L32 Heparin Anticoagulants II Flashcards
Broadly, which coagulation factors does heparin affect?
2a, 9a, 10a, 11a, 12a
Broadly, which coagulation factors does warfarin affect?
2, 7, 9, 10
Warfarin is an analogue and antagonist of ___.
Vitamin K
What is the MOA of warfarin?
Depression of the formation of functional forms of factors 2, 7, 9, 10; this occurs via inhibition of the carboxylation of glutamic acid in these proteins which is essential for calcium binding; this occurs via inhibition of vitamin K formation via inhibition of vitamin K reductase/epoxide reductase
Warfarin works in the ___, where coagulation factors are produced.
Liver
What does a mutation in VKORC1 gene cause?
Lack of epoxide reductase
Reduced/active vitamin K is used to convert the decarboxy form of ___ into the gamma carboxy form.
Prothrombin
What is used to measure the extrinsic coagulation factors?
PT INR
What is the order of reduction of Vitamin K dependent factors after warfarin administration?
7, 9, 10, 2
As the coagulation factors decrease, the INR starts to ___.
Increase
What is the 1st day of dosing for warfarin? The second day?
1st day: 5-10 mg/d
2nd day: 5-7 mg/d
How is warfarin administered?
Orally only
Describe the half life of warfarin.
Long (~36 hours) due to binding to plasma albumin (~99%)
How is warfarin metabolized?
Hydroxylated to inactive compounds by the hepatic ER
What is used to monitor the anticoagulant effects of warfarin?
Prothrombin time (PT/INR)
What is considered therapeutic for warfarin?
A 1.5 time prolongation of the PT from the baseline
Reagent based variations have been noted in PT. To obtain uniform degrees of anticoagulation, the concentp of INR has been introduced to adjust the level of anticoagulant in a given patient. INR = ?
(PT of patient/PT of mean normal control) x ISI
What are 5 factors that affect the dose of oral anticoagulants?
- Nutrition (diet high in vitamin K leads to a need for higher dose)
- Anemia (need a higher dose due to dilution effect)
- Liver disease
- Biliary obstruction (less absorption, lower effect)
- Drugs (increase or decrease effect)
What are important drug interactions that cause potentiation?
- Drugs that cause vitamin K deficiency (antibiotics)
- Drugs that displace warfarin from protein binding sites
- Drugs that decrease clotting-factor synthesis
- Drugs that suppress or compete for microsomal enzymes
- Drugs that have antiplatelet aggregating properties
What are important drug interactions that cause inhibition of anticoagulant action?
- Decreased warfarin absorption
2. Enhanced warfarin metabolism
What is the principal toxicity of warfarin?
Hypoprothrombinemia (ecchymosis, purpura, hematuria, hemorrhage)
Are oral anticoagulants contraindicated in pregnancy?
Yes
Warfarin also produces necrosis - how?
Impairment of the functionality of protein C, which requires gamma-carboxylation of glutamic acid for functionality (lack of functional protein C decreases anticoagulant effect)
How is oral anticoagulant overdose treated?
- Replacement of the 4 factors with infusion of whole fresh blood or frozen plasma
- Recombinant factor 7a
- Vitamin K
Compare and contrast heparin and warfarin vis a vis structure.
H: large acidic polymer
W: small lipid-soluble molecule
Compare and contrast heparin and warfarin vis a vis route of administration.
H: IV, SC
W: Oral
Compare and contrast heparin and warfarin vis a vis site of action.
H: Blood
W: Liver
Compare and contrast heparin and warfarin vis a vis onset of action.
H: rapid (seconds)
W: slow, limited by half-lives of normal clotting factors
Compare and contrast heparin and warfarin vis a vis MOA.
H: activates AT, which inhibits FXa and thrombin
W: impairs synthesis of 2, 7, 9, and 10
Compare and contrast heparin and warfarin vis a vis duration of action.
H: acute (hours)
W: chronic (days)
Compare and contrast heparin and warfarin vis a vis inhibition of coagulation in vitro.
H: yes
W: n
Compare and contrast heparin and warfarin vis a vis treatment of acute overdose
H: protamine sulfate
W: IV vitamin K and fresh frozen plasma
Compare and contrast heparin and warfarin vis a vis monitoring.
H: APTT
W: PT/INR
Compare and contrast heparin and warfarin vis a vis crossing of the placenta.
H: No
W: Yes
What is a naturally occurring fat soluble vitamin found in green vegetables and synthesized by gut flora?
Vitamin K
What is the function of vitamin K?
Required for the synthesis of factors 2, 7, 9, and 10; essential to the attachment of a calcium binding functional group to prothrombin protein
What is the therapeutic use of vitamin K?
Drug induced hypoprothrombinemia antidote, intestinal disorders and surgery, and hypoprothrombinemia of newborns
What are the toxicities of vitamin K?
Non-toxic; high doses sometimes cause hemolysis in infants
What are the new oral anti-10a agents?
Rivaroxaban, Apixaban, Edoxaban, Betrixaban
What is the antidote to the anti-10a agents?
There isn’t one as of right now
What is the new oral anti-thrombin agent?
Dabigatran
What is the antidote to dabigatran?
Idarucizumab
What is the MOA of warfarin?
Competitive antagonist of vitamin K; suppresses the synthesis of 2, 7, 9, and 10 by blocking enzyme epoxide reductase in the liver
What is the MOA of vitamin K?
Cofactor in the synthesis of 2, 7, 9, and 10
What is the MOA of the oral anti-10a drugs?
Inhibits factor 10a
What is the MOA of dabigatran?
Inhibits thrombin
How are the oral anticoagulants monitored?
Warfarin: PT/INR
All others: not required
What are the indications of warfarin?
Prolonged treatment of DVT and AFib
What are the indications of Vitamin K?
Hypoprothrombinemia, intestinal disorders and gastrectomy, reverse warfarin effects
What are the indications of the oral anti-10a’s?
Stroke prevention in patients with AF (all); prophylaxis of DVt (R, A, B); acute coronary syndrome (R)
What are the indications of dabigatran?
Stroke prevention in patients with AFib
What are the side effects of warfarin?
Bleeding, coumadin-induced necrosis; interacts with several medications that can potentiate/inhibit effects; crosses placental barrier and causes birth defects
What are the side effects of Vitamin K?
Hemolysis
What are the side effects of oral anti-10a drugs?
Bleeding, liver toxicity (R, A, E)
What are the side effects of dabigatran?
Bleeding, liver toxicity; cleared by kidney and could be problematic in patients with abnormal kidney function