Introduction to Antithrombotic Medications
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Questions and Answers

What is the mechanism of action of clopidogrel and ticlopidine?

  • Inhibition of platelet activation by PAF
  • Blockade of the ADP receptor (correct)
  • Inhibition of the GPIIB/IIIA receptor
  • Inhibition of thromboxane A2 synthesis

    • Which of the following agents is NOT a GPIIB/IIIA receptor blocker?

  • Eptifibatide
  • Abciximab
  • Tirofiban
  • Dipyridamole (correct)

    • Which of the following statements about the mechanism of action of aspirin is correct?

  • Aspirin inhibits the synthesis of prostaglandin I2.
  • Aspirin directly blocks the GPIIB/IIIA receptor.
  • Aspirin inhibits the synthesis of platelet activating factor (PAF).
  • Aspirin irreversibly inhibits the synthesis of thromboxane A2. (correct)

    • Which of the following anticoagulants acts by directly inhibiting thrombin?

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

    What is the mechanism of action of heparin?

    <p>Activation of antithrombin III (C)</p> Signup and view all the answers

    Which of the following anticoagulants is a vitamin K antagonist?

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

    Which of the following drugs is used to prevent restenosis after coronary angioplasty?

    <p>All of the above (D)</p> Signup and view all the answers

    Which of the following is a small molecule inhibitor of the GPIIB/IIIA receptor?

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

    Which of the following statements accurately describes the mechanism of action of heparin in inhibiting thrombin?

    <p>Heparin enhances the activity of antithrombin III (ATIII) by binding to both ATIII and thrombin. (B)</p> Signup and view all the answers

    What is the primary mechanism of action of heparin?

    <p>Heparin accelerates the inactivation of thrombin by antithrombin III. (C)</p> Signup and view all the answers

    How does low-molecular-weight heparin (LMWH) differ from unfractionated heparin in its mechanism of action?

    <p>LMWH primarily targets factor Xa, while unfractionated heparin targets both factor Xa and thrombin. (B)</p> Signup and view all the answers

    What is the primary mechanism by which warfarin exerts its anticoagulant effect?

    <p>Warfarin indirectly inhibits the synthesis of clotting factors by blocking the action of vitamin K. (A)</p> Signup and view all the answers

    Which of the following clotting factors is NOT primarily inactivated by antithrombin III in the presence of heparin?

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

    What is the key difference between unfractionated heparin and low-molecular-weight heparin (LMWH)?

    <p>LMWH has better bioavailability and a longer half-life than unfractionated heparin. (D)</p> Signup and view all the answers

    Which of the following statements accurately describes the role of vitamin K in coagulation?

    <p>Vitamin K is a cofactor in the carboxylation of glutamate residues in clotting factors. (A)</p> Signup and view all the answers

    What is the primary clinical use of protamine sulfate?

    <p>To prevent and treat haemorrhage associated with heparin therapy. (C)</p> Signup and view all the answers

    How does the intrinsic coagulation pathway differ from the extrinsic coagulation pathway?

    <p>The intrinsic pathway involves the activation of factors XII, XI, and IX, while the extrinsic pathway involves the activation of factor VII. (D)</p> Signup and view all the answers

    Which of the following statements accurately describes the role of thrombin in the coagulation cascade?

    <p>Thrombin plays a central role in amplifying the coagulation cascade by activating factors V, VIII, and XI, leading to further thrombin generation. (A)</p> Signup and view all the answers

    Which of the following anticoagulants is contraindicated in pregnancy?

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

    How does heparin differ from low-molecular-weight heparin (LMWH) in terms of its pharmacokinetic properties?

    <p>LMWH has a longer half-life than heparin resulting in fewer injections needed. (A)</p> Signup and view all the answers

    What is the primary function of tissue factor pathway inhibitor (TFPI)?

    <p>To inhibit the extrinsic coagulation pathway. (C)</p> Signup and view all the answers

    Which of the following anticoagulants is classified as a coumarin derivative?

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

    Why is subcutaneous administration of heparin potentially problematic?

    <p>Subcutaneous injection can lead to unpredictable absorption rates, leading to inconsistent anticoagulant effects. (B)</p> Signup and view all the answers

    Which of the following anticoagulants is NOT a direct thrombin inhibitor?

