Hemostasis and Thrombosis - part 8 pps

147 Antithrombotic Therapy for Cardiac Disease 20 in Table 20.6. It is relatively safe for short periods of time to stop anticoagulation. One should avoid large doses of vitamin K (greater than 1-2 mg) for reversal of warfarin anticoagulation. The higher doses of vitamin K are no more effective than lower doses, and when the patient needs to be restarted on warfarin it will take a much longer time to reach a therapeutic prothrombin time when high doses of vitamin K have been used. Bioprosthetic Heart Valves Although the risk is lower, bioprosthetic hearts valves still have a definite risk of associated embolization. This is highest immediately after surgery and in patients with bioprosthetic valves who have other risk factors such as atrial fibrillation. There- fore patients with a new bioprosthetic valve should be anticoagulated for 3 months after surgery with warfarin to an INR of 2.0-3.0. Furthermore, patients with atrial fibrillation, history of embolism or those with left atrial thrombi should be antico- agulated indefinitely with warfarin. Chronic Heart Failure Patients with left ventricular ejection fractions under 30% associated with global dysfunction have rates of stroke of 3-4%/year. In addition, these patients are also at risk for venous thrombosis with as many as 20% of these patients dying of venous Table 20.5. Risk stratification and therapy of mechanical valve patients High Risk Treat to INR 2.5 - 3.5 + ASA 80-100mg/day. Valve implanted before 1980 Previous embolism Vascular disease Risk of stroke >2%/yr on warfarin alone Medium Risk INR 2.5 - 3.5 Low Risk INR 2-3 Bileaflet valve in aortic position Treatment and Risk Stratification of Bioprosthetic Valves AVR or MVR: INR 2.5 - 3.5 for 3 months then ASA + a fib: INR 2-3 + hx embolism, vascular disease or LA thrombus: INR 2.5-3.5 + ASA 80 - 100 mg/day Table 20.6. Risk(%) for embolic events when off anticoagulation (Pauker, JAMA) Aortic Position One Day Two Weeks One Year Ball 0.03 0.44 11 Bjork 0.03 0.38 10 St Jude 0.02 0.21 5 Mitral Position Ball 0.08 1.13 30 Bjork 0.05 0.74 19 St Jude 0.03 0.48 13 148 Hemostasis and Thrombosis 20 thrombotic disease. Unfortunately this group of patients has not been well-studied, but patients with global cardiac dysfunction should be considered candidates for anticoagulation, especially if they have had previous emboli. Suggested Reading 1. Albers GW, Dalen JE, Laupacis A et al. Antithrombotic therapy in atrial fibrilla- tion. Chest 2001; 119(1 Suppl):194-206. 2. Antman EM. ‘I can see clearly now’: a new view on the use of IV GP IIb/IIIa inhibitors in acute coronary syndromes. Eur Heart J 2002; 23(18):1408-11. 3. Bloomfield P. Choice of heart valve prosthesis. Heart 2002; 87(6):583-9. 4. Braunwald E, Antman EM, Beasley JW et al. ACC/AHA 2002 guideline update for the management of patients with unstable angina and non-ST-segment eleva- tion myocardial infarction—summary article: J Am Coll Cardiol 2002; 40(7):1366-74. 5. Brogan GX Jr. Bench to bedside: pathophysiology of acute coronary syndromes and implications for therapy. Acad Emerg Med 2002; 9(10):1029-44. 6. Chan AW, Moliterno DJ. Defining the role of abciximab for acute coronary syn- dromes: lessons from CADILLAC, ADMIRAL, GUSTO IV, GUSTO V, and TARGET. Curr Opin Cardiol 2001; 16(6):375-83. 7. Choo JK, Young JJ, Kereiakes DJ. A guide to drug use during percutaneous coro- nary intervention. Drugs 2002; 62(18):2589-601. 8. Fuster V, Ryden LE, Asinger RW et al. ACC/AHA/ESC guidelines for the man- agement of patients with atrial fibrillation. Eur Heart J 2001; 22(20):1852-923. 9. Hart RG, Palacio S, Pearce LA. Atrial fibrillation, stroke, and acute antithrombotic therapy: analysis of randomized clinical trials. Stroke 2002; 33(11):2722-7. 