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

2. Causes of death in Canada
1997: 661 deaths/100,000
cancer
heart disease
other
lung
stroke
injuries
liver
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. Coagulation cascade – platelet activation and coagulation
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)
Recanalization fibrinolysis

5. disruption of endothelium
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. (prevents breakdown by phosphodiesterase)
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 ( 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. Ticlopidine (TICLID)- is a prodrug
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 sec – aPTT
Addition of ‘thromboplastin’ (a saline extract of brain – tissue factor and phospholipids) shortens clotting time to 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)

20. 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
Action of Coumarins
Vit.K epoxide
reductase
Coumarins act here
Coumarins are competitive inhibitors

21. inhibits vitamin K reduction
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. Tissue plasminogen activator (t-PA) – (alteplase, ACTIVASE)
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 mg/kg of body weight Male Female Hemoglobin 31 28
Myoglobin and enzymes 6 5
Storage iron 13 4
Total 50 37
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. Treating deficiencies
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