Millions of Americans take aspirin, warfarin (Coumadin) or other medications to reduce the risk for clots, the cause of most heart attacks and strokes. These drugs, known as antithrombotic agents, are very effective, but they have to be used carefully to prevent excessive bleeding, the most serious side effect.

Recent finding: A study that my colleagues and I did found that the incidence of bleeding into the brain (intracerebral hemorrhage) associated with antithrombotic agents increased fivefold between the late 1980s and late 1990s. This rise corresponds to the increased use of warfarin, a commonly used medication.

When antithrombotic medications are used properly, the benefits often outweigh the risks. Yet all of these drugs, including aspirin, are more dangerous than most people think. Here's how to reduce your risks…

How Blood Thinners Work

Although antithrombotic medications are sometimes called blood thinners, they don't actually thin the blood. They inhibit the ability of substances in blood to form clots. They also can prevent some clots from getting bigger.

There are two main categories of anti-thrombotics. Each works at different stages of the clotting process…

  • Antiplatelet drugs inhibit the ability of cell-like structures in blood (platelets) to form clots. Drugs in this class include aspirin, clopidogrel (Plavix), ticlopidine and a combination of aspirin plus dipyridamole (Aggrenox). Antiplatelet drugs are usually recommended for patients with a vascular disease (such as coronary artery disease) that increases their risk for clots.
  • Anticoagulants work to inhibit proteins in the blood that trigger clotting. The most commonly used anticoagulant, warfarin, acts on the liver to inhibit the production of substances that cause clotting. Warfarin is more effective than aspirin for patients with atrial fibrillation (irregular heartbeat)...deep-vein thrombosis (a clot in a deep vein, usually in the legs)...or pulmonary embolism (clot in the lungs).

Some anticoagulants, such as heparin, are given by intravenous infusion or subcutaneous (under the skin injection and are mainly used in hospitalized patients who have a high risk for clots.

Genetic Testing

The American Medical Association estimates that 21% of patients who take warfarin will experience some degree of bleeding because of the drug.

A genetic test now can identify certain at-risk patients. Studies have shown that people with two genetic variations in the CYP2C9 and/or VKORCI genes) metabolize warfarin more slowly and develop a higher blood concentration and so may need to be given a lower initial dose.

Preliminary research indicates that genetic testing can help predict a patient's optimal dose of warfarin when he/she first starts taking the medication. This may help reduce bleeding complications during this period. Genetic testing is not expected to help patients who have been taking warfarin for some time and have already established their optimal dose. Ask your doctor if genetic testing is for you. The test is expensive (up to $500) and may or may not be covered by insurance.

General Safety Tips

To reduce your risks if you're taking any antithrombotic agent…

  • Watch for warning signs of excessive bleeding, in particular unexplained bruising. It's a sign of bleeding under the skin. Other warning signs include bleeding gums when flossing or brushing the teeth...small cuts that continue to bleed...excessive fatigue this could be due to blood loss)...or dark urine or black stools, which can indicate internal bleeding. If you have any of these signs, contact your doctor.
  • Control high blood pressure. This is among the most important things that patients can do. High blood pressure increases the risk for hemorrhagic (bleeding in or around the brain) strokes and the risk is higher in patients who also are taking an antithrombotic medication.
  • Ask your doctor about dangerous interactions. Many common drugs, including some antibiotics, can interact with warfarin and change its effectiveness. Other medications have been reported to interact with antiplatelet drugs such as clopidogrel. If you're getting a prescription from a new doctor, make sure that he/she knows what other drugs you're taking.

Also, let your doctors know about any herbs and supplements you're taking. Some of these products, including fish oil, chamomile and ginger, can increase bleeding when combined with antithrombotic medications. Check with your doctor before taking them-or before you stop taking them.

Warfarin Safety

If you're taking warfarin, be sure to do the following…

  • Know your INR. The International Normalized Ratio (INR) is a measure of how quickly blood clots. It's used to determine the correct dose of warfarin, which differs widely from patient to patient. For most patients, the INR should be between two and three.

Patients often are advised to have a blood test several times a week after starting warfarin. Once they've achieved good control, they are tested monthly-or more often for patients who are starting (or stopping) other medications that can affect blood clotting.

  • Use aspirin and NSAIDs cautiously. Patients taking warfarin can experience unwanted bleeding when they combine it with aspirin, ibuprofen or other nonsteroidal anti-inflammatory drugs (NSAIDs). Patients who need these drugs—for arthritis, for example—should take them only under a doctor's supervision

Helpful: Acetaminophen (Tylenol) is not an NSAID and is less likely than other over-the-counter analgesics to increase bleeding in patients taking warfarin.

  • Don't double up. Patients who miss a scheduled dose of warfarin by about six hours or more should wait until their next scheduled dose before taking it again. Doubling the amount to make up for a missed dose increases risks.
  • Maintain a stable diet. Foods that are high in vitamin K, including leafy green vegetables and cruciferous vegetables, such as broccoli, cauliflower and cabbage, can increase the ability of blood to clot. Patients who are taking an antithrombotic medication who suddenly start eating more or less of these foods can experience changes in the way the drug works.

You don't have to avoid foods high in vitamin K. However, don't make major dietary changes without checking with your doctor. He might recommend a blood test to determine whether drug doses need to be adjusted.

  • Avoid contact sports, such as hockey and football. Traumatic injuries can cause internal bleeding that's difficult to control in patients who are taking warfarin.

Minor cuts or scrapes-from shaving or working in the yard, for example-usually aren't a problem unless there's a significant change in your usual bleeding time. This could mean that the medication dose needs to be adjusted.

Blood Thinner Breakthrough

A new anticoagulant, antithrombotic medication, dabigatran (Pradaxa)—recently approved by the FDA-may be a safer choice than warfarin. Studies indicate that dabigatran is at least as effective as, and possibly more effective than, warfarin at preventing clots. It doesn't require as much blood easier to dose...and interacts with fewer drugs.

Multivitamins Affect Blood Thinning Meds

Vitamin K, which helps blood to clot and can be found in many multivitamins, can impact the effectiveness of blood thinners, such as warfarin (Coumadin).

Important: Talk to your doctor if you are taking a blood thinner and a multivitamin with vitamin K. It is important to keep your levels of vitamin K consistent.

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