Diphenhydramine Dosing for a 13-Month-Old Infant
For a 13-month-old infant (approximately 10 kg) experiencing an acute allergic reaction, administer diphenhydramine at 1.25 mg/kg orally, which equals 12.5 mg for this child. 1
Evidence-Based Dosing
The National Institute of Allergy and Infectious Diseases (NIAID) guidelines explicitly state diphenhydramine dosing for infants as 1.25 mg/kg/dose orally during office-based oral food challenges and allergic reactions. 1
For a 10 kg infant, this translates to 12.5 mg as a single oral dose. 1
The standard adult maximum dose is 50 mg, but pediatric dosing must be weight-based and should not exceed 1.25 mg/kg per dose. 1
Critical Safety Considerations
Diphenhydramine is strictly adjunctive therapy only—it provides no acute benefit in anaphylaxis and must never delay or replace epinephrine administration. 2
If this infant has any signs of anaphylaxis (respiratory distress, wheezing, hypotension, or multi-system involvement), epinephrine 0.01 mg/kg IM (0.1 mg for a 10 kg child) into the anterolateral thigh is the only first-line treatment and must be given immediately. 1, 2
Diphenhydramine should only be considered after epinephrine has been administered in true anaphylaxis, or as monotherapy for mild localized urticaria without systemic symptoms. 1, 2
Route of Administration Matters
Oral liquid formulation is preferred as it is more readily absorbed than tablets and is appropriate for this age group. 1
Avoid intravenous diphenhydramine in infants whenever possible—a case report documented cardiac arrest in a 3-month-old following IV administration of 1.25 mg/kg diphenhydramine, even at the guideline-recommended dose. 3
If IV administration is absolutely necessary in a monitored setting, administer slowly to minimize cardiovascular toxicity risk. 4, 3, 5
Common Pitfalls to Avoid
Do not use diphenhydramine as monotherapy for anaphylaxis—this is a dangerous practice that has led to preventable deaths, as antihistamines do not treat airway obstruction, bronchospasm, or cardiovascular collapse. 2, 6
Do not exceed 1.25 mg/kg per dose in infants, as supratherapeutic dosing increases risk of anticholinergic toxicity including tachycardia, hallucinations, agitation, and seizures. 7
Avoid topical diphenhydramine cream in young children—a case report documented death of a toddler from systemic absorption of topically applied diphenhydramine. 8
Be aware of paradoxical reactions—diphenhydramine can cause agitation and excitation rather than sedation in some infants and young children. 4, 7
When to Escalate Care
If the infant develops any of the following after diphenhydramine administration, immediately administer epinephrine 0.01 mg/kg IM and activate emergency services: 1, 2
- Respiratory distress or stridor
- Wheezing or persistent cough
- Hypotension or altered mental status
- Angioedema involving lips, tongue, or throat
- Vomiting with skin or respiratory symptoms
Observe for at least 4-6 hours after any allergic reaction treatment, as biphasic reactions occur in 7-18% of cases and are unpredictable. 2
Practical Administration
For a 10 kg infant: Give 12.5 mg (2.5 mL of standard 12.5 mg/5 mL pediatric liquid formulation) orally as a single dose. 1
Diphenhydramine can be repeated every 6 hours if needed for ongoing urticaria, but reassess for escalating symptoms before each subsequent dose. 1, 4
Most common adverse effects in this age group include somnolence (34.7%), tachycardia (53.4%), and agitation (33.9%). 7