Which formula represents weight-based dosing?

• A. Dose (mg) = mg/kg × weight (kg)
• B. Dose (mg) = weight (kg) × standard dose
• C. Dose (mg) = body surface area × concentration
• D. Dose (mg) = total mg per administration

Answer: (A)

Weight-based dosing determines the total drug amount by scaling with the patient’s weight. The correct approach is to multiply the prescribed amount in milligrams per kilogram by the patient’s weight in kilograms, giving the total dose in milligrams. For example, if the order is 10 mg/kg and the patient weighs 25 kg, the dose is 250 mg. It’s important to ensure the weight is in kilograms (convert from pounds if needed, by dividing by 2.2046).

This method ties the dose to body size, so smaller patients receive less and larger patients receive more, maintaining a consistent mg per kg exposure. Other formulas don’t reflect this: using a fixed standard dose times weight doesn’t account for per-kilogram scaling; dosing by body surface area uses a different metric (mg per m²) appropriate for certain drugs but not general weight-based dosing; and stating a total milligrams per administration ignores weight entirely, which would misdose patients of differing sizes.