ANTITHROMBOTIC THERAPIES

BY

DR CHUKWUEMEKA S. UGWUADU

MB.BS; MSC; FMCPATH

CLASSES

• Drugs used are to maintain, preserve or restore circulation
• Anticoagulants & antiplatelets (antithrombotics), thrombolytics.
• Anticoagulants - prevent formation of clots that inhibit circulation
• Antiplatelets - prevent platelet aggregation
• Thrombolytics (clot busters) - attack/dissolve formed clots

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�THROMBUS FORMATION

• Clot is a Thrombus formed in an arterial or venous vessel
• thrombophlebitis - Both inflammation and clots are present
• Some thrombus can be superficial but it’s the DVT that’s a concern 🡪 embolism to lungs.

THROMBUS FORMATION

• Arterial formation - begins w/ platelet adhesion to arterial vessel wall 🡪 Adenosine diphosphate (ADP) released from platelets 🡪 more platelet aggregation 🡪 Bld. flow inhibited 🡪 fibrin, platelets & RBC’s surround clot 🡪 build up of size structure 🡪 occludes bld vessels 🡪 tissue ischemia
• The result of Arterial Thrombus is localized tissue injury from lack of perfusion

THROMBUS FORMATION

• Venous Formation - Usually from slow bld flow

- Can occur rapidly Stagnation of the blood flow initiate the coagulation cascade🡪 production of fibrin🡪enmeshes RBC’s & platelets to form the thrombus. Venous thrombus has a long tail that can break off to produce an embolus. These travel to faraway sites then lodge 🡪 in lung (capillary level) 🡪 inadequate O2 & CO2 exchange occur (ie. pulmonary embolism & cerebral embolism)

• Oral & parenteral anticoagulants (Heparin/Warfarin) primarily act by preventing venous thrombosis
• Antiplatelet drugs primarily act by preventing arterial thrombosis

THROMBUS FORMATION�

• Hemostasis is the normal homeostatic process of blood clotting.
• Clotting proteins normally circulate in an inactive state & must be activated to form a fibrin clot. When there is a trigger - inc. bld viscosity from bed rest & stasis - the clotting cascade is activated.
• Bld vessel injured 🡪 platelets adhering to site of injury 🡪 release of ADP🡪 a platelet plug - is ex. of Intrinsic clotting path.
• Tissue injury (outside bld vessels) = extrinsic pathway activated

CIRCULATORY�THROMBUS FORMATION

Risk Factors for Deep Vein Thrombophlebitis and Thromboembolism

• Three factors increasing risk 1) Stasis of venous flow, 2) damage of the endothelium(inner lining of vein), and 3) hypercoagulability of the blood.
• Hx. of thrombophlebitis, abdominal & pelvic surgery, Obesity, neoplasms (lung), CHF, Advanced age, A-fib, vasospasm, Prolonged immobility (bed-rest, long trip spinal cord injury, FX. hip), CVA MI PG, post partum, Estrogen TX (oral contraceptives), IV therapy, trauma, Sepsis, Venous cannulation, Drug abuse, Cigarette smoking Excessive vit E intake Hypercoagulable states (Polycythemia, severe anemias, Dehydration or malnutrition), Antithrombin III deficiency

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ANTICOAGULANTS

• Inhibit clot formation - Do NOT dissolve clots already formed, but prophylactically prevent new clots
• Used in clients w/ venous/arterial disorders that put them at inc. risk of clot formation
• Venous = DVT & Pulmonary embolism
• Arterial = Coronary thrombosis (MI), artificial heart valves, CVA

HEPARIN

• A natural substance in the liver that prevents clot formation.
• Primary use is to prevent venous thrombosis that can lead to pulmonary embolism (PE) or stroke
• Combines w/ antithrombin III 🡪 inactivates thrombin and other clotting factors then the conversion of fibrinogen to fibrin doesn’t occur so the clot is prevented
• Poorly absorbed through GI mucosa - given SQ & IV
• Prolongs clotting time - partial thromboplastin time (PTT) & activated partial thromboplastin time (aPTT) - both bld tests are monitored during therapy

HEPARIN

• Use - DVT, PE, & CVA, Rx of clients w/ heart valve prosthesis, during CV surgery, post op, during hemodialysis

* Low doses = prophylactically to prevent DVT

* Full doses = treats a thromboembolism & promotes neutralization of activated clotting factors = prevents extension of thrombi & formation of emboli

* If started shortly after formation of a thrombus - heparin will also prevent it from developing into an insoluble stable thrombus = reduced tissue damage

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HEPARIN

• Side Effects - Decreased platelet count = thrombocytopenia

Hemorrhage - give protamine sulfate IV (an anticoagulant antagonist)

