Antiplatelet Drugs Flashcards
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Questions and Answers

What are three factors that can cause thrombosis?

Endothelial injury, abnormal blood flow, hypercoagulability

How can antiplatelet drugs prevent platelet activation?

Prevent TXA2 synthesis, antagonize ADP receptors, antagonize the platelet glycoprotein GPIIb/IIIa, inhibit phosphodiesterase (PDE)

What are the major drug targets for inhibiting platelet function?

ADP receptors (P2Y1 & P2Y12), COX-1 enzyme, fibrinogen receptors (GPIIb/IIIa), phosphodiesterases

Why would antiplatelet drugs target COX-1?

<p>Because platelets secrete ADP, which activates COX-1, producing TXA2 which stimulates new platelet activation and increases aggregation.</p> Signup and view all the answers

What are the four clinically used ADP antagonists?

<p>Clopidogrel (Plavix), Ticlopidine (Ticlid), Prasugrel (Effient), Ticagrelor (Brilinta)</p> Signup and view all the answers

What patients are ADP antagonists specifically useful for?

<p>Aspirin-intolerant patients</p> Signup and view all the answers

Since Clopidogrel is a prodrug, what enzymes must activate it?

<p>CYP3A4 and CYP2C19</p> Signup and view all the answers

Can Clopidogrel be combined with aspirin?

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

What does Clopidogrel require to achieve a maximal antiplatelet effect rapidly?

<p>A loading dose (300 mg, then 75 mg daily)</p> Signup and view all the answers

What are side effects of Clopidogrel?

<p>Hemorrhage, neutropenia (very serious ADR)</p> Signup and view all the answers

What are the drug-drug interactions with Clopidogrel?

<p>Drugs that are metabolized by CYP3A4 (e.g. Atorvastatin), PPIs (e.g. Omeprazole), because they inhibit CYP2C19</p> Signup and view all the answers

If someone is on Clopidogrel and needs to have surgery, what would you do?

<p>You would give them a platelet transfusion.</p> Signup and view all the answers

Can Clopidogrel (Plavix) be given in vitro to treat platelets?

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

Which antiplatelet drugs are noncompetitive (irreversible) ADP (P2Y12) receptor antagonists?

<p>Clopidogrel, Ticlopidine, and Prasugrel</p> Signup and view all the answers

Which antiplatelet drugs are prodrugs?

<p>Clopidogrel, Ticlopidine, and Prasugrel</p> Signup and view all the answers

Which antiplatelet drugs require a loading dose?

<p>Clopidogrel, Prasugrel, and Ticagrelor</p> Signup and view all the answers

What is the purpose of a loading dose?

<p>To shorten the time it takes to achieve the steady state concentration.</p> Signup and view all the answers

Why is Ticlopidine less safe than Clopidogrel?

<p>Ticlopidine causes neutropenia and thrombocytopenia; Clopidogrel has a more favorable toxicity profile.</p> Signup and view all the answers

If you are worried about a PPI interaction, which antiplatelet drug should you switch the patient to?

<p>Prasugrel</p> Signup and view all the answers

What is the risk with Prasugrel compared to Clopidogrel?

<p>Higher risk of bleeding</p> Signup and view all the answers

Which drug is the one competitive (reversible) ADP (P2Y12) receptor antagonist?

<p>Ticagrelor</p> Signup and view all the answers

Which patients would benefit from using Ticagrelor?

<p>Those with reduced CYP2C19 activity</p> Signup and view all the answers

Why shouldn't patients with a CYP2C19 polymorphism take Clopidogrel?

<p>They are poor metabolizers and will not respond to Clopidogrel no matter how much you increase the dose.</p> Signup and view all the answers

How do antithromboxane drugs work?

<p>They inhibit COX-1, which prevents the formation of TXA2 and inhibits platelet activation.</p> Signup and view all the answers

Which drug is the only irreversible inhibitor of COX-1 and COX-2?

<p>Aspirin</p> Signup and view all the answers

Chemically, what does Aspirin do to the COX enzymes to inhibit them?

