QuestionSBA
QuestionChoice
No, this is not the correct answer. Amiodarone acts to increase the plasma concentration of warfarin, and hence increase the INR. This would mean the patient is more anticoagulated hence thrombosis would be less likely to occur.
10007946
b
Increased INR and thrombosis
QuestionChoice
No, this is not the correct answer. The patient would have an increased INR associated with an increased risk of bleeding. A malar rash is often seen in cases of systemic lupus erythematosus (SLE). It is not associated with warfarin or amiodarone.
10007948
d
Decreased INR and malar rash
QuestionChoice
No, this is not the correct answer. The patient would have an increased INR associated with an increased risk of bleeding.
10007947
c
Decreased INR and bleeding
QuestionChoice
No, this is not the correct answer.
10007949
e
No change in INR and no adverse effect
QuestionChoice
Yes, this is the correct answer. You are not expected to be able to memorise drug-drug interactions, however, it is helpful to be able to interpret the information given and be able to draw conclusions. Warfarin is metabolised by the cytochrome P450 CYP2C9 enzyme, but amiodarone is an inhibitor of this enzyme. If amiodarone inhibits CYP2C9, then there would be lower amounts of CYP2C9 enzymes which are actually metabolising warfarin. This results in less metabolism of warfarin within the liver, and hence an increased plasma concentration of warfarin.

INR is essentially a measure of a patient's prothrombin time (PT). A high INR means that the patient is more anticoagulated, while a low INR means the patient is less anticoagulated. Warfarin is an anticoagulant. An increased plasma concentration of warfarin as a result of taking amiodarone would make the patient more anticoagulated and at a high risk of bleeding. The INR would also be increased.
10007945
a
Increased INR and bleeding
Concept
Chapter
2693
4115
Warfarin
Topic
203
Pharmacology of Haemostasis and Thrombosis
14136
A 50-year-old man is reviewed in the cardiology clinic for the management of his atrial fibrillation. They discuss the possible benefit of commencing amiodarone, however, the consultant is concerned that this may interact with his existing medications, which include warfarin.

Warfarin is known to become metabolised by the CYP2C9 enzyme during hepatic metabolism.
Amiodarone is an inhibitor of the CYP2C9 enzyme.

Which of the following consequences may result from prescribing warfarin alongside amiodarone?
a