What is the dose of diphenhydramine (Benadryl) for pediatric (peds) patients with allergies?

Diphenhydramine IM Dosing for Pediatric Allergic Reactions

For pediatric patients with allergic reactions, diphenhydramine should be administered at a dose of 1-2 mg/kg per dose intramuscularly, with a maximum single dose of 50 mg. 1

Dosing Guidelines

• The recommended intramuscular (IM) dose of diphenhydramine for pediatric patients with allergic reactions is 1-2 mg/kg per dose 2
• Maximum dose should not exceed 50 mg per single administration, regardless of weight 1
• Diphenhydramine is considered a second-line therapy after epinephrine in anaphylaxis management and should never be administered alone in anaphylactic reactions 1

Age-Specific Considerations

• Children under 6 years of age: Weight-based dosing of 1-2 mg/kg IM is recommended 1
• Children 6 to 12 years of age: Weight-based dosing of 1-2 mg/kg IM is recommended, not exceeding 50 mg 1
• Children over 12 years of age: May receive adult dosing of 25-50 mg IM 1, 3

Administration Considerations

• Parenteral administration provides faster onset of action (within minutes) compared to oral administration in acute allergic reactions 1
• Duration of effect is typically 4-6 hours 1
• For outpatient management following acute treatment, diphenhydramine can be administered every 6 hours for 2-3 days 2

Important Clinical Considerations

• Diphenhydramine should never replace epinephrine as first-line treatment for anaphylaxis 1, 4
• Consider adding an H2-antagonist (such as ranitidine at 1-2 mg/kg, maximum 75-150 mg) as the combination is superior to diphenhydramine alone for urticaria 2, 1
• Monitor for adverse effects including sedation, dizziness, blurred vision, dry mouth, hypotension, and urinary retention 1, 5
• Use with caution in infants, as there have been reports of serious adverse effects including cardiac arrest with IV administration 5

Safety Considerations and Pitfalls

• Avoid exceeding recommended doses, as diphenhydramine toxicity can lead to serious anticholinergic effects 4
• Children who ingest at least 7.5 mg/kg of diphenhydramine should be referred to an emergency department for evaluation 4
• Sedative effects may be increased when combined with other CNS depressants 1
• Pharmacokinetics in pediatric patients differ from adults, requiring careful weight-based dosing rather than simple downscaling of adult doses 6, 7

Treatment Algorithm for Allergic Reactions in Pediatric Patients

1. For anaphylaxis: Administer epinephrine as first-line treatment 1
2. Administer diphenhydramine 1-2 mg/kg IM (max 50 mg) as adjunctive therapy 2, 1
3. Consider adding H2-antagonist (ranitidine 1-2 mg/kg) 2
4. For severe reactions, administer corticosteroids to prevent protracted or biphasic reactions 1
5. Monitor patient for at least 4-6 hours after administration 1, 4