Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4011_Библиотеки_им_академика_М_И_Перельмана
.pdf
360 Part IV / Practical Issues and Future Applications
CONCLUSIONS
Thrombin’s central role in platelet activation, thrombus formation, and propagation
is abundantly clear from numerous animal and human studies. Although unfractionated
heparin has been instrumental in reducing events in many cardiac settings, its practical
and theoretical limitations have become more evident. Low-molecular-weight heparins and
direct thrombin inhibitors, which have theoretical and practical advantages over unfraction-
ated heparin, have shown favorable outcomes when used in a variety of cardiac settings.
In combination with a GPIIb/IIIa antagonist, preliminary data have provided evidence
of safety and efficacy. New randomized clinical trials are under way to determine whether
combination therapy may be the next standard of care in modern practice.
REFERENCES
1. White HD. Improved efficacy and less bleeding: further evidence of a unique uncoupling of benefit
and risk with bivalirudin. Am Heart J 2002;143:189–192.
2. Frishman WH, Burns B, Atac B, et al. Novel antiplatelet therapies for treatment of patients with ische-
mic heart disease: inhibitors of the platelet glycoprotein IIb/IIIa integrin receptor. Am Heart J 1995;130:
877–892.
3. Hynes RO. Integrins: a family of cell surface receptors. Cell 1987;48:549–554.
4. Wagner CL, Mascelli MA, Neblock DS, et al. Analysis of GPIIb/IIIa receptor number by quantification
of 7E3 binding to human platelets. Blood 1996;88:907–914.
5. van Willigen G, Akkerman JW. Regulation of glycoprotein IIB/IIIA exposure on platelets stimulated
with alpha-thrombin. Blood 1992;79:82–90.
6. Fuster V, Stein B, Ambrose JA, et al. Atherosclerotic plaque rupture and thrombosis. Evolving concepts.
Circulation 1990;82:II47–II59.
7. Ambrose JA, Weinrauch M. Thrombosis in ischemic heart disease. Arch Intern Med 1996;156:1382–
1394.
8. Fuster V, Badimon JJ, Badimon L. Clinical-pathological correlations of coronary disease progression
and regression. Circulation 1992;86:III1–III11.
9. Fuster V, Badimon L, Badimon JJ, et al. The pathogenesis of coronary artery disease and the acute
coronary syndromes. N Engl J Med 1992;326:242–250.
10. Lincoff AM. GUSTO IV: expanding therapeutic options in acute coronary syndromes. Am Heart J 2000;
140:S103–S114.
11. Mazur W, Kaluza G, Kleiman NS. Antiplatelet therapy for treatment of acute coronary syndromes. Car-
diol Clin 1999;17:345–357.
12. Kahn ML, Zheng YW, Huang W, et al. A dual thrombin receptor system for platelet activation. Nature
1998;394:690–694.
13. Lawson JH, Kalafatis M, Stram S, et al. A model for the tissue factor pathway to thrombin. I. An empir-
ical study. J Biol Chem 1994;269:23,357–23,366.
14. Fuster V, Lewis A. Conner Memorial Lecture. Mechanisms leading to myocardial infarction: insights
from studies of vascular biology. Circulation 1994;90:2126–2146.
15. Stein B, Fuster V, Halperin JL, et al. Antithrombotic therapy in cardiac disease. An emerging approach
based on pathogenesis and risk. Circulation 1989;80:1501–1513.
16. Fuster V. Elucidation of the role of plaque instability and rupture in acute coronary events. Am J Car-
diol 1995;76:24C–33C.
17. Bode W, Mayr I, Baumann U, et al. The refined 1.9 A crystal structure of human alpha-thrombin:
interaction with D-Phe-Pro-Arg chloromethylketone and significance of the Tyr-Pro-Pro-Trp insertion
segment. EMBO J 1989;8:3467–3475.
18. Dery O, Corvera CU, Steinhoff M, et al. Proteinase-activated receptors: novel mechanisms of signaling
by serine proteases. Am J Physiol 1998;274:C1429–C1452.
19. Liaw PC, Becker DL, Stafford AR, et al. Molecular basis for the susceptibility of fibrin-bound throm-
bin to inactivation by heparin cofactor ii in the presence of dermatan sulfate but not heparin. J Biol
Chem 2001;276:20,959–20,965.
https://t.me/med1917
Chapter 16 / Interaction of GPIIb/IIIa Antagonists with Thrombin Inhibitors 361
20. Hogg PJ, Bock PE. Modulation of thrombin and heparin activities by fibrin. Thromb Haemost 1997;77:
424–433.
