A 67-year-old male with major depressive disorder, atrial fibrillation, chronic pain, and insomnia presents for a psychiatric medication review. His current medications include fluoxetine 40 mg daily, warfarin 5 mg daily, tramadol 50 mg three times daily, and zolpidem 10 mg at bedtime. He reports that his primary care provider recently increased his fluoxetine from 20 mg to 40 mg three weeks ago due to inadequate response. He now presents with increased bruising, occasional nosebleeds, and a new onset of intermittent muscle twitching in his lower extremities. His INR, previously stable at 2.5, is now 4.8. Which assessment of potential medication interactions best explains this patient's current presentation?