Hirudin was used for the first parenteral anticoagulation in

Transcription

1 Cardiovascular Drugs Recombinant Hirudin in Clinical Practice Focus on Lepirudin Andreas Greinacher, MD; Norbert Lubenow, MD Abstract Clinical applications for recombinant hirudins have been investigated for the past 10 years. The first indication for which a hirudin lepirudin has been approved is treatment of heparin-induced thrombocytopenia (HIT). Also, the recently completed trials for use of lepirudin in unstable angina indicate a potentially new indication. This review describes pharmacology and clinical applications of lepirudin with an emphasis on HIT and unstable angina. An overview of usage of lepirudin in acute coronary syndromes is given, as well as a summary of rare indications for lepirudin, such as extracorporeal circulation, for which comprehensive data are lacking. (Circulation. 2001;103: ) Key Words: recombinant hirudin platelets thrombosis cardiovascular diseases heparin Hirudin was used for the first parenteral anticoagulation in humans in and as the anticoagulant for the first hemodialysis in humans. 2 Soon after, heparin became available and has since become the most widely used drug for parenteral anticoagulation. Heparin, however, can induce a life-threatening adverse immune reaction, heparin-induced thrombocytopenia (HIT), which up to 3% of patients receiving unfractionated heparin (UFH) for 5 days will develop. 3 HIT typically manifests 5 to 10 days after the start of heparin therapy. 4 HIT antibodies bind to heparin platelet factor 4 (PF4) complexes, 5 thereby activating platelets, 6 8 generating platelet microparticles, 9 and altering endothelial cells, leading to enhanced thrombin generation and paradoxical development of new thrombi. Two prospective studies led to the first approval of a recombinant hirudin (r-hirudin), lepirudin, as an alternative for further parenteral anticoagulation of HIT patients in the European Union and United States. 13,14 This review provides an overview of pharmacology and relevant clinical data of lepirudin, with a focus on HIT and acute coronary syndromes; key studies on another nearly identical r-hirudin, desirudin (Revasc) are also reported, because experiences gathered with desirudin are certainly helpful in the application of lepirudin. Pharmacology of Lepirudin Lepirudin ([Leu, 1 Thr 2 ]-63-desulfatohirudin; 65 amino acids; molecular weight, Da; Refludan) directly inhibits the active site pocket and the fibrinogen binding site of free and clot-bound thrombin 15,16 ; desirudin differs from lepirudin only in the first two N-terminal amino acids (valine-1, valine-2); antithrombin activities are and antithrombin U/mg, respectively. In healthy subjects, plasma pharmacokinetics follow a 2-compartment model, with a terminal plasma elimination half-life (t 1/2 ) of 0.8 to 1.7 hours after injection of bolus lepirudin doses of 0.01 to 0.5 mg/kg IV and 1.1 to 2.0 hours for continuous intravenous infusions over 6 hours. 17 With subcutaneous administration, bioavailability is nearly 100%. After injection of 0.75 mg/kg SC, a peak lepirudin concentration of 0.7 g/ml occurs in 3 to 4 hours. 18 Renal clearance and degradation account for 90% of the systemic clearance. The t 1/2 of lepirudin lengthens with deterioration of renal function 19,20 to up to 150 hours. Clinical Studies in HIT In 2 prospective, multicenter, historically controlled trials, Heparin-Associated Thrombocytopenia (HAT)-1 (n 82) and HAT-2 (n 112), 13,14 patients with clinical symptoms of HIT (decreased platelet count 50% and/or new thromboembolic complication) and laboratory confirmation of HIT antibodies were enrolled. Lepirudin allowed rapid normalization of low platelet counts or maintained normal platelet counts in 88.7% and 92.6% of patients, respectively, and led to stable therapeutic prolongation of activated partial thromboplastin