Anticoagulants

Mechanisms

Anticoagulants act at different points in the coagulation cascade - vitamin K antagonists (warfarin, inhibiting synthesis of factors II, VII, IX, X), direct oral anticoagulants (direct factor Xa or thrombin inhibition), and heparins (antithrombin-mediated factor Xa/thrombin inhibition) - mechanism determines monitoring requirements, reversal options, and specific clinical use cases
Warfarin inhibits hepatic vitamin K epoxide reductase, reducing synthesis of vitamin K-dependent clotting factors - its delayed onset (days, reflecting the half-life of existing clotting factors already in circulation) and narrow therapeutic index requiring INR monitoring are direct consequences of this mechanism
DOACs directly inhibit a single specific clotting factor (Xa for apixaban/rivaroxaban, thrombin for dabigatran) - producing rapid onset, predictable pharmacokinetics, and generally no requirement for routine monitoring, though renal function must be checked given renal clearance dependence for several agents

Amongst the most widely used drug classes given the breadth of indications (atrial fibrillation, venous thromboembolism, mechanical heart valves, and others)

INR monitoring for warfarin, with dose titration to a target range specific to the indication (e.g. higher target for mechanical valves than for atrial fibrillation)
Renal function monitoring for DOACs given dose adjustment/contraindication at significant renal impairment, particularly relevant for dabigatran given its predominantly renal clearance

Reversal: vitamin K and prothrombin complex concentrate for warfarin; specific reversal agents (idarucizumab for dabigatran, andexanet alfa for factor Xa inhibitors) or prothrombin complex concentrate for DOACs in bleeding emergencies
Mechanical heart valves and warfarin remain the standard - DOACs are specifically contraindicated with mechanical valves given trial evidence of inferior outcomes compared with warfarin in this population

DOAC contraindication with mechanical heart valves (a frequently tested exception), warfarin-drug and warfarin-food interactions (vitamin K-containing foods, CYP interactions), DOAC dose adjustment in renal impairment, specific reversal agent availability
DOACs are specifically contraindicated in patients with mechanical heart valves despite their general advantages over warfarin elsewhere - trial evidence demonstrated inferior outcomes (more thromboembolic and bleeding events) with DOACs in this specific population, making warfarin the required standard of care for mechanical valve patients regardless of DOAC convenience benefits

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