• Drug Interaction - Inc. effects w/ ASA, NSAIDs, thrombolytics

Dec. effect w/ NTG

LMWH

• Low Molecular Weight Heparins (LMWHs) - recently introduced to prevent venous thromboembolism
• Binds to Antithrombin III which inhibits the synthesis of factor Xa & formation of thrombin

- enoxaparin (Lovenox) & dalteparin sodium (Fragmin)

- more stable dose, lower risk of bleeding, freq. lab monitoring not required

LMWHS

• Use - Prevention of DVT after hip & knee replacement surgery & abd. surgery
• Can be administered at home
• Administered SQ BID
• Available in prefilled syringes w/ attached needles
• Usually given in the abdomen
• Average Rx is 7 to 14 days
• Bleeding less likely to occur
• Drug Interactions - caution client not to take antiplatelet drugs (ASA) during therapy

WARFARIN (COUMADIN)

• Action - Inhibits activity of vit. K required for the activation of clotting factors II, VII, IX, & X. Blocking these factors prevents clot formation
• Use - prophylactically to prevent venous thrombosis, A. fib., PE, coronary occlusion, thrombophlebitis
• Prolongs clotting time & is monitored by the lab bld. tests prothrombin time (PT) & International normalized ratio (INR) - usually before administering the next dose until therapeutic levels are reached. INR is 1.3 - 2.0 therapeutic levels on coumadin = 2.0 - 3.0

WARFARIN (COUMADIN)

• INR is replacing the PT 🡪 INR more accurate. Need higher levels for prosthetic heart valves, cardiac valvular disease and recurrent emboli.
• PT not consistent lab to lab or reagents used.
• PT is 1.5 – 2 times the reference value to be therapeutic
• Regular monitoring is required for the duration of drug therapy
• Warfarin is well absorbed through the G.I. tract. Food decreases.

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WARFARIN (COUMADIN)

• Has a long t1/2 & duration of action - drug accumulation poss. and can cause internal bldg.

- Observe for: petechiae, ecchymosis, tarry stools, hematemesis. Monitor menstrual flow

- Teach client importance of bld tests & to look out for signs of bleeding

• DI - LOTS!!! consult a physician before taking any over the counter medications
• Vit. K (phytonadione) = antagonist of Warfarin. Used for OD/ uncontrolled bleeding

Intrinsic Clotting Pathway

Blood or collagen contact

XII

XIIa (H)

XI

XIa (H)

(W) IX

IXa (H)

CA++

PF 3

VIII (W)

Extrinsic Clotting Pathway

Tissue trauma

Tissue factor

(W) VII 🡪 VIIa

Common Pathway

(W) X

Xa (H)

(Next slide)

The Clotting Cascade

Common Pathway

Xa (H)

Ca++

PF 3

V (W)

(W) Prothrombin

Thrombin

Ca++

Fibrinogen

Fibrin (soluble)

CA++

XIIIa

XIII

Fibrin (insoluble)

(H)

(H) (F)

ANTIPLATELET DRUGS

Aspirin, Dipyridamole (Persantine), Ticlopidine (Ticlid)

abciximab (ReoPro), tirofiban (Aggrastat)

• Action: To prevent thrombosis in the arteries by suppressing platelet aggregation via diff. methods
• Use: Prevention of MI/stroke for clients w/ family hx

- prevention of a repeat MI, stroke in clients having TIA’s

• Persantine & Ticlid = similar to ASA but more expensive
• ReoPro & Aggrastat = mainly for acute coronary syndromes. Route = IV

THORMBOLYTICS

• Thromboembolism - Occlusion of an artery or vein caused by a thrombus or embolus - results in ischemia that causes necrosis of the tissue distal to the obstructed area.

- it takes about 1 to 2 weeks for the blood clot to disintegrate by natural fibrinolytic mechanisms

- if new thrombus dissolved quicker damage minimized & bld flow restored faster 🡪 purpose of therapy

• Thrombolytics promote fibrinolytic mechanism (convert plasminogen to plasmin & destroys the fibrin in the clot) - administering a thrombolytic drug = clot disintegrates

THROMBOLYTICS

• Use = Acute MI - w/ in 4 hrs to dissolve clot & unblock artery, so decrease necrosis to myocardium & hospital stay is decreased.
• Other uses: Pulmonary embolism, DVT, Noncoronary arterial occlusion
• Streptokinase, Urokinase, Tissue plasminogen activator (t-PA), anisoylated plasminogen streptokinase activator complex (APSAC)
• Streptokinase & Urokinase are enzymes that act to convert plasminogen to plasmin
• t-PA and APSAC activate plasminogen by acting specifically on clot.

THROMBOLYTICS

• All 5 drugs induce fibrinolysis (fibrin breakdown)
• Side effects: hemorrhage, allergic reactions (anaphylaxis) & vascular collapse-more with Streptokinase
• Onset and peak are immediate and rapid, duration can be 12h.
• t-PA most expensive - $2500/tx, short t1/2 (5-7 min.) not associated with anaphylaxis.
• Aminocaproic acid (Amicar) an antithrombolytic used to stop bleeding by inhibiting plasminogen activation. Used to stop bleeding from heart surgery, trauma & abruptio placenta.

