Diphenhydramine Dosing for Children
The recommended dose of diphenhydramine for children is 1-2 mg/kg per dose with a maximum single dose of 50 mg, administered every 4-6 hours as needed. 1
Age-Based Dosing Guidelines
- Children under 6 years of age: Do not use over-the-counter diphenhydramine without medical supervision 2
- Children 6 to under 12 years of age: 10 mL (25 mg) every 4-6 hours 2
- Children 12 years and older: 10-20 mL (25-50 mg) every 4-6 hours 2
Weight-Based Dosing (for medical use)
- For all pediatric patients: 1-2 mg/kg per dose 1
- Maximum single dose: 50 mg regardless of weight 1
- Maximum daily dose: Do not exceed 6 doses in 24 hours 2
Route of Administration Considerations
- Oral liquid is more readily absorbed than tablets in children 3
- IV administration is preferred in emergency situations for rapid effect 1
- IM administration is an alternative when IV access is unavailable 1
Clinical Pearls and Cautions
- Diphenhydramine is only recommended as a second-line treatment for acute hypersensitivity reactions, after epinephrine 1
- For anaphylaxis management, combining diphenhydramine with H2 antagonists (e.g., ranitidine 1 mg/kg) provides enhanced efficacy 1
- Children metabolize diphenhydramine more rapidly than adults, with a shorter half-life (5.4 hours in children vs. 9.2 hours in young adults) 4
- Monitor closely for common side effects including sedation/drowsiness, anticholinergic effects, hypotension, and dizziness 1
- Paradoxical excitation rather than sedation may occur in some children 1
Toxicity Thresholds
- Children less than 6 years of age who ingest at least 7.5 mg/kg should be referred to an emergency department 5
- Children 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 5
Practical Administration Tips
- Administer IV doses slowly to minimize the risk of hypotension 1
- For allergic reactions, continue diphenhydramine every 6 hours for 2-3 days after the initial event 1
- Consider alternative dosing with non-sedating second-generation antihistamines for longer-term management 1
Remember that children are not simply "small adults" when it comes to medication dosing, as they have different pharmacokinetic parameters that affect drug metabolism and clearance 6, 7.