<p>It irreversibly (covalently) acetylates the serine residue of COX enzymes.</p> Signup and view all the answers

How long does the effect of Aspirin last?

<p>It lasts the life span of the platelets.</p> Signup and view all the answers

Flashcards

Thrombosis factors

Thrombus formation can be triggered by damage to blood vessel lining, abnormal blood flow, or excessive clotting tendency.

Antiplatelet drug mechanism

Antiplatelet drugs work by interfering with platelet activation, preventing them from sticking together and forming clots.

Major drug targets

ADP receptors, COX-1 enzyme, fibrinogen receptors, and phosphodiesterases are the primary targets for antiplatelet drugs.

Targeting COX-1

COX-1 enzyme is targeted because it produces thromboxane A2 (TXA2), a molecule that activates new platelets and promotes aggregation.

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ADP antagonists

Clopidogrel, Ticlopidine, Prasugrel, and Ticagrelor are common drugs that block ADP receptors to prevent platelet activation.

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Patients benefiting from ADP antagonists

ADP antagonists are helpful for patients who cannot tolerate aspirin.

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Clopidogrel activation

Clopidogrel is a prodrug, meaning it's inactive until it's converted into its active form by enzymes in the body.

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Clopidogrel and aspirin combination

Clopidogrel can be safely used in combination with aspirin to further reduce the risk of blood clots.

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Clopidogrel loading dose

A loading dose of 300 mg followed by 75 mg daily is crucial for quickly achieving the maximum antiplatelet effect of Clopidogrel.

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Clopidogrel side effects

Bleeding and the risk of low white blood cell count are potential side effects of Clopidogrel.

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Clopidogrel drug-drug interactions

Clopidogrel can interact with certain medications, such as those metabolized by the same enzymes or those that block those specific enzymes.

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Surgery protocol for Clopidogrel users

For patients who need surgery, a platelet transfusion is recommended, and they should stop taking Clopidogrel for 5-7 days before surgery.

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Clopidogrel in vitro use

Clopidogrel cannot be tested directly in a lab setting because it needs to be converted into its active form by enzymes, which are not present in lab conditions.

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Noncompetitive ADP receptor antagonists

These drugs act on ADP receptors and block their action permanently.

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Prodrugs in antiplatelet therapy

These drugs are inactive until converted into their active form in the body.

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Antiplatelet agents requiring loading dose

These drugs require a higher initial dose to quickly reach the desired level in the body.

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Purpose of loading dose

A loading dose helps the drug reach a stable concentration in the body quicker.

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Ticlopidine safety profile

Ticlopidine has a higher risk of side effects compared to Clopidogrel, including low white blood cell count and low platelet count, requiring frequent blood tests.

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Switching from Clopidogrel due to PPI interaction

Switching to Prasugrel is recommended for patients who need to avoid interactions caused by PPIs, because it is metabolized by different enzymes.

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Risk of Prasugrel

Prasugrel carries a higher risk of bleeding compared to Clopidogrel.

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Competitive ADP receptor antagonist

Ticagrelor is the only drug that temporarily binds to ADP receptors, unlike the permanent block caused by other drugs.

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Ticagrelor usage

Ticagrelor is a good option for individuals who have difficulty metabolizing Clopidogrel.

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CYP2C19 polymorphism and Clopidogrel

Patients with this condition are less efficient at metabolizing Clopidogrel, reducing its effectiveness even with increased doses.

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Antithromboxane drug mechanism

These drugs work by blocking COX-1, which prevents the production of TXA2 and slows down platelet activation.

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Aspirin's role

Aspirin is the only drug that irreversibly inhibits both COX-1 and COX-2 enzymes.

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Aspirin's mechanism of action

Aspirin attaches to COX enzymes and blocks their function permanently.

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Duration of aspirin's effect

The effects of aspirin on platelets last as long as the platelets live, which is about 7-10 days.

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Study Notes

Thrombosis Factors

  • Thrombosis can occur due to endothelial injury, abnormal blood flow, and hypercoagulability.
  • These factors are interconnected and contribute to the formation of occluding thrombi.

