What are the uses of Phenobarbitone (phenobarbital)?

Uses of Phenobarbital (Phenobarbitone)

Phenobarbital is primarily indicated for seizure management, particularly status epilepticus, and can also be used as a sedative, hypnotic, and preanesthetic agent in specific clinical scenarios.

Primary Uses

1. Seizure Management

• Status Epilepticus

  • Effective for emergency control of status epilepticus with a success rate comparable to lorazepam, phenytoin, and phenytoin plus diazepam 1
  • Recommended dose: 10-20 mg/kg IV with a 58% success rate 2
  • Can be administered when patients continue to seize after receiving a benzodiazepine and phenytoin 1
  • Maintenance dose: 1-3 mg/kg IV every 12 hours 2

• Long-term Anticonvulsant

  • For treatment of generalized tonic-clonic and cortical focal seizures 3
  • Not recommended as a first-line agent due to adverse effect profile and drug interactions 2

• Acute Convulsive Episodes

  • Emergency control of acute convulsive episodes associated with:
    • Status epilepticus
    • Cholera
    • Eclampsia
    • Cerebral hemorrhage
    • Meningitis
    • Tetanus
    • Toxic reactions to strychnine or local anesthetics 3

2. Sedation

• Parenteral Sedative

  • Provides sedation within an hour with duration of action exceeding six hours 3
  • Useful for:
    • Anxiety-tension states
    • Hyperthyroidism
    • Essential hypertension
    • Nausea and vomiting of functional origin
    • Motion sickness
    • Acute labyrinthitis
    • Pylorospasm in infants
    • Chorea
    • Cardiac failure 3

• Pediatric Sedation

  • Used for procedural sedation in children, particularly for diagnostic imaging studies 1
  • Effective for sedating children undergoing CT and MRI scans 1
  • Dosage: 2-6 mg/kg IV or 4 mg/kg orally 1

3. Other Uses

• Hypnotic

  • Short-term treatment of insomnia (effectiveness diminishes after 2 weeks) 3

• Preanesthetic

  • Used before and after surgery 3

• Adjunctive Treatment

  • Useful in hemorrhage from respiratory or gastrointestinal tract 3

Administration and Dosing

Status Epilepticus

• Loading dose: 10-20 mg/kg IV 2
• Can be administered intramuscularly or intravenously for emergency use 3
• May require 15+ minutes to reach peak brain concentrations when given IV 3
• Nonresponders should receive additional doses of 5-10 mg/kg until seizures stop 4

Pediatric Dosing

• Neonates and infants: Loading dose of 20 mg/kg IV; maintenance dose of 3-4 mg/kg orally 4
• Children for procedural sedation: 2-6 mg/kg IV or 4 mg/kg orally 1

Pharmacokinetics

• Half-life: 100 hours in adults, 103 hours in term infants, 141 hours in preterm infants 4
• In infants, half-life decreases by 4.6 hours per day, reaching 67 hours at 4 weeks of age 4
• Metabolized in liver primarily by CYP2C9, with minor metabolism by CYP2C19 and CYP2E1 4
• 25% excreted unchanged in urine 4

Adverse Effects and Precautions

Major Concerns

• Respiratory depression and hypotension from vasodilatory and cardiodepressant effects 1
• Adverse reaction rate of approximately 1.6% when used for pediatric procedural sedation 1
• Prolonged sedation and recovery time compared to alternatives like propofol 1

Special Populations

• Thyrotoxic individuals may react poorly to barbiturates 3
• Caution in patients with cardiac conditions, liver disease, renal impairment 2

Comparative Efficacy

Status Epilepticus

• Comparable efficacy to lorazepam, phenytoin, and phenytoin plus diazepam 1
• In one study, status epilepticus duration was shorter with phenobarbital than with diazepam plus phenytoin 1
• 61% of phenobarbital patients did not require additional phenytoin to terminate status epilepticus 1

Pediatric Sedation

• 99% success rate for procedural sedation in children 1
• Similar efficacy to chloral hydrate for pediatric procedural sedation 1
• Superior to midazolam (97% vs 19% success rate) for sedation during CT imaging 1

Important Considerations

• When injecting for seizure control, avoid administering until convulsions stop as this may cause excessive brain levels leading to severe barbiturate-induced depression 3
• Not recommended as first-line agent for epilepsy due to adverse effect profile and drug interactions 2
• Serum concentration should be up to 40 μg/ml, but may reach 100 μg/ml in infants with refractory seizures 4