A patient weighing 22 lb requires 0.2 mg/kg; how many mg should be given?

• A. 22.2 mg
• B. 2 mg
• C. 2.2 mg
• D. 22 mg

Answer: (B)

Dosing is mg per kilogram, so you must convert the patient’s weight from pounds to kilograms and then multiply by the dose per kilogram.

Convert 22 lb to kg: 22 ÷ 2.2046 ≈ 9.99 kg (about 10 kg). Multiply by 0.2 mg/kg: 0.2 × 9.99 ≈ 1.998 mg, which rounds to about 2 mg. So the appropriate dose is ~2 mg.

The other numbers come from treating pounds as kilograms or from multiplying by the wrong factor, which isn’t correct when using mg/kg dosing.