Haemostasis & Thrombosis

Spontaneous arrest of blood loss from damaged blood

vessels

True or False Accompanied by

Vasospasm Adhesion and activation of platelets Fibrin Formation

Physical process of coagulation

injured tissue exposure of vasoconstriction subendothelial cells

platelets adhere to platelets aggregateexposed cells and form a “plug”

blood

subendothelial cells

platelets

Thrombosis ?

Pathological formation of a haemostatic plug within the

vasculature in the absence of bleeding

Right ?

Role of Thrombin in HEMOSTASIS• Thrombin ---- (releases) platelet ADP

---------------------------- induce -------------------------------------- Platelet aggregation

Thrombin ---- (stimulate synthesis of) PGs ----------------- Thromboxane A2 (TXA2) (with in platelets)

• ---------- thrombogenesis

• ----------- vasoconstriction

----- PGI2 (with in vessel walls) -- inhibits thrombogenesis

BLOOD COAGULATION

WHEN DOES BLOOD COAGULATE?

Predisposing factor defined by Rudolph Virshow

But This enzyme cascade has to be controlled

RIGHT

BUT WHY?

Otherwise all the blood in the body would

solidify with in minutes

RIGHT ?

REGUALTION OF COAGULATION AND FIBRINOLYSIS

PLASMA CONTAINS PROTEASE INHIBITORS

α1- ANTIPROTEASE

α2- MACROGLOBULIN

α2- ANTIPLASMIN

ANTITHROMBIN

If this system is overwhelmed

DIC (massive tissue injury, obstetric emergency --- Abruptio placenta, Bacterial sepsis )

VASCULAR ENDOTHELIUM ----- surface heparin sulfate

ANTI THROMBIN III ------------ Neutralizes all serine proteases (Factor XIIa, XIa, Xa, IXa, Thrombin [IIa])

Alpha 1 antiprotease

Alpha 2-macroglobulin

Alpha 2 antiplasmin

PROTEIN C AND S (natural anticoagulants) ---Down regulates the amplification of blood clotting by proteolysis of factor Va and VIIIa

Drugs affect haemostasis and thrombosis in 3 distinct ways

Blood coagulation (fibrin formation) Platelet function Fibrin removal (fibrinolysis)

Indirect anticoagulants

Unfractionated heparin (UFH)

Low molecular weight heparin (LMWH)Enoxaparin (MW: 5000-30,000)DalteparinTinzaparin

Fondaparinux (Synthetic pentasaccharide)

DiscoveryMechanismAdministration/PharmacokineticsUnwanted effectsDosing

HeparinHeterogeneous mixture of sulfated mucopolysaccharides

Discovery • In 1916• 2nd year medical student• John Hopkins Hospital• Attempting to extract thromboplastic

(coagulant) substances from various tissues during a vacation project

• But found instead a powerful anticoagulant

HEPARINIndirect Thrombin Inhibitor

Mechanism

No heparin

Active clotting factors

Slow Antithrombin III

Inactive clotting factors

Heparin

Active clotting factors

Fast Antithrombin III +

Heparin

Inactive clotting factors(IIa, IXa, Xa)

ACTIONS OF HEPARIN

AT III IIa

HEPARIN

AT III

HEPARIN

AT III Xa

LMWH

The active heparin molecule

binds to AT and cause a conformational

Change ----Exposes its active site

for more rapid Interaction

with the proteases(activated clotting factors)

Xa

Heparin PreparationsCommercial heparin consist of a family of molecules of different molecular weights

• Sodium heparin (doses specified in units per milligram)

• Calcium heparin• Lithium heparin (used in vitro as anticoagulant for blood samples).

Extracted from:Porcine intestinal mucosaBovine lung

Enoxaparin (LMWH): obtained from: same source Equal efficacy, increased bioavailability from s/c site, less freq. dosing (doses are specified in milligrams)

Administration and Dosage --- Heparin• A plasma concentration of heparin of 0.2 – 0.4 units/ml usually prevents

pulmonary emboli in patients with established venous thrombosis

• This conc. will ------- prolong the activated partial thromboplastin time (APTT) to ----------------------------------------------------------- 2 - 2.5 times that of control value.

Continuous intravenous administration • Is accomplished via an infusion pump. • After an initial bolus dose of 80-100 units /kg

--------------------------------------------------- a continuous infusion of about 15-22 units/kg is required to maintain the APTT at 2 -2.5 times control.

