Pharmacology_UCP_LNDiogo_2024-2025 Anticoagulants PDF

Cluster Circulation & Lungs Pharmacology of Hemostasis: Anticoagulants Lucília N Diogo...

Cluster Circulation & Lungs Pharmacology of Hemostasis: Anticoagulants Lucília N Diogo PharmD, PhD Integrated Master Degree in Medicine – Year 3 [email protected] SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Overview TOPICS Overview of Secondary Major Pharmacological Strategies and Targets Hemostasis Classes of Anticoagulants > Describe the underlying mechanisms of secondary Hemostasis; LEARNING OBJECTIVES > Identify the main therapeutic targets of Anticoagulants; > List the available pharmacological classes of Anticoagulants and compare them regarding their mechanisms of action, the rational for their therapeutic effect and safety profile; > Describe the PK and PD specificities of the different classes; > Elucidate the differences between Unfractionated Heparin, LMW Heparins and other parenteral Anticoagulants; > Describe the most relevant characteristics of Vitamin K antagonists; > Present the specificities of Novel Oral Anticoagulants (NOACs); > Identify the main differences (pros and cons) between Vitamin K antagonists and NOACs. 2 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 1  Secondary Hemostasis: The coagulation Cascade 3 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Secondary Hemostasis: Coagulation Cascade Key Points: > Coagulation system = Proteolytic cascade; > Inactive proenzymes (liver) are activated Activated leukocytes sequentially, each giving rise to more of the next; Activated endothelial cells Subendothelial smooth muscle cells > Activation is catalytic and not stoichiometric Subendothelial fibroblasts (amplification process); Adapted from Stallone G. et al., 2020 There are two limbs in the cascade: > The in vitro (intrinsic) pathway: Factor XII > The in vivo (extrinsinc) pathway: TF > Both pathways lead to the activation of Factor X into Factor Xa; > Factor Xa: proteolytically cleaves prothrombin (Factor II) to thrombin (factor IIa); Regulation of coagulation activation: > Antithrombin III (AT): blocks thrombin and other coagulation factors; > Tissue factor pathway inhibitor (TFPI): limits the action of TF; > Activated protein C (aPC): proteolytically degrades factor Va and factor VIIIa. 4 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 2  Strategies and Targets 5 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Strategies and Targets Indirect Anticoagulants (Antithrombin III – AT) e.g. UFH; LMWH; VKA vs. Direct Anticoagulants e.g. VKA, Anti-FXa; Anti-FIIa Antithrombin (AT) III Multi-target Agents e.g. VKA; UFH; LMWH Adapted from Kakkos SK. et al., 2021 vs. Single-target Agents e.g. Anti-FXa; Anti-FIIa Prothrombin Parenteral Anticoagulants e.g. UFH; LMWH, Selective Anti-Xa, Anti-FIIa Thrombin vs. Oral Anticoagulants e.g. VKA, Direct Anti-FXa and Anti-FIIa 6 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 3  Strategies and Targets Factor Xa > Activated form of Factor X; Adapted from Haqqani OP. et al., 2016 > Much narrower substrate specificity than Factor X; > Can proteolytically activate: > Factor IIa (Thrombin); > Factors V, VII and VIII. Va- Cofactor (positive feedback loops that amplify the clotting process) > Free Factor Xa in the bloodstream is rapidly inactivated by serine protease inhibitors (e.g. antithrombin III). Factor Xa + Factor Va (Ca2+)>> Phospholipid-bound complex 7 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Strategies and Targets Thrombin is a sodium activated allosteric enzyme: Thrombin Na+ binding is required for cleavage of fibrinogen, and activation of factors V, VIII and XI Substrate docking site: Enhance the affinity of the interaction of thrombin Proteolytically converts with substrates (e.g. fibrinogen or cofactors). fibrinogen to fibrin Coppens M. et al., 2012 Thrombin’s main activities cleavage of peptide bonds Activates factor XIII in its substrates (cross-links fibrin polymers) (e.g. fibrinogen and Siller-Matula et al., 2011 Factors V, VIII, XI, and XIII). Amplifies the Clotting Cascade Protease-activated (feedback activation of FVIII and V) G protein coupled receptor Activates platelets Induces endothelial release of PGI2,NO and t-PA Binding site to indirect thrombin inhibitors Coughlin SR, 2000 (e.g. UFH and LMWH) 8 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 4  Strategies and Targets Antithrombin III (AT III) > Circulating serine protease inhibitor; > Inactivates thrombin and other activated coagulation factors (IXa, Xa, XIa, and XIIa). These reactions are catalyzed: > Physiologically by heparin-like molecules (= endothelial cell surface proteoglycans that are the physiologic equivalent to heparin) > Pharmacologically by exogenously administered heparin. “suicide trap” for serine proteases (covalent stable stoichiometric 1:1 complex) Golan et al., 2017. Principles of Pharmacology, 4th edition 9 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Pharmacologic Classes of Anticoagulants 10 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 5  Anticoagulants * * NOACs – Novel Oral Anticoagulants Heparins Selective Factor Xa Inhibitors (Unfractionated and LMW) * Vitamin K antagonists Direct Thrombin Inhibitors (Warfarin) Anticoagulants selectivity: Selective factor Xa inhibitors and Direct thrombin inhibitors >>> Warfarin and unfractionated heparin (UFH) 11 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Parenteral Anticoagulants Heparins Selective Factor Xa Inhibitors Direct Thrombin Inhibitors Lepirudin Unfractionated Fondaparinux Bivalirudin LMW Argatroban 12 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 6  Heparins Rang & Dale’s Pharmacology, 8th ed, 2015 MAST CELLS Unfractionated Low-Molecular-Weight Heparins LMWH MW= 5-30 KDa MW= 1-5 KDa 13 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Heparins Mechanism of Action I Serves as a catalytic surface to Without Heparin which both AT III and the serine proteases bind. The binding reaction between proteases and AT III proceeds slowly. Complex Formation Heparin, acting as a cofactor, accelerates How? Patel VP. et al., 2007 the reaction by 1,000-fold. Heparin acts as an anticoagulant by accelerating the rate at which antithrombin irreversibly inhibits thrombin and Factor Xa. Induces a conformational Heparin Dissociation Heparin is not consumed by the conjugation change in AT III that makes the reaction with AT III > available to catalyze reactive site of this molecule additional protease–AT III interactions. more accessible to the attacking protease. 14 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 7  Heparins Heparins of different molecular weights have Mechanism of Action II different anticoagulant activities. Why? UFH: efficiently catalyzes the inactivation of both thrombin and factor Xa by AT III. To catalyze the inactivation of thrombin by AT III: Rang & Dale’s Pharmacology, 9th ed, 2020 a single molecule of heparin must bind at the same time to both thrombin (IIa) and AT III. Lai & Coppola., 2013 To catalyze the inactivation of factor Xa by AT III: the heparin molecule must bind only to the AT III, because the conformational change in AT III induced by heparin binding is sufficient by itself to make the AT III susceptible to conjugation with factor Xa. Why? Thrombin is much more sensitive to the inhibitory LMW heparins: efficiently catalyze the inactivation of factor Xa but less efficiently catalyze the effect of ATIII-Heparin complex than Factor Xa. inactivation of thrombin. 15 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Heparins Non-Anticoagulant Effects Adverse Effects Antidote > Antiplatelet Action > Bleeding / Hemorrhage Inhibits platelet aggregation and prolongs bleeding time (high doses); > Heparin-induced thrombocytopenia > Lipemia clearing > Osteoporosis Cleans lipemia of plasma by releasing lipoprotein lipase from blood vessels and > Hypoaldosteronism (hyperkalemia) tissues; Protamine sulfate + Heparin > Inhibits the proliferation of > Hypersensitivity reactions (protamine) = smooth muscle cells protamine-heparin complexes (cleared) > Accelerates fibrinolysis Plasminogen activation 1 mg of protamine sulfate neutralizes 100 units of heparin 16 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 8  Heparins Clinical Uses > Prophylaxis of thromboembolic diseases (venous thromboembolism); Lab Monitoring > Treatment of deep vein thrombosis and pulmonary embolism; > Treatment of unstable angina and acute myocardial infarction (…). Contraindications > Active bleeding, Hemophilia and Thrombocytopenia; > Severe Hypertension; > Severe hepatic and renal disease; Activated partial thromboplastin time assay (aPTT) > Ulcerative lesions in GI tract Test of the intrinsic and common pathways of coagulation Target range: 1.5-2 times the control value. > Intracranial hemorrhage, recent surgery and brain Metastasis (…). 17 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Heparins LMW Heparins Increase the action of antithrombin III on factor Xa but not its action on thrombin Reviparin Enoxaparin Higher affinity for anti-Xa compared to anti-thrombin (5-25 x) Dalteparin sodium Nadroparin calcium Tinzaparin LMWH are a shorter molecular version of UFH 18 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 9  UFH vs LMW Heparins Unfractionated Heparin Low-Molecular-Weight Heparins Lower therapeutic Index Higher therapeutic Index Monitoring usually not required Monitoring required (do not prolong the aPTT) PD AC effect can be rapidly reversed Questionable reversibility (protamine) Low cost and long history of clinical use Higher cost Delay in hospital discharge Can be administered on outpatient basis Increased risk of HIT and major bleeding Lower incidence of HIT and major bleeding No renal failure restriction Weight-based dosing and renal failure restrictions Unpredictable anticoagulant effect More predictable anticoagulant response AC: anticoagulant effect; HIT: heparin-induced thrombocytopenia; aPTT: activated partial thromboplastin time 19 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT UFH vs LMW Heparins Unfractionated Heparin Low-Molecular-Weight Heparins Stable and predictable PK Higher interindividual variability (lower interindividual variability) IV and SC administration PK (immediate AC effect vs onset delayed by up to SC administration 60 min) Short half-life 40-90´ Longer elimination half-life (3-5 h) (dose dependent) (independent of dose – first-order kinetic) Reduced bioavailability (20-30%) Better bioavailability (90%) Higher binding to plasma proteins (95%) Lower binding to plasma proteins Reduced binding to cell surfaces (endothelium and Binding to cell surfaces macrophages) 20 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 10  Selective Factor Xa Inhibitors Fondaparinux Ultra Low Molecular Weight Heparin (ULMWH) Sequence of five essential carbohydrates > Chemically synthetic pentasaccharide; > Indirect inhibitor of Xa; > Negligible anti-IIa activity; > No effect on thrombin. Liu et al., 2014 Mechanism of Action: Binding to AT III and inducing the conformational change required for conjugation to factor Xa. “First selective Factor Xa Inhibitor approved for prevention and treatment of deep vein thrombosis…” 21 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT UFH vs LMWH vs Fondaparinux Major Adverse Effect: Protamine has no effect on its anticoagulant activity because it fails to bind to the drug. Cicci & Clarke, 2016 22 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 11  Direct Thrombin Inhibitors Lepirudin | Bivalirudin | Argatroban Mechanism of Action: inhibit thrombin directly and independently from anthithrombin by binding to its active catalytic site and/or its exosite. > They can inhibit both fibrin/clot bound and free Siller-Matula et al., 2011 circulating thrombin; > These agents are specific and selective inhibitors of thrombin, with negligible anti-factor Xa activity. Bivalirudin: bivalent agent (catalytic site and exosite 1) > reversible inhibition; Lepirudin: bivalent agent (catalytic site and exosite 1) > irreversible inhibition; Argatroban: univalent agent (catalytic site) > reversible inhibition. 23 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Direct Thrombin Inhibitors Adapted from Nisio et al., 2005 Affinity for thrombin: lepirudin > bivalirudin > argatroban Non-organ elimination (proteolysis) 24 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 12  Oral Anticoagulants NOACs – Novel Oral Anticoagulants = Direct Oral Anticoagulants Vitamin K antagonists Direct Thrombin Inhibitors Direct Factor Xa Inhibitors Warfarin Rivaroxaban Dicoumarol Dabigatran Apixaban Phenprocoumon Edoxaban Acenocoumarol 25 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Vitamin K Antagonists Adapted from Napolitano. et al., 2010 Vitamin K Cycle Facts: > Coagulation factors (II, VII, IX, and X), protein C and protein S are biologically inactive; > γ-carboxylation of glutamate residues ensures biological activity; > Carboxylation reaction is catalysed by a vitamin K- dependent carboxylase; Reduced Vitamin K Oxidized Vitamin K (active form) (inactive form) > Carboxylation reaction requires: O2, CO2 and hydroquinone (reduced Vit. K); > Vitamin K-epoxide reductase VKORC1 (VKORC1): convert the inactive form of Vitamin K into the active one. Vitamin K-dependent carboxylation is crucial for the enzymatic activity of factor II, VII, IX and X, protein C and for the cofactor function of protein S. 26 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 13  Vitamin K Antagonists Warfarin Mechanism of Action: competitive inhibition of vitamin K epoxide reductase component 1 (VKORC1); > Delayded action: 18-24 h (≈ (i.e., for 3 to 4 factor VII half-lives); Rang & Dale’s Pharmacology, 9th ed, 2020 > Onset of action depends on elimination half-lives of the Vitamin K-dependent clotting factors: Factor II (Prothrombin): 60 h; Factor VII (Proconvertin): 6 h; Factor IX (Stuart factor): 24 h; Factor X (Antihemophilic factor B): 40 h. Limitation PPSB fraction 27 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Warfarin High interindividual variability of its anticoagulant effect Limitation VKORC1 gene is polymorphic > Different haplotypes Rieder et al., 2005 > Different affinities for warfarin > Maintenance dose adjustments!!! 28 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 14  Warfarin PK > Rapidly and completely absorbed after oral administration; > Bioavailability: ≈ 100%; PK Interactions: > Small distribution volume; > High plasma protein binding capacity: 99% (albumin); Enzyme induction > Peak concentration occurs within 60-90 min after administration; Enzyme inhibition > Long elimination half-life: ≈ 36-40 h (high variability); > Hydroxylated by cytochrome P450 system and Reduced plasma eliminated in urine; protein binding > Crosses placenta and appears in breast milk. Parekh et al., 2014 29 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Warfarin Limitation Food sources of Vitamin K Gogna & Arun, 2005 30 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 15  Warfarin Managing warfarin treatment: Why? 1- Withdrawal of the drug 2- Administration of Vitamin K OR fresh frozen plasma OR PPBS fraction Adverse Effects Narrow therapeutic index Drug-drug interactions > Bleeding/Hemorrhage (bowel or brain); 2–3 days - increase on the INR > Teratogenic effects; 5–7 days - full effect of warfarin on INR > Osteoporosis and abnormal bone formation; Patient with no anticoagulant: INR=1 Good control: 2 Skin necrosis; Risk of bleeding: INR > 5 > Nausea, vomiting, diarrhea and hepatotoxicity; INR [PTpatient / PTcontrol ] > Cholesterol microembolization syndrome Prothrombin Time (PT) is expressed as the International Normalized Ratio (INR) (“Purple toe syndrome”). 31 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Warfarin Clinical Uses Absolute CI Relative CI > Primary and secondary prevention of > Large esophageal varices; > Uncontrolled hypertension; venous thromboembolism; > Significant thrombocytopenia; > Recent surgery; > Prevention of systemic embolism in > Acute clinically significant > Unexplained anemia; patients with prosthetic heart valves; bleed; > Vitamin K deficiency; > Prevention of stroke, recurrent > Decompensated liver disease; > Hemostasis diseases; infarction and death in patients with > Deranged baseline clotting > Malabsorption syndrome; acute myocardial infarction; screen; > Hepatobiliary disorders. > Prophylaxis of genetic thrombophilia; > Treatment of venous > Pregnancy; thromboembolism and pulmonary > Active duodenal ulcer; (…) embolism. (…) > Severe Hypertension. (…) 32 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 16  Novel Oral Anticoagulants (NOACs) Dabigatran is a small- Direct Thrombin Inhibitors molecule reversible inhibitor that binds to the active site of thrombin >>> Univalent direct Thrombin Adapted from Ganetsky et al., 2011 inhibitor Ganetsky et al., 2011 PK Dabigatran etexilate Esterases > Predictable PK profile; > Allows a fixed-dose regimen; > No need for monitoring; > Half-life≈ 12 hours; > Primarily eliminated via the kidney; > Not metabolized by CYP P450 enzymes; > Drug-drug interactions: P-gp. Dabigatran is administered as the etexilate ester prodrug 33 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT NOACs - Direct Thrombin Inhibitors Dabigatran Reversal Irreversibly neutralizes dabigatran activity in a 1:1 stoichiometric relation Proietti & Boriani, 2018 Dabigatran binds with high affinity to the fragment antigen-binding (Fab) cavity of Idarucizumab which prevents dabigatran from binding to thrombin.) 34 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 17  Novel Oral Anticoagulants (NOACs) Direct Factor Xa Inhibitors Adapted from Parekh et al., 2014 Edoxaban Mechanism of Action: direct inhibition of Factor Xa by binding to its active site and competitively inhibiting the enzyme. Apixaban > Do not require antithrombin III as a cofactor. 35 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT Novel Oral Anticoagulants (NOACs) PK Adapted from Bacchus & Schulman, 2014 Bioavailability ≈ 6.5% 80-100% 50-85% 62% 36 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 18  Warfarin vs NOACs Practical aspects that favor NOACs over warfarin: > Confortable therapeutic index; > Rapid onset of action; > Lower interindividual variability; > No need of continuous laboratory monitoring; > Limited drug–drug interactions; > No food interactions; > Fixed-dose regimen; > Predictable anticoagulant activity. (…) Nutescu EA et al., 2016 37 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT References Books: > Principles of Pharmacology. The Pathophysiologic Basis of Drug Therapy (4th Edition). D. E. Golan, E.J. Amstrong, A. W. Armstrong, 4th edition, Wolters Kluwer, 2017. > Rang & Dale´s Pharmacology, 9th Edition. James Ritter, Rod Flower, Graeme Henderson, Yoon Kong Loke, David MacEwan, Humphrey Rang, Elsevier Ltd, 2018. > Goodman & Gilman’s: The Pharmacological Basis of Therapeutics, 13th Edition. Edited by Laurence L. Brunton, Randa Hilal-Dandan and Bjorn Knollman. McGraw-Hill Education LLC, New York. 2018. Suggested reading related to the topic: > Heestermans, M. et al. Anticoagulants: A Short History, Their Mechanism of Action, Pharmacology, and Indications. Cells 2022, 11, 3214. https://doi.org/10.3390/cells11203214. Others: Slides and notes from TRC and Osmosis on the Topic of Antiplatelet Agents: > Teaching Resource Center Database – resource for mechanisms of drug actions in the context of physiology and pathophysiology. https://coo.lumc.nl/trc/default.aspx?direct=true > Osmosis (Health Education Platform): https://www.osmosis.org/ 38 SHAPING THE FUTURE OF MEDICAL EDUCATION FM.UCP.PT 19  Contacts [email protected] 20