Pharmacology Book

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Phenibut

Aka: Phenibut, Phenibut Toxicity, Anvifen, Fenibut, Noofen
  1. Background
    1. Categorized as a dietary supplement (and relatively unregulated in U.S.)
    2. Marketed to consumers in U.S. for anxiety, relaxation, and sleep
    3. Increased poison control related cases 2010-2019 (see MMWR reference below)
    4. Developed in Soviet Union in 1960s as an Anxiolytic and sleep aid
  2. Mechanism
    1. Similar to Baclofen in structure and activity
    2. GABA Agonist (primarily GABA-B)
      1. Sedation
      2. Hypothermia
    3. Beta-Phenylethylamine Antagonist
      1. Anxiolysis
    4. Dopamine increase
      1. Sedation
      2. Dystonic Reaction
  3. Pharmacokinetics
    1. Onset: 2-4 hours after oral dose
    2. Half-Life: 5.3 Hours
    3. Urinary excretion: 65%
  4. Dosing
    1. Typical: 250 mg orally once to three times daily
  5. Adverse Effects: Standard Doses
    1. Nausea and Vomiting
    2. Sedation
    3. Irritability or Agitation
    4. Dizziness
    5. Headache
  6. Adverse Effects: Toxicity (high dose or prolonged use)
    1. Agitated Delirium
    2. Seizures
    3. Respiratory depression
    4. Aspiration
    5. Agitated Withdrawal (prolonged use)
  7. Labs: Toxicity
    1. See Unknown Ingestion
    2. Altered Level of Consiousness
      1. Bedside Glucose
    3. Consider coningestion
      1. Acetaminophen Level
      2. Alcohol Level
      3. Urine Drug Screen
        1. May result in MethamphetamineFalse Positive
  8. Management: Toxicity
    1. See Unknown Ingestion
    2. Consider Activated Charcoal if intake within 1 hour of ingestion (in alert patient)
    3. Supportive Care
      1. Endotracheal Intubation and sedation if unprotected airway
      2. Benzodiazepines for Agitation or withdrawal
      3. Phenobarbital or Baclofen may also be used for withdrawal symptoms
        1. Baclofen is a derivative of Phenibut
    4. Disposition
      1. May discharge home if asymptomatic at 4 hours after ingestion
  9. Resources
    1. Phenibut (Wikipedia)
      1. https://en.wikipedia.org/wiki/Phenibut
  10. References
    1. Tomaszewski (2020) Crit Dec Emerg Med 34(1): 32
    2. Graves (2020) MMWR Morb Mortal Wkly Rep 69:1227-8 [PubMed]
      1. https://www.cdc.gov/mmwr/volumes/69/wr/mm6935a5.htm
    3. Winter (2001) CNS Drug Rev 7(4):471-81 [PubMed]

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