Antiplatelet Drug Mechanism

  • Antiplatelet drugs prevent platelet activation by inhibiting TXA2 synthesis, antagonizing ADP receptors, blocking GPIIb/IIIa glycoprotein, and inhibiting phosphodiesterase (PDE).

Major Drug Targets

  • Key targets for inhibiting platelet function include ADP receptors (P2Y1 & P2Y12), COX-1 enzyme, fibrinogen receptors (GPIIb/IIIa), and phosphodiesterases.

Targeting COX-1

  • Antiplatelet drugs target COX-1 because it produces TXA2, which activates new platelets and increases platelet aggregation.

Clinically Used ADP Antagonists

  • Major ADP antagonists include Clopidogrel (Plavix), Ticlopidine (Ticlid), Prasugrel (Effient), and Ticagrelor (Brilinta).

Patients Benefiting from ADP Antagonists

  • Useful for patients intolerant to aspirin.

Clopidogrel Activation

  • Clopidogrel is a prodrug activated by CYP3A4 and CYP2C19 enzymes.

Clopidogrel and Aspirin Combination

  • Clopidogrel can be safely combined with aspirin.

Clopidogrel Loading Dose

  • A loading dose of 300 mg followed by 75 mg daily is crucial for rapidly achieving maximal antiplatelet effect.

Clopidogrel Side Effects

  • Side effects include hemorrhage and serious risk of neutropenia.

Clopidogrel Drug-Drug Interactions

  • Interactions with drugs metabolized by CYP3A4 (such as Atorvastatin) and PPIs (like Omeprazole, which inhibit CYP2C19) should be noted.

Surgery Protocol for Clopidogrel Users

  • For patients needing surgery, a platelet transfusion is recommended, with a washout period of 5-7 days.

Clopidogrel in Vitro Use

  • Cannot be used in vitro to treat platelets as it is a prodrug reliant on metabolic activation.

Noncompetitive ADP Receptor Antagonists

  • Clopidogrel, Ticlopidine, and Prasugrel act as noncompetitive (irreversible) ADP (P2Y12) receptor antagonists.

Prodrugs in Antiplatelet Therapy

  • Clopidogrel, Ticlopidine, and Prasugrel are all classified as prodrugs.

Antiplatelet Agents Requiring Loading Dose

  • Clopidogrel, Prasugrel, and Ticagrelor require a loading dose for effective action.

Purpose of Loading Dose

  • A loading dose expedites the achievement of steady state concentration of the drug.

Ticlopidine Safety Profile

  • Ticlopidine has a less favorable safety profile than Clopidogrel, causing neutropenia and thrombocytopenia, necessitating frequent blood count monitoring.

Switching from Clopidogrel Due to PPI Interaction

  • Switching to Prasugrel is advisable to avoid PPI interactions, as it is metabolized by CYP3A4 and CYP2B6 instead of CYP2C19.

Risk of Prasugrel

  • Prasugrel presents a higher risk of bleeding compared to Clopidogrel.

Competitive ADP Receptor Antagonist

  • Ticagrelor is the only competitive (reversible) ADP (P2Y12) receptor antagonist and is not a prodrug.

Ticagrelor Usage

  • Beneficial for patients with reduced CYP2C19 activity.

CYP2C19 Polymorphism and Clopidogrel

  • Patients with CYP2C19 polymorphism should avoid Clopidogrel as they are poor metabolizers, reducing its effectiveness despite increased dosing.

Antithromboxane Drug Mechanism

  • Antithromboxane drugs inhibit COX-1, preventing TXA2 formation and subsequent platelet activation.

Aspirin's Role

  • Aspirin is the only irreversible inhibitor of COX-1 and COX-2 enzymes.

Aspirin's Mechanism of Action

  • Aspirin functionally irreversibly acetylates the serine residue of COX enzymes.

Duration of Aspirin's Effect

  • The antiplatelet effect of aspirin lasts the lifetime of the platelets.

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Test your knowledge on antiplatelet drugs with these flashcards. Explore key concepts such as factors causing thrombosis and mechanisms of action for antiplatelet medications. Perfect for students and healthcare professionals alike!

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