Diphenhydramine Dosing in Pediatric Patients
The recommended dose of diphenhydramine for pediatric patients is 1-2 mg/kg/dose, with a maximum of 50 mg per dose, administered every 4-6 hours as needed. 1
Age-Based Dosing Guidelines
Diphenhydramine dosing should follow these specific parameters:
- Children under 6 years: Do not use unless specifically directed by a physician 2
- Children 6 to under 12 years: 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
When more precise dosing is required, particularly in a hospital setting:
- All pediatric patients: 1-2 mg/kg/dose 1
- Maximum single dose: 50 mg 1, 2
- Maximum daily dose: Do not exceed 6 doses in 24 hours 2
Route of Administration Considerations
- Oral administration: Preferred for outpatient management; liquid formulation is more readily absorbed than tablets 1
- Parenteral administration: For emergency situations (such as anaphylaxis), diphenhydramine can be administered at 1-2 mg/kg IV or IM 1
Safety Considerations
Toxicity Thresholds
- Ingestions ≥7.5 mg/kg in children under 6 years warrant emergency department referral 3, 4
- In children 6 years and older, ingestions ≥7.5 mg/kg or ≥300 mg (whichever is less) require emergency department evaluation 3
Monitoring
- Common side effects include drowsiness (most common), paradoxical excitation, and anticholinergic effects 1
- Monitor for respiratory depression, especially when combined with other sedating medications 1
- Be aware that diphenhydramine has a high therapeutic index but can cause significant toxicity at higher doses 3
Special Populations
- Infants under 2 years: Not recommended unless specifically prescribed by a physician with careful monitoring 2
- Patients with developmental disabilities: May be at higher risk for paradoxical behavioral disinhibition 1
Clinical Pearls
- Diphenhydramine is considered a second-line therapy for anaphylaxis (after epinephrine) and should never be administered alone for this indication 1
- For allergic reactions, the combination of diphenhydramine and ranitidine (H2 blocker) is superior to diphenhydramine alone 1
- Liquid formulations are preferred over tablets for pediatric patients due to better absorption and ease of administration 1
- Avoid using diphenhydramine in very young children (under 6 years) without medical supervision due to risk of respiratory depression and paradoxical excitation 2
Remember that while weight-based dosing (1-2 mg/kg) provides more precise dosing, the FDA-approved labeling provides simplified age-based dosing for over-the-counter use, which should be followed in outpatient settings.