Heparin
Unfractionated heparin is an injectable anticoagulant composed of sulfated glycosaminoglycan chains of varying lengths. It is used to limit formation and extension of thrombi in selected veterinary patients. Its principal clinical roles include thromboprophylaxis in high-risk patients and anticoagulation during treatment of established thromboembolic disease or selected procedures.
Group
Unfractionated anticoagulant
Mechanism of Action
Heparin binds antithrombin and accelerates its inhibition of activated coagulation factors, particularly factor Xa and thrombin. Sufficiently long heparin chains can bridge antithrombin and thrombin, supporting thrombin inhibition. Reduced factor activity limits fibrin generation and further clot formation or propagation. Heparin provides anticoagulation while endogenous fibrinolytic processes act on existing thrombi.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Thromboprophylaxis | 70–100 IU/kg | SC | Every 8 h | |
| Ongoing coagulopathy — Loading | 100–200 IU/kg | IV, SC | ||
| Ongoing coagulopathy — Maintenance | 150–300 IU/kg | SC | Every 6 h | Titrate against anti-Xa response; escalation to 500-600 IU/kg may be required. |
| Severe coagulopathy — Initial | 500 IU/kg | SC | ||
| Severe coagulopathy — Maintenance | 500 IU/kg | SC | Every 12 h | |
| Anticoagulant infusion — Loading | 100 IU/kg | IV | ||
| Anticoagulant infusion — Maintenance | 20–30 IU/kg/hour | IV | Continuous | Equivalent to 480-720 IU/kg over 24 hours; titrate to coagulation testing. |
| DIC adjunct | 75 IU/kg | SC | Every 8 h | Control the precipitating cause and assess platelet/factor depletion first. |
| DIC adjunct | 50–100 IU/kg | SC | Every 6 h | |
| DIC low-dose infusion | 5–10 IU/kg/hour | IV | Continuous | |
| Warfarin bridging | 200–500 IU/kg | SC | Every 8 h | Up to 7 days; Usually 5-7 days or until PT confirms adequate warfarin effect; titrate by coagulation testing. |
| Ongoing coagulopathy | 150–300 IU/kg | SC | Every 6–8 h | Separate interval alternative; response is individual. |
| Anticoagulant infusion — Maintenance | 20–50 IU/kg/hour | IV | Continuous | After 100 IU/kg IV loading; titrate in increments of 5 IU/kg/hour using coagulation testing. |
| Lipoprotein-lipase stimulation test | 100 IU/kg | IV | Once | Measure serum lipids before and 15 minutes after dosing. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Thromboprophylaxis | 70–100 IU/kg | SC | Every 8 h | |
| Ongoing coagulopathy | 250 IU/kg | SC | Every 6 h | May be increased gradually to 500 IU/kg if monitoring indicates. |
| DIC adjunct | 75 IU/kg | SC | Every 8 h | Control the precipitating cause and assess platelet/factor depletion first. |
| DIC adjunct | 50–100 IU/kg | SC | Every 6 h | |
| DIC low-dose infusion | 5–10 IU/kg/hour | IV | Continuous | |
| Arterial thromboembolism | 250–300 IU/kg | SC | Every 8 h | |
| Arterial thromboembolism — Initial | 250–300 IU/kg | IV | Initial IV dose described only for cats presenting in shock; then use the SC regimen and monitor. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Thromboprophylaxis | 125 IU/kg | SC | Every 8–12 h | |
| Thromboprophylaxis | 80 IU/kg | SC | Every 12 h | Separate lower-dose alternative. |
| DIC adjunct | 80–100 IU/kg | IV | Every 4–6 h | |
| Low-grade DIC adjunct | 25–40 IU/kg | SC | Every 8–12 h | |
| Endotoxic-shock adjunct | 40 IU/kg | IV, SC | Every 8–12 h | Benefit in preventing microthrombi is not established. |
| Laminitis-associated thromboprophylaxis | 25–100 IU/kg | SC | Every 8 h | Adjust to thrombotic risk and coagulation response. |
| Staged thromboprophylaxis | Reference only | SC | 150 IU/kg initially, then 125 IU/kg every 12 hours for six doses, then 100 IU/kg every 12 hours. Keep the six-dose transition explicit. | |
| Postoperative adhesion-prevention lavage | Reference only | IP | 30,000-50,000 IU in 10 L warm LRS, lavaged at 12, 18, 36 and 48 hours after surgery through a fenestrated drain; allow drainage and remove after final lavage or occlusion. |
Indications
- Thromboprophylaxis in selected dogs and cats with high-risk hypercoagulable disorders, including some immune-mediated hemolytic anemia or protein-losing disease cases.
