II. Indications
- Benzodiazepine Withdrawal
- Alcohol Withdrawal (second-line after Benzodiazepines)
- Status Epilepticus
- Seizure Prophylaxis
III. Pharmacology
- Mechanism
- GABA A Receptor Agonist
- See Barbiturates for more detalied mechanism description
-
Pharmacokinetics
- Half-Life: 53 to 140 hours (very long, self tapering in withdrawal)
- Onset (IV): 5 minutes
- Peak Effect (IV): 30 minutes
IV. Safety
V. Metabolism
- Liver Metabolism
- Renal Dosing: Decrease to twice daily for moderate to severe Renal Insufficiency
VI. Adverse Effects
- Serious
- Respiratory depression or apnea
- Intravenous dosing is higher risk for respiratory depression
- Avoid combining with Benzodiazepines or Opioids (see below)
- Withdrawal
- Avoid abruptly stopping
- Stevens-Johnson Syndrome
- Angioedema
- Suicidality
- Blood dyscrasias (Megaloblastic Anemia, Thrombocytopenia)
- Respiratory depression or apnea
- Common
- Somnolence
- Bradycardia
- Nausea or Vomiting
- Dizziness, Nystagmus or Ataxia
- Decreased cognitive function
VII. Drug Interactions
-
CNS Depressants (Benzodiazepines, Opioids)
- Risk of respiratory depression or apnea
VIII. Dosing: General
- Precautions
- Avoid IV infusion >60 mg/min
-
Status Epilepticus
- Phenobarbital 20-30 mg/kg IV (infusion rate <=100 mg/min)
- Repeat dosing at 10 mg/kg every 1 hour as needed for refractory Seizures
- Phenobarbital 20-30 mg/kg IV (infusion rate <=100 mg/min)
-
Epilepsy
- Phenobarbital 3 to 6 mg/kg/day divided 2-3 times daily, up to 50-100 mg orally twice to three times daily
IX. Dosing: Alcohol Withdrawal
-
General Dosing
- Phenobarbital 5-10 mg/kg IBW up to 130 to 260 mg every 20-30 minutes titrating to light sedation
-
Phenobarbital Single Agent Alcohol Withdrawal Protocol
- Indicated in Alcohol Withdrawal without use of Benzodiazepines or other CNS Depressants and neurologically intact
- Contraindicated with other CNS Depressants (e.g. Benzodiazepines)
- Protocol continued until patient is awake and calm
- IV Phenobarbital Load
- Phenobarbital 10 mg/kg Ideal Body Weight (IBW) over 30 minutes
- Wait 30 minutes before any additional Phenobarbital given
- IV Phenobarbital Titration
- Up to every 30 minutes give one of the 2 following doses as needed (no maximum, titrate to effect)
- Mild Symptoms: 130 mg IV over 3 minutes every 30 minutes as needed
- Severe symptoms 260 mg IV over 5 minutes every 30 minutes as needed
- Oral or IM Phenobarbital Maintenance (non-ED or ICU setting)
- Up to every 60 minutes give one of the 2 following doses as needed
- Mild Symptoms: 100 mg oral or IM every 60 minutes as needed
- Severe symptoms 200 mg oral or IM every 60 minutes as needed
- References
X. Resources
- Phenobarbital Tablet (DailyMed)
- Phenobarbital Injection (DailyMed)
XI. References
- (2020) Pharmacopeia, Tarascon, accessed on IOS 4/9/2021
- Cunningham and LoVecchio (2021) Crit Dec Emerg Med 35(4): 28
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