Preventing Another Stroke with Antiplatelet Medication

Editors Note: Having a stroke or brain attack is a scary thought for most adults. This article describes a treatment called "antiplatelet therapy" and how it helps to prevent having another stroke.

Most strokes are caused by a lack of blood flow to the brain from brain arteries becoming blocked by clots. Such clots form from a mixture of platelets (a type of blood cell) and fibrinogen and other related proteins involved in the clotting process. Normally, platelets are crucial in helping blood cells stick together to form clots that stop bleeding after a cut or injury. However, platelets may become active and may form clots inside arteries as a response to atherosclerosis. It was found that the formation of blood clots could be reduced if activation of the platelets was reduced and ischemic events like stroke or TIA could be prevented or made less severe. However, too few platelets are associated with an increased risk of bruising and bleeding and so physicians assess many factors to determine the medication and dose appropriate for each individual. Antiplatelet drugs thus are designed to reduce platelet aggregation or clumping to each other and to the artery to prevent stroke or heart attack in individuals who are at risk.

Taking antiplatelet drugs after a stroke or transient ischemic attack (TIA or 'mini-stroke') reduces the risk of having another one. There are now several approved medications available. The most commonly used drug for prevention of stroke recurrence is aspirin. Originally, aspirin was marketed primarily as a pain reliever and advertisements for this drug 75 to 100 years ago trumpeted the fact that aspirin had no effect on the heart or brain. Today, aspirin is a major tool in the fight against heart attacks and stroke! However, too high of a dose of aspirin may actually be associated with increased risk of either bleeding or clotting. This may partly explain why some people have strokes even on larger doses of aspirin. In the past, doses up to 1300 mg were used for stroke prevention. Current research suggests that doses as low as 50 mg may be effective for stroke prevention. In the United States, the typical dose is 81 mg (one 'baby aspirin') up to 325 mg (one 'adult aspirin').

Overall, aspirin alone can reduce the risk of stroke by about twenty to twenty-five percent as compared to no drug therapy at all. Still, there are limitations to the use of aspirin. Aspirin cannot prevent all strokes caused by clots, some people may not be able to tolerate the side effects of aspirin (stomach upset or development of ulcers), or may be allergic to it. As a result, newer prescription medications have been developed that further decrease the risk of stroke.

The first of the newer antiplatelet drugs that was approved for stroke prevention was ticlopidine (Ticlid®). The medication reduced the risk of stroke by 21% over aspirin. However, ticlopidine was associated with a number of side effects including stomach upset, nausea, and diarrhea. Additionally, there was a small risk that this medication might decrease the white blood cell count and/or cause irreversible bleeding, so this drug has been largely replaced by clopidogrel (Plavix®).

Clopidogrel is chemically very similar to ticlopidine, but has fewer side effects. It is tolerated as well if not better than aspirin. A study conducted on a large group of stroke, heart attack or peripheral arterial disease (PAD) patients using clopidogrel demonstrated a small (nine percent) relative risk reduction in stroke, heart attack or death as compared with aspirin (325 mg). Additional data from further studies suggests that the benefit of clopidogrel is significantly enhanced in some patients after heart attacks when used in combination with aspirin. Whether such combination therapy is effective and safe in other individuals with stroke, PAD, or heart disease is now being studied.

The alternative to clopidogrel is a sustained-release form of dipyridamole and very low dose of aspirin (25mg) taken twice daily. This combination medication, Aggrenox®, decreases the risk of clot formation. In one large European study with patients with a history of stroke or TIA, the risk of stroke decreased by twenty-three percent as compared with very low dose aspirin.

Antiplatelet drugs do not take away all risk for having another stroke, but they help and are cost-effective. There is strong evidence that antiplatelet therapy is safer and just as effective for most types of stroke as compared to anticoagulation with Coumadin®, a blood thinner, generically known as warfarin. In fact, warfarin should usually be reserved for only very specific circumstances, such as strokes that result from atrial fibrillation (an abnormal heart rhythm), clots in the heart, or strokes that occur as a result of certain specific blood disorders associated with increased risk of clotting. Overall, antiplatelet medications are the preferred drugs following most strokes or TIAs, with Coumadin being the preferred medication for strokes that are caused by atrial fibrillation. Additionally, new combination therapies using aspirin and clopidogrel, or combinations of aspirin and sustained-release dipyridamole, are more effective than aspirin alone. Many factors, including an individual's own medical history and risk of side effects, are taken into account by doctors before prescribing the best treatment for reducing one's risk of having another stroke. If you are at risk of stroke, or have suffered a TIA or stroke, be sure you do all that you can to decrease your future risk. Antiplatelet medications are central to the strategies used today to lower this risk.

About the Author: Michael J. Schneck, MD, is an Associate Professor in the Vascular Neurology and Critical Care Division of the Department of Neurology, Loyola University Chicago, Stritch School of Medicine. He serves on staff at Rush-Presbyterian-St. Luke's Medical Center and Cook County Hospital in Chicago. Dr. Schneck is on the Board of Directors of the American Heart Association of Metropolitan Chicago and chair of the Medical Subcommittee of the American Stroke Association's Operation Stroke of Metropolitan Chicago. Dr. Schneck is also a member of the Advisory Faculty, Stroke Module Quintessential Program of the American Academy of Neurology.