First, a few definitions to clarify the discussion of undesirable blood clots: A clot that adheres to a vessel wall is called a thrombus, whereas an intravascular clot that floats in the blood is termed an embolus. Thus, a detached thrombus becomes an embolus. Both thrombi and emboli are dangerous, because they may occlude blood vessels and deprive tissues of oxygen and nutrients. Arterial thrombosis most often occurs in medium-sized vessels rendered thrombogenic by surface lesions on endothelial cells caused by atherosclerosis. Arterial thrombosis usually consists of a platelet-rich clot. In contrast, venous thrombosis is triggered by blood stasis or inappropriate activation of the coagulation cascade, frequently as a result of a defect in the normal hemostatic defense mechanisms. Venous thrombosis typically involves a clot that is rich in fibrin, with fewer platelets than are observed with arterial clots.
Dissolution of clot with vessel repair or organization of clot Initial vasoconstriction:As soon as the continuity of vessel is disrupted, it goes in constriction Causes:Local myogenic spasm due to direct effect of traumaLocal autocoids secreted by damaged tissuesNervous reflexes:pain and other sensory reflexes sent by surrounding tissuesThis initial vasoconstriction is reinforced by factors released by platelets e.g serotonin, thromboxane A2Clotting or coagulation means the conversion of liquid blood into solid gel, whose primary function is to reinforce the platelet plug Time required: Formation of clot- 15 sec to 2 min Retraction of clot - 20 min -60 min
Extrinsic pathway : occurs rapidly within few seconds after tissue trauma, it is so named because as a consequence of trauma, a tissue protein called tissue factor or thromboplastinot factor III , leaks into blood from cells outside extrinsic to blood vesels. TF activates coagulation factor 7 to 7a , which then combines with and activates factor 10 to 10a, the activated factor 10 then combines with factor 5a in presence of calcium and phospholipids to form prothrombinaseIntrinsic : it occurs more slowly and requires several minutes, it is so named because all factors and activators required are contained within blood , unlike extrinsic pathway outside tissue damage is not needed. However enothelial cells can get damaged and blood can come in contact with collagen in damaged basal lamina. Damaged endothelial cells can activate platelets causing release of phospholipids which are used in cascade , also contact of blood with damaged endothelial or glass tube of blood collection tube activates factor 12 to 12a, 12a activates 11a, which activates 9 to 9a,The 7a can also activate 9 to 9a, the activated 9a joins with 8a PL, calcium to activate factor 10 to 10a, 10a then combines with 5a and ca, PL to form active enzyme prothrombinaseStage2: prothrombinase and calcium catalyze the conversion of ofprothrombin to thrombin. Thrombin has 3 positive feed back effects, 1. through activated factor 5a , accelerates the formation of prothrombinase so more thrombin formation. 2. through platelet activation : promotes their aggregation and release of PL. 3. activation of 8 & 7a. Stage 3: Thrombin in presence of calcium converts fibrinogen to loose fibrin threads. These fibrin threads are insolube. The insoluble fibrin threads are converted to stabilized fibrin threads which are strong and sturdy by activated factor 13 or fibrin stabilizing factor. Thrombin converts 13 to 13a . Thus sturdy clot is formed To prvent the clot from becoming larger and larger because of thrombin activity and its three positive feed back loops. Nature has bestowed upon fibrin with ability to absorb and inactivate upto 90% of thrombin formed from prothrombin. This prevents the spread of thrombin in blood and limits the extension of clot beyond the damage.
Why we need fibrinolysis: because provides check and balances the clotting process so that it should not go out of hand for minor reasons in day to day life. It dissolves clot at the site of damage once the the damage is repaired. The activity of t-PA is checked by Plasminogen activator inhibitor 1 and 2 so that circulating plasminogen may not get activated (it is needed for incorporation in clot) another enzyme alpha 2 antiplasmin also plays important role in fibrinolytic system some of this is bound to fibrin and thereby protects fibrin from premature lysis by plasmin. Secondly it inhibits plasmin which escapes into circulation.
