14 Antiplatelets and Fibrinolytics Flashcards

1
Q

Differentiate between likely mechanisms of action for venous thrombosis and arterial thrombosis.

A
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2
Q

Explain how prostacyclin (PGI2) inhibits platelet aggregation.

A

PGI2:

Released by endothelial cells

Binds to platelet receptors

Increases [cAMP], decrease calcium

This prevents platelet aggregation

  • Decrease in platelet aggregatory agents
  • Stabilises GPIIb/IIIa receptors
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3
Q

Outline the process of platelet activation and aggregation.

  • What’s released?
  • What do the released substances act on?
A
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4
Q

How does aspirin work as an antiplatelet?

(aspirin works as antiplatelet at low doses, works as analgesic at higher doses)

A

Aspirin= cyclo-oxygenase inhibitor (COX-1)

COX-1 = an enzyme

COX-1 converts arachidonic acid to thromboxane A2 (TXA)

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5
Q

Why does aspirin not completely inhibit platelet aggregation?

A

Other pathways for platelet aggregation

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6
Q

How does aspirin get converted to salicylic acid in the body?

A

Aspirin= absorbed by passive diffusion and then hepatic hydrolysis

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7
Q

What are the contraindications for aspirin? (4)

A

+ be careful with other antiplatelets/anticoagulants

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8
Q
  1. Why does inhibition of COX-1 last the lifespan of a platelet?
  2. Why does aspirin lack efficacy in some people?
A
  1. Platelet has no nucleus so can’t change production of COX-1
  2. COX-1 polymorphisms in people- aspirin will lack efficacy
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9
Q

What are the indications for aspirin? (4) What might a patient need to be given if they are using aspirin long term?

A

Patient may need gastric protection eg PPIs if using aspirin long term

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10
Q

Give 3 examples of ADP receptor antagonists (antiplatelets).

(Inhibit binding of ADP to P2Y12 receptors–> inhibit activation of GPIIb/IIIa receptors)

A
  1. Clopidogrel
  2. Prasugrel
  3. Ticagrelor
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11
Q

Give some of the side effects of ADP receptor antagonists.

A
  • Bleeding
  • GI upset- dyspepsia, diarrhoea
  • Thrombocytopenia
  • (Caution: renal and hepatic impairment)
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12
Q

What are some important drug interactions we need to be aware of when prescribing ADP receptor antagonists?

A

Clopidogrel requires CYPs for activation

CYPs also required for:

  • Omeprazole (PPI)
  • Ciprofloxacin
  • Erythromycin

Also be careful with

  • SSRIs
  • Other antiplatelets/anticoagulants
  • NSAIDs
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13
Q

How many days prior to surgery should clopidogrel be stopped? How many days prior to surgery should ticagrelor be stopped?

A

Clopidogrel= 7 days prior to surgery

Ticagrelor= 5 days prior to surgery

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14
Q

Give some indications for the ADP receptor antagonists (antiplatelets) clopidogrel and prasugrel.

A

Clopidogrel

  • Monotherapy- if aspririn contraindicated
  • NSTEMI- up to 12 months
  • STEMI with stent- up to 12 months
  • Secondary prevention:
    • TIA long term
    • Ischaemic stroke

Prasugrel

  • ACS patients- adjunct to aspirin
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15
Q

How does abciximab work as an antiplatelet? What is it used for? How is it administered?

A
  • Blocks binding of fibrinogen and von Willebrand factor
  • –> blocks GPIIb/IIIa receptors

Use:

Specialist use- high risk percutaneous transluminal coronary angioplasty

Administration:

I.V.I with bolus

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16
Q

How does dipyridamole work as an antiplatelet?

A
  • Inhibits cellular reuptake of adenosine within platelet
  • Increase plasma adenosine
  • Inhibits platelet aggregation via A2 receptors
  • Also prevents cAMP degradation- inhibits expression of GPIIb/IIIa
17
Q

What are the indications for dipyridamole?

A

(Antiplatelet)

Secondary prevention: ischaemic stroke/TIA

Adjunct prophylaxis of thromboembolism- following valve replacement

18
Q

What are the side effects (3) and inmportant interactions (3) to remember for dipyridamole?

A
19
Q
A
20
Q

How do streptokinase and alteplase work?

A

BE CAREFUL- potential for haemorrhagic bleeding

21
Q

Give an indication for alteplase.

A

Ischaemic stroke patients- if presents <4.5hrs

Post acute MI instead of primary percutaneous coronary interventions

22
Q

Why can streptokinase only be given once?

A

Develop antibodies to it as derived from streptococci

23
Q

How does tranexamic acid work as an antifibrinolytic? What are some of its indications?

A

Inhibiton of activation of plasminogen from plasmin

Indications:

  • Menorrhagia
  • Hereditary angioedema
  • Epistaxis
  • Haemorrhage following trauma