A 67-year-old male with atrial fibrillation on warfarin with a stable INR of 2.4 is started on fluoxetine 20 mg daily for a new episode of major depressive disorder. Four weeks later, he presents with epistaxis, gingival bleeding, and scattered ecchymoses. His INR is found to be 4.8. His warfarin dose has not changed, and his diet has been consistent. Which of the following best describes the mechanism by which fluoxetine contributed to this patient's elevated INR and bleeding symptoms?