Prostacyclin: metabloite of aarachidonic acid produced by endothelial cells, opposes the action of TXA2 Thus inhibits platelet aggregation and releaseAntiThrombin III: a plasma protein which blocks the action of factors 2,9,10,11,12, two major clotting factors Protein C: plasma protein which inactivates factor 5 &8 2 major clotting factors not blocked by ATIII. Protein C is a vitamin K dependent endogenous anticoagulant which is activated by thrombin through binding to its receptor thrombomodulinheparan Sulfate: proteoglycan related to heparin synthesisized by endothelial cellsserves as a cofactor and enhances the activity of antithrombin III
Phenindione:leukopenia, hepatitis, nephropathy, agranulocytosis, orange urine: not used
Mc Lean a medical student in 1916 discovered that liver contains a powerful anticoagulant Howell and Holt 1918 named it heparin because it was obtained from liver. However it was used clinically only after 1937 when sufficient degree of purification was achievedStrong electronegative compound because of number of anionic SO4-, and COO- acidic groups in its structure It occurs in mast cells as much bigger molecule MW -75K, loosely bound to granular protein Richest sources of heparin: lung, liver, intestine present together with histamine in all mast cell containing tissues of the body
Antithrombin 3 plays a crucial role as natural endogenous anticoagulant by blocking the activity of activated factors 2,9,10,11,12. under physiological setting these interactions are slow and work on demand and supply basis
Heparin is a powerful and instantaneous acting anticoagulant, effective both inVivo & invitro , it acts indirectly by activating plasma antithrombin III, this complex binds to clotting factors of intrinsic as well as common pathways and inactivates them but not factor VIIa operative in extrinsic pathway. At low concentration selectively effects Xa. Main Mech of action: The anticoagulant action is mediated by inhibition of factor Xa as well as Thrombin (IIa) mediated conversion of fibrinogen to fibrin. Low concentration of heparin prolong aPTT without significantly prolonging PT. high conc prolong both aPTT and PT, thus low conc interfere selectively with intrinsic pathway. While high conc affect the common pathway as well.
Both thrombin and factor Xa are sensitive to inhibitory effects of high molecular weight heparin –AT3 complex , but Iia inhibition is much more than Xa. The difference in Iia and Xa binding is that Xa needs to interact with Only AT-III portion of long chain heprin AT-III complex. Once heparin AT-III clotting factor ternary complex is formed heparin is released for renewed interaction with other AT-III molecule. LMWH is too small molecule as compared to heparin to bind AT-III as well as thrombin simultaneously. Higher doses of heparin given for some time cause reduction in AT-III levels probably by compensatory mechanism. Sudden stoppage of heparin conventional dose therapy may result in increase in coagulability for few days.
Lipemia clearing action is not therapeutic or related to its MOA
Large highly ionized molecules, injected IV acts instantly Not to mix in same infusion bottle with peniclillin, tetracycline, hydrocortisone, NA.
Bleeding due to overdosage is most serious adverse effect of heparin therapy, hematuria is the first clinical sign generally, with proper monitoring serious bleeding is reported in 1-3% of the patientsThrombocytopenia (Platelet count less than 1.5 lac or reduction by 50 % of pretreatmrnt value) is another common problem. Occurs in about 0.5 % of the patients 5 to 10 days after initiation of therapy. Incidence of thrombocytopenia is low with LMWH.IgG antibodies against complexes of heparin with platelet factor 4.or other chemokines. These complexes activate platelets by binding to Fc/Iia receptors which results in platelet aggregation, release of more platelet factor and thrombin generation, heparin should be discontinued immediately if unexplained thrombocytopenia occurs an alternative anticoagulant such as lepirudin, argatroban, or danaparoid (see below) should be administered to patients with heparin-induced thrombocytopenia. Low-molecular-weight heparins should be avoided, because these drugs often cross-react with standard heparin in heparin-dependent antibody assays. Warfarin may precipitate venous limb gangrene or multicentric skin necrosis in patients with heparin-induced thrombocytopenia and should not be used until the thrombocytopenia has resolved and the patient is adequately anticoagulated with another agent. Osteoporosis can occur on long term use of relatively high dosesHeparin can inhibit the synthesis of aldosterone by the adrenal glands and occasionally causes hyperkalemia, even when low doses are given.Transient and reversible alopecia is infrequent . Serum transaminase levels may rise Hypersensitivity reactions are rare- urticaria, rigor, fever, and anaphylaxis
For treatment of heparin induced bleeding due consideration should be given to amount of heparin that may have been degraded by patients body in mean time. However it is needed infrequently because the action of heparin disappears by itself in few hour, and whole blood transfusion is indicated to replinishthe loss when bleeding occurs. Protamine is more commonly used when heparin action needs to be terminated rapidly. E.gagter cardiac or vascular surgery. Being basic in nature it can release histamine in body . Hypersensitivity reactions have occurred .
