What is the appropriate dose of diphenhydramine (Benadryl) 12.5 mg/5 mL oral solution for a 65‑lb (≈30 kg) child to be administered every 6 hours?

Diphenhydramine Dosing for a 65-lb Child

For a 65-lb (approximately 30 kg) child, administer 30–60 mg of diphenhydramine (12–24 mL of the 12.5 mg/5 mL solution) every 6 hours, not exceeding 50 mg per single dose. 1

Weight-Based Calculation

• The standard pediatric dosing range is 1–2 mg/kg per dose for diphenhydramine 2, 1
• For a 30 kg child:
  • Lower end: 30 kg × 1 mg/kg = 30 mg (12 mL of solution)
  • Upper end: 30 kg × 2 mg/kg = 60 mg (24 mL of solution)
• However, the maximum single dose is capped at 50 mg regardless of weight 2, 1
• Therefore, the practical dose range for this child is 30–50 mg (12–20 mL) 1

FDA-Approved Labeling Considerations

• The FDA label for over-the-counter diphenhydramine states "Do not use" for children under 6 years, but provides dosing for children 6 to under 12 years at 10 mL (25 mg) 3
• Clinical guidelines from the American Academy of Pediatrics and American Academy of Allergy, Asthma, and Immunology support weight-based dosing (1–2 mg/kg) when prescribed by a physician for appropriate indications such as acute allergic reactions, which supersedes the conservative OTC labeling 1

Dosing Frequency and Administration

• Administer every 6 hours as needed, not exceeding 6 doses in 24 hours 2, 3
• Oral liquid formulations are more readily absorbed than tablets when used for acute allergic reactions 2, 1
• For ease of home administration, the American Academy of Pediatrics permits dose rounding of up to 5% while maintaining safety 1

Clinical Context: When to Use Diphenhydramine

• Appropriate for mild allergic reactions such as flushing, urticaria, isolated mild angioedema, or oral allergy syndrome 1
• In anaphylaxis, diphenhydramine is adjunctive therapy only (never first-line) – epinephrine must be administered first 2, 1
• If symptoms progress or worsen after antihistamine administration, administer epinephrine immediately 1
• For anaphylaxis management after epinephrine, continue diphenhydramine every 6 hours for 2–3 days 2

Safety Considerations and Monitoring

• Monitor for sedation and respiratory suppression, especially if using other sedative agents concurrently 1
• Diphenhydramine may cause paradoxical excitation or agitation in some pediatric patients 1
• Children less than 6 years who ingest at least 7.5 mg/kg (225 mg for this 30 kg child) should be referred to an emergency department for toxicity evaluation 4
• Patients 6 years and older who ingest at least 7.5 mg/kg or 300 mg (whichever is less) should be referred to an emergency department 4

Enhanced Efficacy Strategy

• Combination therapy with ranitidine (1 mg/kg) is superior to diphenhydramine alone when managing anaphylaxis 1
• H1 antihistamines like diphenhydramine remain second-line to epinephrine in anaphylaxis management 1

Common Pitfall to Avoid

• Never rely on diphenhydramine alone for severe reactions involving respiratory symptoms, tongue/lip swelling, or widespread hives – these require epinephrine as first-line treatment 1
• Do not exceed the 50 mg maximum single dose even though weight-based calculation may suggest a higher dose 2, 1