What is the appropriate diphenhydramine (Benadryl) dose for a 15 kg child?

Diphenhydramine Dosing for a 15 kg Child

For a 15 kg child, administer diphenhydramine 15–30 mg per dose (using the standard 1–2 mg/kg dosing range), with a maximum single dose of 50 mg, given every 4–6 hours as needed. 1

Weight-Based Calculation

• The recommended pediatric dose is 1–2 mg/kg per dose for diphenhydramine in children. 1
• For a 15 kg child, this calculates to:
  • Lower end: 15 kg × 1 mg/kg = 15 mg
  • Upper end: 15 kg × 2 mg/kg = 30 mg
• The absolute maximum single dose is 50 mg regardless of weight, though this child's weight-based calculation does not approach this ceiling. 1

Practical Dosing Recommendation

• Start with 15–20 mg for mild allergic symptoms (urticaria, pruritus, mild allergic rhinitis). 1
• Use up to 30 mg for more significant reactions requiring stronger antihistamine effect, but always staying within the 1–2 mg/kg range. 1
• Doses may be repeated every 4–6 hours as needed, but no individual dose should exceed 50 mg. 1
• Dose rounding of up to 5% is acceptable for ease of home administration (e.g., rounding 28 mg to 30 mg). 1

Route and Formulation Considerations

• Oral liquid formulations are absorbed more rapidly than tablets and are preferred for acute allergic reactions in children. 1
• Onset of action is 20–30 minutes, with peak effect at 45–60 minutes and duration of 4–6 hours. 2

Critical Clinical Context: When Diphenhydramine is NOT First-Line

• Diphenhydramine must NEVER be used as monotherapy for anaphylaxis. 1, 2
• Epinephrine is the only first-line treatment for anaphylaxis; diphenhydramine serves only as adjunctive therapy after epinephrine administration. 1
• For a 15 kg child experiencing anaphylaxis:
  • First: Administer epinephrine 0.15 mg IM (using 0.15 mg autoinjector). 3
  • Second: After epinephrine, diphenhydramine 15–30 mg may be given as adjunctive therapy. 1
  • Consider adding ranitidine 1 mg/kg (15 mg for this child) for superior outcomes compared to diphenhydramine alone. 1

Safety Monitoring and Common Pitfalls

• Common adverse effects include sedation, dizziness, dry mouth, and urinary retention. 2
• Paradoxical excitation or agitation may occur, especially in younger children; monitor for these effects. 1, 2
• Never use diphenhydramine as a sleep aid or to "calm" a child—this is explicitly contraindicated. 4
• Avoid rapid IV administration if parenteral route is used, as this may precipitate seizures. 1
• Monitor for respiratory depression if used with other sedating agents (benzodiazepines, opioids). 2

Toxicity Threshold

• Children under 6 years who ingest ≥7.5 mg/kg (≥112.5 mg for a 15 kg child) should be referred to an emergency department for evaluation of potential toxicity. 5
• This threshold is well above therapeutic dosing and represents overdose concern, not routine administration.

Maximum Daily Dosing

• The maximum daily dose is 6 doses in 24 hours, not to exceed 300 mg daily for children in this age/weight range. 2
• For a 15 kg child receiving 30 mg per dose, this would allow up to 6 doses (180 mg total daily), well below the 300 mg ceiling.