MSFinals-5150

A 63-year-old man, who is on warfarin, visits his GP for a blood test to check his international normalised ratio (INR). He has a medical history of atrial fibrillation and epilepsy. His desired INR range is between 2 and 3. However, the test shows an INR of 4. When asked, he discloses that he has recently begun taking a new drug.
Which medication is the probable cause of the INR alteration?