Warfarin

Question 1

Warfarin mechanism of action

Answer 1

Antagonises the effects of vitamin K
Takes 48-72 hours for anticoagulant effect to develop fully
For an immediate effect - give with heparin

Question 2

Indications of warfarin

Answer 2

• Pulmonary embolisms
• Deep venous thromboembolisms
• DVT with AF
• DVT with cardiac valve replacement
• DVT post-myocardial infarction

Question 3

How to counsel on indication of warfarin

Answer 3

Mode of action: Thins the blood or reduces body’s ability to form clots

DVT/PE - To prevent clot getting bigger or returning
AF - When the heart is not beating regularly, the blood will not flow smoothly which increases the risk of getting a clot. This may float through the body and cause further damage i.e. stroke

Question 4

Duration of therapy with warfarin

Answer 4

DVT/PE - maybe short term (3-6months) or life long if recurring
AF/Heart valves - Life long treatment

Question 5

Tablet identification

Answer 5

White = 500mcg
Brown = 1mg
Blue = 3mg
Pink = 5mg

Question 6

Counselling on dose for warfarin

Answer 6

• Taken at same time each day preferably at teatime (6-7pm)
• If dose is missed, never double the dose and just carry on as normal but make a note of the missed dose in the yellow book and let HCP know

Question 7

INR target ranges

Answer 7

For DVT, PE and AF = 2.5
For recurrent DVT and PE = 3.5
For mechanical prosthetic heart valves = 3-3.5

Question 8

Red flag symptoms of warfarin

Answer 8

• Prolonged bleeding from cuts
• Severe bleeding that does not stop by itself
• Multiple bruising
• Nose bleeds if not usually suffered or that last longer than 10 minutes
• Bloody or dark stools/urine
• Coughing or vomiting blood
• Severe or spontaneous bruising
• Unusual headaches
• Vaginal bleeding or very heavy periods for females

Question 9

Drugs to avoid with warfarin

Answer 9

Aspirin - unless prescribed by gp
NSAID’s

Question 10

Warfarin and diet

Answer 10

• Take the same amount of vitamin K on regular basis as it is change that affects INR i.e. leafy veg, broccoli, cabbage, cauliflower, chickpeas, olive oil avocado etc.
• Cranberry juice raises the INR
• If diet changes over a 7 day period, you should have an INR test done

Question 11

Warfarin and alcohol

Answer 11

Don’t take more than the recommended amount of alcohol (14 units weekly for men and women)

Avoid binge drinking

Question 12

Warfarin and contraception

Answer 12

Small risk of damaging the unborn child during the early weeks of pregnancy so need to be started on pregnancy prevention

Question 13

Switching from warfarin to a DOAC

Answer 13

Warfarin treatment needs to be stopped first before starting DOAC as it reduces the risk of over anticoagulation and bleeding

Question 14

Warfarin and NSAID’s

Answer 14

Worsens and induces gastrointestinal bleeding

Question 15

Warfarin and aspirin

Answer 15

Increased risk of bleeding and can put at risk of major haemorrhage

Question 16

Warfarin and azole antifungals

Answer 16

Anticoagulant effect of warfarin increases and risk of bleeding increases

Question 17

Warfarin and erythromycin/ciprofloxacin

Answer 17

Increased risk of bleeding

Question 18

Warfarin and miconazole

Answer 18

Miconazole including the topical oral gel OTC enhances the anticoagulant effect of warfarin causing increased risk of bleeding

Question 19

Warfarin and alcohol

Answer 19

Binge drinking increases the risk of bleeding

Question 20

Warfarin and St. John’s wort

Answer 20

Leads to a reduction in anticoagulant effect of warfarin

Question 21

Warfarin and amiodarone

Answer 21

Metabolism of warfarin is inhibited by amiodarone causing an increased risk of bleeding.

Amiodarone has a long half-life so interaction can occur for several weeks after treatment has stopped

Question 22

Overview of warfarin interactions

Answer 22

• Aspirin - increased risk of bleeding
• NSAID’s - increased risk of bleeding
• Erythromycin/ciprofloxacin - increased bleeding
• Azole antifungals - Increased bleeding
• Miconazole - Increased bleeding
• Binge alcohol - increased bleeding
• St. John’s wort - reduced warfarin
• Amiodarone - increased bleeding
• Anti-epileptics - reduced warfarin