Clopidogrel to Prasugrel in Acute Coronary Syndrome (ACS) Patients

This study will evaluate the use of a prasugrel 60 mg loading dose (LD) administered during percutaneous coronary intervention (PCI) with and without a prior LD of clopidogrel on platelet inhibition in patients presenting with acute coronary syndrome (ACS). Platelet inhibition following a prasugrel LD in clopidogrel pretreated patients' will be determined in a time-dependent manner for two different prasugrel loading doses (30 mg and 60 mg). Understanding the effects of this combination on platelet inhibition will provide guidance to physicians on the use of prasugrel in patients who have already been pretreated with clopidogrel.


Eligibility Criteria:
Inclusion Criteria:

* Participants hospitalized with acute coronary syndrome (ACS) \[unstable angina (UA), non-ST elevation myocardial infarction (NSTEMI), or ST elevation myocardial infarction (STEMI)\] as determined by the investigator, and who are anticipated to undergo percutaneous coronary intervention (PCI) as a treatment for the ACS event within 24 hours of the clopidogrel/placebo loading dose
* Participants provide signed informed consent form (ICF)
* Participants weigh at least 60 kilograms (kg) at the time of screening
* Women of child-bearing potential (that is, women who are not surgically or chemically sterilized and who are between menarche and 1-year postmenopause), test negative for pregnancy at the time of enrollment based on a urine or serum pregnancy test

Exclusion Criteria:

* Have cardiogenic shock at the time of randomization (systolic blood pressure greater than 90 millimeters of mercury (mm Hg) associated with clinical evidence of end-organ hypoperfusion, or participants requiring vasopressors to maintain systolic blood pressure over 90 mm Hg and associated with clinical evidence of end-organ hypoperfusion
* Have refractory ventricular arrhythmias
* Have New York Heart Association (NYHA) Class IV congestive heart failure
* Have systolic blood pressure greater than 180 mm Hg, or diastolic blood pressure greater than 100 mm Hg on more than 1 assessment at any time from participant presentation of ACS treatment to enrollment
* Have received fibrin-specific fibrinolytic therapy less than 24 hours prior to randomization
* Have received nonfibrin-specific fibrinolytic therapy less than 48 hours prior to randomization
* Have active internal bleeding or history of bleeding diathesis
* Have clinical findings, in the judgment of the investigator, associated with an increased risk of bleeding
* Prior history of ischemic or hemorrhagic stroke
* Intracranial neoplasm, arteriovenous malformation, or aneurysm
* Prior history of transient ischemic attack (TIA)
* Have an International Normalized Ratio (INR) known to be greater than 1.5 at the time of evaluation
* Have a platelet count of less than 100,000 per cubic millimeter (mm\^3) at the time of evaluation
* Have anemia \[hemoglobin (Hgb) less than 10 grams per deciliter (g/dL)\] at the time of evaluation
* Have received 1 or more doses of a thienopyridine (ticlopidine, clopidogrel, or prasugrel) or other adenosine diphosphate (ADP) receptor inhibitor within 10 days prior to screening
* Have been administered glycoprotein IIb/IIIa (GPIIb/IIIa) inhibitor within the past 7 days or planned use of a GPIIb/IIIa inhibitor during PCI
* Are receiving or will receive oral anticoagulation or other antiplatelet therapy, other than aspirin (ASA), which cannot be safely discontinued for the duration of the study.
* Are receiving daily treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX2) inhibitors that cannot be discontinued during the study
* Are currently enrolled in, or discontinued within the last 30 days from, a clinical trial involving an investigational drug or device or off-label use of a drug or device, or concurrently enrolled in any other type of medical research judged not to be scientifically or medically compatible with this study
* Have previously completed or withdrawn from this study or any other study investigating prasugrel
* Are women who are known to be pregnant, who have given birth within the past 90 days, or who are breastfeeding
* Have a concomitant medical illness (for example, terminal malignancy) that in the opinion of the investigator, is associated with reduced survival over the expected treatment period
* Have known severe hepatic dysfunction (that is, with cirrhosis or portal hypertension)
* Have a history of intolerance or allergy to aspirin or approved thienopyridines (ticlopidine, clopidogrel or prasugrel)
* May be unable to cooperate with protocol requirements and follow-up procedures