A blood clot or thrombus can form in the vessel walls of arteries or veins. An arterial thrombus is a very dangerous clot that can obstruct the flow of blood to major organs and cause complications such as stroke, transient ischemic attack (TIA or mini-stroke), heart attack, or peripheral arterial disease.
A venous thrombus can occur in the deep veins of the body such as a deep leg vein (deep vein thrombosis, DVT) or a blood vessel of the lung. In DVT, a piece of the clot may detach and travel to the lungs where it can lodge and create another blockage. This is a potentially life-threatening complication of deep vein thrombosis called pulmonary embolism (PE). DVT and PE are collectively termed venous thromboembolism (VTE).
The treatments that are available for treating VTE include anticoagulant medications such as heparin or warfarin. These are also called blood thinners. These drugs do not break a clot down but reduce the clot’s ability to coagulate and prevent further growth of the clot. This can also reduce the risk of a clot fragment breaking off and travelling to the lung or brain. Anti-coagulants also help prevent the recurrence of clots.
In summary, the aims of blood thinning treatments in thrombosis include:
- Preventing the clot from growing bigger
- Preventing the formation of new clots
- Preventing the clot from breaking off and moving to major body organs
- Preventing recurrence
- Preventing long-term complications
Heparin is given by injection or drip into a vein as unfractionated heparin. The blood coagulability needs to be closely monitored while using heparin because blood that has become too thin can lead to uncontrolled bleeding. A calculation called the International Normalized Ratio (INR) is used to standardize the results of prothrombin time and monitor the therapy. Without warfarin, a person with DVT may have an INR of around 1.0 (typically 0.8 to 1.2) and the goal of treatment is usually to achieve an INR of around 2.0 to 3.0.
Low-molecular weight heparin (LMWH)
LMWH is a modification of traditional unfractionated heparin. Examples of these drugs include enoxaparin, dalteparin, fondaparinux and tinzaparin and they are delivered by subcutaneous injection. These LMWH preparations do not require monitoring and have largely replaced unfractionated heparin in the management of VTE.
The fast-acting, injectable blood-thinners heparin and LMWH are eventually replaced by warfarin, a type of anticoagulant that can be taken in tablet form. At the start of therapy, heparin or LMWH is given along with warfarin because it takes several days (at least 5 days) for the protective effects of warfarin to begin. The amount or dosage of warfarin administered varies from person to person.
Other oral blood thinners
The oral blood thinner rivaroxaban has been approved by the Food and Drugs Administration for the treatment of DVT and recurrent VTE. Other examples of orally administered anticoagulants that have been approved for use include dabigatran, apixaban and edoxaban.
Thromoblytics are agents that can break down clots. The drug most commonly used for this purpose is tPA (tissue plasminogen activator), which is administered intravenously. In some cases, clot dissolving medications may being injected directly into the clot itself using a catheter.
Inferior vena cava filter
These vascular filters are implanted into the inferior vena cava to prevent a pulmonary emboli. The filter is designed to capture a blood clot fragment that may have broken loose from a deep vein in the leg and started to move towards the lung or heart.
Reviewed by Sally Robertson, BSc