Drugs influencing coagulation Dr Sanjeewani Fonseka Department of Pharmacology.
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Transcript of Drugs influencing coagulation Dr Sanjeewani Fonseka Department of Pharmacology.
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Drugs influencing coagulation
Dr Sanjeewani Fonseka
Department of Pharmacology
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Classes of Drugs
• Prevent coagulation
• Dissolve clots
• Prevent bleeding and hemorrhage -
Hemostatic
• Overcome clotting deficiencies
(replacement therapies)
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Classes of Drugs
• Prevent coagulation
• Dissolve clots
• Prevent bleeding and hemorrhage -
Hemostatic
• Overcome clotting deficiencies
(replacement therapies)
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Haemostasis
Arrest of blood loss from damaged blood vessels
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Blood Clotting
• Vascular Phase
• Platelet Phase
• Coagulation Phase
• Fibrinolytic Phase
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Vascular Phase
Vasoconstriction Exposure to tissues activate Tissue
factor and initiate coagulation
Tissue Factor
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Coagulation Phase Two major pathways
Intrinsic pathway
Extrinsic pathway
Both converge at a common point
13 soluble factors are involved in clotting
Normally inactive and sequentially activated
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Blood Vessel Injury
IX IXa
XI XIa
X Xa
XII XIIa
Tissue Injury
Tissue Factor
VIIa VII
X
Prothrombin Thrombin
Fibrinogen Fribrin monomer
Intrinsic Pathway Extrinsic Pathway
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Intrinsic Pathway
Activated partial
thromboplastin test
(aPTT)
Extrinsic Pathway
Prothrombin test
(PT/INR)
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Vitamin KVitamin K
Synthesis of Synthesis of Functional Functional
Coagulation Coagulation FactorsFactors
VIIVII
IXIX
XX
IIII
Vitamin K-Dependent Clotting Factors
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Natural anti- coagulant
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Thrombosis
Pathological formation of haemostatic plug within the vasculature in the absence of bleeding
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Arterial
• White • Platelet and WBC• With atheroscerosis • Causes ischemia
Venous
• Red • White head and red tail• Embolus
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Drugs effect ;
• fibrin formation
• Platelet function
• Fibrinolysis
Drugs influencing coagulation
Anticoagulants
• Antiplatelet drugs
• Thrombolytic drugs
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Drugs influencing coagulation
• Anticoagulants
• Antiplatelet drugs
• Thrombolytic drugs
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Anticoagulants
• Antithrombin activators
• Direct thrombin inhibitors
• Direct Factor Xa inhibitors
• Drugs that oppose action of Vitamin K
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Anticoagulants
• Antithrombin activators – Heparin / LMWH– Synthetic pentasaccharide analogues
• Direct thrombin inhibitors
• Direct Factor Xa inhibitors
• Drugs that oppose action of Vitamin K
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Heparin
• Heterogeneous mixture of branched glycosaminoglycans
• Potentiates the inhibition of IIa, IXa, Xa, XIa, XIIa by AT
• Binds to AT through a unique pentasaccharide sequence leading to a conformational change
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Blood Vessel Injury
IX IXa
XI XIa
X Xa
XII XIIa
Tissue Injury
Tissue Factor
Thromboplastin
VIIa VII
X
Prothrombin Thrombin
Fibrinogen Fribrin monomer
Intrinsic Pathway Extrinsic Pathway
Factors affected
By Heparin
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Heparin mechanism of action
Heparin
Antithrombin IIIThrombin
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Heparin
• Given s.c. or i.v.
• Binds to plasma proteins, endothelial cells & macrophages
• Elimination– Depolymerisation in endothelial cells &
macrophages (rapid, saturable)– Renal (slow, non-saturable) and RES
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Heparin: variable anticoagulant effect
• Variable protein binding
• Clearance varies with chain length
• Therefore, anticoagulant response monitored by activated partial thromboplastin time (APTT)
• Target 1.5 – 2.5 times control
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Heparin: clinical uses
• Venous thrombosis ± embolism
• Acute coronary syndromes
• Arterial thrombosis
• Extracorporeal devices (e.g. haemodialysis)
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Heparin: adverse effects
• Bleeding
• Heparin-induced thrombocytopenia (HIT)– Immune-mediated
• Osteoporosis
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Low-molecular-weight heparins (LMWHs)
• Derived from UFH by chemical or enzymatic depolymerization
• Molecular weight 2000 – 9000
• About 15 monosaccharide units per molecule
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Molecular weight distributions of LMWHs and heparin
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Differences in Mechanism of Action
• Any size of heparin chain can inhibit the action of factor Xa by binding to antithrombin (AT)
• In contrast, in order to inactivate thrombin (IIa), the heparin molecule must be long enough to bind both antithrombin and thrombin
• Less than half of the chains of LMWH are long enough
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LMWHs
• Dalteparin
• Enoxaparin
• Tinzaparin
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Synthetic pentasaccharide analogues
Bioavailability(s.c.) elimination half life (h)
LMWH 80-90% renal 4Fondaparinux 100% renal 17Idraparinux 100% renal 80
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Anticoagulants
• Antithrombin activators
• Direct thrombin inhibitors
• Direct Factor Xa inhibitors
• Drugs that oppose action of Vitamin K
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Direct thrombin inhibitors
• Recombinant hirudins
• Bivalirudin
• Ximelagatran / Melagatran
• Dabigatran
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Recombinant hirudins
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Recombinant hirudins
• Given i.v. , s.c.
