What is the recommended dose of diphenhydramine (Benadryl) for a 27-pound child with an allergic reaction?

Diphenhydramine Dosing for a 27-Pound Child

For a 27-pound (12.3 kg) child with an allergic reaction, administer diphenhydramine 12-25 mg intramuscularly or orally as adjunctive therapy after epinephrine. 1, 2

Weight-Based Calculation

• 27 pounds = 12.3 kg
• Recommended dose: 1-2 mg/kg per dose 1, 2
• Calculated range: 12.3-24.6 mg (round to 12-25 mg) 1
• Maximum single dose: 50 mg (not applicable for this weight) 1, 2

Critical Treatment Algorithm

First-Line Treatment (ALWAYS)

• Epinephrine must be administered first for anaphylaxis 1, 2
• For a child weighing 10-25 kg: 0.15 mg epinephrine auto-injector IM (anterior-lateral thigh) 1
• Alternative: Epinephrine 1:1,000 solution at 0.01 mg/kg IM (0.12 mg for this child) 1

Second-Line Treatment (Adjunctive)

• Diphenhydramine 12-25 mg IM or oral 1, 2
• Oral liquid formulation is more rapidly absorbed than tablets 1
• Never administer diphenhydramine alone for anaphylaxis 1, 2

Additional Adjunctive Therapies

• H2-antihistamine (ranitidine): 12.5 mg IV (1 mg/kg) diluted in 5% dextrose over 5 minutes 1
• The combination of diphenhydramine plus ranitidine is superior to diphenhydramine alone 1, 2
• Albuterol nebulized 1.5 mL every 20 minutes if bronchospasm present 1

Administration Route Considerations

• Parenteral (IM) administration preferred for faster onset in acute reactions 2
• Onset of action: several minutes when given parenterally 2
• Duration of effect: 4-6 hours 2
• Oral liquid may be used for milder reactions but has slightly slower onset 1

Common Pitfalls to Avoid

• Never delay or substitute epinephrine with diphenhydramine for anaphylaxis 1, 2
• Diphenhydramine has a much slower onset of action than epinephrine 1
• Do not exceed 50 mg per dose even if calculating 2 mg/kg 1, 2
• Monitor for adverse effects including sedation, dizziness, and hypotension 2
• Avoid rapid IV administration which can cause significant adverse effects 3

Observation and Discharge Planning

• Observe for 2-4 hours minimum after symptom resolution for immediate-type reactions 1
• Prescribe two epinephrine auto-injectors (0.15 mg) at discharge 1
• Continue diphenhydramine every 6 hours for 2-3 days after discharge 1
• Consider adding ranitidine twice daily for 2-3 days 1
• Consider prednisone 0.5-1 mg/kg daily for 2-3 days to prevent biphasic reactions 1