heparin . sodium citrate

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ANTI-COAGULANTS

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Page 1: Heparin . Sodium Citrate

ANTI-COAGULANTS

Page 2: Heparin . Sodium Citrate

SOME POINTS 1. Blood clots in a glass tube in 4-8 min ; this can be

prevented by addition of calcium ion binders (e.g EDTA or sodium citrate ) or by heparin

  - recalcified plasma clots in 2-4 min ( about 50% of original time of clotting) . The end-point of clotting is the formation of fibrin monomer gel.

   - this can be shortened to about ½ min (35 sec) by adding negatively charged phospholipid (PL) (e.g. Cephalin) and a particulate substance like Kaolin (aluminum silicate ) : This is called Kaolin Cephalin Clotting Time (KCCT) or activated partial thromboplastin time (aPPT); it measures the intrinsic system

Page 3: Heparin . Sodium Citrate

 Alternatively, it can be further shortened by the addition

of tissue thromboplastin (thus by-passing the first stage of coagulation ) to about 13 sec (12-14 sec) i.e. <50% of aPPT. This is called the prothrombin time (PT) ; it measures the extrinsic system

( the tissue thromboplastin employed is the saline extract of brain tissue that contains tissue factor (TF) + PL)

The International Normalized Ratio (INR) employs an International Standard of Tissue Thromboplastin

to compare PT of patient to standard PT of a normal person.

- Thrombin Time (TT) : measures the time needed for recalcified plasma to clot after adding thrombin . Normally it is about 10-12 sec.

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2. Natural circulating anti-coagulants in plasma include : a  Anti-thrombin III(AT III): this is alpha2-globulin

synthesized by liver b. Protein C : activated by thrombin in presence of thrombomodulin c. TF pathway inhibitor (TFPI) : binds to Xa to decrease its activity and that of VIIa / TF complex d. Plasmin

Page 5: Heparin . Sodium Citrate

ANTICOAGULANTS : 1. Heparin : is the strongest acid mucopolysaccharide

(glycosaminoglycan) synthesized in body; found in mast cells. Commercial heparin is obtained from porcine intestine or beef lung. One IU of heparin is the quantity that prevents 1 ml of sheep citrated plasma from clotting for 1 h after addition of 0.2 ml calcium chloride. It is equivalent to about 8 ug of porcine heparin.

Heparin in blood binds to circulating anti-thrombin III (AT III ) to enhance its action in inactivating the serine proteases thrombin (IIa) (x 1000) and factor Xa (also factors IXa and XIa).

Thus heparin is a direct acting anticoagulant that acts immediately in vivo when given IV, and this makes it useful in thrombotic or thromboembolic emergency.

 

Page 6: Heparin . Sodium Citrate

Heparin is synthesized as 10-15 chains of glycosaminoglycan molecules and contains 200-300 monosacchride units. It then undergoes a series of modifications esp. sulfation which provides it with anti-coagulant ability.

It is a polymer of alternating N-acetyl-D-glucosamine and D-glucuronic acid with N-sulfated glucosamine

and iduronic acid.The binding site on heparin for AT III is a specific pentasaccharide sequence that contains a specific 3-O-sulfated glucosamine . This sequence is present in only about 30 % of commercial unfractionated heparin (UFH) molecules.

Its MW is about 5000-30000 kD with average of 15000 .

Page 7: Heparin . Sodium Citrate

Administration : Conventional doses 30000 – 40000 IU / d of unfractionated heparin (UFH) are given IV either by :

a. bolus dose of 5000-10000 IU followed by IV infusion using a pump at rate 1000 IU /h (total : 35000-40000 IU/d)

b. intermittent IV injection 5000-10000 IU every 4-6 h

Page 8: Heparin . Sodium Citrate

Lab. Control of heparin anticoagulation is done either by :

1. aPPT : it should become about ( x 2-2.5 normal value ), and should not allowed to exceed 80 sec

2. plasma heparin level measurement using anti-factor Xa assay and aiming at 0.3-0.7 U/ ml :

there is poor corelation between plasma UFH and effect on coagulation because molecules of UFH vary

in MWNotes : Local bruising may occur at site of IV injection

of therapeutic doses; it is less if calcium heparin is used rather than sodium heparin

Heparin is NOT given IM since it results in hematoma formation; it is NOT effective orally since it is destroyed by the gastric acid .

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Elimination of heparin is by macrophages in reticulo-endothelial system esp. liver, and is also excreted

by kidney ; its plasma t½ is about 1 hour, but becomes longer ( x 2 ) if the dose is high.

Indications for anti-coagulant action of heparin : 1. Treatment of acute deep venous thrombosis (DVT) with or without pulmonary thromboembolism (PE) 2. Acute pulmonary thromboembolism 3. Acute arterial thromboembolism 4. Extra-corporeal circulation (e.g. hemodialysis , cardiac surgery), and some capillary or glass tubes e.g. for oximetry

Page 10: Heparin . Sodium Citrate

Adverse effects of Heparin include : 1.  Overdose bleeding : this may be traumatic or

spontaneous. It is treated by reducing dose or stopping drug (transiently) ; the antidote is protamine sulfate IV : this antidote is derived from fish sperm and is basic; it binds to heparin in plasma causing its inactivation (chemical antagonism).

