Pharmacology of Oral Anticoagulants I Flashcards
What are the two types of oral anitcoagulants
Vitamin K antagonists and Direct oral anticoagulants
What is the main Vitamin K antagonist, what is used to monitor its therapy
Warfarin, INR
What are the direct oral anticoagulants
Dabigaratran, Apixaban, Betrixaban, Rivaroxaban, Edoxaban
What are the clotting factors that Warfarin interacts with (SNOT), what other protiens
Factor 7, Factor 9, Factor 10, Factor 2, Protien C and Protein S
What are the contraindications for warfarin
Pregnancy (especially within the first 3 months), active major bleeding, no labs, Hypersensitivity to warfarin
What is the onset of action for warfarin, peak effect
90 minutes, 3-5 days
T/F: Warfarin is freely water soluble and travels freely in the blood
False: Warfarin is highly water soluble but 99% is bound to plasma proteins, mainly albumin
Which enatiomer is more potent for warfarin
S-enatiomer
Which CYP enzyme metabolizes the S-enatiomer of warfarin, R-enatiomer
CYP 2C9, CYP1A2 and CYP 3A4
What is a normal INR for a patient’s blood
1
What is the initial dose of warfarin, when should the initial effect on the INR usually occur
5 mg daily, the first 2 to 3 days
When should a patient recieve an initial dose of warfarin less than 5 mg
Older adult, history of congestive heart failure, Albumin levels less than 3, just had surgery, liver disease, diarrhea, patient is malnourished, renal disease, cardiac valve replacement, alcoholism
T/F: The liver makes albumin and clotting factors
True
T/F: Warfarin monotherapy is acceptable for acute VTE
False: Warfarin monotherapy is unacceptable for acute VTE treatment because slow onset is associated with incidence for recurrent VTE
What is the common target INR range
2.5 (2-3)
T/F: The lower the INR the higher risk for bleeding
False: The higher the INR the higher the risk of bleeding
What are the MAJOR Warfarin drug interactions that increase the risk of bleeding
Bactrim and Metronidazole
What are the minor Warfarin drug interactions that increase the risk of bleeding
Quinolones, Antifungals (Azoles), Erythromycin, Amiodarone
What are the MAJOR Warfarin drug interactions that can be used with warfarin but must be monitored closesly
Statins (Fluvastatin, lovastatin, simvastatin), Asprin, NSAIDs
What are the minor drug interactions but can be used with Warfarin but must be monitored closely
Anabolic Steroids, Cimetidine and omeprazole
What are the moderate drug interactions that DECREASE warfarin effectiveness
Rifampin, Barbituates, Cholestryamine, Carbamazepine
What supplements decrease warfarin effectiveness
Garlic, ginseng, ginger
T/F: Supplements that decrease warfarin effectiveness usually safe when they are cooked
True
What labs should be done before a patient is put on warfarin
INR, CBC, risk of bleeding, BMP for renal function
T/F: Warfarin should be taken at the same time every day with or without food
True
When should maintenance dose changes occur
Should not be made more frequently than every 3 days
When can patients have INR testing with a frequency of up to 12 weeks
Consistently stable INRs
What are ways the a patient could have a decreased INR
Missed dose, Drug interaction, Higher vitamin K intake, Missed appointment for dosing titration
What is a risk of having decreased INR
Increased risk of thrombosis, new VTE, new embolic stroke
What are ways the patient could have increased INR
Taking extra doses of warfarin, less vitamin K intake, Acute illness, Diarrhea
Why should warfarin not be used in pregnant patients
Can cause fetal hemorrhage and teratogenesis
What is a serious adverse effect of using warfarin, how does it present, what can prevent this
warfarin induced skin necrosis, rare condition within 1- 10 days of warfarin initiation, heparinization prevents this thrombosis
What is the intervention if skin necrosis occurs
Discontinue warfarin, supplement with FFP (high in protein C), restart warfarin gradually, consider switching to direct oral anticoagulants
T/F: Purple toe syndrome is a non-hemorrhagic cutaneous complication that presents 3-8 weeks after initiating warfarin therapy
True
If a patient is taking warfarin therapy and their INR is 3.1 to 4 what should be done to get back to goal,4.1 or higher
Hold up to 1 daily dose and decrease weekly dose by 5%-20%, hold up to 2 daily doses and decrease weekly dose by 10%-20%
If a patient is taking warfarin therapy and their INR is 1.5-1.9 what should be done to get back to goal, less than 1.5
Increase weakly dose by 5%-15%, increase weekly dose by 10%-20%
