What is the recommended daily dose of diphenhydramine (Benadryl)?

Recommended Daily Dose of Diphenhydramine (Benadryl)

The standard oral dose of diphenhydramine for adults is 25-50 mg every 4-6 hours, with a maximum of 6 doses (300 mg) in 24 hours. 1, 2

Adult Dosing Guidelines

• For oral administration, adults should take 25-50 mg (10-20 mL of liquid formulation) every 4-6 hours as needed 1
• Maximum daily dose should not exceed 300 mg (6 doses) in a 24-hour period 1, 2
• For parenteral (IV/IM) administration in clinical settings, the standard dose remains 25-50 mg per dose 2
• When used as an adjunct for procedural sedation, 25-50 mg intravenously is the recommended dose 3

Pediatric Dosing Guidelines

• Children 6-12 years: 25 mg (10 mL) every 4-6 hours, not to exceed 6 doses in 24 hours 1
• Children under 6 years: Not recommended for use without physician supervision 1
• Weight-based dosing for children is 1-2 mg/kg per dose, with a maximum single dose of 50 mg 2, 4

Pharmacokinetic Considerations

• Diphenhydramine has an onset of action within minutes when given intravenously 3
• Duration of effect is 4-6 hours for most patients 3, 2
• Elimination half-life varies significantly by age:
  • Children: approximately 5.4 hours 5
  • Young adults: approximately 9.2 hours 5
  • Elderly adults: approximately 13.5 hours 5

Clinical Considerations and Precautions

• Hypnotic effects are increased when combined with alcohol, benzodiazepines, or opioid narcotics 3, 2
• Common adverse effects include:
  • Sedation/drowsiness (most common) 2, 6
  • Dizziness, blurred vision, dry mouth 3, 2
  • Hypotension (particularly with IV administration) 3
  • Urinary retention and wheezing (less common) 3, 2
• Somnolence occurs in approximately 22% of patients taking therapeutic doses 6
• Diphenhydramine has a modest stimulatory effect on ventilation and may counteract opioid-induced hypoventilation 3

Special Populations

• Elderly patients may require lower doses due to prolonged elimination half-life (13.5 hours vs 9.2 hours in younger adults) 5
• Children metabolize diphenhydramine more rapidly than adults, with an elimination half-life of approximately 5.4 hours 5
• Toxic dose thresholds:
  • Children <6 years: Ingestions ≥7.5 mg/kg require medical evaluation 7
  • Patients ≥6 years: Ingestions ≥7.5 mg/kg or ≥300 mg (whichever is less) require medical evaluation 7

Therapeutic Applications

• When used for allergic symptoms, diphenhydramine can be administered every 6 hours for 2-3 days 2
• For insomnia in psychiatric patients, doses of 12.5-50 mg have shown efficacy, with a dose-dependent increase in hypnotic effect 8
• As an adjunct to procedural sedation, diphenhydramine may allow for reduction in doses of other sedatives 2