Anticoagulant Therapy in Cats

The aim of anticoagulant therapy is to reduce the risk of blood clots forming within the circulatory system that could lodge in an inappropriate place and cut off the blood supply to that area. This is analogous to what happens in a stroke, and in the cat the main site for the clot to lodge is in the aorta (the main artery leaving the heart) where it splits into two to supply both back legs. 

This is known as an aortic thromboembolism, which is an extremely painful condition and ultimately life-threatening. Certain cats are most at risk of throwing such a blood clot, which includes those with a heart condition known as hypertrophic cardiomyopathy or those with hypercoagulable blood as a result of other conditions.

In acute illness when a blood clot is causing organ failure or poor circulation to the limbs, treatment can be given by injection. This may be as a loading dose intravenous injection followed by a constant rate infusion (lower doses given continuously for several hours). Alternatively, therapy may be given by deep subcutaneous injection, which prolongs the release of the anticoagulation and extends the benefit. Anticoagulants can also be given by deep intramuscular injection but their is a risk of large hematomas (blood blisters) forming post-therapy. 

Anticoagulant therapy has a role in the prevention of blood clot formation in patients that are at high risk. In this case, the treatment is often a low dose taken by mouth every three to four days. The most commonly prescribed anticoagulant is aspirin, for cats diagnosed with hypertrophic cardiomyopathy. An ultra-low dose is given, because of the feline's inability to break up aspirin and it persisting for a long time in the system. Typically 81 mg per cat is given every three days. The use of soluble aspirin helps to reduce the risk of gastric ulceration, as does giving the medication with food. Treatment should be stopped if the cat vomits or has diarrhea. 

The use of anticoagulants in cats is far less advanced than in humans. For several reasons, therapy is often disappointing, and cats that have already thrown a blood clot end up being euthanized because of severe pain and the poor prognosis. 

In part, this is due to the different ways in which anticoagulants are metabolised by cats. This means substances such as heparin, which are a mainstay in human medicine, are more rapidly broken down making therapeutic levels more difficult to obtain.

The use of anticoagulants also has to be balanced against an increased risk of bleeding. This means therapy is not always appropriate given the lifestyle of some cats and a propensity to fight or hunt. Indeed, for cases of DIC, anticoagulants such as heparin should not be given unless the patient also receives a blood transfusion. 

The idea of anticoagulant therapy is to prevent a catastrophic event such as a blood clot forming. Thus, successful treatment maintains a state of normalcy, such that the cat doesn't deteriorate. In this regard, there is no period of recovery from treatment.

The most commonly used anticoagulant in the cat, aspirin, costs just a few cents per dose. However, the workup to diagnose the hypertrophic cardiomyopathy is likely to involve a cardiac ultrasound costing anywhere from $180 to $500 depending on the skill and experience of the operator. 

Few controlled studies using heparin in animals and due to the complexity of balancing the risks and benefits, it is not commonly used outside of specialist referral hospitals. Other drugs widely used in people, such as warfarin, are used sparingly and rarely in cats, because unpredictability of response can lead to active bleeding. 

The most commonly used anticoagulant in cats is aspirin, used in ultra-low doses. The benefit in high risk cases is dubious, but for those animals that don't suffer side effects (such as gastric ulceration) then it's worth a try. Aspirin is inexpensive and the small doses involved mean the minimum of inconvenience to patient and owner.

Hypertrophic cardiomyopathy (HCM) is the main indication for prescribing anticoagulant therapy in cats. Feeding a high quality meat based diet, rich in taurine, helps provide vital nutrition to promote a healthy heart muscle. 

There are well-recognized links between hyperthyroidism (overactive thyroid glands) and HCM. Since there is no proven cause for hyperthyroidism, an owner should be vigilant for clues and seek early treatment to control and correct the condition. 

Symptoms of hyperthyroidism include: 

• Ravenous appetite and yet weight loss
• Drinking excessively and excessive wet patches in the litter tray
• Dull, stary coat
• Poor body condition
• Hyperactivity

There are many different ways of treating hyperthyroidism so early identification and control could prevent HCM and the need for anticoagulants.