Oral anticoagulants Flashcards
1
Q
What is an example of an oral anticoagulant?
A
Warfarin
2
Q
What is the method of action of Warfarin?
A
- Inhibits the production of Vit K dependent coagulation factors/co-factors
- Does this by inhibiting the enzyme vitamin K epoxide reductase – this enzyme activates vitamin K so it can be used to make coagulation factors
3
Q
What are the indications of warfarin?
A
- Prevent clot recurrence in DVT
- Prevent clot recurrence in PE
- Prevent emboli in AF patients which can cause stroke
- Prevent emboli in heart valve replacement patients which can cause stroke – short term treatment in tissue valve replacement and lifelong in mechanical valve replacement
4
Q
What are the contraindications of warfarin?
A
- Immediate risk of haemorrhage – trauma, surgery
- Liver disease – less able to metabolise the drug
- Pregnancy during 1st trimester/towards term – foetal malformations and maternal haemorrhage
5
Q
What are the side effects of warfarin?
A
• Bleeding – peptic ulcers, intracerebral haemorrhage, epistaxis, retroperitoneal haemorrhage
6
Q
What are the interactions with warfarin?
A
- Fluconazole – cytochrome P450 inhibitors therefore increase bleeding risk
- Macrolides – cytochrome P450 inhibitors therefore increase bleeding risk
- Protease inhibitors – cytochrome P450 inhibitors therefore increase bleeding risk
- Phenytoin - cytochrome P450 inducers therefore increase clot risk
- Carbamazepine - cytochrome P450 inducers therefore increase clot risk
- Rifampicin - cytochrome P450 inducers therefore increase clot risk
- Antibiotics – many increase anticoagulation by killing gut flora which synthesises vitamin K
7
Q
What organ eliminates warfarin?
A
• Kidney and liver (metabolised)
8
Q
What patient information should be given to someone taking warfarin?
A
- INR monitoring required frequently
- All details about warfarin doses, blood test results, treatment indication and duration are recorded in an anticoagulant ‘yellow book’
