What is the usual diphenhydramine dose, route, and maximum daily dose in the described protocol?

• A. 50 mg, q6-8 hr; max 400 mg/day; PO
• B. 25 mg, q4-6 hr prn; max 300 mg/day; IM/IO/IV
• C. 10 mg, q4-6 hr; max 100 mg/day; IV
• D. 100 mg, single dose; IM

Answer: (B)

Dosing in this protocol centers on getting fast antihistamine effect in a field setting while keeping safety at the forefront. The usual approach is 25 mg per dose, given every 4–6 hours as needed, with a maximum of 300 mg in 24 hours. This per-dose amount is small enough to minimize excessive sedation and anticholinergic effects, yet frequent enough to control allergic symptoms as they recur. The maximum daily limit protects against cumulative toxicity, which can cause confusion, dizziness, dry mouth, urinary retention, or even heart rhythm issues in a harsh environment where monitoring is limited.

The chosen routes—intramuscular, intraosseous, or intravenous—are selected to ensure rapid and reliable absorption when oral administration might be impractical due to vomiting, altered mental status, or injury. Oral dosing isn’t used in this protocol because in combat casualty care those conditions are common and we need predictable onset and delivery.

Higher per-dose amounts or a focus on oral dosing could increase the risk of sedation, hypotension, and anticholinergic side effects, or yield unreliable absorption in a trauma setting.