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Coagulation cascade
After injury to a vessel wall, tissue factor is exposed on
the surface of the damaged endothelium.
The interaction of tissue factor with plasma factor VII
activates the coagulation cascade, producing thrombin by
stepwise activation of a series of proenzymes
The coagulation cascade is regulated by natural
anticoagulants, such as tissue factor pathway inhibitor
TFPI, the protein C and protein S system, and
antithrombin, all of which help to restrict the formation
of the hemostatic plug to the site of injury.
Effects of thrombin
converts soluble fibrinogen to fibrinactivates factors V, VIII, and XI, which generates more
thrombin
stimulates platelets
by activating factor XIII, thrombin favours the
formation of cross-linked bonds among the fibrin
molecules, stabilizing the clot
Activated platelets
An activated platelet exposes surface
receptors for specific clotting factors,
such as factor Va, and anionic
phospholipids that function as binding
sites for factor Xa.
An analogous system exists for
binding factor IXa.
Endogenous inhibitors of coagulation
antithrombin III
from a family of serine protease
inhibitors (serpins)
glycose aminoglycans (GAGs)
highly sulphated sugars bind to
antithrombin by ionic interaction
associated with surfaces of endothelial
cells and subendothelial structures
smaller heparin molecules inhibit Xa
more effectively
tissue factor pathway inhibitor
(TFPI)
inhibits Xa by forming a complex that
can also inhibit VIIa bound to TF, but
not free VII
important for blocking the effect of TF
where it is expressed on endothelial
cells and subendothelial structures
proteins C and Sthrombin in conjunction withthrombomodulin, activates protein CProtein C proteolytically cleaves VIIIa
and Va (major cofactors that helpproduce Xa and IIa), with protein Sacting as cofactorin septic patients, activated protein C(available as a recombinant product)inhibit DIVC that occurs in smallvesselsprotein C may down-regulateinflammatory cytokines
thrombomodulin
a constituent of the endothelial cell
membrane, very small amounts arepresent in blood
binds thrombin and begins the
sequence of protein C activation
functions as cell-based
inhibition of coagulation
probably facilitates thrombin
catabolism
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Thrombus formation at the site of damaged vessels
Platelet factors
platelet factor 1: coagulation factor V
platelet factor 2: thromboplastic material
platelet factor 3: platelet thromboplastin
platelet factor 4: antiheparin factor
platelet factor 5: fibrinogen coagulation factor
platelet factor 6: antifibrinolytic factor
platelet factor 7: platelet cothromboplastin
Platelet membrane glycoproteins
GP Ia: receptor for subendothelium
GP Ib: receptor for von Willebrand
GP IIb: receptor for von Willebrand, fibrinogen
GP IIIa: receptor for von Willebrand, fibrinogen
Prothrombin time
monitoring of extrinsic coagulation pathway
normal range between 9 to 15 seconds
"normal" varies according to batch of thromboplastin in
test reagent in different laboratories, hence the use ofInternational Normalised Ratio (INR)
for a person on full anticoagulant therapy, the PT should
be 2 to 3 times the laboratory "control" value (INR of 2-
3)
prolonged PT (more than 3 times control value)
bile duct obstruction
cirrhosis
disseminated intravascular coagulation
hepatitis
malabsorption
warfarin therapy
> 10% deficiency in any of the following
Vitamin K, VII, X, II, V, I
Partial thromboplastin time
monitoring of intrinsic and common coagulation
pathways
partial thromboplastin time (PTT):3045 s
activated partial thromboplastin time (APTT):2539 s
value will vary between laboratories
patients receiving anticoagulant therapy usually will
have value within 1.5 to 2.5 times control values
not valid for patients on low molecular weight heparin
therapy (anti Xa heparin assay)
prolonged PTT may indicate
cirrhosis
disseminated intravascular coagulation (DIC)
factor XII deficiency
hemophilia A (factor VIII deficiency)
hemophilia B (factor IX deficiency)
hypofibrinogenemia
malabsorption (inadequate absorption of
nutrients from the intestinal tract)
von Willebrand's disease
lupus anticoagulant
decreased aPTT can occur due to:digitalis
tetracyclines
antihistamines
nicotine
elevated factor VIII
tissue inflammation or trauma
Fibrinolytic system
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DRUGS USED IN COAGULATION DISORDERS
ANTICOAGULANTS
Heparina heterogeneous groupa member of the heparan sulphate family of complexsugars classified under glycosaminoglycans
glycosaminoglycans or mucopolysaccharides
are polymers of repeating disaccharideswithin the disaccharides, the sugars
tend to be modified, with acidic
groups, amino groups, sulfated
hydroxyl and amino groups
tend to be negatively charged, because
of the prevalence of acidic groups
heparan sulphate family of complex sugars is
composed of long chains of alternating
disaccharide units of uronic acid (glucuronic
and iduronic acid) and glucosamine residues
the backbone structure is thendecorated by with complex patterns of
sulphate and carboxyl groups at various
positions, giving rise to a very strongly
negative charged molecule.
