This is a Phase 4, multicenter, open-label (blinded Pharmacodynamic PD results), randomized, 3-arm, parallel-design study of subjects with stable Coronary Artery Disease CAD. This study will compare the PD effect of prasugrel 10 mg QD (once-daily) maintenance dose with ticagrelor 90 mg BID (twice daily) maintenance dose in subjects with stable CAD who have previously received ticagrelor loading does (LD) and maintenance dose (MD)..

Inclusion Criteria:

• Male or female; age >= 18 and < 75 years

• Weight >= 60 kg

• Receiving low dose ASA (75 mg to 150 mg daily) for at least 7 days at the time of Visit 1 and able to continue the same regimen throughout the study

• Stable CAD. CAD is defined as any of the following:

• History of a positive stress test

• Previous coronary revascularization including percutaneous coronary intervention (PCI), stent, or coronary artery bypass graft (CABG)

• Angiographic demonstration of CAD (at least

  1 lesion >= 50 percent)

• Presence of at least moderate plaque by computed tomography (CT) angiography

• Electron beam CT coronary artery calcification score >= 100 Agatston units

• If female, may be enrolled if

One of the following 3 criteria are met:

• Had a hysterectomy or tubal ligation at least 6 months prior to signing the informed consent form (ICF)
• Post-menopausal for at least 1 year
• If of childbearing potential, will practice 1 of the following methods of birth control throughout the study: oral, injectable, or implantable hormonal contraceptives; intrauterine device; diaphragm plus spermicide; or female condom plus spermicide. Methods of contraception that are not acceptable are partner's use of condoms or partner's vasectomy
• Able and willing to provide written informed consent before entering the study

Exclusion Criteria:

• Have a defined need for adenosine diphosphate (ADP)-receptor inhibitor therapy, such as any of the following (or any other condition that in the Investigator's judgment would require such therapy):
• Within =< 12 months of an acute coronary syndrome (ACS) event (unstable angina [UA], non-ST-elevation myocardial infarction [NSTEMI], or ST-elevation myocardial infarction [STEMI]) regardless of initial treatment (that is, invasive versus noninvasive)
• Subjects who underwent angioplasty within 12 months including bare-metal stent and/or a drug-eluting stent
• Had any stent placed in an unprotected left main coronary artery or in the last patent artery within the last 12 months
• Received thienopyridine therapy within 30 days of study entry
• Plan to undergo coronary revascularization at any time during the trial
• Presence or history of any of the following: ischemic or hemorrhagic stroke; transient ischemic attack (TIA); intracranial neoplasm; arteriovenous malformation, or aneurysm; intracranial hemorrhage; head trauma (within 3 months of study entry)
• History of refractory ventricular arrhythmias with an increased risk of bradycardic events (eg, subjects without a pacemaker who have sick sinus syndrome, 2nd or 3rd degree atrioventricular (AV) block or bradycardic-related syncope)
• History or evidence of congestive heart failure (New York Heart Association Class III or above =< 6 months before screening
• Severe hepatic impairment
• History of uric acid nephropathy
• Uncontrolled hypertension, or systolic blood pressure > 180 mmHg or diastolic blood pressure > 110 mmHg at screening
• Severely impaired renal function (glomerular filtration rate < 30 mL/minute) or on dialysis
• At risk for bleeding
• Taking prohibited medications

De-identified individual participant data (IPD) and applicable supporting clinical trial documents may be available upon request at https://vivli.org/. In cases where clinical trial data and supporting documents are provided pursuant to our company policies and procedures, Daiichi Sankyo will continue to protect the privacy of our clinical trial participants. Details on data sharing criteria and the procedure for requesting access can be found at this web address: https://vivli.org/ourmember/daiichi-sankyo/

Studies for which the medicine and indication have received European Union (EU) and United States (US), and/or Japan (JP) marketing approval on or after 01 January 2014 or by the US or EU or JP Health Authorities when regulatory submissions in all regions are not planned and after the primary study results have been accepted for publication.

Formal request from qualified scientific and medical researchers on IPD and clinical study documents from clinical trials supporting products submitted and licensed in the United States, the European Union and/or Japan from 01 January 2014 and beyond for the purpose of conducting legitimate research. This must be consistent with the principle of safeguarding study participants' privacy and consistent with provision of informed consent.