Veterinary Antithrombotic Calculator: When and Which to Use

Quick answer

• How to use
• Who needs antithrombotics
• Venous vs arterial
• Dose table
• Drugs in detail
• By condition
• Monitoring
• Stopping before surgery
• Common mistakes
• FAQs
• Glossary
• References

How to use this calculator

1. Choose a mode. Use Decision + plan to work a patient up from their conditions, or Drug dose lookup to jump straight to any drug’s dose card.
2. Set species and weight. Pick dog or cat and enter the body weight in kg or lb. The decision logic works without a weight; the weight unlocks the calculated doses.
3. Tick conditions and risk factors. Select everything that applies. Dogs with IMHA or PLN, cats with cardiomyopathy plus a risk factor, and any patient with more than one risk factor are flagged as mandatory-therapy patients.
4. Add patient factors. Bleeding risks (active haemorrhage, coagulopathy, GI ulceration, NSAIDs) and planning flags (surgery, transient condition) adjust the warnings.
5. Read the plan. The verdict, thrombus type, first-line drugs and calculated doses appear with the working shown. Doses are in mg or units per dose, not mL – convert against your own product’s concentration.
6. Record it. Copy, print (with a signature line), email, download or share the plan as a link that restores the exact same inputs.

One deliberate design choice: results are in mg or units per dose, never mL. Injectable concentrations vary between products and countries, so the millilitre conversion belongs at the bench, against the vial in your hand. For CRI dilutions and mL/h, the dilution calculator does that step properly.

Which dogs and cats need antithrombotics?

The CURATIVE consensus splits patients into those in whom antithrombotic therapy is effectively mandatory and those less likely to need it.

The single-risk-factor group is where clinical judgment earns its keep. A dog with mild pancreatitis that is eating again tomorrow is a very different proposition from a dog with pancreatitis on a jugular catheter receiving glucocorticoids. Every additional prothrombotic hit moves the patient toward the mandatory group.

Venous vs arterial thrombosis: why the drug class changes

The drug choice follows the biology of the clot. Venous thromboembolism – the pattern behind pulmonary thromboembolism in IMHA and PLN – forms under low-shear conditions. These thrombi are fibrin rich and depend relatively little on platelet number or function, so anticoagulants (heparins, factor Xa inhibitors) are the convention.

Arterial thrombosis – the pattern behind aortic thromboembolism in feline cardiomyopathy – forms under high-shear conditions and is platelet rich, so drugs that stop platelets activating, aggregating and adhering are most effective: antiplatelets. Clopidogrel is recommended instead of aspirin in cats at ATE risk, and may be more effective than aspirin in dogs.

Patients with risk factors in both columns (a cat with cardiomyopathy that also has sepsis, say) sit in a mixed category where both classes come into play and combination therapy may be weighed against bleeding risk.

Antithrombotic dose table for dogs and cats

These are the doses from the CURATIVE guideline summary this calculator runs on. The calculator above multiplies them out for your patient’s weight and shows the working.

Antithrombotic drugs in detail

Every drug in the calculator, with its guideline dose, monitoring and stopping rules. Each section is deep-linkable, and the dose lines are checked at runtime against the calculator’s own data so this reference can never silently drift from what the tool computes.

Antithrombotics by condition

Blood thinners for dogs with IMHA

Immune-mediated haemolytic anaemia is the textbook mandatory indication. IMHA dogs die of pulmonary thromboembolism as often as they die of anaemia, and the CURATIVE consensus treats antithrombotic therapy as non-negotiable in this disease. The thrombi are venous-pattern – fibrin rich, formed under low shear – so the first-line choice is an anticoagulant, with LMWH (dalteparin or enoxaparin) preferred over UFH. In dogs at the highest VTE risk, adding an antiplatelet to the anticoagulant may be considered where clot risk is felt to outweigh the extra bleeding risk. Most IMHA dogs are also on glucocorticoids, which stack a further prothrombotic hit on top of the disease itself.

Antithrombotics for protein-losing nephropathy in dogs

PLN earns its mandatory status through a specific mechanism: the glomerulus that leaks albumin also leaks antithrombin, stripping out one of the blood’s main brakes on coagulation. The result is a venous-pattern hypercoagulable state, and the approach mirrors IMHA: an anticoagulant first, LMWH preferred, with anti-Xa monitoring where available. Because PLN is usually a chronic disease, discontinuation rarely arises – these patients tend to stay on therapy, and the stopping-before-surgery rules matter more than any endpoint.

Preventing arterial thromboembolism in cats with cardiomyopathy

Feline aortic thromboembolism – the “saddle thrombus” – is one of the most distressing emergencies in practice, and it is exactly the event this branch of the guideline exists to prevent. A cat with cardiomyopathy plus any associated risk factor (left atrial enlargement, spontaneous echo contrast, reduced left auricular flow velocity, a previous ATE, congestive heart failure) needs antithrombotic therapy. Because these are platelet-rich arterial clots, the drug is an antiplatelet: clopidogrel, 18.75 mg once daily, recommended instead of aspirin. Cardiomyopathy without any of those risk factors sits in the judgment zone – which is a reason to look for them on echo, not a reason to relax.

