Pharmacology 301 6 Module 6 DRUGS BLOOD

Pharmacology 301. 6 Module 6 DRUGS & BLOOD Anticoagulants, anti-platelet & fibrinolytics Treatment of anemia

Causes of death in Canada 1997: 661 deaths/100, 000 http: //www. statcan. ca/english/Pgdb/health 30 b. htm stroke injuries liver cancer lung other heart disease Heart disease and stroke = 1 of 3 deaths, due to clotting

Blood fluidity § The endothelial lining is non-thrombogenic § Balance between procoagulants (thromboxane, thrombin, activated platelets, platelet factor 4) and anticoagulants (heparan sulfate, prostacyclin, nitric oxide, antithrombin) § 1. heparin & derivatives – stimulate natural inhibitors of coagulant proteases (antithrombin) § 2. coumarin anticoagulants – block multiple steps in the coagulation cascade § 3. fibrinolytic agents – lyse pathological thrombi § 4. antiplatelet agents – aspirin

The Hemostatic System Accidental injury vs. pathological injury hypercholesterolemia, diabets, hypertension Coagulation cascade – platelet activation and coagulation vasospasm platelet plug fibrin plug Recanalization platelets (5 HT, TXA 2) adhesion, activation, aggregation extrinsic, intrinsic (humoral) fibrinolysis

Platelet function disruption of endothelium platelet adhesion agonist binding • thrombin platelet activation platelet release platelet aggregation • serotonin • ADP • TXA 2

Platelet adhesion and aggregation Platelet activation

Antiplatelet drugs Arachidonic acid Aspirin ADP Thromboxane (from activated platelets) stimulates Clopidogrel ticlopidine inhibit P 2 Y receptor TXA 2 recep clotting Ca 2+ Lowers c. AMP Increased c. AMP clotting Prevents clotting Gp. IIb-IIIa Receptor for Eptifibatide fibrinogen and Abciximab platelet adhesion Tirofiban Dipyridamole (prevents breakdown by phosphodiesterase)

How does it work? Aspirin efficacy Aspirin irreversibly inhibits platelet COX enzyme Platelets cannot synthesize new COX (no nucleus) No thromboxane (procoagulant, vasoconstrictor) synthesis Low dose aspirin (80 -160 mg) does not inhibit endothelial COX Prostacyclin (anticoagulant, vasodilator) formation not affected Aspirin reduces clots by 15%, on average. 2% have a bleed, that is serious each year. Use in high risk clotters.

Antiplatelet drugs Ticlopidine (TICLID)- is a prodrug § Blocks platelet ADP receptor and prevents activation and aggregation § Is often used in combination with aspirin (synergistic action), for angioplasty and stenting surgery § To prevent secondary strokes and in unstable angina § Severe neutropenia – 1% of patients Clopidogrel (PLAVIX) § Similar to ticlopidine and used same way § Less incidence of neutropenia or thrombocytopenia § Used in combination with aspirin

Blood coagulation cascade See the figure in textbook Brenner’s Factor IIa

Activated partial thromboplastin time (a. PTT) & prothrombin time (PT) Blood clots in 4 -8 min in a glass tube Chelation of ca 2+ prevents clotting Recalcified plasma clots in 2 -4 min Addition of negatively charged phospholipids and kaolin (aluminium silicate) shortens clotting time to 26 -33 sec – a. PTT § Addition of ‘thromboplastin’ (a saline extract of brain – tissue factor and phospholipids) shortens clotting time to 12 -14 sec – prothrombin time (PT) § §

Anticoagulants - Heparin § Heparin is a glycoasminoglycan – alternating glucuronic acid and N-acetyl-D-glucosamine residues – sulfate and acetyl groups. Avg mol. wt - 12, 000 daltons § Heparin is negatively charged Heparin HEPALEAN

Heparin – Source and function § Heparin - originally isolated from the liver § Found in mast cells -storage of histamine & proteases § Rapidly destroyed by macrophages § Normally not detected in the blood § Heparan sulfate - similar to heparin but less polymerized - contains fewer sulfate groups § Found on the surface of endothelial cells and in the extracellular matrix § Interacts with circulating antithrombin to provide a natural antithrombotic mechanism

