What are the volumes of Ibuprofen (IBU) and Diphenhydramine (Benadryl) needed for a one-time 10 mg/kg dose in a 16.5 kg child, given IBU 100 mg/5 ml and Benadryl 12.5 mg/5 ml concentrations?

Dosing Calculation for Ibuprofen and Diphenhydramine in a 16.5 kg Child

For this 16.5 kg child requiring a one-time 10 mg/kg dose, administer 8.25 mL of ibuprofen (IBU 100 mg/5 mL) and 33 mL of diphenhydramine (Benadryl 12.5 mg/5 mL).

Ibuprofen Calculation

The child requires 165 mg of ibuprofen total (16.5 kg × 10 mg/kg = 165 mg). 1

• Given the concentration of 100 mg/5 mL, this equals 20 mg/mL 1
• Volume needed: 165 mg ÷ 20 mg/mL = 8.25 mL 1

Diphenhydramine (Benadryl) Calculation

For diphenhydramine, the standard pediatric dose is 1-2 mg/kg per dose, with a maximum of 50 mg per dose. 1

• Using the 10 mg/kg dosing mentioned in your question would result in 165 mg, which far exceeds the safe maximum dose of 50 mg 1
• The appropriate dose should be 1-2 mg/kg, which equals 16.5-33 mg for this child 1
• Using the upper end of the safe range (2 mg/kg = 33 mg): 1
• Given the concentration of 12.5 mg/5 mL, this equals 2.5 mg/mL 1
• Volume needed: 33 mg ÷ 2.5 mg/mL = 13.2 mL 1

Critical Safety Warning

The 10 mg/kg dosing for diphenhydramine mentioned in your question is NOT appropriate and would result in a dangerous overdose. 1

• The maximum single dose of diphenhydramine for children is 25-50 mg, regardless of weight 1
• A 10 mg/kg dose in this 16.5 kg child (165 mg) is more than 3 times the maximum safe dose 1
• Always use 1-2 mg/kg for diphenhydramine dosing in children, not 10 mg/kg 1

Final Dosing Summary

• Ibuprofen: 8.25 mL (165 mg) - appropriate at 10 mg/kg 1
• Diphenhydramine: 13.2 mL (33 mg at 2 mg/kg) OR 6.6 mL (16.5 mg at 1 mg/kg) - NOT 10 mg/kg 1