21. Eisenberg PR, Sobel BE, Jaffe AS. Activation of prothrombin accompanying thrombolysis with recom-
binant tissue-type plasminogen activator. J Am Coll Cardiol 1992;19:1065–1069.
22. Winters KJ, Santoro SA, Miletich JP, et al. Relative importance of thrombin compared with plasmin-
mediated platelet activation in response to plasminogen activation with streptokinase. Circulation 1991;
84:1552–1560.
23. Helft G, Abdelouahed M, Vacheron A, et al. [Effects of thrombolysis on platelets and coagulation].
Ann Cardiol Angeiol (Paris) 1995;44:354–360.
24. Becker R. Dynamics of coronary thrombolysis and reocclusion. Clin Cardiol 1997;20:III2–III5.
25. Aronson DL, Chang P, Kessler CM. Platelet-dependent thrombin generation after in vitro fibrinolytic
treatment. Circulation 1992;85:1706–1712.
26. Oler A, Whooley MA, Oler J, et al. Adding heparin to aspirin reduces the incidence of myocardial
infarction and death in patients with unstable angina. A meta-analysis. JAMA 1996;276:811–815.
27. Inhibition of the platelet glycoprotein IIb/IIIa receptor with tirofiban in unstable angina and non-Q-wave
myocardial infarction. Platelet Receptor Inhibition in Ischemic Syndrome Management in Patients
Limited by Unstable Signs and Symptoms (PRISM-PLUS) Study Investigators. N Engl J Med 1998;
338:1488–1497.
28. International, randomized, controlled trial of lamifiban (a platelet glycoprotein IIb/IIIa inhibitor),
heparin, or both in unstable angina. The PARAGON Investigators. Platelet IIb/IIIa Antagonism for the
Reduction of Acute coronary syndrome events in a Global Organization Network. Circulation 1998;
97:2386–2395.
29. Olson ST, Bjork I. Regulation of thrombin activity by antithrombin and heparin. Semin Thromb
Hemost 1994;20:373–409.
30. He L, Vicente CP, Westrick RJ, et al. Heparin cofactor II inhibits arterial thrombosis after endothelial
injury. J Clin Invest 2002;109:213–219.
31. Hirsh J. Heparin. N Engl J Med 1991;324:1565–1574.
32. Weitz JI, Buller HR. Direct thrombin inhibitors in acute coronary syndromes: present and future. Cir-
culation 2002;105:1004–1011.
33. Hirsh J, Warkentin TE, Shaughnessy SG, et al. Heparin and low-molecular-weight heparin: mecha-
nisms of action, pharmacokinetics, dosing, monitoring, efficacy, and safety. Chest 2001;119:64S–94S.
34. Mascelli MA, Kleiman NS, Marciniak SJ Jr, et al. Therapeutic heparin concentrations augment platelet
reactivity: implications for the pharmacologic assessment of the glycoprotein IIb/IIIa antagonist abcixi-
mab. Am Heart J 2000;139:696–703.
35. Xiao Z, Theroux P. Platelet activation with unfractionated heparin at therapeutic concentrations and
comparisons with a low-molecular-weight heparin and with a direct thrombin inhibitor. Circulation
1998;97:251–256.
36. Poletti LF, Bird KE, Marques D, et al. Structural aspects of heparin responsible for interactions with
von Willebrand factor. Arterioscler Thromb Vasc Biol 1997;17:925–931.
37. An international randomized trial comparing four thrombolytic strategies for acute myocardial infarc-
tion. The GUSTO investigators. N Engl J Med 1993;329:673–682.
38. Randomized trial of intravenous heparin versus recombinant hirudin for acute coronary syndromes. The
Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) IIa Investigators. Circulation
1994;90:1631–1637.
39. A comparison of recombinant hirudin with heparin for the treatment of acute coronary syndromes. The
Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) IIb investigators. N Engl J
Med 1996;335:775–782.
40. Theroux P, Ouimet H, McCans J, et al. Aspirin, heparin, or both to treat acute unstable angina. N Engl
J Med 1988;319:1105–1111.
