PTCB Certified Pharmacy Technician (PTCE)MedicationsHard
A pharmacy technician is entering a prescription for 'warfarin 5 mg, take 1 tablet daily'. The patient's profile also shows they recently started taking 'amiodarone 200 mg, take 1 tablet daily' for an arrhythmia. Which of the following best describes the potential drug interaction between these two medications?
- AAmiodarone and warfarin should be taken at least 4 hours apart to prevent interaction.
- BThere is no significant drug interaction between amiodarone and warfarin.
- CAmiodarone can decrease the anticoagulant effect of warfarin, increasing the risk of clotting.
- DAmiodarone can increase the anticoagulant effect of warfarin, increasing the risk of bleeding.
Show answer & explanationAnswer & explanation
Correct answer: D. Amiodarone can increase the anticoagulant effect of warfarin, increasing the risk of bleeding.
Amiodarone is a potent inhibitor of CYP2C9, the primary enzyme responsible for metabolizing warfarin. When amiodarone is added to a patient's regimen, it significantly reduces warfarin's metabolism, leading to increased warfarin levels and a heightened anticoagulant effect. This interaction increases the risk of bleeding and requires close monitoring of INR and potential warfarin dose reduction.
Why the other options are wrong
- A. Separating administration times does not prevent this pharmacokinetic (metabolic) interaction; dose adjustment and monitoring are required.
- B. This is incorrect; it is a very significant and clinically important interaction.
- C. This is incorrect; amiodarone increases, not decreases, warfarin's effect.
Warfarin-Amiodarone Interaction
A significant drug-drug interaction where amiodarone inhibits the metabolism of warfarin, leading to increased anticoagulant effect.
- Mechanism: Amiodarone inhibits CYP2C9, the enzyme metabolizing warfarin.
- Result: Increased INR, increased risk of bleeding.
- Management: Close INR monitoring, significant warfarin dose reduction (often 30-50%).
Memory trick: Warfarin's Weakness: Inhibitors Increase Bleeding