Warfarin

Question 1

How much of the drug warfarin is bound to plasma proteins and how much is freely dissolved in plasma?

Answer 1

(1. ) 99% of warfarin is bound to plasma proteins and 1% is free in plasma.
(2. ) It is only the free warfarin which is responsible for the action of the drug.

Question 2

What happens if tamoxifen is given to a patient taking warfarin?

Answer 2

(1.) Tamoxifen increases the effects of warfarin and so increases the risk of bleeding by an unknown mechanism.

NOTE: tamoxifen is used to block the effects of oestrogen in the breast tissue

Question 3

What substances are produced in the liver using vitamin K? What affect would be seen when blocking its action?

Answer 3

(1. ) Vitamin K is used within the liver to make clotting factors II, VII, IX and X.
(2. ) Blocking the action of vitamin K leads to an inability to form blood clots efficiently.
(3. ) Warfarin is a vitamin K antagonist

Question 4

What is the effect of drinking alcohol whilst on warfarin?

Answer 4

(1. ) Drinking alcohol can affect the ability of the liver to manufacture the clotting factors II, VII, IX and X
(2. ) This will increase the anticoagulant effects of the warfarin causing bleeding.

Question 5

What would be the consequences of missing a dose of warfarin?

Answer 5

(1. ) A missed dose of warfarin will result in the blood clotting returning to a more normal level, usually within a 2-5 days period.
(2. ) This will reduce the ability of the warfarin to reduce the risk of a stroke, but will also reduce the side effects such as bleeding.
(3. ) The risk of taking warfarin reduces but so does the benefit.

Question 6

What would be the risk of accidentally taking a double dose of warfarin

Answer 6

(1. ) Accidentally taking a double dose of warfarin will result in a further reduction in the ability of the blood to clot which may lead to uncontrolled bleeding.
(2. ) In this case the risks of taking the warfarin is massively increased whilst there is no additional increase in benefit.

Question 7

Would you give warfarin to a pt who is at risk of falls? What alternatives could you consider?

Answer 7

(1. ) Pt who is at risk of falls, the risk of warfarin treatment outweighs the benefits.
(2. ) An alternative - DOAC (Apixiban, Rivaroxaban) which do not require ongoing monitoring.
(3. ) These however do carry a risk in that they cannot easily be reversed so again an appropriate risk/benefit assessment needs to be carried out.