Effect of Two Weeks of Low-Dose Apixaban on Platelet Reactivity in Patients With Stable Coronary Artery Disease on Dual Antiplatelet Therapy (Aspirin and Clopidogrel)

The goal of this clinical trial is to learn whether a low dose of apixaban, a blood-thinning medicine, changes how active the platelets are in adults with stable coronary artery disease who are already taking aspirin and clopidogrel. Platelets are small blood cells that help form clots. Aspirin and clopidogrel are used to keep platelets from clumping and to lower the risk of heart attack and stroke. In some people, however, platelets stay very active even while taking these medicines, which raises the risk of future heart problems. Apixaban works on a different part of the clotting process, and researchers want to find out whether it lowers platelet activity further. The main questions it aims to answer are: Does taking low-dose apixaban for 14 days lower platelet activity, as measured by the VerifyNow P2Y12 test (reported as P2Y12 reaction units, or PRU)? Does low-dose apixaban change how platelets respond to aspirin, as measured by the VerifyNow aspirin test (reported as aspirin reaction units, or ARU)? Is 14 days of low-dose apixaban, added to aspirin and clopidogrel, safe and well tolerated? There is no separate comparison group. Researchers will compare each participant's platelet test results before starting apixaban with that same participant's results after 14 days of apixaban. Participants will: Have a screening interview and a review of their medical history and current medicines Give a small blood sample (about 5 mL) for platelet function testing before starting apixaban Take apixaban 2.5 mg by mouth twice a day for 14 days, while continuing their usual aspirin and clopidogrel Return on Day 14 to give a second blood sample for platelet function testing and safety blood tests Receive a phone call from a study doctor at Day 30 to check for side effects or other health problems Participants will receive a copy of their platelet test results. This is a small pilot study of about 16 participants at one site in Trinidad and Tobago.