Enoxaparin = clexanepre-filled syringe
Better S.C Bioavailability (70-90%) than unfractionated heparin (20-30%)Longer t1/2 (S.C/O.D)Smaller effect on aPTT /clotting time(chances of thrombocytopenia low)
Heparansulphate: is heparin like natural substance found on cell surface and intercellular matrix in many tissues. Less potent anticoagulant than heparin, but may have more favourable profile of actionDanaparoid: is a preparation containing mainly heparansulphate obtained from pig GUT mucosa, used in heparin induced thrombocytopeniaLepuridin: recombinant preparation of (hirudin, polypeptide anticoagulant secreted by salivary glands of leech) acts by inhibiting thrombin directly. It is indicated in patients with heparin induced thrombocytopenia.Ancrod: enzyme obtained from Malayan pit viper venom. It degrades fibrinogen into unstable form of fibrin which is taken uo by RE cells. Thus fibrinogen gets depleted and an apparent heparin like effect results given by slow IV infusion 2 Units /kg over 6 hrs for DVT. IN patients who develop thrombocytopenia or hypersensitivity reaction to heparin and require immediate anticoagulation. Drotrecogin Alfa.Drotrecoginalfa (XIGRIS) is a recombinant form of human activated protein C that inhibits coagulation by proteolytic inactivation of factors Va and VIIIa. It also has antiinflammatory effects (Esmon, 2003). A 96-hour continuous infusion of drotrecoginalfa decreases mortality in adult patients who are at high risk for death from severe sepsis if given within 48 hours of the onset of organ dysfunction (e.g., shock, hypoxemia, oliguria). The major adverse effect is bleeding.
The disorder was thought to be due to prothrombin deficiency and toxic principal identified was bishydroxy-coumarin , it was cured by feeding alpha alpha grass rich in Vit K, first clinical use in 1941.
Warfarin and its congeners act as anti-coagulants only in vivo. They act by interfering with synthesis of Vit K dependent clotting factors in liver. They are competitive antagonists of vit k Carboxylation is essential for clotting factors to bind calcium, and get bound to phospholipid surfaces, necessary for coagulation sequence to proceed. The reduced form of vit K Hydroxyquinione form is required for activation of 27910 factors Factor 7 has shortest half life 6 hrs, levels fall first when warfarin started, 9- 24 hrs, 10= 40 hrs , 2= 60 hrs Though synthesis of clotting factors diminishes within 2-4 hrs anticoagunt effect takes 1-3 days , delay between administration of drug and anticoagulat effect
Treatment for bleeding: Stop anticoagulants , give fresh blood transfusion, supply the clotting factors and replinish the blood loss, alternatively the fresh frozen plasma may be used as a source of clotting factors Give Vit K1 : physiological antidote for 10 mg IM Followed by 5 mg 4 hrly till bleeding stops
Aim of using anticoagulants is prevent thrombus extension and embolic complications by reducing rate of fibrin formation, they do not dissolve already formed clot but prevent the recurrences. Heparin is utilized for short term rapid action while anticoagulants are suitable for maintenance therapy. Deep vein thrombosis and pulmonary embolism: because venous thrombi are mainly fibrin thrombi, they are used for treatment and prophylaxis of DVT, prophylaxis is needed in bedridden, old, postoperative, postpartum, post stroke and leg fracture patients. , when DVT or pulmonary embolism has occurred, 3 months anticoagulation therapy(Continued if further risk factors persist ) Now a days prefering LMWH, factor X prevents further amplifiction of active products , this is the tretment of choice as as it does not need laboratory monitoring. Spontaneous bleeding does not occur , anticoagulants are of little value in chronic peripheral vascular disease Myocardial infarction: Arterial thrombi are mainly platelet thrombi, anticoagulants are of ? Value, their use in acute MI has decloined, they do not alter immediate mortrality of MI Angina: short term use of heparin has reduced the occurrence of MI inunstable angina patients, aspirin is equally effective , current recommendation is to use aspirin + heparin followed by warfarin.
