Warfarin
Trade names
COUMADIN, JANTOVEN
Actions
- Vitamin K antagonist
Route of Administration
Oral
Bioavailability
79-100%
Plasma protein binding
99%
Time to peak plasma concentration
Variable
Half-life
20–60 h
Duration of action
48–96 h
Metabolism
Hepatic
Enzymes involved
- CYP2C9
- CYP3A4
- CYP1A1
- CYP1A2
Elimination
Renal 92% (excretion of inactive metabolites)
Interactions
Drugs that inhibit or induce CYP2C9, CYP3A4, CYP1A2
Recommended dose
Individualized. Dose is adjusted by monitoring the INR.
In patients with atrial fibrillation as well as in patients with pulmonary embolism or DVT the recommended INR range is 2.0 - 3.0
In patients with mechanical valves the recommended INR range is usually 2.5 - 3.5
Renal impairment
No dose adjustment is necessary.
Discontinuation before invasive procedures
Warfarin should be stopped 5 days prior to surgery. The thromboembolic risk should be individually assessed. In patients with low risk no bridging with LMWH is required. In patients with moderate risk, bridging should be considered. In patients with high risk, bridging is recommended.
Start LMWH or unfractionated heparin in therapeutic doses as soon as the INR is under the therapeutic lower limit.
Discontinue LMWH 24 hours before the procedure. If UFH is used, discontinue 4-6 hours before the procedure.
The efficacy of bridging remains unclear and some studies suggest it carries a higher bleeding risk.