Diphenhydramine Dosing for Infants
The recommended dose of diphenhydramine for infants is 1-2 mg/kg per dose, with a maximum single dose of 50 mg. 1
Dosing Guidelines for Infants
- Standard dosing: 1-2 mg/kg per dose 2, 1
- Maximum single dose: 50 mg 1
- Administration frequency: Every 6 hours as needed 1
Route of Administration Considerations
Parenteral Administration
- IV/IM route: 1-2 mg/kg (maximum initial dose: 50 mg) 2
- IV administration caution: Administer slowly to minimize hypotension risk 1
- IV route preferred: For emergency situations requiring rapid effect 1
Oral Administration
- Same dosing (1-2 mg/kg) but slower onset of action
- Less appropriate for acute severe reactions due to delayed onset 1
Safety Considerations
Monitoring Requirements
- Watch for sedation: Particularly important in infants 1
- Monitor for hypotension: Especially with parenteral administration 1
- Observe for paradoxical effects: May cause paradoxical excitement or agitation in infants rather than sedation 2, 3
Toxicity Thresholds
- Toxic threshold: Ingestions ≥7.5 mg/kg require emergency department referral 4, 5
- Fatal cases: Documented in infants with blood levels as low as 1.1-1.6 mg/L 3
Clinical Applications
Appropriate Indications
- Acute hypersensitivity reactions: Second-line after epinephrine 2, 1
- Urticaria and pruritus: For type I hypersensitivity reactions 1
Important Cautions
- Never as monotherapy for anaphylaxis: Always use after epinephrine 1
- Enhanced efficacy: Combination with H2 antagonists (e.g., ranitidine 1 mg/kg) is superior for anaphylaxis management 2, 1
- Avoid in very young infants: Fatal intoxications have been reported in infants as young as 6-12 weeks 3
Post-Treatment Considerations
- Duration of therapy: Continue diphenhydramine every 6 hours for 2-3 days after acute reactions 1
- Follow-up monitoring: Consider follow-up within 4-6 hours after administration to assess response and side effects 1, 4
Remember that diphenhydramine can cause serious adverse effects in infants, including CNS stimulation rather than sedation, which can range from excitation to seizures. The therapeutic window is narrower in infants compared to older children and adults 3.