2.  Thrombocytopenia : this can occur early and is usually transient and benign, OR it may occur late after 1-2 weeks when it is usually immune due to antibodies . Heparin immune thrombocytopenia (HIT) is serious since it is accompanied by thrombosis and bleeding , with resistance to action of heparin ; thus, drug must be stopped.

Page 11: Heparin . Sodium Citrate

3.  Allergy : less to porcine than to beef heparin; porcine heparin is commonly used 4.  Alopecia sometimes occur ; Prolonged use of heparin for weeks or months may produce osteoporosis

Notes : Heparin , if used during pregnancy, does not

cross the placenta , thus does not reach the foetus, and is therefore not teratogenic

Page 12: Heparin . Sodium Citrate

Low-dose UFH : given SC 5000-8000 IU x 2-3 / d, usually injected in abdominal wall . It acts by antagonizing factor Xa but not thrombin,

and usually does not need lab control of anti-coagulation since the risk of bleeding is very low .

It is used to prevent DVT in patients at risk; it also used in treatment of acute DVT, although it

is less effective than IV UFH

Page 13: Heparin . Sodium Citrate

Low Molecular Weight (LMW) heparins : are heparin fragments that contain < 18 monosaccharide units(MW is 3-4 kD); they contain the active penta-saccharide sequence of heparin , and this after binding to AT III results in inhibition of factor Xa , but thrombin is not inhibited (because they are too short for that ). These drugs have equal efficacy to UFH.

They usually do not need lab. control of anticoagulation since risk of bleeding is low

Examples are : enoxaparin, dalteparin, and tinzaparin

They are longer acting than heparin , and have predictable kinetics & bioavailability; their dose is usually lower.

Their weight-adjusted doses result in predictable blood levels as estimated by anti-factor Xa assay .

Page 14: Heparin . Sodium Citrate

Their risk of HIT is low, and are not teratogenic

They are given SC (in mgs for enoxaparin; IU for dalteparin) once or twice daily for prevention of DVT or for treatment of acute DVT +/- PE.

They can also be used for acute coronary syndromes.

Protamine reverses partially effect of LMW heparin esp. enoxaparin.

Use of LMW is contra-indicated in obese patients and those in RF when they are more likely to cause bleeding .

Page 15: Heparin . Sodium Citrate

Fondaparinux : This is synthetic pentasaccharide molecule , binds specifically to AT III to inactivate factor Xa. It is given SC in single daily dose 5 mg, and has long t½ of 15 h.

It is effective in prevention of DVT & for HIT .

Heparinoids e.g. danaproid : are a mixture of non-heparin glycosaminoglycans that contain about 80 %

heparan (extracted from porcine intestine) ; heparan contains less sulfate groups than heparin.

Danaproid may be used sometimes as anti-coagulant if there is heparin allergy or HIT

Page 16: Heparin . Sodium Citrate

Prevention of DVT : Susceptible patients to DVT

are either: a. Obese b. Diabetic c. had previous DVT d. elderly e. Debilitated patients esp. cancer   DVT prophylaxis may given to these susceptible patient

in the following situations , if applicable to them : 1. Prolonged recumbency for any cause e.g. myocardial infarction or heart failure; strokes, fractured femur, spine, or pelvis 2. Post-operatively after major surgery : since this increases risk of DVT 3. Pregnancy

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This prophylaxis is done by the following :1. Early ambulation and leg exercises , if possible2. Low dose heparin SC 3. LMW heparin SC : preferred at present4. Fondaparinux SC daily5. Post-operatively , Dextran 70 may be given as IV infusion . It inhibits platelet aggregation and enhances fibrin lysis .

Its side effects include : volume overload , interference with cross-matching of blood , and rarely allergy

6. Only rarely is the oral anti-coagulant warfarin used for DVT prevention.

The anti-platelet drugs e.g. low dose aspirin have poor efficacy in preventing DVT

Page 18: Heparin . Sodium Citrate

2. Thrombin inhibitors :A. Hirudin (from medicinal leeches) and Lepirudin ( from yeast by DNA recombinant techniques) : these are

given by IV infusion, and act directly by antagonizing thrombin. It is eliminated by kidney

They may be used for heparin allergy or HIT. There is no drug antidote for overdose bleeding B. Argatroban : It is a small MW thrombin inhibitor that is

used for HIT or heparin allergy. It is given by IV infusion and is mainly eliminated by liver; it has short t½. It is monitored by Thrombin time. There is no antidote for overdose

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3. Sodium citrate : This is employed as anti-coagulant in blood transfusion units or bottles in blood banks. It acts by binding ionized calcium in plasma leading to anti-coagulation of blood

( ionized calcium is essential for all stages of blood coagulation).

It is available as either ACD ( citric acid, sodium citrate , and dextrose or CPD ( sodium citrate, sodium dihydrogen phosphate, and dextrose ) in an amount of about 100 ml in each unit of 500 ml blood ( 1 : 5 ratio)

Page 21: Heparin . Sodium Citrate

Overtransfusion of blood to a patient may cause citrate toxicity due to hypocalcemia which may lead to tetany and sometimes myocardial failure. It is treated by giving calcium gluconate 10 ml of 10 % solution IV ( 1 g) .

To prevent citrate toxicity in such patients, this dose of calcium gluconate is given after transfusion of every 4-5 units (or bottles) of blood.