strongly acidic because of its content of covalently
linked sulfate and carboxylic acid groups (heparin
sodium)
has an extended helical conformation due to
charge repulsion by the many negatively
charged groups
naturally occurring in the secretory granules of mastcells
has no anticoagulation effect by itself
biologic activity is dependent upon the plasma protease
inhibitor, anti-thrombin III (AT III) (heparin cofactor)
a specific pentasaccharide sequence containing a 3-O-
sulphated glucosamine residue forms a high-affinity
binding site for AT III
AT III is one of the many naturally occurring
inhibitors in coagulation but its action is slow
small amounts of heparin (with AT III) inhibit
thrombosis by inactivating activated Factor X
(Xa) and inhibiting the conversion of
prothrombin to thrombin (II to IIa)
tight binding of heparin molecule to AT III
causes a conformational change in this inhibitor,
which exposes the active binding site of
antithrombin III for more rapid interaction with
the proteases (activated clotting factors) to
inhibit the enzymes
in the absence of heparin, formation of heparin-
antithrombin-protease complexes is slow, in the presence
of heparin, they are accelerated 1000-fold
heparin catalyses the antithrombin-protease reaction
without being consumed
once the antithrombin-protease complex is
formed, heparin is released intact for renewed
binding to more AT III
heparin-antithrombin III complex inactivates
serine esterases
factors XIIa, XIa, Xa, IXa, IIa
plasmin
kallilrein
only unbound Xa is sensitive to heparin activity
Xa bound to platelets in the prothrombinase
complex is protected from the heparin actiononce active thrombosis has developed, larger amounts of
heparin inhibit further coagulation by inactivating
thrombin (IIa) and preventing the conversion of
fibrinogen to fibrin (I to Ia)
decreased platelet aggregation
reduction of platelet membrane receptors for
von Willebrand factor and fibrinogen (Ia)
inhibition of VIIIa, Va
facilitating the release of tissue plasminogen
activator (tPA), resulting in an increase in
plasmin and D-dimer concentrations, both ofwhich interfere with platelet aggregation
increased platelet aggregation
binding of antiplatelet IgG antibodies to
platelet-bound heparin, activates platelets and
induces platelet clumping (heparin-induced
thrombocytopaenia, HIT)
inhibition of VIIa-TF complex
by releasing TFPI from endothelial cells, renal
cells, carcinoma cells and lipoprotein fraction of
plasma
TFPI also inhibits Xa on TF bearing cellreleases lipoprotein lipase from capillary endothelial
surfaces
the enzyme hydrolyzes triacylglycerols in
chylomicrons, very-low-density lipoproteins,
low-density lipoproteins, and diacylglycerols
inhibits growth of capillary endothelial cells but
potentiates the activity of acid fibroblasts growth factors
on these cells
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commercial preparations
consists of repeated sulphated mucopolysaccharides
D-glucosamine-L-iduronic acid, and
D-glucosamine-D-glucuronic acid
source
porcine intestinal mucosa (higher potency)
bovine lung
partial substitution of acidic protons of the sulfate units
by
Na+ (as heparin sodium)
Ca++ (as calcium heparin)
Li+ (as lithium heparin)
used in vitro as an anticoagulant for blood
samples
pH adjustment (between 5.0 and 7.5)
titrated with HCl or NaOH
standardization of activity
regular heparin consists of a family of
molecules of different molecular weights, the
correlation between the concentration of a given
heparin preparation and its effect on coagulationoften is low
therefore standardized as units of activity by
bioassay
heparin sodium must contain at least 120 USP
units per milligram
1 U stops 1 ml of citrated sheep plasma from
clotting for 1 hour after the addition of 0.2 ml of
1% calcium chloride
high molecular weight (HMW) fractions
with high affinity for AT III, markedly inhibit
blood coagulationfractions have a MW range of 5 000-30 000
low molecular weight (LMW) fractions
MW 1 000-10 000 (1-10kDa, mean 4.5 kDa)
less effect on antithrombin III
activity dependent on number of
monosaccharide units per molecule
< 8, no significant antithrombotic
activity
8-18, potentiate inhibition of factor Xa
>18, potentiate inhibition of both
factor Xa and thrombinisolated from standard heparin
by gel filtration chromatography
by differential precipitation with
ethanol
by partial depolymerization with
nitrous acid
by alkaline degradation of heparin
benzyl ester / beta elimination
degradation (enoxaparin Na)
by enzymatic degradation
