Warfarin Flashcards
What clotting factors are inhibited by warfarin
Factors 2,7,9,10 and protein C and S
Why is it important to consider the half life of these factors and proteins inhabited by warfarin
To know when steady state is reached
Compared with warfarin when is steady state reached with most drugs
3-5 day of warfarin 1/2 life and 3-5 days of clotting factor 1/2 life
Which clotting factor have the longest half life
Factor 2 (thrombin) - 60 hours
The initial effect of warfarin may be seen within how many days
2-7 days
When is steady state achieved with warfarin
10-14 days
For most patient what is the starting dose of warfarin
5 mg
Which patient group would have 2.5 mg as a starting dose
Frail and elderly
Malnourished and debilitated
Heart failure unstable
Severe liver disease
Post heart Value replacement
When should INR be monitored after initiation of Warfarin for outpatient
After the 3rd dose
After dose adjustment hour often should INR be monitoredfor outpatient
1-2 times weekly
For outpatient how often should a patient be monitored if patient INR is therapeutic or close to therapeutic or stable
Every 2 weeks
If therapeutic maintenance dose is achieved, how often should INR be monitored
Every 4 weeks
For most patient taking warfarin when is steady state achieved
After 2 weeks
How is warfarin dose adjusted?
Determine weekly warfarin dose
Adjusted weekly dose by 5-15%
When is exception to adjustment indicated
Very high or low INR or recent therapy initiation
If INR is at therapeutic and steady state now often should be patient monitored
4 weeks
According to the 2012 chest 2C recommendation is is monitoring INR every 12 months recommended
If patient has been at therapeutic INR for 3 months
What is the maximum that most pharmacist would go before checking INR if patient is at steady state or therapeutic INR
6 weeks
How is severe bleeding for warfarin managed or an INR > 10
Four factor PCC and 5-10mg vitamin K slow infusion
How is minor bleeding risk for warfarin managed
Discontinue temporarily
If patient is not experiencing clinically significant bleeding but has an INR >10’ how is warfarin effect reversed
Hold warfarin and give 2.5-5 mg of vitamin K by mouth
If no clinically significant bleeding and INR 4.5-10
Hold one or more doses, monitor more frequently and lower dose if appropriate
If INR < 4.5 and no significant bleeding
Hold zero or one dose and monitor and lower dose if needed
How is warfarin generally reversed
Vitamin K
True/False: platelet inhibition do not affect INR but can increase the risk of bleeding event
True
What drugs inhibit 2C9 with what effect on INR
Amiodarone
Co-trimoxazole (bactrim)
Metronidazole
Fluconazole or Azole antifungals
They increase INR
What medication induces 2C9 and with what effect on INR
Carbamazepine
Nafcillin
Phenobarbital
Phenytoin
Rifampin
They decrease INR
What major factor can alter INR, influencing warfarin response
Drug-drug interaction
Changes in vitamin K
Disease state
Changes in health or weight
Patient non-adherence
What can cause a subtherapeutic INR or an INR lower than goal
Missed dose
Increased vitamin K
Medication that induces 2C9
Chewing tobacco
Drug interaction/ multivitamin/ dietary supplement
Weight gain
Hypothyroidism
Signs of thromboembolism or stroke
What factors causes supatherapentic INR or higher INR than goal
Drugs that inhibit 2C9
Low vitamin K
Weight loss
Acute illness, persistent fever or diarrhea
Hyperthyroidism or thyroid replacement therapy
Heart failure exacerbation
Alcohol binging
Incorrect dose
Signs and symptoms of bleeding
In which patient is warfarin use contradicted
Pregnant women
