Also known as thrombolytics, clot busters are medications used to break up a blood clot. Other medications are able to prevent a blood clot from forming or growing (anticoagulants), but clot busters are the only medications currently available that can actually destroy an existing blood clot. They are often used in emergency situations, particularly among people suffering from the most common form of stroke or heart attack. If administered early in these situations, clot busters have the proven ability to lessen the long-term damage from stroke or heart attack. Clot-busting drugs may also be used to treat pulmonary embolisms and clots that form around artificial heart valves.

Administering clot busters is complex and usually done through an intravenous (I.V.) line in the arm by hospital personnel. Alternatively, clot busters may be administered directly to the site of the clot using a thin tube (catheter), allowing for a greater dose of the drug with fewer potential side effects. Paramedics are also increasingly giving these medications (under a physician’s direction) while a patient is en route to the hospital.

Although clot busters can save the life of a person having a heart attack or the most common type of stroke, there is also a higher risk of bleeding associated with clot busters than with anticoagulants. Clot busters are most effective when given within a few hours after the onset of symptoms. Therefore, it is important to recognize the signs and symptoms early.

Also known as thrombolytics, clot busters are medications given intravenously (I.V.) to a patient to break up a blood clot. If the patient is having a heart attack or an ischemic stroke, in which the blood supply to the brain is disrupted by a blood clot, clot busters may reduce the damage to the heart or brain and prevent death. To be most effective, clot busters need to be administered fairly quickly. 

Blood clotting is a vital and natural bodily function. However, a blood clot can be deadly if it is large enough to block a blood vessel (thrombus), or if either part of the blood clot  or the entire clot breaks off and travels through the bloodstream to lodge in a blood vessel elsewhere (embolism). Unlike anticoagulants, which can prevent blood clots from forming or becoming larger, clot busters are the only types of medication currently available that can actually destroy a existing blood clot.

Clot-busters must be administered quickly and properly through several specifically timed intravenous (I.V.) infusions according to a rigid protocol established for each drug and the body weight of the patient. Research has shown that these medications are most effective when given within four hours of the onset of symptoms for heart attack, particularly within the first 70 minutes,  or within three hours for stroke. Better recognition of the signs and symptoms of these conditions could increase the number of patients who benefit from the use of clot-busting drugs.

Clot-busting drugs are more likely than anticoagulants to cause bleeding problems, and errors in dosage or timing of delivery can be fatal. Because they are complicated drugs to administer, they are generally used only when the patient is in a hospital (although they could be used by emergency personnel outside the hospital). Emergency room teams must start the treatment as soon as possible, usually within half an hour of the patient’s arrival.

Unfortunately, many heart attack patients, particularly those who experience heart attacks at night, arrive late at the hospital. In this case, it may still be reasonable to administer clot-busting drugs up to 24 hours after the event has occurred, according to guidelines issued in 2004 by the American College of Cardiology and American Heart Association. Whether or not these drugs should be used in this case depends on the specifics of the patient's electrocardiogram, or ECG.

Instead of using the traditional I.V. method, a physician may choose to use a thin tube called a catheter to administer the medication. The catheter is threaded through a blood vessel to deliver the medication directly to the site of the blood clot. With this method, higher concentrations of clot-busters can be used, and there may be fewer side effects than with the traditional I.V. infusion method. Studies have also shown that combination therapy, which uses traditional I.V. delivery and a catheter delivery system, is effective in certain situations.

Some types of clot busting drugs include:

• Anistreplase
• Anisoylated plasminogen-streptokinase activator complex (APSAC)
• Tissue plasminogen activator (tPA or t-PA), such as urokinase, tenectplase, lanoteplase or reteplase
• Recombinant t-PA (rtPA or rt-PA), such as alteplase
• Streptokinase

A  new type of thrombolytic medication called desmoteplase is currently being investigated for use in stroke treatment. The medication was created from the saliva of vampire bats. While this medication will not likely be approved for general use for several years, results so far have been promising. Research has suggested that desmoteplase may be effective up to nine hours after the onset of stroke symptoms. Currently, the most commonly used clot busting medication (t-PA) needs to be given within three hours of the initial symptoms starting to be most effective.

