Involves interaction of 4 systems Vascular system Platelet system* Clotting proteins* Fibrinolytic system

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1 Angela Foley, MS, MLS(ASCP)SH Associate Professor LSUHSC CLS Department Contrast primary hemostasis vs secondary hemostasis Compare the use and mode of action of various anticoagulant drugs Discuss the utilization of the PT/INR, PTT, ACT, Anti-Xa Assay, Dilute TT, DRVVC and the Ecarin Clot Assay in monitoring anticoagulant therapy Myths Called blood thinners Do NOT thin blood Blood viscosity is a fxn mostly of the hematocrit Do NOT dissolve clots Clot busting or thrombolytic drugs do this Truths DO prevent clot formation or extension DO help promote recovery after a patient has had a thrombotic event Prophylactic use Stroke prevention in people with chronic atrial fibrillation (AF) Prevention of venous thromboembolic (VTE) disease Deep vein thrombosis (DVT) Pulmonary Emboli (PE) Post orthopedic or neurosurgery During a complicated pregnancy Therapeutic use (higher doses) Patient with current VTE or Coronary Artery Disease with cardiac insufficiency Keeps blood flowing within vessels Requires balance of clot promoting and clot inhibiting systems Involves interaction of 4 systems Vascular system Platelet system* Clotting proteins* Fibrinolytic system Clotting Bleeding 1

2 Activation of clotting proteins to form fibrin-platelet plug Interaction of damaged vessels with platelets Intrinsic Pathway Extrinsic Pathway Common Pathway Fibrin Clot I - Fibrinogen II - Prothrombin III - Tissue Factor IV - Ca++ V VII VIII IX X XI XII* XIII PK* HMWK* PK Prekallekrein HMWK- High Molecular Weight Kininogen Clotting Cascade (in vitro) Intrinsic Pathway Neg charged surface HMWK XII XIIa *Ca++ K XI IX PK XIa IXa * VIII PL Extrinsic Pathway VIIa VII * Tissue Factor III Common Pathway X Xa * V PL Prothrombin * Thrombin II IIa Fibrinogen Fibrin Stable clot I XIII PL Phospholipid on plt membrane * 2

3 Traditional Aspirin Warfarin/Coumadin Heparin Continue to dominate market despite birth of many new drugs Platelets Clotting factors Oral Aspirin Clopidogrel (Plavix ) Prasugrel (Effient ) IV Abciximab Eptifibatide Tirofiban Use has largely been replaced by clopidogrel or prasugrel Salicylic acid Used for thousands of years Fever, pain, inflammation Source - ground willow bark French chemist 1883 Treated acetyl chloride with Na salicylate Acetylsalicylic acid (ASA) Pure synthetic compound 1899 Bayer dubbed it Aspirin Spirea ulmaria plant Aspirin is derived from the chemical name ASA Acetylspirsäure in German Spirsäure (salicylic acid) named for the Spirea ulmaria plant A for acetylation -spir- for Spirsaure Added in to make it easy to say 3

4 Conditions associated with risk of platelet driven arterial thrombosis Heart attack and angina Stroke Cardiac stent Diabetes in patients >30 Peripheral arterial disease US Preventive Services Task Force recommends prophylactic low dose aspirin Men between ages of 45 and 79 Women between 55 and 79 History of Stomach ulcers Bleeding strokes On other anticoagulant drugs or other meds associated with bleeding Not for venous blood clots, e.g. DVT Ca++ ADP vasoconstriction Agonist Surface receptor Arachidonic Acid Prostaglandin Thromboxane A2 Secretion Collagen ADP Thrombin Arachidonic Acid Platelet Aspirin Cyclooxygenase COX Irreversible COX1 inhibitor Ibuprofen Advil Naproxen sodium Aleve Competitive COX inhibitors Transient affect Appear to block the COX1 site for aspirin Can have prothrombotic affect Don t take within 2 hours of time of aspirin ingestion 4

