Ch. 51 Anti-Coag, Anti-platelet, Thrombolytic Drugs - KEY POINTS

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Exam 3

Fibrin is produced by 2 pathways (intrinsic and extrinsic pathways) and they converge at which clotting factor?

factor Xa

Plasmin

the active form of plasminogen serves to degrade the fibrin meshwork of clots.

The thrombolytic drugs (stroptokinase, alteplase) act by promoting conversion of plasminogen to PLASMIN

The drugs for thromboembolic disorders fall into 3 major groups

1. anti-coagulants
2. anti-platelets
3. thrombolytic drugs

Anticoagulants (heparin, warfarin) disrupt

the coagulation cascade

thereby, suppress fibrin production

Anti-platelet drugs (aspirin, clopidogrel (Plavix), inhibit what?

platelet aggregation

Thrombolytic drugs (alteplase, streptokinase) promote what?

lysis of fibrin, causing dissolution of the thrombi

Arterial thrombi are BEST prevented with which class of drugs?

Anti-platelet drugs (aspirin)

Venous thrombi are BEST prevented with what class of drugs?

Anti-coagulants (heparin, warfarin)

Anti-coagulants are drugs that

reduce the formation of fibrin

Warfarin inhibits the synthesis or activity of clotting factors?

inhibits the SYNTHESIS of clotting factors, including factor Xa and thrombin

All other anti-coagulants inhibit the synthesis or activity of clotting factors?

inhibit the ACTIVITY of clotting factors (either factor Xa, thrombin or both

Heparin suppresses coagulation by

helping Anti-thrombin inactivate thrombin and factor Xa

Heparin is administred through what 2 routes?

IV or subcut

Heparin is a preferred anti-coagulant for use during

1. PREGNANCY
2. & in situations that require rapid onset of anti-coag effects such as

PE
evolving stroke
massive DVT

Heparin is also used for patients undergoing

open heart surgery
&
dialysis

low dose therapy is used to prevent

post-op venous thrombosis

Anti-coagulation effects of HEPARIN DRIP within

minutes of IV admin

What is the MAJOR ADVERSE EFFECT of Heparin?

BLEEDING

Severe Heparin induced bleeding can be treated with what antidote?

Protamine sulfate

- a drug that binds to heparin and stops it from working

Heparin Induced Thrombocytopenia (HIT) is a

potentially fatal condition caused by development of antibodies against heparin-platelet protein complexes

Heparin Induced Thrombocytopenia HIT should be suspected whenever

1. platelet counts fall significantly
2. or when thrombosis develops despite adequate anti-coagulation

Heparin is CONTRAINDICATED for patients with

1. thrombocytopenia
2. uncontrollable bleeding

Heparin must be used with EXTREME CAUTION in all patients who have

a high likelihood of bleeding

Heparin therapy is monitored by measuring what lab?

aPTT

The target aPTT is how many seconds?

60-80 seconds

Antidote for severe Heparin OD

Protamine Sulfate

Low molecular weight Heparins are produced by

breaking molecules of unfractionated heparin into smaller pieces

Unfractionated Heparins inactivate what?

factor Xa and thrombin equally

Low molecular weight Heparins inactivate what?

only factor Xa

LMW heparin's plasma levels are more predictable than

unfractionated heparins

What type of schedule is LMW heparin on?

LMW heparin's plasma levels are predictable, therefore they can be administered on a fixed schedule with no need for routine lab monitoring

LMW heparins can be used at home

LMW heparins are approved for what 3 things?

1. PREVENTION of DVT following
- abdominal surgery
- hip replacement
- knee replacement

2. Tx of established DVT with or without PE.

3. PREVENTION of ischemic complications in patients with
- unstable angina
- non-Q wave MI
- STEMI

Compared with unfractionated heparin, LMW heparins have

higher bioavailability and longer half-lives.

Direct Thrombin Inhibitors work by

direct inhibition of THROMBIN

Hence, they differ from the heparin life anti-coags, which inhibit THROMBIN INDIRECTLY (by enhancing anti-thrombin activity)

What is one Direct Thrombin Inhibitor prototype?

dabigatran (Pradaxa)
p.o. only

what is the effect of greatest concern with Direct Thrombin Inhibitor dabigatran (Pradaxa)?