Researchers are also exploring the use of other medications in combination with clot busters. For instance, one study found that administering low doses of insulin along with clot busters and anticoagulants helped to decrease the inflammation of blood vessels in patients following a heart attack. Aspirin and anticoagulation medications, such as heparin, are also routinely administered in conjunction with clot-busting drugs to heart attack patients.

Combined therapies are also being researched, such as a study using clot busters in conjunction with stenting procedures for patients with ischemic stroke. Researchers found the combination to be beneficial in preventing or reducing damage caused by the stroke in most of the small number of patients studied. Another catheter-based therapy, using a special corkscrew-like coil, was approved by the FDA in 2004 for use in acute stroke. However, while the device is designed to improve blood flow, early studies show that it may not be substantially more effective than conventional treatments and it has a greater risk of complications. Thus, although the device has been approved, it has not been incorporated into widespread clinical use.

The use of ultrasound, or sound waves, in conjunction with clot-busting drugs, has also been studied among patients with ischemic stroke. Although some early results have been promising, there appears to be an increased risk of hemorrhage in the brain and further study is needed before this practice is approved for use.

Anticoagulants are still the first-line prevention for most blood clots. The use of clot busters is reserved for acute cases in which a clot is seriously obstructing blood flow to an area of the body. The most common examples of this are during a heart attack and ischemic stroke, which are caused by a blockage in the flow of oxygen-rich blood to the heart or brain. Administering clot busters within four hours, particularly in the first 70 minutes, or three hours for a stroke, following the onset of symptoms, can greatly decrease the amount of tissue damage to the heart or brain caused by a lack of oxygen (hypoxia). The benefits of clot busters decrease over time. After 24 hours, they offer no advantage over anticoagulants for treatment of these conditions.

Clot-busting therapy remains an important rapid treatment method for people who have an ischemic stroke, in which the blood supply to the brain is disrupted by a blood clot. However, it is considered controversial by some because of the relatively high risk of bleeding in the body. It is also for this reason that people who suffer from hemorrhagic strokes, caused by excess bleeding in the brain, should not be given clot busters. These drugs may increase the bleeding and worsen the stroke. 

Before administering a clot buster to a stroke patient, the physician will always order a computed tomography (CT scan, which is a painless x-ray procedure that can determine whether the stroke is due to obstruction by a blood clot (ischemic) or by bleeding into the brain (hemorrhagic). Besides late arrival at the hospital, this need for a CT scan is the principle delay in administering clot busters. 

Despite the effectiveness of clot-busting medications for treating ischemic stroke, many patients are not able to benefit from their use. Researchers have found that as few as 22 percent of patients suffering a stroke arrive at the hospital within three hours of the onset of symptoms. Of these, only about 8 percent are candidates for clot-buster therapy.  Better recognition of the signs and symptoms of stroke could increase the number of patients who benefit from the use of clot-busting drugs.

With heart attack patients, clot–busting therapy is generally considered slightly less effective than rapid access to balloon angioplasty (within two hours of onset of symptoms), which also helps reestablish blood flow to the heart. However, clot-busting therapy remains a very important part of heart attack treatment because of the limited access to angioplasty treatment for many heart attack patients.

In addition to treating heart attack and stroke, other conditions that may be treated by clot busters include:

• Deep vein thrombosis. The formation of a blood clot in the deep veins of the legs. Clot busters are somewhat controversial in this area because of the risk of serious bleeding complications.
  
  
• Pulmonary embolism. A clump of material (e.g., a blood clot) that has traveled through the bloodstream and lodged within a blood vessel in the lungs, blocking blood flow. Clot-busting drugs may be used when the clot is large and is associated with low blood pressure and/or dysfunction of the right side of the heart.
  
  
• Thrombosis of an artificial heart valve. This is especially common in patients with artificial hearts valves who stop using necessary anticoagulants or receive an inefficient dose. The condition may result in severe obstruction of the heart valve resulting in pulmonary edema or collapse. Clot-busting drugs may dissolve the valve clot and allow normal flow through these valves.
  