time (aptt) in 77.2% and 72.3% of patients over a mean treatment duration of 14.4 and 15.5 days. Both studies had similar mortality rates (7.3% and 9.8%); however, limb amputations (3.7% and 8.9%) and new thromboembolic complications (9.8% and 17.9%) differed. All fatalities were judged to be due to the underlying disease rather than to use of lepirudin. Laboratory confirmation of the clinical diagnosis of HIT led to a delay in the start of treatment with lepirudin. Even though the pretreatment periods accounted for only 8.5% (2.6 days, HAT-1) and 6% (1.9 days, HAT-2) of the duration of each study, more than one third of all new thromboembolic From the Institute for Immunology and Transfusion Medicine, Ernst-Moritz-Arndt-University Greifswald, Greifswald, Germany. Correspondence to Prof Dr A. Greinacher, Ernst-Moritz-Arndt-Universität, Institut für Immunologie und Transfusionsmedizin, Klinikum/Sauerbruchstrasse, Greifswald, Germany American Heart Association, Inc. Circulation is available at

2 1480 Circulation March 13, 2001 TABLE 1. Dosing Schedules Tested in Lepirudin Studies Bolus* Intravenous Infusion* Target aptt Ratio HIT and thrombosis 13, mg/kg IV 0.15 mg kg 1 h HIT with thrombosis and concomitant 0.2 mg/kg IV 0.1 mg kg 1 h thrombolysis 13,14 HIT with isolated thrombocytopenia 13, mg kg 1 h Thrombosis prophylaxis in patients with 0.1 mg kg 1 h history of HIT 13,14 Renal dialysis every alternate day 20,23 # mg/kg intravenous predialysis Renal dialysis or CVVH in intensive care mg kg 1 h unit patients CPB surgery mg/kg IV 0.2 mg/kg in the priming fluid of the HLM 0.5 mg/min** Monitored by ECT: 2.5 g/ml before start of HLM; g/ml during CPB Unstable angina mg/kg IV 0.15 mg kg 1 h 1 aptt s PTCA or 0.5 mg/kg IV 0.12 mg kg 1 h 1 for 24 h or 0.24 mg kg 1 h 1 for 24 h followed by 0.04 mg kg 1 h 1 for 24 h Acute MI mg/kg IV 0.5 mg kg 1 h 1 BID SC CVVH indicates chronic veno-venous hemofiltration; CPB, cardiopulmonary bypass; and HLM, heart-lung machine. Few data are available for dose recommendations in children 28 ; because of a lack of data, lepirudin cannot be recommended during pregnancy and lactation. During concomitant treatment with ASA, GP IIb/IIIa inhibitors, and fibrinolysis and in patients with platelet counts L, bleeding risk is increased and dosage may have to be reduced. In patients with renal impairment, dosage must be reduced to avoid overdosage. *Maximum body weight for calculation of dosage: 110 kg. If Actin FS or Neothromtin reagents are used in Europe, different ranges may apply (eg, ). Approved indication in the European Union and the United States. From prospective multicenter trials (historical control groups). Desirudin has been shown to be effective in a dosage of 15 mg SC BID following orthopedic hip replacement surgery. 29 From case observations. #From crossover study, dose-escalation trial. **Stop 15 minutes before end of CPB. Put 5 mg of lepirudin into CPB machine after disconnection to avoid clotting. From prospective, randomized, double-blind trials. From prospective, randomized, open trial. complications and limb amputations occurred during this time period. When these studies were conducted, a placebo-control study design was considered unethical, and no other active treatment was approved for further anticoagulation in HIT; therefore, results of lepirudin treatment were compared with those of a historical control group (n 120). The incidence of the combined end point (new thromboembolic complications, limb amputation, death) at day 35 was 52.1% in the historical control group, 25.4% in HAT-1 (P 0.014; adjusted risk ratio, 0.508; 95% CI, to 0.892), and 31.9% in HAT-2 (P 0.15; adjusted risk ratio, 0.709; 95% CI, 0.44 to 1.14). It must be taken into consideration, however, that the use of a historical control population is a major limitation when these treatment effects are estimated. In both studies, there were more bleeding events in the lepirudin-treated group compared with historical control subjects, primarily in perioperative settings and at sites of catheter insertion (39.1% [HAT-1], 44.6% [HAT-2], and 27.2% [control group]). However, there was no significant difference in the frequency of bleedings requiring transfusion (9.9% [HAT-1], 12.9% [HAT-2], and 9.1% [control group]). Other treatment options in HIT are summarized elsewhere. 