(4.5) ANTI-PLATELET PHARMACOLOGY
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Questions and Answers

What role does phosphodiesterase play in platelet activation?

  • It promotes the formation of fibrin.
  • It activates cyclic AMP.
  • It breaks down cyclic AMP into other products. (correct)
  • It inhibits platelet plug disintegration.

How does increasing cyclic AMP levels affect platelets?

  • It inhibits platelet activation. (correct)
  • It activates fibrinogen conversion.
  • It promotes platelet aggregation.
  • It increases clot production.

What is the function of TPA in the context of clot formation?

  • To stimulate platelet aggregation.
  • To promote the formation of fibrinogen.
  • To initiate the disintegration of clots. (correct)
  • To prevent the breakdown of fibrin.

Which factors contribute to the finalization of clot formation?

<p>Fibrin and fibrinogen. (A)</p> Signup and view all the answers

Which statement accurately describes glycoproteins in platelet physiology?

<p>They are identified by distinct numbering. (A)</p> Signup and view all the answers

What would be the clinical implication of inhibiting phosphodiesterase?

<p>Increased cyclic AMP levels leading to reduced clot production. (C)</p> Signup and view all the answers

What is the primary mechanism by which antiplatelet therapies may act?

<p>By inhibiting phosphodiesterase activity. (A)</p> Signup and view all the answers

What is the main reason for chewing enteric-coated baby aspirin during a heart attack?

<p>To break the enteric coating for faster absorption (B)</p> Signup and view all the answers

What type of bond does clopidogrel create with its receptor during activation?

<p>Disulfide bond (D)</p> Signup and view all the answers

Which factor is essential for the activation of clopidogrel into its active form?

<p>CYP2C19 enzyme (D)</p> Signup and view all the answers

Which scenario makes clopidogrel an unsuitable choice for a patient?

<p>Being a poor metabolizer of CYP2C19 (C)</p> Signup and view all the answers

In what clinical situations would clopidogrel be administered?

<p>Post myocardial infarction and after stent placement (B)</p> Signup and view all the answers

What mechanism allows aspirin to bind irreversibly to COX-1?

<p>Acetylation of a serine residue (D)</p> Signup and view all the answers

Why is the irreversible action of aspirin particularly significant for platelets?

<p>Platelets cannot synthesize new COX-1 (B)</p> Signup and view all the answers

How does the action of reversible inhibitors like ibuprofen differ from aspirin?

<p>Reversible inhibitors dissociate easily from receptors (B)</p> Signup and view all the answers

What is the average lifespan of a platelet that has been inhibited by aspirin?

<p>28 days (B)</p> Signup and view all the answers

In patients with ischemic events, why is aspirin often recommended as part of their treatment?

<p>It prevents further clot formation (C)</p> Signup and view all the answers

When a stent is inserted, why is aspirin commonly administered?

<p>To prevent clot formation on the stent (D)</p> Signup and view all the answers

Which of the following best describes the nature of aspirin as an antiplatelet therapy?

<p>It is an irreversible inhibitor of COX-1 (B)</p> Signup and view all the answers

What is a common side effect of taking NSAIDs, specifically related to cardiovascular health?

<p>Increased risk of myocardial infarction upon discontinuation (D)</p> Signup and view all the answers

Which antiplatelet drug class does aspirin belong to?

<p>Irreversible inhibitors (B)</p> Signup and view all the answers

What role does acetylation play in the mechanism of action of aspirin?

<p>It leads to irreversible inhibition of COX-1 (B)</p> Signup and view all the answers

Which antiplatelet agent irreversibly inhibits P2Y12 receptors on platelets?

<p>Clopidogrel (C)</p> Signup and view all the answers

What mechanism does aspirin use to exert its antiplatelet effects?

<p>Acetylation of cyclooxygenase-1 (D)</p> Signup and view all the answers

Which antiplatelet drug is known to inhibit the final common pathway of platelet aggregation?

<p>Eptifibatide (A)</p> Signup and view all the answers

What is a common adverse effect of antiplatelet medications?

<p>Risk of gastrointestinal bleeding (A)</p> Signup and view all the answers

In which clinical situation is the use of Vorapaxar particularly indicated?

<p>Long-term prevention of thrombotic cardiovascular events (A)</p> Signup and view all the answers

Which mechanism is primarily targeted by PAR-1 antagonists in antiplatelet therapy?

<p>Inhibition of protease-activated receptor signaling (A)</p> Signup and view all the answers

What is a key adverse effect commonly associated with the use of antiplatelet medications?

<p>Gastrointestinal bleeding (B)</p> Signup and view all the answers

In the context of thrombosis pathophysiology, the role of thromboxane A2 (TxA2) is best described as:

<p>Stimulating platelet activation and aggregation (D)</p> Signup and view all the answers

Which antiplatelet drug is known for its irreversible inhibition of cyclooxygenase (COX-1)?