Anticoagulants Dr Naser
Case study• A 25-year-old woman presents to the emergency department complaining of acute onset of shortness of breath & pleuritic pain. she noted that her left leg was swollen and red 2 days prior . Her only medication was oral contraceptives. Family history was significant for a history of "blood clots" in multiple members of the maternal side of her family. The left lower extremity demonstrates erythema and edema and is tender to touch.
Common Thrombo Embolic Disorders For Drug Intervention• Post myocardial infarction• Prosthetic heart valves• Chronic atrial fibrillation• Acute deep vein thrombosis• Pulmonary embolism• Patients undergone orthopedic or gynecological surgery & in bed ridden patients
Hemostasis• Hemostasis: – Minimization or arrest of blood loss• Haemostatic mechanisms – Vasoconstriction – Platelet plug formation – Blood coagulation (Formation of clot)
Extrinsic Pathway Intrinsic Pathway Tissue Trauma Damaged endothelial cells/ contact with glass VII TF XII XIIa XIa XI Activation of VIIa platelets VIIa Ca2+ Ca2+ IXa IX PL Ca2+ PL VIIIa VIII PL (Used in X Xa X cascade) Va Ca2+ PL XIII Prothrombinase Ca2+Prothrombin Thrombin XIIIa Stabilized Fibrin Fibrinogen fibrin threads insoluble
Fibrinolytic system • The process of dissolution of clot is called fibrinolysis Endothelial cells t-PAPlasminogen Plasmin Digests fibrin
Natural anticoagulant mechanisms• Prostacyclin (PGI2) – Inhibits action of TXA2• Antithrombin III: – blocks the action of factors II,IX,X,XI,XII• Protein C: – Blocks the action of factors V &VIII – ↑ t-PA action• Heparan sulphate : – Cofactor , enhances activity of antithrombin III
Classification of anticoagulants• Used in vivo – Parenteral • Heparin, Low molecular weight heparins, heparinoids – Oral • Coumarin derivatives • Indandione derivatives• Used in vitro – Heparin – Calcium complexing agents • Sodium citrate, sodium oxalate, sodium edetate
Heparin• Discovered by Mc Lean in 1916• Mixture of sulfated mucopolysaccharides 10,000 to 20000 MW• Strong electronegative compound• Strongest organic acid in body• Present in all tissues containing mast cells• Commercially prepared from beef lung and pig intestinal mucosa
Mechanism of action SlowlyAntithrombin III Inactive Coagulation factors
+ AT-III Heparin Heparin AT- Fast III complex•Heparin providesscaffolding for Heparin acceleratesclotting factors & Antithrombin IIIAT-III activity by 1000 fold•Induces Especially against IIaconfirmational & Xachanges in AT-IIIto expose itsinteractive site
Other actions of heparin• Antiplatelet – High doses inhibits platelet aggregation and prolongs bleeding time• Lipaemia clearing – Clears turbid postprandial lipaemic plasma by releasing lipoprotein lipase from vessel wall & tissues
Pharmacokinetics• Orally not absorbed -Large molecules• Route – IV/SC• Does not cross BBB/ Placenta• Metabolised by Heparinase in Liver• Heparin sodium - 5ml vials 1000 & 5000 units/ml• t1/2 – 1 hr
Dosage• 5000-10000 units I.V , 4-6 hrly or• IV bolus 5000 units followed by continuous 750- 1000 units/IV/hr• Deep SC 10000-20000 units every 8-12hrly• Low dose SC regimen 5000 units every 8-12hrly to prevent post operative DVT• Dose controlled by APTT (1.5-2.5 times normal) Total Clotting time (2 times the normal)
