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Pharmacology > Pharm 13-Direct/Indirect Thrombin Inhibitors > Flashcards

Pharm 13-Direct/Indirect Thrombin Inhibitors Flashcards

1
Q

How are anticoagulants classified?

A

Direct or indirect thrombin inhibitors

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2
Q

What drugs are indirect thrombin inhibitors? (Anticoagulants)

A

Warfarin (Coumadin)
Unfractionated Heparin/LMWH (Lovenox)
Fondaparinux (Arixtra)

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3
Q

What drugs are direct thrombin inhibitors? (Anticoagulants)

A

Lepirudin (Refludon)
Argatroban (No brand name)
Bivalirudin (Angiomax)

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4
Q

How do anticoagulants work?

A

Inhibit one or more steps in the clotting cascade that lead to fibrin formation; they do not dissolve clots

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5
Q

What is the single most important drug you will use as a perfusionist?

A

Heparin

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6
Q

What is heparin made out of?

A

Mix of straight-chain polymers consisting of extremely anionic repeating dissacharide units

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7
Q

Why is heparin so acidic?

A

So many carboxyl and sulfate groups attached

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8
Q

Which critters produce heparin?

A

virtually all critters, even ones lacking traditional blood so its an ancient molecule on the evolutionary tree

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9
Q

What are circulating mast cells?

A

basophils

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10
Q

Where does heparin “live”?

A

Mast cells

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11
Q

What do mast cells produce?

A

Histamine

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12
Q

What is the kind of heparin that is used the most?

A

Unfractionated heparin

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13
Q

How big is unfractionated heparin?

A

5000-30,000 Daltons

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14
Q

How many daltons is water?

A

Daltons

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15
Q

What is a Dalton?

A

a unit used in expressing the molecular weight of proteins, equivalent to atomic mass unit.

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16
Q

What is heparin measured in?

A

Units

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17
Q

What is 1 unit of heparin?

A

The quantity of heparin required to keep 1 mL of cat’s blood fluid for 24 hours at 0 degrees C

0.002 mg of heparin/ unit

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18
Q

What are the two main sources of heparin?

A
  1. Porcine intestinal-derived heparin

2. Bovine lung

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19
Q

Which source of heparin may be better in preventing some complications (such as HIT)?

A

Porcine intestinal-derived heparin

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20
Q

How is heparin administered?

A

Parenterally

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21
Q

Unfractionated heparin

A

High molecular weight heparin (HMWH)

5,000- 30,000 Daltons

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22
Q

Fractionated heparin

A

Low molecular weight heparin (LMWH)

5500 Daltons

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23
Q

Which type of heparin is much more uniform, contains less contaminants and inactive forms of heparin?

A

Fractionated heparin

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24
Q

What does heparin do?

