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# Anticoagulant reversal agents

Antidotes that switch off an anticoagulant when there is serious bleeding or urgent surgery. Each one fits a specific drug.

Updated 2026-11-01

## What they are

Medicines that undo the effect of an anticoagulant: vitamin K and prothrombin complex concentrate for vitamin K antagonists, protamine for heparin, idarucizumab for dabigatran and andexanet alfa for the factor Xa inhibitors.

## Mechanism of action

They work in three ways. Some bind the anticoagulant and take it out of action: protamine (a strongly basic protein) neutralises acidic heparin, idarucizumab is an antibody fragment that holds dabigatran, and andexanet alfa is a decoy factor Xa that captures apixaban or rivaroxaban. Vitamin K lets the liver make working clotting factors again, which takes hours. Prothrombin complex concentrate replaces the missing factors directly and acts within minutes.

Target: The anticoagulant itself, or the clotting factors it lowers

## Key points

- Warfarin: vitamin K restores factor production over hours; prothrombin complex concentrate replaces factors II, VII, IX and X within minutes for life-threatening bleeding.
- Heparin: protamine neutralises it within minutes; it only partly reverses enoxaparin and does not reverse fondaparinux.
- Dabigatran: idarucizumab, a humanised antibody fragment that binds it.
- Rivaroxaban and apixaban: andexanet alfa, a modified, inactive factor Xa that binds them.
- Protamine and vitamin K do not reverse the direct oral anticoagulants.

## Drugs in this class

- [**Phytomenadione (vitamin K1)** Vitamin K1 as a medicine. It lets the liver make working clotting factors again: it reverses warfarin and prevents… Vitamin K-dependent gamma-glutamyl carboxylase (GGCX), which uses vitamin K as its cofactor](https://durgical.com/en/pharmacology/phytomenadione/)
- [**Protamine sulfate** A strongly basic fish protein that binds heparin and cancels its effect within minutes. It can cause severe drops in… Heparin (binds the drug itself)](https://durgical.com/en/pharmacology/protamine-sulfate/)
- [**Idarucizumab** A humanised antibody fragment that grabs dabigatran and quickly switches off its effect, for urgent surgery or… Dabigatran (binds the drug itself)](https://durgical.com/en/pharmacology/idarucizumab/)
- [**Andexanet alfa** An inactive decoy copy of factor Xa that soaks up apixaban or rivaroxaban, used when they cause life-threatening… Factor Xa inhibitors (apixaban, rivaroxaban), which it captures](https://durgical.com/en/pharmacology/andexanet-alfa/)

## Others in the class

- prothrombin complex concentrate
- fresh frozen plasma

## Test yourself

Think of the answer, then tap the question to see it.

## Which antidote matches each anticoagulant: heparin, warfarin, dabigatran, apixaban?

Heparin: protamine. Warfarin: vitamin K, plus prothrombin complex concentrate for serious bleeding. Dabigatran: idarucizumab. Apixaban: andexanet alfa.

## Why is vitamin K alone too slow for life-threatening bleeding on warfarin?

The liver needs hours to make new working factors after vitamin K is given; prothrombin complex concentrate supplies the factors at once.

## Why does protamine have no effect on apixaban?

Protamine works by binding the negatively charged heparin chains; apixaban is a small molecule that binds factor Xa directly, so there is nothing for protamine to neutralise.

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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 - PHYTONADIONE injection, emulsion](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=226c0a5c-3e04-65a9-01ac-e67aad9a430a) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - APIXABAN tablet, film coated](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=19a60552-374d-4b8b-a8ce-ceae252ea5ba) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=V03AB&showdescription=no) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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