10. Kereiakes DJ, Montalescot G, Antman EM et al. Low-molecular-weight heparin therapy for non-ST-elevation acute coronary syndromes and during percutaneous coronary intervention: an expert consensus. Am Heart J 2002; 144(4):615-24. 11. McKay RG, Boden WE. Small peptide GP IIb/IIIa receptor inhibitors as upstream therapy in non-ST-segment elevation acute coronary syndromes: results of the PURSUIT, PRISM, PRISM-PLUS, TACTICS, and PARAGON trials. Curr Opin Cardiol 2001; 16(6):364-9. 12. Mukherjee D, Topol EJ. The role of low-molecular-weight heparin in cardiovascu- lar diseases. Prog Cardiovasc Dis 2002; 45(2):139-56. 13. Ohman EM, Harrington RA, Cannon CP et al. Intravenous thrombolysis in acute myocardial infarction. Chest 2001; 119(1 Suppl):253-277. 14. Osula S, Bell GM, Hornung RS. Acute myocardial infarction in young adults: causes and management. Postgrad Med J 2002; 78(915):27-30. 15. Stein PD, Alpert JS, Bussey HI et al. Antithrombotic therapy in patients with mechanical and biological prosthetic heart valves. Chest 2001; 119(1 Suppl):220-227. 16. Crowther MA, Ginsberg JS, Julian J et al. A comparison of two intensities of war- farin for the prevention of recurrent thrombosis in patients with the antiphos- pholipid antibody syndrome. N Engl J Med 2003; 349(12):1133-8. 17. Hanly JG. Antiphospholipid syndrome: an overview. CMAJ 2003; 16(13):1675-82. 18. Kearon C, Ginsberg JS, Kovacs MJ et al. Extended low-intensity anticoagulation for thrombo-embolism investigators. Comparison of low-intensity warfarin therapy with conventional-intensity warfarin therapy for long-term prevention of recur- rent venous thromboembolism. N Engl J Med 2003; 349(7):631-9. CHAPTER 21 Hemostasis and Thrombosis, 2nd Edition, by Thomas G. DeLoughery. ©2004 Landes Bioscience. Stroke and Peripheral Vascular Disease Stroke Cerebrovascular disease may be caused by atherosclerosis, embolism, or unusual causes such as vasculitis. Most strokes are due to either atherosclerosis or embolism and discussion here will focus on these causes. However, the clinician must be alert to more unusual causes of stroke in selected cases. Acute Stroke The patient with acute neurological defects demands a rapid decision as to whether the defect is ischemic in nature and, if so, what therapy should be instituted (Table 21.1). Patients with symptoms less than three hours old are candidates for throm- bolytic therapy. Evaluation of these patients should be rapid. Patients should un- dergo a CT scan to rule out hemorrhage or mass lesion. Evaluation for an underlying systemic process should also be undertaken. Patients who meet rigorous NINDS trial criteria should be considered for throm- bolytic therapy (Table 21.2). Thrombolytic therapy is believed to be associated with an improvement in clinical outcome but the rate of intracranial hemorrhage is high and patient selection is crucial. The rate of bleeding complications is increased in patients who did not meet the NINDS criteria but still received thrombolytic therapy. Absolute contraindications to thrombolytic therapy include CT evidence of intrac- ranial hemorrhage, systolic blood pressure greater than 185 mmHg or diastolic greater than 110 mm Hg, or a seizure with or before stroke onset. Patients who undergo thrombolytic therapy should receive tPA 0.9 mg/kg (maximum 90 mg) with ten percent of the dose given in one minute. The rest should be given over one hour. Patients who receive thrombolytic therapy should not receive any other form of anticoagulation including aspirin for 24 hours. These patients should be carefully monitored for signs of bleeding. Table 21.1. Antithrombotic therapy of cerebrovascular disease Transient Ischemic Attack Ipsilateral carotid stenosis > 69%: endarterectomy Others: aspirin 75-160 mg/day or clopidogrel in aspirin-intolerant patients Acute Stroke Thrombolytic candidates: tPA 0.9 mg/kg (maximum 90 mg) with ten percent of the dose given in one minute Embolic stroke: anticoagulation