compared with regular heparinincreased bioavailability after
subcutaneous administration
less frequent dosing requirements
units of reference
milligrams for enoxaparin
anti-factor Xa units for dalteparin and
danaproid
indications
prevention of deep venous thrombosis
after hip replacement surgery
treatment of acute deep vein
thrombosis
prophylaxis for ischaemic
complications in unstable angina and
non-Q-wave myocardial infarction
pharmacokinetics
absorption
not absorbed from the intestinal mucosa,
therefore administered parenterally (continuous
infusion, intermittent intravenous injection, deep
subcutaneous injection)
onset of action
after intravenous administration, immediate
after subcutaneous administration, delay of 1-2
hours
clearance
degraded primarily by reticuloendothelial
system, and heparinase
small amount of undegraded heparin appears in
urine
t
dose-dependent
100 U/kg, 1 hour
400 U/kg, 2.5 hours
800 U/kg, 5 hours
shortened in patients with pulmonary embolism
prolonged in patients with hepatic cirrhosis or
renal failure
LMW heparins have longer biological half-lives than do standard heparin
adverse effects
bleeding
monitor partial thromboplastin time (PTT)
elderly women and patients with renal failure
are more prone to haemorrhage
platelet dysfunction
thrombocytopenia (HIT)
platelet count of less than 50% of pretreatment
value or
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contraindications
hypersensitivity
active bleeding
haemophilia
thrombocytopaenia and history of HIT
purpura
severe hypertension
intracranial haemorrhage
infective endocarditis
active tuberculosis
ulcerative lesions of gastrointestinal tract
threatened abortion
visceral carcinoma
advance hepatic or renal disease
during or after surgery of brain, spinal cord, or eye
undergoing lumbar puncture or regional anaesthesia
blocks
administration and dosages
used in pregnant women only when clearly indicated
established venous thrombosis
maintain plasma concentration of 0.2 U/ml toprolong the PTT to INR 2-2.5
initial bolus injection of 5000-10000 U,
followed by infusion of 10-15 U/kg/h
with acute pulmonary embolism,
larger doses require during the first few
days because of increased heparin
clearance
intermittent administration, 75-100 U/kg every
4 hours
heparin resistance - causes
increased serum concentration of other (acute reactant)proteins that have affinity for heparin
fibroblast growth factors (FGFs)
vascular endothelial growth factor (VEGF)
heparin-binding EGF-like growth factor
hepatocyte growth factor (HGF)
transforming growth factor-beta (TGF-beta)
interferon-gamma (IFN-gamma)
platelet-derived growth factor (PDGF)
platelet factor-4 (PF-4)
interleukin-8 (IL-8)
macrophage inflammatory protein-1 (MIP-1)interferon-gamma inducible protein-10 (IP-10)
insulin-like growth factors I or II
fibronectin
laminin
histidine-rich glycoprotein vitronectin
increased concentration of factor VIII, a cofactor that
increases the proteolytic activity of IXa
congenital deficiency of AT III (concentration less than
50% of normal), may be precipitated by pregnancy,
infection or surgery
acquired deficiency of AT III (concentration less than25% of normal), may occur in patients with hepatic
cirrhosis, nephrotic syndrome, disseminated intravascular
coagulation
accelerated clearance of heparin, as may occur with
massive pulmonary embolism
reversal of heparinisation
discontinuation of the drug
protamine sulphate
highly basic peptide that combines with heparin
as an ion pair to form a stable complex devoid
of anticoagulant activity
for every 100 U of heparin remaining in the
patient, 1 mg of protamine sulphate is
administered intravenously
excess protamine has an anticoagulant effect
binds to platelets and fibrinogen
metabolized by N-carboxypeptidase
Enoxaparin
obtained by alkaline degradation of heparin benzyl ester
approximately one-third molecular size of standard
heparin
Fondaparinux sodium
synthetic and specific inhibitor of activated factor X
(Xa)
molecular weight is 1728
supplied as a clear and colorless liquid with a pH
between 5.0 and 8.0
mechanism of action
antithrombin III-mediated selective inhibition of factor
Xa, and potentiates (about 300 times) the innate
neutralization of factor Xa by AT III
does not inactivate thrombin and has no known effect on
platelet function
does not bind significantly to other plasma proteins
(including platelet factor 4) or red blood cellsabsorption
rapidly and completely absorbed after administration by
subcutaneous injection, bioavailability is 100%
distribution
in healthy adults, volume of distribution of 7-11 L
