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Cyclooxygenase inhibition and thrombogenicity
Cyclooxygenase Inhibition and Thrombogenicity Francesca Catella-Lawson, MD, Leslie J. Crofford, MD
Cyclooxygenase (COX)-1 and COX-2 catalyze the formation of prothrombotic and antithrombotic eicosanoids, respectively. Aspirin, conventional nonsteroidal anti-inflammatory drugs (NSAIDs), and COX-2– specific inhibitors exhibit different patterns of inhibition of COX-1–mediated thromboxane biosynthesis and COX-2–mediated prostacyclin biosynthesis. The relationship between the pharmacologic inhibition of these vasoactive eicosanoids and the thromboprophylaxis or thrombogenicity exhibited by different therapeutic agents is currently unclear. Future studies are needed to assess the antithrombotic properties of commonly used NSAIDs, the hypothetical thrombogenicity of COX-2–specific inhibitors in high-risk patients, the need for concomitant aspirin with selective versus nonselective COX inhibitors, and the antiplatelet and gastric toxicity of the aspirin/ COX-2–specific inhibitor combination in comparison with the aspirin/conventional NSAID combination. Am J Med. 2001;110(3A):28S–32S. © 2001 by Excerpta Medica, Inc.
ROLE OF THROMBOXANE A2 IN CARDIOVASCULAR CONDITIONS
T
he isozymes cyclooxygenase (COX)-1 and -2 catalyze the conversion of arachidonic acid to eicosanoids, which play an important role in platelet– vessel wall interactions. The eicosanoid thromboxane (Tx)A2 causes irreversible platelet aggregation, vasoconstriction, and smooth muscle proliferation.1 It is the major COX-1 product of arachidonic acid metabolism in platelets, and its biosynthesis is increased in syndromes of platelet activation, such as unstable angina2 and peripheral arterial obstructive disease (PAOD).3–5 In patients with unstable angina, 84% of the episodes of chest pain are associated with phasic increases in the excretion of thromboxane metabolites.2 In patients with PAOD, increased thromboxane generation is associated with a higher risk of major vascular events.6 Inhibition of thromboxane synthesis underlies the efficacy of aspirin in significantly reducing the incidence of cardiovascular death, myocardial infarction, and stroke in high-risk patients.7,8
ANTITHROMBOTIC EFFECT OF PROSTACYCLIN
From the Division of Experimental Therapeutics, University of Pennsylvania, Philadelphia, Pennsylvania, USA (FCL) and the Division of Rheumatology, University of Michigan Medical Center, Ann Arbor, Michigan, USA (LJC). Requests for reprints should be addressed to Francesca Catella-Lawson, MD, University of Pennsylvania, GCRC 160 Dulles Building, 3400 Spruce Street, Philadelphia, Pennsylvania 19014. 28S © 2001 by Excerpta Medica, Inc. All rights reserved.
In contrast to TxA2, prostacyclin (PGI2) is a potent platelet inhibitor, a vasodilator, and an inhibitor of vascular smooth muscle cell proliferation. It is the major COX-2 product of arachidonic acid metabolism in the macrovascular endothelium in vitro.9 Its effects are mediated by a single membrane G protein coupled receptor,10 and Murata et al11 have reported that inactivation of the prostacyclin receptor gene results in an increased susceptibility to thrombosis in vivo. Although this study provides the first evidence for the homeostatic antithrombotic effect of endogenous prostacyclin in vivo, infusion of exogenous prostacyclin is an effective platelet inhibitor in vivo, albeit limited by gastrointestinal and vasoactive side effects.12,13 These results are consistent with experimental data that demonstrate that the antithrombotic effect of combining thromboxane synthase inhibitors with thromboxane receptor antagonists are largely attributable to augmented prostacyclin formation.14 Fitzgerald et al showed that prostacyclin biosynthesis is increased in syndromes of platelet activation, such as unstable angina.2 In these patients, phasic increases in thromboxane biosynthesis during chest pain are accompanied by a parallel increase in prostacyclin biosynthesis. This probably reflects a local compensatory response by the vascular endothelium stimulated by the platelets during ischemia. 0002-9343/01/$20.00 PII S0002-9343(00)00683-5
A Symposium: Cyclooxygenase Inhibition and Thrombogenicity/Catella-Lawson and Crofford
Figure 1. Aspirin, conventional NSAIDs, and COX-2–specific inhibitors exhibit a different pattern of inhibition of COX-1– mediated thromboxane (TxA2) biosynthesis and COX-2–mediated prostacyclin (PGI2) biosynthesis.