5 Affect of Antiplatlet Drugs on Platelet Receptors and Release P2Y 12 inhibitors Clopidogrel(Plavix ) Prasugrel(Effient ) Bleeding Time Technically demanding Poor correlation with intraoperative bleeding risk Platelet Function Analyzer (PFA) Measures time required for platelet plug to occlude an aperture coated with collagen/adp, collagen/epinephrine, ADP/prostaglandin Closure Time Sensitive to Aspirin Clopidogrel and Prasugrel Multiplate Platelet Function Analyzer Looks at aggregation velocity, maximum aggregation and area under aggregation curve Detects effects of Aspirin Clopidogrel GPIIb/IIIa antagonists (administered IV) Vitamin K inhibitors Oral Warfarin/Coumadin Vitamin K antagonist Vit K necessary for carboxylation of Factors II, VII, IX, X COOH - needed for binding with Ca++ and PL on platelet membrane Factors non-functional without COOH - First used clinically in the 1950 s 5

6 Discovered in 1930 s by Karl Paul Link Biochemist at University of Wisconsin Investigating epidemic of fatal cattle hemorrhages Mold in rotting sweet clover converted coumarin to dicoumarol Soluble form of dicumarol is warfarin Link s research was funded by Wisconsin Alumni Research Foundation 1948 used in rat poison President Dwight D. Eisenhower Medical version of Warfarin/Coumadin released in 1954 Gained fame in 1955 when it was given to Eisenhower following heart attack Used to prevent MI until 2000 Replaced by antiplatelet therapy Extrinsic system test Used to monitor warfarin/coumarin therapy and screen for bleeding disorders Reference range 12 to 15 sec Therapeutic range 1.5 to 2.5 mean normal Prothrombin Time Extrinsic Pathway VIIa * VII * Tissue Thromboplastin III X Xa Common Pathway * V PL Prothrombin * *Ca++ Thrombin II IIa Fibrinogen Fibrin (I) Difficult to standardize from lab to lab due to differences in reagent sensitivity INR (International Normalized Ratio) was developed ISI* PT INR = Patient Patient mean normal *International Sensitivity Index 6

7 2 to 3 DVT, Pulmonary embolus, AF 2.5 to 3.5 Mechanical heart valves Slow onset Needs monitoring Daily initially Monthly after stabilized POC instruments available for home monitoring Food and drug interactions Vitamin K rich foods Statins/other drugs Age, weight, sex and genetic factors influence effective dose Code for enzymes responsible for warfarin metabolism or Vitamin K inhibitory effect May need less coumadin to achieve desired anticoagulant affect To test or not? Recent studies show conflicting results May take 6 to 30 days to get PGx results Cost is upwards of $500 Doc has already figured out INR was too high and patient needs less warfarin American College of Chest Physicians Not currently recommending PGx testing prior to warfarin therapy In use since 1926 For treatment and prevention of thrombosis VTE, PE, Stroke, CABG surgery Extracted from porcine intestinal mucosa or beef lung Heterogeneous mixture of sulfated mucopolysaccharides 2,000-30,000 Daltons Potentiates activity of AT Enhances ability of AT to inhibit Xa, thrombin (IIa), other serine proteases Administered IV for usually no more than 5 days CABG surgery, angioplasty, stent placement 7

8 Mechanism of UH IX IXa VIIIa Heparin + AT X II Xa Va IIa Clot inhibiting AT Antithrombin Can be monitored by PTT Easily neutralized by protamine sulfate Anticoagulant of choice when rapid effect is needed Relatively inexpensive Variation in drug sensitivity Inhibited by PF4 Can bind to other plasma proteins Inhibits platelet function and increases vascular permeability Can lead to bleeding/hemorrhage May bind to endothelium Adds to short plasma half-life problem Side effects Can cause osteoporosis with longterm use Heparin-induced thrombocytopenia (HIT) 1 5% of patients develop IgG ab s to platelets Derived commercially by chemical or enzymatic fractionation of UH Lovenox (Enoxaparin) Fragmin (Daltaparin) Innohep (Tinzaparin) Smaller heparin molecule than UH Short chains of mucopolysaccharides Daltons 8

9 Administered subq Preferentially enhances inhibition of Xa and to a lesser extent thrombin Safer to use in settings when less anticoagulant effect is needed VTE prevention Treatment of DVT and PE IX IXa VIIIa Mechanism of LMWH X II Xa Va IIa LMWH + AT AT Antithrombin Clot inhibiting LMWH Low Molecular Weight Heparin Reduced interference with platelet function and vascular permeability Less non-specific binding to proteins and cell surfaces Easier to calculate dosage established by weight-based nomograms More predictable response Longer plasma half-life Resists inhibition by PF4 Prophylactic doses do not have to be monitored with PTT Monitoring is indicated in some situations Renal impairment Morbid obesity/extreme thinness Children Pregnant women Diabetic patients Chronic inflammation Liver disease Can be administered SubQ so patients do not have to remain in hospital Frequency of Heparin Induced Thrombocytopenia (HIT) is reduced by 90% in patients who have never received heparin 9