41. Bahit MC, Topol EJ, Califf RM, et al. Reactivation of ischemic events in acute coronary syndromes:
results from GUSTO-IIb. Gobal Use of Strategies To Open occluded arteries in acute coronary syn-
dromes. J Am Coll Cardiol 2001;37:1001–1007.
42. 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;332:1330–1335.
43. Kaplan KL, Francis CW. Heparin-induced thrombocytopenia. Blood Rev 1999;13:1–7.
44. Antman EM, Cohen M. Newer antithrombin agents in acute coronary syndromes. Am Heart J 1999;
138:S563–S569.
https://t.me/med1917
362 Part IV / Practical Issues and Future Applications
45. Padilla A, Gray E, Pepper DS, et al. Inhibition of thrombin generation by heparin and low molecular weight
(LMW) heparins in the absence and presence of platelet factor 4 (PF4). Br J Haematol 1992;82:406–413.
46. Cohen M. Heparin-induced thrombocytopenia and the clinical use of low molecular weight heparins
in acute coronary syndromes. Semin Hematol 1999;36:33–36.
47. Comparison of two treatment durations (6 d and 14 d) of a low molecular weight heparin with a 6-d
treatment of unfractionated heparin in the initial management of unstable angina or non-Q wave myo-
cardial infarction: FRAX.I.S. (FRAxiparine in Ischaemic Syndrome). Eur Heart J 1999;20:1553–1562.
48. Cohen M, Demers C, Gurfinkel EP, et al. Low-molecular-weight heparins in non-ST-segment eleva-
tion ischemia: the ESSENCE trial. Efficacy and safety of subcutaneous enoxaparin versus intravenous
unfractionated heparin, in non-Q-wave coronary events. Am J Cardiol 1998;82:19L–24L.
49. Greinacher A, Volpel H, Janssens U, et al. Recombinant hirudin (lepirudin) provides safe and effective
anticoagulation in patients with heparin-induced thrombocytopenia: a prospective study. Circulation
1999;99:73–80.
50. Lewis BE, Walenga JM, Wallis DE. Anticoagulation with Novastan (argatroban) in patients with hepa-
rin- induced thrombocytopenia and heparin-induced thrombocytopenia and thrombosis syndrome.
Semin Thromb Hemost 1997;23:197–202.
51. Bates SM, Weitz JI. The mechanism of action of thrombin inhibitors. J Invasive Cardiol 2000;12(Suppl
F):27F–32F.
52. Levy JH. Novel intravenous antithrombins. Am Heart J 2001;141:1043–1047.
53. Wallis RB. Hirudins: from leeches to man. Semin Thromb Hemost 1996;22:185–196.
54. Hirsh J. New anticoagulants. Am Heart J 2001;142:S3–S8.
55. 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;86:385–391.
56. Visentin GP, Ford SE, Scott JP, et al. Antibodies from patients with heparin-induced thrombocytope-
nia/thrombosis are specific for platelet factor 4 complexed with heparin or bound to endothelial cells.
J Clin Invest 1994;93:81–88.
57. Weitz JI, Hirsh J. New antithrombotic agents. Chest 1998;114:715S–727S.
58. Kelly AB, Maraganore JM, Bourdon P, et al. Antithrombotic effects of synthetic peptides targeting
various functional domains of thrombin. Proc Natl Acad Sci USA 1992;89:6040–6044.
59. Fox I, Dawson A, Loynds P, et al. Anticoagulant activity of Hirulog, a direct thrombin inhibitor, in
humans. Thromb Haemost 1993;69:157–163.
60. Robson R. The use of bivalirudin in patients with renal impairment. J Invasive Cardiol 2000;12(Suppl F):
33F–36F.
61. Lewis BE, Wallis DE, Berkowitz SD, et al. Argatroban anticoagulant therapy in patients with heparin-
induced thrombocytopenia. Circulation 2001;103:1838–1843.
62. Matsuo T, Koide M, Kario K. Development of argatroban, a direct thrombin inhibitor, and its clinical
application. Semin Thromb Hemost 1997;23:517–522.
63. Tran JQ, Di Cicco RA, Sheth SB, et al. Assessment of the potential pharmacokinetic and pharmaco-
dynamic interactions between erythromycin and argatroban. J Clin Pharmacol 1999;39:513–519.
