The lowdown on blood thinners

Blood thinners are among the most misunderstood drugs. Despite their name, they don't "thin" blood, Rather, they discourage blood from clotting.

"Anti-clotting drugs prevent potentially dangerous blood clots from developing in people at high risk," says Dr. Gregory Piazza, a cardiologist with Harvard-affiliated Brigham and Women's Hospital.

Candidates for anti-clotting medications include people who have atrial fibrillation, or afib (a rapid, irregular heart rhythm that causes blood to pool in the heart's upper chambers), or who recently received a stent (a tiny metal mesh tube that is inserted into a clogged blood vessel to increase blood flow).

Others who can benefit from anti-clotting drugs are people who are immobile after surgery and people who have suffered from deep-vein thrombosis, or DVT (clots in the veins of the legs or arms), or pulmonary embolism (clots in the lungs).

How anti-clotting drugs work

Why are blood clots so dangerous? And how do anti-clotting drugs help?

A clot has two main components: fibrin and platelets. Fibrin is a protein that forms a mesh to trap red blood cells, while platelets are tiny cells that clump together. They work together to keep the clot intact and stop or slow blood flow.

Blood clots are usually a good thing. When you get a cut, a clot forms to stop excessive bleeding. However, when clots form in the wrong places, they can cause harm and even death.

Where a dangerous clot develops is often linked to how much of each type of material they contain. For instance, clots causing DVTs and those inside the heart are made mostly of fibrin. Clots in the arteries that feed blood to the heart and brain are more often triggered by platelet action.

Typically, a clot on a cut dissolves after the injury has healed. But a blood clot that forms inside an artery or vein might not spontaneously dissolve, and it can even grow larger. As a result, it can block blood flow, which may lead to a heart attack or stroke.

Many factors contribute to these types of clots, such as inflammation, infection, immobility, cancer, and surgery. "In these cases, you need anti-clotting drugs to help the body dissolve the existing unwanted clots and stop new ones from forming, while still allowing the blood to clot when needed, like after an injury," says Dr. Piazza.

Two categories

Anti-clotting drugs fall into two categories: anticoagulants and antiplatelet drugs. Which one you need depends on your clot risk.

Anticoagulants interfere with fibrin. Besides treating and preventing DVT and other vein clots, they are commonly prescribed for people with afib.

Antiplatelet drugs prevent platelets from sticking together. They are used to prevent heart attacks and strokes in people who have cardiovascular disease or are otherwise at high risk.

The main side effect of anti-­clotting medications is excessive bleeding. Contact your doctor if you notice any of these symptoms:

• recurrent bleeding in your gums after you brush or floss
• nosebleeds or minor cuts that take longer than usual to stop bleeding
• frequent bruising, especially around the torso.

In some cases, the fear of bleeding can prevent people who need anti-­clotting drugs from taking them. This is especially true for those with afib who already take regular aspirin (which also can affect clotting) and are concerned about a higher bleeding risk from adding an anticoagulant.

"But many times, these individuals don't need to take aspirin and can just take the anticoagulant," says Dr. Piazza. (Check with your doctor if you are on aspirin therapy.)

People ages 75 and older also have a higher risk of bleeding from anti-clotting drugs than younger folks. Still, Dr. Piazza adds that most people can tolerate the medication, and if they are concerned about bleeding, they should discuss it with their doctor. "You and your doctor will weigh the risk of heart attack or stroke versus the chance of major bleeding," he says.

Dosage and needs

How long you need an anti-clotting drug and how much you should take depend on your situation. For example, people typically take two antiplatelet drugs for six months to a year after getting a stent. Then they stay on just one antiplatelet drug, usually low-dose aspirin, indefinitely.

"People with afib may take anti­coagulants for the rest of their life," says Dr. Piazza. "But they should review this with their doctor every year to see if they need to make changes to their dose or even whether they need to continue taking it."

Other situations require short-term drug therapy, such as for 14 days to six weeks after a knee or hip replacement to prevent DVT. "Sometimes people need to take both an anticoagulant and an antiplatelet at the same time if they are being treated for separate issues, like afib and a stent," says Dr. Piazza.

Also, certain underlying medical conditions influence the choice and dose of an anti-clotting drug. For instance, people with impaired kidney function may not be able to take newer anticoagulants. Those who have had intestinal bleeding need to balance the risk of a clot versus the risk of severe blood loss.

Some over-the-counter pain relievers like ibuprofen (Advil, Motrin) and naproxen (Aleve) also can interact with anti-clotting drugs, so check with your doctor before taking them.

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