Introduction
Blood clots can be a life-threatening condition in dogs. They occur when the blood changes from a liquid to a solid state and gets stuck in a blood vessel, blocking proper blood flow. This is known medically as thromboembolism. Some common causes of dangerous blood clots in dogs include heart disease, cancer, inflammation, infections, hormones, and injury or trauma.
If a blood clot blocks a major blood vessel, it can cut off blood flow and oxygen to major organs like the brain, lungs, heart, liver, intestines, and kidneys. This can result in severe damage, organ failure, and even death if not treated quickly. That’s why blood thinning medications are often used in dogs who have clots or are at high risk of developing them.
Blood thinners work by preventing the blood from clotting too much. This helps maintain proper blood flow and reduces the risk of additional clots forming. Some types of blood thinners used in veterinary medicine include aspirin, clopidogrel, heparin, and warfarin. It’s important to monitor dogs on these medications and use proper dosing to balance the risks of thinning the blood too much versus allowing clots to form.
Types of Blood Thinners
There are several types of blood thinners that may be used in dogs, including:
Aspirin
Aspirin is sometimes used as a blood thinner in dogs, though it’s typically not the first choice. Aspirin can help prevent clot formation and reduce the risk of stroke or heart attack. However, aspirin carries a risk of stomach and intestinal irritation and bleeding. According to the veterinarians at VCA Hospitals, the dose for dogs is 5-10 mg/kg every 12 hours.
Clopidogrel
Clopidogrel (brand name Plavix®) is a platelet aggregation inhibitor that helps prevent blood clots (VCA Hospitals, 2022). It is often used in dogs who have suffered a stroke or have heart disease. According to VCA, the typical dosage is 18.75 mg/kg once daily. Side effects may include vomiting, diarrhea, and hemorrhage.
Heparin
Heparin is an injectable anticoagulant used in dogs to treat existing blood clots and prevent new clots from forming. According to WagWalking, it is often used before surgery in dogs at risk of developing clots. Heparin must be given by injection or IV due to poor oral absorption.
Warfarin
Warfarin (brand names Coumadin, Jantoven, Panwarfin) is an oral anticoagulant that helps prevent blood clot formation and stroke in dogs with heart disease (VCA Hospitals, 2022). It may take several days to start working. Side effects can include internal bleeding or hemorrhage. Regular blood testing is needed to monitor warfarin levels.
Aspirin
Aspirin is one of the most commonly used blood thinners for dogs. Its main mechanism of action is preventing the formation of thromboxane A2 by blocking cyclooxygenase in platelets. This inhibits platelet aggregation and prevents clot formation.
The typical dosage of aspirin for dogs is 10-25 mg per pound every 12-24 hours. It’s important not to exceed this dosage as high doses can lead to toxicity and be dangerous for dogs.
Potential side effects of aspirin in dogs include:
- Stomach upset, vomiting, diarrhea
- Ulceration of the stomach and intestinal lining
- Bleeding disorders
- Allergic reaction in some dogs
Aspirin requires close monitoring and should not be given long-term without veterinary supervision. Safer prescription alternatives are usually recommended over aspirin when more chronic therapy is needed.
Clopidogrel
Clopidogrel (brand name: Plavix®) is a platelet aggregation inhibitor used to prevent abnormal blood clot formation in dogs and cats [1]. It works by preventing platelets from clumping together and forming blood clots. This helps maintain normal blood flow and reduces the risk of stroke, heart attack, pulmonary embolism, or other thromboembolic disorders.
The typical dosage of clopidogrel for dogs is 1-2 mg/kg once daily, according to the prescribing veterinarian’s recommendations [2]. For cats, a dose of 18.75 mg (one-fourth of a 75 mg tablet) is given once daily. Clopidogrel is given orally and can be administered with or without food.
Potential side effects of clopidogrel include vomiting, diarrhea, loss of appetite, lethargy, bruising, nosebleeds, and bloody urine. Rarely, it may also lead to thrombocytopenia (low platelet count). Dogs taking this medication should be monitored through regular veterinary exams and bloodwork.
Clopidogrel is contraindicated in pets with hypersensitivity to the drug. Caution should be used in patients with liver disease, kidney disease, bleeding disorders, or gastrointestinal ulcers, as they may be at higher risk of side effects.
Heparin
Heparin is an anticoagulant that works by binding to antithrombin III, which inhibits the coagulation factors thrombin and factor Xa. This prevents the formation of clots. It is available in unfractionated heparin (UFH) and low molecular weight heparin (LMWH) formulations.
The dosage for dogs is:
– UFH: High dose 400-800 U/kg/day; Low dose 200-300 U/kg/day
– LMWH: High dose 100 U/kg every 12 hours; Low dose 2,000-5,000 U/adult/day
Potential side effects include:
– Hemorrhage
– Thrombocytopenia
– Hyperkalemia
– Alopecia
– Osteoporosis with prolonged use
Heparin levels and clotting times should be monitored and the dose adjusted accordingly. The aPTT test is used to monitor heparin therapy. The target range is 1.5-2 times higher than baseline.1
Warfarin
Warfarin is an anticoagulant that works by inhibiting the synthesis of vitamin K-dependent clotting factors, preventing normal coagulation and increasing bleeding risk (Source). In dogs, warfarin is most commonly used for the prevention of thromboembolic complications associated with atrial fibrillation, prosthetic heart valves, and other conditions (Source).
The typical starting dose of warfarin in dogs is 0.13 mg/kg once daily, adjusted based on regular monitoring of the prothrombin time (PT) or international normalized ratio (INR). The PT/INR is used to assess the level of anticoagulation and guide dosing adjustments. Excessive prolongation of PT/INR indicates overanticoagulation and bleeding risk (Source).
Side effects of warfarin include hemorrhage, bruising, hematuria, melena. Vitamin K can be administered as an antidote in cases of overdose or excessive bleeding. Frequent laboratory monitoring is essential with warfarin therapy.
Monitoring
Monitoring anticoagulation therapy in dogs receiving warfarin is crucial for maintaining appropriate dosing and avoiding complications. The primary test used is measuring the international normalized ratio (INR), which evaluates the extrinsic pathway of coagulation. The target INR range for dogs on warfarin therapy is typically 2.0-3.0. Frequent monitoring, often weekly at first, allows veterinarians to make dosage adjustments to maintain the INR in the therapeutic range. INR values outside the target range, either too high or too low, increase the risk of bleeding or clotting issues respectively. According to a case report on using warfarin for a dog with acute arterial thrombosis, the starting dose was 0.2 mg/kg PO q24h, with subsequent dosing adjusted based on weekly INR results. The warfarin dose was gradually lowered over several weeks as the INR stabilized in the target range.
Monitoring protocols are less established for newer anticoagulant medications like apixaban. However, anti-Xa activity assays can be used to measure the level of anticoagulant effect. According to Cornell’s Animal Health Diagnostic Center, this allows veterinarians to correlate drug levels with clinical signs and make dosage adjustments accordingly.
Contraindications
Blood thinners should be avoided or used with caution in certain situations. According to the VCA Hospitals, warfarin should be avoided in pets with an aneurysm, acute kidney disease, brain bleeds, blood cell diseases, uncontrolled high blood pressure, liver disease, protein C deficiency, recent surgery, trauma or hemorrhage, endocarditis, and certain cancers like leukemia (source). Clopidogrel is also not recommended for pets with active bleeding issues like ulcers or hemorrhage, or platelet function abnormalities according to the VCA (source). In general, blood thinners can cause serious side effects like hemorrhaging, anemia, hematomas, and bleeding, so caution should be exercised in dogs that have conditions that put them at higher risk.
Side Effects
The most common side effect of blood thinners in dogs is increased bleeding and bruising. This occurs because these medications inhibit the blood’s ability to clot. Dogs on blood thinners may experience nose bleeds, blood in the stool or urine, bleeding gums, and unexplained bruising or hematomas under the skin. Prolonged bleeding from minor cuts is also common. According to the VCA Hospitals, signs of abnormal bleeding in dogs include pale gums, weakness, swollen areas of the body, and blood in vomit or stools.
Warfarin can also cause side effects such as lack of appetite, vomiting, and diarrhea, as noted by VCA Hospitals (https://vcahospitals.com/know-your-pet/warfarin). The anticoagulant effects of warfarin may lead to bleeding complications. Clopidogrel side effects can also include stomach upset and vomiting, according to the Wedgewood Pharmacy (https://www.wedgewoodpharmacy.com/medications/clopidogrel/).
It’s important to monitor dogs on blood thinners for signs of bleeding or bruising and to be cautious of interactions with other drugs that affect clotting. Vet supervision is essential when using these medications in dogs.
Conclusion
Blood thinners are important medications used in veterinary medicine to prevent and treat blood clots in dogs. The key takeaways are:
- Common blood thinners used in dogs include aspirin, clopidogrel, heparin, and warfarin.
- These medications help prevent blood clots from forming or growing larger by inhibiting platelet aggregation and blood coagulation.
- Monitoring is essential when using blood thinners to watch for potential side effects like bleeding or clotting issues.
- Certain health conditions may preclude the use of blood thinners if bleeding risk is too high.
- Veterinary oversight is critical when using blood thinners in dogs given the potential side effects and monitoring required.
- Pet owners should never give blood thinning medication without the guidance of their veterinarian.
In summary, while blood thinners can be very helpful for preventing and treating blood clots in dogs, they require careful administration and monitoring under veterinary supervision to balance their benefits and risks.