• Elimination renal
• Half life 1-2 h
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Bivalirudin
• Given i.v.
• Elimination renal & hepatic
• Half life 25 min
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Ximelagatran
• Promising oral direct thrombin inhibitor
• Converted to the active form melagatran in vivo
• No dosing problems
• No monitoring needed.
• Recent atrial fibrillation study showed it to possibly be superior to warfarin.
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Dabigatran
• Given orally
• Elimination renal
• Half life 12 h
• Substrate for P-glycoprotein in kidney, GIT
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Anticoagulants
• Antithrombin activators
• Direct thrombin inhibitors
• Direct Factor Xa inhibitors
• Drugs that oppose action of Vitamin K
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Apixaban
• Direct Factor Xa inhibitor
• Oral bioavailability 60%
• Half life 12 h
• Elimination hepatic > renal
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Rivaroxaban
• Direct Factor Xa inhibitor
• Oral bioavailability 80%
• Half life 7-11 h
• Elimination renal > hepatic
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Anticoagulants
• Antithrombin activators
• Direct thrombin inhibitors
• Direct Factor Xa inhibitors
• Drugs that oppose action of Vitamin K
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Warfarin
Reduces the post-translational carboxylation of glutamate residues of factors II, VII, IX, X
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WarfarinWarfarin
Synthesis of Synthesis of Non Functional Non Functional
Coagulation Coagulation FactorsFactors
Antagonismof
Vitamin K
Warfarin Mechanism of Action
Vitamin KVitamin K
VIIVII
IXIX
XX
IIII
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Blood Vessel Injury
IX IXa
XI XIa
X Xa
XII XIIa
Tissue Injury
Tissue Factor
Thromboplastin
VIIa VII
X
Prothrombin Thrombin
Fibrinogen Fribrin monomer
Intrinsic Pathway Extrinsic Pathway
Vit. K dependent FactorsAffected by Oral Anticoagulants
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Warfarin
• Anticoagulant effect seen after 2-3 days
• Monitored by international normalized ratio (INR)
• Well absorbed form GIT
• Highly protein bound
• Metabolised by CYP-450
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Warfarin cont
• Clearance is slow - 36 hrs
• Can cross placenta - do not use during pregnancies
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Drug interaction- with Warfarin
Drugs that Increase Warfarin Activity
Decrease binding toAlbumin
Inhibit hepatic metaboli;
Decrease synthesis ofClotting Factors
NSAID,
Cimetidine, antifungals
Antibiotics (oral)
Category Mechanism Representative Drugs
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Drug interaction with Warfarin cont:
Drugs that promotebleeding
Inhibition of platelets NSAID, Aspirin
Inhibition of clotting heparinFactors
Drugs that decreaseWarfarin activity
Induction of metabolizing BarbituratesEnzymes Griseofulvin
Promote clotting factor Vitamin KSynthesis
Reduced absorption cholestyraminecolestipol
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Warfarin: adverse effects
• Bleeding
• Rashes
• Alopecia
• Teratogenicity
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Warfarin-induced Skin Necrosis
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Blann, A. D et al. BMJ 2003;326:153-156
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Reversing action of warfarin
• Plasma– Rapid but short-lasting
• Vitamin K– Not rapid, but lasts 1-2 weeks. Do not use if
wishing to restart warfarin within next week.
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Drugs influencing coagulation
• Anticoagulants
• Antiplatelet drugs
• Thrombolytic drugs
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Antiplatelet drugs
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PG
thromboxane sys PC syntase
Thromboxane A2 PC
(plt) (endothe)
adenylase cyclase
Plt C AMP
Phosphodiesterase
Plt adhesion/Aggregation/
release of substances
PG
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Antiplatelet drugs
• COX inhibitors
• Adenosine diphosphate P2Y12 receptor antagonists (thienopyridines)
• Phosphodiesterase inhibitors
• Glycoprotein IIb/IIIa receptor antagonists
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Antiplatelet drugs
• COX inhibitors– Aspirin
• Adenosine diphosphate P2Y12 receptor antagonists (thienopyridines)
• Phosphodiesterase inhibitors
• Glycoprotein IIb/IIIa receptor antagonists
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Aspirin
• Irreversible acetylation of cyclo-oxygenase-1 in platelets
endotheliumplatelet
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Aspirin cont;
• Prevents platelet aggregation /adhesion
• Clinical use - prevents arterial thrombus
– Myocardial infarction (MI)
– stroke
– heart valve replacement and shunts
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Aspirin cont;
• Low doses (75 – 300 mg)
• Rapidly absorbed from GIT
• Absorption delayed with enteric-coated formulations
• Hydrolysed by esterases in GI mucosa & liver
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Prophylactic use of Aspirin
Low dose daily.
