Diphenhydramine

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General

  • Type: Antihistamines / H1 blocker
  • Dosage Forms: Oral, IM, IV
  • Common Trade Names: Benadryl

Adult Dosing

  • Allergic reaction
    • Oral: 25-50mg q4-8h, max 300mg/day
    • IM/IV: 10-50mg/dose
  • Parkinsonian symptoms
    • Oral: 25-50mg tid-QID
    • IM/IV: 10-50mg/dose
  • Insomnia: 50mg PO qhs

Pediatric Dosing

  • Allergic reaction
    • Oral/IM/IV: 5mg/kg/day divided q6-8h (1.25-1.67mg/kg/dose)
    • Alternate PO dosing
      • 2-6 yo: 6.25mg q4-6h
      • 6-12 yo: 12-25mg q4-6h
      • >12 yo: Adult dosing

Special Populations

  • Pregnancy Rating: B
  • Lactation Risk: Enters breast milk
  • Renal Dosing: n/a
  • Hepatic Dosing: n/a

Contraindications

  • Allergy to class/drug

Adverse Reactions

Serious

Common

  • Sedation

Overdose related

  • Opsoclonus - conjugate irregular and nonrhythmical jerking movements of the eyes was reported in a 20-year-old woman who had ingested 5 grams[1]

Pharmacology

  • Half-life: Children 5 hours, Adults 9 hours, Elderly 13.5 hours
  • Metabolism: Hepatic
  • Excretion: Urine
  • Mechanism of Action: Antihistamines / H1 blocker

See Also

References

  1. NEJM. http://www.nejm.org/action/showMediaPlayer?doi=10.1056%2FNEJMicm1002035&aid=NEJMicm1002035_attach_1&area=&