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Family Health Magazine
PHARMACY CARE

Blood Thinners
Why they are used, how they work and why regular testing is important

One commonly prescribed medication is Coumadin™, often called an anticoagulant or ‘blood thinner.’ To understand why it’s prescribed and how it works, it helps to understand a little bit about blood and its functions.

Blood is a very complex fluid with many vital roles. It carries oxygen and nutrients to all body tissues and brings white blood cells to infected areas. Blood even carries messages between cells in the form of hormones. Blood must flow freely through the veins and arteries to be able to reach all of the cells of the body. However, if a blood vessel breaks, the blood must also be able to create a clot to prevent further blood loss. Your blood has a complex system of proteins called clotting factors, which form these blood clots when needed.

Your body maintains a delicate balance when it decides how quickly to form clots. Blood that does not clot quickly enough can put you in danger of bleeding to death from a small cut. Blood that clots too easily can clog a blood vessel. When a vessel becomes completely clogged so no blood can pass through, tissues of the body downstream may become damaged and even die from lack of oxygen.

Most of the time, your body does a perfect job of deciding how easily blood should clot. Still, there are a number of medical conditions where it is better for blood to clot less easily. For instance, some people have genetic (hereditary) conditions in which their blood clots too fast. Atrial fibrillation is a condition in which the upper chambers of the heart do not contract in a coordinated way. Since these chambers do not contract properly, they do not empty with each beat and a pool of blood builds up. This stagnant pool of blood is at risk of forming a clot. If a blood clot forms in the heart, it can get swept with the flow of blood along the arteries. It will eventually lodge in a small artery and block the blood supply to the neighboring tissues. Similarly, a person with a mechanical heart valve can have abnormal flow of blood around the valve, which can lead to formation of a blood clot. In all these cases, it is important to prevent blood clots. If an abnormal clot has already formed, it is important that the clot not become any larger while the body works to break it down.

How does Coumadin™ help?

Coumadin™ (also called warfarin) is a medication that affects the blood’s ability to clot. It reduces the supply of clotting factors made by the liver so that the blood takes longer to form a clot. Since the blood coagulates (clots) less easily, this type of medication is often referred to as a ‘blood thinner’ or anticoagulant.

Blood thinners such as Coumadin™ don’t have any effect on an existing clot. They also cannot fix damage caused from lack of oxygen after a clot. However, once a clot has formed, Coumadin™ should prevent the clot from getting any larger and causing further problems. Depending on why it is prescribed, Coumadin™ use may be temporary (usually six months to a year) or lifelong.

Why do I need so many blood tests when I’m on Coumadin™ ?

Unlike many other medications, the dose of Coumadin™ needed is quite individual. It depends on your age, your diet, and other medications you are on. The only way to be sure your blood thinned the correct amount is by checking with regular blood tests.

This blood test is called an INR (International Normalized Ratio). Basically, the test result number tells you how long your blood takes to clot compared to regular blood. A person who is not taking any Coumadin™ should have an INR of about one (1.0). Any result higher than one means that the blood is thinner, taking longer to form a clot. The higher the number, the more slowly the blood clots.

Your doctor tries to maintain your INR in a certain target range, depending on the reason you are on Coumadin™. Often the goal is to keep the INR between two and three. For people at higher risk of forming clots, such as those with mechanical heart valves, the target range is even higher, usually about three to four. However, everyone is different, and your doctor will determine what target range is best for you.

If your INR is out of the target range, your doctor will adjust your Coumadin™ dose, and ask you to recheck your blood in a few days. Be aware that Coumadin™ can be tricky and it is dangerous to adjust your dose yourself. Please rely on your doctor to adjust your Coumadin™ dose!

Some other blood thinners do not require regular blood tests. Unfortunately, these other medications can only be given by injection, not by mouth. This makes Coumadin™ more suitable for use outside the hospital.

How can my diet affect Coumadin™ therapy?

Vitamin K is an important vitamin in the production of factors that help your blood to clot. Many foods contain vitamin K and can affect your Coumadin™ treatment. By monitoring your INR, your Coumadin™ dose can be tailored to your typical vitamin K intake. It doesn’t matter whether you eat a little or a lot of this vitamin, but it is essential that you keep the same amount of vitamin K in your diet. If you are planning to make any major changes to your diet while on Coumadin™, please talk to your doctor first. The doctor can help ensure that your INR does not become dangerously high or low during that time. It is a mistake to think that you should eliminate vitamin K, since many foods important to a healthy diet are rich in it. Examples of foods high in vitamin K are listed in the table. You can get a more complete list of the vitamin K content of foods from your doctor, dietitian or pharmacist. Try to keep your average weekly vitamin K intake steady.

Alcohol also interacts with Coumadin™. A small amount of alcohol on occasion (one standard drink or less) should not cause problems, but in general, limiting alcohol intake is best.

What about drug interactions?

Many medications, including over-the-counter medications, can interact with Coumadin™. Don’t forget that herbals are drugs too – ‘natural’ does not equal ‘safe.’ Many herbals, such as dong quai, ginkgo and St. John’s wort can interfere with the action of Coumadin™. Talk to your doctor and pharmacist before starting or stopping other drugs or supplements while on Coumadin™.

What are the side effects of Coumadin™ ?

As you may have guessed, the most common side effect of Coumadin™ therapy is bleeding. Expect to bruise a bit more easily while on Coumadin™. The following signs and symptoms can be related to bleeding: pain, swelling or discomfort, increased menstrual flow, nosebleeds, bleeding of gums from brushing, unusual bruising, red or dark brown urine, red or tar black stools, headache, dizziness, or weakness. If you have any of these symptoms, mention them to your doctor at your next visit. If the appear severe or if you are concerned, call your doctor right away.

Who should not take Coumadin™?

Pregnant women should not take Coumadin™. It can pass through the placenta to the unborn baby, and cause bleeding or malformations in the baby. Women on Coumadin™ should not become pregnant, and if they do should notify their doctor immediately. Coumadin™ can be dangerous if taken after certain types of surgery, since major bleeding can occur. Please be certain your doctor is aware of your medical history before you start taking Coumadin™.

If you need more information about Coumadin™, ask your doctor. You can also check out the website www.Coumadin.com provided by the manufacturers of Coumadin™.