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951 Block 3 > 3. Parenteral Anticoagulants > Flashcards

3. Parenteral Anticoagulants Flashcards

1
Q

What is the major plasma protease inhibitor of thrombin?

A

antithrombin

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2
Q

Antithrombin inhibits what clotting factors?

A

Xa > IXa > XIIa

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3
Q

The rate of formation of inactivating complexes is increased several thousand fold in the presence of what?

A

heparin

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4
Q

Heparin is present as an endogenous component of vessel walls. (T/F)

A

True

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5
Q

Heparin is present in the fluid phase of plasma. (T/F)

A

False

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6
Q

Unfractionated heparin MW ranges from ______ - ______ .

A

3,000 - 30,000

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7
Q

What causes the anticoagulant effect produced by heparin?

A

interaction with antithrombin

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8
Q

What pharmacological compound neutralizes thrombin and other activated clotting factors?

A

heparin-bound antithrombin

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9
Q

Antithrombin is a ______ substrate.

A

suicide

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10
Q

Describe antithrombin’s “suicidal” mechanism

A

protease attacks a specific Arg-Ser peptide bond in antithrombin and becomes trapped as a 1:1 complex

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11
Q

______ serves as a catalytic template for inhibitor and protease to bind.

A

Heparin

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12
Q

Only heparin molecules that contain less than 18 monosaccharide units can catalyze inhibition of thrombin by antithrombin.

A

False: Heparin molecules of this size do not catalyze inhibition of thrombin by antithrombin

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13
Q

Heparin molecules of 18 monosaccharide units or more are required to bind thrombin and antithrombin _______.

A

simultaneously

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14
Q

Shorter heparin polysaccharides catalyze primarily inhibition of factor __ by antithrombin.

A

Xa

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15
Q

Heparin is ______ absorbed from the GI tract.

A

poorly

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16
Q

Heparin must be administered ________.

A

parenterally

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17
Q

IV infusion of heparin has a ________ effect.

A

immediate

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18
Q

Subcutaneous injection of heparin has a ________ effect.

A

delayed

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19
Q

SQ administration of heparin takes how long to take effect?

A

1-2 hours

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20
Q

What method of administration of heparin causes more bleeding complications?

A

intermittent IV injections

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21
Q

In addition to ACS, what other conditions are treated with heparin?

A
  • venous thrombosis

- pulmonary embolism

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22
Q

Why is heparin used in ACS, DVT, and PE instead of warfarin, for example?

A

rapid onset of action

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23
Q

Unfractionated heparin has ________ PK and _______ therapeutic range.

A
  • unpredictable

- narrow

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24
Q

What labs should be monitored when using unfractionated heparin?

A

activated partial thromboplastin time (aPTT)

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25
Q

What is the usual dose for unfractionated heparin in a UA/NSTEMI?

A
  • IV bolus of 60u/kg (4000 u max)
  • 12 u/kg/hr (1000 u/hr max)
  • adjust to maintain aPTT at 1.5 - 2 times the control
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26
Q

What should aPTT value be after administration of heparin?

A

1.5 - 2 times the control value

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27
Q

When might very high doses of unfractionated heparin be given?

A
  • PCI

- cardiac bypass surgery

28
Q

In patients who require very high doses of unfractionated heparin, what lab values should be monitored?

A
  • aPTT

- ACT

29
Q

What are the 3 main limitations of heparin therapy?

A
  • PK: binds to plasma proteins
  • does not inactivate thrombin already bound to fibrin
  • binds to platelets and inhibits function: could lead to uncontrolled bleeding
30
Q

Why is the plasma protein binding of heparin an issue?

A
  • Poor BA at low doses
  • variability in dose response
  • dose-dependent clearance
31
Q

Why is it a problem that heparin does not bind thrombin that is already bound to fibrin?

A

It limits the effectiveness in preventing arterial thrombosis.

32
Q

Why is it a problem that heparin binds to platelets and inhibits function?

A

heparin-induced bleeding

33
Q

The half-life of heparin in plasma depends on ______.

A

dose

34
Q

What is the half-life of 100 u/kg IV heparin?

A

1 hr

35
Q

What is the half-life of 400 u/kg IV heparin?

A

2.5 hours

36
Q

What is the half-life of 800 u/kg IV heparin?

A

5 hours

37
Q

What are contraindications of heparin?

A
  • surgery within 10 days
  • serious GI bleed
  • HTN
  • active bleeding
  • previous stroke
38
Q

What are the ADRs of heparin?

A
  • hemorrhage
  • thrombocytopenia
  • osteoporosis
39
Q

What is the antidote to heparin?

A

protamine

40
Q

How does protamine stop heparin action?

A

protamine binds mostly long heparin molecules, thereby preventing complex with antithrombin III

41
Q

How is protamine administered?

A

IV infusion

42
Q

What is the onset of action of protamine?

A

5 minutes

43
Q

What is the low molecular weight heparin agent?

A

enoxaparin (Lovenox)

44
Q

What is the average weight of LMWH?

A

4,500 daltons

45
Q

How is the MOA of LMWH different than unfractionated heparin?

A
  • ↑ inhibition of factor Xa
  • ↓ inhibition of thrombin
  • shorter molecules can’t bind antithrombin III and thrombin together
  • anti-factor Xa/antithrombin activity is 4:1 vs 1:1 for unfractionated heparin
46
Q

________ has easier administration. (UH/LMWH)

A

LMWH

47
Q

________ has a shorter half life. (UH/LMWH)

A

UH

48
Q

________ has a more predictable response. (UH/LMWH)

A

LMWH

49
Q

_______ is administered by once or twice daily SQ injections. (UH/LMWH)

A

LMWH

50
Q

_______ has a higher incidence of thrombocytopenia. (UH/LMWH)

A

UH

51
Q

________ has a lower incidence of major bleeding complications. (UH/LMWH)

A

LMWH

52
Q

Osteoporosis occurs more often with _______ long-term administration. (UH/LMWH)

A

UH

53
Q

What is the factor Xa selective inhibitor agent?

A

fondaparinux (Arixtra)

54
Q

What is the MOA of fondaparinux?

A
  • binds antithrombin to selectively inhibit factor Xa

- does not inhibit thrombin

55
Q

What are the approved indications of fondaparinux?

A
  • DVT

- PE

56
Q

In what condition is fondaparinux used off label in the US?

A

ACS

57
Q

What are the advantages of using fondaparinux over heparin?

A
  • easier administration
  • more predictable response
  • long half-life
  • increased efficacy
  • less variation between preparations
58
Q

What is the disadvantage of using fondaparinux over heparin?

A

no antidote

59
Q

Which parenteral anticoagulant is synthetic?

A

fondaparinux

60
Q

Which parenteral anticoagulant has the highest bioavailability?

A

fondaparinux

61
Q

Which parenteral anticoagulant has the longest half-life?

A

fondaparinux

62
Q

Which parenteral anticoagulant is NOT eliminated renally?

A

unfractionated heparin

63
Q

What are the hirudin analog agents?

A
  • argatroban (Acova)
  • lepirudin (Refludan)
  • bivalirudin (Angiomax)
  • desirudin ( Ipravask)
64
Q

Where is hirudin naturally found?

A

produced by leeches

65
Q

What is the route of administration of hirudin analogs?

A

injection

66
Q

Which hirudin analogs are approved for heparin-induced thrombocytopenia?

A
  • argatroban

- lepirudin

67
Q

What is the MOA of hirudin analogs?

A
  • direct inhibitor of thrombin (independent of antithrombin III)
  • effectively inhibits thrombin bound to fibrin

951 Block 3 (10 decks)

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