5. Mrs S is a 65-year-old lady who presents with new-onset atrial fibrillation. She has a history of hypertension and hyperlipidemia. She does not have a history of stroke or major bleeding. She was started on diltiazem for heart rate control. Following a discussion of the risks and benefits, she agrees to commence anticoagulation for the prevention of stroke. 

(a) What is the mechanism of action of warfarin? (2 marks) 

(b) Name THREE important drug-drug interactions that will reduce the international normalised ratio ("INR") in patients treated with warfarin. (3 marks) 

(c) Name FOUR direct oral anticoagulants ("DOACS") that can reduce the risk of thromboembolism from atrial fibrillation. (2 marks) 

(d) Describe the mechanisms of action, similarities and differences in the pharmacokinetics of these DOACs. (6 marks) 

(e) The patient has a planned elective colonoscopy with polypectomy. She has normal creatinine clearance. When should her DOAC be discontinued? (3 marks) 

(f) What management options for DOAC-related major life-threatening bleeding events are there? (4 marks)