Pediatric Antihistamine (Diphenhydramine) Dosing Guidelines
The recommended dose of diphenhydramine for pediatric patients is 1-2 mg/kg per dose (maximum 50 mg per dose), with age-specific dosing of 25 mg for children 6-12 years and 25-50 mg for children over 12 years, administered every 4-6 hours as needed. 1, 2
Age-Based Dosing Recommendations
- For children under 6 years of age: Diphenhydramine is not recommended according to FDA labeling 2
- For children 6 to under 12 years of age: 10 mL (25 mg) every 4-6 hours 2
- For children 12 years and older: 10-20 mL (25-50 mg) every 4-6 hours 2
- Maximum dosing frequency: Do not exceed 6 doses in 24 hours 2
- Weight-based dosing (when applicable): 1-2 mg/kg per dose, not exceeding 50 mg maximum single dose 1, 3
Administration Considerations
- Oral liquid formulations are more readily absorbed than tablets when used for acute allergic reactions 1
- Duration of effect is typically 4-6 hours 3
- For severe reactions requiring faster onset, parenteral (IM/IV) administration may be considered at the same dosage (1-2 mg/kg, maximum 50 mg) 1, 3
- When administered IV, diphenhydramine should be given slowly to prevent potential seizures 1
Clinical Applications
- Diphenhydramine is effective for treating allergic conditions including urticaria, rhinitis, and as adjunctive therapy for anaphylaxis 1, 3, 4
- For anaphylaxis management, diphenhydramine should always be considered second-line therapy to epinephrine and should never be administered alone 1, 3
- For persistent allergic symptoms, combination therapy with H1 (diphenhydramine) and H2 antagonists (e.g., ranitidine at 1-2 mg/kg) may be more effective than diphenhydramine alone 3
Important Precautions
- Monitor for sedation, which occurs in more than 50% of patients receiving therapeutic doses 5
- First-generation antihistamines like diphenhydramine may adversely affect a child's learning ability due to sedative effects 5
- May cause paradoxical excitation or agitation in some pediatric patients 1
- Reduce dose by 50% in patients with renal impairment 1
- Use caution when combining with other sedative medications due to potential for respiratory suppression 1
Special Considerations
- For infants and young children (when use is necessary despite FDA labeling), the lower end of the dosing range (1 mg/kg) is recommended 1
- Second-generation (non-sedating) antihistamines may be preferable for ongoing management of chronic allergic conditions to avoid sedation 3, 4, 5
- Pediatric dosing cannot simply be scaled down from adult doses based solely on weight, as drug elimination does not change in direct proportion to weight 6