Top 300 Pharmacy Drug Cards

WARFARIN: Coumadin, Various

Class: Anticoagulant

Dosage Forms. Tablet: 1 mg, 2 mg, 2.5 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7.5 mg, 10 mg

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Common FDA Label Indication, Dosing, and Titration.

1. Multiple FDA-labeled indications, all dosed similarly, including atrial fibrillation; myocardial infarction; prosthetic cardiac valve component embolism; pulmonary embolism; thrombosis, postmyocardial infarction; venous thromboembolism: Initial, 2-5 mg po daily, adjust dose based on INR; usual maintenance 2-10 mg po daily

Off-Label Uses.

1. Antiphospholipid syndrome; cancer—venous thromboembolism: Initial, 2-5 mg po daily, adjust dose based on INR; usual maintenance 2-10 mg po daily

MOA. Warfarin 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).

Drug Characteristics: Warfarin

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Medication Safety Issues: Warfarin

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Drug Interactions: Warfarin

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Adverse Reactions: Warfarin

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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; patients at high risk of 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 infarction, 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.

Key Patient Counseling Points. Report signs/symptoms of hemorrhage, skin and tissue necrosis, and hepatitis. Avoid situations/activities in which cuts, bruising, or injury is likely to occur. Many significant drug-drug interactions, consult healthcare professional prior to new prescription or OTC use. Avoid alcohol, cranberry products, and drastic changes in vitamin K consumption from diet (cruciferous vegetables).

Clinical Pearls. Patients often managed in pharmacist run anticoagulation clinics. Consult local protocols. Excessive anticoagulation with warfarin can be corrected with vitamin K.



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