t.i.d. or q.i.d.; ≥5 y, 32–64 mg t.i.d. or q.i.d.

Delirium Tremens
Adult: PO 200 mg t.i.d. or q.i.d.

Administration

Oral
  • Change from other anticonvulsant by gradually tapering off the former as mephobarbital doses are increased to maintain seizure control.
  • When prescribed concurrently with phenobarbital, dose should be about one-half the amount of each used alone. When prescribed concurrently with phenytoin, the dose of phenytoin is usually reduced.
  • Reduce discontinued drug dosage gradually over 4 or 5 d to avoid precipitating seizures of status epilepticus.

Adverse Effects (≥1%)

CNS: Drowsiness, dizziness, unsteadiness, hangover, paradoxical excitement. GI: Nausea, vomiting, constipation. Body as a Whole: Hypersensitivity reactions, respiratory depression.

Interactions

Drug: Alcohol, cns depressants compound CNS depression; may decrease absorption and increase metabolism of oral anticoagulants; increases metabolism of corticosteroids, oral contraceptives, anticonvulsants, digitoxin, possibly decreasing their effects; antidepressants potentiate adverse effects; griseofulvin decreases absorption of mephobarbitol. Herbal: Kava, valerian may potentiate sedation.

Pharmacokinetics

Absorption: 50% from GI tract. Onset: 60 min. Duration: 10–12 h. Metabolism: In liver to phenobarbital. Elimination: In urine. Alkalinization of urine or increase of urinary flow significantly increases the rate of phenobarbital excretion. Half-Life: 34 h.

Nursing Implications

Assessment & Drug Effects

  • Monitor respiratory status, especially with concurrent CNS therapy with other drugs.
  • Be prepared for paradoxical response to barbiturate therapy (i.e., irritability, marked excitement, aggression in children, depression, confusion) in older adults, debilitated patients, or children.

Patient & Family Education

  • Be aware that abrupt cessation after prolonged therapy may result in withdrawal symptoms (tremulousness, weakness, insomnia, delirium, convulsions).
  • Avoid driving and potentially hazardous activities until response to drug has stabilized.
  • Do not take alcohol in any amount with a barbiturate.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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