Comparing Anticoagulants for treatment of Atrial Fibrillation

As seen in Consultant Connection March 2012 Issue
Cindy DeRan, RPh. Consultant Pharmacist, ICP, Inc.

AFib is a type of irregular heartbeat. It occurs when one or both of the upper chambers of the heart - called the atria - beat erratically. This puts them out of sync with the heart’s 2 lower chambers - called the ventricles. AFib affects more than 2 million people in the United States. The odds of developing AFib go up with age. In fact, the American Heart Association states that AFib is the most common serious type of irregular heartbeat in people over age 65. It’s also sometimes associated with other health problems, such as heart disease, diabetes, or high blood pressure.

Having AFib puts you at a nearly 5 times greater risk of a stroke than if you don’t have it, even if you have no symptoms. When your heart beats irregularly, it doesn’t pump blood as it should. This can cause blood to pool in the upper chambers of your heart (called the atria). This pooling can cause a blood clot to form in your heart. A clot in your heart can break away and travel directly to your brain. There, it can block an artery and cause a stroke.

Stroke can be prevented in most AF patients by using anticoagulants, or blood thinners. Anticoagulants reduce your blood’s ability to clot (coagulate). Most people over age 60 who have atrial fi brillation can be treated with a blood thinner. Warfarin (Coumadin and Jantoven) is an anticoagulant that has been extensively studied and prescribed by doctors to help reduce the risk of stroke in people with AFib since 1954. These drugs must be very carefully monitored because too much blood thinner can cause abnormal bleeding.

To be sure you’re getting the right amount of warfarin, your doctor will do a test called a Prothrombin Time. (This test is also called “ProTime” or “PT.”) The results of this test may be reported to you as an “INR” number. By using an INR (International Normalized Ratio), your doctor can keep your blood clotting at a safe and effective level. Your INR should usually test between 2.0 and 3.0. Long-term use of warfarin in patients with atrial fibrillation and other stroke risk factors can reduce stroke by upwards of 70 percent. Warfarin can prevent stroke when used as directed, and the risk of stroke is greater than the risk of bleeding if you have AFib.

Since the introduction of the new anticoagulants, dabigatran (Pradaxa) and rivaroxaban (Xarelto), there are now alternatives to warfarin for the treatment of atrial fibrillation. While both dabigatran and warfarin are anticoagulants, they work differently to help reduce the risk of stroke due to AFib not caused by a heart valve problem. Warfarin is a vitamin K antagonist that helps to stop clots from forming by interfering with vitamin K—a vitamin your body needs to form clots. Dabigatran is a direct thrombin inhibitor that helps to stop clots from forming by working directly on thrombin.

Dabigatran may be more effective than warfarin in some patients. Results from the RE-LY study showed that compared to warfarin, dabigatran may give slightly better stroke prevention, with similar chances for bleeding on either blood thinner. Other advantages of dabigatran over warfarin include the lack of requirement for changes to your diet. When you take warfarin, you need to avoid foods high in vitamin K, such as large amounts of leafy green vegetables and some vegetable oils. This is because Vitamin K can affect the way warfarin works in your body. You also need to avoid alcohol, cranberry juice, and products containing cranberries.

There are some disadvantages of dabigatran over warfarin. Dabigatran is taken by mouth 2 times each day— with or without food. Warfarin is taken by mouth once every day—with or without food. Dabigatran is known to cause more stomach pain and/or stomach upset than warfarin. Also, dabigatran should be used cautiously in people with kidney problems, and dose adjustments are sometimes required. Your doctor should test your kidney function before you start dabigatran and in some cases yearly thereafter.

Dabigatran tablets are only good for 4 months after opening the bottle. In emergencies that involve bleeding, there are currently no medications available to reverse the effects of dabigatran. In contrast, the effects of warfarin can be reversed by giving vitamin K. And, Compared to warfarin, dabigatran has been associated with a very slight increase in the incidence of heart attacks.

Recently, the FDA has approved Xarelto (rivaroxaban) to prevent stroke in patients with atrial fi brillation – with a strong “black box” warning. A black box warning is the FDA’s strongest warning. Xarelto had previously been approved to prevent blood clots in patients receiving hip and knee replacements.

Rivaroxaban now joins dabigatran as alternatives to warfarin to prevent stroke-causing blood clots in patients with atrial fi brillation not caused by a heart valve problem. Like warfarin and dabigatran, rivaroxaban is a blood thinner. It is the fi rst direct factor Xa (pronounced 10a) inhibitor and can cause dangerous bleeding. Xarelto can also increase the risk of stroke or forming blood clots in other parts of your body if people stop taking it without medical supervision. That’s the main warning in the “black box” on the Xarelto label.

Rivaroxaban has once-daily dosing with no routine monitoring of the international normalized ratio (INR) or other coagulation parameters required. This eliminates the need for multiple daily doses or routine dose adjustments. Rivaroxaban has no reported food or drug interactions and has no special storage requirement. However, renal function should be monitored and a dosage adjustment may be needed based on your level of renal impairment. When you have atrial fi brillation (or AFib) not caused by a heart valve problem, you’ll need to work closely with your doctor to help reduce your risk of stroke.

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