Aspirin and Antiplatelet Medications (cont.)

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How quickly do aspirin and antiplatelet agents work?


When aspirin is given in low doses (75 mg/day), the complete inhibition of the COX-1 enzyme and hence maximal antiplatelet effect may take several days. At a dose of 160-325 mg/day, the maximal antiplatelet effect of aspirin occurs within 30 minutes. Thus, aspirin at low doses (75-150 mg/day) is used for the long term prevention of heart attacks and strokes, whereas moderate doses (160-325 mg/day) of aspirin are given in situations where an immediate anti-clotting effects are needed (such as in the treatment of acute heart attacks and unstable angina).


Like aspirin, the onset of action of clopidogrel (Plavix) is dose related. Maximal antiplatelet effect occurs several days after initiation of clopidogrel (75 mg/daily), but can occur within hours after larger doses of 300 or 600 mg. Therefore, larger doses of clopidogrel are used initially when immediate antiplatelet actions are needed (such as after placement of intracoronary stents) while the lower doses are used as maintenance.

Glycoprotein IIb/IIIa inhibitors

The glycoprotein IIb/IIIa inhibitors have a rapid onset of action. Their maximal antiplatelet effect occur within minutes after an intravenous infusion, and are used mainly in patients with unstable angina or acute heart attack (myocardial infarction).

Par-1 antagonist

Vorapaxar blocks about 80% or more of platelet clumping within a week of treatment. The duration of its effect depends on the dose given. Even 4 weeks after stopping vorapaxar it can still block platelet clumping by 50%.

What is dipyridamole for heart attack and stroke prevention and treatment?

Dipyridamole (Persantine IV, Persantine) is another medication that decreases platelet aggregation, though the exact mechanism of its antiplatelet action is not well understood. Dipyridamole is not commonly used in heart attack prevention although it is sometimes used with aspirin to lessen the chance of stroke.

When is aspirin used for preventing and treating heart attacks and strokes?

Aspirin is widely used either alone or in combination with other antiplatelet agents to prevent blood clots from forming in arteries. Aspirin is used specifically in several situations including:

  1. Aspirin often is prescribed in moderate doses (160-325 mg/day) for people who are having heart attacks to limit the extent of damage to the heart's muscle (by preventing further blood clot formation in the blood vessels of the heart), prevent additional heart attacks, and improve survival.
  2. Aspirin often is prescribed to patients undergoing surgery to open or bypass blocked arteries, including percutaneous transluminal coronary angioplasty (PTCA) with or without placement of coronary stents and coronary artery bypass surgery (CABG). Aspirin also is prescribed on a long-term basis to prevent clotting in the stents and/or the bypassed blood vessels.
  3. Aspirin often is prescribed in low doses (75-160 mg/day) on a long-term basis to patients with prior heart attacks or strokes and to patients with TIAs (transient ischemic attacks or mini-strokes) and exertional angina to prevent heart attacks and ischemic strokes.
  4. Aspirin is prescribed in moderate doses (160-325 mg/day) to patients who are having unstable angina to prevent heart attacks and improve survival.
  5. Aspirin is prescribed in moderate doses (160-325 mg/day) to selected patients who are having ischemic strokes to limit damage to the brain, prevent a second stroke, and improve survival.
Medically Reviewed by a Doctor on 10/15/2015

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