A 55-year-old male was admitted 1 week ago for a left lower leg venous thromboembolism, confirmed by ultrasound. He started to work from home 4 months ago and reports that his activity level has significantly decreased. When admitted, his left lower leg had 3+ edema and was warm and reddened over the calf area. He was immediately started on intravenous heparin therapy, with warfarin (Coumadin) on the same day. The patient asks the nurse why two medications are necessary. Which response by the nurse is accurate?

Choice A reason: This statement is incorrect because the combination of heparin and warfarin does not dissolve the blood clot faster. Instead, these medications have different mechanisms of action. Heparin works quickly to prevent further clot formation, while warfarin takes several days to reach therapeutic levels and maintain anticoagulation over the long term.
Choice B reason: While the risk of a blood clot in the lungs (pulmonary embolism) is a concern, the necessity of using both heparin and warfarin is not because of the need for multiple blood thinners but rather due to their complementary pharmacokinetics. Heparin provides immediate anticoagulation, whereas warfarin requires time to become effective.
Choice C reason: This statement is also incorrect. Heparin does not dissolve clots but works to prevent the extension of existing clots and the formation of new ones. Warfarin, likewise, does not dissolve clots but prevents further clot formation by inhibiting vitamin K-dependent clotting factors.
Choice D reason: This is the accurate response. Heparin works immediately, providing rapid anticoagulation, which is essential for acute management of venous thromboembolism. On the other hand, warfarin takes several days to achieve its anticoagulant effect because it works by inhibiting the synthesis of vitamin K-dependent clotting factors. Therefore, the patient is initially placed on heparin to provide immediate protection against clotting while warfarin is started simultaneously. Once warfarin reaches a therapeutic level, heparin can be discontinued, and warfarin can maintain long-term anticoagulation.