ADJUNCTS - ANTILIPEMICS

• Used to Lower bld. lipid levels
• Cholesterol, triglycerides & phospholipids transported in the body bound to protein in various amounts - chylomicrons, very low-density lipoproteins (VLDL), low-density lipoproteins (LDL), high-density lipoproteins (HDL) - more protein & less lipid (removes chol. from bld. stream & deliver it to the liver)
• VLDL & LDL contribute to atheroslerotic plaque in bld vessels - composed of mainly cholesterol & triglycerides

ADJUNCTS - ANTILIPEMICS

• Nonpharmacologic = before drugs to dec. BP

- Reduce saturated fats & chol intake in the diet

- Exercise

- Body wt. reduction

- Eliminate smoking

• If drug therapy needs to be initiated, clients still need to make lifestyle changes
• Compliance an issue

ADJUNCTS - ANTILIPEMICS

• Cholestyramine (Questran) - Powder form, Colestipol (Colestid) - a newer resin - both lower chol.
• Clofibrate (Atromid-S), gemfibrozil (Lopid) - fibric acid derivatives effective in reducing triglyceride & VLDL levels.

- Highly protein bound. do not take w/ anticoagulants - compete

- Clofibrate - many side effects - dysrhythmias, angina

• Nicotinic acid or niacin (vit B2) - reduces VLDL & LDL - effective in dec. chol levels, Many SE’s

ADJUNCTS - ANTILIPEMICS

• Statin drugs inhibit enzyme HMG CoA reductase in chol biosynthesis ( HMG CoA reductase inhibitors) = Dec. the concentration of chol & dec. LDL & sl. inc. in HDL
• atorvastatin calcium (Lipitor), cerivastatin (Baycol), fluvastatin (Lescol), lovastatin (Mevacor) -

- SE = GI disturbances, headaches, muscle cramps & tiredness (all complaints early in tx.)

- monitor serum liver enzymes

- Annual Eye exams d/t poss cataract formation

- Useful in coronary artery disease (CAD) & mortality rate

ADJUNCTS - ANTILIPEMICS

• If therapy withdrawn, cholesterol levels return to pretreatment levels 🡪 lifetime commitment
• Lovastatin is absorbed with food. High 1^st hepatic pass -50%
• Onset and peak occurs in hours , but takes several days to have a therapeutic effect. Duration is up to 3 weeks.
• NI 🡪Monitor blood lipid levels, liver functions, if GI upset occurs have client take with sufficient water or with meals.
• Desired Lab Values = CHOL <200; triglyceride <150; LDL < 130; HDL > 60

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ADJUNCTS - PERIPHERAL VASODILATORS

• Peripheral Vasodilators - Increase bld flow to extremities
• Peripheral vascular disease is a problem in the elderly

- Numbness & coolness of extremities, intermittent claudication (pain/weakness of limb when walking - symptoms absent at rest), poss. leg ulcers

- Primary cause is hyperlipemia from atherosclerosis & arteriosclerosis - arteries become occluded

ADJUNCTS - PERIPHERAL VASODILATORS

• Peripheral vasodilators more effective for disorders resulting from vasospasm (Raynaud’s disease) than from vessel occlusion or arteriosclerosis
• Vasodilators have diff. actions but all promote vasodilation
• Isoxsuprine (Vasodilan) - Beta-2 adrenergic agonist - causes vasodilation on arteries w/in skeletal muscles, bronchodilation may also occur

- SE = lightheadedness, dizziness, orthostatic hypotension, tachycardia, GI distress

ADJUNCTS - PERIPHERAL VASODILATORS

• Pentoxifylline (Trental) - an antihemorrheologic agent - improves microcirculation & tissue perfusion inc. in tissue O2. Not a vasodilator, but dilates rigid arteriosclerotic bld vessels - arterioles, capillaries & venules

- Use = clients w/ intermittent claudication

- Take w/ food

- Avoid smoking d/t nicotine increases vasoconstriction

MATH

The order for medication is 12 mg. The medication you have is labeled 5 mg per ml. How much do you give?

12mg X 1 ml. 5 mg

= 2.4 ml

You have a vial labeled 40 mg/mL. You need to give 0.1 g. How much should you give.

Convert 0.1g to mg.

= 100mg

100 mg X 1 mL = 40 mg

2.5 mL

MATH

You have an order to give 250 mcg. A dosage of 0.2 mg. per 2 ml. is what’s available.

Convert 0.2 mg. to mcg.

= 200 mcg.

250 mcg X 2 ml. = 200 mcg

5 X 2 ml. = 4

10 4

= 2.5

ml.