When reversing 150 units of heparin using a ratio of 1 mg per 100 units, how many milligrams of protamine are needed?

• A. 1.0 mg
• B. 1.5 mg
• C. 2.0 mg
• D. 3.0 mg

Answer: (B)

Protamine dosing is based on a fixed ratio to heparin: 1 mg of protamine neutralizes 100 units of heparin. To reverse 150 units, multiply 150 by the ratio 1 mg/100 units, which gives 1.5 mg. So you need 1.5 mg of protamine. Using less would leave heparin partially active, while using more could increase the risk of protamine-related adverse effects.