Subcutaneous Administration• As in low dose prophylaxis• 5000 units every 8-12 hours

Intramuscular Administration• CONTRAINDICATED ---------------------------- Why? -------- HEMATOMA

Administration and Dosage --Enoxaparin

Prophylactic:• Given S/C• Dose: 30 mg twice daily or 40 mg once dailyFull dose therapy: 1 mg/kg S/C every 12 hoursLevels are determined by: anti-Xa units

FONDAPARINUXFactor Xa inhibitorDose: 2.5 mg S/C once dailyUsed for: Prevention of deep vein thrombosis in patients who have had orthopedic surgery Treatment of deep vein thrombosis and pulmonary embolism.

Advantages of LMWH Equal efficacy Increased bioavailability from SC site of injection Less frequent dosing requirments

Indication •Prophylaxis and/or treatment of:

–Venous thrombosis and its extension

–Pulmonary embolism

–Thromboembolic complications associated with

AF and cardiac valve replacement

•Post MI, to reduce the risk of death

•Recurrent MI, and thromboembolic events such as stroke or systemic embolization

•Heart Failure

Osteoporosis: spontaneous fractures long term (6 month use) / Safe in Pregnancy ------- Y or N

Severe HypertensionIntracranial hemorrhageUlcerative lesions of GITThreatened abortionVisceral carcinoma

Reversal of heparin action

Discontinuance of drug Protamine sulfate

For every 100 units of heparin administer 1 mg of protamine sulfate IV

ANTI THROMBIN III Independent Anticoagulants

Hirudin – irreversible thrombin inhibitor from leech has been synthesized by DNA recombinant technology (Lepirudin) Can reach and inactivates fibrin bound thrombin in thrombi Bivalirudin Argatroban – thrombin inhibitorapproved for use in patients with heparin induced thrombocytopenia (HIT) with or without thrombosis and coronary angioplasty in patients with HIT Melagatran

DIRECT THROMBIN INHIBITORS

Binds to active site of thrombin

ORAL ANTICOAGULANTS

Coumarins

Warfarin

• History• Chemistry• Mechanism• Indications• Pharmacokinetics• Adverse effects• Dosing

History • The early 1920 saw the outbreak of a previously unrecognized disease of cattle

in the northern United Sates and Canada. Cattle would die of uncontrollable bleeding from very minor injuries or sometimes drop dead of internal hemorrhage with no external signs of injury. In 1922 Frank Schofield, a Canadian veterinarian determined that the cattle were ingesting a toxin from moldy silage made from sweet clover that function as a potent anticoagulant.

• In 1940 Carl Link and Harold Campbell chemists working at the University of Wisconsin determined that it was the coumarin derivative 4-hydroxycoumarin.

• Link continued working on developing more potent coumarin based anticoagulants for use as a rodent poisons resulting in Warfarin in 1948.

• The name warfarin stems from the acronym WARF for (Wisconsin Alumni Research Foundation + the ending –arin indicating its link with coumarin).

• In 1954 was approved for medical use in humans after an accident in 1951 where a naval enlisted man unsuccessfully attempted suicide with warfarin an recovered fully

Other coumarins

• Dicumarol • Phenindione

Chemistry

• Source: derivative of coumarin, a chemical found in many plants notably woodruff (Galium Odoratum), and at lower level in licorice and lavender.

Vitamin KVitamin K

Synthesis of Synthesis of Functional Functional

Coagulation Coagulation FactorsFactors

VIIVII

IXIX

XX

IIII

Vitamin K-Dependent Clotting Factors

WarfarinSynthesis of Synthesis of

Non Non Functional Functional

Coagulation Coagulation FactorsFactors

Antagonismof

Vitamin K

Warfarin Mechanism of Action

Vitamin K

VIIVII

IXIX

XXIIII

WARFARIN: MECHANISM OF ACTION

Inactive factors II, VII, IX, and X

Proteins S and C

Active factors II, VII, IX, and X

Proteins S and C

Vitamin K epoxide

Vitamin K reduced

WA

RFA

RIN

Prevents the reduction of vitamin K, which is essential for Prevents the reduction of vitamin K, which is essential for activation of certain factorsactivation of certain factors

Has no effect on previously formed thrombusHas no effect on previously formed thrombus

Inhibition of protein C and S(Natural Anticoagulants)

Beneficial or Harmful?

