Warfarin
typical INR targets
- either 2.5 or 3.5
- higher target for:
- mechanical valves
- recurrent VTE
High INR on warfarin - NICE guidelines
major bleeding - same guidelines regardless of INR
- stop warfarin (obviously)
- Give IV Vitamin K
- Give prothrombin complex
otherwise:
| No bleeding | Minor bleed | |
|---|---|---|
| INR 5-8 | Hold 1-2 doses Restart with ↓ dose |
Stop warfarin IV Vit K Restart when INR<5 |
| INR >8 | Stop warfarin Give Vit K PO Repeat Vit K if INR still high after 24h Restart when INR <5 |
Stop warfarin IV Vit K Repeat Vit K if INR still high after 24h Restart when INR <5 |
adverse effects
- alopecia
- pancreatitis
- skin necrosis
- calciphylaxis
- hepatic dysfunction
warfarin in peri-operative period
- Warfarin should be stopped 3–5 days prior to the surgery or procedure.
- Where it is necessary to continue anticoagulation, for example with life-threatening thromboembolism, the INR should be reduced to less than 2.5 and heparin therapy should be started.
drug interactions
↑ effect = CYP450 inhibitors
- NSAIDs, thyroxine
- amiodarone
- abx
- corticosteroids
↓ effect = CYP450 inducers
- st john's wort
- rifampicin
- anti-epileptics: carbamazepine, phenytoin, phenobarbitol