Introduction
anticoagulants (DOACs).
Mechanism of action
Indications
- Venous thromboembolism: target INR = 2.5, if recurrent 3.5
- Atrial fibrillation, target INR = 2.5
- Mechanical heart valves, target INR depends on the valve type and location. Mitral valves generally require a higher INR than aortic valves.
Adverse effects
- Haemorrhage
- Teratogenic, although can be used in breastfeeding mothers
- Skin necrosis: when warfarin is first started biosynthesis of protein C is reduced. This results in a temporary procoagulant state after initially starting warfarin, normally avoided by concurrent heparin administration. Thrombosis may occur in venules leading to skin necrosis
- Purple toes
Contraindications
- Liver disease
- P450 enzyme inhibitors (see below)
- Cranberry juice
- Drugs which displace warfarin from plasma albumin, e.g. NSAIDs
- Inhibit platelet function: NSAIDs
Drugs which either inhibit or induce the P450 system may affect the metabolism of warfarin and hence the INR:
Inducers of the P450 system include - INR will decrease | Inhibitors of the P450 system include - INR will increase |
---|---|
|
|