with heparin after 12-24 hours in patients with no significant hemorrhage All others: aspirin 160 mg/day or clopidogrel in aspirin-intolerant patients 150 Hemostasis and Thrombosis 21 Patients who do not undergo thrombolytic therapy and do not have an obvious embolic source for their stroke should be started on aspirin. Two large trials have shown a small but real benefit of aspirin in preventing death or disability. Since patients with stroke also have risk factors for ischemic heart disease the aspirin will be of benefit for this as well. Clopidogrel can be substituted in the aspirin-intolerant patient. Currently the combination of aspirin and clopidogrel is being examined in a large trial to see if it has any advantage over single drug therapy. Recently a trial using a novel sustained-release form of dipyridamole and aspirin showed greater benefit in secondary stroke prevention than with aspirin alone. How- ever, the results of this isolated trial have been controversial and in this trial the combination pill had no effect on cardiovascular events. Until further data is avail- able from an ongoing trial, the role of dipyridamole in stroke prevention remains unknown. Patients who clearly have an embolic source for their stroke require life-long anti- coagulation. The timing of the initiation of heparin therapy is controversial, but patients with small strokes without significant hemorrhage should be started on heparin within 24 - 48 hours of the event and maintained on warfarin at an INR of 2-3. It is not clear how long the patient who suffers an intracranial hemorrhage on warfarin should remain off this drug. Recent data suggest that one to two weeks off warfarin may be appropriate if the patient has a very strong indication for antico- agulation such as a mechanical valve. One should carefully investigate the circum- stances around the time of the bleed to see if there are any reversible factors such as a very high INR. Given the lack of data, treatment should be tailored to the indi- vidual patient’s circumstances. Table 21.2. NINDS trial criteria for tPA Patients Must Have All the Following An ischemic stroke with a clearly defined time of onset, A deficit measurable on the NIHSS (National Institutes of Health Stroke Scale), and Baseline computed tomographic (CT) scan of the brain showing no evidence of intracranial hemorrhage. Exclusions (Any of the following) Stroke or serious head trauma within the preceding 3 months; Major surgery within the prior 14 days; History of intracranial hemorrhage; Systolic blood pressure above 185 mm Hg or diastolic blood pressure above 110 mm Hg; Rapidly improving or minor symptoms; Symptoms suggestive of subarachnoid hemorrhage; Gastrointestinal hemorrhage or urinary tract hemorrhage within the previous 21 days; Arterial puncture at a noncompressible site within the previous 7 days; Seizure at the onset of stroke; Patient on oral anticoagulants with INR >1.7; Patients on heparin within the previous 48 hours and still with an elevated aPTT; Platelet count below 100,000; Prothrombin time higher than 15 seconds; Glucose concentration below 50 mg/dl or above 400 mg/dl. N Engl J Med 1995; 333(24):1581-7. 151 Stroke and Peripheral Vascular Disease 21 A frequent cause of morbidity and mortality in the stroke patient is deep venous thrombosis and pulmonary embolism. Stroke patients should receive prophylaxis with low molecular weight heparin which has been shown to be safe and effective in these patients and does not increase the risk of bleeding. Transient Ischemic Attacks Patients with a transient neurological syndrome should be evaluated for the pres- ence of carotid stenosis. Patients with ipsilateral carotid stenosis of over 70% should receive endarterectomy if they are surgical candidates. All patients with TIA should be started on aspirin. Clinical trials have shown that 30-75 mg of