Bleeding on Anticoagulants: Emergency Reversal
Match each drug to its antidote — and reverse only when the bleed earns it.
Grading the bleed and first steps
Major vs minor. Reversal agents are costly and prothrombotic, so first decide whether the bleed is major: hemodynamic instability, a critical site (intracranial, intraspinal, intraocular, airway, pericardial, retroperitoneal, or intramuscular with compartment syndrome), or a hemoglobin fall of at least 2 g/dL or a need for 2 or more units of red cells. Epistaxis that stops with pressure, bruising, and minor hematuria are handled by holding the next dose and treating the local source.
- Stop the agentHold anticoagulants and antiplatelets; document the drug, dose, and time of the last dose.
- Local hemostasisPressure, packing, endoscopy, embolization, or surgery.
- ResuscitateTwo large-bore IVs; CBC, PT/INR, aPTT, fibrinogen, creatinine, type and crossmatch; balanced transfusion in massive hemorrhage.
- Reverse the specific drugAgent-matched antidote when the bleed is major.
- Plan resumptionOnce hemostasis is secure.
Timing and kidneys. DOAC half-lives are roughly 12 hours (dabigatran much longer with poor renal function), so creatinine clearance and the time since the last dose tell you how much drug remains; a dose taken several half-lives ago may need no antidote.
Warfarin
Major bleeding. Four-factor prothrombin complex concentrate (4F-PCC) directly replaces the vitamin K–dependent factors II, VII, IX, and X, plus proteins C and S. Dosed by weight and INR (about 25–50 U/kg), it needs no ABO matching, comes in a small volume, and normalizes the INR within roughly 30 minutes. Always add vitamin K 10 mg by slow IV infusion: infused factors are consumed within hours (factor VII half-life about 6 hours), and without new hepatic synthesis the INR rebounds. IV vitamin K acts in 4–6 hours and peaks at 12–24 hours; subcutaneous absorption is erratic.
Plasma is second-line. Fresh frozen plasma needs thawing and ABO compatibility, and the 10–15 mL/kg required (often more than a liter) corrects the INR slowly and incompletely while risking transfusion-associated circulatory overload (TACO) and TRALI. PCC carries a small thrombotic risk, and heparin-containing products are avoided in heparin-induced thrombocytopenia.
High INR without bleeding. Below 4.5: reduce or skip a dose. From 4.5 to 10: hold one or two doses and recheck; routine vitamin K is not needed. Above 10: hold and give oral vitamin K 2.5–5 mg. Never give PCC or plasma just to fix a number; for an urgent procedure that cannot wait about a day for vitamin K to act, use PCC plus IV vitamin K.
Direct oral anticoagulants
Dabigatran. Idarucizumab (5 g IV), a humanized monoclonal antibody fragment that binds dabigatran far more tightly than thrombin does, neutralizes this direct thrombin inhibitor within minutes. Dabigatran is about 80% renally excreted and weakly protein-bound, so hemodialysis is an alternative. A normal thrombin time essentially excludes a relevant level; the aPTT is only a rough screen.
Factor Xa inhibitors. For life-threatening bleeding on apixaban or rivaroxaban, give 4F-PCC (25–50 U/kg); andexanet alfa, a recombinant, catalytically inactive factor Xa decoy that binds the circulating drug, was withdrawn from the US market in December 2025 over thromboembolic risk. These drugs are highly protein-bound and not dialyzable. PT and aPTT are insensitive, especially to apixaban, so a drug-calibrated anti-Xa assay is needed to quantify the effect. Activated charcoal within about 2–4 hours of the last dose limits further absorption of any DOAC.
