Warfarin Therapy and INR Management

Warfarin is a vitamin K antagonist that inhibits gamma carboxylation of clotting factors two seven nine and ten as well as proteins C and S. It remains widely used for mechanical heart valves, certain antiphospholipid antibody syndromes and patients who cannot take direct oral anticoagulants. The therapeutic INR range is typically two to three for most indications and two and a half to three and a half for mitral mechanical valves.

Initiation usually begins with five milligram daily doses with INR checks every two to three days until target is reached. Loading doses risk over anticoagulation. Maintenance dosing requires regular monitoring at intervals of one to four weeks once stable, with adjustments guided by both current INR and recent trends.

Drug and food interactions are extensive. Antibiotics, amiodarone, fluconazole and many over the counter products can increase or decrease INR. Patient education on consistent vitamin K intake, alcohol limitation and prompt reporting of bleeding or new medications is central to safe long term use of warfarin.