- Anticoagulant treatment of selected venous thrombosis, pulmonary thromboembolism or other established thromboembolic disease.
- Specialist management of selected thrombosis-predominant disseminated intravascular coagulation, with uncertain benefit and patient-specific selection.
- Anticoagulation for selected extracorporeal circuits or vascular procedures requiring temporary suppression of coagulation.
Contraindications
- Active uncontrolled bleeding
- Inability to monitor anticoagulation
- Avoid intramuscular administration because of haematoma risk.
- Severe thrombocytopenia or active bleeding with major coagulation-factor depletion; DIC treatment requires individual assessment rather than automatic anticoagulation.
Interactions
- Aspirin, warfarin and other agents that impair haemostasis increase bleeding risk.
- Use cautiously with glycosaminoglycan products.
- Dextran and NSAIDs increase haemorrhage risk. Antihistamines, IV nitroglycerin, propylene glycol, digoxin or tetracyclines may reduce anticoagulant effect.
Adverse effects
- Haemorrhage and injection-site haematoma
Toxicity
Protamine sulfate can reverse excessive heparin anticoagulation; administer slowly intravenously with monitoring.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Heparin 1000 IU/mL injection | Injection | 1000 IU / mL | IV, SC |
| Heparin 10000 IU/mL injection | Injection | 10000 IU / mL | IV, SC |
| Heparin sodium 2000 IU/mL injection | Injection | 2000 IU / mL | IV, SC |
| Heparin sodium 2500 IU/mL injection | Injection | 2500 IU / mL | IV, SC |
| Heparin sodium 5000 IU/mL injection | Injection | 5000 IU / mL | IV, SC |
| Heparin sodium 20000 IU/mL injection | Injection | 20000 IU / mL | IV, SC |
| Heparin sodium 40000 IU/mL injection | Injection | 40000 IU / mL | IV, SC |
Monitoring and Administration
Adjust treatment using aPTT or anti-Xa activity rather than a fixed dose alone. The supplied guidance targets aPTT 1.5-2 times baseline or anti-Xa 0.35-0.70 IU/mL; reduce dose by 25% if anti-Xa exceeds 0.7 IU/mL.
Heparinized catheter-flush solutions contain 0.25-10 IU/mL: 0.25 mL of 1000 IU/mL per litre or 1 mL of 10000 IU/mL per litre, respectively. A clinical advantage over plain saline for flushing has not been established.
Protect from light and store tightly closed at room temperature.
The nonspecific large-animal section gives 125 IU/kg SC or IM every 8-12 hours. Its IM route conflicts with the same monograph’s warning against haematoma risk; IM administration should be avoided. The explicit equine 80 IU/kg SC alternative is retained.
Follow platelets, PCV and occult urine/faecal bleeding as well as coagulation assays. Avoid freezing. Heparin is incompatible with several aminoglycosides, diazepam, phenytoin and vancomycin; hydrocortisone-succinate compatibility is concentration-dependent or conflicting.
Pyothorax lavage: heparin 1000 IU/L in warmed saline, instilled at 20 mL/kg twice daily for 5-7 days as part of a chest-lavage protocol. This is not a systemic heparin dose.
Adrenalectomy thromboprophylaxis described in hyperadrenocorticoid dogs uses heparinized plasma at induction, then 35 IU/kg twice 8 hours apart on surgery day, 25 IU/kg SC the next day and a four-day taper; plasma and taper details require an individualized plan.