HEPARIN – ADVERSE EFFECTS1. Bleeding due to overdose2. Osteoporosis3. Thrombocytopenia4. Hypersensitivity (Anaphylaxis)5. Transient alopecia• Antidote – Protamine sulphate 50 mg in 5ml for IV 1mg IV for 100 units heparin
Contraindications• Bleeding disorders• Heparin induced thrombocytopenia• Severe hypertension• Threatened abortion, piles• SABE• Occular , neurosurgery , lumbar puncture• Chronic alcoholics, cirrhosis• Aspirin other antiplatelet drugs use cautiously
Protamine sulfate• Strongly basic LMW protein• Obtained from sperm of certain fish• 1 mg IV neutralizes 100 U of heparin• Needed infrequently to antagonize heparin action rapidly• Can act as week anticoagulant in absence of heparin• Rapid IV injection causes flushing and breathing difficulty
Low Molecular Weight Heparins• M.Wt : 3000-7000• Selectively inhibit factor Xa ,No effect on IIa• Used for prophylaxis of Deep Vein Thrombosis Pulmonary Embolism, Unstable angina • ENOXAPARIN: 20-40 mg S.C , O.D • REVIPARIN:13.8mg(0.25ml) S.C/OD for 5-10 days • NADROPORIN :0.3ml(3075 units) • TINZAPARIN :3500 units S.C every 24hr)
LOW MOLECULAR WEIGHT HEPARINS• Higher S.C bioavailability• Longer duration of action• Do not routinely require aPTT monitoring• Lesser antiplatelet action• Less antigenic• Less hemorrhagic complications• Better patient compliance
HEPARINOIDS• Used In patients developing thrombocytopenia with Heparin1. HEPARAN SULPHATE : less potent, better profile.2. LEPIRUDIN : Recombinant preparation of Hirudin . Inhibits Thrombin directly, it is indicated in patients with heparin induced thrombocytopenia.3. ANCROD : enzyme from Malayan Pit Viper venom Fibrinogen Slow IV infusion 2units/kg over 6hrs for DVT Unstable fibrin (Taken up by RE cells)
Oral Anticoagulants1924 – Hemorrhagic disease in cattle due to feeding of spoiledsweet clover (contained bishydroxy coumarin)
Mechanism of action carboxylated Descarboxy factors II,VII,IX,X factors II,VII,IX,XVitamin K reduced form Vitamin K oxidized formHydroquinone KH Epoxide KO VitK reductase Warfarin NAD NADH
Warfarin Sodium• Most popular oral anticoagulant• Racemate• Absorbed orally, crosses placenta• 99% pl.protein bound• Partially conjugated with glucuronic acid• Available as 1,2.5 mg tablet• Can be given parenterally as it is water soluble
• Dose Regulation Of Oral Anticoagulants : By Prothrombin time• INR
DRUG INTERACTIONS Oral anticoagulant effect ed by ed by• Broad spectrum antibiotics • Barbiturates• Phenylbutazone • Rifampin• Aspirin • Oral contraceptives• Sulfonamides• Phenytoin
Uses of anticoagulants• Deep Vein Thrombosis & Pulmonary Embolism in bed ridden , old , post operative, leg fracture pts• MI – for short period till pts become ambulatory• Unstable angina• Rheumatic Heart Disease , Atrial Fibrillation• CerebroVascular Diseases• Prosthetic heart valves• Hemodialysis• Disseminated Intravascular Coagulation
ComparisonHEPARIN WARFARIN• Mucopolysaccharide • Coumarin derivative• Parenteral • Oral• Immediate onset • Delayed onset of action• Duration of action 4-6 hrs • 3-6 days• Activity invitro & in vivo • Only invivo• Blocks action of factor X & II • X synthesis of clotting factors• Antagonist - protamine • Antagonist is Vit K• Monitor aPTT • Monitor PT/INR