21,22 Clinical Use of Lepirudin Dosage and Monitoring An overview of the lepirudin dose regimens tested is given in Table Generally, treatment with lepirudin can be monitored with the aptt, which should be determined before treatment, 4 hours after the start of intravenous lepirudin treatment, 4 hours after every dosage change, and then at least once daily. In case of underdosage, the infusion rate should be increased by 20%; in overdosage, the infusion should be stopped for 2 hours and restarted at a dose reduced by 50% if the aptt is within the therapeutic range. 13 According to the manufacturer, in patients with serum creatinine values 1.5 mg/dl, the bolus should be reduced to 0.2 mg/kg. Infusion rates should be reduced by 50% if serum creatinine values are 1.6 to 2.0 mg/dl, by 70% for values of 2.1 to 3.0 mg/dl, and by 85% for values of 3.1 to 6.0 mg/dl. Patients with serum creatinine 6.0 mg/dl either should receive a bolus of 0.1 mg/kg on alternate days only, and only if the aptt ratio is 1.5, or may be treated with an infusion starting at mg kg 1 h 1 IV. When a switch is made to oral anticoagulation, the lepirudin dose may be lowered to reach an aptt ratio of 1.5 and discontinued when the international normalized ratio exceeds ,14,30

3 Greinacher and Lubenow Lepirudin Review 1481 Potential problems with the use of the aptt are its considerable variability between patients 31 and a nonlinear correlation with lepirudin plasma levels. Especially at higher concentrations, 32,33 the ecarin clotting time (ECT) shows a more linear correlation to lepirudin plasma levels. 33 Prospective comparative studies between the 2 monitoring methods are lacking. The activated clotting time was found to correlate poorly with hirudin plasma levels ( 0.07 g/ml) during cardiopulmonary bypass. 33 Hemorrhage In all reported clinical studies, minor bleedings were more frequent in lepirudin-treated patients than in control patients. Incidences of bleeding complications were strongly related to duration of treatment, underlying disease, and comedication, particularly thrombolysis. For different syndromes treated with the same lepirudin dose (0.4 mg/kg IV bolus followed by 0.15-mg kg 1 h 1 IV infusion), bleeding risk was therefore different. Major hemorrhage occurred in HIT in 12% of patients treated with lepirudin (historical control, 9%), 13,14 in myocardial infarction (MI) plus acetyl salicylic acid (ASA) plus thrombolysis in 8% (heparin 2%), 34 and in unstable angina (UA) plus ASA in 1.2% of patients (heparin, 0.7%). 25 Neutralization of r-hirudin No specific antidote is available to neutralize r-hirudin. Small studies in human volunteers demonstrated a reversing effect of Desmopressin. 35,36 Hirudin-induced bleeding diathesis was reversed by prothrombin complex, 37 hemofiltration, hollowfiber filters (cutoff, Da), and high- and low-flux polysulfondialysers. 20 Drug Interactions Lepirudin and desirudin have been assessed together with ASA, tissue plasminogen activator, and streptokinase (SK) in patients with acute coronary syndromes. Although several thrombolysis studies had to be stopped prematurely because of an unacceptably high rate of cerebral hemorrhage with higher hirudin doses (0.4 mg/kg bolus plus 0.15 mg kg 1 h 1 IV infusion 34 or 0.6 mg/kg bolus plus 0.2 mg kg 1 h 1 IV infusion), 38,39 the Global Utilization of Streptokinase and TPA for Occluded Arteries (GUSTO II) study suggested clinical benefit of hirudin for the SK-treated patients, 40 and the Hirulog versus heparin in patients receiving streptokinase (HERO-I) trial showed higher patency with bivalirudin and SK compared with heparin and SK. 41 ASA shows an additive effect on bleeding time in individuals treated with hirudin. 