aspirin is equiva- lent to higher doses in secondary prevention. For patients who are intolerant of aspirin or who are aspirin failures clopidogrel is of benefit. Patients with atheroscle- rosis should also receive aggressive treatment of risk factors such as adverse lipid profiles and smoking. Patients with Recurrent Strokes Except for a small effect of aspirin, there is no good strategy for secondary pre- vention of nonembolic stroke. Patients who fail antiplatelet therapy are often placed on warfarin. Warfarin at high INRs (3-4.5) is associated with a high rate of intracra- nial bleeding and should not be used. A trial looking at lower INRs (1.4- 2.8) also demonstrated that warfarin fails to offers any benefit over aspirin in the secondary prevention of non-embolic strokes. Currently a clinical trial is underway to see if warfarin at an INR 2-3 is effective for stroke prevention. As noted above, trials are ongoing to study novel approaches to antiplatelet therapy. Patent Foramen Ovale and Stroke Patent foramen ovale (PFO) exists in 20% of normal individuals and the inci- dence in young stroke patients, especially those with idiopathic stroke, may be as high as 60%. Much controversy exists over the value of diagnosing PFO and ap- proach to management. In general the PFO is more likely to be a source of embo- lism if: • There is no evidence of atherosclerosis; • There is a source of venous thrombosis; • MRI shows areas of multiple infarcts; • The PFO shows significant shunting; • There is the presence of atrial septal aneurysm. Management options for PFO are to 1) close the PFO either surgically or with catheter devices, 2) use aspirin, or 3) use warfarin. Presently there is much interest in transcatheter closure devices. However, studies demonstrate a residual risk of throm- bosis and if the patient has an underlying hypercoagulable state, closure alone is not adequate therapy. Although data is conflicting, a meta-analysis has demonstrated warfarin still should be considered for patients with presumed embolic stroke and PFO. Stroke in Young Patients Patients under age 50 with a stroke should receive aggressive evaluation (Table 21.3). In younger patients, premature atherosclerosis and embolism are still the two most common causes of stroke. Patients should undergo a transesophageal echocardiogram to investigate for any underlying cardiac source of stroke. 152 Hemostasis and Thrombosis 21 Management of patients who have an embolic source of stroke and abnormali- ties on echocardiography is still controversial. The rate of recurrent stroke in pa- tients with patent foreman ovale is approximately 1-2% per year. Therapeutic options include surgical correction or life-long anticoagulation. Patients with large defects, more than one event, or posterior circulation events appear to be at higher risk of recurrence. Patients with premature strokes should receive a limited evaluation for hyperco- agulable states. There is no convincing evidence that deficiency of protein S, protein C, antithrombin or the presence of the factor V Leiden mutation increases risk of stroke. Patients should be evaluated for the presence of antiphospholipid antibod- ies, obtain a full lipid profile and have a homocysteine level determined. Given the association with premature atherosclerosis, levels of lipoprotein(a) should also be determined. Peripheral Vascular Disease Acute Ischemia Patients who present with an acute occlusion of the arterial blood supply of a limb require rapid intervention to save the limb. The time window is only four to six hours from onset of ischemia for limb salvage. Patient may suffer either an embo- lism or sudden thrombosis of a pre-existent atherosclerotic area. Patients with em- bolic disease often just require removal of the thrombus. Patients with thrombosis over atherosclerosis often require re-vascularization; therefore, differentiating