Pancreatitis, sepsis and stacking risk factors

Most antithrombotic decisions in general practice are not about IMHA – they are about the patient with two moderate problems at once. The guideline’s rule is clean: one risk factor alone means the patient is less likely to need therapy; more than one makes it mandatory, and pancreatitis with sepsis is the consensus’s own worked example. Neoplasia, hyperadrenocorticism, glucocorticoid therapy, protein-losing enteropathy and previous thromboembolism all count toward the tally. The counterweight is the transient-condition rule: a risk factor likely to resolve within days to weeks with treatment lowers the case for starting, and any therapy begun should be re-questioned as the underlying disease resolves.

Monitoring heparin therapy

Stopping antithrombotics before surgery

Discontinuation is a risk-level decision, not a drug habit. For antiplatelets: high-risk patients should generally not have them stopped; moderate-risk patients – consider stopping 5–7 days before surgery; low-risk patients – stop 5–7 days before. Unfractionated heparin must be tapered rather than stopped abruptly, whether given by CRI or SC injection, and surgery is best planned at the nadir of effect, roughly 6–8 hours after the last SC dose, with close attention to surgical haemostasis. LMWH needs no weaning but is stopped before procedures in low-to-moderate-risk patients. For rivaroxaban, weaning should be considered.

Common mistakes with antithrombotics in practice

The mistakes we see repeatedly: reaching for aspirin in cats when clopidogrel is the recommended antiplatelet; giving a cat an unfractionated heparin CRI when the feline evidence in the summary is for SC dosing; stopping a heparin CRI abruptly instead of weaning it; using warfarin at all; treating a fibrin-rich venous problem (IMHA) with an antiplatelet alone; forgetting that when two risk factors stack – pancreatitis plus sepsis, neoplasia plus glucocorticoids – prophylaxis stops being optional; and dosing enoxaparin once daily when the canine dose in the summary is every six hours.

Frequently asked questions

Glossary

ATE (arterial thromboembolism)

A clot forming in, or lodging in, an artery – classically the distal aortic 'saddle thrombus' of feline cardiomyopathy. Arterial thrombi form under high shear and are platelet rich, which is why antiplatelet drugs are the mainstay.

VTE (venous thromboembolism)

Clot formation on the venous side, including pulmonary thromboembolism. Venous thrombi form under low shear, are fibrin rich, and respond to anticoagulants rather than antiplatelet drugs alone.

IMHA

Immune-mediated haemolytic anaemia. Dogs with IMHA are at such high risk of thromboembolism that antithrombotic therapy is considered mandatory.

PLN (protein-losing nephropathy)

Renal protein loss that also loses antithrombin, tipping the coagulation balance toward clotting. The second canine condition in which antithrombotics are mandatory.

Spontaneous echo contrast (smoke)

Swirling echogenic blood seen in an enlarged left atrium on echocardiography – a marker of blood stasis and a recognised risk factor that makes antithrombotic therapy mandatory in a cat with cardiomyopathy.

Anti-Xa activity

The laboratory assay used to measure heparin effect. Targets: 0.35–0.7 U/mL for unfractionated heparin, 0.5–1.0 U/mL (2–4 h post-dose) for LMWH.

LMWH

Low molecular weight heparin – dalteparin or enoxaparin. Preferred over unfractionated heparin for its safety profile and more reliable bioavailability.

UFH

Unfractionated heparin. Titratable by IV CRI against anti-Xa, but must be tapered rather than stopped abruptly.

CRI

Constant rate infusion – continuous IV delivery, used for UFH in dogs at 20–37.5 U/kg/h after a 100 U/kg loading bolus.

Thromboprophylaxis

Antithrombotic therapy given to prevent a first clot in an at-risk patient, as opposed to treating an existing thrombus.

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References

1. Goggs R, et al. American College of Veterinary Emergency and Critical Care (ACVECC) Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE) guidelines: Small animal. J Vet Emerg Crit Care. 2019;29(1). doi:10.1111/vec.12801
2. deLaforcade A, et al. CURATIVE: Domain 1 – Defining populations at risk. J Vet Emerg Crit Care. 2019;29(1). PMID 30654424
3. Goggs R, et al. CURATIVE: Domain 2 – Defining rational therapeutic usage. J Vet Emerg Crit Care. 2019;29(1). PMID 30654415
4. Blais MC, et al. CURATIVE: Domain 3 – Defining antithrombotic protocols. J Vet Emerg Crit Care. 2019;29(1). doi:10.1111/vec.12795
5. Sharp CR, et al. Clinical application of the ACVECC CURATIVE guidelines to small animal cases. J Vet Emerg Crit Care. 2019;29(1). PMID 30729652
6. deLaforcade A, et al. 2022 Update of the CURATIVE consensus: Domain 1 – Defining populations at risk. J Vet Emerg Crit Care. 2022. PMID 35499966

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