What is the weight-based dosing for diphenhydramine in allergic reactions?

• A. 0.5 mg/kg
• B. 1 mg/kg
• C. 2 mg/kg
• D. 3 mg/kg

Answer: (B)

Understanding weight-based dosing for diphenhydramine in allergic reactions means dosing by body weight to achieve the right amount for each patient. The standard approach is to give 1 mg of diphenhydramine per kilogram of body weight per dose. This scale ensures children and adults receive an effective amount without risking under-treatment in larger patients or excessive side effects in smaller ones. Dosing less than this (such as 0.5 mg/kg) may be inadequate for suppressing histamine-driven symptoms in an active reaction, while doses well above (2 mg/kg or 3 mg/kg) increase the risk of strong sedation, anticholinergic effects, and toxicity. In practice, this antihistamine is used as an adjunct to epinephrine in allergic reactions, not as the primary life-saving treatment, which is epinephrine.