Phenobarbital

Pronunciation

Pronunciation: fee-no-BAR-bih-tahl
Class: Barbiturate, long-acting, Sedative and hypnotic Phenobarbital

Trade Names

Solfoton
- Tablets 16 mg
- Capsules 16 mg

Phenobarbital Sodium

Luminal Sodium
- Injection 130 mg/mL

PMS-Phenobarbital (Canada)

Pharmacology

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

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Pharmacokinetics

Absorption

The T max is 8 to 12 h (oral).

Distribution

Rapidly distributed to all tissues and fluids with high concentrations in the brain, liver, and kidneys. Lipid solubility plays a dominant factor in distribution. Protein binding is 20% to 45%.

Metabolism

Detoxified in liver by microsomal enzyme system.

Elimination

Eliminated in urine (25% to 50% as unchanged), and small amount in the feces. The t ½ plasma is 53 to 118 h (adults), 60 to 180 h (children).

Onset

Onset of action is 30 min.

Duration

Duration is 5 to 6 h (oral).

Indications and Usage

Short-term treatment of insomnia; long-term treatment of generalized tonic-clonic and cortical focal seizures; emergency control of acute convulsions; preanesthetic sedation.

Unlabeled Uses

Treatment of febrile seizures in children; treatment and prevention of hyperbilirubinemia in newborns; 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.

Dosage and Administration

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 (max, 600 mg per 24 h).

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. Max IV rate 60 mg/min. Max adult IM dose is 500 mg or 5 mL volume regardless of concentration.

General Advice

  • For oral administration, tablets may be crushed and mixed with fluid or food.
  • For IM administration, inject deeply into large muscle. Do not exceed max IM dose of 500 mg or 5 mL of volume (regardless of concentration).
  • For IV administration, inject into large vein. Do not exceed max IV rate of 60 mg/min; respiratory depression, apnea and hypotension may result.
  • Avoid inadvertent intra-arterial injection; arterial spasm, thrombosis, and gangrene may result.

Storage/Stability

Store at room temperature. Protect from light.

Drug 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.

Laboratory Test Interactions

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

Adverse Reactions

Cardiovascular

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.

Hematologic

Blood dyscrasias (eg, agranulocytosis, thrombocytopenia).

Hepatic

Liver damage.

Respiratory

Hypoventilation; apnea; laryngospasm; bronchospasm.

Miscellaneous

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.

Renal Function

Use drug with caution; dosage reduction may be required.

Hepatic Function

Use drug with caution; dosage reduction may be required.

Abuse

Administer drug with caution to patients with history of drug abuse.

Debilitated patients

Use drug with extreme caution.

Dependence

Tolerance or psychologic and physical dependence may occur with continued use.

Seizure disorders

Status epilepticus may result from abrupt discontinuation.

Overdosage

Symptoms

CNS and respiratory depression, Cheyne-Stokes respiration, areflexia, constriction of pupils, oliguria, tachycardia, hypotension, lowered body temperature, coma, shock syndrome, pneumonia, pulmonary edema, cardiac arrhythmias, CHF, renal failure.

Patient Information

  • 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 health care provider: 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 health care provider.

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