What is the recommended dose and frequency of Benadryl (diphenhydramine)?

Benadryl (Diphenhydramine) Dosing and Frequency

For adults and children over 12 years, the standard dose is 25-50 mg (10-20 mL) every 4-6 hours, not exceeding 6 doses in 24 hours; for children 6 to under 12 years, give 25 mg (10 mL) every 4-6 hours. 1

Standard Dosing by Age

Adults and Children ≥12 Years

• Dose: 25-50 mg (10-20 mL) per dose 1
• Frequency: Every 4-6 hours 1
• Maximum: 6 doses in 24 hours 1

Children 6 to <12 Years

• Dose: 25 mg (10 mL) per dose 1
• Frequency: Every 4-6 hours 1
• Maximum: 6 doses in 24 hours 1

Children <6 Years

• Do not use without physician direction 1

Context-Specific Dosing

Acute Allergic Reactions (Outpatient/Emergency)

• Dose: 1-2 mg/kg per dose 2
• Maximum single dose: 50 mg 2
• Route: IV or oral (oral liquid absorbs better than tablets) 2
• Post-discharge: Continue every 6 hours for 2-3 days 2
• Alternative: Consider non-sedating second-generation antihistamines when sedation is problematic 2

Acute Dystonic Reactions

• Dose: 1-2 mg/kg 3
• Maximum initial dose: 50 mg 3
• Route: IV or IM 3
• Frequency: Every 4-6 hours as needed 3
• Critical warning: Rapid IV administration may precipitate seizures 3

Premedication (e.g., for immunosuppressive therapy)

• Pediatric dose: 1 mg/kg 2
• Given before agents like thymoglobulin, rituximab, or IVIg 2

Critical Dosing Considerations for Elderly Patients

Patients over 85 years require reduced doses due to heightened anticholinergic sensitivity and increased risk of delirium, cognitive impairment, and falls. 4, 3

• Strongly consider alternative non-sedating antihistamines instead 4
• If diphenhydramine must be used, reduce standard adult doses 4, 3
• Monitor closely for confusion, delirium, urinary retention, and falls 4, 3

Important Clinical Pitfalls

Inappropriate Uses to Avoid

• Do NOT use for insomnia: The American Academy of Sleep Medicine explicitly recommends against diphenhydramine for sleep disorders (only 8-minute reduction in sleep latency vs placebo, no quality improvement) 3
• For elderly insomnia, consider doxepin 3-6 mg instead 4, 3

Toxicity Thresholds

• Children <6 years: Refer to emergency department if ingestion ≥7.5 mg/kg 5
• Patients ≥6 years: Refer to emergency department if ingestion ≥7.5 mg/kg OR ≥300 mg (whichever is less) 5

Adverse Effects Requiring Monitoring

• CNS effects: Confusion, delirium (especially elderly), impaired psychomotor performance 4, 3
• Anticholinergic effects: Dry mouth, blurred vision, urinary retention, constipation 4, 3
• Cardiovascular effects: Hypotension, tachycardia, cardiac toxicity with rapid IV administration 3

Safer Alternatives

Second-generation antihistamines (cetirizine, fexofenadine, loratadine) provide equivalent efficacy with significantly less sedation and cognitive impairment, making them preferable for most indications. 6, 7

• Cetirizine has the fastest onset among newer antihistamines 7
• Fexofenadine causes no psychomotor or cognitive impairment 7
• Cost difference is minimal ($0.52-2.39 more per dose) 7
• Consider these alternatives particularly when sedation poses safety concerns (driving, operating machinery, elderly patients) 7