Similarly, in patients with PAOD who have accelerated platelet turnover,3–5 prostacyclin biosynthesis is also increased.15 Again, this is compatible with the postulated role of prostacyclin as a local regulator of platelet–vessel wall interactions.
ROLE OF COX-2 IN THE BIOSYNTHESIS OF PROSTACYCLIN Thromboxane A2 is primarily synthesized by platelet COX-1, whereas PGI2 biosynthesis is largely mediated by the COX-2 isoform. This is inferred by our findings that pharmacologic inhibition of COX-2 leads to selective inhibition of prostacyclin biosynthesis.16,17 Catella-Lawson et al assessed the effects of the dual COX-1/COX-2 inhibitor indomethacin, the specific COX-2 inhibitor rofecoxib, and placebo on the biosynthesis of vasoactive eicosanoids.16 COX-1– dependent thromboxane biosynthesis by platelets was assessed by measurement of urinary 11-dehydro-TxB2 (Tx-M), the major metabolite of TxB2.3,5,18 This was decreased by 59.9 ⫾ 16.6% (percent least square mean change ⫾ SEM) by indomethacin, but was not inhibited by rofecoxib (⫹1.74 ⫾ 15.2%), or placebo (⫹11.1 ⫾ 13.8%). Biosynthesis of prostacyclin was assessed by measurement of urinary 6 keto-prostaglandin F1␣ (6-keto-PG F1␣) and 2,3-dinor 6-keto-PGF1␣ (PGIM). Urinary excretion of 6-keto-PGF1␣, which is a hydration product of PGI2, predominantly reflects renal biosynthesis of PGI2.19 Thus, urinary 6-keto-PGF1␣ shows a significant linear correlation with renal function, as assessed by creatinine clearance and the para-aminohippurate clearance rate, in healthy women and patients who have chronic glomerular disease and systemic lupus erythematosus (SLE) with active and inactive renal lesions.20 Also in the same patient population, inhibition of urinary 6-keto-PGF1␣ by a nonsteroidal anti-inflammatory drug (NSAID) correlates with the reduction in renal function associated with NSAID treatment.20 In contrast, urinary excretion of PGI-M largely reflects extra-renal biosynthesis of prostacyclin.18,19 PGI-M is the major enzymatic metabolite of prostacyclin,21 and its excretion rate increases in a concentration-dependent manner in urine collections performed during and after intravenous infusion of PGI2 at three escalating concentra-
tions in healthy volunteers.22 In addition, urinary excretion of PGI-M increases almost threefold in response to localized trauma of the coronary arteries, such as induced by percutaneous transluminal coronary angioplasty (PTCA).23 Urinary 6-keto-PGF1␣ and PGI-M were similarly inhibited by indomethacin and rofecoxib but were not affected by placebo. The least square mean change from baseline for urinary PGI-M was ⫺64.8 ⫾ 10.8 (P ⬍0.05), ⫺73.6 ⫾ 9.1 (P ⬍0.05), and ⫺0.27 ⫾ 9.1 pg/mg (P ⫽ not significant) creatinine in the indomethacin, rofecoxib, and placebo groups, respectively. No differences were noted between rofecoxib and indomethacin with respect to their inhibitory effects on urinary PGI-M excretion (P ⫽ 0.55). Similarly, the least square mean change from baseline for urinary 6-keto PGF1␣ was ⫺25.3 ⫾ 7.0 (P ⫽ 0.05), ⫺27.1 ⫾ 6.3 (P ⱕ0.05), and ⫹2.03 ⫾ 6.4 pg/mg (P ⫽ not significant) creatinine in the indomethacin, rofecoxib, and placebo groups, respectively.16 McAdam et al assessed the effects of another chemically distinct specific inhibitor of COX-2 (celecoxib) on eicosanoid biosynthesis.17 Celecoxib, like rofecoxib, did not suppress urinary excretion of Tx-M but significantly decreased systemic biosynthesis of prostacyclin, as assessed by the excretion of PGI-M in the urine collections performed 4 to 6 and 6 to 12 hours after dosing. The degree of PGI-M inhibition induced by celecoxib was similar to that induced by the nonspecific COX-1/COX-2 inhibitor, ibuprofen.17
SELECTIVE VERSUS NONSELECTIVE INHIBITION The clinical implications of selective versus nonselective inhibition of vasoactive eicosanoids currently are unclear. Aspirin is a more potent inhibitor of COX-1 than of COX-2, and its antithrombotic efficacy has been clearly demonstrated.7,8 Aspirin induces irreversible inhibition of platelet COX-1 and consequent long-term, complete enzyme blockade without the recovery of activity at trough drug levels exhibited by other NSAIDs.24 In addition, at low doses, aspirin selectively inhibits TxA2 formation without inhibiting basal prostacyclin biosynthesis (Figure 1).23,25 It is unclear which of these two unique
