12 Blood Clotting.pdf

Blood Clotting Presented by Dr. Zahi Damuni Professor of Biochemistry 1 1 • Office hours: typically, online via https://teach.webex.com/meet/zahi.damuni • Email for questions or to set up a one-on-one meeting: [email protected] • Reading: Simmons, Gerhard Meisenberg, W. Principles of Medical...

Blood Clotting Presented by Dr. Zahi Damuni Professor of Biochemistry 1 1 • Office hours: typically, online via https://teach.webex.com/meet/zahi.damuni • Email for questions or to set up a one-on-one meeting: [email protected] • Reading: Simmons, Gerhard Meisenberg, W. Principles of Medical Biochemistry (3rd Edition), Chapter 15 2 2 Learning Objectives 1. Know the sequential mechanisms involved in normal hemostasis and summarize the process by which the vessel wall regulates hemostatsis and thrombosis. 2. Describe the role of platelets in blood clotting. 3. Know the pathway of blood coagulation and its regulation. 4. List the physiological and therapeutic inhibitors of blood coagulation and their mode of action. 5. Describe the tests used in the laboratory to identify coagulation disorders. 6. Know the main components of the fibrinolytic system and anti-fibrin drugs. 7. Define the role of vitamin K in blood coagulation and the factors that need the vitamin K cycle. 3 3 Hemostasis Hemostasis is the process of blood clotting. I. Occurs when small blood vessel (capillary) is damaged II. Clot seals the blood vessel until it regenerates III. Occurs in just 3-6 minutes - injury aggregation of platelets rush To inj ury site 4 4 Process of Hemostasis Three major events occur all beginning the moment the vessel is damaged: 1. Vasoconstriction 2. Platelet plug formation 3. Coagulation of blood Coagulation takes longer, and is completed after vasoconstriction and platelet plug formation occur 5 5 Process of Hemostasis This is a simplified overview of the clotting cascade. 6 Thromboplastin is the combination of both phospholipids and tissue factor III, both of which are needed in the activation of the extrinsic pathway. In contrast, partial thromboplastin is just phospholipids, and no tissue factor III. Platelet factor 3 is the same as tissue factor. Tissue factor, also called platelet tissue factor, factor III, or CD142. Prothrombin activator is a complex of a dozen blood coagulation factors that function to catalyze prothrombin into thrombin. The prothrombin activator complex is activated by a cascade of reactions in response to damage in a blood vessel. 6 Hemostatic Disorders – Blood Clots A thrombus is a blood clot that forms in an unbroken vessel. A large thrombus may block blood flow, causing tissue death. An embolus is a blood clot that forms then breaks away and floats freely in the blood vessels. An embolus may then lodge in a capillary and block blood flow. ↓ Coronary thrombosis Cerebral embolism Pulmonary embolism 7 Myocardial infarction (coronary thrombosis or heart attack) results from the complete occlusion (blockage) of one or more coronary arteries. It arises when atherosclerotic plaques rupture, causing platelet activation, adhesion and aggregation with subsequent thrombus formation within the coronary circulation. A pulmonary embolism (PE) is a blood clot that develops in a blood vessel in the body (often in the leg). It then travels to a lung artery where it suddenly blocks blood flow. 7 Hemostatic Disorders – Blood Clots Causes of thrombus • Injury to blood vessel or build-up of fatty plaques  Both create rough surfaces inside vessel, which may activate platelets ● Poor blood circulation  Clotting factors may accumulate Immobility increases the risk of deep vein thrombus in legs! 8 Deep vein thrombosis (DVT) is a medical condition that occurs when a blood clot forms in a deep vein. These clots usually develop in the lower leg, thigh, or pelvis, but they can also occur in the arm. 8 Hemostatic Disorders – Hemophilia Causes • Lack of Factor VIII ( Hemophilia A) or Factor IX (Hemophilia B) • Recessive sex-linked trait (more common in men) Symptoms • Prolonged bleeding even from minor injuries • Excessive bruising • Bruised and swollen joints • Excessive clumsiness and falling Treatment • Intravenous injection of clotting factors • Donated plasma • Synthetic clotting factors 9 Hemophilia C is a rare genetic disorder caused by missing or defective blot clotting protein called Factor XI. The