10 Synthetic form of the active pentasaccharide sequence in UH and LMWH FDA approved in 2001 Selective for Factor Xa Equivalent to UH and LMWH in clinical efficacy and safety Lowest risk of HIT (<0.01%) Administered SubQ like LMWH Approved for treatment of VTE and for surgical prophylaxis Does not need frequent monitoring Most common drug induced thrombocytopenia (3%) HIT type I - Non-immune and self-limiting Occurs within first 1 3 days of heparin HIT type II - Immune mediated Occurs in 1-5% of patients receiving UH after several days of therapy or earlier in individuals who have been previously sensitized Antibodies form to platelets Can cause activation and aggregation Complication of heparin therapy Platelet rich thrombi which have a white appearance Most significant adverse effect of heparin after bleeding 30% to 50% will develop venous and/or arterial thrombosis (HITT) 40-60% will recover 20-30% will have permanent disability (amputation, stroke) 20-30% will die Heparin must be DQ d Use DTIs such as Argatroban, or Angiomax /Bilvalirudin (synthetic hirudin) PTT Anti-Xa assay Acitivated Clotting Time (ACT) 10

11 Intrinsic system test Tests for all clotting proteins except VII and XIII Traditionally used to screen for bleeding disorders and to monitor patients on heparin therapy Can also be used for Argatroban Reference Range - 20 to 35 seconds Therapeutic Range to 3.0 times mean normal Intrinsic Pathway XII XI IX XIIa XIa IXa VIII PL X Prothrombin (II) Fibrinogen (I) Xa V PL Thrombin (IIa) Fibrin Common Pathway Inexpensive Well-controlled in the lab Available 24 hrs/day Great variation in patient response Not sensitive to LMWH Accuracy and reproducibility is affected by: Presence of heparin neutralizing proteins (PF4) Acute phase responses - lead to variations in coagulation factor levels (Fibrinogen, VIII) Hypofibrinogenemia, factor deficiencies, LA s, etc., can prolong APTT Differences between APTT reagents/methods BETTER method for monitoring heparin therapy More sensitive than PTT More expensive but much easier to calibrate Replacing PTT for monitoring UH therapy Most labs already have instrumentation needed Economic impact studies show anti-xa assays save cost of repeat assays Shorter time to achieve therapeutic range 11

12 Not affected by LA, specific factor inhibitors or deficiencies Can be used for LMWH and Fondaparinux when monitoring is needed Children, morbidly obese or grossly underweight adults, pregnant women Mixture of AT and a measured excess of Xa is mixed with patient plasma Note: Some reagents use the patient s own AT AT binds heparin present in patient s plasma and the AT/heparin complex then binds Xa Chromogenic substrate specific to Xa is added to mixture Any excess free Xa digests substrate and liberates a color Amount of color liberated is inversely proportional to heparin concentration Standard curve is constructed using known amounts of heparin POCT Blood is drawn into tube with activator then placed in electromechanical instrument with timer Used to measure high dose heparin therapy and bivalirudin therapy e.g. CABG surgery, PCI Also called NOACs New Oral AntiCoagulants Percutaneous Coronary Intervention also called angioplasty Direct Thrombin Inhibitor (DTI) Approved by US FDA in 2010 First successful oral anticoagulant since warfarin Initially only cleared for AF Now cleared for acute and extended treatment of VTE Xa Inhibitors RivaroXaban (Xarelto ) ApiXaban (Eliquis ) EdoXaban (Savaysa, Lixiana ) Approved by FDA in January 2015 FDA approved oral alternatives to warfarin for AF VTE treatment and prevention Thromboprophylaxis in hip or knee replacement surgery 12

