A 70-year-old man with chronic atrial fibrillation on warfarin (INR stable at 2.5 for 3 weeks) is started on amiodarone for rate control. One week later, he presents with gross hematuria and petechiae. Vital signs: BP 128/76, HR 62, RR 16, Temp 37°C, SpO2 98%. Laboratory studies reveal INR 8.2 and hemoglobin 9.8 g/dL. Urinalysis shows blood without proteinuria. Which mechanism explains this serious drug interaction?
- A)Amiodarone increases hepatic synthesis of clotting factors
- B)Amiodarone inhibits CYP2C9, decreasing warfarin metabolismGABARITO
- C)Amiodarone inhibits CYP3A4, decreasing warfarin metabolism
- D)Amiodarone increases warfarin clearance via renal excretion
- E)Amiodarone displaces warfarin from plasma protein binding
Explicação
Warfarin is metabolized primarily by CYP2C9 and CYP2C8. Amiodarone is a potent inhibitor of CYP2C9, reducing warfarin metabolism and increasing its plasma concentration, leading to supratherapeutic INR and bleeding risk. Ver explicação completa e trilha adaptativa →