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“Clot-busting” medicines that dissolve blood clots work well—but they are costly and have substantial risks. Now, a large study suggests that clot-busters may often be no better for treating leg clots than cheaper, less risky drugs.

To understand why, first you need to know a little about a blood clot condition called deep vein thrombosis (DVT).

The hazards of deep vein thrombosis

When an injury causes a wound to open, you depend on your blood to clot. Clotting on the surface of your skin enables a scab to form, stopping blood loss and keeping germs out. But sometimes a clot develops where it shouldn’t. If a clot forms inside a blood vessel, it could reduce blood flow, leading to painful symptoms or life-threatening problems.

Deep vein thrombosis is a blood clot in a vein deep within the body. It most often develops in the legs. Sometimes DVT is painful and causes swelling, but in other cases no symptoms are noticed. DVT can be dangerous because the clot could break off and travel through the bloodstream to your heart, lungs, or elsewhere—causing such problems as a heart attack, stroke, or a blood-flow blockage in the lungs called pulmonary embolism.

Every year, DVT strikes an estimated 300,000 to 600,000 people in the United States for the first time. About half of them will go on to develop a long-term complication called post-thrombotic syndrome, causing limb pain, swelling, and difficulties with walking and other everyday activities.

Blood thinners are the most common treatment for deep vein thrombosis. They help keep clots from getting bigger and reduce the risk of additional clots. In time, existing clots may dissolve on their own.

To bust or not to bust

The new study included nearly 700 people with deep vein thrombosis. One group was given only blood thinners, while the other group got blood thinners and clot-busting medication. They were followed for two years.

Researchers wanted to see whether adding clot-busters would reduce the number of people who developed post-thrombotic syndrome. Doctors have long believed that it would, helping justify the widespread use of these medicines.

The results were clear: both groups fared about the same. Post-thrombotic syndrome developed in 47 percent of the people who got clot-busters and 48 percent of the people who didn’t. The group that received clot-busters had slightly milder symptoms, but they also had an increased risk of dangerous bleeding—a good reason to avoid the drugs.

“What we know now is that we can spare most patients the need to undergo a risky and costly treatment,” said principal investigator Suresh Vedantham, MD, a professor of radiology and surgery at Washington University School of Medicine in St. Louis, in a news release.

Vedantham said clot-busters might still be useful in severe cases when post-thrombotic syndrome doesn’t respond to blood thinners.

The study was funded by the National Heart, Lung, and Blood Institute.

Signs and symptoms

Only about half of all people who have DVT have any noticeable symptoms, but it’s still important to watch for them. Possible warning signs include:

• Swelling of the leg, or swelling along a vein in a leg
• Pain or tenderness in the leg, which you may only feel when standing or walking
• Unusual warmth in the area of the leg that’s swollen or painful
• Red or discolored skin on the leg

When DVT causes pulmonary embolism, possible symptoms include:

• Shortness of breath
• Pain with deep breathing
• Coughing up blood
• Rapid breathing
• Rapid heart rate

Call your doctor right away if you have any of these signs and symptoms.

Have you been treated with a clot-busting medicine? What happened? Share your experience with our community by commenting below.