64. Swan SK, Hursting MJ. The pharmacokinetics and pharmacodynamics of argatroban: effects of age,
gender, and hepatic or renal dysfunction. Pharmacotherapy 2000;20:318–329.
65. Mousa SA. Comparative efficacy of different low-molecular-weight heparins (LMWHs) and drug inter-
actions with LMWH: implications for management of vascular disorders. Semin Thromb Hemost 2000;
26(Suppl 1):39–46.
66. Pratico D, Murphy NP, Fitzgerald DJ. Interaction of a thrombin inhibitor and a platelet GP IIb/IIIa
antagonist in vivo: evidence that thrombin mediates platelet aggregation and subsequent thromboxane
A2 formation during coronary thrombolysis. J Pharmacol Exp Ther 1997;281:1178–1185.
67. Ahmad S, Jeske WP, Ma Q, et al. Inhibition of tissue factor-activated platelets by low-molecular-weight
heparins and glycoprotein IIb/IIIa receptor antagonist. Thromb Res 2001;102:143–151.
68. Antman EM, McCabe CH, Gurfinkel EP, et al. Enoxaparin prevents death and cardiac ischemic events
in unstable angina/non-Q-wave myocardial infarction. Results of the thrombolysis in myocardial infarc-
tion (TIMI) 11B trial. Circulation 1999;100:1593–1601.
69. Heras M, Chesebro JH, Penny WJ, et al. Effects of thrombin inhibition on the development of acute
platelet-thrombus deposition during angioplasty in pigs. Heparin versus recombinant hirudin, a specific
thrombin inhibitor. Circulation 1989;79:657–665.
https://t.me/med1917
Chapter 16 / Interaction of GPIIb/IIIa Antagonists with Thrombin Inhibitors 363
70. Roque M, Rauch U, Reis ED, et al. Comparative study of antithrombotic effect of a low molecular
weight heparin and unfractionated heparin in an ex vivo model of deep arterial injury. Thromb Res
2000;98:499–505.
71. Leadley RJ Jr, Kasiewski CJ, Bostwick JS, et al. Inhibition of repetitive thrombus formation in the
stenosed canine coronary artery by enoxaparin, but not by unfractionated heparin. Arterioscler Thromb
Vasc Biol 1998;18:908–914.
72. Laposata M, Green D, Van Cott EM, et al. College of American Pathologists Conference XXXI on
laboratory monitoring of anticoagulant therapy: the clinical use and laboratory monitoring of low-molec-
ular-weight heparin, danaparoid, hirudin and related compounds, and argatroban. Arch Pathol Lab Med
1998;122:799–807.
73. Nieuwenhuis HK, Albada J, Banga JD, et al. Identification of risk factors for bleeding during treat-
ment of acute venous thromboembolism with heparin or low molecular weight heparin. Blood 1991;78:
2337–2343.
74. Levine MN, Planes A, Hirsh J, et al. The relationship between anti-factor Xa level and clinical outcome
in patients receiving enoxaparine low molecular weight heparin to prevent deep vein thrombosis after
hip replacement. Thromb Haemost 1989;62:940–944.
75. College of American Pathologists. Coagulation (Comprehensive) Survey. Set CG2-B. College of Amer-
ican Pathologists, Northfield, IL, 1999.
76. Narins CR, Hillegass WB Jr, Nelson CL, et al. Relation between activated clotting time during angio-
plasty and abrupt closure. Circulation 1996;93:667–671.
77. Chew DP, Bhatt DL, Lincoff AM, et al. Defining the optimal activated clotting time during percutane-
ous coronary intervention: aggregate results from 6 randomized, controlled trials. Circulation 2001;
103:961–966.
78. Ferguson JJ, Dougherty KG, Gaos CM, et al. Relation between procedural activated coagulation time and
outcome after percutaneous transluminal coronary angioplasty. J Am Coll Cardiol 1994;23:1061–1065.
79. Schaffer LW, Davidson JT, Vlasuk GP, et al. Selective factor Xa inhibition by recombinant antistasin
prevents vascular graft thrombosis in baboons. Arterioscler Thromb 1992;12:879–885.
80. Henry TD, Satran D, Knox LL, et al. Are activated clotting times helpful in the management of anti-
coagulation with subcutaneous low-molecular-weight heparin? Am Heart J 2001;142:590–593.