clearance
in healthy individuals up to 75 years of age, up to 77%
of a single subcutaneous or intravenous fondaparinux
dose is eliminated in urine as unchanged drug in 72 hours
25% lower in patients over 75 years of age
elimination half-life is 17-21 hourstotal clearance is approximately lower in patients with
renal impairment
drug interactions
concomitant use of oral anticoagulants (warfarin),
platelet inhibitors (acetylsalicylic acid), NSAIDs
(piroxicam) and digoxin did not significantly affect the
pharmacokinetics/pharmacodynamics of fondaparinux
sodium
does not influence the pharmacodynamics of warfarin,
acetylsalicylic acid, piroxicam, and digoxin, nor the
pharmacokinetics of digoxin at steady statedoes not bind significantly to plasma proteins other than
AT III, no drug interactions by protein-binding
displacement are expected
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Warfarin
oral anticoagulant introduced as rodenticide in 1948
Wisconsin Alumni Research Foundation - arin
discovery of anticoagulant substance formed in spoiled
sweet clover silage which produced a deficiency of
plasma prothrombin and haemorrhagic disease in cattle
toxic agent identified as bishydroxycoumarin
and synthesized as dicoumarol
structure
4-hydroxycoumarin residue, with a non-polar carbon
substituent at the 3-position, is the minimal structural
requirement for activity
this carbon is asymmetrical in warfarin
commercial preparations are racemic
mixture of 2 enantiomorphs
levorotatory S-warfarin
dextrorotatory R-warfarin
potency: S-warfarin > R-warfarin, 4:1
mechanism of action
warfarin prevents the -carboxylation of glutamate
residues in factors II, VII, IX, and Xby blocking the reduction of inactive vitamin K
epoxide (by vitamin K epoxide reductase) back
to its active hydroquinone form
results in incomplete molecules that are
biologically inactive in coagulation
role of vitamin K
post-ribosomal modification of factors II, VII, IX, and
X, and the endogenous anticoagulant protein C and S in
the liver
involves -carboxylation of glutamate residuesin them
the carboxyl-glutamyl residues are responsible for the
binding of Ca++ which are necessary for the binding of
the activated factors to phospholipid vesicles
this process is coupled with the oxidative deactivation of
vitamin K
in vitamin K deficiency, inactive precursors are
liberated
anticoagulant effects
8-12 hour delay in the action of warfarin, duration of
action 2-5 daysanticoagulant effect of warfarin results from a balance
between partially inhibited synthesis and degradation rate
of the 4 vitamin K-dependent clotting factors
t: 6 h (VII), 24 h (IX), 36 h (X), 50 h (II)
large initial doses of warfarin (0.75/kg) hasten the onset
of anticoagulation effect, beyond this dosage, the speed
of onset is independent of the dose size; only effect of a
large loading dose is the prolongation of t of the drug
pharmacokinetics
absorption
acidic, available as a sodium salt
rapid oral absorption, 100% bioavailability
decreased in malabsorption
detectable in plasma within 1 hour of oral
administration
peak plasma concentration in 2-8 hours
crosses placenta
distribution
99% of racemic warfarin bound to plasma
albumin, which may contribute to its
small Vd (the albumin space) 0.14L/kg
clearance
0.045 ml/kg/min
transformed by CYP 1A2, CYP2C9 into
inactive metabolite by the liver and kidney
long t of 25-60 hours in plasma,
prolonged with liver disease
excreted via urine and stool
adverse effects
crosses placenta readily
causing haemorrhagic disorder in the foetus
affecting -carboxyglutamate residues in foetal
bone and blood proteins and causing birth defect
characterised by bone malformation
cutaneous necrosis
sometimes occur during the first week of
therapy resulting from venous thrombosis
due to reduced activity of protein C
(endogenous anticoagulant)
rarely same process causes haemorrhagicinfarction of the breast, fatty tissues, intestine,
and extremities
administration and dosages
start with small daily dose of 5-10 mg, may be up to 40
mg; initial adjustment of prothrombin time takes about 1
week
maintenance dose of 5-7 mg/day, may be up to 15
mg/day
INR of 2.5-3.5 for patients with prosthetic heart valves
drug interactions
pharmacokinetic mechanismsincreasing or decreasing anticoagulant effect
and the risk of bleeding by
enzyme induction or inhibition
variation in plasma protein binding
increasing activity of warfarin
stereoselective inhibition of oxidative
metabolism of S-warfarin, resulting in
hypoprothrombinaemia
pyrazolones, phenylbutazone,
metronidazole, fluconazole,
