About platelets and antiplatelets
Antiplatelets are medications that inhibit the activity of platelets, which help the blood clot after injury. Antiplatelets are used to avoid situations where the blood can clot excessively, potentially causing a heart attack or stroke.
Under normal circumstances, platelets play a crucial role in blood coagulation, clotting and hemostasis (stoppage of bleeding). When a small blood vessel is injured, platelets begin to stick to each other (platelet aggregation). They also adhere to the sides of the injured tissue to form a plug, which becomes covered with strands of thread-like fibrin. Soon the blood clot (plug) shrinks into place and blocks any further loss of blood. Platelets also release chemicals that begin the healing process. Without this important clotting function of the platelets, excessive and potentially life-threatening amounts of blood would be lost after simple cuts or scrapes.
While this process is essential to healing, the activity of platelets can be dangerous in some situations. If a blood clot is formed inside a blood vessel, often as a response to injury to the vessel such as occurs with atherosclerosis, it raises the risk of heart attack or stroke. This may occur when a blood clot grows large enough to block a blood vessel (thrombus), or a piece of clot breaks off, travels through the bloodstream and blocks a blood vessel in another part of the body (embolism).
To help prevent this, physicians may prescribe antiplatelets in patients who are at high risk for developing a thrombus within their blood vessels. Antiplatelets are types of anticoagulants – medications used to help prevent the formation of blood clots when no injury has occurred. They work by reducing the platelets’ stickiness (viscosity). The most common antiplatelet in use today is the over-the-counter drug aspirin, which has been found to prevent platelet binding and clot formation. Today, many physicians place their heart patients on a small daily dose of aspirin (generally 81 milligrams) to prevent the formation of blood clots that may injure the heart. For patients who do not respond to aspirin as a preventive therapy, other antiplatelet medications are available. The most common are clopidogrel and ticlopidine.
Aspirin is an analgesic (pain reliever) that has anti-clotting properties that benefit the heart. However, many other over-the-counter pain relievers do not have the anti–clotting properties of aspirin. These drugs cannot be used as an aspirin substitute to prevent clot-related heart problems. Studies suggest that more than 20 percent of people taking an analgesic for heart disease prevention are taking non-aspirin medications that actually provide no anti-clotting or cardiovascular benefit.
Patients should never take aspirin or any other antiplatelet drug as a preventive measure unless advised to do so by a physician. In addition, antiplatelets should not be taken with anticoagulants unless directed by a physician. While antiplatelets are a valuable preventive tool when used properly, they can cause serious bleeding in some people, and their activity may be affected by a wide range of other medications and substances. Therefore, a physician always needs to carefully review a patient’s condition and medical history before prescribing antiplatelet therapy. In general, patients with a history of internal bleeding (most often gastrointestinal) should not take aspirin.
Types of antiplatelets include:
- aspirin (acetylsalicylic acid)
- choline salicylate
- choline magnesium trisalicylate
- magnesium salicylate
- salicylic acid
- sodium salicylate
- ticlopidine hydrochloride
Antiplatelets are prescribed for a variety of conditions, including:
- Coronary artery disease. Antiplatelets may help to prevent a heart attack or stroke in patients who are at high risk of developing obstructive blood clots (coronary thrombosiscoronary thrombosis). Aspirin has been shown to prevent first heart attacks in middle-aged men who are asymptomatic and without any known heart disease. However, the recent CHARISMA study showed that certain antiplatelets do not provide a benefit to middle-aged people without known heart disease.
- Heart attack. An event in which the heart muscle does not receive enough oxygen-rich blood as a result of a blockage in the coronary blood vessels. Antiplatelets may reduce the damage to the heart if taken while an attack is in progress or immediately afterward (preferably within 30 minutes). Recent research also indicates that a combination of aspirin and other antiplatelets administered after a heart attack may reduce the risk of death, stroke or another heart attack.
- Angina. A temporary and often recurring chest pain, pressure or discomfort caused by inadequate oxygen-rich blood flow (ischemia) to some parts of the heart.
- Stroke. An event in which the brain does not receive enough oxygen-rich blood, usually due to blockage of a cerebral blood vessel by a blood clot. In high-risk patients, taking antiplatelets regularly has been found to prevent the formation of blood clots that cause first or second strokes. However, patients should not take aspirin or any other antiplatelet during a suspected stroke because it may cause further damage. Antiplatelets are contraindicated when the stroke is associated with brain hemorrhage or when the brain is likely to develop hemorrhagic transformation.
- Transient ischemic attacks (TIAs, or mini-strokes). A brief interruption of oxygen to the brain due to decreased blood flow through the arteries, usually because of an obstructing blood clot. Antiplatelet drugs have been found to be effective in the prevention of TIAs, and they also help prevent against ensuing strokes. TIAs are considered a major warning sign of impending stroke.
- Angioplasty. A catheter-based technique used to open arteries obstructed by a blood clot. Whether or not stenting is performed immediately after this procedure to keep the artery open, antiplatelets may reduce the risk of forming additional blood clots following the procedure(s). Aspirin and clopidogrel can reduce the chance of heart attack and death, especially if taken several hours before the procedure.
- Coronary bypass surgery. A surgical procedure in which an artery or vein is taken from elsewhere in the body and grafted to a blocked coronary artery, rerouting blood around the blockage and through the newly attached vessel. After the procedure, antiplatelets may reduce the risk of secondary blood clots.
- Atrial fibrillation. The most common type of sustained abnormal heart rhythm (arrhythmia), atrial fibrillation affects about 2 million Americans every year. During atrial fibrillation, the atria (the heart’s upper chambers) rapidly fire electrical signals that cause them to quiver rather than contract normally. This may lead to the creation of blood clots within the atria that can travel to the brain or other organs (embolism), potentially causing a stroke. Antiplatelets may reduce this risk. However, most patients with atrial fibrillation need to take anticoagulants because antiplatelets alone are not sufficient to reduce the risk of an embolism.
