Warfarin Drug prevents the conversion of vitamin K back to its active form from vitamin K epoxide. This impairs Formation of the vitamin K–dependent clotting Factors II, VII, IX, and X (prothrombin) and proteins C and S (physiologic anticoagulants).
Efficacy Monitoring Parameters:
Measure initial INR after the first 2-3 doses and subsequently at intervals no longer than every 4 wk, once stable dose has been achieved; may monitor every 12 wk in stable patients, use clinical judgment; patients at high risk o bleeding require more frequent monitoring. INR target and therapeutic range depend on indication. Atrial fibrillation/atrial flutter: target 2.5 (range 2-3); prosthetic heart valves: target 2.5 (range 2-3); mechanical mitral or aortic valve: target 3 (range 2.5-3.5); myocardial in faction, ST segment elevation: target 3 (2.5-3.5, with aspirin); venous thromboembolism, prophylaxis and treatment (including pulmonary embolism, DVT, hip/knee arthroplasty): target 2.5 (range 2-3).
Toxicity Monitoring Parameters:
Signs/symptoms of bleeding, CBC, LFT, stool guaiac test
Clinical Pearls:
Patients of ten managed in pharmacist-run anticoagulation clinics. Consult local protocols. Excessive anticoagulation with warfarin can be corrected with vitamin K. Pharmacogenetic testing or initial dosing o warfarin decreases the time required to achieve a therapeutic INR, but improved clinical efficacy and decreased adverse effects have not been achieved; there ore pharmacogenetic testing is not routine.
