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Drug Interactions
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| 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) | ↓ |
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| Capecitabine (Xeloda) | ↑ |
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| Carbamazepine | ↓ |
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| Dicloxacillin | ↓ | More significant if course >14 days. |
| Doxycycline | ↑ | Not always clinically significant if pt not systemically ill. |
| Fibrates | ↑ |
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| 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 | ↓ |
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| 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 | ↑ |
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| Thyroid replacement | ↑ |
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Increased Risk of Bleeding is Possible when Combining Warfarin With:
- Antiplatelets
- Fish Oil/Omega 3 Fatty Acids
- NSAIDs
- Other Anticoagulants
- Steroids
- Vitamin E