Heparin & LMW Heparins difference in action Heparin ~ 45 saccaharide units MW ~ 13, 500 This reaction goes 1000 to 3000 times faster with heparin. Antithrombin inhibits thrombin, Xa, IXa and to a lesser extent VIIa Low Mol. Wt. Heparin ~ 15 saccaharide units MW ~ 4, 500 circulates in the plasma rapidly inhibits thrombin only in the presence of heparin

Heparin – Toxicity - Hemorrhage § Hemorrhage – recent surgery, trauma, peptic ulcer disease, platelet dysfunction § Life-threatening bleeding can be reversed by protamine sulfate - 1 mg of protamine sulfate for every 100 U of heparin - slow iv infusion – 50 mg over 10 min) § Protamine sulfate interacts with platelets, fibrinogen, and other clotting factors - an anticoagulant effect – at higher doses § Anaphylactic reactions to protamine (a basic protein isolated from Salmon sperm)

Heparin-induced Thrombocytopenia § 50% decrease in platelet count - <150, 000/μl) § Antibodies against complexes of heparin with platelet factor 4 § In 3 -5% of patients 5 to 10 days after initiation of heparin therapy § Lower incidence with low mol wt heparin § In 1/3 of pts is preceded by thrombosis § Can be life-threatening § Stop heparin immediately § Alternative anticoagulants – lepirudin or danaparoid

Low Molecular Weight Heparins § Avg mol. wt 4, 500 daltons - 15 monosaccharide units § Better absorbed - higher bioavailability § Longer biological half-life § More predictable dose-response - does not bind to plasma proteins, macrophages, or endothelial cells § Can be given s. c. without lab monitoring in an outpatient setting § Cleared unchanged by kidney (do not use in renal failure!) rather than by the reticuloendothelial system § Lower risks of thrombocytopenia and bleeding § Safety and use during pregnancy not evaluated

LMW heparins § Dalteparin (FRAGMIN) § Enoxaparin (LOVENOX) Uses: 1. prevention of venous thromboembolism 2. Treatment of venous thrombosis, pulmonary embolism and unstable angina 3. prophylaxis following total knee arthroplasty

Other parenteral anticoagulants Danaparoid (ORGARAN) § nonheparin glycosaminoglycans (84% heparan sulfate) § Promotes inhibition of Xa by antithrombin § Prophylaxis of deep vein thrombosis § In patients with heparin-induced thrombocytopenia Lepirudin (REFLUDAN) § recombinant derivative of hirudin (a direct thrombin inhibitor in leech) § In patients with heparin-induced thrombocytopenia

Action of Coumarins Oral anticoagulants – 4 -hydroxycoumarins Gamma glutamic acid residues of clotting factors must be carboxylated for enzyme activity factors II, VII, IX, X, Prots C and S Vitamin K Vit. K epoxide Coumarins reductase Coumarins are act here competitive inhibitors

Warfarin COUMADIN Coumarins (warfarin) • inhibits vitamin K reduction • efficacy measured by INR (International Normalized Ratio), the patient’s PT divided by the PT in pooled plasma • takes 4 -5 days to become effective – active carboxylated factors in plasma need to be cleared • small Vd, steep D-R curve, metabolized by CYP 1 A and CYP 2 C 9 (interactions) • Warfarin crosses placenta – is teratogenic – birth defects and abortion • major indications: DVT, PE and atrial fibrillation

Warfarin – drug & other interactions § Any substance or condition is dangerous if it alters: 1. the uptake or metabolism of oral anticoagulant or vitamin K 2. the synthesis function or clearance of any factor or cell involved in hemostasis or fibrinolysis 3. the integrity of any epithelial surface

Warfarin - Clinical uses § Prevent acute deep vein thrombosis or pulmonary embolism § Prevent venous throboembolism in patients undergoing orthopedic or gynecological surgery § Prevent systemic embolization in patients with myocardial infarction, prosthetic heart valves or chronic atrial fibrillation Warfarin - Antidote §Vitamin K (oral or parenteral) INR = (PTpt / PTref)ISI Target 2. 0 to 3. 0