Prevents ischemic attack and MI
Aspirin cont;
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Antiplatelet drugs
• COX inhibitors
• Adenosine diphosphate P2Y12 receptor antagonists (thienopyridines)– Clopidogrel, Prasugrel, Ticagrelor
• Phosphodiesterase inhibitors
• Glycoprotein IIb/IIIa receptor antagonists
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Thienopyridines
• Ticlopidine
• Clopidogrel
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Clopidogrel
• Slightly more effective than aspirin
• Additive effect to aspirin
Use
• MI
• Stroke
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Ticlopidine
• Slow onset of action - 3-7 days
• Idiosyncratic neutropenia
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Antiplatelet drugs
• COX inhibitors
• Adenosine diphosphate P2Y12 receptor antagonists (thienopyridines)
• Phosphodiesterase inhibitors– Dipyridamole
• Glycoprotein IIb/IIIa receptor antagonists
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Dipyridamole
• Phosphodiesterase inhibitor
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PG
thromboxane sys PC syntase
Thromboxane A2 PC
(plt) (endothe)
adenylase cyclase
Plt C AMP
Phosphodiesterase
Plt adhesion/Aggregation/
release of substances
PG
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Dipyridamole cont;
Clinical use
• Ischemic stroke
• TIA
Side effects
headache
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Antiplatelet drugs
• COX inhibitors
• Adenosine diphosphate P2Y12 receptor antagonists (thienopyridines)
• Phosphodiesterase inhibitors
• Glycoprotein IIb/IIIa receptor antagonists– Abciximab, Eptifibatide
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Glycoprotein IIb/IIIa receptor antagonists
– Abciximab, Eptifibatide
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• More complete inbibition of platlet function
• inceased risk of bleeding
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Drugs influencing coagulation
• Anticoagulants
• Antiplatelet drugs
• Thrombolytic drugs
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Fibrinolysis
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Fibrinolysis
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Fibrinolysis
• Exogenously administered drugs
–Streptokinase
–Urokinase
–Tissue plasminogen activator (tPA)
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Streptokinase (SK)
• Binds to plasminogen & activates it
• Source: β haemolytic streptococci
• Immunogenic ; not repeated within one years of administration
• T 1/2 - 20 min
• IV
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Clinical uses
• STEMI
• Massive pulmonary embolism
• Ischaemic stroke
• Better if give within first 3 h
SK cont ;
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Side effects
• Bleeding
• Multiple microemboli
• Cardic arrhythmias
• Allergy
SK cont
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Urokinase
• Human fetal kdney tisssue
• Activate plaminogen
• T1/2 – 15 min
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tPA
• Produced by recombinant DNA technology
• Not immunogenic
• More clot-specific than SK – fibrin selective
• Less coagulation disturbance in plasma
• Short half life – iv infusion
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Drug preparations: clotting deficiencies
• Vitamin K ( Phytonadione (K1), Mephyton– Oral : 5 mg tablets
• Plasma fractions - for hemophilia– Antihemophilic factor ( VIII, AHF)– Parenteral
• Factor IX complex (konyne HT, proplex T)
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Drug preparations : to stop bleeding
• Systemic use : Tranexamic acid
• Inhibit plasminogen activation
Use –
bleeding from thrombolytic drugs• Hemorrhage form surgery• Menorrhagia
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Summary
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Drugs influencing coagulation
• Anticoagulants
• Antiplatelet drugs
• Thrombolytic drugs
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Blood Vessel Injury
IX IXa
XI XIa
X Xa
XII XIIa
Tissue Injury
Tissue Factor
Thromboplastin
VIIa VII
X
Prothrombin Thrombin
Fibrinogen Fribrin monomer
Fibrin polymerXIII
Intrinsic Pathway Extrinsic Pathway
Factors affected
By Heparin
Vit. K dependent FactorsAffected by Oral Anticoagulants
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Why do we need new anticoagulation drugs?
• Heparin-induced thrombocytopenia• Heparin prophylaxis is imperfect• Heparin - iv• Heparin-associated osteoporosis• Warfarin takes several days for its effect• Warfarin is not as effective in some situations
e.g antiphospholipid syndrome• Warfarin interacts with many other drugs• Warfarin is dangerous if not monitored