Protamine Sulfate

Mechanism

Pharmacological Group and Molecular Target

Low molecular weight cationic basic polypeptide that acts through electrostatic neutralization.

Detailed Mechanism of Action

Unfractionated heparin (UFH) is a polysaccharide with a high density of negative electrical charges (the most acidic and negatively charged biological compound in the human body) that enhances the affinity of antithrombin III for thrombin and factor Xa. Protamine is a protein purified from salmon sperm that has an enormous density of positive electrical charges (arginine polycations). Upon contact with free heparin in the plasma, protamine binds immediately and stoichiometrically by strong ionic bonds, forming an inert and stable salt complex without anticoagulant activity that is rapidly cleared by the reticuloendothelial system.

Pharmacokinetics

Calculation Based on the Half-Life of Heparin

Since intravenous heparin has a half-life of approximately 60-90 minutes, the dose of protamine required decreases rapidly as a function of the time elapsed since the heparin infusion is stopped:

• Elapsed time <30 min: Administer 1 mg of protamine for every 100 IU of heparin administered.
• Elapsed time 30-60 min: Administer 0.5 mg of protamine for every 100 IU of heparin administered.
• Elapsed time >2 hours: Administer 0.25 mg of protamine per 100 IU of heparin.
• Maximum recommended single bolus dose: 50 mg IV; Non-heparin-bound free protamine has mild intrinsic anticoagulant properties by negatively interacting with platelets and fibrinogen.

Indicators and dose

Specific Clinical Indications

• Rapid and complete neutralization of the anticoagulant activity of Unfractionated Heparin in cases of severe active bleeding or post-cardiovascular surgery with extracorporeal circulation.
• Partial reversal (approximately 60%) of the anticoagulant effects of Low Molecular Weight Heparins (LMWH, such as Enoxaparin).

Dosage Scheme and Infusion Protocols

Security

Contraindications and Precautions

• Anaphylactic Hypersensitivity Reactions: Patients with a history of vasectomy (develop circulating anti-protamine antibodies), diabetics previously treated with insulin-zinc-protamine (NPH) or patients with severe allergy to fish. Systematic premedication is recommended in these risk groups.
• A rapid intravenous infusion can cause a massive release of endothelial nitric oxide, triggering transient severe hypotension and catastrophic pulmonary hypertension. Always infuse at rates less than 5 mg per minute.