BLEEDING

Warfarin is the only

oral anti-coag currently available

Warfarin prevents what?

the activation of Vitamin K synthesis (hence why foods with vitamin K must be avoided when taking coumadin)

thereby, blocks the biosynthesis of vitamin K depending clotting factors

Warfarin is readily absorbed following oral dosing. Once in the blood, what % of coumadin binds to albumin?

99%

Anti-coagulant responses to warfarin develop

slowly and persisnt for several days after warfarin is discontinued

Warfarin is employed most frequently for what?

long term prophylaxis of thrombosis

3 specific indications for Warfarin are

1. prevention of VENOUS THROMBOSIS and associated PE

2. prevention of thromboembolism in patients with prosthetic heart valves (higher INR)

3. prevention of thrombosis during A fibb (higher INR)

Warfarin therapy is MONITORED by measuring what?

PT & INR

What is the INR target for MOST patients?

2 - 3

what is the MAJOR COMPLICATION of warfarin therapy?

BLEEDING

Moderate Warfarin OD is treated with what antidote?

Vitamin K

Can warfarin be used during pregnancy?

NO.

The drugs can cause
- fetal malformation
- CNS defects
- optic atrophy

Drugs that promote bleeding such as Heparin and Aspirin do what when taking with Warfarin?

INCREASE the risk of bleeding in patients taking warfarin.

When patients are on Warfarin, instruct them to avoid

ALL DRUGS (prescript and non-perscrip) that have NOT been approved by the MD.

Dietary Vitamin K can REDUCE the Anti-Coag effect of Warfarin.

Rich dietary sources include

- mayo
- canola oil
- soybean oil
- green leafy veggies
- eggs

Aspirin and other Anti-platelet drugs suppress what?

thrombus formation in arteries

Aspirin inhibits platelet aggregation by

causing irreversible inhibition of CYCLOOXYGENASE

Since platelets are unable to synthesize NEW CYCLOOXYGENASE, inhibition

persists for the life of the platelet (7-10days)

Aspirin is given for

1. PRIMARY prophylaxis od MI
2. PREVENTION of MI recurrence
3. PREVENTION of stroke in patients with Hx of transient ischemic attacks

When used to suppress platelet aggregation, aspirin is admin. in

LOW doses

typically 80 - 325 mg/day

Even in low doses, aspirin increases the RISK of what?

GI bleed and hemorrhagic stroke

Another Anti-platelet is Clopidogrel (PLAVIX) which cause (class)

irreversible blockade of ADP receptors on the platelet surface, thereby preventing ADP stimulated aggregation.

Indications for clopidogrel (PLAVIX) ADP inhibitor includes:

1. recent stroke
2. acute coronary syndromes

Anti-platelet Drug class Glycoprotein IIb/IIIa Antagonists include the following drugs?

1. tirofiban (Aggrastat)
2. eptifibatide (Integrilin
3 abciximab (ReoPro)

The GP IIb/IIIa antagonists receptor blockers (abciximab) ReoPro inhibit what?

the FINAL common step in the platelet aggregation and hence are the MOST EFFECT ANTI-PLATELET DRUGS AVAIL

The GP IIb/IIIa antagonists are used

short term to prevent ischemic events in patients with acute coronary artery syndrome and those undergoing PCI

The MAJOR SIDE EFFECT of GP IIb/IIIa antagonists (ReoPro, Integrillin, Aggrastat) is

BLEEDING

A client is to undergo a coronary angioplasty. The nurse acknowledges that which drug is used primarily for preventing reocclusion of coronary arteries following a coronary angioplasty?

abciximab (ReoPro)

Thrombolytic Drugs are given to

remove thrombi that have ALREADY formed.

vs. anti-coags which are given to PREVENT thrombus formation.

Thrombolytic Drugs (streptokinase, alteplase tPA) are used to

dissolve existing thrombi (rather than prevent thrombi formation)

Thrombolytic drugs work by

converting plasminogen to PLASMIN, an enzyme that degrades the fibrin matrix of thrombi.

Thrombolytic therapy is most effective when

STARTED EARLY (within 2-6 hours of Sx onset and pref. sooner)

For patients with acute MI, tPA is slightly more effective than

streptokinase BUT costs more and causes intracranial bleeding

Streptokinase may cause

significant HYPOTENSION soon after dosing.

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