Pharm

Diphenhydramine

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Diphenhydramine, Benadryl

  • Indications
  • Dosing
  • Standard
  1. Adult: 25-50 mg PO/IV/IM q6h
  2. Child: 5 mg/kg/day divided qid (12.5 mg/5 ml)
  • Dosing
  • Local Injection
  1. Diphenhydramine may be used for local injection when patients are allergic to other Local Anesthesia
  2. Diphenhydramine 1% (for Local Anesthesia)
    1. Dilute Diphenhydramine 5% in Normal Saline (1:4)
    2. Longer delay to onset of action than Lidocaine
    3. Shorter duration of action than Lidocaine
  • Adverse Effects
  1. See Sedating Antihistamine
  2. Poisoning
    1. See Anticholinergic Toxicity
    2. Mild Overdose
      1. Causes sedation and muscarinic Anticholinergic Toxicity (Dry Mouth, Tachycardia, Mydriasis)
    3. Severe Overdose
      1. Causes Agitation, Delirium, Hallucinations, Seizures and coma
      2. Diphenhydramine blocks myocardial Sodium and Potassium channels (Wide QRS, QTc Prolongation)
      3. Diphenhydramine Overdose is responsible for >3% of U.S. Overdose deaths (within top 15 drugs)
    4. References
      1. Lacey and Dietrich (2023) Crit Dec Emerg Med 37(3): 18-9