Heparin Sodium
Unfractionated Heparin (UFH)
Also known as: Hep-Lock · Hep-Loc U/P · Hepflush-10 · Unfractionated Heparin · UHF · heparinum natricum · sodium heparin · soluble heparin
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceThromboprophylaxis (extra-label)
Verified clinician required
- q6h
NA
Governing clinical context (2)
- Heparin is an anionic, heterogeneous sulfated glycosaminoglycan molecule with an average molecular weight of 12,000 daltons that is found naturally in mast cells. It is available commercially as the sodium salt and is obtained from either porcine intestinal mucosa or bovine lung tissue (sodium salt only). Heparin sodium occurs as a white, amorphous, hygroscopic powder having a faint odor. It is soluble in water and practically insoluble in alcohol; the commercial injections have a pH of 5 to 7.5. Heparin potency is expressed in terms of USP heparin units, and values are obtained by comparing against a standard reference from the USP. The USP requires that potencies be not less than 180 units/mg on a dried basis for heparin derived from lung tissue, and 140 units/mg when derived from all other tissue sources.
- Heparin solutions should be stored at room temperature (15°C-30°C [59°F-86°F]) and not frozen. Avoid excessive exposure to heat.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Heparin sodium is a parenteral anticoagulant primarily utilized in veterinary medicine for the management of thromboembolic disease and, more controversially, disseminated intravascular coagulation (DIC).
Key clinical applications include:
- Thromboembolic Prophylaxis: Strong evidence supports its use in reducing macrovascular thromboembolism in high-risk patients.
- DIC Management: Historically used for DIC, though current consensus advises against its use in DIC patients with concurrent inflammatory processes.
- Equine Medicine: Used for laminitis prophylaxis, DIC, and as an intraperitoneal lavage to prevent post-surgical intestinal adhesions.
Clinical Pearl: Unfractionated heparin (UFH) has a highly variable pharmacokinetic profile compared to low-molecular-weight heparins (LMWH) like dalteparin or enoxaparin. UFH requires intensive monitoring of aPTT or anti-Xa activity to ensure therapeutic efficacy and avoid catastrophic hemorrhage.
Mechanism of action
Heparin acts as an indirect anticoagulant by binding to and potentiating the activity of Antithrombin III (ATIII).
- Low Concentrations: The Heparin-ATIII complex rapidly inactivates Factor Xa, preventing the conversion of prothrombin to thrombin.
- High Concentrations: The complex inactivates Thrombin (Factor IIa), blocking the conversion of fibrinogen to fibrin, and also inactivates factors IX, XI, and XII.
- Fibrin Stabilization: By inhibiting the activation of Factor XIII, heparin prevents the formation of stable fibrin clots.
Note: Heparin does not lyse existing clots (it is not a thrombolytic); rather, it prevents the expansion of existing thrombi and the formation of new ones. It also increases the release of lipoprotein lipase, boosting the clearance of circulating lipids.
Safety & warnings
Contraindications
- Known hypersensitivity to heparin
- Severe thrombocytopenia
- Uncontrollable bleeding (not caused by DIC)
- Intramuscular (IM) administration (causes hematomas)
- Actively bleeding DIC patients with severe factor depletion
Adverse effects
- Hemorrhage (most common)
- Thrombocytopenia
- Hypersensitivity reactions (derived from bovine/porcine tissue)
- Anemia in horses (due to erythrocyte agglutination)
- Injection site pain and hematoma (especially if given IM)
- Vasospastic reactions
- Osteoporosis (with long-term use)
- Rebound hyperlipidemia
- Hyperkalemia
- Alopecia
Precautions
Use with extreme caution in patients with dysfunctional interactions between inflammatory and hemostatic systems (e.g., DIC with concurrent inflammation). Do not administer IM due to the risk of severe hematoma formation. Deep SC dosing may cause pain and irritation. Dogs with renal insufficiency may have lower plasma levels and faster elimination rates, requiring dosage adjustments. Safe use in pregnancy is not firmly established (FDA Category C).
Drug interactions
May increase the risk for hemorrhage
May increase the risk for hemorrhage
May increase the risk for hemorrhage
May increase the risk for hemorrhage
May partially counteract heparin's anticoagulant effects
May partially counteract heparin's anticoagulant effects
May partially counteract heparin's anticoagulant effects
May partially counteract heparin's anticoagulant effects
May partially counteract heparin's anticoagulant effects
Monitoring
- Activated partial thromboplastin time (aPTT) - most often recommended
- Whole blood clotting time (WBCT)
- Partial thromboplastin time (PTT)
- Activated clotting time (ACT)
- Thromboelastography (TEG)
- Platelet counts
- Packed cell volume (PCV) / Hematocrit
- Occult blood in stool and urine
- Clinical signs of bleeding or efficacy
Pharmacokinetics
Absorption
Not absorbed orally; must be given parenterally. Anticoagulant activity begins immediately after direct IV bolus, but may take up to 1 hour after deep SC injection. Bioavailability after SC injection in healthy dogs is about 50%.
Distribution
Extensively protein bound, primarily to fibrinogen, low-density lipoproteins, and globulins. Does not appreciably cross the placenta or enter milk.
Metabolism
Metabolic fate is not completely understood. Partially metabolized by the liver and inactivated by the reticuloendothelial system.
Elimination
Eliminated via hepatic metabolism and the reticuloendothelial system. Dogs with renal insufficiency may have faster elimination rates.
Overdose
Overdosage of heparin is directly associated with severe bleeding.
Clinical signs preceding frank hemorrhage include:
- Hematuria
- Tarry stools (melena)
- Petechiae and ecchymoses (bruising)
Reversal: Protamine sulfate can be administered to reverse heparin's anticoagulant effects. It binds to heparin to form a stable, inactive complex.
Available products
Formulations
- Injection solutions (1,000 to 40,000 Units/mL)
- Unit-Dose injections
- Heparin Sodium Lock Flush (10 to 100 Units/mL)
- Heparin Sodium in 0.9% or 0.45% Sodium Chloride
Human-labeled
- Heparin Sodium Injection: 1000, 2000, 2500, 5000, 10,000, 20,000, & 40,000 Units/mL
- Heparin Unit-Dose Sodium Injection: 1000 to 20,000 Units/dose
- Heparin Sodium and 0.9% or 0.45% Sodium Chloride Injection
- Heparin Sodium Lock Flush (IV use) Injection: 1, 10, and 100 Units/mL
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store solutions at room temperature (15-30°C). Do not freeze. Avoid excessive exposure to heat.
Client information
Heparin is a potent blood thinner used to treat or prevent life-threatening blood clots.
- Inpatient Care: Because of the intense monitoring required (frequent blood tests to check clotting times) and the serious nature of the diseases it treats, heparin is almost exclusively used in a hospital setting by veterinary professionals.
- Bleeding Risk: The most significant risk is bleeding. If your pet is discharged on a heparin-like drug, watch closely for any signs of bruising, bleeding gums, blood in the urine or stool, or extreme lethargy, and contact your veterinarian immediately.
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.