Blood clot is an accumulation of blood that has thickened and clumped together. The body creates clots to stop bleeding after a cut or an injury. While this process is important to prevent excessive blood loss, clots can sometimes form when they are not needed. In such cases, they can block blood flow and prevent oxygen from reaching vital parts of the body, leading to serious complications.

Venous Thromboembolism (VTE)

VTE is a condition that affects approximately 10 million people globally every year). VTE occurs when a blood clot forms in a vein, which is a blood vessel that carries blood back to the heart. This condition includes both deep vein thrombosis (DVT) and pulmonary embolism (PE). DVT occurs when a clot forms in a deep vein, usually in the legs. Symptoms of DVT may include leg pain, localized tenderness when touching the area, swelling, and redness. PE occurs when part of a clot breaks off and travels to the lungs. Symptoms of PE may include difficulty breathing, a fast heartbeat, chest pain, etc. Risk factors of VTE may include prolonged immobility (e.g., bedridden), major trauma or fractures, surgeries, active cancer, etc. Experiencing any of these symptoms should prompt immediate medical attention, as early treatment of VTE can help prevent complications.

Management of VTE: Focus on Blood Thinning Medications

Blood thinners are medications used to treat and prevent VTE. These include heparins (e.g., enoxaparin), warfarin, and direct oral anticoagulants (or DOACs e.g., apixaban). An important consideration with heparin, warfarin, and DOACs is their interaction with other blood thinners, such as aspirin and clopidogrel. Using more than one blood thinner at the same time can increase the risk of bleeding. This is particularly relevant for patients who use blood thinners to prevent heart attacks or strokes. (Readers can refer to the American Society of Hematology Guidelines for Management of VTE for further information on the treatment of DVT and PE.)

Warfarin interacts with many other medications. For instance, some antibiotics (e.g., clarithromycin), heart medications (e.g., amiodarone), and other medications (e.g., phenytoin) may increase the effects of warfarin, raising the risk of bleeding. Speak to your pharmacist to learn more about interactions with warfarin if you are taking this medication.

DOACs, particularly apixaban, edoxaban, and rivaroxaban, could be influenced by certain enzymes (e.g., CYP3A4) and/or proteins (e.g., P-glycoprotein) in your body. It is important to note that some medications may affect how CYP3A4 and/or P-glycoprotein work, resulting in potential drug-drug interactions with DOACs. For example, certain antifungals (e.g., ketoconazole), antibiotics (e.g., rifampin), seizure medications (e.g., carbamazepine), and HIV medications (e.g., ritonavir), etc., may need to be avoided due to their effects on CYP3A4 and/or P-glycoprotein. In some cases, your doctor may need to adjust the dose of your blood thinner, change the timing of your medications, or monitor you more closely.

After experiencing a VTE, treatment usually lasts at least three to six months. In some cases, ongoing treatment, referred to as secondary prevention, may be needed for several years or for a lifetime. For patients taking apixaban or rivaroxaban as part of secondary prevention, a lower dose might be used. It is also important to consider other health related conditions, such as kidney function, liver function, pregnancy, breastfeeding, etc., when taking blood thinning medications. For example, DOACs are not recommended for patients with severe kidney or liver dysfunction.

Approaches to Safe Medication Practices in VTE

Blood thinning medications should always be taken exactly as directed. It is also important to let your pharmacist or doctor know about the use of any over-the-counter medications, vitamins, minerals, or supplements, and if there is a change in your diet. This allows them to monitor for any drug-drug or drug-food interactions that could potentially increase the risk of bleeding or the formation of blood clots. Having an open dialogue with your healthcare team can help manage potential side effects and ensure your medications are safe and effective.

By Samir Kanji, Huy Pham, and Certina Ho
Samir Kanji is a PharmD Student at the Leslie Dan Faculty of Pharmacy, University of Toronto; Huy Pham is a 2024 PharmD Graduate at the Leslie Dan Faculty of Pharmacy, University of Toronto; and Certina Ho is an Assistant Professor at the Department of Psychiatry and Leslie Dan Faculty of Pharmacy, University of Toronto.