42 It is unknown how hirudin interacts in vivo with GP IIb/IIIa inhibitors, ADP receptor antagonists, 43 UFH, or low-molecular-weight heparin. In vitro experiments indicate that GP IIb/IIIa inhibitors also inhibit thrombin generation on the platelet surface, 44,45 suggesting that combined use could increase bleeding risk. Induction of Antibodies Lepirudin has immunogenic properties. 46 Of 198 HIT patients treated for 5 days with lepirudin, 45% developed antihirudin antibodies. In 2% to 3% of them, the antibodies seemed to have an enhancing effect, because hirudin dose had to be decreased by 60% to maintain the aptt within the target range, probably by a decreased renal clearance of the lepirudin-immunoglobulin complexes. 47 Lepirudin in Coronary Artery Disease Hirudin but not heparin significantly reduced platelet deposition and eliminated mural thrombosis in a deep carotid injury animal model. 48 In humans, hirudins have been shown to be effective in acute coronary syndromes without ST elevation (UA), PTCA, and MI. The therapeutic window of hirudins, however, is very narrow. Acute Coronary Syndromes Without ST Elevation Lepirudin has been evaluated in patients with UA as an adjunct to ASA in 3 trials: the Antiplatelet Trials (APT) pilot study, 49 Organization to Assess Strategies for Ischemic Syndromes (OASIS-I), and OASIS-II. In OASIS-I, 50 patients with acute chest pain suspected to be due to acute coronary syndrome without ST elevation were randomized to receive 1 of 2 lepirudin doses or UFH for 72 hours (Table 2). At 7 days, fewer subjects in the group treated with lepirudin (0.4 mg/kg bolus plus 0.15 mg kg 1 h 1 ) experienced the primary outcome (combined incidence of cardiovascular death, new MI, refractory angina; relative risk [RR], 0.46; 95% CI, 0.21 to 1.02; P 0.047). In the double-blind OASIS-II trial, 25 the primary end point of cardiovascular death or new MI at day 7 showed a trend in favor of lepirudin-treated patients (Table 2). Fewer interventions (CABG, PTCA, intra-aortic balloon pump, thrombolytic therapy) were needed in lepirudin-treated patients (Table 2). A meta-analysis of the combined data of the 2 OASIS studies at 7 days showed that compared with UFH, lepirudin provided a 19% RR reduction (95% CI, 2 to 33; P 0.039) in cardiovascular death or MI; a 20% RR reduction (95% CI, 6 to 32; P 0.005) in cardiovascular death, MI, or refractory angina; a 17% RR reduction (95% CI, 5 to 28; P 0.009) in need for interventions during the first 7 days; and a 14% RR reduction (95% CI, 1 to 26; P 0.04) in death or MI at 35 days. In OASIS-II, there was an increase of 0.5% in major bleedings in lepirudin-treated patients (0.7% versus 1.2%; RR, 1.73; 95% CI, 1.13 to 2.63; P 0.01) but no difference in life-threatening bleedings (0.4% versus 0.4%). Similar trends were observed in the GUSTO IIb trial comparing desirudin (0.1 mg/kg bolus plus 0.1 mg kg 1 h 1 infusion) with UFH. The rate of death and MI at 30 days was lower in the desirudin group (9.8% versus 8.9%; OR, 0.89; 95% CI, 0.79 to 1.00; P 0.058) without reaching statistical significance, whereas the risk of moderate bleeding was slightly higher (8.8% versus 7.7%; P 0.03). 51 Acute MI Lepirudin has been assessed in patients with acute MI as an adjunct to thrombolytic therapy with alteplase or SK and ASA in 5 studies (Hirudin for the Improvement of Thrombolysis [HIT]-I, 52 HIT-II, 53 HIT-III, 34 HIT-IV, 27 and HIT- SK 54 ). In essence, lepirudin, as an adjunct to thrombolytic therapy and ASA, is at least as effective as UFH with respect to early and sustained patency rates and clinical outcome.

