Coumarins Flashcards
Give an example of a coumarin
Warfarin
What is the mechanism of action of warfarin?
It is a vitamin K antagonist, and interferes with the vitamin K cycle by inhibiting the enzyme vitamin K epoxide reductase. Vitamin K is needed to form clotting factors, hence the use of warfarin to reduce the likelihood of clot formation
What is the route of delivery of warfarin?
PO
What is warfarin available in?
Different colours, representing different strengths
How much warfarin in brown tablet?
1mg
How much warfarin in blue tablet?
3mg
What colours of warfarin are not used often?
White and pink (because they can get mixed up)
How much warfarin in white tablet?
0.5mg
How much warfarin in pink tablet?
5mg
What are the indications for warfarin?
- Prophylaxis and treatment of DVT and PE
- Prophylaxis of embolism in prosthetic valves
- Atrial fibrillation
What is the duration of treatment with warfarin in DVT/PE?
Variable, dependent on how many times patient has had DVT/PE and if it was spontaneous or provoked
What is the duration of treatment with warfarin in embolism in prosthetic valve?
Lifelong
What is the duration of treatment with warfarin with atrial fibrillation?
Lifelong
What are the contraindications to warfarin treatment?
- Haemorrhagic stroke
- Significant bleeding
What are the cautions in warfarin treatment?
- Bacterial endocarditis
- Conditions in which risk of bleeding is increased
- Up to 48 hours postpartum
- History of GI bleeding
- Hyperthyroidism or hypothyroidism
- Peptic ulcer
- Recent ischaemic stroke
- Recent surgery
- Uncontrolled hypertension
- Severe hepatic impairment
Is warfarin safe in pregnancy?
No, dangerous in 1st and 3rd trimester
What are the potential teratogenic effects of warfarin?
- Facial deformities
- Cardiac defects
- Blindness
- Mental retardation
What should be done if warfarin is given in severe renal impairment?
Monitor INR more frequently
Why should you avoid warfarin with severe hepatic impairment?
Patients with liver disease may have coagulopathies
What monitoring is required with warfarin?
INR monitoring
How is INR monitored?
GP monitors by finger prick blood test
What is INR?
A measure of how likely the patients blood is to clot
How often is INR measured?
Every day for 1 week, then once a week until INR satisfactory level, then every 3 months
What INR level is aimed for?
Every patient has INR level that is appropriate for them, but normally INR should be maintained between 2.5-3.5
What might warfarin interact with?
- Food and drink
- Medications
- Smoking
- Herbal remedies
What foods might warfarin interact with?
- Vitamin-K containing foods, e.g. leafy green veg
- Grapefruit
- Cranberries
What drinks might warfarin interact with?
- Grapefruit juice
- Cranberry juice
- Alcohol
What medications might warfarin interact with?
- Certain types of antibiotics, e.g. macrolides
- Amiodarone
- Antidepressants
- OCP
- Carbamazepine
What are the common side effects of warfarin?
- Bleeding and bruising
- Rash
- Diarrhoea
What are the less common side effects of warfarin?
- Hypersensitivity
- Warfarin-induced skin necrosis
- Alopecia
What patient counselling is required with warfarin?
- Mode of action and side effects
- Yellow book and heparin
- How to take warfarin and missed doses
- Food and drug interactions
- Pregnancy
- Inform health professionals about warfarin
- Emergencies
- Contact sports
What should the patient be told regarding the mode of action and side effects of warfarin?
Explain that warfarin thins the blood and may cause bleeding and bruising. If bleeding is excessive, e.g. patient suffers from nosebleeds that don’t stop, if there is blood in urine or in stool, or patient notices severe bruising, should attend A&E immediately
What should the patient be told regarding heparin when starting on warfarin?
Told they will have to take heparin for a couple of days
What should the patient be told regarding Yellow Book with warfarin?
They will receive a yellow book to bring to appointments to record their INR results and warfarin prescriptions
Emphasise importance of bringing to appointments
Why is heparin required for a few days at the start of warfarin treatment?
Warfarin takes a couple of days to start working
How is heparin administered?
SC injection
What should the patient be told regarding how to take warfarin and missed doses?
Warfarin should be taken once a day, at the same time every day. It is important not to miss doses. If a dose is missed, advisable that the patient contacts their GP or anticoagulation clinic for advise
What might the patient be advised regarding missed doses of warfarin?
Depending on how late the dose is, the patient may be advised to take the missed dose or omit it
Should patients take a double dose of warfarin if more than 24 hours have passed since missed dose?
NO
What should the patient be told regarding pregnancy with warfarin?
If they become pregnant should stop taking warfarin immediately
What should the patient be told regarding emergencies with warfarin?
Attend A&E immediately in cases of head injury
Useful to wear medical alert bracelet to inform others of warfarin use in case of emergency
What should the patient be told regarding contact sports with warfarin?
Contact sports and other high risk activities should be avoided whilst on warfarin due to increased risk of bleeding in event of minor injury or trauma