disease was first recognized in 1953 in patients who experienced severe bleeding after dental extractions and, to this day, it is still not very well-known. Hemophilia C (also known as plasma thromboplastin antecedent (PTA) deficiency or Rosenthal syndrome) is a mild form of hemophilia affecting both sexes, due to factor XI deficiency. It predominantly occurs in Ashkenazi Jews. 9 Endothelium vs. Subendothelium Endothelial cells – line the vessels. Are thromboresistant in nature. They express thrombomodulin and heparin sulfate to keep inappropriate thrombi from forming. They also release tissue plasminogen activator and urokinase to shut off the coagulation cascade in the presence of Factor IIa (thrombin). Subendothelium – beneath the endothelium. Are thrombogenic in nature. Express collagen, and tissue factor to kick off the coagulation cascade. Contain binding sites for von Willebrand Factor (vWF). Subendothelium Endothelium Source: http://facstaff.gpc.edu/~jaliff/vein1.gif 10 10 Formation of the Platelet Plug: A. Platelets adhere to exposed subendothelium. The binding is mediated by von Willebrand factor (vWF). Direct binding to tissue fibronectin or other tissue components occur as well. B. Platelets become activated after binding to the subendothelial tissue and exposure of thrombin (T), resulting in shape change and degranulation. Functional fibrinogen receptors are assembled on the cell surface. C. Continued thrombin exposure together with some of the released mediators (ADP, thromboxane, serotonin) activates more and more platelets. The platelets are glued together by fibrinogen and the platelet plug forms. The action of thrombin on fibrinogen forms insoluble fibrin, and the platelets become enmeshed in the fibrin clot. 5HT, 5-Hydroxytryptamine; PDGF, Plateletderived Growth Factor. 11 11 The Adhesive Nature of Platelets 12 12 Prostacyclin (PGI2) generated by the vascular wall is a potent vasodilator, and the most potent endogenous inhibitor of platelet aggregation so far discovered. Prostacyclin inhibits platelet aggregation by increasing cyclic AMP levels. 13 Arachidonic acid is a polyunsaturated omega-6 fatty acid. Thromboxane A2 (TXA2) is a short-lived, lipid mediator synthesized by platelets from arachidonic acid and released from the phospholipid membrane upon platelet activation. Its main role is in amplification of platelet activation and recruitment of additional platelets to the site of injury. Thromboxane B2 is an inactive metabolite/product of thromboxane A2. 6 keto PGF1 alpha is the inactive hydrolysis product of PGI2 prostacyclin. 13 Hemostasis: Coagulation & Clot Stabilization • • • • • Prothrombin Ca++ Fibrinogen Fibrin Polymerization Figure 16-13: The Coagulation Cascade 14 Factor VIII (FVIII) functions as a co-factor in the blood coagulation cascade for the proteolytic activation of factor X by factor IXa. Deficiency of FVIII causes hemophilia A, the most commonly inherited bleeding disorder. 14 Extrinsic v Intrinsic Pathways • The extrinsic pathway is activated by external trauma that causes blood to escape from the vascular system. • The intrinsic pathway is activated by trauma inside the vascular system, and is activated by platelets, exposed endothelium, chemicals, or collagen. • Both the intrinsic and extrinsic pathways are needed for efficient clotting in the body. In a test tube, fibrin can form along either pathway. But, in the body, the pathways are intertwined in such a way that if some step is missing on either the extrinsic or intrinsic side, a clot won’t be able to form properly or as efficiently. 15 15 Damuni Notes In our bodies, the clotting cascade is kicked off by tissue factor “exposure.” Tissue factor is not floating around in the blood normally – or at least, it isn’t normally “visible” to the blood (it might be in little membrane fragments, but it’s not active until needed). When formation of a clot is needed, tissue factor appears, and together with factor VIIa (which is present in the blood), converts factor X to Xa (which then converts prothrombin to thrombin, which converts fibrinogen to fibrin). So: clotting initially begins along the extrinsic pathway. As as soon as a little Xa is produced, that Xa along with the aptly-named tissue factor pathway inhibitor turns off the extrinsic pathway! A little thrombin is formed, though, before the pathway gets turned off – and that thrombin kicks off the intrinsic pathway (the other side of the cascade, with factors VIII and IX). Fibrin formation then proceeds along this pathway until it’s no longer needed. The bottom line: both the intrinsic and extrinsic pathways are needed to form fibrin in vivo. If factors VIII or IX are deficient, very little fibrin is formed efficiently! 