# Heparin (Unfractionated): veterinary dose and monograph

> Heparin (Unfractionated) is a veterinary drug. Unfractionated heparin is a rapid-acting injectable ANTICOAGULANT used to treat and prevent thromboembolism — feline arterial thromboembolism (ATE) secondary to cardiomyopathy, pulmonary thromboembolism, DIC (in the hypercoagulable… Indications include feline arterial thromboembolism (cardiomyopathy-associated); pulmonary thromboembolism / venous thromboembolism; disseminated intravascular coagulation (hypercoagulable phase). This monograph lists 5 reference doses for dogs, cats and horses, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/heparin · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Veterinary drug
- **Also known as:** UFH, Heparin sodium, Beparine, Thrombophob (topical)
- **Species with doses:** Dogs, Cats and Horses
- **Routes:** SC, IV
- **Last reviewed:** 1 October 2026

## Indications

- Feline arterial thromboembolism (cardiomyopathy-associated)
- Pulmonary thromboembolism / venous thromboembolism
- Disseminated intravascular coagulation (hypercoagulable phase)
- Thromboprophylaxis in high-risk disease (IMHA, PLN, sepsis)

## Heparin (Unfractionated) 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 (Unfractionated) doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Treatment of thrombosis / coagulopathy | 150–300 mg/kg | SC | q6–8h | — |
| Low-dose prophylaxis / DIC | 50–100 mg/kg | SC | q6–8h | — |
| Anticoagulation CRI | 20–50 U/kg/h | IV | CRI after 100 U/kg IV load | — |

- Treatment of thrombosis / coagulopathy: UNITS/kg. Papich 5e: 100–200 U/kg IV or SC load, then 150–300 U/kg q6h SC, adjusted by anti-Xa (up to 500–600 U/kg). Plumb’s p.605: 150–300 U/kg SC q6–8h monitored by aPTT (Brainard 2008); warfarin bridging 200–500 U/kg SC q8h to aPTT 1.5–2× or anti-Xa 0.35–0.7 U/mL. Taper over 3–4 days to avoid rebound.
- Low-dose prophylaxis / DIC: UNITS/kg. Papich 5e: prophylaxis 70–100 U/kg q8h SC. Plumb’s p.605 (DIC): 75 U/kg SC q8h (Wingfield; Slappendel) or 50–100 U/kg SC q6h after replacing platelets/fibrinogen with fresh blood (Green).
- Anticoagulation CRI: Papich 5e: 100 U/kg IV, then 20–30 U/kg/h. Plumb’s p.605 (Brainard 2008): 100 U/kg load then 20–50 U/kg/h, adjusting in 5 U/kg/h steps by aPTT.

### Cats

*Heparin (Unfractionated) doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Arterial thromboembolism (ATE) | 250–300 mg/kg | SC | q6–8h | — |

- Arterial thromboembolism (ATE): UNITS/kg. Plumb’s p.605: 250–300 U/kg SC q8h, the first dose IV in shocked cats (Smith 2004; Lunsford & Mackin 2007). Papich 5e: 250 U/kg SC q6h, increasing up to 500 U/kg if needed; prophylaxis 70–100 U/kg q8h. aPTT/ACT targets are rough guides only.

### Horses

*Heparin (Unfractionated) doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Anticoagulation (e.g. laminitis-associated, DIC) | 80–125 mg/kg | SC | q8–12h | — |

- Anticoagulation (e.g. laminitis-associated, DIC): UNITS/kg. Papich 5e: 125 U/kg SC or IM q8–12h (80 U/kg SC q12h also used). Plumb’s p.605: hypercoagulable states 150 U/kg SC, then 125 U/kg q12h for 6 doses, then 100 U/kg q12h; laminitis prevention 25–100 U/kg SC three times daily; DIC 80–100 U/kg IV q4–6h. Heparin causes RBC agglutination and falling PCV in horses — monitor.

## Contraindications

Active uncontrolled haemorrhage, severe thrombocytopenia, recent surgery/trauma with bleeding risk, and known heparin hypersensitivity (heparin-induced thrombocytopenia in people). Antithrombin deficiency markedly reduces efficacy. Reduce/avoid with other anticoagulants unless intended.

## Species-specific warnings

> **Caution:** Horses: Heparin can cause red-cell agglutination and a drop in PCV in horses — monitor haematocrit during therapy.