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properties plays a more important role in the cardioprophylactic properties of aspirin. In contrast to aspirin, other NSAIDs inhibit both COX-1– derived TxA2 and COX-2– derived PGI2 with limited selectivity,26 –28 and their cardiovascular protection has not been established. There is limited prospective evidence that some NSAIDs may reduce the risk of thromboembolic complications in high-risk patients.29,30 A retrospective epidemiologic study has recently concluded that chronic use of NSAIDs is not associated with a reduced risk of developing a first myocardial infarction in women.31 COX-2–specific inhibitors, a new subclass of NSAIDs, suppress prostacyclin formation without a concomitant inhibition of thromboxane biosynthesis (Figure 1).16,17 The clinical consequences of these effects currently are unknown. The patient population most likely to use chronic anti-inflammatory therapy, the elderly, is also at highest risk for atherosclerotic disease. In these patients, COX-2–specific inhibitors might lead to loss of the homeostatic platelet inhibition normally induced by prostacyclin and consequently promotion or enhancement of platelet activation. Conventional NSAIDs, which inhibit both prostacyclin and thromboxane, do not pose this theoretical risk (Figure 1). It has been suggested that acetaminophen also selectively inhibits prostacyclin biosynthesis.32 However, lack of inhibition of thromboxane biosynthesis by acetaminophen was based on a very small sample size32,33 and confounded by high variability of urinary Tx-M.32 CatellaLawson et al recently reported that administration of a single dose of acetaminophen 1,000 mg to healthy subjects caused a similar, nonselective inhibition (approximately 40%) of both COX-1 and COX-2 isozymes.34 The speculative thrombogenicity of COX-2–specific inhibitors has not been documented in clinical trials to date. The incidence of myocardial infarction in all controlled arthritis trials of celecoxib was 0.1% in the placebo arm, 0.2% in the celecoxib arm, and 0.1% in the NSAID arm. A vascular event occurred in 7 of 1,864 placebotreated patients (0.4%), 32 of 6,376 celecoxib-treated patients (0.5%), and 16 of 2,768 patients treated with conventional NSAIDs (0.6%). A similar incidence of thromboembolic cardiovascular events was also seen with rofecoxib (3.0% per year; n ⫽ 3,595), placebo (2.9% per year; n ⫽ 783) and NSAID comparators (3.0% per year; n ⫽ 1,565) when the overall rofecoxib osteoarthritis safety database was reviewed.35 In the 6-month osteoarthritis studies, the incidence of thromboembolic events was 0.8% in the placebo arm (n ⫽ 371), and 1.2%, 1.0%, and 1.1% in the rofecoxib 12.5-, 25-, and 50-mg arms, respectively (n ⫽ 490, 879, and 379, respectively); 0.5% in the ibuprofen arm (n ⫽ 377), and 1.8% in the diclofenac arm (n ⫽ 498). However, the total sample size and treatment duration of these phase III trials were not powered 30S February 19, 2001
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to identify an increased incidence of major thrombotic events in subjects treated with COX-2–specific inhibitors as compared with NSAID-treated patients. Also, the eligibility criteria, such as the exclusion of patients at risk of cardiovascular events from some pivotal studies, or some concomitant medications, such as aspirin at low doses, which was allowed in some studies, might have precluded the precise assessment of the postulated thrombogenic risk of COX-2–specific inhibitors. More recently, the results of two large, double-blind, randomized, controlled trials of COX-2–specific inhibitors have been released. The Celecoxib Long-term Arthritis Safety Study (CLASS) was designed to determine the safety profile of celecoxib (400 mg twice daily) in comparison with ibuprofen (800 mg three times daily), or diclofenac (75 mg twice daily). A total of 4,573 patients with osteoarthritis or rheumatoid arthritis