Diphenhydramine

General

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

Adult Dosing

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

Pediatric Dosing

• Allergic Reaction
  • Oral/IM/IV: 5mg/kg/day divided q6-8h (1.25-1.67 mg/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: Category B
• Lactation: Enters breast milk
• Renal Dosing: n/a
• Hepatic Dosing: n/a

Contraindications

• Allergy to class/drug

Adverse Reactions

Serious

• CNS depression
• Anticholinergic sx

Common

• Sedation

Pharmacology

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

References

Lexicomp