Which of the following best describes the protamine dose relative to heparin in reversal?

• A. 0.5 mg per 100 units
• B. 1 mg per 100 units
• C. 2 mg per 100 units
• D. 5 mg per 100 units

Answer: (B)

Protamine reverses heparin by forming a stable complex, and the dosing is guided by a rough 1:1 ratio by units of heparin given. For every 100 units of heparin, about 1 mg of protamine is used to neutralize it. This balance aims to stop excessive anticoagulation without tipping into protamine overdosage, which can cause its own adverse effects and even coagulopathy. So the best choice is 1 mg of protamine per 100 units of heparin.

Under-dosing (less than 1 mg per 100 units) risks residual heparin and bleeding; over-dosing (more protamine than needed) risks adverse reactions and potential interference with clotting. In practice, the exact amount may be adjusted based on the patient’s response and intraoperative coagulation monitoring.