81. Dose-ranging trial of enoxaparin for unstable angina: results of TIMI 11A. The Thrombolysis in Myo-
cardial Infarction (TIMI) 11A Trial Investigators. J Am Coll Cardiol 1997;29:1474–1482.
82. Collet JP, Montalescot G, Lison L, et al. Percutaneous coronary intervention after subcutaneous eno-
xaparin pretreatment in patients with unstable angina pectoris. Circulation 2001;103:658–663.
83. Martin J, et al. Eur Heart J 2002;22(abstract Suppl):14.
84. Hansen R, Koster A, Kukucka M, et al. A quick anti-Xa-activity-based whole blood coagulation assay
for monitoring unfractionated heparin during cardiopulmonary bypass: a pilot investigation. Anesth
Analg 2000;91:533–538.
85. Holmes MB, Schneider DJ, Hayes MG, et al. Novel, bedside, tissue factor-dependent clotting assay
permits improved assessment of combination antithrombotic and antiplatelet therapy. Circulation 2000;
102:2051–2057.
86. Kereiakes DJ, Grines C, Fry E, et al. Enoxaparin and abciximab adjunctive pharmacotherapy during
percutaneous coronary intervention. J Invasive Cardiol 2001;13:272–278.
87. Karsch KR, Preisack MB, Baildon R, et al. Low molecular weight heparin (reviparin) in percutaneous
transluminal coronary angioplasty. Results of a randomized, double-blind, unfractionated heparin and
placebo-controlled, multicenter trial (REDUCE trial). Reduction of Restenosis after PTCA, Early
Administration of Reviparin in a Double-Blind Unfractionated Heparin and Placebo-Controlled Evalu-
ation. J Am Coll Cardiol 1996;28:1437–1443.
88. Ferguson J. NICE 3 Preliminary Results. Theheart.org cybersession. Available from: URL: http://dev.
cybersessions.com/conference/06nov01/. Website accessed 5/16/2002.
89. Kereiakes DJ, Kleiman NS, Fry E, et al. Dalteparin in combination with abciximab during percutane-
ous coronary intervention. Am Heart J 2001;141:348–352.
90. Cohen M, Theroux P, Borzak S, et al. Randomized double-blind safety study of enoxaparin versus
unfractionated heparin in patients with non-ST-segment elevation acute coronary syndromes treated
with tirofiban and aspirin: The ACUTE II study. Am Heart J 2002;144:470–477.
91. Detournay B, Huet X, Fagnani F, et al. Economic evaluation of enoxaparin sodium versus heparin in
unstable angina. A French sub-study of the ESSENCE trial. Pharmacoeconomics 2000;18:83–89.
https://t.me/med1917
364 Part IV / Practical Issues and Future Applications
92. Goodman S. Integrilin and Enoxaparin Randomized assessment of Acute Coronary Syndromes Treat-
ment (INTERACT). Late breaking session, American College of Cardiology, 2002.
93. Cohen M, Maritz F, Gensini GF, et al. The TETAMI trial: the safety and efficacy of subcutaneous
enoxaparin versus intravenous unfractionated heparin and of tirofiban versus placebo in the treatment
of acute myocardial infarction for patients not thrombolyzed: methods and design. J Thromb Throm-
bolysis 2000;10:241–246.
94. Antman EM. Hirudin in acute myocardial infarction. Safety report from the Thrombolysis and Throm-
bin Inhibition in Myocardial Infarction (TIMI) 9A trial. Circulation 1994;90:1624–1630.
95. Antman EM. Hirudin in acute myocardial infarction. Thrombolysis and Thrombin Inhibition in Myo-
cardial Infarction (TIMI) 9B trial. Circulation 1996;94:911–921.
96. Yusuf S. Design, baseline characteristics, and preliminary clinical results of the Organization to Assess
Strategies for Ischemic Syndromes-2 (OASIS- 2) trial. Am J Cardiol 1999;84:20M–25M.
97. White H. Thrombin-specific anticoagulation with bivalirudin versus heparin in patients receiving fibrinol-
ytic therapy for acute myocardial infarction: the HERO-2 randomised trial. Lancet 2001;358:1855–1863.
98. Vermeer F, Vahanian A, Fels PW, et al. Argatroban and alteplase in patients with acute myocardial
infarction: the ARGAMI Study. J Thromb Thrombolysis 2000;10:233–240.
