Phenobarbital

Aka: Phenobarbital

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II. Indications

  1. Benzodiazepine Withdrawal
  2. Alcohol Withdrawal (second-line after Benzodiazepines)
  3. Status Epilepticus
  4. Seizure Prophylaxis

III. Pharmacology

  1. Mechanism
    1. GABA A Receptor Agonist
    2. See Barbiturates for more detalied mechanism description
  2. Pharmacokinetics
    1. Half-Life: 53 to 140 hours (very long, self tapering in withdrawal)
    2. Onset (IV): 5 minutes
    3. Peak Effect (IV): 30 minutes

IV. Safety

  1. Pregnancy Category D
  2. Lactation: Not safe
  3. FDA Controlled Substance IV
  4. Therapeutic level: 15-40 mg/ml
  5. May be less addictive than Valium in outpatient withdrawal protocols

V. Metabolism

  1. Liver Metabolism
  2. Renal Dosing: Decrease to twice daily for moderate to severe Renal Insufficiency

VI. Adverse Effects

  1. Serious
    1. Respiratory depression or apnea
      1. Intravenous dosing is higher risk for respiratory depression
      2. Avoid combining with Benzodiazepines or Opioids (see below)
    2. Withdrawal
      1. Avoid abruptly stopping
    3. Stevens-Johnson Syndrome
    4. Angioedema
    5. Suicidality
    6. Blood dyscrasias (Megaloblastic Anemia, Thrombocytopenia)
  2. Common
    1. Somnolence
    2. Bradycardia
    3. Nausea or Vomiting
    4. Dizziness, Nystagmus or Ataxia
    5. Decreased cognitive function

VII. Drug Interactions

  1. CNS Depressants (Benzodiazepines, Opioids)
    1. Risk of respiratory depression or apnea

VIII. Dosing

  1. Precautions
    1. Avoid IV infusion >60 mg/min
  2. Status Epilepticus
    1. Phenobarbital 20-30 mg/kg IV (infusion rate <=100 mg/min)
      1. Repeat dosing at 10 mg/kg every 1 hour as needed
  3. Epilepsy
    1. Phenobarbital 3 to 6 mg/kg/day divided 2-3 times daily, up to 50-100 mg orally twice to three times daily
  4. Alcohol Withdrawal
    1. Phenobarbital 5-10 mg/kg IBW up to 130 to 260 mg every 20-30 minutes titrating to light sedation
    2. Nisavic (2019) Psychosomatics 60(5):458-67 [PubMed]
    3. Nelson (2019) Am J Emerg Med 37(4):733-6 [PubMed]
    4. Tidwell (2018) Am J Crit Care 27(6):454-60 [PubMed]

IX. References

  1. (2020) Pharmacopeia, Tarascon, accessed on IOS 4/9/2021
  2. Cunningham and LoVecchio (2021) Crit Dec Emerg Med 35(4): 28

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Cost: Medications

phenobarbital (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
PHENOBARBITAL 100 MG TABLET Generic $0.32 each
PHENOBARBITAL 15 MG TABLET Generic $0.18 each
PHENOBARBITAL 16.2 MG TABLET Generic $0.18 each
PHENOBARBITAL 20 MG/5 ML ELIX Generic $0.06 per ml
PHENOBARBITAL 20 MG/5 ML SOLN Generic $0.06 per ml
PHENOBARBITAL 30 MG TABLET Generic $0.19 each
PHENOBARBITAL 32.4 MG TABLET Generic $0.23 each
PHENOBARBITAL 60 MG TABLET Generic $0.27 each
PHENOBARBITAL 64.8 MG TABLET Generic $0.29 each
PHENOBARBITAL 97.2 MG TABLET Generic $0.38 each
FPNotebook does not benefit financially from showing this medication data or their pharmacy links. This information is provided only to help medical providers and their patients see relative costs. Insurance plans negotiate lower medication prices with suppliers. Prices shown here are out of pocket, non-negotiated rates. See Needy Meds for financial assistance information. GoodRx is another tool for finding lower drug prices.

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