<p>Aspirin (D)</p> Signup and view all the answers

Which of the following antiplatelet medications specifically targets the ADP receptor?

<p>Clopidogrel (B)</p> Signup and view all the answers

Platelet plug formation primarily requires which of the following factors to stabilize the plug?

<p>Fibrinogen (D)</p> Signup and view all the answers

What is a primary clinical application of antiplatelet therapy?

<p>To prevent arterial thrombosis and myocardial infarction (C)</p> Signup and view all the answers

Which of the following antiplatelet agents acts by irreversibly binding to the ADP receptor?

<p>Clopidogrel (D)</p> Signup and view all the answers

What is one of the main adverse effects associated with the use of GPIIb/IIIa inhibitors?

<p>Bleeding (C)</p> Signup and view all the answers

Which mechanism describes how aspirin functions as an antiplatelet drug?

<p>Irreversible acetylation of COX-1 (D)</p> Signup and view all the answers

What does the administration of phosphodiesterase inhibitors like Cilostazol primarily help achieve?

<p>Inhibit platelet activation via cAMP (D)</p> Signup and view all the answers

Which condition is NOT an indication for the use of Ticagrelor?

<p>Treatment of acute asthma exacerbation (D)</p> Signup and view all the answers

What important enzyme does Clopidogrel require for its activation?

<p>CYP2C19 (C)</p> Signup and view all the answers

Which kind of drug is Abciximab classified as and what is its primary function?

<p>Antibody; inhibits GPIIb/IIIa receptors (D)</p> Signup and view all the answers

In patients classified as CYP2C19 poor metabolizers, what is a potential risk with Clopidogrel?

<p>Ineffective activation leading to increased thrombotic events (C)</p> Signup and view all the answers

What is a common indication for GPIIb/IIIa inhibitors like Eptifibatide?

<p>Prevention of thrombotic events during PCI (B)</p> Signup and view all the answers

What is the expected clinical effect of using phosphodiesterase inhibitors in platelet management?

<p>Inhibition of platelet aggregation (B)</p> Signup and view all the answers

Flashcards

Phosphodiesterase's Function

Phosphodiesterase breaks down cyclic AMP into other products.

Cyclic AMP's Role in Platelets

Cyclic AMP inhibits platelet activation, preventing excessive clot formation.

Increasing Cyclic AMP Levels

Increasing cyclic AMP levels reduces harmful clot formation.

Inhibiting Phosphodiesterase

Inhibiting the breakdown of cyclic AMP (by blocking phosphodiesterase) increases its levels.

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TPA's Role in Clot Breakdown

Tissue plasminogen activator (TPA) breaks down both fibrin and platelet-derived clots.

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Key Steps in Clot Formation

Clot formation involves several steps, from initial activation to plug formation to fibrin tangling. The initial steps (1-7) are critical in physiology.

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Importance of Glycoproteins in Clot Formation

Glycoproteins (with varying numbers) play a role in the interactions and processes of clot formation.

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Aspirin's Mechanism

Aspirin works by irreversibly inhibiting the enzyme COX-1, preventing the formation of prostaglandins that promote platelet aggregation and blood clotting.

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Why Aspirin Matters

Because platelets lack nuclei, they cannot replace the COX-1 enzyme that aspirin irreversibly inhibits, making aspirin's effect long-lasting.

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Aspirin vs. Ibuprofen

Ibuprofen is a reversible inhibitor of COX-1, meaning its effect is temporary and platelet function can return, increasing the risk of clotting.

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Aspirin and Cardiovascular Disease

Aspirin is commonly used to prevent heart attacks and strokes in patients with history of these events because it reduces long-term clotting risk.

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Aspirin After Stenting

Aspirin is prescribed after stent placement to prevent clots from forming on the artificial material, which platelets tend to adhere to.

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Enteric-Coated Aspirin

Aspirin coated to prevent breakdown in the stomach, releasing it in the intestines for slower absorption.

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Why Chew Enteric-Coated Aspirin?

Chewing breaks the coating, allowing immediate absorption in the stomach for faster action, especially during a heart attack.

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Clopidogrel Mechanism

Clopidogrel irreversibly binds to the ADP receptor, preventing platelet aggregation and clot formation.

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Clopidogrel Activation

Clopidogrel is a prodrug activated by CYP2C19 enzyme, becoming effective only after conversion.

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Clopidogrel's Sulfur Role

Clopidogrel contains sulfur which forms a disulfide bond with the ADP receptor, ensuring its strong attachment.

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Platelet Plug Formation

The process of platelets clumping together to form a plug at the site of a blood vessel injury, stopping bleeding.

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Cyclic AMP (cAMP) in Platelets

cAMP is a molecule that inhibits platelet activation, preventing excessive clot formation.

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How does vWF help platelets?

von Willebrand factor (vWF) helps platelets stick to the damaged blood vessel wall, initiating the clotting cascade.

