Warfarin FAQ

How do I take warfarin?

Your warfarin dose is carefully chosen to meet your medical needs. The dose chosen for you is influenced by many factors, some include: your gender, age and other medications you are taking.

Because it is important to maintain your blood levels, it is important to take your warfarin medication exactly as your healthcare professional prescribes. You should try to take your warfarin at the same time every day. If you miss a dose, check with your doctor for instructions.

Why is controlling blood clotting so important?

A blood clot is essential to life and forms whenever we experience any type of cut or injury. Because of certain medical conditions, blood clots can form irregularly, leading to heart attack, stroke, or pulmonary embolism.

Warfarin is often prescribed for people to prevent abnormal clot formation. Some medical conditions include¹:

• Mechanical Heart Valve (MHV)
• Atrial Fibrillation
• Venous Thromboembolism or Deep Vein Thrombosis (DVT)
• Pulmonary Embolism
• Hypercoagulable state

How does the blood clot and how is vitamin K involved in the clotting process?

The U.S. National Library of Medicine defines the process of blood clotting and repairing the injured tissue is called hemostasis. The blood vessels constrict to limit blood flow to the area affected. A substance called thrombin activates platelets cells to “plug” the injury.

A group of proteins made in the liver, called clotting factors, help to stabilize the plug by forming a fibrin. Once a clot is formed around and within the injured area, the clot then dissolves and normal blood flow can resume.

Warfarin affects the activity of some of the proteins involved with the clotting process by inhibiting the activity of the vitamin K-dependent clotting factors. All vitamins act as catalysts in chemical reactions in the body. Warfarin blocks the availability of vitamin K and limits the production of the clotting factors.

The more vitamin K in your diet, the less effective warfarin can become. As long as your diet remains constant, specifically remaining constant with your vitamin k intake, the dose of warfarin can be adjusted to overcome this effect.

Why do I need my blood tested?

To avoid any adverse drug reactions, it is important to test or monitor your blood regularly by testing your INR or International Normalized Ratio. The INR test measures the time it takes our blood to clot, or prothrombin time (PT). This standardized test is often referred to as PT/INR test. The INR measures the clotting time in a standard way, taking age, gender, and testing method into account.

The test also measures the time it takes our blood to clot and is expressed as a number. Your doctor will give you an INR target range specifically for your condition. The higher the number the longer it will take your blood to clot.

This test can be performed in your doctor’s office, a clinic/lab, or at home, depending on your needs. Because your dose is based on the INR blood test, it is very important your INR is checked regularly.

1. CMS Manual Change Pub 100-04 Transmittal 1562 July 25, 2008.