| Agent | First-line reversal | Alternative or adjunct | Key point |
|---|---|---|---|
| Warfarin | 4F-PCC + vitamin K 10 mg IV | FFP if no PCC | Vitamin K prevents INR rebound |
| Dabigatran | Idarucizumab 5 g IV | Hemodialysis; charcoal if recent dose | Normal thrombin time excludes drug effect |
| Apixaban, rivaroxaban | 4F-PCC 25–50 U/kg (andexanet alfa withdrawn in US, Dec 2025) | Charcoal if recent dose | Not dialyzable; follow anti-Xa level |
| Unfractionated heparin | Protamine 1 mg per 100 U (last 2–3 h) | Supportive care | Maximum 50 mg; follow aPTT |
| Enoxaparin | Protamine 1 mg per 1 mg (dose ≤8 h ago) | 0.5 mg per mg if 8–12 h ago | Only ~60% of anti-Xa activity reversed |
| Alteplase, tenecteplase | Stop infusion; cryoprecipitate | Tranexamic or aminocaproic acid | Check fibrinogen |
| Aspirin, P2Y12 inhibitors | No routine platelets in spontaneous ICH | Desmopressin; platelets if neurosurgery | Irreversible for the platelet lifespan |
Heparins, thrombolytics and antiplatelet agents
Unfractionated heparin. Protamine sulfate, a strongly basic protein, binds acidic heparin. Because heparin's half-life is 60–90 minutes, give 1 mg per 100 units received over the previous 2–3 hours (about 20–30 mg for a 1,000 U/h infusion), maximum 50 mg, slowly (no faster than 5 mg/min, over about 10 minutes), while following the aPTT. Fast infusion causes hypotension and bradycardia; anaphylactoid reactions are more likely after NPH insulin use, with fish allergy, or after vasectomy.
LMWH and fondaparinux. Protamine neutralizes enoxaparin's anti-IIa activity but only about 60% of its anti-Xa activity: 1 mg per 1 mg enoxaparin given within 8 hours, or 0.5 mg per mg if 8–12 hours earlier. Fondaparinux is not reversed by protamine.
Thrombolytic-associated hemorrhage. Headache, vomiting, rising blood pressure, or neurologic decline within 24 hours of alteplase or tenecteplase means intracranial hemorrhage until proven otherwise. Stop any running infusion, obtain an emergent noncontrast CT, and send CBC, coagulation studies, fibrinogen, and a crossmatch. Lytics consume fibrinogen, so give cryoprecipitate (about 10 units, supplying fibrinogen, factors VIII and XIII, and von Willebrand factor) plus tranexamic acid 1 g IV or ε-aminocaproic acid, control blood pressure, and involve neurosurgery.
Antiplatelet agents. Aspirin and clopidogrel inhibit platelets irreversibly, so function returns only as new platelets appear over 7–10 days. In spontaneous intracerebral hemorrhage on antiplatelets, platelet transfusion increased death or dependence (PATCH trial) and is reserved for patients going to emergent neurosurgery. Desmopressin (0.3 μg/kg IV) releases von Willebrand factor and factor VIII from endothelial Weibel–Palade bodies within about an hour and may be considered; it wanes after one or two doses (tachyphylaxis) and can cause hyponatremia.
Uremic bleeding reflects platelet dysfunction, not a low count: use desmopressin, dialysis, anemia correction, and conjugated estrogens for a longer effect: transfused platelets quickly become dysfunctional in uremic plasma.
Tranexamic acid and restarting anticoagulation
Tranexamic acid. TXA, a lysine analog, blocks plasminogen binding to fibrin and so prevents fibrinolysis. In bleeding trauma, 1 g IV over 10 minutes then 1 g over 8 hours lowers hemorrhage deaths when started within 3 hours of injury (CRASH-2); doses given later were associated with more bleeding deaths. In GI bleeding, TXA did not reduce mortality and increased venous thromboembolism (HALT-IT).
Resumption. Reversal treats the bleed, not the thrombotic risk. Once hemostasis is secure, weigh the indication (mechanical valve, recent VTE, high CHA2DS2-VASc score) against rebleeding. Resuming after GI bleeding is associated with fewer thromboses and lower mortality; after intracranial hemorrhage, timing is individualized and generally later. PCC and andexanet (no longer sold in the US) are themselves prothrombotic, which makes a planned restart all the more important.
Classic wrong answers: plasma as first-line reversal for warfarin-associated intracranial hemorrhage, and platelet transfusion for spontaneous ICH on aspirin when no surgery is planned.