A woman in her 80s had a hospital acquired pneumonia (HAP). During this time, her INRs did the following whilst her dose of warfarin was maintained at 5mg OD (except for a reduction to 4mg on Day 5):
|Day 1 of HAP||Day 4||Day 5||Day 6|
She was started on tazocin and clarithromycin on Day 1 of the HAP too.
Why did the INR rise so dramatically?