Pharmacology 301.6 Module 6

1. Pharmacology 301.6Module 6 DRUGS & BLOOD Anticoagulants, anti-platelet & fibrinolytics Treatment of anemia

2. Causes of death in Canada 1997: 661 deaths/100,000 http://www.statcan.ca/english/Pgdb/health30b.htm stroke liver cancer injuries lung other heart disease Heart disease and stroke = 1 of 3 deaths, due to clotting

3. 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

4. The Hemostatic System Accidental injury vs. pathological injury hypercholesterolemia, diabets, hypertension Coagulation cascade – platelet activation and coagulation vasospasm platelets (5HT, TXA2) platelet plug adhesion, activation, aggregation fibrin plug extrinsic, intrinsic (humoral) Recanalizationfibrinolysis

5. Platelet function disruption of endothelium agonist binding platelet adhesion • thrombin • serotonin • ADP • TXA2 platelet activation platelet release platelet aggregation

6. Platelet adhesion and aggregation Platelet activation

7. Antiplatelet drugs Arachidonic acid Aspirin Thromboxane (from activated platelets) Clopidogrel ticlopidine ADP stimulates inhibit P2Y receptor TXA2 recep clotting Lowers cAMP Ca2+ Increased cAMP clotting Prevents clotting Dipyridamole (prevents breakdown by phosphodiesterase) GpIIb-IIIa Receptor for fibrinogen and platelet adhesion Eptifibatide Abciximab Tirofiban

8. Aspirin efficacy How does it work? 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.

9. 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

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

11. Activated partial thromboplastin time (aPTT) & prothrombin time (PT) • Blood clots in 4-8 min in a glass tube • Chelation of ca2+ 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 – aPTT • Addition of ‘thromboplastin’ (a saline extract of brain – tissue factor and phospholipids) shortens clotting time to 12-14 sec – prothrombin time (PT)

12. 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

13. 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

14. Heparin & LMW Heparins difference in action circulates in the plasma - rapidly inhibits thrombin only in the presence of heparin 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

15. 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)

16. 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

17. 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

18. 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

19. 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

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

21. 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 CYP1A and CYP2C9 (interactions) • Warfarin crosses placenta – is teratogenic – birth defects and abortion • major indications: DVT, PE and atrial fibrillation

22. 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

23. 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

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

25. Efficacy of thromobolytics 1.8% have serious bleeding; 0.7% have IC haemorrhage

26. 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

27. 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.

28. 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.

29. 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

30. Iron in the body Essential iron

31. 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

32. Megaloblastic (macrocytic) anemias • Due to lack of folic acid or vitamin B12 • 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

33. Folate and Vitamin B12 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

34. Pernicious anemia • Lack of intrinsic factor – Vit. B12 not absorbed • Injury to parietal cells or autoantibodies • Vitamin B12 - must be administered– is not synthesized in body Treating deficiencies • Distinguishing B12 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

35. 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 high-dose methotrexate therapy • To counteract the toxicity of folate antagonists such as pyrimethamine or trimethoprim • More expensive