Prasugrel Versus Placebo in Adult Sickle Cell Disease

Inclusion Criteria:

• Adults with Sickle Cell Disease (SCD).

• Are greater than or equal to 50 kilograms (kg) at time of screening.

• Are not currently being treated with an investigational drug (use of hydroxyurea,which is not an investigational drug, is permitted under this protocol if the patienthas been on a stable dose for at least 30 days prior to randomization and has no signsof hematological toxicity at screening.

• Agree to use a reliable method of birth control during the study or are women not ofchild-bearing potential due to surgical sterilization (hysterectomy or bilateraloophorectomy or tubal ligation) or menopause.

Exclusion Criteria:

• Acute painful crisis (requiring medical attention) within 30 days prior to screening.

• Have a concomitant medical illness (for example, terminal malignancy) that, in theopinion of the investigator, is associated with reduced survival over the expectedtreatment period (approximately 30 days).

• Severe hepatic dysfunction (cirrhosis, portal hypertension, or aspartateaminotransferase (AST) greater than or equal to 3x upper limit of normal [ULN]).

• Renal dysfunction requiring chronic dialysis.

• Contraindication for antiplatelet therapy.

• History of intolerance or allergy to approved thienopyridines.

• Have signs or symptoms of an infection.

• Hypertension (systolic blood pressure >180 millimeters of mercury (mm Hg) or diastolicblood pressure >110 mm Hg) at the time of screening or randomization.

• Hematocrit <18%.

• Any history of bleeding diathesis, bleeding requiring in-hospital treatment, orpapillary necrosis.

• Active internal bleeding.

• History of spontaneous gastrointestinal (GI) bleeding requiring in-hospital treatment.

• Gross hematuria. Microhematuria, common in SCD patients, is not a contraindication.

• Platelet count <100,000 per cubic millimeter.

• Any history of intraocular hemorrhage.

• Prior history of transient ischemic attack (TIA), ischemic stroke, hemorrhagic stroke,or other intracranial hemorrhage.

• Known history of intracranial neoplasm, arteriovenous malformation, or aneurysm.

• Have clinical findings, in the judgment of the investigator, associated with anincreased risk of bleeding.

• Have an international normalized ratio (INR) of greater than 1.5 at screening.

• Have had recent surgery (within 30 days prior to screening) or are scheduled toundergo surgery within the next 60 days.

• History of menorrhagia requiring medical intervention.