4 1482 Circulation March 13, 2001 TABLE 2. Outcomes of OASIS I and OASIS II in Patients With Acute Coronary Syndromes Without ST Elevation 25,50 Heparin, 5000 U bolus 15 U kg 1 h 1 IV for 72 h, n (%) Lepirudin, 0.4 mg/kg bolus 0.15 mg kg 1 h 1 IV for 72 h*, n (%) RR (95% CI) Unadjusted P Cardiovascular death/mi at 7 d OASIS I 18/371 (4.9) 14/538 (2.6) 0.54 ( ) 0.07 OASIS II 213/5058 (4.2) 182/5083 (3.6) 0.84 ( ) Total 231/5429 (4.3) 196/5621 (3.5) 0.81 ( ) Need for interventions (CABG, PTCA), intra-aortic balloon pump, thrombolytic therapy at 7 d OASIS I 32/371 (8.6) 36/538 (6.7) 0.78 ( ) OASIS II 411/5058 (8.1) 349/5083 (6.8) 0.84 ( ) Total 433/5429 (8.2) 385/5621 (6.8) 0.83 ( ) Death/MI at 35 d OASIS I 32/371 (8.6) 33/538 (6.1) 0.71 ( ) 0.15 OASIS II 388/5058 (7.7) 345/5083 (6.8) 0.87 ( ) 0.06 Total 420/5429 (7.7) 378/5621 (6.7) 0.86 ( ) 0.04 *In OASIS I, 271 patients received a reduced dose of 0.2 mg/kg bolus plus 0.1 mg/kg IV. However, the drug was associated with an unacceptably high risk of severe hemorrhages when used at the highest dosage (0.4 mg/kg plus 0.15 mg kg 1 h 1 ). 34,54 Similar data have been obtained with desirudin (0.6 mg/kg plus 0.2 mg kg 1 h 1 ). 38,39 The safety problem can be solved at the cost of reduced efficacy by use of a substantially reduced hirudin dosage. In the HIT-IV study (n 1208), a subcutaneous regimen of lepirudin (0.2 mg/kg plus 0.5 mg/kg SC BID for 5 to 7 days) was compared with UFH in conjunction with SK. The clinical outcome was similar in both groups with respect to bleeding events and efficacy end points; complete resolution of ST-segment elevation at 90 minutes was 28% versus 22% (P 0.05) and at 180 minutes was 52% versus 48% (P 0.18). Similarly, compared with UFH, desirudin at a reduced dose (0.1 mg/kg bolus followed by 0.1 mg kg 1 h 1 ) showed equal effects as an adjunctive therapy to tissue plasminogen activator and SK in MI patients, with similar rates of major bleeding. 55 PTCA A multicenter, open pilot trial 56 comparing the effects of 2 lepirudin dose regimens with UFH in patients undergoing coronary angioplasty for UA (n 61; for doses, see Table 1) suggested a dose-dependent reduction in troponin T levels after the procedure. Desirudin (40 mg bolus plus 0.2 mg kg 1 h 1 for 24 hours, followed by 40 mg SC BID or placebo for 72 hours, compared with UFH for 24 hours) reduced early cardiac events in a prospective, randomized trial of 1141 patients undergoing PTCA but had no apparent benefit with longer-term follow-up. 26 Other Indications Deep Vein Thrombosis Desirudin (15 mg SC BID) has been shown to be more effective than low-molecular-weight heparin in preventing deep vein thrombosis in orthopedic hip replacement surgery. 29 No conclusive data are available for lepirudin. At present, hirudins are much more expensive than lowmolecular-weight heparins. However, no cost-effectiveness data assessing the overall cost are available. For treatment of deep vein thrombosis (other than in HIT patients), no recommendations can be made yet for lepirudin because of small numbers in the only randomized trial. 57 Dialysis In a crossover study (n 11), lepirudin (0.15 mg/kg) and heparin (5000 to IU) were similarly effective with respect to urea, uric acid, and creatinine. 23 On the basis of a dose-escalation study, a bolus of 0.08 mg/kg lepirudin before regular hemodialysis is recommended. 20 Nowak et al 19 reported on a patient dialyzed 50 times with hirudin (r-hirudin HV1) with dosages of 0.16 and mg/kg. In patients with HIT and acute renal failure, a reduced dosage is often sufficient for safe hemodialysis or hemofiltration (0.005 mg kg 1 h 1 ; unpublished observation). Recovering diuresis, however, can lead to the need for drastically increased lepirudin doses. CABG Surgery In humans undergoing cardiac pulmonary bypass surgery with lepirudin, close monitoring by use of the ECT is essential. Pötzsch and Madlener 24 developed an algorithm suggesting a pre cardiac pulmonary bypass bolus of 0.25 mg/kg, with 0.2 mg/kg added to the priming solution. Plasma levels at the start of cardiac pulmonary bypass surgery should be 2.5 g/ml. During the surgery, 0.5 mg/min should be infused continuously and adjusted with the use of ECT measurements every 15 minutes. The infusion should be stopped 15 minutes before the end of cardiac pulmonary bypass surgery. Patients with impaired renal function may require hemofiltration to reduce lepirudin plasma levels. 24 The use of lepirudin in cardiac pulmonary bypass surgery is currently restricted to patients with HIT. Conclusions Lepirudin has a definite role in the treatment of patients with HIT and desirudin in thrombosis prophylaxis. UA is a