99. Serruys PW, Herrman JP, Simon R, et al. A comparison of hirudin with heparin in the prevention of
restenosis after coronary angioplasty. Helvetica investigators. N Engl J Med 1995;333:757–763.
100. Bittl JA, Chaitman BR, Feit F, et al. Bivalirudin versus heparin during coronary angioplasty for unstable
or postinfarction angina: final report reanalysis of the Bivalirudin Angioplasty Study. Am Heart J 2001;
142:952–959.
101. Direct thrombin inhibitors in acute coronary syndromes: principal results of a meta-analysis based on
individual patients’ data. Lancet 2002;359:294–302.
102. Lincoff AM, Kleiman N, Kottke-Marchant K, et al. Bivalirudin with planned or provisional abciximab
versus low-dose heparin and abciximab during percutaneous coronary revascularization: results of the
Comparison of Abciximab Complications with Hirulog for Ischemic Events Trial (CACHET). Am Heart
J 2002;143:847–853.
103. Kleiman NS, Klem J, Fernandes LS, et al. Pharmacodynamic profile of the direct thrombin antagonist
bivalirudin given in combination with the glycoprotein IIb/IIIa antagonist eptifibatide. Am Heart J 2002;
143:585–593.
104. Lincoff AM, Bittl JA, Kleiman N, et al. The REPLACE 1 Trial: a pilot study of bivalirudin versus
heparin during percutaneous coronary intervention with stenting and GP IIb/IIIa blockade. J Am Coll
Cardiol 2002;39(Suppl A):1053–1053 (abstract).
105. Bode W, Turk D, Karshikov A. The refined 1.9-angstrom X-ray crystal structure of D-Phe-Pro-Arg
chloromethylketone-inhibited human alpha-thrombin: structure analysis, overall structure, electro-
static properties, detailed active-site geometry, and structure-function relationships. Protein Sci 1992;
1:426–471.
https://t.me/med1917
Chapter 17 / Oral Agents 365
365
From: Contemporary Cardiology: Platelet Glycoprotein IIb/IIIa
Inhibitors in Cardiovascular Disease, 2nd Edition
Edited by: A. M. Lincoff © Humana Press Inc., Totowa, NJ
17 Oral Agents
CONTENTS
INTRODUCTION
THE ORAL GLYCOPROTEIN IIb/IIIa INHIBITORS
THE ORAL AGENTS IN PHASE II STUDIES
THE ORAL AGENTS IN PHASE III TRIALS
SYSTEMATIC OVERVIEWS OF PHASE III TRIALS
THE FAILURE OF THE ORAL AGENTS: WHAT WENT WRONG?
R
EFERENCES
L. Kristin Newby, MD
INTRODUCTION
As discussed in previous chapters, platelets play a central role in the pathogenesis of
thrombosis and acute coronary events. Thus, antiplatelet therapy is a cornerstone of treat-
ment for patients with atherosclerotic coronary artery disease. Despite the effectiveness
of intravenous inhibitors of the platelet glycoprotein (GP) IIb/IIIa receptor in patients
with acute coronary syndromes or undergoing percutaneous coronary intervention (PCI),
little additional benefit is realized beyond the termination of therapy, and 30-d death or
myocardial infarction rates remain in the 7–13% range (1,2).
Aspirin, a weak inhibitor of platelet activation and aggregation via inhibition of the
cyclooxygenase-1 enzyme and thromboxane A
2
production, is effective for long-term
secondary prevention of vascular events (3,4). However, many patients have ischemic
coronary events while taking aspirin, suggesting resistance to its antiplatelet effects, and
outcomes among these patients are worse than for patients not taking aspirin when they
have an event (5). Furthermore, in vitro studies have demonstrated that as many as 9.5%
of patients have platelets that are resistant to the antiaggregatory effects of aspirin (6). As
shown in Fig. 1, in a small study of stroke patients who were defined as “nonresponders”
to aspirin, based on in vitro platelet function assessment, the rate of death, myocardial
infarction, or recurrent stroke at 2 yr was 40% compared with 5% among “responders” (7).