received treatment for 6 months.36 The Vioxx Gastrointestinal Outcomes Research (VIGOR) study was a 12-month trial comparing the safety of rofecoxib (50 mg once daily) and naproxen (500 mg twice daily) in more than 8,000 patients with rheumatoid arthritis. In the CLASS study no difference was noted in the incidence of cardiovascular events between celecoxib and NSAIDs, whereas in the VIGOR study patients randomized to receive rofecoxib had a statistically significant increase in the incidence of major cardiovascular events, as compared with patients randomized to naproxen. The apparent discrepancy in cardiovascular outcome among the two studies is unlikely to be related to specific pharmacologic properties of the two molecules, which induce a similar selective suppression of systemic prostacyclin without a concomitant inhibition of platelet aggregation. In contrast, the uneven distribution of a very small number of cardiovascular events may reflect a mere play of chance or differences in eligibility criteria, study population, study duration, and active control among the two trials. Cardioprotective doses of aspirin were taken by 20% of the patients enrolled in the CLASS study, whereas concomitant use of low doses of aspirin was an exclusion criterium in the VIGOR study. Also, the percentage of patients with rheumatoid arthritis, a condition known to be associated with a higher risk of cardiovascular complications, was 27% versus 100% in the CLASS and VIGOR studies, respectively. The study duration was 6 months and 12 months in the CLASS and VIGOR studies, respectively. Finally, the two studies used different NSAIDs as control (ibuprofen or diclofenac in the CLASS study and naproxen in the VIGOR study), and neither study included a placebo arm. Therefore, it is possible that a more effective cardioprotection exhibited by naproxen, in comparison to the other NSAIDs, may have led to an apparent increased incidence of cardiovascular events in rofecoxib-treated patients. Increased thrombogenic risk in certain patient populations, if confirmed, is likely to be a class-specific comVolume 110 (3A)
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plication of COX-2–specific inhibitors. Crofford et al recently reported a temporal association between celecoxib treatment and ischemic complications in 4 patients with connective tissue diseases.37 All patients had a history of Raynaud’s phenomenon, as well as elevated anticardiolipin antibodies, lupus anticoagulant, or a history compatible with antiphospholipid syndrome. In addition, they had evidence of ongoing inflammation by elevated erythrocyte sedimentation rate, hypocomplementemia, and/or elevated levels of anti-DNA antibodies. After vascular thrombosis and discontinuation of celecoxib treatment, we measured urinary eicosanoids in 2 of the patients. Urinary excretion of PGI-M was greatly elevated (348 and 472 pg/mg creatinine, respectively, versus 25 and 67 pg/mg creatinine assessed in 2 age-matched healthy women). Urinary Tx-M was 1,890 and 4,110 pg/mg creatinine in the 2 patients and 180 and 520 pg/mg creatinine in the 2 control subjects. These results suggest that in patients with connective tissue diseases platelet activation had led to a compensatory increase of prostacyclin biosynthesis. Celecoxib, by inhibiting prostacyclin, may have suppressed this negative feedback mechanism, contributing to the thrombotic complications of these patients. These reports should be interpreted with caution, because these patients had multiple risk factors for hypercoagulability, and the association between celecoxib treatment and the thrombotic episodes could have been only temporal rather than of causative nature. However, our observations raise the potential of clinically important drug reactions. COX-2–specific inhibitors should be used with caution in patients with underlying prothrombotic states. In these patients use of low-dose aspirin or appropriate anticoagulant treatment should be used as clinically indicated. In patients taking warfarin, the prothrombin time should be reassessed after start of treatment with a COX-2–specific inhibitor.