5 Greinacher and Lubenow Lepirudin Review 1483 potential new indication for the drug; however, r-hirudin should be compared with low-molecular-weight heparins for effectiveness and cost. There are many other indications in which lepirudin has shown feasibility, but insufficient data allow only limited conclusions. The most important adverse effects of lepirudin treatment are hemorrhages and the induction of anti-hirudin antibodies. Definition of the optimal method of lepirudin monitoring and availability of an antidote for hirudin would probably increase drug safety. Anti-hirudin antibodies paradoxically enhance the pharmacological effect of lepirudin in a subset of patients but otherwise seem to be clinically irrelevant. Other thrombin antagonists, such as argatroban or PEGhirudin, are currently undergoing clinical trials and will probably add to the scope of clinical uses that this class of drugs has. References 1. Engelmann F, Stade C. Über die Bedeutung des Blutegelextraktes für die Therapie der Eklampsie. Münchner Medizinische Wochenschrift. 1909; 43: Haas G. Über Versuche der Blutauswaschung am Lebenden mit Hilfe der Dialyse. Arch Pharmacol. 1926;116: Warkentin TE, Levine MN, Hirsh J, et al. Heparin-induced thrombocytopenia in patients treated with low-molecular-weight heparin or unfractionated heparin. N Engl J Med. 1995;332: Warkentin TE, Chong BH, Greinacher A. Heparin-induced thrombocytopenia: towards consensus. Thromb Haemost. 1998;79: Amiral J, Marfaing-Koka A, Wolf M, et al. Presence of autoantibodies to interleucin-8 or neutrophil-activating peptide-2 in patients with heparinassociated thrombocytopenia. Blood. 1996;88: Chong BH, Murray B, Berndt MC, et al. Plasma P-selectin is increased in thrombotic consumptive platelet disorders. Blood. 1994;83: Kelton JG, Sheridan D, Santos A, et al. Heparin-induced thrombocytopenia. Blood. 1988;72: Greinacher A, Michels I, Mueller-Eckhardt C. Heparin-associated thrombocytopenia: the antibody is not heparin specific. Thromb Haemost. 1992;67: Warkentin TE, Hayward CP, Boshkov LK, et al. Sera from patients with heparin-induced thrombocytopenia generate platelet-derived microparticles with procoagulant activity: an explanation for the thrombotic complications of heparin-induced thrombocytopenia. Blood. 1994;84: Cines DB, Tomaski A, Tannenbaum S. Immune endothelial-cell injury in heparin-associated thrombocytopenia. N Engl J Med. 1987;316: Visentin GP, Ford SE, Scott JP, et al. Antibodies from patients with heparin-induced thrombocytopenia/thrombosis are specific for platelet factor 4 complexed with heparin or bound to endothelial cells. J Clin Invest. 1994;93: Greinacher A, Poetzsch B, Amiral J, et al. Heparin-associated thrombocytopenia: isolation of the antibody and characterization of a multimolecular PF4-heparin complex as the major antigen. Thromb Haemost. 1994;71: Greinacher A, Völpel H, Janssens U, et al. Recombinant hirudin (lepirudin) provides safe and effective anticoagulation in patients with the immunologic type of heparin-induced thrombocytopenia: a prospective study. Circulation. 1999;99: Greinacher A, Janssens U, Berg G, et al. Lepirudin (recombinant hirudin) for parenteral anticoagulation in patients with heparin-induced thrombocytopenia. Circulation. 1999;100: Weitz JI, Hudoba M, Massel D, et al. Clot-bound thrombin is protected from inhibition by heparin-antithrombin III but is susceptible to inactivation by antithrombin III-independent inhibitors. J Clin Invest. 