What is the recommended pediatric dose of injectable Avil (diphenhydramine) for children, including infants?

Pediatric Injectable Diphenhydramine (Avil) Dosing

Critical Safety Warning: Avoid in Young Children

Injectable diphenhydramine should NOT be used routinely in children under 6 years of age due to significant mortality risk, with 33 deaths attributed to diphenhydramine in this age group between 1969-2006. 1

• The FDA and Pediatric Advisory Committees explicitly recommend against using first-generation antihistamines (including diphenhydramine) in children below 6 years of age for routine allergic symptoms. 1
• Between 1969-2006, there were 69 total antihistamine-related deaths in children under 6 years, with diphenhydramine responsible for 33 of these fatalities. 1

FDA-Approved Dosing (When Medically Necessary)

For children (excluding premature infants and neonates), the FDA-approved dose is 5 mg/kg/24 hours or 150 mg/m²/24 hours, divided into four doses, with a maximum daily dosage of 300 mg. 2

Practical Dosing Calculation:

• Per-dose calculation: 1.25 mg/kg per dose (since 5 mg/kg/24 hr ÷ 4 doses = 1.25 mg/kg/dose) 2
• Maximum single dose: 50 mg per dose (300 mg/day ÷ 4 = 75 mg, but clinical guidelines cap single doses at 50 mg) 3
• Administration route: Deep intramuscular or intravenous at a rate not exceeding 25 mg/min 2
• Dosing interval: Every 6 hours (four times daily) 2

Clinical Dosing Guidelines (Emergency Use Only)

When diphenhydramine is used as adjunctive therapy in anaphylaxis (never first-line), the recommended dose is 1-2 mg/kg per dose, with a maximum of 50 mg per dose. 3

Age-Specific Considerations:

• Infants and young children: Use the lower end of the dosing range (1 mg/kg) to minimize toxicity risk 3
• Older children and adolescents: The full 1-2 mg/kg dose can be used, not exceeding 50 mg maximum 3

Dosing Examples by Weight:

Weight	Lower Dose (1 mg/kg)	Upper Dose (2 mg/kg)	Maximum Allowed
10 kg	10 mg	20 mg	20 mg
20 kg	20 mg	40 mg	40 mg
30 kg	30 mg	60 mg	50 mg (cap)
40 kg	40 mg	80 mg	50 mg (cap)

3

Critical Context: Anaphylaxis Management

Diphenhydramine must NEVER replace epinephrine in anaphylaxis—it is purely adjunctive therapy after epinephrine has been administered. 1, 3

Anaphylaxis Treatment Algorithm:

1. First-line: Epinephrine 0.01 mg/kg IM (1:1000 dilution) into anterolateral thigh, maximum 0.3-0.5 mg 4
2. Repeat epinephrine every 5-15 minutes if symptoms persist 4
3. Adjunctive therapy (only after epinephrine): Diphenhydramine 1-2 mg/kg IV/IM (maximum 50 mg) 3, 4
4. Additional adjuncts: H2-antihistamine (ranitidine 1 mg/kg) and corticosteroids (methylprednisolone 1-2 mg/kg) 4

Administration Safety

Intravenous diphenhydramine must be administered slowly (not exceeding 25 mg/min) to prevent seizures and cardiovascular collapse. 2

• Rapid IV administration can precipitate seizures and cardiac arrest, particularly in infants with underlying cardiac conditions 5
• A case report documented cardiac arrest in a 3-month-old infant following a single 1.25 mg/kg IV dose of diphenhydramine 5
• Oral liquid formulations are absorbed more rapidly than tablets and are preferred for acute allergic reactions when the oral route is feasible 3

Monitoring Requirements

Close monitoring for sedation, respiratory suppression, and paradoxical excitation is mandatory, especially when using other sedative agents concurrently. 3

• Paradoxical excitation or agitation may occur in pediatric patients 3
• Monitor for anticholinergic effects including tachycardia, urinary retention, and hyperthermia 3
• Continuous cardiac monitoring is recommended during IV administration 4

Common Pitfalls to Avoid

• Never use diphenhydramine as a sleep aid or to "calm" a child—this is explicitly contraindicated 1
• Never delay epinephrine in anaphylaxis to administer diphenhydramine first 1, 3
• Avoid in children under 6 years for routine allergic symptoms; use second-generation antihistamines (cetirizine, loratadine) instead 1
• Do not exceed 50 mg per single dose regardless of weight-based calculation 3, 2
• Reduce dose by 50% in patients with renal impairment 3

Preferred Alternatives for Routine Allergic Symptoms

Second-generation antihistamines (cetirizine, loratadine) are first-line for pediatric allergic symptoms due to superior safety profiles. 1

• Cetirizine: 2.5 mg once or twice daily for children aged 2-5 years 1
• Loratadine: 5 mg once daily for children aged 2-5 years 1
• These agents have significantly lower rates of serious adverse events compared to diphenhydramine 1