INTERACTIONS AMONG CYCLOOXYGENASE INHIBITORS Low-dose aspirin prophylaxis in high-risk patients is also recommended when conventional NSAIDs are chronically administered for osteoarthritis or rheumatoid arthritis. This combination is usually prescribed, because the cardiovascular benefit exhibited by conventional NSAIDs has not been established. However, it carries an additive risk of upper gastrointestinal bleeding and perforation.38 – 40 In addition, NSAID binding to COX-1 competes with aspirin binding and subsequent acetylation of Ser-530.41 This is the primary mechanism of aspirin-induced irreversible inactivation of the enzyme on platelets.42 Therefore, concomitant administration of aspirin and other NSAIDs might lead to competitive antagonism, as suggested by studies performed in the early 1980s43– 45 and recently confirmed by our group.34 In contrast, COX-2–specific inhibitors do not bind to plate-
let COX-1, and their administration in conjunction with low doses of aspirin does not lead to a competitive interaction.34 In conclusion, conventional NSAIDs and COX-2–specific NSAIDs differentially inhibit the biosynthesis of vasoactive eicosanoids and may decrease, or increase, respectively, the risk of cardiovascular complications in patients with underlying prothrombotic states. Future investigations of drug interactions will determine the optimum therapeutic combinations for the cardioprophylaxis of patients with arthritis.
REFERENCES 1. Hamberg M, Sevensson J, Samuelsson B. Thromboxanes: a new group of biologically active compounds derived from prostaglandin endoperoxides. Proc Natl Acad Sci USA. 1975;72:2294 –2298. 2. Fitzgerald DJ, Roy L, Catella F, FitzGerald GA. Platelet activation in unstable coronary disease. N Engl J Med. 1986;315:983–989. 3. Catella F, Healy D, Lawson JA, FitzGerald GA. 11-dehydrothromboxane B2: a quantitative index of thromboxane A2 formation in the human circulation. Proc Natl Acad Sci USA. 1986;83:5861–5865. 4. Reilly IAG, Doran JB, Smith B, FitzGerald GA. Increased thromboxane biosynthesis in a human preparation of platelet activation: biochemical and functional consequences of selective inhibition of thromboxane synthase. Circulation. 1986;73:1300 –1309. 5. Catella F, FitzGerald GA. Paired analysis of urinary thromboxane B2 metabolites in humans. Thromb Res. 1987;47: 647– 656. 6. Davi G, Gresele P, Violi F, et al. Diabetes mellitus, hypercholesterolemia and hypertension but not vascular disease per se are associated with persistent platelet activation in vivo. Evidence derived from the study of peripheral arterial disease. Circulation. 1997;96:69 –75. 7. Antiplatelet Trialists’ Collaboration. Secondary prevention of vascular disease by prolonged antiplatelet treatment. BMJ. 1988;296:320 –331. 8. Antiplatelet Trialists’ Collaboration. Collaborative overview of randomised trials of antiplatelet therapy. I: prevention of death, myocardial infarction, and stroke by prolonged antiplatelet therapy in various categories of patients. BMJ. 1994;308:81–106. 9. Weksler BB, Marcus AJ, Jaffe EA. Synthesis of prostaglandin I2 (prostacylin) by cultured human and bovine endothelial cells. Proc Natl Acad Sci USA. 1977;74:3922–3926. 10. Namba T, Oida HO, Sugimoto Y, et al. cDNA cloning of a mouse prostacyclin receptor. Multiple signaling pathways and expression in thymic medulla. J Biol Chem. 1994;269: 9986 –9992. 11. Murata T, Ushikubi F, Matsuoka T, et al. Altered pain perception and inflammatory response in mice lacking prostacyclin receptor. Nature. 1997;388:678 – 682. 12. FitzGerald GA, Friedman LA, Miyamori I, O’Grady J, Lewis PJ. A double-blind placebo-controlled evaluation of prostacyclin in man. Life Sci. 1979;25:665– 672. 13. Belch JJ, Capell HA, Cooke, ED, et al. Oral iloprost as a treatment for Raynaud’s syndrome: a double blind multicentre placebo controlled study. Ann Rheum Dis. 1995;54: 197–200. 14. Fitzgerald DJ, Fragetta J, FitzGerald GA. Prostaglandin en-
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15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
