MEDizzy - A 64-year-old woman was diagnosed with hypothyroidism and

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Drugs Affecting Hemostasis-II

A 64-year-old woman was diagnosed with hypothyroidism and started on levothyroxine replacement therapy. For the previous 8 months, she had been receiving warfarin therapy for the treatment of recurrent deep venous thrombosis. Her warfarin dose was adjusted to maintain her international normalized ratio (INR) between 2 and 3. When she started thyroxine replacement therapy, her physician reduced the dosage of warfarin by 50% and advised her that her INR would need to be monitored on a weekly basis until a new appropriate dose of warfarin was determined. Which of the following statements best explains why the warfarin dose was reduced?

ExplanationD Thyroid hormones increase the catabolism of m any endogenous com pounds, including clotting factors. This action results in a decreased coagulability of blood, so the effects of anticoagulants are enhanced. In this case, the woman’s initial warfarin dose was appropriate to provide a safe level of anticoagulation therapy for her hypothyroid state, but w hen her thyroid level was raised to norm al, the warfarin dose needed to be adjusted to adapt to the increased catabolic rate of clotting factors that would occur in the presence of higher thyroxine levels. Monitoring must be carried out to reestablish the appropriate new, lower dose of warfarin.