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Arachidonic Acid Pathway

A metabolic pathway where arachidonic acid is converted into various substances like prostaglandins (e.g., TxA2) and leukotrienes, all involved in inflammation and clotting.

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TXA2's Role in Platelet Activation

Thromboxane A2 (TXA2) is a powerful platelet activator, promoting platelet clumping and clot formation.

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ADP's role in Platelet Activation

Adenosine diphosphate (ADP) is a chemical messenger that activates platelets, encouraging them to stick together.

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Antiplatelets: How They Work

Antiplatelet drugs target different steps in the platelet activation process to reduce the likelihood of clot formation.

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Antiplatelet drug targets

Antiplatelet drugs work by targeting specific pathways and receptors involved in platelet activation and aggregation.

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Aspirin's action

Aspirin irreversibly inhibits COX-1, preventing the synthesis of thromboxane A2 (TXA2), a key molecule for platelet activation.

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P2Y12 receptor blockers

Clopidogrel, ticlopidine, and prasugrel are irreversible inhibitors of P2Y12, an ADP receptor on platelets, preventing their activation.

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GP IIb/IIIa inhibitors

Abciximab, eptifibatide, and tirofiban block the final step of platelet aggregation by preventing fibrinogen and von Willebrand factor (vWF) from binding to GP IIb/IIIa.

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Vorapaxar's mechanism

Vorapaxar blocks thrombin-mediated platelet activation by targeting PAR-1, the primary thrombin receptor on platelets.

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Platelet Aggregation Inhibitors

Drugs that prevent platelets from clumping together and forming blood clots. They work by inhibiting different steps in the platelet activation process.

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COX-1 Inhibitors

Drugs like Aspirin that block the COX-1 enzyme, preventing the production of thromboxane A2, a powerful platelet activator.

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P2Y12 ADP Receptor Inhibitors

Drugs like Clopidogrel, Prasugrel, Ticagrelor, Cangrelor that block the ADP receptor on platelets, preventing them from activating and sticking together.

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Phosphodiesterase Inhibitors

Drugs like Cilostazol that block phosphodiesterase, an enzyme that breaks down cAMP. Increasing cAMP levels in platelets helps prevent activation and clotting.

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Ticagrelor: Mechanism

Ticagrelor is an active drug that reversibly binds to the ADP receptor by mimicking adenosine, a molecule that inhibits platelet activation.

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Abciximab: Mechanism

Abciximab is a monoclonal antibody that reversibly binds to the GPIIb/IIIa receptor on platelets, preventing them from sticking to fibrinogen.

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Cilostazol: Mechanism

Cilostazol inhibits phosphodiesterase-3 (PDE3), increasing cAMP levels in platelets. This leads to stabilization of inactive GP IIb/IIIa receptors, decreased thromboxane A2 production, and smooth muscle relaxation.

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Study Notes

Anti-Platelet Pharmacology

  • Goal: Prevent heart attacks and strokes by inhibiting platelet activation.
  • Electron micrograph shows inactivated vs. activated platelets.
  • Key markers (from the presentation) are essential for understanding drug effects on platelet levels.
  • Focus is on one drug per drug class.

Platelet Activation

  • Cholesterol deposits in artery walls, exposing collagen.
  • Collagen triggers platelet activation cascade.
  • Three main steps in platelet plug formation:
    • Adhesion (platelets stick to collagen).
    • Granule release (messengers attract other platelets).
    • Aggregation (platelets clump together).
  • Healthy endothelium prevents collagen exposure.
  • Nitric oxide and prostacyclin regulate platelet activation by increasing cyclic AMP, reducing calcium availability.

Aspirin

  • Inhibits cyclooxygenase (COX-1) irreversibly.
  • Prevents thromboxane A2 production.
  • Prevents platelet aggregation.
  • Adverse effect: GI bleeding.

Other Antiplatelet Drugs

  • P2Y12 inhibitors (e.g., clopidogrel):
    • Inhibit ADP-induced platelet aggregation.
    • Clopidogrel requires metabolism by CYP2C19.
  • GP2B3A inhibitors (e.g., abciximab, tirofiban):
    • Block fibrinogen binding.
    • Used primarily during procedures (e.g., angioplasty).
  • Adverse effects vary by drug.
  • Important to consider individual patient factors such as metabolic rate of CYP2C19, and whether they have known bleeding issues

Phosphodiesterase inhibitors

  • Inhibit cyclic AMP breakdown, increasing cyclic AMP levels which inhibits platelet activation.
  • Psilocybin/PDE3 inhibitors work on similar mechanism.
  • Usage varies based on individual patient factors and condition.

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Description

This quiz focuses on the pharmacology of anti-platelet drugs, specifically their role in preventing heart attacks and strokes. It covers platelets' activation process, including crucial steps such as adhesion, granule release, and aggregation. Key drugs like Aspirin and their mechanisms will also be highlighted.

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