For these reasons, more potent, long-term inhibition of the final common pathway to
platelet aggregation with orally administered GPIIb/IIIa receptor inhibitors similar to the
successful intravenous compounds appeared attractive.
https://t.me/med1917
366 Part IV / Practical Issues and Future Applications
Unfortunately, despite more potent antiplatelet effect than aspirin, none of the oral
agents that have been tested have succeeded in improving outcomes in cardiovascular
disease secondary prevention. In fact, each agent tested in Phase III trials has resulted in
increased mortality relative to aspirin-treated patients that in aggregate is statistically
significant. This chapter discusses the oral class of GPIIb/IIIa inhibitors and the unexpected
results of the large-scale trials designed to evaluate their effect in secondary prevention.
THE ORAL GLYCOPROTEIN IIb/IIIa INHIBITORS
Shown in Table 1 are the intrinsic pharmacokinetic and pharmacodynamic properties
of the oral GPIIb/IIIa inhibitors that have been tested in Phase II and III studies (8–11). All
are synthetic, small-molecule inhibitors that competitively and reversibly bind the plate-
let GPIIb/IIIa receptor via an RGD binding sequence mimicking that of fibrinogen. Sibrafi-
ban, lefradafiban, Klerval, and roxifiban were selective for α
IIb
β
3
, whereas xemilofiban,
lotrafiban, and orbofiban also could bind α
v
β
3
. Xemilofiban, orbofiban, sibrafiban, Klerval,
and lefradafiban were considered first-generation agents, characterized by shorter half-
lives and twice-daily to three times a day dosing, weaker receptor binding, and more rapid
dissociation from the receptor than roxifiban, a newer agent considered the prototypical
second-generation compound. Although lotrafiban had a short half-life and high peak/
trough ratio similar to other first-generation agents, its affinity for the α
IIb
β
3
receptor (K
d
= 2.5 nM) approached that for roxifiban (K
d
= 1–2 nM). All first-generation agents except
Klerval were exclusively renally eliminated. Lotrafiban and Klerval were both active in
the orally administered form, which for Klerval was the same as the available intravenous
form, allowing consideration of intravenous to oral treatment transition.
Of these agents, xemilofiban, orbofiban, sibrafiban, lotrafiban, and roxifiban were tested
in large-scale Phase III effectiveness trials. Klerval was not taken to Phase III testing, partly
because of the expense of preparing the compound, the low bioavailability, and the neces-
sity for multiple daily dosing. Lefradafiban was successfully tested in Phase II trials and
provided some potentially interesting insights into mechanisms of the oral agents, but it
was not taken into Phase III testing after the failures of orbofiban, xemilofiban, and
sibrafiban in four large-scale Phase III trials. Phase III trials of lotrafiban in coronary and
Fig. 1. Event-free survival among “responders” and “nonresponders” to the antiplatelet effects of
aspirin. (Adapted from ref. 7.)
https://t.me/med1917
Chapter 17 / Oral Agents 367
Table 1
Overview of Oral Glycoprotein IIb/IIIa Inhibitors
Receptor Peak/
Bioavailability affinity Half-life trough Phase II Phase III
Drug Oral form (%) (nM) (h) Dosing ratio Excretion studies studies
Xemilofiban Prodrug 13 20.7 4–6 tid 4.5 Renal ORBIT EXCITE
Orbofiban Prodrug 9 52 16–18 bid 2.7 Renal SOAR OPUS- TIMI 16
Sibrafiban Prodrug 38 20 11–12 bid 2.0 Renal TIMI 12 SYMPHONY
2nd SYMPHONY
Lefradafiban Prodrug 25 35 11–13 bid 2.0-2.4 Renal FROST NA
Klerval Active drug 2.3 16 4–5 tid 1.4–2.7 Renal/ TIMI 15 A/B NA
106 nonrenal
Lotrafiban Active drug NA 2.5 6–8 bid NA Renal APLAUD BRAVO
Roxifiban Prodrug 21 1-2 5 d qd 1.8 Nonrenal ROCKET PURPOSE
https://t.me/med1917
368 Part IV / Practical Issues and Future Applications
cerebrovascular disease and roxifiban in peripheral vascular disease were stopped early
after the unfavorable results of the trials of orbofiban, xemilofiban, and sibrafiban, and
Phase III testing of roxifiban for coronary disease secondary prevention was not initiated.
THE ORAL AGENTS IN PHASE II STUDIES
Seven oral GPIIb/IIIa receptor inhibitors have been evaluated in Phase II studies (Table
2) (12–18). The primary concern of these studies was further investigation of the pharma-
cokinetics, pharmacodynamics, and safety of these agents in patients with cardiovascular
disease, as well as dose finding for Phase III investigation. The largest of these studies
enrolled only 614 patients.