be- tween these two entities is important in order to formulate therapy. Patients who have embolic occlusion have sudden onset of symptoms and rarely have pre-existing symptoms. Often there will an obvious source of the embolism such as atrial fibril- lation. Patients with underlying atherosclerosis will have previous symptoms of pe- ripheral vascular disease. The presentation of acute ischemia is the classic “Five P’s”: Pain, Pallor, Paralysis Paresthesia, and Pulselessness. The affected limb should undergo evaluation to de- termine the degree of ischemia. Patients with mild weakness and sensory loss but without profound paralysis of the limb need emergent therapy to salvage the limb. The patient should undergo rapid evaluation for systemic disease. Although embo- lic occlusion can often be diagnosed on clinical grounds, angiography is indicated in many cases to determine the underlying cause by either demonstrating diffuse ath- erosclerotic disease or a discrete embolism. Patients with acute ischemia require rapid anticoagulation with heparin. Patients with embolic disease and salvageable limbs require embolectomy via a Fogarty cath- eter. Catheter- based thrombolytic therapy is required for thrombi that cannot be removed with the catheter or for multiple small vessel thrombi. Patients with embolic Table 21.3. Evaluation of the young patient with stroke • Angiogram • Antiphospholipid antibodies • Lipoprotein (a) • Plasma homocysteine •Transesophageal echocardiogram 154 Hemostasis and Thrombosis 21 Patients who have thrombosed their bypass grafts are often treated with warfarin anticoagulation with or without aspirin. Patients whose grafts fail due to thrombosis and not due to technical reasons or fibrous hyperplasia should be given a trial of warfarin combined with low-dose aspirin. Suggested Reading 1. Albers GW, Amarenco P, Easton JD, Sacco RL, Teal P. Antithrombotic and throm- bolytic therapy for ischemic stroke. Chest 2001; 119(1 Suppl):300-320. 2. Chant H, McCollum C. Stroke in young adults: the role of paradoxical embolism. Thromb Haemost 2001; 85(1):22-9. 3. Hiatt WR. Medical treatment of peripheral arterial disease and claudication. N Engl J Med 2001; 344(21):1608-21. 4. Jackson MR, Clagett GP. Antithrombotic therapy in peripheral arterial occlusive disease. Chest 2001; 119(1 Suppl):283-299. 5. Johnston SC. Clinical practice. Transient ischemic attack. N Engl J Med 2002; 347(21):1687-92. 6. Klausner HA, Lewandowski C. Infrequent causes of stroke. Emerg Med Clin North Am 2002; 20(3):657-70. 7. MacWalter RS, Shirley CP. A benefit-risk assessment of agents used in the second- ary prevention of stroke. Drug Saf 2002; 25(13):943-63. 8. Makin AJ, Silverman SH, Lip GY. Antithrombotic therapy in peripheral vascular disease. BMJ 2002; 325(7372):1101-4. 9. Mohr JP, Thompson JL, Lazar RM et al. A comparison of warfarin and aspirin for the prevention of recurrent ischemic stroke. N Engl J Med 2001; 345(20):1444-51. 10. O’Keeffe ST, Woods BO, Breslin DJ et al. Blue toe syndrome. Causes and man- agement. Arch Intern Med 1992; 152(11):2197-202. 11. Schievink WI. Spontaneous dissection of the carotid and vertebral arteries. N Engl J Med 2001; 344(12):898-906. 12. Straus SE, Majumdar SR, McAlister FA. New evidence for stroke prevention: sci- entific review. JAMA 2002; 288(11):1388-95. 