13 /wepdwu /wedaam Roles of Thrombin and Xa in clotting XII XI IX XIIa XIa IXa VIII PL X Prothrombin II Fibrinogen Xa V PL Thrombin IIa Fibrin PL Phospholipid on plt membrane No lab test currently cleared by FDA to detect and measure plasma concentration PT not sensitive PTT Great variability among assays Semiquantitative at best and not linear Fibrinogen (I) Thrombin (IIa) Fibrin TT too sensitive for monitoring Dabigatran which is a Direct Thrombin Inhibitor Uses lower concentration of thrombin Linear and sensitive to plasma levels of Dabigatran Monitoring possibilities for Dabigatran Time in seconds TT: Too sensitive Dilute TT: Linear and sensitive PTT: Not linear PT: Too insensitive Dabigatran concentration in blood Laposata, M., Latest Anticoagulants-nuts and bolts for labs, CAP Today, Feb 2013, 13

14 RVV activates FX drvv Test Has low levels of phospholipid to make it sensitive to LA Traditionally used to screen for presence of a Lupus Anticoagulant drvvc (Confirm) Has high levels of phospholipid Traditionally used to confirm the presence of LA Recent study Showed drvvc could be used off-label to monitor dabigatran David L. McGlasson, George A. Fritsma, Blood Coagulation and Fibrinolysis, Measuring dabigatran with the dilute Russell viper venom confirm assay in an anticoagulation clinic population, July Ecarin enzyme from Echis carinatus venom Converts prothrombin to meizothrombin Meizothrombin cleaves a chromogenic substrate with release of a chromogen and change in OD DTIs bind meizothrombin so concentration of DTI is inversely proportional to change in OD No FDA approved calibrators or controls Apixaban, Rivaroxaban and Endoxaban PTT insensitive PT can be linear and sensitive but only with certain PT reagents TT insensitive drvvt Several recent articles have shown this assay to be useful for monitoring all DOACs including the Xa inhibitors Rapid onset No important dietary interactions Fewer problems with drug interactions As good or better in preventing stroke in AF Same or less bleeding than warfarin Lower rates of strokes and intracranial hemorrhages for all ages Slightly less (10%) mortality Fixed Dosing Do not require laboratory monitoring EXCEPT Patients with extremes of body weight Patients who are experiencing hemorrhage or thrombosis Patients requiring emergent surgical procedure while on therapy Rapid offset - missing a dose could put patient at risk for clotting however Recent studies indicate effects of dabigatran remain for at least 12 hours despite missing dose GI pain in up to 30% of patients on Dabigatran 14

15 No reversal agent for bleeding patients Vit K and FFP do nothing PCCs seem to help but are very expensive FFP Fresh Frozen Plasma PCC Prothrombin Complex Concentrates More expensive $5.46/day for dabigatran vs $0.37/day for warfarin But, recent studies investigating long term cost effectiveness Dabigatran cost-effective vs warfarin in patients with AF regardless of age of treatment initiation (US) Renal insufficiency may prohibit use Three companies working on reversal agents Idarucizumab for Dabigatran currently being considered by FDA (Boehringer Ingelheims) Also, one in the works that seems to immediately reverse all four DOAC s Primary hemostasis vs secondary hemostasis Use and mode of action of various anticoagulants Aspirin Warfarin Heparin, LMWHs Direct thrombin inhibitors Anti Xa agents Utilization of lab tests in monitoring anticoagulants PT/INR, PTT, Anti-Xa Assay, ACT, Dilute TT, drvvc and Ecarin Clot Assay Check W. Elders hang tough against newcomers, CAP Today, Jan 2012 Exner T, Ellwood L, Rubie J, Barancewicz A. Testing for new oral anticoagulants with LA-resistant Russells viper venom reagents. An in vitro study. Thromb Haemost 2013; 109: Douxfils J, Classen J-F, Baudar J, Walbrecq S, Chatelain C, Chatelam B,et al. Dilute Russell viper venom time: a useful assay for the monitoring of direct oral anticoagulants in patients? 2013 International Society on Thromb Haemost 2013; 11: ; [Abs PB ]. Laposata, M., Latest Anticoagulants-nuts and bolts for labs, CAP Today, Feb 2013 McGlasson D, Fritsma, G. Measuring dabigatran with the dilute Russell viper venom confirm assay in an anticoagulation clinic population. Blood Coagulation and Fibrinolysis 2015, 26:00-00 McKenzie S, Williams L, Clinical Laboratory Hematology, 3 rd Ed., 2015 Rodak B, Fritsma G, Keohane E, Hematology, Clinical Principles and Applications, 4 th Ed.,