16 Tissue factor pathway inhibitor 1 is a single-chain polypeptide which can reversibly inhibit Factor Xa. While Xa is inhibited, the Xa-TFPI complex can subsequently also inhibit the FVIIa-tissue factor complex. 16 Von Willebrand factor and Factor VIII Factor VIII is bound to VWF while inactive in circulation; factor VIII degrades rapidly when not bound to VWF. Factor VIII is released from VWF by the action of thrombin. In the absence of VWF, factor VIII has a half-life of 1-2 hours; when carried by intact VWF, factor VIII has a half-life of 8-12 hours. VWF binds to collagen, e.g., when collagen is exposed beneath endothelial cells due to damage occurring to the blood vessel. This results in the release of factor VIII which then functions as a co-factor in the blood coagulation cascade for the proteolytic activation of factor X by factor IXa. 17 17 Factors Involved In Blood Clotting • • • • • • • • • • • • • Factor I – Fibrinogen Factor II – Prothrombin Factor III - Tissue Thromboplastin (Tissue Factor) Factor IV - Ionized Calcium ( Ca++ ) Factor V - Labile Factor or Proaccelerin Factor VI – Unassigned Factor VII - Stable Factor or Pro-convertin Factor VIII - Antihemophilic Factor Factor IX - Christmas Factor, Plasma Thromboplastin Component Factor X - Stuart-Prower Factor Factor XI - Plasma Thromboplastin Antecedent Factor XII - Hageman Factor Factor XIII - Fibrin-stabilizing Factor 18 18 Formation of Fibrin Polymer 19 19 Transglutaminase Reaction Fibrin Dimer Fibrin Polymer 20 Transglutaminase catalyzes acyl transfer reactions, deamidation, and crosslinking (polymerization) between protein intra- or interchain glutamine (acyl donor) and lysine (acyl acceptor) peptide residues. 20 Pharmacologic Considerations • PT (prothrombin time) – measures the function of the extrinsic pathway and the common pathway. • aPTT (partial thromboplastin time) – measures the function of the intrinsic pathway and the common pathway. In vitro extension by heparin. • Vitamin-K dependent coagulation components – Factors X, IX, VII, II, proteins C, S (mnemonic: 1972 [10, 9, 7, 2]). Deficiency of Vit K • Warfarin (Coumadin) – inhibits vitamin-K epoxide reductase and effective levels of vitamin-K dependent coagulation components. Will extend the PT and aPTT. • Heparin (used as drug) – purified from animals. Increases the activity of Antithrombin III. Will increase the aPTT in vitro. • Thromboxane A2 (TXA2) – synthesis of TXA2 is initiated by activated platelets. TXA2 increases platelet activation and aggregation. Its synthesis is inhibited by aspirin. 21 Thromboplastin is the combination of both phospholipids and tissue factor III, both of which are needed in the activation of the extrinsic pathway. In contrast, partial thromboplastin is just phospholipids, and no tissue factor III. 21 Reference range: 10-13 secs Reference range: 25-35 sec. 22 22 Bleeding Time • Bleeding time (BT): A normal bleeding time indicates adequate platelet hemostatic function. An incision is made under the forearm (standard size with an automatic device) and the amount of time it takes for the bleeding to stop is recorded. • Reference range: 3-9 minutes 23 23 Dissolving The Clot & Anticoagulants Figure 16-14: Coagulation and Fibrinolysis 24 24 Fibrinolysis As soon as the injury is healed, clot dissolution starts to restore the normal flow of blood 2. Plasminogen is converted to the active form Plasmin by 2 distinct Plasminogen Activators (PAs): a) Tissue plasminogen activator (t-PA) from injured endothelial cells b) Urokinase from kidney endothelial cells and plasma 1. 25 25 Breakdown of Fibrin 26  TPA and urokinase activate plasminogen  Plasmin breaks down the fibrin clot into di-fibrinopeptides  D-dimer (or D dimer) is a fibrin degradation product (or FDP), a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis. It is so named because it contains two D fragments of the fibrin protein joined by a crosslink. 