Warfarin Dosing

If you've been diagnosed with a deep venous thrombosis (DVT), you can expect at least three months of continued anticoagulants, or blood-thinning medications, such as warfarin, after you leave the hospital.

Deep venous thrombosis (or deep vein thrombosis) is a dangerous condition in which your body forms a clot, typically in the leg, that can potentially break off and travel to the lungs, where it will clog circulation. This deadly event is known as pulmonary embolism.

With continued anticoagulant therapy after you leave the hospital, you minimize the risk of re-forming such deadly blood clots. Note that anticoagulant therapy is not only given with deep venous thrombosis. For example, if you are currently being treated for stroke or have a condition that increases your risk for clots (a hypercoagulable condition), you can expect a lifetime of anticoagulation therapy.

Anticoagulation can be maintained by several medications, including low-molecular-weight heparin (subcutaneous injection) such as Lovenox (enoxaparin sodium), fondaparinux (subcutaneous injection), oral Xa inhibitors like Eliquis (apixaban) and Xarelto (rivaroxaban), or the oral direct thrombin inhibitor Pradaxa (dabigatran).

In this article, we'll focus on warfarin (brand name Coumadin), an oral medication. When choosing an anticoagulant therapy, please keep in mind that options do exist, and your healthcare provider can further discuss these options with you. Many warfarin clinics are run by other healthcare providers, such as pharmacists and nurses. It is very important that you take your warfarin dose exactly as prescribed, to avoid risks for clotting and bleeding.

How Warfarin Works

Warfarin interferes with the hepatic synthesis of clotting factors, which are vitamin K dependent. It blocks the process of coagulation and decreases the body's ability to form new clots. Warfarin can prevent clots from forming and getting larger. Until it reaches therapeutic levels in the body, warfarin is paired with a parenteral, or injectable, anticoagulant like Lovenox (enoxaparin injection), generally for five days or until there are two consecutive therapeutic international normalized ratio (INR) test results.

Typically, people are started on an initial warfarin oral dose of about 5 milligrams daily for a few days. Your warfarin dose is then adjusted in order to maintain therapeutic INR (international normalized ratio) levels, The laboratory measure INR is used to determine your coagulation status, which is needed in order to adjust your dosage of warfarin.

In most people, normal INR levels range from 0.8 to 1.2. People on warfarin for DVT are typically maintained at an INR level between 2 and 3, meaning that these patients are significantly more anticoagulated (have thinner blood) than average people. While receiving warfarin, INR levels should be regularly monitored by your healthcare provider.

A higher INR means it takes longer for your blood to clot, which can also mean a higher risk for bleeding. A lower INR means it takes less time for your blood to clot, which can also mean a higher risk for clotting.

Your healthcare provider will closely monitor your INR through regular blood tests and adjust your warfarin dose as needed based on your INR levels. It is very important to keep all of your blood test appointments for this reason.

Who Needs Higher Doses?

Higher doses of warfarin may be required for the following populations:

• People who have obesity
• People with hypothyroid (underactive thyroid) conditions

Who Needs Lower Doses?

Conversely, the following populations may need to receive lower doses of warfarin:

• Older adults
• People with hyperthyroid (overactive thyroid) conditions
• People who have heart failure
• People with liver disease
• Anyone with a history of major surgery

Some people may also respond differently to warfarin based on their genetic make-up. For example, those with with polymorphisms in the CYP2C9 or VKORC1 genes may require lower doses. That said, your healthcare provider may order a blood test to help determine the best dose for you.

In addition to the above patient characteristics, warfarin dosage is also adjusted depending on the medications that you're taking. For example, Bactrim (sulfamethoxazole and trimethoprim, an antibiotic combination product) increases the action of warfarin and thus increases INR levels.

It is very important that you do not stop or change your warfarin dose on your own without talking with your healthcare provider. If you don't take your prescribed dose of warfarin, this can put you at risk for negative health consequences, like a clot or a bleed.

How Diet Affects Dosage

Because warfarin is a vitamin K antagonist, a diet rich in vitamin K can lower your INR levels. Specifically, leafy green vegetables like kale and spinach tend to be high in vitamin K. On the other hand, potatoes, fruits, and cereals are low in vitamin K. You can still continue eating nutritious portions of leafy green vegetables, but try to remain consistent in your daily consumption so that your INR levels don't fluctuate.

Risks

Adverse effects of warfarin therapy typically are limited to nausea and cramps. However, warfarin increases your ​risk for bleeding, which can be serious. Look out for any signs of unusual bleeding, such as blood in the urine, bloody or dark stool, vomiting blood, or a severe or unusual headache that may signal a hemorrhage.

If you notice signs of unusual bleeding, seek immediate medical attention. In case of serious bleeding due to warfarin, healthcare providers can administer vitamin K to help clot your blood. People who have a history of hemorrhage should be especially careful when taking warfarin.

Make sure to tell all of your healthcare providers that you are taking warfarin. Inform your dentist that you're on warfarin before any dental work is done. Tell your healthcare team that you're taking warfarin before undergoing any medical procedures or surgeries, as your warfarin dose may need to be adjusted or temporarily paused before the procedure.

Furthermore, when taking warfarin, it's best to use an electric razor and soft-bristled toothbrush to reduce the risk of bleeding. Avoid handling sharp objects and be cautious when moving around, avoiding activities that have a higher risk of falling. If you have a fall or injury to the head, seek immediate medical attention to be checked out.

A Word From Verywell

If you or a loved one needs to take warfarin for deep venous thrombosis, stroke, or a hypercoagulable condition, please remember that anticoagulant therapy with this drug is an involved process. To establish and maintain proper anticoagulation status, you will need to work closely with your healthcare team.

Let your healthcare team know of any changes to your diet. For example, if you want to start eating salads but have not in the past, your dietitian or other healthcare provider will work with you to ensure that your Coumadin dose is adjusted as needed. Keeping your diet consistent is key. Remember to remain vigilant, get your INR levels checked regularly, and work with your healthcare team.