trimethoprim-sulpha methoxazoleinhibition of metabolism of warfarin
amiodarone, disulfiram, cimetidine,
chloramphenicol
displacement of albumin-bound warfarin,
increasing the free fraction
pyrazolones, phenylbutazone,
sulfinpyrazone, NSAID, chloral
hydrate, mefenamic acid
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decreasing activity of warfarin
induction of hepatic enzymes that metabolise
warfarin
barbiturates, rifampicin, alcohol
reduction in absorption and bioavailability
cholestyramine binds warfarin in the
intestine
increased albumin binding
pharmacodynamic mechanisms
synergism(impaired haemostasis, reduced
clotting factor synthesis in hepatic disease,
heparin, NSAIDs)
competitive antagonism (vitamin K)
altered physiologic control loop for vitamin K
(hereditary resistance to oral anticoagulant
augmentation of anticoagulant effect
inhibition of platelet function
pyrazolones, phenylbutazone, aspirin
increasing turnover of clotting factors
liver disease, hyperthyroidism
inhibition of activity of VIIa, IXa, Xa, IIaheparin, (prolonging prothombin time)
vitamin K production
elimination of vitamin K producing
bacteria in gastrointestinal tract by
third generation cephalosporins
direct inhibition of vitamin K epoxide
reductase
third generation cephalosporins
reduction of anticoagulant effect
increase synthesis of clotting factors with
vitamin Kincrease supply of clotting factors with
transfusion of fresh frozen plasma
clotting factor concentration through
haemoconcentration with diuretics
hereditary resistance to warfarin via mutation
of vitamin K epoxide reductase
decreasing turnover rate of clotting factors
hypothyroidism
reversal of antocoagulant effects
disappearance of anticoagulant effect is due toreestablishment of normal activity of the
clotting factors
does not correlate with plasma concentration of
warfarin
depends on the degree of correction required
stopping warfarin alone with or without
large doses of vitamin K (phytonadione)
50 mg infusion
fresh frozen plasma
factor IX concentrates
whole blood transfusion
Direct thrombin inhibitor
bind directly to thrombin and block its interaction with
its substrates
recombinant hirudins, bivalirudin, and
ximelagatran
parenteral DTIs:
hirudin and argatroban for the treatment of
heparin-induced thrombocytopenia
bivalirudin as an alternative to heparin in
percutaneous coronary intervention, and
desirudin as prophylaxis against venous
thromboembolism in hip replacement
Hirudin
source
Hirudo medicinalis leeches,
powerful and specific thrombin inhibitor
recombinant DNA
mechanism of action
binds to active site of thrombin
can reach and inactivate fibrin-bound thrombin
little effects on platelets or bleeding time
administration
parenterally
monitored by partial thromboplastin time
Ximelagatran
first oral direct thrombin inhibitor to be introduced
a prodrug, its active metabolite is melagatran which
directly inhibits thrombin
ximelagatran developed to enhance bioavailability of
melagatran, the molecules of latter are charged and
become highly hydrophilic at intestinal pH, resulting in
low absorption
melagatran can also be given by injection
melagatran resembles a peptide sequence on
fibrinogens A- chain, where thrombin-inducedcleavage occurs
it binds reversibly to the active site of thrombin and
inhibits the normal function of thrombin, including both
free and clot-bound thrombin
the ability to bind clot-bound thrombin is an
advantage since clot-bound thrombin may retain
its enzymatic activity and continue to stimulate
the coagulation cascade
regulatory approval for ximelagatran in France for the
prevention of venous thromboembolic events in major
orthopaedic (hip or knee replacement) surgerydoes not have the same difficulties with dose adjustment
or drug interaction as warfarin does
no known antidote
pharmacokinetics
rapidly absorbed after oral administration, peak
concentration Cmax achieved 1 h after administration
has a rapid onset and offset of action and shows low
potential for food and drug interactions
oral bioavailability approximately 20%, compared with
3%-7% for melagatran
ximelagatran Vd 2.53L/kgpharmaokinetics of melagatran described as linear, first-
order, one compartment model
melagatran excreted unchanged via kidneys, t 3h
renal clearance rate
young 7.7L/h, elderly 5 L/h
affected in patients with severe renal
impairment, defined as creatinine
clearance rate of
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adverse effects
nausea, diarrhoea, headache
bleeding, but not worse than with enoxaparin or
dalteparin