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

    Study Notes

    Introduction to Antithrombotic and Antiplatelet Medications

    • Overview of antithrombotic and antiplatelet medications
    • Presented by Dr. Mitchell Lai, Department of Pharmacology, National University of Singapore.

    Haemostasis

    • Haemostasis is the process of stopping bleeding.
    • Phases of haemostasis:
      • Vasoconstriction (vascular spasm)
      • Platelet plug formation (adhesion, activation, aggregation)
      • Fibrin formation

    Anticlotting Drugs

    • Categorization of anticlotting drugs:
      • Antiplatelet drugs
      • Anticoagulants
      • Thrombolytics

    Antiplatelet Drugs

    • Non-steroidal anti-inflammatory drugs (Aspirin)
    • Platelet GPIIB/IIIA receptor blockers (Abciximab, Eptifibatide, Tirofiban)
    • ADP receptor blockers (Ticlopidine, Clopidogrel)
    • PDE inhibitor (Dipyridamole)

    Platelet Activation and Aggregation

    • Platelet activation involves a complex series of events triggered by damaged endothelium or collagen.
    • Thromboxane A2 plays a key role in initiating platelet aggregation.
    • Prostacyclin opposes platelet aggregation.
    • Aspirin inhibits Thromboxane A2 synthesis.

    Aspirin

    • Actions: Inhibits cyclooxygenase, reducing Thromboxane A2 production thereby inhibiting platelet aggregation.
    • Pharmacokinetics: Duration of effect is related to the life of the platelet, approximately 7-10 days.
    • Clinical Uses: Prophylactic treatment of transient cerebral ischaemia, to reduce the incidence of recurrent myocardial infarction, to decrease post-myocardial infarction mortality.
    • Adverse Effects: Bleeding, gastric upset, ulcers, gastrointestinal bleeding.

    GP IIB/IIIA Receptors

    • Glycoprotein (GP) IIb/IIIa is a platelet membrane protein involved in platelet aggregation.
    • Activation of this receptor is the final common pathway for platelet aggregation.
    • GP IIb/IIIa inhibitors (Abciximab, Eptifibatide, Tirofiban) are used during procedures.

    Other Platelet Aggregation Inhibitors

    • Clopidogrel and Ticlopidine act by blocking ADP receptors on platelets.
    • Dipyridamole inhibits the breakdown of cAMP, thereby preventing platelet activation.

    Anticoagulants

    • Heparin derivatives
    • Coumarin derivatives (warfarin)
    • Lepirudin hirudin
    • Antithrombin III

    Thrombin

    • Thrombin (factor IIa) plays a crucial role in the coagulation cascade.
    • Thrombin activates other factors in the coagulation cascade, leading to fibrin formation and clot stabilization.
    • It is important for platelet aggregation and cell proliferation.

    Intrinsic and Extrinsic Pathways

    • These are pathways involved in blood clotting.
    • Heparin, along with other anticoagulants, inhibits the coagulation cascade and prevents or reduces clot formation.

    Antithrombin III and Heparin

    • Antithrombin III (ATIII) is an endogenous anticoagulant protein.
    • Heparin enhances the action of ATIII on clotting factors to prevent or reduce clot formation.
    • LMWHs (Low Molecular Weight Heparins) have better bioavailability and longer half-life.
    • Heparin is a family of sulfated glycosaminoglycans.

    Actions of Heparins

    • Heparin binds to ATIII, causing a conformational change, exposing its active site, leading to inhibition of proteases (thrombin, Xa).

    Heparin Clinical Uses

    • Treatment of deep vein thrombosis, pulmonary embolism, myocardial infarction.
    • Used in combination with thrombolytics for revascularization procedures and GPIIb/IIIa inhibitors during angioplasty and stenting.

    Heparin Adverse Effects

    • Haemorrhage (stop therapy + protamine sulfate)
    • Thrombocytopenia

    Vitamin K

    • Vitamin K is a fat-soluble vitamin essential for the formation of clotting factors (II, VII, IX, X).
    • Reduced vitamin K is a crucial cofactor in the carboxylation of glutamate residues.