  
• Occlusive peripheral artery disease (PAD). An advanced form of PAD in which the plaque that has formed within a peripheral artery accumulates to the point where blood flow within the artery is blocked (occluded).

Clot busters can also be rinsed through a catheter to clear any obstructing blood clots during a catheter-based procedure. While such procedures (e.g., balloon angioplasty) are generally scheduled to prevent the risk of a coronary event, they can also be used to reduce the damage caused by such events as they are occurring. In fact, research has suggested that women, people with diabetes and older stroke patients may benefit more from angioplasty than clot-busting medications.

However, the benefit of clot-busting medications is that they can be given "in the field," whereas angioplasty procedures must take place in a medical setting. Under a physician’s direction, first-responders, such as paramedics, can administer these medications for heart attack patients. This can shave valuable minutes off the time it takes to begin treatment. Research has shown that “the earlier, the better” applies to both clot-busting medication and angioplasty.

In deciding whether to use a clot buster, its potential benefits must be weighed against its risks. In most cases, people with the following conditions should avoid the use of clot-busting drugs:

In addition, research has suggested that heart attack patients with diabetes may not get the same benefit from the use of clot-busting drugs as people with normal blood sugar control. While the reason for this is not fully understood, physicians may choose alternate therapies for diabetic patients. Among stroke patients, a study is underway to determine if lowering blood sugar levels before administration of clot-busting drugs will improve outcomes.

The most serious potential side effect associated with clot-busting medications is bleeding inside the body, which may increase the risk for hemorrhagic stroke. While medical staff will monitor the patient for this problem, patients should also be aware of associated signs and symptoms, which may occur 24 hours after administering the clot-buster. They include:

Common side effects of clot busters include:

• Bleeding or oozing from cuts, gums or wounds, or around the area of injection
• Allergic reaction
• Fever
• Low blood pressure (hypotension)

Less common side effects include:

• Unusual bruising
• Headache
• Chest pain or tightness (with or without or wheezing)
• Shortness of breath, troubled breathing or fast/irregular breathing
• Muscle pain or weakness, weakness in arms or legs
• Swelling of eyes, face, lips or tongue
• Flushing, redness of skin or changes in skin color, especially on the face
• Confusion
• Blurred or double vision
• Difficulty speaking
• Nausea

Patients should consult their physician before taking any other medication (either prescription or over-the-counter), herbal remedies or nutritional supplements. Of particular danger to individuals taking clot busters are some forms of:

Clot-busting drugs are universally administered in a hospital or emergency medical setting while the patient is being closely monitored.This is because of the high risk of bleeding complications These drugs are not taken by individual patients. Signs and symptoms of internal bleeding include:

Some clot-busting drugs have been used in pregnant patients with no adverse effects reported in either the mother or fetus. However, if used in the first five months of pregnancy, clot-busting drugs could cause a miscarriage. Patients who are pregnant or are trying to become pregnant should inform their physician before being given clot busters.

It is unknown whether clot-busting drugs pass through breast milk to nursing infants. Patients are advised to discuss the risks of breast feeding with their physicians. 

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to clot-busting drugs:

1. Are clot-busting drugs used for my type of heart attack or stroke?
   
   
2. How quickly were they administered in my case?
   
   
3. Do I need to give consent before a physician administers clot-busting drugs?
   
   
4. Will I need to continue with anticoagulant medication? For how long? Which one?
   
   
5. What other medications will I need to take? Antiplatelets?
   
   
6. How long will it be before the risk of complications from the clot-busting drugs decreases?
   
   
7. What kind of complications can occur? Is there an increased risk of hemorrhage due to the clot-busting drugs even days or weeks after they are used?
   
   
8. Is it possible I will still need surgery for heart disease?
   
   
9. Are any other procedures, such as balloon angioplasty and stenting, warranted in my case?
   
   
10. Are there any lifestyle changes I can make to help prevent another vascular event?