As a pharmacist, you will see warfarin (Marevan) used in combination with aspirin AND clopidogrel (Plavix) in more cardiac patients especially the elderly. Older patients are at higher risk for conditions that require two antiplatelet drugs plus anticoagulation.
A common scenario is a patient who needs clopidogrel and aspirin after a coronary stent plus warfarin for atrial fibrillation, deep venous thrombosis, or mechanical heart valves. These drugs prevent different types of clots. Anticoagulants (warfarin, etc) are for "red clots", red blood cells and fibrin that form in the veins or atrium of the heart. Antiplatelet drugs (aspirin, clopidogrel, etc) are more specific for "white clots", mostly platelets that form in the arteries. The problem is triple antithrombotic therapy can increase bleeding risk especially in the elderly.
Try to lower bleeding risk when triple therapy is needed. For warfarin, suggest a lower-end INR target of 2 to 2.5 unless patients have a higher risk of thrombosis. For aspirin, suggest a low dose just 75 to 81 mg/day. For clopidogrel (Plavix), suggest stopping as soon as it's safe, often after 4 weeks for a bare-metal stent or one year for a drug-eluting stent, but this can vary.
Be cautious about using prasugrel instead of clopidogrel because prasugrel causes more bleeding. Recommend GI prophylaxis for patients with risk factors for GI bleeding such as previous gastritis or ulcers. There's still controversy about using PPIs in patients taking clopidogrel. PPIs may reduce clopidogrel efficacy by inhibiting CYP2C19. For now, lean toward using an H2-blocker (famotidine, etc) in patients on clopidogrel. But suggest a PPI for patients at higher bleeding risk such as those with a recent GI bleed. To try to lessen the potential interaction with clopidogrel, pick a weaker 2C19 inhibitor like pantoprazole (Controloc) or rabeprazole (Pariet, Bepra). Get our note on, "Oral proton pump inhibitors (PPIs); pharmacotherapy", section on: PPI clinical notes.
REFERENCES
Hermosillo, A.J. and Spinler, S.A. (2008). Aspirin, clopidogrel, and warfarin: is the combination appropriate and effective or inappropriate and too dangerous? The Annals of Pharmacotherapy, [online] 42(6), pp.790–805. Available at: https://pubmed.ncbi.nlm.nih.gov/18477734