A

Isn’t an anticoagulant by itself

Acts on AT-III

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25
Heparin + ATIII is how many more x active than ATIII by itself?
>1000x
26
IV Half Life: Heparin vs. LMWH
Heparin: 2 hours LMWH: 4 hours
27
Anticoagulant Response: Heparin vs LMWH
Heparin: Variable LMWH: Predictable
28
Bioavailability: Heparin vs LMWH
Heparin 20 % | LMWH: 90%
29
Major adverse effect: Heparin vs. LMWH
Heparin: Frequent bleeding LMWH: Less frequent bleeding
30
Setting for therapy: Heparin vs LMWH
Heparin: Hospital LMWH: Hospital and outpatient
31
Heparin Time to Effect: IV vs SQ
IV: a few minutes SQ: 1-2 hours
32
How is heparin cleared?
Binding to macrophages and being depolymerized and desulfonated in the liver
33
How are heparin metabolites excreted?
Urine
34
What happens to heparin's half-life with renal and/or liver dysfunction?
Half-life is prolonged
35
What is unfractionated heparin's half-life?
1-2 hours
36
What is fractionated heparin's half-life?
3-7 hours
37
How do different doses of heparin change clearance rate?
Lower doses of heparin are cleared at a faster rate than higher doses; implying the process is saturable
38
How does temperature affect heparin's metabolic process?
Heparin clearance is naturally slow at lower temps and accelerated at higher temps (metabolic process)
39
How is heparin chemically reversed?
Protamine
40
What are some major side effects of heparin?
Excessive bleeding | HIT I and II
41
What is an example of a synthetic LMWH (a pentasaccharide?
Fondaparinux (Arixtra)
42
What is the half-life of Fondaparinux (Arixtra)?
20 hours
43
How is Fondaparinux (Arixtra) eliminated?
Unchanged in the urine
44
What is the major advantage of Fondaparinux (Arixtra)?
Elimination of the risk of bad (Type II) HIT
45
Who is warfarin (coumadin) sponsored by?
Wisconsin Alumni Research Foundation
46
How does Warfarin (Coumadin) work?
Inhibiting Vitamin K (phytonadione/Mephyton) | Blocks an enzyme (Vitamin K epoxide reductase)
47
What are the Vitamin K meds
Phytonadione/Mephyton
48
What is Vitamin K epoxide reductase required for?
Allow the liver to recycle spent (oxidized) Vitamin K so eventually stores of Vitamin K are simply depleted
49
What readily reverses the effects of Warfarin (Coumadin)?
Vitamin K
50
The liver requires vitamin K to produce what factors?
II: Prothrombin VII: Proconvertin IX: Plasma Thromboplastin Component X: Stuart-Prower Factor
51
Warfarin (Coumadin) blocks carboxylation sites of what factors and proteins?
Factors II, VII, IX, X | Proteins C and S
52
Why are Proteins C and S anticoagulants?
Ability to block factors Va and VIIIa
53
Administering Warfarin (Coumadin) causes the liver to produce what?
Incomplete, biologically inactive molecules instead of functioning clotting factors
54
How long does it take for Warfarin (Coumadin) to exert its clinical effect? Why?
8-24 hours; since those Vitamin K stores have to be depleted
55
When is the peak effect of Warfarin (Coumadin)
2-4 days (once those stores are completely empty)
56
What effects how long warfarin (coumadin) lasts?
Drugs, genetics, foods, spices
57
What is warfarin (coumadin)'s half life and duration of action?
Insanely variable; normally 40 hours
58
Warfarm (Coumadin) side effects
Bleeding Birth/fetal deformities Death necrosis
59
What is the warfarin (coumadin) loading dose?
Humans >/= 10mg; but this greatly incresaes the risk of side effects
60
What is the typical dose of warfarin (coumadin)?
5-7 mg/day with adjustments made after one week
61
How is warfarin (coumadin) typically monitored?
Prothrombin Time (PT)
62
PT measures the activity of which factors?
X/V?
63
Why do PTs vary from lab to lab?
Reagent variability
64
What is added to the critter's plasma in order to perform a PT test?
``` Tissue Factor (Factor III) Calcium (Factor IV) ```
65
How long is a normal PT time?
12-13 seconds; time required for a clot to form to a standardized level
66
If a lab determines the "normal" PT time to be 12.5 seconds, what will it set its normal PT range to?
80-120% of that (10-15 seconds)
67
What is INR?
International Normalizing Ratio; it's a way for controlling variability
68
How do you calculate INR?
Critter's PT/ lab "normal" PT mean
69
How do direct thrombin inhibitors work?
All bind directly to thrombin; vary in their affinities for thrombin, half-lives and how they are cleared from the body
70
Hirudin
First iteration of "leech spit" | Irreversibly binds to and deactivates thrombin; contains many contaminants and hard to produce
71
What is Lepirudin (Refludan) and how does it work?
Synthetic purified form of hirudin Bivalently and irreversibly binds to thrombin No dependent on interactions with ATIII for its function
72
One molecule of Lepirudin (Refludan) binds with how many molecules of thrombin?
One
73
How is Lepirudin (Refludan) administered?
Parenterally
74
How is Lepirudin (Refludan) cleared?
Kidneys
75
What is the half-life of Lepirudin (Refludan)
1 hour; but can increase to several days in renal insufficiency/failure patients
76
What percent of patients who receive Lepirudin (Refludan) get antibodies to the lepirudin-thrombin complex?
Very antigenic, 50%
77
What do Lepirudin-Thrombin Complex antibodies do?
Prevent Lepirudin's clearance by the kidneys and increase its anticoagulant effect and or can cause an anaphylactic reaction
78
Those on Lepirudin (Refludan) must have what monitored?
aPTTs | Renal Functions
79
What is Lepirudin (Refludan) used as a therapy for?
HIT or as an alternative anticoagulant (in place of heparin) in patients with HIT
80
What is the reversal agent for Lepirudin (Refludan)?
None exists; make sure the surgeon understands this
81
What is Bivalirudin (angiomax)?
Completely synthetic yet chemically smaller cousin of hirudin Bivalent direct thrombin inhibitor; operates independently of ATIII and is given parenterally Expensve
82
Bivalirudin (Angiomax) Clearance
Less renal clearance (20%) tahn lepirudin (Refludan); the remainder being metabolized
83
What is the half life of Bivalirudin (Angiomax)?
Short 20-25 minutes that is somewhat affected by renal Fx: Mod renal dysfunction: 35 minutes Severe dysfunction: 1 hour Dialysis patient: 3.5 hours
84
How can bivalirudin (Angiomax) be removed?
Hemoconcentrators
85
When is Bivalirudin (Angiomax) commonly used?
PTCA to prevent platelet activation | Anticoagulation for patients with HIT
86
How is Bivalirudin (Angiomax) monitored?
Anticoagulation is measured with Ecarin Clotting Time (ECT); practically monitored with ACTs
87
What is Argatroban and how is it administered?
parenterally-administered small molecule direct thrombin inhibitor
88
What is the half-life of argatroban?
40-50 minutes
89
How is argatroban monitored?
aPTTs
90
How is argatroban cleared?
Eliminated by hepatic clearance
91
How do decide between Bivalirudin (Angiomax) and Argatroban?
Choice is made by whether the patient has intact renal or hepatic function and ease of monitoring anticoagulation
92
What are some oral anticoagulants?
``` Dabigatran etexilate (Pradaxa) Apixiban (Eliquis) Rivaroxaban (Xarelto) ```
93
What is Dabigatran etexilate (Pradaxa) and how is it cleared?
Oral anticoagulant Cleared by kidneys direct thrombin inhibitor
94
What is a possible future replacement for oral warfarin (coumadin)? Why?
Dabigatran etexilate (Pradaxa); dont need to test INRs fewer drug interactions, less variable half life
95
What is Dabigatran etexilate (pradaxa) currently used for the tx of ?
A-fib
96
What do Apixiban (Eliquis) and Rivaroxaban (Xarelto) inhibit? How are they cleared? What do they treat?
Factor Xa; cleared renally, used for a-fib

Pharmacology (23 decks)

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