Therapeutic test (INR)
- Warfarin therapy is monitored using the INR
- Aims
- INR 2–3: DVT/PE, hypercoagulable states, AF
- INR 2.5–3.5: aortic metallic heart valves (higher pressure blood flow reduced embolic risk)
- INR 3–4: mitral metallic heart valves
Reversal
- Major bleeding → stop warfarin, prothrombin complex concentrate, 5–10 mg IV vitamin K
- Non-major bleeding
- INR >8 → stop warfarin, PLUS 0.5–2.5 mg PO vitamin K if other risk factors for bleeding
- INR 6–8 → stop warfarin
- INR 3–6 → reduce/stop warfarin
Notes
- Stop warfarin for 2–4 days to see effect
- Oral vitamin K takes 24–48 hours, IV vitamin K takes 6 hours, prothrombin complex concentrate takes 15 minutes
- FFP may be used instead of prothrombin complex concentrate if this is unavailable
Q&A
Q: Which medications and foods can increase the levels of warfarin?
A: Cimetidine, metronidazole, trimethoprim-sulfamethoxazole, fluconazole, amiodarone, and grapefruit—they share in common the liver enzyme CYP3A418
A: Cimetidine, metronidazole, trimethoprim-sulfamethoxazole, fluconazole, amiodarone, and grapefruit—they share in common the liver enzyme CYP3A418
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