26 Plasminogen Activators 1. Tissue Plasminogen Activator (tPA) 2. Urokinase 3. Streptokinase 27 27 Physiological Inhibitors of Coagulation 1. Antithrombin III - activated by heparin and heparan 2. Activated Thrombomodulin - Activates Protein C, which in turn inhibits Factors Va and VIIIa 28 28 Anticoagulant Activity of Thrombomodulin 29 Protein S is a vitamin K-dependent plasma glycoprotein synthesized in the liver. In the circulation, Protein S exists in two forms: a free form and a complex form bound to complement protein C4b-binding protein (C4BP). Protein C is a zymogen, i.e., an inactive enzyme. The activated form plays an important role in regulating anticoagulation, inflammation, and cell death and maintaining the permeability of blood vessel walls in humans and other animals. Thrombomodulin (TM), a high affinity thrombin receptor present on endothelial cell membrane, plays an important role as a natural anticoagulant. It acts as a cofactor of thrombin-catalyzed activation of protein C and inhibits the procoagulant functions of thrombin. 29 Process of Hemostasis 30 30 Non-Physiological Inhibitors of Coagulation A. B. C. D. Vitamin K antagonists (in vivo) e.g., Warfarin EDTA (Ethylenediaminotetraacetic acid) Citrate Oxalate Calcium/divalent cation chelators 31 31 Vitamin K in Blood Coagulation 32 32 33 Warfarin inhibits both the epoxide reductase and the quinone reductase. 33 Vitamin K deficiency • Vitamin K deficiency – results in prolonged bleeding and coagulation time (PT and aPTT), even though normal blood calcium levels and normal liver function may be indicated. • The most common causes of vitamin K deficiency are insufficient dietary intake, inadequate absorption, and decreased storage of the vitamin due to liver disease, but it may also be caused by decreased production in the intestines. 34 34 Plasma D-Dimers • Cross-linked fragments containing D-Dimer epitopes • D-Dimer test is used to diagnose: Deep Vein Thrombosis Pulmonary Embolism Disseminated Intravascular Coagulation (DIC) • D-Dimer levels are elevated in these conditions 35 D-dimer (or D dimer) is a fibrin degradation product (or FDP), a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis. It is so named because it contains two D fragments of the fibrin protein joined by a crosslink. Disseminated intravascular coagulation (DIC) is a rare but serious condition that causes abnormal blood clotting throughout the body's blood vessels. It is caused by another disease or condition, such as an infection or injury, that makes the body's normal blood clotting process become overactive. 35 Screening Tests Used in the Diagnosis of Coagulation Disorders Test Reference Range Abnormalities Indicated Common Cause of Disorder PT or International Normalized Ratio (INR) 11-13.5s (PT) 0.8-1.1 (INR) Extrinsic + Common Deficiency/Inhibition VII, X, V, II, I Liver disease, warfarin therapy, DIC (disseminated intravascular coagulation) APTT/PTT with Kaolin/Kaolin Cephalin Clotting Time 25-35 s Intrinsic + Common Deficiency/Inhibition XII, IX, VIII, X, V, II, I Liver disease, heparin therapy, VIII, IX, DIC Thrombin Time (TT) 14-19 s Deficiency/abnormal I, inhibition of II by heparin or FDPs DIC, Heparin therapy, fibrin clot therapy Fibrin Degradation Products (FDPs) or Fibrin Split Products (FSP) < 10 g/mL (1.25 -10 g/mL) Accelerated destruction of fibrinogen DIC (disseminated intravascular coagulation) Bleeding Time 3-9 min Abnormal platelet function Aspirin, uremia, von Willebrand disease 36 The international normalized ratio (INR) is a calculation based on results of a PT and is used to monitor individuals who are being treated with the blood-thinning medication (anticoagulant) warfarin (Coumadin®). The PT and INR are used to monitor the effectiveness of the anticoagulant warfarin. Kaolin clotting time (KCT) is a sensitive test to detect lupus anticoagulants. There is evidence that suggests it is the most sensitive test for detecting lupus anticoagulants. It can also detect factor VIII inhibitors but is sensitive to unfractionated heparin as well. FDP’s – fibrin degradation products. For patients on warfarin, the therapeutic range is 2.0 to 3.0. A normal thrombin time is about 14 to 19 seconds. A longer thrombin time can mean low fibrinogen, high fibrinogen, or fibrinogen that's not working normally. It can also be because of medicines that affect blood clotting, such as heparin or argatroban. 36 PT PTT Bleeding Time Platelet Count Thrombocytopenia (decreased platelet number) IgG CONDITION unaffected unaffected prolonged low Early liver failure prolonged unaffected unaffected unaffected End-stage liver failure prolonged prolonged prolonged decreased Uremia unaffected unaffected prolonged unaffected Afibrinogenemia prolonged prolonged prolonged unaffected Factor V & X deficiency prolonged prolonged unaffected unaffected Von Willebrand disease unaffected prolonged prolonged unaffected Hemophilia unaffected prolonged unaffected unaffected DIC prolonged prolonged prolonged low Vit. K deficiency/ Warfarin prolonged prolonged unaffected unaffected Aspirin unaffected unaffected prolonged unaffected TPA/Streptokinase prolonged prolonged prolonged unaffected 37 37 Blood Clotting and Drugs for Hemostasis Dr. Mayers-Aymes, PharmD [email protected] Turning point: pharmmcqs 1 Reading List Access Medicine supplemental reading: Chapter 34, Drugs Used in Disorders of Coagulation. In: Basic & Clinical Pharmacology, 14th Edition, by Bertram Katzung Access Medicine https://accessmedicine-mhmedicalcom.rossuniversity.idm.oclc.org/content.aspx?bookid=2249&sectionid=1752 20898 USMLE Rx Bricks created for the purpose of this lecture and available in the Additional Information Section Practice questions in Canvas 2 Learning Objectives (Pharmacology) • Describe the mechanism of action of antiplatelet drugs. • Describe the mechanism of action of anticoagulants. • Identify which tests are used to determine therapeutic success of the drugs used for management of hemostasis. • Describe the mechanism of action of anti fibrin drugs • Describe the mechanism of action warfarin. • For each drug class (antiplatelets, anticoagulants and fibrinolytics),  State the therapeutic uses & pharmacological effects  Describe the adverse effects, contraindications & precautions  Describe key pharmacokinetic properties 3 Introduction • Hemostasis refers to the finely regulated process of maintaining fluidity of the blood, repairing vascular injury, and limiting blood loss while avoiding vessel occlusion (thrombosis) and inadequate perfusion of vital organs. • Either extreme: excessive bleeding or thrombosis—represents a breakdown of the hemostatic mechanism. • Thrombosis describes a pathologic state in which normal hemostatic processes are activated inappropriately. - Recall the distinction between a thrombus and embolus breakso moves 4 Blood Clotting Lecture 5 Process of Hemostasis • Localized vasoconstriction occurs as a response to the secretion of endothelium-derived vasoconstrictors such as endothelin. • Primary hemostasis: platelet activation (change in shape and release of secretory granule contents which recruit other platelets, causing more platelets to adhere to the subendothelial matrix and to aggregate with one another at the site of vascular injury) - primary hemostatic plug. • Secondary hemostasis (coagulation cascade) - the activated endothelium and other nearby cells express tissue factor, which complexes with coagulation factor VII to initiate the coagulation cascade • Activation of thrombin is the end result of the cascade 6 vasoconstrictor due ehange >binds - of platelets (Katzung, 12/2017)Katzung, B., Trevor, A. (2017). Pharmacology: Basic and Clinical Pharmacology, 14th Edition. [[VitalSource Bookshelf version]]. Retrieved from vbk://1260135993 7 8 Regulation of Hemostasis • Antithrombin: inactivates thrombin (IIa) and other coagulation factors (IXa, Xa, XIa, and XIIa) by forming stable complexes with them • Proteins C and S: proteolysis of Va and VIIIa • Prostacyclin (PGI2): a metabolite of arachidonic acid that is synthesized and secreted by the endothelium. Increases cAMP levels within platelets and thereby inhibits platelet aggregation and platelet granule release. • Tissue factor pathway inhibitor (TFPI): limits the action of tissue factor (TF). 9 ANTI-PLATELET DRUGS 10 Main targets for antiplatelet drugs • Inhibition of ADP-induced platelet aggregation – e.g. clopidogrel • Inhibition of prostaglandin synthesis (thromboxane A2) – e.g. aspirin • Blockade of glycoprotein IIb/IIIa (GP IIb/IIIa) receptors on platelets – e.g. abciximab 11 Platelet activation by ADP 1. Binding of ADP to the P2Y (ADP) receptor also called P2Y12 2. Activation of a Gi protein which inhibits adenylyl cyclase 3. Decrease synthesis of cAMP which leads to decreased protein kinase A activation 4. Platelet aggregation Modified from: Golan, D. E. (2016). Principles of Pharmacology: The Pathophysiologic Basis of Drug Therapy. [VitalSource Bookshelf]. Retrieved 12 from https://bookshelf.vitalsource.com/#/books/9781496327062/ Antiplatelets (e.g. clopidogrel) Mechanism of action: • Irreversibly blocks ADP P2Y12 receptors on platelets thereby inhibiting activation of glycoprotein IIb/IIIa receptors. This reduces platelet aggregation and binding to fibrinogen. Therapeutic Uses (1)secondary prevention of atherosclerotic events in patients with recent MI, stroke and PVD (2) treatment of acute coronary syndromes (3) prevention of stent thrombosis (in combination with aspirin). 13 Antiplatelets (e.g. clopidogrel) Pharmacokinetics • Undergoes oxidation by hepatic P450 CYP2C19 to the active drug • Administration: oral • Excretion: equally in urine and feces Adverse effects • Diarrhea, abdominal pain (3%), Bleeding (2%) (intracranial, gastrointestinal), Thrombotic thrombocytopenic purpura ( very rare) 1. What type of drug is clopidogrel (based on the fact that it is oxidized to an active drug)? 2. What will be the result of co-prescribing a CYP2C19 inhibitor (or inducer) with clopidogrel? 14 Pharmacogenomics and Clopidogrel • Variability in response to clopidogrel administration may be due to genetic differences in CYP2C19. • Poor metabolizers of clopidogrel may experience an inadequate drug effect leading to increased cardiovascular events. • FDA recommendation: use of other anti-platelet drugs • Also drug interactions possible: e.g. clopidogrel and omeprazole (inhibits CYP 2C19 function) 15 Antiplatelets (e.g. abciximab) Mechanism of action: • • • A glycoprotein IIb/IIIa antagonist. Abciximab is humanized monoclonal antibody, which binds non-competitively to the platelet glycoprotein IIb/IIIa receptor complex to prevent the binding of any aggregating substance to prevents platelet aggregation. Eptifibatide and Tirofiban are competitive antagonists of the glycoprotein IIb/IIIa receptor complex which appear to be less effective than abciximab.. Therapeutic Uses • used in patients undergoing percutaneous coronary intervention (PCI) to prevent acute cardiac ischemic complications, manage patients with unstable angina not responding to conventional therapy in patients scheduled for PCI. 16 Prostanoid biosynthesis Katzung, B. G. (2017). Basic and Clinical Pharmacology 14th Edition. [VitalSource Bookshelf]. Retrieved from https://bookshelf.vitalsource.com/#/books/9781259641169/ 17 Antiplatelets (e.g., aspirin) Mechanism of action: • Aspirin inhibits the action of the enzyme cyclooxygenase (COX) • COX blockade reduces both the platelet-mediated production of TA2 (via COX-1) which promotes aggregation, and the endothelial cells-mediated production of prostacyclin (PGI2) (via COX-2), which inhibits aggregation. • Low doses of aspirin provide an antiplatelet effect via the inhibition of synthesis of thromboxane A2 by irreversible acetylation of ↓ the enzyme COX- I only NSAID that binds irreversibly 18 Antiplatelets (e.g., aspirin) Therapeutic uses (1) prophylaxis against transient ischemic attack, MI and thromboembolic disorders (2) treatment of Acute Coronary Syndromes (ACS) (3) prevention of re-occlusion in coronary artery revascularization procedures and stent placement. 19 Contraindications and precautions of anti-platelet drugs • • • • Bleeding (gastrointestinal, intracranial, retinal) Surgery Coagulopathy (hemophilia, etc.) Any disease that increases the risk of hemorrhage (i.e., aplastic anemia, leukemia, thrombocytopenia, infective endocarditis, inflammatory bowel disease, gastrointestinal neoplasms, etc.) • Venous thromboembolism (antiplatelet effect can increase the risk of thromboembolism. Reasons are unknown) 20 ANTI-COAGULANT DRUGS 21 Recall Antithrombin inactivates coagulation factors by forming stable complexes with them. Whalen, K. (2018). Lippincott Illustrated Reviews: Pharmacology. [VitalSource Bookshelf]. Retrieved from https://bookshelf.vitalsource.com/#/books/9781496386113/ 22 Heparins Whalen, K. (2018). Lippincott Illustrated Reviews: Pharmacology. [VitalSource Bookshelf]. Retrieved from https://bookshelf.vitalsource.com/#/books/9781496386113/ 23 Heparin Mechanism of action: • binds tightly to antithrombin and causes a conformational change which exposes the active site for more rapid interaction with the activated clotting factors. • Functions as a cofactor for the antithrombin-protease reaction without being consumed • High molecular weight fractions inhibit blood coagulation by inhibiting IIa, IXa, Xa • Lower molecular weight heparin have less effect on IIa and a greater effect on Xa. 24 Heparins Pharmacological Effect • limit the expansion of thrombi by preventing fibrin formation Therapeutic Use: • both prophylaxis and treatment of thromboembolic diseases • for prophylaxis of postoperative venous thrombosis in patients undergoing surgery and those with acute myocardial infarction 25 Heparins Pharmacokinetics • Administration: IV, SC • Onset of action: IV (within minutes), SC (1-2 hours) • UFH has unpredictable PK so monitor (aPTT), LMWH have more predictable PK so monitoring not necessary for most patients • Elimination: LMWH (primarily urine – why is this important to note?), UFH: small amounts in urine (primarily non-renal elimination) Adverse Effects • Bleeding, chills, fever, urticaria, osteoporosis, heparin induced thrombocytopenia (HIT) • LMWH has a lower risk of adverse effects particularly HIT and osteoporosis 26 Heparins The preferred treatment of thromboembolism in pregnancy is anticoagulation with low molecular weight heparin (LMWH) LMWHs in comparison to UFH have: • equal efficacy • increased bioavailability from the SC site of injection • A more predictable response • less frequent dosing requirements • Less Adverse Drug Reactions (ADRs) 27 Heparins Precautions • Linked closely to adverse effects (e.g. osteoporosis) Contraindications • hypersensitivity to heparin, bleeding disorders, alcoholism, or who have had recent surgery of the brain, eye, or spinal cord. Excessive bleeding may managed with protamine sulphate - it combines with heparin to form a stable 1:1 inactive complex 28 Warfarin (Mechanism of action): 1. Factors II, VII, IX and X (as well as proteins C and S require vitamin K as a cofactor for their synthesis in the liver. 2. During this reaction, vitamin K is oxidized to the inactive form. 3. An enzyme, vitamin K epoxide reductase (also called VKORC1), is then required to convert the inactive 2,3-epoxide into the active, reduced form of vitamin K. 4. Warfarin inhibits epoxide reductase. 29 Warfarin Pharmacological effect • Decreases blood coagulation Therapeutic Use: • prevention and treatment of DVT and PE, stroke prevention, atrial fibrillation Pharmacokinetics: • Administration: Oral (100% bioavailability) • Highly bound to albumin (99%) • Peak effects: 72 – 96 hours after initiation (what is the implication of this?) • Excretion: Primarily urine as metabolites Monitoring: PT/INR test 30 Warfarin Adverse Effects • Bleeding, skin and tissue necrosis • Minor bleeding may be treated by withdrawal of the drug or administration of oral vitamin K, but severe bleeding may require greater doses of vitamin K given intravenously, whole blood or fresh frozen plasma. Precautions • Elderly more sensitive to anticoagulation effects • Dietary insufficiency (vitamin K) – what happens if a patient consumes large quantities of green leafy vegetables while on warfarin? & adds Vit K doseis : Contraindications • Teratogenic (Pregnancy Category X) , active bleeding or an increase risk for hemorrhage 31 Direct Thrombin Inhibitors (Bivalirudin, argatroban, dabigatran) Mechanism of action • DTIs bind to the active site of both free and fibrin-bound thrombin, thus preventing its coagulant activity. Pharmacokinetics • Bivalirudin and argatroban are parenteral DTIs whereas dabigatran is an oral DTI. Therapeutic Uses: Bivalirudin: as an alternative to heparin in patients with or at risk of heparin-induced thrombocytopenia. Also, for use in patients undergoing PCI. Dabigatran: prophylaxis and treatment of DVT and PE, to reduce the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation. When used to treat, VTE, dabigatran follows 5–7 days of initial heparin or LMWH therapy. 32 Direct Thrombin Inhibitors (Bivalirudin, argatroban, dabigatran) Adverse Effects • Bleeding • With dabigatran, gastrointestinal adverse effects are common (up to 20%) and include epigastric discomfort, abdominal pain, gastroesophageal reflux, peptic ulcer, esophagitis,). – The antidote for dabigatran is a monoclonal antibody, idarucizumab that can effectively neutralize the dabigatran molecule in the blood. 33 Rivaroxaban Mechanism of action • binds to the active site of factor Xa, preventing its coagulant activity (direct factor Xa inhibitor). Pharmacokinetics: • It is administered orally. Has an oral bioavailability ≈90%. When compared to warfarin, rivaroxaban has a faster onset of action and a shorter half-life. Adverse effects: • Include bleeding. Andexanet alfa is the antidote for reversing the effects of rivaroxaban. The precautions and contraindications are similar to those of other anticoagulants. 34 FIBRINOLYTICS 35 Alteplase Fibrinolytic/thrombolytic agents are used to lyse already-formed clots Thrombolytic agents act by converting the inactive zymogen plasminogen to the active protease plasmin. Tissue plasminogen activator (t-PA) achieves this: t-PA is a serine protease produced by human endothelial cells; it is a potent activator of plasminogen. Whalen, K. (2018). Lippincott Illustrated Reviews: Pharmacology. [VitalSource Bookshelf]. Retrieved from https://bookshelf.vitalsource.com/#/books/9781496386113/ Alteplase is recombinant t-PA 36 Alteplase Mechanism of action: • Converts plasminogen into active plasmin. The massive activation of plasminogen causes a ‘systemic lytic state’ in which hemostasis is impaired. Pharmacological effect • Breakdown fibrin (lyse clots) Therapeutic use • Myocardial infarction, stroke, thromboembolism 37 Alteplase Pharmacokinetics • Administration: IV • Elimination: primarily hepatic Adverse Effects: • bleeding Contraindications and precautions • Any active internal bleeding or hemorrhagic disorder, Recent severe trauma or major surgery, pregnancy, Severe hypertension (>180/110 mm Hg). 38 Drugs used for bleeding disorders • Vitamin K (discussed previously) vegetables. found primarily in leafy green • Factor VIII deficiency (classic hemophilia, or hemophilia A) and factor IX deficiency (Christmas disease, or hemophilia B) account for most of the heritable coagulation defects. • Recombinant factor VIII and IX, are used to treat hemophilia. • Desmopressin increases factor VIII activity and is used to treat hemophilia and von Willebrand disease. 39 A 34-year-old man presents to the ED with complaints of severe shortness of breath and chest pain. After appropriate investigations, the patient was diagnosed with a pulmonary embolism and was started on a medication which binds to antithrombin. Which drug did the patient receive to manage the pulmonary embolism? A. B. C. D. E. Clopidogrel Alteplase Warfarin Heparin Desmopressin Turning point: pharmmcqs 40 b) Which laboratory test should the physician use to monitor heparin therapy? 41 (c) The patient started to experience adverse effects to heparin therapy. Which drug should be used to reverse the action of heparin? 42 A transition from heparin to warfarin anticoagulant therapy is initiated while the patient is in the hospital. After discharge of the patient from the hospital, warfarin anticoagulant therapy is continued. Following discharge, the patient decides to institute lifestyle changes, including diet and exercise. His dietary plan is to dramatically decrease his intake of meat to try to become a vegetarian. How would an increased consumption of green leafy vegetables be expected to alter the patient’s International Normalized Ratio (INR)? A. B. C. D. It would be increased. It would be decreased. It would be unchanged. It would be doubled. 43 A patient undergoes a percutaneous coronary angiography procedure and placement of a stent in a coronary blood vessel, he will need to be on dual antiplatelet therapy, for example, aspirin and clopidogrel, for at least a year. Which of the following most accurately describes the mechanism of action of clopidogrel? A. B. C. D. Clopidogrel irreversibly inhibits cyclooxygenase Clopidogrel facilitates the action of antithrombin III The active metabolite of clopidogrel binds to and inhibits the platelet ADP receptors The active metabolite of clopidogrel binds to and inhibits the platelet glycoprotein IIb/IIIa receptors 44 A 46-year-old man presents to the emergency department with severe chest pain. After doing appropriate tests(ECG and cardiac enzymes) the physician confirmed that he had a myocardial infarction and therapy was initiated with a fibrinolytic drug. Which one of the following drugs was used to manage the man? A. B. C. D. E. Clopidogrel Warfarin Alteplase Desmopressin Heparin 45