2. Hemostasis Overview
• Definition
- Heme = blood
- stasis = to halt
• Hemostasis is the process of forming clots in
the wall of damaged blood vessels &
preventing blood loss, while maintaining blood
in a fluid state within the vascular system.
• It can be said to involve the spontaneous arrest
of bleeding by a physiological process.
4. 5
I-Vascular spasm
• Vascular spasm reduces flow of blood
from the injured vessel.
Cause:
1 Sympathetic reflex
2 Release of vasoconstrictors (TXA2
and serotonin) from platelets that
adhere to the walls of damaged
vessels.
7. 17
Mechanism of platelet plug formation contd
* Platelet adhesion: When a blood vessel
wall is injured, platelets adhere to the
exposed collagen and von Willebrand
factor in the wall via platelet receptors →
Platelet activation.
*Activated platelets release the contents of
their granules including ADP and secrete TXA2
→ activates nearby platelets to produce further
accumulation of more platelets (platelet
aggregation) and form a platelet plug.
12. 21
Blood Coagulation (clotting)
• The clotting mechanism involves a cascade of
reactions in which clotting factors are
activated.
• Most of them are plasma proteins synthesized by
the liver (vitamin K is needed for the synthesis of
factor II, VII, IX and X).
• The clotting factors are always present in the
plasma in an inactive form.
• When activated, they act as proteolytic enzymes
which activate other inactive enzymes.
• Several of these steps require Ca2+ and platelet
phospholipid.
13. Cascade of Reactions
• The “Cascade of reactions” states
that ‘inactive’ enzymes are activated,
and the ‘activated’ enzymes in turn
activate other inactive enzymes until
final step is reached.
14. 27
Intrinsic pathway
• The initial reaction is the conversion of
inactive factor XII to active factor XIIa.
• Factor XII is activated invitro by exposing
blood to foreign surface (glass test
tube).
• Activation invivo occurs when blood is
exposed to collagen fibers underlying
the endothelium in the blood vessels.
16. 29
Extrinsic pathway
• Requires contact with tissue factors
external to blood.
• This occurs when there is trauma to the
vascular wall and surrounding tissues.
• The extrinsic system is triggered by the
release of tissue factor (thromboplastin)
from damaged tissue, that activates
factor VII.
• The tissue thromboplastin and factor VII
activate factor X.
18. Enzyme Cascade Sequence
Stage 1: Formation of prothrombin activator
Stage 2: Conversion of prothrombin into
thrombin
Stage 3: Conversion of fibrinogen into fibrin
21. Factor X can be activated by
reactions in either the Intrinsic
or extrinsic system
26
22. Definition
• An anticoagulant is a substance that prevents
coagulation or clotting of blood but does not dissolve
an already formed clot.
•Uses
• Storage of blood for blood transfusion or
hematological testing
• Therapeutic purposes
23. Number and/or name Function
I (fibrinogen) Forms clot (fibrin)
II (prothrombin) Its active form (IIa) activates I, V, VII, VIII,
XI, XIII, protein C, platelets
Tissue factor(formerly known as
factor III)
Co-factor of VIIa
Calcium(formerly known as factor IV) Required for coagulation factors to bind
to phospholipid
V (proaccelerin, labile factor) Co-factor of X with which it forms the
prothrombinase complex
VI Unassigned – old name of Factor Va
24. VII (stable factor, proconvertin) Activates IX, X
VIII (Antihemophilic factor A) Co-factor of IX with which it
forms the tenase complex
IX (Antihemophilic factor B or
Christmas factor)
Activates X: forms tenase
complex with factor VIII
X (Stuart-Prower factor) Activates II: forms
prothrombinase complex with
factor V
XI (plasma thromboplastin
antecedent)
Activates IX
XII (Hageman factor) Activates factor XI, VII and
prekallikrein
XIII (fibrin-stabilizing factor) Crosslinks fibrin
25. AvailableAnticoagulants
Usedin vivo:
1. Parenteralanticoagulants:
a. Indirect thrombin inhibitors: Heparin, Low molecular
weightheparin, Fondaparinux, Danaparoid
b. Direct thrombin inhibitors: Lepirudin,Bivalirudin
2.Oralanticoagulants:
a. Coumarin Derivative: Bishydroxycoumarin (dicumarol),
Warfarin sodium, Acenocoumarol
b. Inandione derivatives:Phenindione
c. Direct factor Xa inhibitors:
Rivaroxaban
26. Anticoagulants contd..
Used in vitro:
a. Heparin: (150 U in 100 ml of blood)
b. Calcium complexing agents: Sodium citrate
1.65 gm for 350 ml of blood – acid citrate
dextrose solution – 75 ml in one unit of blood
c. For investigation: Sodium oxalate (10 mg for 1
ml blood and Sodium edetate – 2 mg for 1 ml of
blood)
27. HeparinasPrototype
Endogenous - strongestorganicacidpresent in the Body
P r e s e n t in mastcells(MW –75,000)–lungs,liver and
ntestinal mucosa
Commercially - from OxlungandPigmucosa
(slaughterhouse)
Chemically, non-uniform mixture of straight
chain mucopolysaccharideswith MW 10,000to
20,000
Car r ies strong electro-negativecharges
T y p e s - (i) Regularor unfractionated (UFH)Heparin(MW
5000to 30,000)–IVor SCand(ii) LMWH(MW 2000to 6000)
–mostlySC
28. Heparin
• Heparin is a naturally-occurring anticoagulant
produced by basophils and mast cells.
• Heparin acts as an anticoagulant, preventing
the formation of clots.
• While heparin does not break down clots
that have already formed (unlike tissue
plasminogen activator), it allows the body's
natural clot to lysis
29. Heparin contd..
• Mechanism of action:
Heparin binds to anti thrombin,
inhibiting interaction of various clotting
factors i.e. Xa, IX a, XIa, XIIa & plasmin.
31. LowMolecular
WeightHeparin
(LMWH)
•
•
MW :2000to6000
MOA:Actsonly byinterfering with Xa–
inducing conformational changein ATIII–
smallereffect onaPTT–whole blood
clotting time
–
–
–
– Lesserantipatelet actionand lower
incidenceof haemorrhagiccomplications
Better Bioavailability onSCadministration
(oncedailydosing)
Better half life (4-6Hrs)
Laboratorymonitoring not needed(aPTT
andclotting time affectedlittle)
• Uses:(1)Prophylaxisof DVTandPulmonary
embolismin Surgery,strokeand immobilized
patients(2)DVT(3)UAandMI
(4)RHDandAF(5)Haemodialysispatients
Interfered PT aPTT
IP N P
EP P N
CP P P
32. Dosageof Heparin
Unitage:Expressedin units asit isstandardizedby
bioassay– variable molecularsize
1mg=120-140Uactivity
Administered asIVbolus5000-10,000u followed by1000
u/hr IVdrip
– Pretreatment aPTTvalue and followed by 1.5 to
2.5 timesduring therapy
Alternate: 10,000-20,000deepSCevery8Hrs (fine
needle)
Or,LowdoseSC–5000SC8-12Hrsbefore andafter
surgery to preventDVT
ProtamineSulfate:Heparinantagonist –givenIV
(1mg= 100U)–cardiac andvascularsurgery
34. Warfarin
•In vivo not invitro
MOA: Competitive antagonist of
Vit.K – lowers the plasma level of
vit. Kdependent clottingfactors
– Inhibits VKOR needed to
generate activeVit.K
•Synthesisof clotting factors
diminishes within few hours-at
different times by different
factors
•But anticoagulantaction starts
in 1-3daysonly
•Commercially, mixture of R and
Senantiomers
35. Warfarin –contd.
• Kinetics:Completelyabsorbedfrom intestine
and 99% plasma protein bound –only 1%free
(many drugscandisplace(sulfonamides,
phenytoin – toxicity) –half life 36hrs.
• Dosing:Risky–calculate risk-benefit ratio
– Doseisindividualized by repeated
measurement of PT
– Optimum ratio of PT: 2-2.5 in prophylaxis of
DVT,2-3 in DVTtreatment and3-3.5in MI
etc.
• Uses:DVT,Pulmonaryembolismandatrial
fibrillation (drugof choice–3-4wksbefore
and after conversion)
36. Warfarin contd..
• ADRs:Bleeding–epistaxis,haematuria, bleeding GIT
Intracranial haemorrhage
– Minor bleeding–Vit K(takeslong)
– Freshblood transfusion or bloodfactors
– Other ADRs:Alopecia, dermatitis anddiarrhoea
etc.
• Contraindications:Sameasheparin
– Foetalwarfarin syndrome:skeletal
abnormality– hypoplasia of nose,eye
socket,handbonesand growthretardation
40. Fibrinolytic system
• The process of dissolution of clot is called
fibrinolysis (also called thrombolysis)
Plasminogen
t-PA
Endothelial
cells
Plasmin
fibrin Fibrin degraded
products
41. Fibrinolysis (Thrombolysis)
Plasminogen, an inactive precursor is
converted to plasmin by cleavage of a
single peptide bond.
Plasmin is a relatively non-specific
protease that digests fibrin clots and
other plasma proteins, including
several coagulationfactors. 41
44. Fibrinolytic drugs catalyze the conversion
of precursor plasminogen into active
plasmin
Plasmin is an endogenous fibrinolytic
enzyme that degrades clots by splitting
fibrin into fragments
It rapidlylysesor breaksdownthrombi 44
45. Thrombolytics (Fibrinolytics)
• They lyse the thrombi/clot to
recanalize the occluded blood vessel
(mainly coronary artery)
• They work by activating the fibrinolytic
system (produce more plasmin to
dissolve the fibrin thread)
• Examples: Streptokinase, Urokinase,
Alteplase (t- PA ), Reteplase (analogue
of alteplase),, Tenecteplase
46. Streptokinase
• Obtained from β-hemolytic streptococci
• Binds with circulating plasminogen to
form complex that activates
plasminogen to plasmin
• t ½ = 30-80 min
• Antigenic, Pyrogenic
• Destroyed by circulating
antistreptococcal antibodies
• Hypotension & arrhythmia can occur
47. Streptokinase contd..
Uses
• In acute myocardial infarction
–adminstered intravenously over 1 hr period
•In deep vein thrombosis , pulmonary embolism
•Adverse effects
• Bleeding, hypotension, allergic reactions, fever,
arrhythmias
Contraindications
• Recent trauma, surgery, abortion, stroke, severe
hypertension, peptic ulcer, bleeding disorders
48. Urokinase
• Enzyme isolated from human urine, now
prepared from cultured human kidney
cells
• Direct plasminogen activator
• t ½ = 10 to 15 min
• Fever can occur but hypotension rare
• Indicated in patients in whom
streptokinase has been for an earlier
episode
49. Alteplase
• recombinant tissue Plasminogen Activator (rt-
PA)
• Selectively activates plasminogen bound to
fibrin
• Non-antigenic, not destroyed by antibodies
• Rapid acting, more potent
• Superior in dissolving old clots
• Short half life: 4-8 min
• Nausea, mild hypotension, fever may occur
• Expensive
50. • Reteplase:
–Modified rt-PA
–Longer half life 15 -20 min, but less specific for
fibrin bound plasminogen
• Tenecteplase:
–Genetically engineered mutant form of alteplase
–fibrin-specific tissue-plasminogen activator
–longer half life =2 hrs
–Single bolus dose 0.5 mg/kg sufficient
–Very expensive
Newer recombinant tissue
Plasminogen Activators
52. ANTIFIBRINOLYTICS
•1.Epsilon amino-caproic acid
(EACA)
•MOA: Inhibits plasminogen activation
and thus prevents clot dissolution
•EACA: Is a specific antidote for fibrinolytic
agents; it also has adjunctive value in other
conditions
•2.Tranexamicacid:More potent thanEACA
–Uses: Bypass surgery, Menorrhagia,
Recurrent epistaxis, tonsillectomy &
tooth extraction (haemophiliacs)
ANTI-FIBRINOLYTICS
54. Antiplatelet Drugs (Antithrombotic
drugs)
•These are drugs which interfere with
platelet function and are used in
prophylaxis of thromboembolic disorders.
•Examples of antiplatelet drugs include:
Aspirin, Dipyridamole, Ticlodipine,
Clopidogrel and Prasugrel
57. Aspirin Contd…
–Irreversibly Inhibits COX1 and TXsynthase
–Suppresses ThromboxaneA2 (generated
by platelets) in low doses(75-150 mg) –
leadingtoprolonged bleedingtime
–SuppressesCOX-1and decreasesPGI2
synthesis in vesselwall
–Alsoinhibits release of ADPfrom
platelets and their sticking toeach other
Aspirin contd…
58. Dipyridamole
• Dipyridamole is a coronary
vasodilator and a relatively weak
antiplatelet drug
• Mechanism of Action
–Potentiates effect of endogenous
prostacycline
• Dose = 100 mg BD/TDS
• used with aspirin to prevent ischemic
stroke in patients of TIA
59. Ticlodipine & clopidogrel
• ADP antagonists, inhibit binding of ADP to its
receptors irreversibly
• Also Inhibit fibrinogen induced platelet
aggregation without modifying GPIIb/IIIa
• Synergistic action with aspirin
• Both are prodrugs and have long duration
of antiplatelet effect
• Clopidogrel, a congener of ticlodipine, is safer
and better tolerated
60. Ticlodipine Vs Clopidogrel
Ticlodipine
• Adverse effects:
– Diarrrhoea, vomiting, abdominal pain
– Headache, tinnitus, skin rash
– Bleeding, neutropenia,
thrombocytopenia
•dose= 250 mg BD
Clopidogrel
• Adverse effects
– Bleeding most IMP
– Less bone marrow toxicity
– Diarrhoea, epigastric pain, rashes
• Dose = 75 mg OD
61. Antithrombotics –OtherDrugs
• A. Prasugrel: Faster and potent P2Y12
(P2YAC) purinergic receptors Blocker
• B. Newer Drugs: Glycoprotein (GP) IIb/IIIa
receptor antagonists: Abciximab, Ebtifibatide
and Tirofiban
– Newer class of drugs
– Block (antagonize) the key receptor,
GP IIb/IIIa receptor, involved in
platelet aggregation
– Collagens, thrombin, TXA2 and ADP etc
act through GP IIb/IIIa receptor
62. Abciximab
• Abciximab is a glycoprotein IIb/IIIa receptor
antagonist
• It is a platelet aggregation inhibitor mainly
used during and after coronary procedures
like angioplasty
• It is administered along with aspirin &
heparin or LMW heparin
• Most common adverse effect is bleeding
• May cause thrombocytopenia,
hypotension, bradycardia
• Non antigenic