raised hepatic ALT and bilirubin concentrations
contraindications
renal, and hepatic impairment
pregnancy
infant and children
precautions
lactating women
main properties and pharmacokinetic characteristics
FIBRINOLYTIC DRUGS
mode of action
rapid lysis of haemostatic thrombus and target
thromboemboli by catalysing the formation of serine
protease plasmin from its precursor zymogen
plasminogencan cause a generalized lytic state after
intravenous administration
(zymogen = inactive precursor of proteolytic
enzyme)
activation of free circulating plasminogen
streptokinase
urokinase
activation of fibrin bound plasminogen
anistreplase
alteplase
reteplasetissue plasminogen activator (t-PA)
indications
multiple pulmonary emboli that are massive enough to
require surgical intervention
central deep vein thrombosis of the superior venous
cava, iliofemoral veins
coronary thrombolysis after acute myocardial infarction
peripheral arterial disease
Streptokinase
exotoxin of-haemolytic streptococci
antigenic
forms a stable, noncovalent 1:1 complex with free
circulating plasminogen
produces a conformational change that exposes the
active site on plasminogen that cleaves arginine 560 on
free plasminogen molecules to form free plasmin
complex is not inhibited by 2-antiplasmin
not fibrin specific, readily induces a systemic lytic state
t 40-80 minutes
adverse effects
bleeding, allergic reactions, fever, anaphylaxis
Anistreplase
anisolyated plasminogen streptokinase
activator complex, APSAC
a complex of purified human plasminogen and
bacterial streptokinase
lys-plasminogen has been acylated at its
catalytic site to protect the enzymes active site
when administered, the acyl group
spontaneously hydrolyses, allows the
plasminogen-streptokinase complex to bind to
fibrin prior to activation,
this modification confers clot selectivity
advantages
allows for rapid intravenous injection
greater clot selectivity
Tissue plasminogen activator
preferentially activates plasminogen that is bound tofibrin, several hundredfold more rapidly than free
plasminogen in the circulation
theoretically confines fibrinolysis to the formed
thrombus and avoids systemic activation
binds to fibrin via lysine binding sites at its amino
terminus
metabolised by liver, t 5-10 minutes
produced by recombinant DNA technology
alteplase is unmodified t-PA
reteplase is t-PA from which several amino
acids have been deleted
Urokinase
human enzyme synthesized by kidney, therefore not
antigenic
directly converts free plasminogen to plasmin
lacks fibrin specificity, readily induces a systemic lytic
state
metabolised by liver, t of 15-20 minutes
Prourokinase
a zymogenic plasminogen activator, a precursor ofurokinase
binds to fibrin before activation
has selectivity for clots
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administration and dosages
streptokinase (US$_00)
intravenous infusion, loading dose 250 000 U
to overcome plasma antibodies directed against
the protein (from prior streptococcal infection),
followed by maintenance dose of 100 000
U/hour for 24-72 hours
follow with full heparinisation as plasminogen
is exhausted
can act as antigen, patients with antibodies to
streptokinase can develop fever, allergic
reactions, therapeutic resistance
urokinase (US$_000)
intravenous infusion, loading dose 1000 to
4500 U/kg over 10 minutes, followed by
maintenance dose of 4400 U/kg/hour for 12
hours
alteplase (t-PA) ($_000)
accelerated regime for coronary thrombolysis
intravenous infusion, loading dose 15 mg
followed by 0.75mg/kg over 30 minutes(maximum 50mg), followed by 0.5mg/kg
(maximum 35mg) over the following hour
reteplase ($_000)
administered as 2 intravenous bolus injections
of 10 U each separated by 30 minutes
anistreplase ($_000)
single intravenous bolus injection of 30 U over
3-5 minutes
ANTITHROMBOTIC DRUGS
prevention of vascular events among patients withtransient ischaemic attacks
complete strokes
angina pectoris
4 main groups
cyclo-oxygenase inhibitors: e.g. aspirin
increasing platelet cAMP:
by stimulation of adenylyl cyclase:
adenosine
by inhibition of phosphodiesterase:
dipyrimadole
ADP receptor antagonists: e.g. clopidogrelGP IIb,IIIa blockers: tirofiban, abciximab
target sites of antithrombotic drugs on the platelet
Cyclooxygenase inhibition
aspirin
inhibition of the synthesis of thromboxane A2
by irreversible, covalent acetylation of a serine
residue near the active site of cyclooxygenase
the anuclear platelet cannot synthesize new
proteins or enzymes during its 7-10-day life-
span
repeated doses produce a cumulative effect on
platelet function
