Diphenhydramine (Benadryl) Dosing for Pediatric Patients
The recommended dose of diphenhydramine (Benadryl) for pediatric patients is 1-2 mg/kg per dose, with a maximum single dose of 50 mg, administered every 6 hours as needed. 1
Dosing Guidelines by Age and Route
Standard Dosing
Route-Specific Considerations
- IV/IM route: 1-2 mg/kg per dose (maximum 50 mg) 1
- Oral route: Same dosing, but note that liquid formulations are more readily absorbed than tablets in children 1
Safety Considerations
Toxicity Thresholds
- Children under 6 years: Doses ≥7.5 mg/kg require emergency department referral 2, 3
- Children 6 years and older: Doses ≥7.5 mg/kg or ≥300 mg (whichever is less) require emergency department referral 2
Monitoring Parameters
- Common side effects: Sedation/drowsiness, anticholinergic effects (dry mouth, blurred vision, urinary retention), hypotension, dizziness 1
- Paradoxical effects: Monitor for excitement or agitation in infants instead of expected sedation 1
- Serious adverse effects: At toxic doses, patients may experience hallucinations, seizures, QRS widening, dysrhythmias, or respiratory depression 2
Duration of Treatment
- Acute allergic reactions: Limit treatment to 2-3 days 1
- Extended use: First-generation antihistamines like diphenhydramine should generally be limited to short courses due to tolerance development and side effects 1
Special Considerations
- Allergy testing: Discontinue diphenhydramine 3 days before allergy testing 1
- IV administration: Administer slowly to minimize risk of hypotension 1
- Hypersensitivity reactions: Diphenhydramine is second-line treatment after epinephrine for anaphylaxis 1
- Enhanced efficacy: Consider combination with H2 antagonists (e.g., ranitidine 1 mg/kg) for management of anaphylaxis 1
Clinical Pearls
- Dose-response studies support the 7.5 mg/kg toxicity threshold, with a 47-fold increase in odds of developing clinically significant responses for every log10 unit increase in mg/kg dose 4
- In children with sleep disorders, diphenhydramine at 1.0 mg/kg at bedtime has been shown to reduce sleep latency time and number of awakenings 5
- For unintentional ingestions, 99.7% of children who ingested less than 7.5 mg/kg did not develop serious clinical effects or require critical treatments 3
Remember that while diphenhydramine is effective for various allergic conditions, its sedative properties warrant careful dosing and monitoring, particularly in young children.