Clotting of the blood is essential to prevent excessive bleeding whenever a small cut or abrasion occurs. However, when blood clots form inside the body they can cause serious health problems and even death.
The Centers for Disease Control (CDC) reports that 60,000 to 100,000 Americans die every year from clots that form in the veins, a condition commonly referred to as deep vein thrombosis (DVT).1 If a clot that formed in the veins travels to the lungs it is called a pulmonary embolism (PE). Blood clots can also cause strokes and heart attacks.
What is Warfarin?
Warfarin, which is sold under the brand name Coumadin, is commonly known as a blood thinner or an anti-coagulant. It is given to patients to prevent blood clots from forming in the veins. It is a tablet that is taken by mouth once a day.
Who Uses Warfarin?
Anyone who has a medical condition that increases the risk of developing blood clots may be prescribed warfarin. The most common indications are atrial fibrillation, artificial heart valves, and a history of DVT or PE.
What Dose of Warfarin is Taken?
Unlike most drugs, there isn't one known dose of Warfarin that works for everyone. Instead, doctors need to perform blood tests in order to establish the ideal dose for each person. Warfarin therapy management can be tricky- too much and the patient is at risk of excessive bleeding; too little, and the patient is at risk of developing clots. Most patients will have a blood test performed once a week during the initial dose-finding period.
The doctor will adjust the daily dose of Warfarin until the INR test results reach and stay within the desired range. Once the desired INR result has been achieved, the frequency of blood tests can decrease to only once a month.
What is an INR Test?
The blood test used to measure the clotting speed of blood is called a prothrombin time (PT) test.2 The results of a PT test are reported as the International Normalized Ratio (INR). The normal range for an INR is 0.8 to 1.1. Doctors usually try to keep individuals taking Warfarin within an INR range of 2.0 to 3.0. A higher INR value indicates a slower blood clotting time.
How Long Does Someone Take Warfarin?
The length of time a person is prescribed Warfarin depends on the medical condition they experience. Some people are placed on Warfarin for only a few weeks. These people include those who recently had surgery and are at-risk of getting blood clots. The Warfarin therapy is only used as a precaution.
For patients who have recently had a DVT or PE, some doctors suggest treatment for three to six months; while other doctors suggest continuing it for longer periods.3
What is Vitamin K and How Can it Affect Warfarin?
Warfarin acts to deplete the body's supply of vitamin K, which prevents Vitamin K dependent proteins from being able to clot blood. Consuming large amounts of vitamin K can restore the blood's ability to clot a day or two after eating the vitamin, putting the patient at risk of a clotting event.
High vitamin K foods include spinach, broccoli, kale and other leafy green vegetables. Patients should not limit consumption of these healthy foods while on warfarin; instead, they should try to consume the same amount of these foods each day so the regular vitamin K intake can be incorporated into Warfarin therapy management decisions.
What Other Things Can Interact With Warfarin?
A complication of Warfarin therapy management is that a wide variety of common foods, medications and supplements can interfere with Warfarin:
- Aspirin, ibuprofen or naproxen
- Cold and cough medicines
- Herbal products
- Changes in dietary habits
- Vomiting or diarrhea
The doctor should know about all of the supplements and vitamins that a patient takes before starting on Warfarin. Patients already on Warfarin need to talk to their doctors before taking any new medication or supplement, and also before making any major dietary changes.
What Are The Complications Of Warfarin?
Complications of Warfarin are usually related to taking the wrong dose or consuming some substance that interacts with Warfarin. If blood clotting is inhibited too much, patients can experience excessive bleeding. This excessive bleeding is sometimes fatal- 72 deaths due to Warfarin-related bleeding were reported in 2011.4
Citations (view all)
- 1. Centers for Disease Control and Prevention. Deep Vein Thrombosis (DVT)/Pulmonary Embolism (PE)- Blood Clot Forming in a Vein. http://www.cdc.gov/ncbddd/dvt/data.html.
- 2. Medline Plus. Prothrombin Time. http://www.nlm.nih.gov/medlineplus/ency/article/003652.htm.
- 3. Goldhaber and Piazza. Circulation. Feb 15, 2011; 123(6): 664–667. Optimal Duration of Anticoagulation after Venous Thromboembolism. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3074464/.
- 4. Institute for Safe Medication Practices. Anticoagulants the Leading Reported Drug Risk of 2011. http://www.ismp.org/quarterwatch/pdfs/2011Q4.pdf.