What is the pediatric dose for diphenhydramine in a mild allergic reaction?

• A. Diphenhydramine 1 mg/kg IM/IV/IO/PO; max 50 mg
• B. Diphenhydramine 0.5 mg/kg IM/IV/IO/PO; max 25 mg
• C. Diphenhydramine 2 mg/kg IM/IV/IO/PO; max 100 mg
• D. Diphenhydramine 0.25 mg/kg IM/IV/IO/PO; max 10 mg

Answer: (B)

Dosing antihistamines in pediatric patients is weight-based and capped to prevent excessive sedation and anticholinergic effects. For a mild allergic reaction, diphenhydramine given at 0.5 mg/kg per dose, up to a maximum of 25 mg, via IM, IV, IO, or PO, provides antihistaminic relief while keeping safety in check. For example, a 20 kg child would receive about 10 mg per dose; a 40 kg child would receive about 20 mg per dose; once the child approaches 50 kg, the maximum dose limits to 25 mg. Diphenhydramine is used as an adjunct in mild reactions, and epinephrine remains the first-line treatment for suspected anaphylaxis. The other dosing options either exceed safe limits or are too low to provide consistent relief for most pediatric patients, which is why this 0.5 mg/kg up to 25 mg dose fits standard practice.