A new drug is just as effective as warfarin (Coumadin) for preventing a second blood clot in a vein, new research finds. More important, researchers said, the drug, dabigatran, is easier to manage. Both drugs are blood thinners. People taking warfarin need frequent blood tests to make sure their blood clotting time is neither too fast nor too slow. Unlike warfarin, dabigatran does not interact with foods or most other drugs. People don't need regular blood tests. The study included 2,500 people with venous thromboembolism. This is a clot in a vein. People were assigned at random to receive one of the two drugs. After 6 months, about 2% of each group had another clot in a vein. People who took dabigatran were less likely to have any bleeding than those who took warfarin. Serious side effects were similar in both groups. The New England Journal of Medicine published the study online. HealthDay News wrote about it December 7.

By Howard LeWine, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

Drugs that prevent unwanted clots are often called "blood thinners." But they actually don't thin the blood.

Blood clots form through a series of biological steps. "Blood thinners" block one or more of these steps. Some of these drugs more effectively prevent blood clots in arteries. Others are used to prevent blood clots in veins and inside the heart. (For example, people with persistent atrial fibrillation often form small blood clots in the heart.) Some anti-clotting drugs work in both arteries and veins.

Heparin and related products such as enoxaparin (Lovenox) prevent and treat blood clots in arteries and veins. However, they can be used only by injection.

A few drugs that you can take as pills help to prevent clots in arteries. Aspirin is used most often. Aspirin binds to platelets in the blood and prevents them from sticking together. Clopidogrel (Plavix) and prasugrel (Effient) are also platelet inhibitors.

Until recently, only one drug has been available in pill form to prevent and treat blood clots that form in veins (deep vein thrombosis or DVT for short) and inside the heart. That drug is warfarin (Coumadin). Recently, a new drug called dabigatran has become available in Europe. It likely will be approved for use in the United States in 2010.

An earlier study showed that dabigatran was just as effective and safe as warfarin in people with atrial fibrillation. With this condition, small blood clots form in the upper left chamber of the heart (the left atrium). These clots can break away and travel to the brain, causing a stroke.

Results of a new study show that dabigatran is also very effective in the treatment of deep vein thrombosis and pulmonary embolism (a clot in the lungs). It works as well as warfarin and appears to be just as safe. The new results were published online by the New England Journal of Medicine.

What Changes Can I Make Now?

Taking warfarin is not a simple task. People need regular blood tests to make sure that they are taking the right dose.

Warfarin acts by partially blocking the action of vitamin K in the liver. The liver needs vitamin K to make clotting proteins.

This is how it works. If you are taking too high a dose of warfarin, it overtakes the vitamin K and your blood gets "too thin." This increases your risk of bleeding. If you have too much vitamin K in your diet, then it will overtake the warfarin and now your blood is not "thin" enough. You are once again at risk for blood clots.

There is no correct fixed dose of warfarin. The dose is adjusted based on a blood test called an INR. This is why people who take warfarin need regular blood tests. Some people are very sensitive to small doses of warfarin and others need high doses. How people will react is not predictable. Only blood tests can determine the right dose.

Some doctors advise people on warfarin to avoid foods high in vitamin K. However, many of these foods are very healthy, including green leafy vegetables. Therefore, I give patients a list of the foods that have high amounts of vitamin K. They can use the list to take in about the same amount of vitamin K each day. It does not need to be exact. The goal is to avoid eating a bunch of broccoli one day and then none for a couple of days.

Warfarin also interacts with many drugs and supplements. Antibiotics often will cause the blood to become too "thin."

What Can I Expect Looking to the Future?

Dabigatran is on track for approval in the United States this coming year. The great advantage of dabigatran over warfarin is that no blood tests are needed. It is given in a fixed dose. Dabigatran directly blocks one of the key clotting proteins. The protein is called thrombin. It is not dependent on the amount of any vitamin or mineral.

Dabigatran works as well as warfarin, and the short term safety record looks good. Three important questions remain:

• Will dabigatran be just as effective as warfarin to prevent blood clotting on artificial heart valves?
• Will it be much more expensive than warfarin?
• Will there be side effects after long-term use?