A dose calls for 0.3 mg/kg; the patient weighs 70 kg. What is the total dose?

A dose calls for 0.3 mg/kg; the patient weighs 70 kg. What is the total dose?

• A. 2.1 mg
• B. 210 mg
• C. 7 mg
• D. 21 mg

Answer: (D)

Dosing by weight is calculated by multiplying the dose per kilogram by the patient’s weight in kilograms. Here, 0.3 mg per kg for a patient weighing 70 kg means 0.3 × 70 mg. That equals 21 mg. The units work out because kilograms cancel, leaving milligrams. If weight were given in pounds, you’d first convert to kilograms (divide by 2.2) before multiplying. Common errors involve decimal placement or using a different weight, which would lead to 2.1 mg, 7 mg, or 210 mg.

Dosing by weight is calculated by multiplying the dose per kilogram by the patient’s weight in kilograms. Here, 0.3 mg per kg for a patient weighing 70 kg means 0.3 × 70 mg. That equals 21 mg. The units work out because kilograms cancel, leaving milligrams.

If weight were given in pounds, you’d first convert to kilograms (divide by 2.2) before multiplying. Common errors involve decimal placement or using a different weight, which would lead to 2.1 mg, 7 mg, or 210 mg.