Protamine Sulfate Dosing for Unfractionated Heparin Reversal

Dosing Algorithm for Protamine Sulfate

The American College of Cardiology recommends administering 1 mg of protamine sulfate for every 100 units of unfractionated heparin given in the previous 2-3 hours, with a maximum single dose of 50 mg, delivered by slow IV injection over 10 minutes 1, 2, 3
For patients who received heparin 30-60 minutes before protamine administration, the American Heart Association suggests using 0.5-0.75 mg protamine per 100 units of heparin 4
The European Society of Cardiology recommends that if heparin was discontinued 60-120 minutes before protamine administration, 0.375-0.5 mg protamine per 100 units of heparin should be used 4
For heparin infusion stopped >30 minutes but <2 hours, the European Heart Journal recommends using half the calculated protamine dose 5
Monitoring of activated partial thromboplastin time (aPTT) 5-10 minutes after protamine administration is recommended to confirm adequate reversal, as suggested by the American College of Cardiology 6
If aPTT remains elevated, additional protamine at a dose of 0.5 mg per 100 units of unfractionated heparin may be administered, as recommended by the American College of Cardiology 1, 2, 3

Rapid administration of protamine sulfate can cause severe systemic hypotension, according to the American Heart Association 4

The American College of Chest Physicians recommends that for immediate reversal of 5,000 units of intravenous heparin, 50 mg of protamine sulfate should be administered intravenously, based on a standard dosing of 1 mg per 100 units of heparin received when administered within 30 minutes of heparin administration 7, 8
The calculation for 5,000 units of heparin administered intravenously is 5,000 units ÷ 100 units/mg = 50 mg protamine sulfate, which should not exceed the maximum recommended single dose of 50 mg 7, 8

The dosing schedule for protamine sulfate recommends reducing the dose according to the time elapsed since heparin administration, with a full dose of 1.0 mg/100 units heparin for administration within 30 minutes, and reduced doses for administration between 30-60 minutes, 60-120 minutes, and over 120 minutes 7, 9

Patients with known fish allergies, previous exposure to protamine, or protamine-containing insulin are at increased risk of hypersensitivity reactions to protamine sulfate 7, 8