Warfarin Flashcards
What kind of drug is warfarin and how does it work?
anticoagulant
inhibits formation of new vitamin K dependent clotting factors (in the liver)
How does warfarin inhibit the formation of the clotting factors?
inhibits 2 key enzymes involved in the formation of Vitamin KH2 (co-factor)
- Vit K epoxide reductase
- Vit K quinone reductase
What are the Vit K dependent clotting factors?
2, 7, 9, 10 and proteins C and S
Which of the clotting factors are anti-coags and which are procoags?
2, 7, 9, 10 are procoags
protein C and S are ANTI-coags
Which of the clotting factors have longer half lives?
procoags (6h-60h)
protein C and S have shorter half lives
How long will it take to see the effects of warfarin? What does this mean when dosing and monitoring the initial dose of warfarin?
24-48h because you have to wait for the clotting levels to decrease
-be patient when dosing! wait 72h to check an INR and make adjustments
Because protein C and S have shorter half lives, what does this mean for the first few days that you are on warfarin?
if you eliminate the anti-coagulants (protein C and S), and the procoagulants (2, 7, 9, 10) are still in your system, then for those first few days, you are actually hyperCOAGULABLE. Why? because you eliminated the clotting factors that thin the blood first, and the clotting factors that are in favor of clotting are still around because they have longer half lives and warfarin has not been able to decrease their levels yet!
What do you do when starting warfarin that takes care of the hypercoagulable state that the patient is in during the first few days?
BRIDGE-THERAPY. you start heparin that has its effect immediately and for the first 48-72 hours, the patient has a less likely chance of clotting (with the additional anti-coag).
If you are already protein C and S deficient, what does this mean? What condition can develop when starting warfarin? Why?
You have less anti-coags, so you are hypercoagulable.
Warfarin induced necrosis – caused by thrombosis and eventual ischemia of the tissue.
Why start warfarin on a low dose?
you are not sure how the patient will respond. there is no standard dose of warfarin, so a patient could be extremely sensitive and be at high risk of bleeding.
-Also, if they have a protein C and S deficiency that you are unaware of, this could cause warfarin induced necrosis much quicker.
if a patient has liver disease, how should you dose warfarin? why?
give them a lower dose. if their liver is diseased, it is likely that are making LESS clotting factors to begin with (they’re made in the liver). So, they would need less warfarin to inhibit them.
A vegan patient (or someone who takes a multi-vitamin regularly) needs anticoagulation. How should you dose their warfarin?
if they eat a lot of leafy vegetables, then they probably have higher Vit K levels. So, they would have MORE Vit K dependent clotting factors and would need a HIGHER dose of warfarin.
-“Warfarin effects are antagonized by the exogenous administration of Vit K”
If you give someone too much warfarin, what should you do next?
stop the warfarin. Give Vitamin K if necessary. Start a lower dose in a few days.
If someone has chronic diarrhea, how should you adjust the warfarin dose?
Lower the dose. It Vit K is not being absorbed, then less clotting factors are made.
T or F, warfarin can cross the placenta.
T or F, warfarin appears to enter the breast milk.
True
False. Warfarin does NOT appear to enter the breast milk.
