Protamine Sulfate: veterinary dose and monograph

At a glance

Drug class

Veterinary drug

Also known as

Protamine, Protamine sulphate

Species with doses

Dogs, Cats, Cattle and Horses

Routes

IV

Last reviewed

1 October 2026

Indications

• Reversal of unfractionated heparin (overdose, bleeding, end of procedure)
• Partial reversal of low-molecular-weight heparin (enoxaparin/dalteparin) — incomplete

Protamine Sulfate dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Heparin reversal: Plumb’s p.1021 (Bailey; Adams): 1–1.5 mg per 100 U heparin by slow IV injection; after 30 min give only 0.5 mg per 100 U; no faster than 50 mg over 10 min. May be ineffective after deep SC heparin. Recheck aPTT; excess protamine is itself anticoagulant. Not in Papich 5e.

Cats

• Heparin reversal: Plumb’s p.1021 (dogs/cats): as for dogs; no faster than 50 mg over 10 min. Monitor for hypotension and anaphylactoid reactions.

Cattle

• Bracken fern poisoning (with whole blood): Plumb’s p.1021 (Osweiler & Ruhr 1986). Obtain a FARAD withdrawal.

Horses

• Heparin reversal: Plumb’s p.1021: dogs and cats “and presumably other species” — no horse-specific data.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Bracken fern poisoning (with whole blood): Plumb’s p.1021 (Osweiler & Ruhr 1986). Obtain a FARAD withdrawal.

Contraindications

Rapid IV injection (hypotension/anaphylactoid reaction). Overdosing relative to circulating heparin (excess protamine is itself anticoagulant). Known fish-protein/protamine hypersensitivity (it is salmon-derived) — and prior protamine exposure (e.g. protamine insulin) raises reaction risk. Known hypersensitivity.

Adverse effects

• Hypotension and bradycardia (rapid injection)
• Anaphylactoid/anaphylactic reactions (especially with prior protamine exposure or fish allergy)
• Paradoxical ANTICOAGULATION / bleeding if given in excess of circulating heparin
• Pulmonary hypertension/dyspnoea (rare)

Drug interactions

• Heparin: the target (neutralised). LMWH (enoxaparin/dalteparin): only partial reversal
• Protamine-containing insulins (NPH/protamine zinc): prior exposure increases hypersensitivity risk
• No other major interactions

Pregnancy and lactation

Used when heparin reversal is clinically necessary; standard caution applies.

Monitoring

• aPTT / coagulation status (confirm reversal; avoid over-correction)
• Blood pressure and heart rate during/after slow IV injection (hypotension/bradycardia)
• Anaphylactoid reaction surveillance (especially prior protamine exposure)
• Re-bleeding / heparin rebound (with LMWH, partial reversal)

Toxicity and overdose

Rapid IV administration causes hypotension, bradycardia and anaphylactoid reactions (histamine/complement-mediated). EXCESS protamine (more than the circulating heparin) acts as an anticoagulant itself, paradoxically worsening bleeding. Severe anaphylaxis is more likely in patients previously exposed to protamine (e.g. protamine insulins) or with fish-protein allergy.

Management: Stop/slow the infusion. Manage hypotension (IV fluids, vasopressors) and anaphylactoid reactions (antihistamine, corticosteroid, epinephrine if severe). For protamine-induced anticoagulation/bleeding, supportive care (fresh frozen plasma/transfusion if needed) and avoid further protamine. Monitor coagulation (aPTT) and re-titrate.

Clinical pearls

• The heparin antidote — dose AGAINST the heparin still circulating (≈1 mg per 100 IU), and give LESS the more time has passed since the heparin dose
• Give SLOWLY IV — rapid injection causes hypotension/bradycardia/anaphylactoid reactions; and don't over-dose, because excess protamine is itself an anticoagulant
• It only PARTIALLY reverses low-molecular-weight heparins (enoxaparin) — expect incomplete effect
• Higher anaphylaxis risk in patients previously exposed to protamine (e.g. protamine/NPH insulins) or with fish allergy

Mechanism of action

Protamine is a small, strongly cationic (arginine-rich, positively charged) protein that binds tightly to the strongly anionic (negatively charged) heparin molecule, forming an inactive, stable salt complex — neutralising heparin's ability to potentiate antithrombin and thus reversing its anticoagulant effect within minutes. It only partially binds the shorter low-molecular-weight heparin chains (incomplete LMWH reversal). Given alone or in excess of heparin, the protamine-heparin imbalance can itself impair coagulation.

Formulations and products

• Injection 10 mg/mL
• Protamine Sulfate — 10 mg/mL injection, Injection (human-label)

Storage

Injection: 15–30 °C (refrigerate per some labels), protect from light; do not freeze.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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Frequently asked questions