Diphenhydramine Dosing for 16.5 kg Child
For a child weighing 16.5 kg with diphenhydramine 12.5 mg per 5 mL concentration, give 16.5 mL (approximately 16-17 mL) to deliver the recommended dose of 1-2 mg/kg. 1
Dose Calculation
The standard pediatric dose of diphenhydramine is 1-2 mg/kg per dose, with a maximum of 50 mg per single dose 1, 2
For a 16.5 kg child:
- Minimum dose: 16.5 mg (1 mg/kg × 16.5 kg)
- Maximum dose: 33 mg (2 mg/kg × 16.5 kg)
- Practical dose range: 16.5-33 mg 1
With a concentration of 12.5 mg per 5 mL, this translates to:
- For 16.5 mg: give 6.6 mL
- For 25 mg (mid-range): give 10 mL
- For 33 mg: give 13.2 mL
- Most clinicians would give 10-13 mL as a practical dose 1
Critical Context: When Diphenhydramine Should NOT Be Used
Diphenhydramine must NEVER be used as first-line treatment for anaphylaxis—epinephrine 0.01 mg/kg IM (0.165 mg for this child) is the only appropriate first-line treatment. 1, 3, 2
- Diphenhydramine is second-line therapy only, administered AFTER epinephrine in anaphylaxis 1, 3, 2
- H1-antihistamines like diphenhydramine have a much slower onset of action than epinephrine and should never be used alone in anaphylaxis treatment 1, 2
- Delayed epinephrine administration is associated with poor outcomes and fatality 3
Administration Safety Considerations
If giving IV diphenhydramine, administer slowly over several minutes—rapid IV bolus can precipitate seizures. 2
- Monitor for significant sedation and respiratory depression, particularly if combined with other sedatives 2, 4
- Watch for paradoxical excitation or agitation in some pediatric patients 2
- Diphenhydramine has a problematic adverse effect profile in children, with second-generation antihistamines offering better safety profiles for non-emergent allergic reactions 5, 6
Common Pitfalls to Avoid
- Never substitute diphenhydramine for epinephrine in anaphylaxis—this is a potentially fatal error 1, 3, 2
- Do not administer as rapid IV push due to seizure risk 2
- Do not exceed 50 mg per single dose regardless of weight-based calculation 1, 2
- Consider whether a second-generation antihistamine would be more appropriate for non-emergent allergic reactions 2, 5, 6