This initial procoagulant effect is eventually over come by the inhibition of clotting factors

Pharmacokinetics • Administration: orally• Absorbed quickly and totally • Bioavailability: 100%• Strongly bound to plasma albumin• Onset of action: 12-16 hours • Peak : 48 hours (depends upon half lives of circulating factor II 60 hours, VII

6-8 hours, IIX 20 hours, X 40 hours, C & S 4-6 hours)

• Duration of action: 4-5 days• Metabolism: Hepatic mixed function oxidase P450 system• Half life: Variable / 40 hours • Excretion : Renal• Pregnancy: crosses the placenta -- teratogenic • Appears in milk during lactation (infants are routinely

prescribed Vitamin K )

Warfarin: Indications

• DVT and PE• Non-Valvular Atrial Fibrillation/Atrial Flutter• Mechanical Heart Valve

Warfarin: Major Adverse Effect —

• Hemorrhage• Factors that may influence bleeding risk:

– Intensity of anticoagulation– Concomitant clinical disorders– Concomitant use of other medications

• TERATOGENIC

WARFARIN NECROSIS (in patients with deficiency of protein C)

rare but severe complication

Drug interaction: PotentiationAgents that inhibit metabolism of warfarin• Cimetidine• Imipramine• Co- trimoxazole• Chloramphenicol• Ciprofloxacin• Metronidazole• AmiodaroneDrugs that inhibit platelet function• Aspirin• CarbenicillinDrugs that displace warfarin from binding sites on plasma albumin• Chloral hydrate• NSAIDsDrugs that decrease the availability of Vitamin K• Broad spectrum antibiotics

Dietary consideration with warfarin

• Vitamin K --- can decrease warfarin effects• Beef liver, pork liver, green tea, cabbage,

spinach.

• Vitamin E --- may increase warfarin effects

DOSE

Loading dose ---- ?Initial daily dose: 5-10mg

Initial adjustment of PT takes about 1 week

Maintenance dose: 5-7 mg/d

Therapeutic range is now defined in terms of INR

INRway of expressing a PT in a standardized way

• Target range: 2.0-3.0 (may vary in diff • situations)

• INR below target range --- under coagulated ------- risk of clotting

• INR above target range --- over coagulated ------- risk of bleeding

For acute ingestions

• Obtain a baseline PT/INR and make arrangements for a repeat measurement in 24-48 hours.

• Administer activated charcoal if it was not already given in the field.

• Gastric lavage is unnecessary if rapid administration of activated charcoal is feasible. Do not induce emesis.

• Do not administer vitamin K prophylactically because (1) it is not needed in most patients, and (2) its presence masks the onset of anticoagulant effects in the few patients who do require prolonged treatment and follow-up care.

Packed red cells and FFP

• Active, serious hemorrhage should be treated with FFP. This therapeutic strategy immediately restores therapeutic levels of coagulation

factors. A volume of 15 mL/kg is typically sufficient to completely reverse coagulopathy.

Alternatively, • Recombinant factor VIIa (rFVIIa) or • Prothrombin complex concentrate (PCC) ----------------may be used.

While costly, an essential advantage these therapies confer to emergency care is that, in contrast to

FFP, they do not require thawing, smaller infusion volumes, and decreased risk of transfusion-

associated adverse reactions.

• Administer vitamin K-1, 10 mg by slow IV infusion. only effective antidote for long-term management, but reversal of anticoagulation takes several

hours.

MONITORING OF WARFARIN THERAPY

Prothrombin time

PT ratio

INR (International Normalized Ratio)

WHY TO MONITOR WARFARIN THERAPY?

• Narrow therapeutic range

• Can increase risk of bleeding

Conversion from Heparin to Warfarin

• May begin concomitantly with heparin therapy

• Heparin should be continued for a minimum of four days– Time to peak antithrombotic effect of warfarin

is delayed 96 hours (despite INR)• When INR reaches desired therapeutic

range, discontinue heparin (after a minimum of four days)

DURATION OF THERAPY

• Venous thromboembolism: Minimum 3 months, usually 6 months

• AMI: During initial 10-14 days of hospitalization or until patient is ambulatory

• Mitral valve disease/Mechanical heart valves: Lifelong

• Bioprosthetic heart valves: 3 months• Atrial fibrillation: Lifelong• Prevention of cerebral embolism: 3-6 months