Phenobarbital


Concise Prescribing Info
Indications/Uses
Listed in Dosage.
Dosage/Direction for Use
Adult : PO Sedation 30-120 mg/day in 2-3 divided doses. Hypnotic 100-320 mg. Do not admin for >2 wk for the treatment of insomnia. Status epilepticus; Emergency management of acute seizures 100-300 mg/day at bedtime. IM Pre-op sedation As phenobarbital Na: 100-200 mg 60-90 min pre-op. IM/IV Hypnotic 100-320 mg. Do not admin for >2 wk for the treatment of insomnia. Status epilepticus; Emergency management of acute seizures As phenobarbital Na: 200-600 mg.
Dosage Details
Intramuscular
Preoperative sedation
Adult: As phenobarbital Na: 100-200 mg 60-90 min pre-op.
Child: As phenobarbital Na: 16-100 mg 60-90 min pre-op.
Elderly: Reduce dose.

Intravenous
Preoperative sedation
Child: 1-3 mg/kg pre-op.

Oral
Emergency management of acute seizures, Status epilepticus
Adult: 100-300 mg daily at bedtime.
Child: 3-5 mg/kg or 125 mg/m2 daily.
Elderly: Reduce dose.

Oral
Hypnotic
Adult: 100-320 mg. Do not admin for >2 wk for the treatment of insomnia.
Elderly: Reduce dose.

Oral
Preoperative sedation
Child: 1-3 mg/kg pre-op.

Oral
Sedation
Adult: 30-120 mg daily in 2-3 divided doses.
Child: 6 mg/kg daily or 180 mg/m2 daily in 3 divided doses.
Elderly: Reduce dose.

Parenteral
Hypnotic
Adult: 100-320 mg. Do not admin for >2 wk for the treatment of insomnia.
Elderly: Reduce dose.

Parenteral
Emergency management of acute seizures, Status epilepticus
Adult: As phenobarbital Na: 200-600 mg.
Child: As phenobarbital Na: 100-400 mg.
Elderly: Reduce dose.
Special Patient Group
Debilitated patient: Reduce dose.
Renal Impairment
Reduce dose. Severe: Contraindicated.
Hepatic Impairment
Reduce dose. Severe: Contraindicated.
Administration
May be taken with or without food.
Reconstitution
Dilute w/ most IV infusion soln (e.g. NaCl 0.45% or 0.9%, lactated Ringer's, dextrose 5%, Ringer's).
Incompatibility
Y-site: Pantoprazole, amphotericin B cholesteryl sulfate complex. Syringe: Ranitidine, hydromorphone, sufentanil.
Contraindications
Severe resp depression, acute intermittent porphyria. Severe renal and hepatic impairment. Intra-arterial and SC admin.
Special Precautions
Patient w/ history or sedative/hypnotic addiction; resp disease, depression or suicidal tendencies, hypoadrenalism. Avoid abrupt withdrawal. Mild to moderate renal and hepatic impairment. Elderly or debilitated patient, childn. Pregnancy and lactation.
Adverse Reactions
Bradycardia, syncope, hypotension; anxiety, agitation, ataxia, CNS excitation or depression, confusion, dizziness, drowsiness, hallucinations, hangover effect, headache, hyperkinesias; constipation, nausea, vomiting; agranulocytosis, thrombocytopenia, megaloblastic anaemia; oliguria; pain at inj site, thrombophlebitis (w/ IV use); laryngospasm, resp depression, apnoea (esp w/ rapid IV use), hypoventilation; gangrene (w/ unintentional intra-arterial inj).
Potentially Fatal: Stevens-Johnson syndrome, toxic epidermal necrolysis.
IM/IV/Parenteral/PO: D
Patient Counseling Information
May impair ability to drive or operate machinery.
MonitoringParameters
Monitor CBC, LFTs, mental status and seizure activity.
Overdosage
Symptoms: Drowsiness, dysarthria, ataxia, nystagmus, disinhibition, hypotension, hypotonia, hyporeflexia, hypothermia, absent bowel sounds, cardiac arrest, resp and CV depression, shock leading to renal failure, prolonged coma. Management: Symptomatic and supportive treatment. Admin activated charcoal w/in 1 hr prior to ingestion. Maintain adequate airway. Admin dopamine or dobutamine in severe hypotension. Perform haemodialysis or charcoal haemoperfusion in renal failure.
Drug Interactions
May reduce plasma levels of oral anticoagulants (e.g. warfarin, dicoumarol, acenocoumarol, phenprocoumon), corticosteroids, griseofulvin, doxycycline, Na valproate and valproic acid. May increase CNS depressant effect w/ phenytoin, antihistamines, sedative/hypnotics, tranquilisers. May prolong the effect w/ MAOIs. May reduce the effect of estradiol, progesterone, estrone and other steroidal hormones.
Food Interaction
May enhance CNS depressant effect of alcohol. May reduce the effect w/ St John's wort.
Lab Interference
May interfere w/ the results of metyrapone test, serum bilirubin estimation and phenlolamine test.
Action
Description: Phenobarbital is a long-acting barbiturate. It depresses the sensory cortex, reduces motor activity, changes cerebellar function and produces drowsiness, sedation and hypnosis. Its anticonvulsant property is exhibited at high doses.
Onset: Hypnosis: 20-60 min (oral); approx 5 min (IV).
Duration: 6-10 hr (oral); 4-10 hr (IV).
Pharmacokinetics:
Absorption: Readily absorbed from the GI tract. Time to peak plasma concentration: Approx 2 hr (oral); w/in 4 hr (IM).
Distribution: Crosses the placenta; enters breast milk. Plasma protein binding: Approx 45-60%.
Metabolism: Undergoes partial hepatic metabolism via hydroxylation and glucuronide conjugation.
Excretion: Via urine (approx 25% as unchanged drug). Plasma half-life: Approx 75-120 hr.
Chemical Structure

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Storage
Store between 20-25°C.
ATC Classification
N03AA02 - phenobarbital ; Belongs to the class of barbiturates and derivatives antiepileptics.
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