Cardiovascular Drugs and Medications Q 57

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During the warfarin (Coumadin) administration, the nurse can expect that the initial extension of PT occurs within how many hours after therapy begins?

  

     A. 1 to 2

     B. 4 to 6

     C. 8 to 12

     D. 12 to 24

    

    

Correct Answer: C. 8 to 12.

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Initial extension of PT occurs within 8 to 12 hours after warfarin therapy begins. Warfarin is an oral anticoagulant commonly used to treat and prevent blood clots. Warfarin has multiple FDA-approved and off-label clinical uses.

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Option A: Warfarin competitively inhibits the vitamin K epoxide reductase complex 1 (VKORC1), which is an essential enzyme for activating the vitamin K available in the body. Through this mechanism, warfarin can deplete functional vitamin K reserves and therefore reduce the synthesis of active clotting factors. The hepatic synthesis of coagulation factors II, VII, IX, and X, as well as coagulation regulatory factors protein C and protein S, require the presence of vitamin K. Vitamin K is an essential cofactor for the synthesis of all of these vitamin K-dependent clotting factors.

Option B: Warfarin is a once-daily oral medication. Warfarin administration can be at any time during the day, but recommendations are for administration in the afternoon or evening. By instructing patients to take warfarin later in the day, healthcare providers can have the opportunity to individualize a patient’s warfarin dose the same day based on their most current lab values.

Option D: Patients receiving treatment with warfarin should have close monitoring to ensure the safety and efficacy of the medication. Periodic blood testing is the recommendation to assess the patient’s prothrombin time (PT) and the international normalized ratio (INR).

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