Reversal agent
Protamine
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Heparin vs Warfarin: aPTT vs INR, HIT, Bridging, Antidotes and DOAC Reversal
Indications
- Neutralizing heparin at the end of cardiopulmonary bypass, its most common use
- Heparin overdose or bleeding on heparin, the labeled indication
- Reversing heparin after vascular and catheter procedures, ECMO decannulation or dialysis (off-label)
- Partial reversal of enoxaparin and other LMWHs in serious bleeding (off-label)
Dosing
| Where | Dose |
|---|---|
| Reversal and antidotes | Protamine: 1 mg per 100 units of heparin in the last 2–3 h, max 50 mg, slowly |
On the quick cards
Mechanism of action
Protamine is a strongly basic, arginine-rich protein. Its positively charged guanidino groups pair with heparin's negatively charged sulfate and carboxyl groups, forming a stable salt with no anticoagulant activity and pulling heparin off antithrombin within 5 minutes. LMWH chains are too short to bind completely, so protamine neutralizes enoxaparin's anti-IIa activity but at most about 60% of its anti-Xa activity, and none of fondaparinux. Alone or in excess, protamine is itself a weak anticoagulant.
Pharmacology
- Hematologic: neutralizes heparin; excess free protamine interacts with platelets and fibrinogen, prolonging the ACT and worsening bleeding
- Cardiovascular: fast injection releases histamine, causing vasodilation, hypotension and bradycardia
- Respiratory: heparin–protamine complexes can activate complement and release thromboxane A₂, causing acute pulmonary vasoconstriction, pulmonary hypertension and right heart failure; noncardiogenic pulmonary edema can follow
- Immunologic: sensitization (NPH insulin, earlier protamine, fish allergy, vasectomy) can lead to IgE- or IgG-mediated anaphylaxis
Pharmacokinetics
| Onset | IV: neutralizes heparin within 5 min |
|---|---|
| Duration | Shorter than heparin's: heparin rebound can appear 30 min to 18 h after bypass (label) |
| Half-life | About 5 min (median 4.5 min after 250 mg in cardiac surgery; Butterworth 2002); StatPearls gives about 10 min |
| Distribution | Vd about 5.4 L, near the blood volume |
| Clearance | About 1.4 L/min (Butterworth 2002) |
| Metabolism | Poorly understood; studies point to hepatic or renal handling of the heparin–protamine complex |
| Routes | IV only, no faster than 50 mg over 10 min |
Chemistry
- Low-MW proteins (about 4,000–5,000 Da) from the sperm of salmon and related fish, where protamines pack DNA; salmine has 32 residues, 21 of them arginine
- A polycation: arginine side chains stay protonated at any body pH, giving the charge that binds heparin's polyanion
- Ratio: each mg neutralizes at least 100 USP heparin units (label), so give about 1 mg per 100 units still circulating; half the dose 30 min after a bolus; EACTS 2024 advises under 1:1 of the initial dose after bypass
- 10 mg/mL in 0.9% sodium chloride, preservative-free, pH 6.0–7.0; Fresenius vials are stored at 20–25 °C, not frozen
Adverse effects and cautions
In the one-pagers
- Bleeding, Reversal, HIT and DICReversing anticoagulants in major bleeding: Unfractionated heparin: Protamine 1 mg per 100 units given in last 2–3 h (max 50 mg): Fast; watch for hypotension, anaphylaxis
- After Cardiac SurgeryFirst hours and bleeding: Residual heparin or rebound (ACT up): Protamine
- Pulmonary EmbolismNursing: monitoring and bleeding watch: Major bleeding: cryoprecipitate to fibrinogen ≥150 mg/dL, tranexamic acid, protamine for UFH
- Subarachnoid HemorrhageUntil the aneurysm is secured: Reverse anticoagulants now: warfarin, 4F-PCC plus IV vitamin K; dabigatran, idarucizumab; factor Xa inhibitors, 4F-PCC; heparin, protamine.
- ACS and STEMIAfter the cath lab: access sites, bleeding and discharge: A puncture above the inguinal ligament can bleed into the retroperitoneum, often without a groin hematoma. Clues are back, flank or lower abdominal pain, unexplained hypotension or tachycardia, a falling hemoglobin, or thigh numbness from femoral nerve compression; Grey Turner flank bruising is late. Call the operator, give fluid and blood
- Neuro: ICP and StrokeHemorrhagic stroke (ICH): Heparin: protamine
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Sources
- FDA label: Protamine Sulfate, Fresenius Kabi (2024)
- StatPearls: Protamine (accessed 2026)
- Butterworth et al., Anesth Analg (2002)
- Horrow, Anesth Analg (1985)
For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow the order, the label and your institution's protocols.