    Warfarin

    • Warfarin is an anticoagulant that inhibits vitamin K epoxide reductase activity and prevents the carboxylation of vitamin K-dependent proteins.
    • Clinical uses are similar to heparin but Warfarin is contraindicated in pregnancy.
    • Pharmacokinetics: Elimination depends on hepatic cytochrome P450 metabolism.
    • Adverse Effects: Bleeding, hemorrhagic disorder in the fetus.

    Thrombolytic Agents

    • t-PA (alteplase), Urokinase, Streptokinase, Anistreplase
    • These are used to break down existing blood clots

    Fibrinolytic System

    • Thrombolytic agents activate the fibrinolytic system which leads to the degradation of fibrin, breaking down the blood clot.

    Thrombolytic Agents Clinical Uses

    • Emergency treatment of coronary artery thrombosis, peripheral arterial thrombosis, and emboli, ischaemic stroke (under 4.5 hours window).

    Summary of Anticlotting Drugs

    • Provides a comprehensive overview of the different classes of anticlotting drugs, their mechanisms of action, clinical uses, and adverse effects.

    Medications for Coronary Ischemic Heart Disease

    • Introduction to medications for Coronary Ischemic Heart Disease.
    • Discusses different types of angina (atherosclerotic, vasospastic, unstable).

    Types of Angina

    • Atherosclerotic angina: Associated with plaque buildup.
    • Vasospastic angina (Prinzmetal): Due to coronary artery spasm.
    • Unstable angina (acute coronary syndrome): Sudden worsening of angina that can lead to a heart attack.

    Determinants of Cardiac Oxygen Requirement

    • Preload: Diastolic filling pressure of the heart, reliant on blood volume and venous tone
    • Afterload: Resistance against ejection of blood, affected by arterial blood pressure.

    Drug Therapy for Angina

    • Vasodilators (including nitrates)
    • Cardiac depressants (including β-blockers)
    • Calcium channel blockers

    Nitrates

    • Mechanism of action: Nitrates cause vasodilation by stimulating the formation of cyclic GMP, relaxing vascular smooth muscle and thus reducing preload and afterload, and thus reducing pain and requirement for oxygen.

    Glycerol Nitrates

    • Nitroglycerin is a potent vasodilator, specifically targeted for acute treatment of angina.
    • Administration methods: Sublingual for rapid relief, transdermal for more prolonged effect.

    Isosorbide Dinitrate (ISDN)

    • Pharmacokinetics: Longer duration of action in comparison to nitroglycerin.
    • ISDN is administered orally, with sustained or immediate release forms available.

    ISDN and ISMN Clinical Uses

    • Prophylaxis for angina.
    • For the treatment of heart failure.

    Nitrates: Side Effects

    • Baroreflex activation
    • Reflex tachycardia
    • Hypotension
    • Headaches

    β-Blockers

    • MOA involves blocking β1 receptors in cardiac myocytes, decreasing heart rate and contractility, thus lowering oxygen demand.

    Calcium Channel Blockers

    • MOA involves preventing calcium from entering muscle cells, causing vasodilation and lowering blood pressure.
    • Divided into two categories in relation to their structure: dihydropyridines (DHPs) and non-DHPs.

    DHP Calcium Channel Blockers

    • Clinical uses: Hypertension, stable angina, reducing myocardial infarction and stroke risk.
    • Adverse Effects: Hypotension, heart failure, myocardial infarction,

    Ivabradine

    • Ivabradine is a unique heart rate-lowering drug.
    • Indications: Stable angina, chronic heart failure.
    • Mechanism of action: Specifically targets the If current in the sino-atrial node.

    Concomitant Diseases and Drug Considerations

    • Review of commonly used drugs for treating hypertension in conjunction with various diseases.

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    Related Documents

    MBBS Antithrombotic & Antiplatelet Medications PDF

    Description

    This quiz covers essential concepts regarding antithrombotic and antiplatelet medications. It includes an overview of haemostasis, the categorization of anticlotting drugs, and specific antiplatelet drugs used in clinical practice. Test your knowledge on these vital pharmacological agents!

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