Pharmacology of Oral Anticoagulants I

Question 1

What are the two types of oral anitcoagulants

Answer 1

Vitamin K antagonists and Direct oral anticoagulants

Question 2

What is the main Vitamin K antagonist, what is used to monitor its therapy

Answer 2

Warfarin, INR

Question 3

What are the direct oral anticoagulants

Answer 3

Dabigaratran, Apixaban, Betrixaban, Rivaroxaban, Edoxaban

Question 4

What are the clotting factors that Warfarin interacts with (SNOT), what other protiens

Answer 4

Factor 7, Factor 9, Factor 10, Factor 2, Protien C and Protein S

Question 5

What are the contraindications for warfarin

Answer 5

Pregnancy (especially within the first 3 months), active major bleeding, no labs, Hypersensitivity to warfarin

Question 6

What is the onset of action for warfarin, peak effect

Answer 6

90 minutes, 3-5 days

Question 7

T/F: Warfarin is freely water soluble and travels freely in the blood

Answer 7

False: Warfarin is highly water soluble but 99% is bound to plasma proteins, mainly albumin

Question 8

Which enatiomer is more potent for warfarin

Answer 8

S-enatiomer

Question 9

Which CYP enzyme metabolizes the S-enatiomer of warfarin, R-enatiomer

Answer 9

CYP 2C9, CYP1A2 and CYP 3A4

Question 10

What is a normal INR for a patient’s blood

Answer 10

1

Question 11

What is the initial dose of warfarin, when should the initial effect on the INR usually occur

Answer 11

5 mg daily, the first 2 to 3 days

Question 12

When should a patient recieve an initial dose of warfarin less than 5 mg

Answer 12

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

Question 13

T/F: The liver makes albumin and clotting factors

Answer 13

True

Question 14

T/F: Warfarin monotherapy is acceptable for acute VTE

Answer 14

False: Warfarin monotherapy is unacceptable for acute VTE treatment because slow onset is associated with incidence for recurrent VTE

Question 15

What is the common target INR range

Answer 15

2.5 (2-3)

Question 16

T/F: The lower the INR the higher risk for bleeding

Answer 16

False: The higher the INR the higher the risk of bleeding

Question 17

What are the MAJOR Warfarin drug interactions that increase the risk of bleeding

Answer 17

Bactrim and Metronidazole

Question 18

What are the minor Warfarin drug interactions that increase the risk of bleeding

Answer 18

Quinolones, Antifungals (Azoles), Erythromycin, Amiodarone

Question 19

What are the MAJOR Warfarin drug interactions that can be used with warfarin but must be monitored closesly

Answer 19

Statins (Fluvastatin, lovastatin, simvastatin), Asprin, NSAIDs

Question 20

What are the minor drug interactions but can be used with Warfarin but must be monitored closely

Answer 20

Anabolic Steroids, Cimetidine and omeprazole

Question 21

What are the moderate drug interactions that DECREASE warfarin effectiveness

Answer 21

Rifampin, Barbituates, Cholestryamine, Carbamazepine

Question 22

What supplements decrease warfarin effectiveness

Answer 22

Garlic, ginseng, ginger

Question 23

T/F: Supplements that decrease warfarin effectiveness usually safe when they are cooked

Answer 23

True

Question 24

What labs should be done before a patient is put on warfarin

Answer 24

INR, CBC, risk of bleeding, BMP for renal function

Question 25

T/F: Warfarin should be taken at the same time every day with or without food

Answer 25

True

Question 26

When should maintenance dose changes occur

Answer 26

Should not be made more frequently than every 3 days

Question 27

When can patients have INR testing with a frequency of up to 12 weeks

Answer 27

Consistently stable INRs

Question 28

What are ways the a patient could have a decreased INR

Answer 28

Missed dose, Drug interaction, Higher vitamin K intake, Missed appointment for dosing titration

Question 29

What is a risk of having decreased INR

Answer 29

Increased risk of thrombosis, new VTE, new embolic stroke

Question 30

What are ways the patient could have increased INR

Answer 30

Taking extra doses of warfarin, less vitamin K intake, Acute illness, Diarrhea

Question 31

Why should warfarin not be used in pregnant patients

Answer 31

Can cause fetal hemorrhage and teratogenesis

Question 32

What is a serious adverse effect of using warfarin, how does it present, what can prevent this

Answer 32

warfarin induced skin necrosis, rare condition within 1- 10 days of warfarin initiation, heparinization prevents this thrombosis

Question 33

What is the intervention if skin necrosis occurs

Answer 33

Discontinue warfarin, supplement with FFP (high in protein C), restart warfarin gradually, consider switching to direct oral anticoagulants

Question 34

T/F: Purple toe syndrome is a non-hemorrhagic cutaneous complication that presents 3-8 weeks after initiating warfarin therapy

Answer 34

True

Question 35

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

Answer 35

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%

Question 36

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

Answer 36

Increase weakly dose by 5%-15%, increase weekly dose by 10%-20%