Protamine Sulfate
**Protamine sulfate** is a simple, low molecular weight, cationic protein originally derived from the sperm or mature testes of salmon and related fish species. In veterinary medicine, it is primarily utilized as a specific, life-saving **antidote for heparin overdose** when significant, uncontrolled bleeding occurs. Key clinical points: * **Unfractionated vs. LMWH:** While protamine completely neutralizes unfractionated heparin, it only *partially* neutralizes the anti-Xa activity of low molecular weight heparins (LMWH) like dalteparin or enoxaparin. However, it still improves microvascular bleeding in LMWH overdoses. * **Alternative Uses:** It has been suggested as an adjunctive treatment for Bracken Fern (*Pteridium spp.*) toxicity in ruminants. > **Clinical Pearl:** Because protamine is a foreign protein, hypersensitivity reactions (including anaphylaxis) are possible, particularly in patients with previous exposure or fish allergies.
Mechanism: Protamine works via direct **acid-base neutralization**. * **Mechanism:** Heparin is a strongly acidic molecule, while protamine is strongly basic. * **Pathway:** Protamine → binds directly to circulating heparin → forms an inactive, stable salt complex → neutralizes heparin's anticoagulant activity. > **Pharmacology Note:** Protamine possesses weak intrinsic anticoagulant activity of its own. If administered in large doses without heparin present, it can theoretically interfere with coagulation, though this rarely causes clinical hemorrhage.
Dosing by species
- Heparin overdosage · 1-1.5 mg protamine sulfate to antagonize each mg (100 units) of heparin via slow IV injection. Reduce dose as time increases between heparin dose and start of treatment (after 30 minutes give only 0.5 mg). · IV · Single dose · Give slowly.
- Heparin overdosage · Administer 1 mg protamine for each 100 Units of heparin to be inactivated. Decrease protamine dose by ½ for every 30 minutes that have lapsed since heparin was administered · IV · Single dose · May be ineffective if heparin was given deep SC. Do not give faster than 50 mg over 10 minutes.
- Bracken Fern (Pteridium spp.) poisoning · 1 injection of 10 mL of 1% protamine sulfate IV · IV · Single dose · In combination with whole blood (2.25-4.5 L)
- Heparin overdosage · 1-1.5 mg protamine sulfate to antagonize each mg (100 units) of heparin via slow IV injection. Reduce dose as time increases between heparin dose and start of treatment (after 30 minutes give only 0.5 mg). · IV · Single dose · Give slowly.
- Heparin overdosage · Administer 1 mg protamine for each 100 Units of heparin to be inactivated. Decrease protamine dose by ½ for every 30 minutes that have lapsed since heparin was administered · IV · Single dose · May be ineffective if heparin was given deep SC. Do not give faster than 50 mg over 10 minutes.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Known hypersensitivity or intolerance to protamine
- Hypersensitivity to protamine
- Conditions where heparin has not been administered
Adverse effects
- Acute hypotension (if given too rapidly)
- Bradycardia
- Pulmonary hypertension
- Dyspnea
- Hypersensitivity/Anaphylaxis
- Heparin 'rebound' effect (bleeding hours after neutralization)
- Hypotension
- Anaphylactoid reactions
- Paradoxical bleeding (at high doses)
Drug interactions
- Heparin · Forms a stable salt, causing the loss of anticoagulant activity of both compounds (therapeutic intent). · major
Monitoring
- Coagulation parameters (e.g., aPTT, ACT) to assess heparin neutralization
- Blood pressure (monitor for hypotension during administration)
- Heart rate and rhythm (monitor for bradycardia)
- Respiratory rate and effort
- Signs of recurrent bleeding (heparin rebound effect) for several hours post-administration
- Coagulation times (aPTT, ACT)
- Heart rate
- Blood pressure
- Signs of anaphylaxis during administration
Overdose
Because protamine has inherent, albeit weak, anticoagulant activity, massive overdoses could theoretically result in **hemorrhage**. However, clinical data in humans suggests that significant overdoses (600-800 mg) typically result in only mild, transient effects on coagulation. The LD50 of protamine in mice is reported to be 100 mg/kg. Treatment of overdose should be supportive.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.