1990;86: Weitz JI, Leslie B, Hudoba M. Thrombin binds to soluble fibrin degradation products where it is protected from inhibition by heparinantithrombin but susceptible to inactivation by antithrombin-independent inhibitors. Circulation. 1998;97: Markwardt F, Nowak G, Stürzebecher J, et al. Clinicopharmacological studies with recombinant hirudin. Thromb Res. 1988;52: Schiele F, Vuillemenot A, Kramarz P, et al. A pilot study of subcutaneous recombinant hirudin (HBW 023) in the treatment of deep vein thrombosis. Thromb Haemost. 1994;71: Nowak G, Bucha E, Brauns I, et al. Anticoagulation with r-hirudin in regular haemodialysis with heparin-induced thrombocytopenia (HIT II). Wien Klin Wochenschr. 1997;109: Vanholder R, Dhondt A. Recombinant hirudin: clinical pharmacology and potential applications in nephrology. Biol Drugs. 1999;11: Chong BH. Danaparoid for the treatment of heparin-induced thrombocytopenia. In: Warkentin TE, Greinacher A. eds. Heparin-Induced Thrombocytopenia. New York: Marcel Dekker; 2000: Greinacher A. Treatment of heparin-induced thrombocytopenia. Thromb Haemost. 1999;82: van Wyk V, Badenhorst PN, Luus HG, et al. A comparison between the use of recombinant hirudin and heparin during hemodialysis. Kidney Int. 1995;48: Pötzsch B, Madlener K. Management of cardiopulmonary bypass anticoagulation in patients with heparin-induced thrombocytopenia. In: Warkentin TE, Greinacher A. eds. Heparin-Induced Thrombocytopenia. New York: Marcel Dekker; 2000: Organization to Assess Strategies for Ischemic Syndromes (OASIS-2) Investigators. Effects of recombinant hirudin (lepirudin) compared with heparin on death, myocardial infarction, refractory angina, and revascularization procedures in patients with acute myocardial ischaemia without ST elevation: a randomized trial. Lancet. 1999;353: Serruys PW, Herrman J-PR, Simon R, et al, for the Helvetica Investigators. A comparison of hirudin with heparin in the prevention of restenosis after coronary angioplasty. N Engl J Med. 1995;333: Neuhaus KL, Molhoek GP, Zeymer U, et al. Recombinant hirudin (lepirudin) for the improvement of thrombolysis with streptokinase in patients with acute myocardial infarction: results of the HIT-4 trial. J Am Coll Cardiol. 1999;34: Schiffmann H, Unterhalt M, Harms K, et al. Successful treatment of heparin-induced thrombocytopenia (HIT) type II in childhood with recombinant hirudin. Monatsschr Kinderheilkd. 1997;145: Eriksson BI, Wille-Jörgensen P, Kälebo P, et al. A comparison of recombinant hirudin with a low-molecular weight heparin to prevent thromboembolic complications after total hip replacement. N Engl J Med. 1997; 337: Greinacher A, Eichler P, Lubenow N, et al. Heparin-induced thrombocytopenia with thromboembolic complications: meta-analysis of two prospective trials to assess the value of parenteral treatment with lepirudin and its therapeutic aptt range. Blood. 2000;96: Hafner G, Rupprecht HJ, Luz M, et al. Recombinant hirudin as a periprocedural antithrombotic in coronary angioplasty for unstable angina pectoris. Eur Heart J. 1996;17: Nurmohamed MT, Berckmans RJ, Morrien-Salomons WM, et al. Monitoring anticoagulant therapy by activated partial thromboplastin time: hirudin assessment. Thromb Haemost. 1994;72: Pötzsch B, Madlener K, Seelig C, et al. Monitoring of r-hirudin anticoagulation during cardiopulmonary bypass: assessment of the whole blood ecarin clotting time. Thromb Haemost. 1997;77: Neuhaus KL, von Essen R, Tebbe U, et al. Safety observations from the pilot phase of the randomized r-hirudin for Improvement of Thrombolysis (HIT-III) Study: a study of the Arbeitsgemeinschaft Leitender Kardiologischer Krankenhausarzte (ALKK). Circulation. 1994;90: Ibbotson SH, Grant PJ, Kerry R, et al. The influence of infusions of 1-desamino-8-D-arginine vasopressin (DDAVP) in vivo on the anticoagulant effect of recombinant hirudin (CGP39393) in vitro. Thromb Haemost. 1991;65: Amin DM, Mant TG, Walker SM, et al. Effect of a 15 minute infusion of DDAVP on the pharmacokinetics and pharmacodynamics on Revasc during a four-hour intravenous infusion in healthy volunteers. Thromb Haemost. 1997;77: Irami MS, Harvey JW, Sexon RG. Reversal of hirudin-induced bleeding diathesis by prothrombin complex concentrate. Am J Cardiol. 1995;75: Antman EM. Hirudin in acute myocardial infarction: safety report from the Thrombolysis and Thrombin Inhibition in Myocardial Infarction (TIMI) 9A Trial. Circulation. 1994;90: Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) IIa Investigators. Randomized trial of intravenous heparin versus recombinant hirudin for acute coronary syndromes. Circulation. 1994;90:

6 1484 Circulation March 13, Metz BK, White HD, Granger CB, et al. Randomized comparison of direct thrombin inhibition versus heparin in conjunction with fibrinolytic therapy for acute myocardial infarction: results from the GUSTO-IIb trial. J Am Coll Cardiol. 1998;31: White HD, Aylward PE, Frey MJ, et al. Randomized, double-blind comparison of hirulog versus heparin in patients receiving streptokinase and aspirin for acute myocardial infarction (HERO). Circulation. 1997; 96: Breddin HK. Neue Aspekte zu Hirudin. Medwelt. 1997;48: Hirsh J, Weitz JI. New antithrombotic agents. Lancet. 1999;353: Keularts IMLW, Béguin S, de Zwaan C, et al. Treatment with a GPIIb/IIIa antagonist inhibits thrombin generation in platelet rich plasma from patients. Thromb Haemost. 1998;80: Hérault JP, Peyrou V, Savi P, et al. Effect of SR A, a potent GP IIb-IIIa antagonist, on platelet-mediated thrombin generation in vitro and in vivo. Thromb Haemost. 1998;79: Song X, Huhle G, Wang L, et al. Generation of anti-hirudin antibodies in heparin-induced thrombocytopenic patients treated with r-hirudin. Circulation. 1999;100: Eichler P, Friesen H-J, Lubenow N, et al. Anti-hirudin antibodies in patients with heparin-induced thrombocytopenia treated with lepirudin: incidence, effects on aptt, and clinical relevance. Blood. 2000;96: Heras M, Chesebro JH, Webster MW, et al. Hirudin, heparin, and placebo during deep arterial injury in the pig: the in vivo role of thrombin in platelet-mediated thrombosis. Circulation. 1990;82: Fox KAA. r-hirudin in unstable angina pectoris: rationale and preliminary data from the APT pilot study. Eur Heart J. 1995;16: Organization to Assess Strategies for Ischemic Syndromes (OASIS) Investigators. Comparison of the effects of two doses of recombinant hirudin compared with heparin in patients with acute myocardial ischaemia without ST elevation: a pilot study. Circulation. 1997;96: Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) IIb Investigators. A comparison of recombinant hirudin with heparin for the treatment of acute coronary syndromes. N Engl J Med. 1996;335: Zeymer U, von Essen R, Tebbe U, et al. Recombinant hirudin and front-loaded alteplase in acute myocardial infarction: final results of a pilot study, HIT-I (Hirudin for the Improvement of Thrombolysis). Eur Heart J. 1995;16(suppl D): von Essen R, Zeymer U, Tebbe U, et al. HBW 023 (recombinant hirudin) for the acceleration of thrombolysis and prevention of coronary reocclusion in acute myocardial infarction: results of a dose-finding study (HIT II) by the Arbeitsgemeinschaft Leitender Kardiologischer Krankenhausärzte. Coron Artery Dis. 1998;9: Molhoek GP, Laarman GJ, Lok DJ, et al. Angiographic dose-finding study with r-hirudin (HBW 023) for the improvement of thrombolytic therapy with streptokinase (HIT-SK): interim results. Eur Heart J. 1995; 16(suppl D): Antman EM. Hirudin in acute myocardial infarction: Thrombolysis and Thrombin Inhibition in Myocardial Infarction (TIMI) 9B trial. Circulation. 1996;94: Rupprecht HJ, Terres W, Ozbek C, et al. Recombinant hirudin (HBW 023) prevents troponin T release after coronary angioplasty in patients with unstable angina. J Am Coll Cardiol. 1995;26: Schiele F, Lindgaerde F, Eriksson H, et al, for the International Multicentre Hirudin Study Group. Subcutaneous recombinant hirudin (HBW 023) versus intravenous sodium heparin in treatment of established acute deep vein thrombosis of the legs: a multicentre prospective dose-ranging randomized trial. Thromb Haemost. 1997;77: