Heparin
Heparin is a medication that inhibits blood clotting and thus prevents or dissolves the formation of blood clots. Blood clots can lead to serious complications such as thrombosis, embolism or stroke. Heparin can also be used in animals, including dogs, to prevent or treat blood clots. In this article you will learn more about the effects, use and side effects of heparin in dogs.
How does heparin work?
Heparin is a naturally occurring molecule that consists of a chain of sugars. It binds to a factor in the blood called antithrombin III. This factor normally inhibits the activity of various clotting factors involved in the formation of fibrin. Fibrin is a protein that forms the basis for blood clots. When heparin binds to antithrombin III, its effect is enhanced and the coagulation factors are thus more strongly inhibited. The result is reduced fibrin formation and a reduced tendency of the blood to clot.
When is heparin used?
Heparin can be used for various diseases or situations that lead to an increased tendency of the blood to clot. These include
- DIC (disseminated intravascular coagulation): This is a life-threatening disorder in which there is uncontrolled activation of coagulation throughout the body. This leads to consumption coagulopathy, in which the coagulation factors and platelets are used up, resulting in severe bleeding. The causes of DIC can be varied, such as infections, cancer, poisoning or shock.
- Thrombosis: This is the formation of a blood clot in a blood vessel that obstructs or blocks the flow of blood. This can lead to tissue damage or organ failure. The most common sites for thrombosis are the veins of the legs or the lungs (pulmonary embolism).
- Diseases with potential hypercoagulability: These are diseases that can increase the risk of thrombosis, such as Cushing's syndrome, nephrotic syndrome or cardiomyopathy.
- Surgical interventions: This can result in damage to the blood vessels, which can trigger a clotting reaction. It can also lead to reduced mobility of the animal, which slows down the blood flow and thus increases the risk of thrombosis.
- Burns: This can cause damage to the skin and blood vessels, which can trigger a clotting reaction. An inflammatory reaction can also occur, which increases the tendency to clot.
How is heparin used?
Heparin is available in various forms and dosages. The most common forms are
- Unfractionated heparin (UFH): This is the original heparin obtained from animal tissues. It has a high molecular mass and a variable effect. It must therefore be monitored regularly in order to adjust the correct dosage. It is usually administered as an intravenous infusion or subcutaneous injection.
- Low molecular weight heparin (NMH): This is a synthetic heparin produced from UFH. It has a lower molecular mass and a more uniform effect. It therefore requires less monitoring and can be administered in fixed doses. It is usually administered as a subcutaneous injection.
The dosage of heparin depends on the indication, weight and condition of the animal. There are no standard recommendations for the dosage of heparin in dogs, so the vet must determine the optimum dosage on an individual basis. As a general rule, a higher dosage has a stronger anticoagulant effect, but also increases the risk of bleeding. A lower dosage has a weaker anticoagulant effect, but also a lower risk of bleeding.
The following dosages are usually recommended for UFH:
- For the treatment of thrombosis or DIC: 150-250 IU/kg every 8 hours as a subcutaneous injection or as a continuous intravenous infusion.
- For the prophylaxis of thrombosis: 75 IU/kg every 8 hours as a subcutaneous injection.
The following dosages are usually recommended for NMH:
- For the treatment of thrombosis or DIC: 100-200 IU/kg every 12 hours as a subcutaneous injection.
- For the prophylaxis of thrombosis: 50-100 IU/kg every 12 hours as a subcutaneous injection.
The effect of heparin can be monitored by various coagulation tests, such as the aPTT (activated partial thromboplastin time), the TT (thrombin time) or the anti-factor Xa test. These tests measure the time it takes for the blood to clot. The longer the time, the stronger the inhibition of clotting. The target values for these tests depend on the indication and the heparin used. In general, the aPTT should be prolonged by 1.5 to 2.5 times and the TT by 2 to 4 times the normal value. The anti-factor Xa test should show a value between 0.2 and 0.7 IU/ml.
What are the side effects of heparin?
The most common and most serious side effect of heparin is bleeding. This can lead to anemia, shock or death. Bleeding can occur in various places, such as the gastrointestinal tract, the lungs, the brain or at the injection site. The symptoms of bleeding can be
- Pale mucous membranes
- Weakness
- shortness of breath
- Vomiting or diarrhea with blood
- Blood in the urine
- Behavioral changes
- seizures
Another possible side effect of heparin is thrombocytopenia. This is a lack of platelets, which are important for blood clotting. Paradoxically, thrombocytopenia can lead to an increased tendency to bleed. The cause of thrombocytopenia is not fully understood, but it is thought to be an immune-mediated reaction in which antibodies are produced against heparin or antithrombin III. The symptoms of thrombocytopenia can be
- Petechiae (small red dots) on the skin or mucous membranes
- Hematomas (bruises)
- nosebleeds
- Bleeding gums
A rare but potentially life-threatening side effect of heparin is hyperkalemia. This is an increased potassium level in the blood, which can lead to cardiac arrhythmia.
The authors assume that a veterinarian should be consulted if an animal is ill and that medication should only be taken after consultation with a doctor or pharmacist. Only an individual examination can lead to a diagnosis and treatment decision.
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