[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Anticoagulant reversal agents](https://durgical.com/en/pharmacology/classes/anticoagulant-reversal-agents/) › Protamine sulfate [Pharmacology](https://durgical.com/en/pharmacology/) · [Anticoagulant reversal agents](https://durgical.com/en/pharmacology/classes/anticoagulant-reversal-agents/) # Protamine sulfate A strongly basic fish protein that binds heparin and cancels its effect within minutes. It can cause severe drops in blood pressure. Updated 2026-11-01 - Class: [Anticoagulant reversal agents](https://durgical.com/en/pharmacology/classes/anticoagulant-reversal-agents/) - Target: Heparin (binds the drug itself) - ATC code: V03AB14 - WHO Model List of Essential Medicines Also called: protamine ## Mechanism of action Protamines are small proteins rich in arginine, so they carry a strong positive charge. Heparin is strongly negative. Given together, they form a stable salt and both lose their anticoagulant activity. Given alone, protamine itself has a weak anticoagulant effect, through interactions with platelets and with proteins such as fibrinogen. - Positively charged protamine meets negatively charged heparin - They form a stable, inactive salt - Heparin can no longer activate antithrombin: clotting returns within minutes ## Pharmacokinetics **Metabolism** The heparin-protamine complex may be partly broken down, which can free heparin again (rebound). **Onset and duration** Rapid: heparin is neutralised within about five minutes of the intravenous injection. ## Indications - Heparin overdose or bleeding on heparin. [Anticoagulant poisoning (warfarin and superwarfarins) →](https://durgical.com/en/conditions/anticoagulant-poisoning/) - Reversal of heparin at the end of cardiac surgery with cardiopulmonary bypass. - Partial reversal of low-molecular-weight heparins such as enoxaparin. ## Adverse effects ### Common - Sudden fall in blood pressure and slow heart rate - Flushing and a feeling of warmth - Shortness of breath, nausea, vomiting, tiredness - Back pain in awake patients ### Serious (rare, important) - Severe hypotension, cardiovascular collapse and anaphylaxis - Catastrophic pulmonary vasoconstriction and pulmonary hypertension - Noncardiogenic pulmonary oedema - Rebound bleeding from 30 minutes to 18 hours after reversal ## Contraindications - Previous intolerance to protamine - Bleeding without prior heparin use (it does not treat other causes) ## Key interactions **Heparin and low-molecular-weight heparins** Neutralises unfractionated heparin; only partly reverses the anti-Xa effect of enoxaparin. **Protamine-containing insulins (NPH) and earlier protamine exposure** Raise the risk of severe allergic reactions. **Some penicillins and cephalosporins in the same line** Physically incompatible; not mixed. ## What is monitored - Blood pressure, heart rate and oxygen saturation during and after the injection - Coagulation tests to guide and confirm reversal - Signs of rebound bleeding over the next hours, especially after cardiac surgery ## Administration and safety - Slow intravenous injection only: too-fast injection causes severe hypotension and anaphylactoid reactions - Not mixed with other drugs (incompatible with several penicillins and cephalosporins) - Vasopressors and resuscitation equipment are ready before the first dose - The amount needed falls quickly with time since the last heparin dose; it is guided by coagulation tests ## Nursing care - Ask about fish allergy, vasectomy, NPH insulin use and earlier protamine before giving it - Stay with the patient during the injection; stop and call for help if blood pressure drops or breathing worsens - Recheck coagulation and watch drains and wounds for rebound bleeding - Document the time of the last heparin dose ## Pregnancy and breastfeeding Safety in pregnancy is not established; it is used only when clearly needed. ## Memory aid Protamine is Positive, heparin is negative: opposite charges stick and cancel out. Push it slowly or the pressure falls. ## Test yourself Think of the answer, then tap the question to see it. ## How does protamine neutralise heparin? It is strongly basic (positive) and heparin is strongly acidic (negative); they form a stable salt and both lose anticoagulant activity. ## Which risk factors raise the chance of a severe reaction to protamine? Fast injection, high doses, earlier protamine exposure, protamine-containing insulin (NPH), fish allergy, previous vasectomy and severe left ventricular dysfunction. ## Why can bleeding come back hours after heparin was reversed with protamine? Rebound: the heparin-protamine complex may break down and free heparin, from about 30 minutes to 18 hours after cardiac surgery. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/protamine-sulfate/) ## Related drugs - [Heparin](https://durgical.com/en/pharmacology/heparin/) - [Enoxaparin](https://durgical.com/en/pharmacology/enoxaparin/) - [Phytomenadione (vitamin K1)](https://durgical.com/en/pharmacology/phytomenadione/) ## Related conditions - [Anticoagulant poisoning (warfarin and superwarfarins)](https://durgical.com/en/conditions/anticoagulant-poisoning/) [← Back to the class: Anticoagulant reversal agents](https://durgical.com/en/pharmacology/classes/anticoagulant-reversal-agents/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [DailyMed - PROTAMINE SULFATE injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c76876da-b9a8-45d0-9278-7df3288d3a06) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - ENOXAPARIN SODIUM injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=31e7c4d0-ba45-4b20-8e25-2d12892372e5) (DailyMed (U.S. National Library of Medicine), 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/?query=protamine) (World Health Organization, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/protamine-sulfate/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/protamine-sulfate/