maximally effective as an antithrombotic agent
at doses of 160mg to 320 mg/day
higher doses inhibit the production of
prostacyclin, an antithrombotic eicosanoid
produced by the endothelium
prolongs bleeding time
other NSAIDS
other salicylates and other nonsteroidal anti-
inflammatory drugs also inhibit cyclooxygenase
but have a shorter duration of inhibitory action
because they cannot acetylate cyclooxygenase,
therefore their action is reversible
Increasing platelet cAMP
following platelet activation, Ca++ is released from its
storage sites (platelet dense tubular systems) to the
platelet cytoplasm resulting in an increase of cytosolic
free Ca++
Ca++ mobilization is directly involved in
platelet activation and Ca++ is an important
second messenger for signal transduction in
plateletscAMP is another second messenger which opposes the
effect of Ca++by causing sequestration of cytosolic Ca++
to the Ca++ storage sites
agents which increase cAMP will suppress platelet
activation
stimulation of platelet adenylyl cyclase: action
of adenosine on platelet A2 receptor
inhibition of platelet phosphodiesterase:
dipyridamole
does not prolong bleeding time
only current recommendation is for
primary prophylaxis of thromboemboli
in patients with prosthetic heart valves,
and is given in combination with
warfarin
dipyridamole is metabolized in the
liver and has a terminal half-life of 10h
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ADP receptor antagonism
Ticlopidine
a thienopyridine derivative, interferes selectively with
ADP-induced transformation of GPIIb/IIIa complex
expression in activated platelets
it also inhibits platelet aggregation induced by thrombin,
collagen, arachidonic acid, platelet-activating factor,
prostaglandin endoperoxides, thromboxane A2-like
substance, serotonin, and epinephrine
pharmacokinetics
absorption
well absorbed after oral administration
effect within 48 hours
maximal effect after approximately 3 to 5 days
activity still present 72 hours after last dose
absorption decreased by concurrent antacid
therapy
metabolism
rapidly and extensively metabolised in liver
and excreted in urineone of its metabolite is active
half-life at steady state is 4-5 days
effects
prolongs bleeding time, maximum effect after several
days of treatment
antiplatelet activity persists for a week or longer after
treatment is discontinued
possibly due to action of active metabolite
act independent of aspirin with no effect on eicosanoid
metabolism
adverse effects
gastrointestinal (20%): nausea, dyspepsia, diarrhoea
haemorrhage (5%)
bone marrow suppression
leucopenia (1%): detected by regular
monitoring of white cell count during the first 3
months of therapy
thrombocytopenia
agranulocytosis
aplastic anaemiacholestatic jaundice
elevated serum cholesterol concentration
rashes
indications
prevention of thrombosis in cerebral vascular and
coronary artery disease
for patients who are unable to tolerate aspirin
Clopidogrel
analogue of ticlopidine, another ADP antagonist from
the thienopyridine group that inhibits ADP and thrombin-
induced platelet aggregation
a prodrug, activated by cytochrome P450 predominantly
by CYP3A4 (less by CYP3A5) to a metabolite that
inhibits ADP-induced platelet aggregation
by binding the ADP receptor the drug selectively
reduces the number of functional ADP receptors
mediating the inhibition of stimulated adenylate cyclase
inhibits the binding of fibrinogen to its platelet
receptor, the GPIIb/IIIa integrin
it does not modify the GPIIb/IIIa complex
after oral administration, clopidogrel is rapidly absorbed
and undergoes metabolic activation by CYP3A4 in the
liver
antiplatelet activity of clopidogrel can be inhibited by
the CYP3A4 substrates erythromycin, troleadomycin,
and HMG-CoA reductase inhibitors (atorvastatin,
cerivastatin, lovastatin, and simvastatin) and enhanced by
the CYP3A4 inducer rifampin
co-administration of HMG-CoA reductase
inhibitors will diminish the activation of
clopidogrel
the principal circulating metabolite is an inactive
carboxylic acid derivative
has an 8 hour elimination half-life, but the
pharmacologic half-life is relatively long and it takes 4 to
7 days of administration to reach a steady state effect on
platelets
side effects include thrombocytopenia, neutropenia
clopidogrel-induced platelet inhibition persists severaldays after withdrawal of the drug and diminishes in
proportion to platelet renewal
in comparison with ticlopidine, clopidogrel is more
potent, with less degree of neutropenia
clopidogrel is significantly more active than aspirin.
compared with aspirin, clopidogrel has less
severe gastrointestinal bleeding but more severe
rash incidence
Platelet GP IIb/IIIa receptor antagonism
mechanism of actionblocks platelet receptors for integrin and fibrinogen
adverse effects
bleeding
immunogenicity
thrombocytopenia
in approximately 0.1% to 0.5% of patients,
platelet count of
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free unbound abciximab undergoes rapid proteolytic
degradation, resulting in a 10- to 15-minute plasma half-
life
once bound to platelet receptors, resolution of
abciximab blockade is prolonged
50-60% residual inhibition remains 24 hours after
terminating the infusion
effective or biologic half-life for abciximab is estimated
to be > 12 to 24 hours
indications
used together with aspirin and heparin as adjuvant
therapy in patients undergoing high-risk angioplasty and
atherectomy
Integrelin
synthetic peptide with high affinity for the GP IIb/IIIa
integrin receptor protein
for prevention of thrombosis in percutaneous coronary
angioplasty
Eptifibatide and tirofiban
binds selectively to GP IIb/IIIa receptor
renally excreted, no active metabolites
half-life of 1.5 to 2.5 hours
rapidly dissociate from glycoprotein receptors, with
platelet aggregation returning to normal within 4 hours
after discontinuation of the drug
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Drugs used in bleeding disorders
correction of prothrombin activity: vitamin K
plasma fractions: factors VIII, IX, and I
fibrinolytic inhibitors: aminocaproic acid, tranexamic
acid
serine protease inhibitor: aprotinin
CORRECTION OF PROTHROMBIN ACTIVITY
Vitamin K
being lipid soluble, vitamin K1 and K2 require bile salts
for absorption from the intestinal tract
available as 5 mg tablet, or 50 mg ampoule
effect delayed for 6 hours, completed by 24 hours when
treating depression of prothrombin activity after warfarin
therapy or vitamin K deficiency
intravenous infusion must be slow, rapid infusion can
cause dyspnoea, chest and back pain, even death
indications
correction of prothrombin activity
after warfarin therapy
vitamin K deficiency in premature infants, inhospitalised patients in intensive care units
because of poor diet, parenteral nutrition, recent
surgery, multiple antibiotic therapy, uraemia
severe hepatic failure results in loss of protein synthesis
and a haemorrhagic diathesis that is unresponsive to
vitamin K
FIBRINOLYTIC INHIBITORS
target sites
Aminocaproic acid
chemically similar to lysine, is a synthetic inhibitor of
fibrinolysis
mechanism of action
binds to lysine residues on plasminogen and plasmin
competitively inhibits plasminogen activation
blocks binding of plasmin to fibrin
pharmacokinetics
rapidly absorbed orally
cleared from the body via the kidney, 50% excretedunchanged in the urine within 12 hours
indications
haemophilia
bleeding from fibrinolytic therapy
prophylaxis for rebleeding from intracranial aneurysms
postsurgical gastrointestinal bleeding
postprostatectomy bleeeding
adverse effects
intravascular thrombosis from inhibition of plasminogen
activator
hypotension
ureteral obstruction by clot formation in patients with
haematuria
myopathy and muscle necrosis
abdominal discomfort
diarrhoea
nasal stuffiness
Tranexamic acid
trans-amino-methyl-cyclo-hexanoic acid (AMCHA)
analog of aminocaproic acid and has the same properties
potency increased by factor of 6-10 due to the distance
between the 2 function groups in the AMCHA molecule
is fixed by a cyclic structure
mechanism of action
occupies the lysine binding site of the plasminogen
molecule producing a conformational change in the
molecule, resulting in a fibrin polymer with greater
resistance to natural fibrinolysis
plasminogen activators when released, find less
substrate that can be converted to plasmin
dosing
intravenously, 10-15 mg/kg 2-3 times a day
oral dose 1-1.5g up to 4 times a day
SERINE PROTEINASE INHIBITORS
Aprotinin
originally found to be a kallikrein inhibitor (1930) and
trypsin inhibitor (1936)serine protease inhibitor (serpin) that
inhibits fibrinolysis by free plasmin
inhibits plasmin-streptokinase complex in
patients who received the thrombolytic agent
mechanism of action
fits into enzyme where the contact region for the normal
enzyme substrate is located
forms 1:1 complexes with the enzymes which include
trypsin, kallikreins from organs, tissues and
plasma, and plasmin
aprotinin acts as pseudo-substrate that prevents furtherproteolytic activity while it remains tightly bound to the
enzyme
administration and dosage
aqueous solution is stable at room temperature without
loss of activity
historical reasons, quantities and concentrations
expressed as kallikrein inactivator units KIU
administered by infusion
4 M results in 100% plasmin inhibition
15M results in only 90% kallikrein inhibition
t is 5-8 hoursindications
patients at high risk of excessive bleeding
cardiac reoperations
adverse effects
anaphylaxis
first exposure, 6 months
Drugs used in Bleeding DisordersNC Hwang 2008