What is the recommended dose of Benadryl (diphenhydramine) for a 4-year-old child weighing 38 pounds?

Diphenhydramine Dosing for a 4-Year-Old Child Weighing 38 Pounds

For a 4-year-old child weighing 38 pounds (approximately 17.3 kg), the recommended dose of diphenhydramine (Benadryl) is 12.5-25 mg orally every 4-6 hours, not to exceed 75 mg in 24 hours. 1

Dosing Calculation

• The FDA-approved diphenhydramine label clearly states that for children 6 to under 12 years of age, the dose is 10 mL (25 mg), while children under 6 years of age should not use the medication without physician direction 1
• When physician-directed, the standard pediatric diphenhydramine dosing for treatment purposes is 1-2 mg/kg/dose 2
• For this 17.3 kg child:
  • At 1 mg/kg: 17.3 mg (round to 12.5 mg or half of a 25 mg tablet/10 mL of liquid)
  • At 2 mg/kg: 34.6 mg (round to 25 mg or one 25 mg tablet/10 mL of liquid)

Administration Guidelines

• Diphenhydramine can be administered every 4-6 hours as needed 1
• Do not exceed 6 doses in 24 hours (75 mg total daily dose for this child) 1
• Available formulations for children include:
  • Liquid: 12.5 mg/5 mL
  • Chewable tablets: 12.5 mg
  • Regular tablets: 25 mg (can be split for 12.5 mg dose) 1

Important Considerations

• Diphenhydramine is considered second-line therapy for allergic reactions and should never be administered alone in the treatment of anaphylaxis 2
• For anaphylaxis, epinephrine is the first-line treatment, with diphenhydramine serving as adjunctive therapy 2
• Common side effects include drowsiness, which can affect school performance or activities requiring alertness 3
• Monitor for paradoxical excitation, which can occasionally occur in young children 2

Safety Thresholds

• Toxic dose threshold: Children who ingest ≥7.5 mg/kg of diphenhydramine should be referred to an emergency department 3
• For this 17.3 kg child, ingestion of more than 130 mg would warrant medical evaluation 3

Clinical Pearls

• When using liquid formulations, use a proper measuring device (not household spoons) to ensure accurate dosing 4
• Administer with food if stomach upset occurs 3
• Avoid use with other medications containing antihistamines to prevent overdosage 3
• The medication typically takes effect within 15-30 minutes and lasts 4-6 hours 3

Remember that diphenhydramine has sedative properties and should be used with caution in young children, particularly when driving or operating machinery is a concern for caregivers 3.