Tutorial - BNF Warfarin CPSA station

Question 1

what type of therapy is warfarin?

Answer 1

anticoagulant

Question 2

why is anticoagulant therapy important for patients with mechanical heart valve replacement?

Answer 2

• mechanical = less adaptable, more prone to clots, increased risk of embolism

Question 3

what is thrombosis?

Answer 3

inappropriate clotting which blocks an artery or vein
- hemostasis gone wrong

Question 4

what is the mechanism of action of the anticoagulant warfarin?

Answer 4

• warfarin blocks the function of vitamin K epoxide reductase in the liver, leading to less active vit K produced
• Vit K is a cofactor for many factors in the coagulation cascade ( II, VII, IX, X), therefore blocking it reduces/stops the coagulation cascade from forming a clot
  (vitamin K antagonist)

Question 5

In relation to thrombosis and anticoagulation, what terms would you look for in the BNF?

Answer 5

• look under summaries
• cardiovascular
• anticoagulants
• or just try searching the name

Question 6

what foods affect the action of warfarin and why?

Answer 6

• foods that contain vitamin k e.g. kale, spinach…
• because warfarin is a vitamin k antagonist, so vit k competes with warfarin

Question 7

how is the dose of warfarin monitored?

Answer 7

• INR = international normalised ratio
• also called prothrombin time, measures time it takes for blood to clot
• normal = 1.1 or less

Question 8

what is the recommended INR range for patients with mechanical mitral valve replacements?

Answer 8

• 2.5-3.5

Question 9

how often should INR be measured on a patient with a mechanical mitral valve replacement on warfarin therapy?

Answer 9

• every month

Question 10

what does an unusually low INR mean?

Answer 10

• more prone thrombosis/clots

Question 11

what does an unusually high INR mean?

Answer 11

• more prone to prolonged bleeding/haemorrhage

Question 12

how does heparin work?

Answer 12

• inhibits thrombin and factor Xa in the coagulation cascade through antithrombin

Question 13

how do direct oral anticoagulants (DOACs) work?

Answer 13

• selectively target specific clotting factors, such as thrombin or factor Xa and have a shorter half life and fewer drug interactions than traditional anticoagulants

Question 14

why should anticoagulant therapy be stopped before any surgery?

Answer 14

• to reduce the risk of prolonged/excess bleeding/haemorrhage

Question 15

how is heparin given to patients?

Answer 15

• subcutaneous injection
• as it is a low weight molecule it will be digested and lost in the gut if taken orally

Question 16

what is the purpose of throbolytics?

Answer 16

• to dissolve blood clots that have already formed

Question 17

why is aspirin a useful prevention in arterial thrombosis?

Answer 17

• it is a potent inhibitor of platelet aggregation