A 78-year-old man with a background of atrial fibrillation on Warfarin is found to have an INR of 1.4 at a routine check. He has been adherent to his ...

Question

A 78-year-old man with a background of atrial fibrillation on Warfarin is found to have an INR of 1.4 at a routine check. He has been adherent to his medication. He was started on Carbamazepine 200 mg BD by the neurology team 4 weeks ago for trigeminal neuralgia. What is the MOST likely explanation for his subtherapeutic INR?

Accepted Answer

Carbamazepine is a hepatic enzyme inducer (CYP3A4 and CYP2C9) that increases Warfarin metabolism, reducing its anticoagulant effect

Answer

Natural fluctuation in INR

Answer

He has been taking too much Warfarin

Answer

Carbamazepine inhibits Warfarin metabolism

Answer

His atrial fibrillation has resolved spontaneously

uk-dgm MCQ (SBA): Carbamazepine-Warfarin Enzyme Induction Interaction