Aspirin and clopidogrel primarily affect which component of the coagulation system?

Aspirin irreversibly inhibits cyclooxygenase-1 (COX-1), reducing thromboxane A2 synthesis and thereby inhibiting platelet aggregation. Clopidogrel irreversibly blocks the P2Y12 ADP receptor on platelets, also inhibiting aggregation. Both drugs affect platelet function rather than platelet count or clotting cascade times (PT/INR or PTT). These drugs will prolong the bleeding time but will NOT alter PT/INR (affected by warfarin) or PTT (affected by heparin). This distinction is important for preoperative dental assessment.