Warfarin Flashcards
Explain the route of Warfarin in the body
oral route—> binds to plasma proteins(albumin)—> excreted in urine and stool
What is warfarin used for
recurrence of acute deep vein thrombosis leading to pulmonary embolism even while heparin
What types of surgery should you take warfarin to prevent venous thromboembolism
orthopedic and gynecological surgery
What is warfarin used to protect against
patients with acute MI, prosthetic heart valves and chronic atrial fibrillation
what does vitamin K epioxide normally do
posttranscriptional carboxylation of factors 2, 7, 9, and 10 and the anticoagulant proteins C and S.
What are the side effects of warfarin
bleedings, especially internal bleeding
skin lesions and skin necrosis
purple toe syndrome
many drug interactions
How soon after starting warfarin treat can you see skin lesions/ necrosis. How common is it and who develops
its rare; usually happens 3-10 days after therapy initiation; primarily women
What is purple toe syndrome
its painful, blue tinge discoloration- due to cholesterol emboli breaking from plaques
When purple syndrome does occur, how soon after treatment does it occur
it happens 3-8 after therapy begins
explain how Warfarin interacts with aspirin and phenylbutazone
aspirin and phenylbutazone (NSAID) removes warfarin from albumin—increases bleeding and decreases platelet aggregation
How do antibiotics and warfarin interact with each other
decrease microbial vitamin K production–no competition and doesn’t stop Warfarin from working
How do oral contraceptives and warfarin interacts together
oral contraceptives decrease warfarin effectiveness by increasing plasma clotting factors and decreasing antithrombin III–no point
How do barbiturates and rifampin interact with warfarin
it induces microsomal P450 system and breaks down Warfarin faster
What is the half life of warfarin
its about 40 hours but varies (kind of like heparin) but its variable among individuals
Can Warfarin be given to pregnant women
NO
What effect will warfarin have on pregnant women; what dose should be given
Warfarin crosses the placenta and causes fetal hemorrhage and malformation; TEROGENIC
don’t give any time of dose…instead give heparin or lmwh
What is the half life of factor 7
6 hours
What is the half life of factor 9
24 hours
What is the half life of factor 10
40 hours
What is the half life of factor 2 (prothrombin)
60 hours
What does time Warfarin action depend on
it depends on the disappearance of factors 2, 7, 9, 10
How fast does Warfarin work
anticoagulant effects can usually be seen in 24 hours but peak may take 72-96 hours (3-5 days) because pool of clotting factors have to decrease
Which drugs can interact and decrease anticoagulant effects of warfarin
- estrogen-increases clotting factors
- phenytoin-increases metabolism
- rifampin -increase metabolism
- baribiturates
- vitamin K-completes with warfarin
What drugs increase the bleeding tendencies of Warfarin
- cephalosporins-decrease vitamin K
- salicyclates-
- adrenal corticosteroids
- NSAIDS-remove warfarin from albumin
What enhances the anticoagulant effects of warfarin
- oral antibiotics
- salicylates
- alcohol sulfonamides
- cimetidine
- amiodarone
What do you tell patient on Warfarin about food rich in vitamin K example green leafy vegetables?
be consistent
What test can be used to monitor warfarin
prothrombin time- it measure the extrinsic system
What standard was used to monitor warfarin concentrations
the international normalized ration adopted in the 1990 to monitor warfarin concentration—it corrects for variations that would occur with different thromboplastin reagents b/w hospitals, or when a single hospital gets a new lot reagents
what is the equation of monitoring parameters INR
the equation is INR= (patient thrombin time/ reference prothrombin time) to the power of international sensitivity time
What is the goal of therapy for INR
the goal of therapy is an INR of 2.0-3.0 for most indications
Why would a patients INR be 2.5-3.5
because the person has mechanical heart valves
after myocardial infaraction
antiphopholipid syndrome thrombosis
A what point would you discontinue warfarin
if the INR is below 5 and you can some modest anticoagulant activity w/o too much bleeding
What should be done if the INR is higher than 5
administer large amounts of vitamin K (phytonatoide) because too much anticoagulation and bleeding is occuring
If INR is equal or to 20, what should the doctor do
the anticoagulation is way too high, give the patient vitamin K, factor 9 concentrates, and fresh frozen plasma-to replace clotting factors
