Heparin

Heparin is an anticoagulant (blood-thinning medication) used in dogs to prevent the formation of blood clots (thrombi) or to dissolve existing clots. It is a naturally occurring molecule produced in small amounts in the body and is synthesised medically to inhibit blood clotting. Heparin is useful in the treatment of thrombosis, embolism and certain heart diseases.

What is heparin?

Heparin is a molecule that inhibits blood clotting by blocking the activity of certain clotting factors, particularly thrombin. It is derived from animal tissue or produced synthetically and used in veterinary medicine to prevent or treat the formation of blood clots.

• Unfractionated heparin (UFH): This form is used to control blood clotting over short periods, for example after surgery or in acute thrombotic events.
• Low-molecular-weight heparin (LMWH): This form is used long-term as it has a longer half-life and a more stable effect.

Areas of use in dogs

Heparin is used in dogs in various situations where blood clotting needs to be controlled:

Prevention and treatment of thrombosis

Heparin prevents the formation of blood clots (thrombi) that can form in blood vessels and block blood flow. This is relevant for dogs with heart or lung diseases that increase the risk of thrombosis.

Treatment of pulmonary embolism

If a blood clot travels to the lungs and blocks blood flow there, this is known as a pulmonary embolism. Heparin helps prevent or dissolve these clots.

Kidney disease

In kidney diseases, particularly nephrotic syndrome, the risk of blood clots may be increased. Heparin is used to reduce this risk.

Surgical procedures

After major surgery or during prolonged immobilisation, heparin is sometimes used to prevent the formation of post-operative blood clots.

Heart disease

Dogs with heart diseases such as valvular heart disease or heart failure have an increased risk of thromboembolism (blood clots that break loose and travel to other parts of the body). Heparin minimises this risk.

Mechanism of action

Heparin inhibits clotting factors that normally activate blood clotting. It binds to a protein called antithrombin III, which reduces the activity of thrombin and other clotting factors. Thrombin is responsible for converting fibrinogen into fibrin, a protein necessary for the formation of blood clots. By blocking this conversion, heparin prevents the formation of stable clots and reduces the risk of thrombosis.

Heparin begins to work quickly once injected into the body, inhibiting clotting factors within minutes. The effect of unfractionated heparin lasts only a few hours, which is why it often needs to be administered at regular intervals.

Administration

Heparin is usually administered by injection, either subcutaneously (under the skin) or intravenously (directly into a vein). The vet adjusts the dosage and administration schedule based on the specific needs of the dog. The dosage depends on the size of the dog, the severity of the disease, and the desired degree of blood thinning.

Side effects and risks

Risk of bleeding

As heparin inhibits blood clotting, the main risk is an increased tendency to bleed. Dogs receiving heparin have an increased risk of internal bleeding, particularly in the gastrointestinal tract or joints. Signs of bleeding can include bloody urine, bloody faeces, skin bleeding (small red spots on the skin), or weakness.

Allergic reactions

In rare cases, dogs may have an allergic reaction to heparin. Symptoms of an allergic reaction can include swelling, itching, difficulty breathing, or skin rashes.

Thrombocytopenia

In some cases, heparin can lead to thrombocytopenia, a reduction in the number of platelets (thrombocytes), which further increases the risk of bleeding.

Osteoporosis with long-term use

With prolonged use of heparin, bone loss (osteoporosis) can occur as the medication can affect calcium metabolism.

Injuries from injections

If heparin is injected, especially with frequent administration, bruising or hardening at the injection sites can occur.

Monitoring

Dogs treated with heparin should be monitored regularly by a vet. The vet checks the dog’s blood clotting values to ensure that the heparin dosage is correct and there is no risk of excessive bleeding.

• Blood tests: Regular blood tests are necessary to check the blood’s clotting ability and optimise therapy.
• Clinical monitoring: Regular examinations help detect signs of bleeding or side effects at an early stage.

Contraindications

There are certain conditions under which heparin should not be used in dogs:

• Active bleeding: Dogs already suffering from internal or external bleeding should not receive heparin as it significantly increases the risk of bleeding.
• Severe liver or kidney disease: Dogs with severe liver or kidney disease may have difficulty processing heparin, which can lead to complications.
• Pregnancy: Heparin should be used with caution in pregnant bitches as it could increase the risk of bleeding during birth.