13. Olsson SB. Stroke prevention with the oral direct thrombin inhibitor ximelagatran compared with warfarin in patients with non-valvular atrial fibrillation (SPORTIF III): randomized controlled trial. Lancet 2003; 362(9397):1691-1698. Table 21.4. Blue toe syndrome (after O’Keefe) Atheroembolism Platelet aggregates Cholesterol crystals Warfarin-related cholesterol embolism Cardiac Embolism Infective endocarditis Non-thrombotic endocarditis Cardiac myxoma Atrial fibrillation Prosthetic valve embolism Hyperviscocity Syndromes Cryoglobulinemia Cryofibrinogen Cold agglutinins Polycythemia rubra vera Leukemias Macroglobulinemia Hypercoagulable States Malignancy Diabetes Antiphospholipid antibodies Essential thrombocytosis Erythromelalgia Disseminated intravascular coagulation Deep venous thrombosis Vasculitis Microscopic polyarteritis Classic polyarteritis nodosa Lupus vasculitis 156 Hemostasis and Thrombosis 22 For acute venous thrombosis the approved doses are either enoxaparin 1 mg/kg every 12 hours or tinzaparin 175 µ/kg every day (see Table 22.2 for all LMWH doses). For low-risk patients (calf vein thrombosis, upper extremity thrombosis), once-a-day therapy with 1.5 mg/kg of enoxaparin can be used, but this may not be adequate for higher-risk patients and twice a day therapy should be used. One trial did demonstrate that once daily dalteparin was inferior to twice a day therapy for venous disease and this dosing should not be used. For short courses of therapy, most patients do not need to have LMW heparin levels drawn. Patients who are very obese (>two times ideal body weight), who have severe liver or heart failure, who are pregnant, or on long-term LMWH therapy should have levels performed. LMWH are renally cleared and the dose needs to be adjusted for renal function. For patients with creatinine clearance between 10-30 cc/hr the dose of enoxaparin is 0.65 mg/kg q12 hours. In patients on dialysis or with creatinine clearances less that 30 cc, the dose of enoxaparin should be 1 mg/kg/day. The pharmacokinetics of LMWH are not affected by weight and there should be no capping or adjusting of doses for overweight patients. Levels are drawn four hours after injection and the therapeutic range for enoxaparin is 0.7-1.2 anti-Xa units. Therapeutic ranges for other low molecular heparins have not been as well established. The LMW heparins can be used in either inpatient or outpatient settings. Al- though LMW heparin is more expensive, inpatient savings can be realized since multiple aPTT’s, daily platelet counts, and continuous intravenous therapy are not needed. In addition, it was in the general inpatient population that clinical trials demonstrated LMW heparin’s effectiveness and safety over that of standard heparin. Table 22.2. Agents and dosing Heparin Route of administration: Subcutaneous or intravenous Prophylactic: 5,000 units tid Therapeutic: Bolus 5-10,000 units followed by 1-2,000 units/hour to achieve heparin levels of 0.35-0.7 anti-Xa units Low Molecular Weight Heparin Daltaparin Prophylactic: 2500 units qday (low risk); 5000 units q day (high-risk abdominal surgery) Therapy: 100 units/kg every 12 hours Enoxaparin Prophylactic: 40 mg/day or 30 mg every 12 hours (orthopedic indications) Therapy: 1 mg/kg every 12 hours or 1.5 mg/kg in low risk patients Nadroparin Prophylactic: 2850 units every 24 hours (38 units/kg in high risk patients) Therapy: 86 units/kg every 12 hours or 171 units/kg every 24 hours Tinzaparin Prophylactic: 3500 units every 24 hours (4500 units in high risk patients) Therapy: 175 units every 24 hours Pentasaccharide Fondaparinux Prophylaxis: 2.5 mg every 24 hours Therapy: 7.5 mg every 24 hours (consider 5.0 mg in patients under 50kg and 10 mg in patients over 100 kg) [...]... 1. 5-1 .9 2. 0-2 .5 2. 5-3 .0 >3.0 3.0 3.0 3.0 Dosage (Mg) 5.0 5.0 2.5 1. 0-2 .5 0.0 5. 0-1 0.0 2. 5-5 .0 0. 0-2 .5 0. 0-2 .5 0.0 10.0 5. 0-7 .5 0. 0-0 .5 0.0 10.0 7. 5-1 0.0 0. 0-5 .0 0.0 7. 5-1 2.5 5. 0-1 0.0 0. 0-7 .5 0.0 10 mg Warfarin Nomogram 1 2 3 4 5 6 10.0 < 1.5 1. 5-1 .9 2. 0-2 .5 >2.5 3.0 3.0 2.5 3.0 3.0 3.0 3.0 7. 5-1 0.0 2.5 1. 0-2 .5 0.0 5. 0-1 0.0 2. 5-5 .0 0. 0-2 .5 0. 0-2 .5 0.0 10.0 5. 0-7 .5 0. 0-0 .5 0.0 10.0 7. 5-1 0.0 0. 0-5 .0 0.0 7. 5-1 2.5 5. 0-1 0.0 0. 