As expected, for each agent there was dose-dependent inhibition of platelet aggrega-
tion, and each study established dose ranges associated with acceptable safety and toler-
ability as measured primarily by bleeding, which was also increased in a dose-dependent
fashion. Of importance, the Thrombolysis In Myocardial Infarction (TIMI) 12 investiga-
tors noted an association among dose, renal function, and bleeding, which led to renal
function-based dosing in Phase III investigation (14). No concerns regarding thrombocyto-
penia were raised in Phase II investigations, but, unlike other agents, lefradafiban adminis-
tration was associated with an increased incidence of neutropenia, 5.2% overall compared
with 1.5% in the placebo group (15).
Phase II studies of the oral agents were not powered to study the effect of these drugs
on efficacy endpoints. However, no concerns were raised of increased ischemic events
in any of the Phase II studies. In fact, several studies suggested trends toward reductions in
efficacy composites that were driven largely by reductions in measures of recurrent ische-
mia (12,15,18). Deaths were few, and there was no pattern with respect to treatment. Of
interest, after the failed Phase III trials of xemilofiban, orbofiban, and sibrafiban, the Fibri-
nogen Receptor Occupancy Study (FROST) investigators noted that at minimum fibrino-
gen receptor occupancy levels <50%, there was a tendency toward increased thrombotic
events in patients treated with lefradafiban compared with aspirin control group patients
(15). Rates of the composite of death, myocardial infarction (MI), or recurrent angina were
lowest when minimum fibrinogen receptor occupancy levels were >70%. Furthermore,
the FROST investigators noted a trend toward benefit on their efficacy composite among
patients who were troponin-positive at presentation (15), a finding similar to the enhanced
benefit shown for the intravenous agents lamifiban and tirofiban among troponin-positive
patients (19,20). However, with the mounting evidence of harm associated with similar
agents in Phase III testing and concerns about neutropenia, these interesting observations
were never tested in further studies.
THE ORAL AGENTS IN PHASE III TRIALS
Based on favorable safety and tolerability profiles in Phase II testing, five agents were
tested further in large-scale Phase III clinical outcomes trials: xemilofiban, orbofiban, sib-
rafiban, lotrafiban, and roxifiban.
Study Design
The key features of five Phase III trials of four oral GPIIb/IIIa inhibitors (xemilofiban,
orbofiban, sibrafiban, and lotrafiban) are reviewed in Table 3 (21–26). In these studies,
the agents were tested in four clinical indications: PCI, Evaluation of Xemilofiban in
https://t.me/med1917
Chapter 17 / Oral Agents 369
Table 2
Phase II Studies of Oral Agents
Sample Agent Treatment
Study size studied Population duration Major findings
ORBIT 549 Xemilofiban PCI 4 wk Dose-dependent platelet inhibition; trend toward reduction in
composite cardiovascular endpoint
SOAR 279 Orbofiban Post-ACS Up to 3 mo Dose-dependent platelet inhibition
TIMI-12 329 Sibrafiban Post-ACS 28 d Dose-dependent platelet inhibition; relationship among plasma
concentration, renal function, and bleeding; high incidence
of minor bleeding
TIMI 15A/B 89 (A) Klerval ACS 1 mo Dose-dependent platelet inhibition; iv to oral transition feasible
FROST 531 Lefradafiban ACS/Post-ACS 1 mo Dose-dependent platelet inhibition; excess bleeding at highest
dose; leukopenia/neutropenia with all doses; benefit on
composite endpoint in troponin-positive patients; increased
thrombotic events at fibrinogen receptor occupancy <50%
APLAUD 444 Lotrafiban Post-ACS/CVA/TIA 12 wk Dose-dependent platelet inhibition; high incidence of minor
bleeding (highest dose arm stopped owing to bleeding)
ROCKET 614 Roxifiban High-risk stable CAD 6 mo Major bleeding and thrombocytopenia within acceptable limits
at each of two doses; trend toward benefit on a composite
clinical endpoint
Abbreviations: ACS, acute coronary syndrome; CAD, coronary artery disease; CVA, cerebrovascular accident; PCI, percutaneous coronary intervention; TIA,
transient ischemic attack.
https://t.me/med1917
Соседние файлы в папке Библиотека им академика М.И. Перельмана