Conditions of concern
Patients should consult with their physician before taking antiplatelets. This is particularly important if an individual is allergic to aspirin or other analgesics. Also, antiplatelets may not be recommended if any of the following conditions apply:
- Impending surgery. Individuals who plan to undergo any surgical procedure requiring local, general or spinal anesthesia (including dental surgery) within two to three weeks. Surgery always carries the risk of uncontrolled and excessive bleeding, and antiplatelet medication could seriously increase that risk.
- Bleeding disorders. Antiplatelet medication could cause uncontrolled bleeding.
- Liver or kidney disease.
- Vitamin K deficiency (rare). Vitamin K is necessary to the natural formation of blood clots. Use of antiplatelet medication could potentially lead to uncontrolled bleeding.
- History of gastrointestinal bleeding or other bleeding problem.
- Thrombotic thrombocytopenic purpura (TTP). A rare, life-threatening blood disorder in which platelets are destroyed by antibodies. Antiplatelet medication could potentially lead to uncontrolled bleeding.
In addition, antiplatelets may make the following conditions worse:
- Anemia. A reduced number and or mass of red blood cells.
- Overactive thyroid. Overproduction of hormones by the thyroid gland, located in the front of the neck.
- Stomach ulcer. An open sore or crater in the stomach lining.
Side effects from antiplatelets may be increased in patients with the following conditions:
- High blood pressure (hypertension), which can increase the risk of bleeding into or around the brain
- Nasal polyps (or history of nasal polyps)
- Side effects
Potential side effects
Possible side effects of antiplatelet medication include:
- Allergic reaction (sneezing, respiratory congestion, swelling of throat, restricted breathing, itching or skin rashes)
- Nausea, indigestion or stomach pain
Adjusting when antiplatelets are taking may help reduce some side effects. For example, if the drug is taken after meals rather than on an empty stomach, it may reduce upset stomach and nausea. Patients are urged to contact their physician if they experience the side effects are severe, become worse or do not go away.
In addition, patients should contact their physician immediately if the experience:
- Unusual heavy bleeding (e.g., from a cut, during menstruation)
- Dark red or black, tarry stools
- Vomiting that looks like coffee grounds
- Coughing up blood
- Unusual bruising
- Feeling faint, dizzy or disoriented
- Ringing in the ears
- Chest pain or tightness in the chest
- Difficulty breathing
- Swallowing problems
Drug or other interactions
Patients should consult their physician before taking any other medication (either prescription or over-the-counter), nutritional supplements or herbal remedies. Some of these substances, such as cold medicine or antibiotics, can affect the way antiplatelets work. Non-steroidal anti-inflammatory drugs (NSAIDs) and medicines that contain aspirin may cause bleeding problems in individuals who take antiplatelets.
Patients should remember that antiplatelets can control many conditions, but cannot cure them. Even if all their symptoms are relieved, patients should continue to take their medication exactly as directed and to keep all scheduled follow-up appointments with their physician.
Patients taking antiplatelets or other anticoagulants may need to undergo regular blood tests to monitor their medication dosage. These tests usually require the patient to visit a hospital, physician’s office or laboratory on a monthly, bimonthly or weekly basis.
Approximately 5 to 10 percent of patients have been shown to have some type of platelet resistance. Preliminary evidence suggests that these people may be at higher risk of subsequent clotting events such as heart attack or stroke. It is not currently clear if a higher dose of antiplatelets can overcome these problems.
Regular use of some antiplatelets can add a significant amount of sodium to the diet. Patients adhering to a low-sodium diet may need to make further dietary adjustments when taking antiplatelets.
- How to use
Pregnancy use issues
Taking antiplatelets in the last two weeks of pregnancy may cause bleeding problems in the baby both before and after delivery. When taken in the last three months of pregnancy, antiplatelets may prolong the length of the pregnancy and the delivery. Studies on antiplatelet use earlier in pregnancy have been inconclusive. Patients who are pregnant or are trying to become pregnant should inform their physician before taking antiplatelets. In general, aspirin should be avoided during pregnancy.
Antiplatelets can pass through breast milk to the infant. However, their effect on nursing infants is unknown. Parents should weigh the benefits and risks in consultation with their physician.
Child use issues
Children should never be given an antiplatelet unless under the direction of a physician. aspirin given to children under 15 has been linked to the onset of Reye syndrome, a potentially fatal inflammation of the brain. Whether other types of antiplatelets are safe for children has not yet been scientifically established.
Elderly use issues
Older adults report a higher frequency and intensity of side effects. Generally, older patients require lower doses of antiplatelets.
Symptoms of medication overdose
Patients exhibiting any of the following symptoms should contact their physician immediately
Questions for your doctorPatients may wish to ask their doctors the following questions about antiplatelet medications:
- Why have you prescribed an antiplatelet?
- If I take a prescription antiplatelet, can I still take aspirin for a headache?
- What do I need to tell other physicians or my dentist about my antiplatelet medications?
- Is it possible to still get a blood clot while taking antiplatelets?
- I take anti-inflammatory drugs for arthritis. Should I still take aspirin as a preventative?
- What side effects of antiplatelet medications I should report to you?
- What symptoms indicate a medical emergency?
- I had a stroke several years ago. What antiplatelet regimen do you recommend now?
- How soon after heart surgery can I resume taking my antiplatelet medication?
- Can I take other anticoagulants with antiplatelets?
- How does exercise affect antiplatelets medication?
- How long will I need to be on this medication?