0-7 .5 0.0 Crowther MA, Harrison L, Hirsh J Ann Internal Med 1997; 127:333 24 ... monitoring of low-molecular-weight heparin, danaparoid, hirudin and related compounds, and argatroban Arch Pathol Lab Med 19 98; 122(9):79 9 -8 07 Heparin and Heparin-Like Drugs 6 7 8 9 10 11 163 O’Shea SI, Ortel TL Issues in the utilization of low molecular weight heparins Semin Hematol 2002; 39(3):17 2 -8 Turpie AG Pentasaccharides Semin Hematol 2002; 39(3):15 8- 7 1 Warkentin TE Platelet count monitoring and laboratory... after day 10 Thrombosis New thrombosis or skin necrosis or systemic reaction with heparin Progressive or None recurrent thrombosis or suspected but not proven thrombosis OTher cause for thrombocytopenia No Possible platelets falls < 5 days and no recent (100 days) heparin Definite Pretest Score 6 -8 =high, 4-5 intermediate, 0-3 low Warkentin, Heddle Current Hematology Reports 2:1 48; 2003 heparin and can be... vary from aPTT ratios of 1. 8- 2 .5 to 2. 5-4 .8! Some patients may require as much as 2,000 to 2,400 units/hour 1 58 22 Hemostasis and Thrombosis When using standard heparin, one must be very aggressive in rapidly achieving a therapeutic aPTT Unlike the relationship of subtherapeutic heparin levels to recurrent thrombosis, there is no association between supratherapeutic aPTT’s and bleeding Thus, one should... venous catheters and intra-aortic balloon pumps are coated with heparin The presence of heparin-coated catheters is enough to perpetuate the HIT process, and these must be changed to non-heparin coated devices Patients with HIT and active thrombosis are difficult to manage since these patients cannot receive heparin Low molecular weight heparins cross-react with the HIT antibodies and therefore these... effect and are listed in Table 24.3 Unfortunately, many drugs may have an unpredictable effect on the INR The most prudent strategy is to check the INR several days after starting a new drug and then Hemostasis and Thrombosis, 2nd Edition, by Thomas G DeLoughery ©2004 Landes Bioscience 169 Warfarin Table 24.1 Nomograms for warfarin loading 5 Mg Warfarin Nomogram Day 1 2 3 4 5 6 INR < 1.5 1. 5-1 .9 2. 0-2 .5... the half-life increasing to more than 50 hours There is no antidote for lepirudin Patients with even slight renal insufficiency (creatinine greater than 1.5) must have lepirudin doses adjusted to avoid over-anticoagulation 22 162 22 Hemostasis and Thrombosis Up to 80 % of patients receiving long- term lepirudin therapy will develop antibodies These antibodies reduce the metabolism of hirudin and increase... 61(4):51 5-2 2 Direct Thrombin Inhibitors 4 5 6 7 8 167 Nowak G Clinical monitoring of hirudin and direct thrombin inhibitors Semin Thromb Hemost 2001; 27(5):53 7-4 1 Robson R, White H, Aylward P et al Bivalirudin pharmacokinetics and pharmacodynamics: effect of renal function, dose, and gender Clin Pharmacol Ther 2002; 71(6):43 3-9 Weitz JI, Hirsh J New anticoagulant drugs Chest 2001; 119(1 Suppl):9 5-1 07 Schulman... Argatroban, hirudin and bivalirudin Argatroban Therapy: 2 µg/kg/min infusion with dose adjustments to keep aPTT 1.5 - 3 times normal For patients with severe liver disease, start with 0.5 µg/kg/min infusion and follow aPTT to same goal of aPTT 1.5 - 3 times normal For PCI: Bolus with 350 µg/kg over 3-5 minutes and then infuse with a maintenance drip of 25 µg/kg/min adjusting to a ACT of 35 0-4 00 minutes Hirudin . Definite thrombocytopenia Pretest Score 6 -8 =high, 4-5 intermediate, 0-3 low Warkentin, Heddle Current Hematology Reports 2:1 48; 2003. 162 Hemostasis and Thrombosis 22 Up to 80 % of patients receiving long- term lepirudin. ratios of 1. 8- 2 .5 to 2. 5-4 .8! Some patients may require as much as 2,000 to 2,400 units/hour. Fig. 22.1. Mechanism of actions of heparin and heparin like anticoagulants. 1 58 Hemostasis and Thrombosis 22 When. and laboratory monitoring of low-molecular-weight heparin, danaparoid, hirudin and related compounds, and argatroban. Arch Pathol Lab Med 19 98; 122(9):79 9 -8 07. 163 Heparin and Heparin-Like Drugs 22 6. O’Shea