Drug Interactions
| Drug/Drug Class | Effect on INR | Recommendations/Comments |
|---|---|---|
| Acetaminophen/APAP | ↑ with higher doses |
Limit APAP to 2000mg/day |
| Alcohol |
↑ with binging
↓ with chronic use
|
Limit to 1-2 EtOH drinks/day |
| Amiodarone | slow ↑ over time |
Complex interaction that takes place over 6-8 weeks. Ultimately expect 25-50% warfarin dose reduction. Check INR q1-2 weeks and make serial adjustments per INR. |
| Bosentan (Tracleer) | ↓ |
|
| Capecitabine (Xeloda) | ↑ |
|
| Carbamazepine | ↓ |
|
| Dicloxacillin | ↓ |
More significant if course >14 days. |
| Doxycycline | ↑ |
Not always clinically significant if pt not systemically ill. |
| Fibrates | ↑ |
|
| Flu Vaccine | ↑ |
Varies from year to year, but may cause transient rise in INR. |
| Fluconazole | ↑ |
Hold warfarin x1 for single dose. Expect 25-50% warfarin dose reduction for extended course. |
| Fluoroquinolones | ↑ |
Not always clinically significant if pt not systemically ill. |
| Mercaptopurine | ↓ |
|
| Metronidazole (Flagyl) | ↑ |
Expect 25-50% warfarin dose reduction. |
| Phenytoin | ↓ or ↑ |
Complex interaction: initially ↑ INR, but then ↓ after prolonged administration. Additionally, warfarin may alter serum phenytoin concentrations. |
| Rifampin | ↓ |
Expect 2- to 5-fold increase in warfarin dose requirements. |
| Sulfamethoxazole (Septra/Bactrim) | ↑ |
Expect 25-50% warfarin dose reduction |
| Testosterone | ↑ |
|
| Thyroid replacement | ↑ |
|
Increased Risk of Bleeding is Possible when Combining Warfarin With:
- Antiplatelets
- Fish Oil/Omega 3 Fatty Acids
- NSAIDs
- Other Anticoagulants
- Steroids
- Vitamin E