Phenobarbital

A to Z Drug Facts

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

 Indications Short-term treatment of insomnia; long-term treatment of generalized tonic-clonic and cortical focal seizures; emergency control of acute convulsions; preanesthetic sedation. Unlabeled use(s): Treatment of febrile seizures in children; treatment and prevention of hyperbilirubinemia in neonates; management of chronic cholestasis.

 Contraindications Hypersensitivity to barbiturates; history of addiction to sedative/hypnotic drugs; history of porphyria; severe liver impairment; respiratory disease with dyspnea; nephritic patients.

 Route/Dosage

Insomnia

ADULTS: PO/IM/IV 100 to 320 mg.

Sedation

ADULTS: PO 30 to 120 mg/day in 2 to 3 divided doses.

Epilepsy

ADULTS: PO 60 to 250 mg/day.

Convulsions

ADULTS: IV 100 to 320 mg. Repeat if needed (maximum 600 mg/24 hr).

Status Epilepticus

ADULTS: IV 10 to 20 mg/kg. Repeat if needed. CHILDREN: IV 15 to 20 mg/kg over 10 to 15 min.

Preoperative Sedation

CHILDREN: PO/IM/IV 1 to 3 mg/kg.

Anticonvulsant

CHILDREN: IM/IV 4 to 6 mg/kg/day. For 10 days, then adjust to blood level. Alternatively, use IM/IV 10 to 15 mg/kg/day to reach therapeutic level more quickly. Maximum IV rate 60 mg/min. Maximum adult IM dose 500 mg or 5 ml volume regardless of concentration.

 Interactions

Alcohol, CNS depressants: May enhance CNS depressant effects. Anticoagulants (eg, warfarin), beta-blockers (eg, metoprolol, propranolol), doxycycline, metronidazole, quinidine, theophyllines, verapamil: Activity of these drugs may be reduced. Anticonvulsants: Serum concentrations of carbamazepine, valproic acid and succinimides may be reduced. Valproic acid may increase barbiturate serum levels. Corticosteroids: May reduce effectiveness of corticosteroids. Estrogens, estrogen-containing oral contraceptives: May reduce contraceptive effectiveness. Phenytoin: May increase phenobarbital levels while phenytoin levels may increase or decrease.

 Lab Test Interferences May cause decreased serum bilirubin concentrations; false-positive phentolamine test results; decreased response to metyrapone; impaired absorption of radioactive cyanocobalamin.

 Adverse Reactions

CV: Bradycardia; hypotension; syncope. CNS: Drowsiness; agitation; confusion; anxiety; headache; hyperkinesia; ataxia; CNS depression; paradoxical excitement; nightmares; psychiatric disturbances; hallucinations; insomnia; dizziness. GI: Nausea; vomiting; constipation. HEMA: Blood dyscrasias (eg, agranulocytosis, thrombocytopenia). HEPA: Liver damage. RESP: Hypoventilation; apnea; laryngospasm; bronchospasm. OTHER: Hypersensitivity reactions (eg, angioedema, rashes, exfoliative dermatitis); fever; injection site reactions (eg, local pain, thrombophlebitis).

 Precautions

Pregnancy: Category D. Lactation: Excreted in breast milk. Children: May respond with excitement rather than depression. Elderly: More sensitive to drug effects; dosage reduction is required. Debilitated patients: Use drug with extreme caution. Abuse: Administer drug with caution to patients with history of drug abuse. Dependence: Tolerance or psychologic and physical dependence may occur with continued use. Renal or hepatic impairment: Use drug with caution; dosage reduction may be required. Seizure disorders: Status epilepticus may result from abrupt discontinuation.

 Administration/Storage

• For oral administration, tablets may be crushed and mixed with fluid or food.
• For IM administration, inject deeply into large muscle. Do not exceed maximum IM dose of 500 mg or 5 ml of volume (regardless of concentration).
• For IV administration, inject into large vein. Do not exceed maximum IV rate of 60 mg/min; respiratory depression, apnea and hypotension may result.
• Do not base IV administration on response as there may be > 15-min delay in peak concentrations in brain.
• Avoid inadvertent intra-arterial injection; arterial spasm, thrombosis, and gangrene may result.
• Do not use as sleeping aid for > 2 wk.
• Store at room temperature. Protect from light.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies. Evaluate for history of substance abuse, liver disease, respiratory disease and porphyria.
• Monitor vital signs of patient undergoing IV administration at least every hour if indicated. Keep resuscitation equipment and drugs readily available.
• After IM administration (1 g dose), observe patient closely for ³ 30 min to ensure that necrosis is not excessive.
• Observe for common side effects such as sedation and dizziness and, if excessive, report to physician. Institute safety precautions for elderly patients to prevent accidental falls.
• In children, monitor for possible paradoxical response of increased agitation and notify physician.
• Be alert for evidence of barbiturate intoxication (eg, unsteady gait, slurred speech, confusion, irritability) and report to physician.
• Watch for behavior indicative of drug dependence such as inordinate requests for more medication or need to refill prescription early.
• With prolonged therapy monitor lab tests for liver, renal, and hematopoietic functions.

 Patient/Family Education

• Advise patient to increase intake of vitamin D-fortified foods (eg, milk products) while taking this medication.
• Explain the following importances of maintaining adequate intake of folic acid: Fresh vegetables, fruits, whole grains, liver.
• Instruct patient to report the following symptoms to physician: Nausea, vomiting, drowsiness, dizziness, fever, sore throat, mouth sores or easy bleeding or bruising.
• Caution patient to avoid intake of alcoholic beverages or other CNS depressants.
• Warn patient that medication may be habit forming, and for that reason, it is important to take medicine as directed.
• Advise patient that drug may cause drowsiness, and to use caution while driving or performing other tasks requiring mental alertness.
• Instruct patient not to stop taking medication abruptly without consulting physician.

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Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts