1. Pharmacology-I (PHR 213) Anti-coagulating agents Course Instructor: Md. Samiul Alam Rajib Senior Lecturer Department of Pharmacy BRAC University

2. General Terms  Hemostasis:  Hemostasis: Is the arrest of blood loss from damaged vessels and is essential to life. The main phenomena are- Platelet adhesion and activation Blood coagulation (Fibrin formation)  Thrombosis:  Thrombosis: Is the pathological condition resulting from inappropriate activation of hemostatic mechanisms: Venous thrombosis: Stasis of blood; small platelet component and large fibrin component Arterial thrombosis: Atherosclerosis associated; large platelet component  A portion of thrombus may break away and travel to heart causing ischemia and infraction.  Blood coagulation:  Blood coagulation: The conversion of fluid blood to a solid gel or clot  Hemostasis:  Hemostasis: Is the arrest of blood loss from damaged vessels and is essential to life. The main phenomena are- Platelet adhesion and activation Blood coagulation (Fibrin formation)  Thrombosis:  Thrombosis: Is the pathological condition resulting from inappropriate activation of hemostatic mechanisms: Venous thrombosis: Stasis of blood; small platelet component and large fibrin component Arterial thrombosis: Atherosclerosis associated; large platelet component  A portion of thrombus may break away and travel to heart causing ischemia and infraction.  Blood coagulation:  Blood coagulation: The conversion of fluid blood to a solid gel or clot

3. Stages of Hemostasis There are 4 stages of Hemostasis: 1.Constriction of the injured vessel. 2.Formation of loose temporary platelet aggregate at the site of injury. 3.Formation of fibrin mesh that binds to the platelet aggregate, forming a more stable haemostatic plug or thrombus. 4.Partial or complete dissolution of the haemostatic plug or thrombus by plasmin. There are 4 stages of Hemostasis: 1.Constriction of the injured vessel. 2.Formation of loose temporary platelet aggregate at the site of injury. 3.Formation of fibrin mesh that binds to the platelet aggregate, forming a more stable haemostatic plug or thrombus. 4.Partial or complete dissolution of the haemostatic plug or thrombus by plasmin.

4. Blood Clotting factors FactorsNameRemarks IFibrinogenForms Fibrin IIProthrombinVit. K in necessary for formation IIITissue ThromboplastinDerived from intrinsic and extrinsic sources IVCalciumHelps in intrinsic and extrinsic thomboplastin formation VProaccelerin/ labile factorConverts Prothrombin to Thrombin VI---There is no factor VI VIISerum prothrombin conversion accelerator/ Stable factor Stays in plasma but not used up in clotting, accelerates thromboplastin formation. Retarded by Dicoumarin, and low Vitamin K VIIIAnti-Haemophillic factor (AHF) Helps in formation of intrinsic thromboplastin. Deficiency results in classical Hemophillia IXPlasma Throboplastin component/ Christmas factor Helps in formation of intrinsic thromboplastin. Deficiency influence Hemophillia (Hemophillia B)

5. Blood Clotting factors FactorsNameRemarks XStuart factorThis factor has similar properties as factor VII XIPlasma thromboplastin antecedent This factor is activated by activated Hagman factor and leads to formation of thrombin. XIIHagman or surface factor gets activated when it comes in contact with surface. This is in turn activates protein splitting enzyme kallikarin to produce plasma kinins. Resulting affects are increased vascular permeability and dilation of blood vessels. XIIIFibrin stabilizing factor It along with calcium ions, converts soft clot to solid. It also decreases solubility of clot in urea solution. People deficient in this factor present with poor wound healing.

6. Blood coagulation mechanism Hemostasis and blood coagulation involve complex interaction between the injured vessel wall, platelets and coagulation factors. Following reaction cascade takes place: 1.Contact activation of Hageman factor (Factor XII): intrinsic system, in which all the factors needed for coagulation are present in plasma. This is a slow pathway and takes several minutes to activate factor X 2.Tisue thromboplastin: extrinsic system, needs a tissue factor, but activates factor X in seconds. Subsequent events are common in 2 systems and result in formation of fibrin meshwork and trap blood cells and form clot Hemostasis and blood coagulation involve complex interaction between the injured vessel wall, platelets and coagulation factors. Following reaction cascade takes place: 1.Contact activation of Hageman factor (Factor XII): intrinsic system, in which all the factors needed for coagulation are present in plasma. This is a slow pathway and takes several minutes to activate factor X 2.Tisue thromboplastin: extrinsic system, needs a tissue factor, but activates factor X in seconds. Subsequent events are common in 2 systems and result in formation of fibrin meshwork and trap blood cells and form clot

7. Blood coagulation cascade

8. The role of thrombin  Thrombin cleaves fibrinogen, producing fragments that polymerise to form fibrin.  Activates Fibrin stabilizing factor (XII), fibrinoligase which strengthens fibrin to fibrin links  Causes platelet aggregation  Stimulates cell proliferation and modulates smooth muscle contraction.  It can inhibit coagulation (PARADOX)

9. Blood coagulation cascade in summary Inactivated precursors are activated in series, gives rise to more of the next. The last enzyme thrombin, derived from prothrombin, converts soluble fibrinogen to insoluble mesh of fibrin where blood cells are trapped forming clot. Tow pathways in the cascade- I.Intrinsic pathways; in vivo II.Extrinsic pathway; in vitro Both pathway results in activation of Factor X Calcium ions and negatively charged phospholipids are essential for 3 steps: IXa on X, VIIa on X, Xa on II Phospholipids are provided by activated platelets adhering to the damaged vessel. Blood coagulation is controlled by: I.Enzyme inhibitors II.Fibrinolysis

10. Drugs that act on coagulation cascade Coagulation defects:  Deficiencies of clotting factors are rare (mostly genetic).  Classical Hemophilia (Deficiency of factor VIII)  Hemophilia B (Deficiency of factor IX)  Remedy: Provide fresh plasma or concentrated preparation of factor VII and factor IX  Acquired clotting defects are more common such as liver disease, Vitamin K deficiency (Universal in neonates), excessive oral anticoagulants therapy. Each of them can be treated by Vitamin K.

11. Drugs that act on coagulation cascade Vitamin K (K for Koagulation in German)  Fat soluble vitamin found naturally in plants.  Essential for formation of clotting factors II, VII, IX and X.  Vitamin K acts as a cofactor in carboxylase enzyme which converts Glutamic acid residues of factor II,VII, IX, X into γ-carboxyglutamic acid (Gla)

12. Drugs that act on coagulation cascade

13. Vitamin K administration and pharmacokinetic aspects:  Natural vitamin K (Phytomenandione) may be given orally or by IV injection.  Requires bile salts for absorption.  Synthetic menandiol sodium phosphate, also available and does not require bile salts for absorption.  Synthetic Vitamin K takes longer time than natural Vitamin K for action.  Very little storage in the body and metabolized to polar substances that are excreted in the urine and bile.

14. Drugs that act on coagulation cascade Clinical Use of Vitamin K:  Treatment and prevention of bleeding  Resulting from the use of other anticoagulants (Warfarin)  Prevent haemorrhagic disease in new born babies.  Vitamin K deficiency in adults:  Sprue, coeliac disease, steatorrhoea  Lack of bile (e.g. Obstructive jaundice) triggers Hypoprothrombinemia  Dietary deficiency  Liver disease  Newborns

15. Drugs that act on coagulation cascade (Anticoagulants) These are drugs used to reduce the coagulability of blood. They may be classified into: I. Used in vivo A. Parenteral anticoagulants Heparin, Low molecular weight heparins (ii) Direct thrombin inhibitors: Lepirudin, Bivalirudin, Argatroban B. Oral anticoagulants (i) Coumarin derivatives: Bishydroxycoumarin (dicumarol), Warfarin sodium (ii) Indandione derivative: Phenindione. II. Used in vitro A A. Heparin B. Calcium complexing agents: Sodium citrate Sodium oxalate Sodium edetate

16. Drugs that act on coagulation cascade (Anticoagulants) : Heparin

17. Drugs that act on coagulation cascade (Anticoagulants) : Antiplatelet agents Heparin in higher doses inhibits platelet aggregation and prolongs bleeding time. Antiplatelet drugs are the agents which can interfere with the platelet aggregation and platelet adherence and thus inhibit thrombus formation. E.g. aspirin, dihydrochloropuin, dextran. Aspirin is used in lower dose 75mg/day for heart patient but normally 300 mg/tablet Therapeutic indications: Cerebrovascular accident/ brain stroke Venous thrombosis Chronic hypertension Pulmonary embolism Coronary Thrombosis Atherosclerosis Angina Pectoris

18. Drugs that act on coagulation cascade (Anticoagulants) : Heparin antagonists Protamine sulfate: It is a strongly basic, low molecular weight protein obtained from the sperm of certain fish.  Given I.V.  It neutralises heparin weight for weight, i.e. 1 mg is needed for every 100 U of heparin.  However, it is needed infrequently because the action of heparin disappears by itself in a few hours, and whole blood transfusion is needed to replenish the loss when bleeding occurs.  Protamine is more commonly used when heparin action needs to be terminated rapidly, e.g. after cardiac or vascular surgery.  In the absence of heparin, protamine itself acts as a weak anticoagulant by interacting with platelets and fibrinogen.  Being basic in nature it can release histamine in the body. Hypersensitivity reactions have occurred.  Rapid i.v. injection causes flushing and breathing difficulty. PROTA, PROTAMINE SULFATE 50 mg in 5 ml inj.

19. Uses of anticoagulants 1. Deep vein thrombosis (DVT) and pulmonary embolism (PE) 2. Myocardial infarction (MI) 3. Unstable angina 4. Rheumatic heart disease; Atrial fibrillation (AF) 5. Cerebrovascular disease 6. Vascular surgery, prosthetic heart valves, retinal vessel thrombosis, extracorporeal circulation, haemodialysis 7. Defibrination syndrome

20. Drugs that act on coagulation cascade (Anticoagulants) : Warfarin Mechanism of Action of oral anticoagulants: Dicoumarol has structural similarity with Vit-K. So this drug competitively inhibits Vit-K-epoxide reductase enzyme which is responsible for conversion of Vit-K epoxide into Vit-K. Dicoumarol (-) Vitamin-K epoxide reductase Vit-K epoxide Vitamin K Activation of factor VIII, IX, X Blood coagulation

21. Drugs that act on coagulation cascade (Anticoagulants) : Warfarin Vitamin-K epoxide in time causes activation of coagulation factors VIII, IX, and X. So inhibition of Vit-K-epoxide conversion results in anti coagulant activity of the drug. Therapeutic Indications of Oral anti-coagulant: -Venous thrombosis -Pulmonary embolism -Acute MI patient -Ischemic heart disease/ Angina Pectoris patient -Brain stroke/ Cerebral infraction patient -Arterilal embolism -Frost bite -Acute Gangrena