Fibrinolytic process Streptokinase binds here – generalized action t-PA has to bind here – localized ation

Efficacy of thromobolytics 1. 8% have serious bleeding; 0. 7% have IC haemorrhage

Streptokinase (STREPTASE) § Binds plasminogen- coverts to plasmin § Dissolve clots after myocardial infarction, deep vein thrombosis, massive pulmonary emboli § Side effects: Bleeding, allergic reactions, hypotension, fever. Tissue plasminogen activator (t-PA) – (alteplase, ACTIVASE) § activates fibrin bound plasminogen (less systemic plasmin formation) § More expensive than streptokinase

Summary • we have lots of drugs that affect hemostasis • they can inhibit platelet function, fibrin formation, or fibrinolysis. • using combinations prevents more clots, but causes more bleeding. • look at the risk/benefit ratio.

Anemia § a reduction in the hemoglobin, hematocrit ( % of whole blood that is comprised of red blood cells) or red cell number § Erythropoiesis - Pluripotent stem cells differentiate under the influence of growth factors (erythropoietin) to form erythrocytes § controlled by a feedback system in the kidney - responds to changes in oxygen delivery - secretes erythropoietin (a glycoprotein) from peritubular interstitial cells - stimulates the marrow cells § Feedback - disrupted by kidney disease, marrow damage or a deficiency in iron or an essential vitamin.

Anemia § Iron deficiency is the most common cause of anemia § Results in microcytic hypochromic anemia § Iron deficiency also affects iron-dependent enzymes such as cytochromes, catalase, peroxidase, xanthine oxidase and mitochondrial enzyme α-glycerophosphate oxidase § Iron deficiency has also been associated with learning problems in children

Iron in the body mg/kg of body weight Essential iron Male Female Hemoglobin 31 28 Myoglobin 6 and enzymes Storage iron 13 5 Total 37 50 4

Treatment of Iron Deficiency § The ability of the patient to tolerate and absorb medicinal iron is important § Gastrointestinal tolerance to oral iron is limited § Mainly absorbed only in the upper small intestinal (delayed-release preparations ? ) Parenteral iron Iron dextran injection (INFED, DEXFERRUM) § Acute hypersensitivity, including anaphylactic reactions, can occur in from 0. 2% to 3% of patients. § Iv is preferred – more reliable response § Im route – more local side effects – skin discoloration, long-term discomfort, concern about malignant change at injection site

Megaloblastic (macrocytic) anemias § Due to lack of folic acid or vitamin B 12 § Deficiency more common in older adults § Folate – food fortification – masks cobalamin deficiency (neurologic damage) § In pregnancy - prevention of folate deficiency and permanent neural tube defects in children minimized

Folate and Vitamin B 12 Interaction § Tetrahydrofolate is necessary for DNA synthesis § Cobalamin and folate are cofactors for tetrahydrofolate production § Deficiency of either impairs cell division in the bone marrow while RNA and protein synthesis continues – enlarged erythrocytes § Cobalamin deficiency – impairs synthesis of S -adenosylmethionine – necessary for proper nervous system functioning

Pernicious anemia § Lack of intrinsic factor – Vit. B 12 not absorbed § Injury to parietal cells or autoantibodies § Vitamin B 12 - must be administered– is not synthesized in body Treating deficiencies § Distinguishing B 12 deficiency from folic acid deficiency § Folic acid will supply folate needed for DNA synthesis § Anemia corrected § It DOES NOT correct the lack of methionine and succinyl Co-A synthesis – this will cause neurological deficits

Folic acid therapy § Rule out underlying cobalamin deficiency Folinic acid (leucovorin calcium, citrovorum factor) – 5 -formyl derivative of tetrahydrofolic acid § To circumvent the inhibition of dihydrofolate reductase as a part of highdose methotrexate therapy § To counteract the toxicity of folate antagonists such as pyrimethamine or trimethoprim § More expensive