## Adverse effects

- Haemorrhage (the principal risk) — dose/aPTT-dependent
- Injection-site bruising/haematoma
- Thrombocytopenia (reported)
- Variable, unpredictable response between patients (hence monitoring)

## Drug interactions

- Other anticoagulants/antiplatelets (clopidogrel, aspirin, warfarin, NSAIDs): additive bleeding risk
- Drugs reducing antithrombin: reduced heparin efficacy
- Protamine: specific reversal agent
- Incompatible in line with many drugs (aminoglycosides, etc.)

## Pregnancy and lactation

Heparin does not cross the placenta and is the anticoagulant of choice when anticoagulation is needed in pregnancy (preferred over warfarin).

## Monitoring

- aPTT (target ~1.5–2× baseline) or anti-Xa activity — titrate dose to it
- PCV/platelets and any signs of bleeding
- Antithrombin level if response is poor
- Double-check vial concentration (IU/mL) before every dose

## Toxicity and overdose

The dose-limiting toxicity is HAEMORRHAGE (from over-anticoagulation), with variable inter-patient response making monitoring essential. Thrombocytopenia can occur. In horses, heparin can cause red-cell agglutination and anaemia. Overdose risk is bleeding into any site.

Management: Antidote: PROTAMINE SULPHATE neutralises heparin (≈1 mg protamine per 100 IU heparin still circulating; give slowly — protamine itself can cause hypotension/anaphylaxis and, in excess, is itself an anticoagulant). Stop heparin; support with transfusion/plasma for significant bleeding; monitor aPTT.

## Clinical pearls

- Dose in IU/kg and TITRATE to aPTT — heparin response is highly variable, so fixed dosing without monitoring is unreliable
- It prevents clot growth but does NOT dissolve existing clots (not a thrombolytic) and needs antithrombin to work
- Protamine is the antidote for over-anticoagulation — keep it in mind, and give protamine slowly
- A notorious source of dosing errors — always confirm whether the vial is 1000 vs 5000 vs 25000 IU/mL
- In feline ATE it's an acute measure; transition to longer-term antithrombotics (clopidogrel) for prevention

## Mechanism of action

Heparin binds and dramatically accelerates ANTITHROMBIN, which then inactivates thrombin (factor IIa) and factor Xa (and other serine-protease clotting factors), preventing fibrin formation and clot propagation. Because it acts THROUGH antithrombin, efficacy depends on adequate antithrombin levels. It is an anticoagulant (prevents new/extending clots), not a thrombolytic (it does not dissolve existing clots).

## Formulations and products

- Injection 1000 IU/mL
- Injection 5000 IU/mL
- Injection 25000 IU/mL (concentrated)
- Beparine — 1000 / 5000 / 25000 IU/mL injection, Injection (human-label)
- Heparin sodium — 5000 IU/mL injection, Injection (human-label)

## Storage

Injection: 15–30 °C (do not freeze), protect from light. Verify the concentration carefully — heparin dosing errors (wrong vial strength) are a classic, dangerous medication error.

## Before you use this dose

> **Caution:** 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

### What is the dose of Heparin (Unfractionated) for dogs?

Reference doses for Heparin (Unfractionated) in dogs: 150–300 mg/kg SC q6–8h (Treatment of thrombosis / coagulopathy); 50–100 mg/kg SC q6–8h (Low-dose prophylaxis / DIC); 20–50 U/kg/h IV CRI after 100 U/kg IV load (Anticoagulation CRI). Confirm against the label and the patient before use.

### What is the dose of Heparin (Unfractionated) for cats?

Reference doses for Heparin (Unfractionated) in cats: 250–300 mg/kg SC q6–8h (Arterial thromboembolism (ATE)). Confirm against the label and the patient before use.

### What is the dose of Heparin (Unfractionated) for horses?

Reference doses for Heparin (Unfractionated) in horses: 80–125 mg/kg SC q8–12h (Anticoagulation (e.g. laminitis-associated, DIC)). Confirm against the label and the patient before use.

### When should Heparin (Unfractionated) not be used?

Active uncontrolled haemorrhage, severe thrombocytopenia, recent surgery/trauma with bleeding risk, and known heparin hypersensitivity (heparin-induced thrombocytopenia in people). Antithrombin deficiency markedly reduces efficacy. Reduce/avoid with other anticoagulants unless intended.

### What are the side effects of Heparin (Unfractionated) in animals?

Haemorrhage (the principal risk) — dose/aPTT-dependent; Injection-site bruising/haematoma; Thrombocytopenia (reported); Variable, unpredictable response between patients (hence monitoring).

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.