Clot Busters

What Are Clot Busters?

Clot busting medications break up blood clots. During a heart attack, clot busters—also called thrombolytics—dissolve the blood clot that is blocking the artery and help restore blood flow to the heart. These medications are injected into the arm through an intravenous (IV) line. They are usually given to heart attack patients in the emergency department; however, they may sometimes be given in the ambulance en route to the hospital.

Benefits of Clot Busters

Women treated with clot busting drugs during a heart attack fare better than women who do not receive these medications. In an overview of nine research studies, clot busting medications reduced the risk of a woman dying within 35 days after a heart attack by 12%.¹

The benefits are even greater if nonfatal complications are counted. An analysis of the national registry of heart attack patients (called the National Registry of Myocardial Infarction, or NRMI for short) found that 13% of women treated with the clot buster tissue plasminogen activator (tPA or Activase), died or had a stroke while in-hospital compared with nearly 21% of women who did not receive clot busting drugs.²

Even so, women did not benefit from clot busting drugs as much as men. Significantly more women treated with clot busters died or had a stroke compared with men treated with clot busters. This is partly because clot busters may be more likely to trigger a stroke in women than in men.

In terms of restoring blood flow to blocked arteries, clot busters work equally well in men and women.³ Why this does not translate into a similar reduction in death rates is unclear. Some researchers suggest that factors other than clogged arteries may play more of a role in women and elderly patients.²

Risks of Clot Busters

There are different types of stroke; the most common type is due to blockages in the arteries supplying blood to the brain. Clot busters are more often associated with hemorrhagic stroke, which occurs when these arteries rupture and there is bleeding in the brain. Women treated with clot busters are 2 to 3 times more likely to suffer such a stroke than men treated with the same drugs.⁴ African Americans are more likely to suffer a stroke after treatment with clot busting drugs than white patients. Some research suggests that the increased risk of stroke in women is because women who have heart attacks are generally older and sicker than men.⁵ But other studies have found that even when you take this into account, women are still more likely to suffer a stroke than men.^{6, 7}

Because clot busters increase bleeding, there were initial concerns that they may be unsafe for women during menstruation; however, there is now evidence to show that clot busters are safe for women during their menstrual period.⁸

Dosing of Clot Busters in Low-weight Patients

The risks of stroke and bleeding complications after treatment with clot busting medications are higher in patients who weigh less than 155 lbs.⁶ It is thought that smaller patients, who are more likely to be women, might benefit if drug doses were lowered. A study comparing the standard clot buster, tPA (Activase), with tenecteplase (TNKase), a newer clot buster given in different doses depending on the patient's weight, found little overall difference between the two. Patients weighing less than 155 lbs were more likely to die or suffer a stroke than heavier patients regardless of the clot buster they received.¹⁰ However, bleeding complications were lower with TNKase and there was suggestive — but not conclusive — evidence that this clot buster was less likely than Activase to trigger a stroke among women older than 75 years weighing less than 148 lbs.¹¹

Choice of Clot Buster

Each clot buster has advantages and disadvantages and no one drug is clearly better than any other. For example, studies suggest that alteplase and reteplase are best for quickly restoring blood flow to the heart, but these clot busters have a higher risk of stroke than others.¹² There is some evidence suggesting that tissue plasminogen activator (Activase) is associated with more bleeding in African American patients than streptokinase but more research is needed. Physicians choose which drug to use based on their assessment of each patient's particular risks.