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doperoxides modulate the response to thromboxane synthase inhibition during coronary thrombosis. J Clin Invest. 1988;82:1708 –1713. FitzGerald GA, Smith B, Pedersen AK, Brash AR. Increased prostacyclin biosynthesis is increased in patients with severe atherosclerosis and platelet activation. N Engl J Med. 1984;310:1065–1068. Catella-Lawson F, McAdam B, Morrison BW, et al. Effects of selective inhibition of cyclooxygenase II on sodium balance, hemodynamics, and vasoactive eicosanoids. J Pharm Exp Ther. 1999;289:735–741. McAdam BF, Catella-Lawson F, Mardini I, et al. Systemic biosynthesis of prostacyclin by cyclooxygenase (COX)-2: the human pharmacology of a selective inhibitor of COX-2. Proc Natl Acad Sci USA. 1999;96:272–277. FitzGerald GA, Pedersen AK, Patrono C. Analysis of prostacyclin and thromboxane A2 biosynthesis in cardiovascular disease. Circulation. 1983;67:1174 –1177. Catella F, Nowak J, FitzGerald GA. Measurement of renal and nonrenal eicosanoid synthesis. Am J Med. 1986; 81(suppl 2B):23–29. Patrono C, Ciabattoni C, Remuzzi G, et al. Functional significance of renal prostacyclin and thromboxane A2 production in patients with systemic lupus erythematosus. J Clin Invest. 1985;76:1011–1018. Brash AR, Jackson EK, Saggese C, et al. The metabolic disposition of prostacyclin in man. J Pharm Exp Ther. 1983; 266:78 – 87. FitzGerald GA, Brash AR, Falardeau P, Oates JA. Estimated rate of prostacyclin secretion into the circulation of normal man. J Clin Invest. 1981;68:1272–1275. Braden GA, Knapp HR, FitzGerald GA. Suppression of eicosanoid biosynthesis during coronary angioplasty by fish oil and aspirin. Circulation. 1991;84:679 – 685. Patrono C, Ciabattoni G, Patrignani P, et al. Clinical pharmacology of platelet cyclooxygenase inhibition. Circulation. 1985;72:1177–1183. Patrignani P, Filabozzi P, Patrono C. Selective cumulative inhibition of platelet thromboxane production by low-dose aspirin in healthy subjects. J Clin Invest. 1982;69:1366 – 1372. Mitchell JA, Akarasereenont P, Thiemermann C, Flower RF, Vane JR. Selectivity of nonsteroidal antiinflammatory drugs as inhibitors of constitutive and inducible cyclooxygenase. Proc Natl Acad Sci USA. 1994;90:11693–11697. Laneuville O, Breuer DK, DeWitt DL, et al. Differential inhibition of human prostaglandin endoperoxide H synthases-1 and -2 by nonsteroidal anti-inflammatory drugs. J Pharm Exp Ther. 1994;271:927–934. Patrignani P, Panara MR, Greco A, et al. Biochemical and pharmacological characterization of the cyclooxygenase activity of human blood prostaglandin endoperoxide synthases. J Pharm Exp Ther. 1994;271:1706 –1712. Brochier ML. Evaluation of flurbiprofen for prevention of reinfarction and reocclusion after successful thrombolysis or angioplasty in acute myocardial infarction. Eur Heart J. 1993;14:951–957. Fornaro G, Rossi P, Mantica PG, et al. Indobufen in the prevention of thromboembolic complications in patients with heart disease. A randomized, placebo-controlled, double-blind study. Circulation. 1993;87:162–164.
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31. Garcı´a Rodrı´guez LA, Varas C, Patrono C. Differential effects of aspirin and non-aspirin nonsteroidal antiinflammatory drugs in the primary prevention of myocardial infarction in postmenopausal women. Epidemiology. 2000;11:382– 387. 32. Green K, Drvota V, Vesterqvist O. Pronounced reduction of in vivo prostacyclin synthesis in humans by acetaminophen (paracetamol). Prostaglandins. 1989;37:311–315. 33. Green K, Vesterqvist O. Urinary excretion of 2,3-dinorthromboxane B2 in man under normal conditions, following drugs and during some pathological conditions. Prostaglandins. 1984;27:627– 643. 34. Catella-Lawson F, Kapoor S, Reilly MP, De Marco S, FitzGerald GA. Ibuprofen, but not rofecoxib or acetaminophen, antagonizes the irreversible anti-platelet effect of aspirin [abstract]. Arthritis Rheum. 2000;43:S298. 35. Daniels B, Seidenberg B. Cardiovascular safety profile of rofecoxib in controlled clinical trials [abstract]. Arthritis Rheum. 1999;42:435. 36. Silverstein FE, Faich G, Goldstein JL, et al. Gastrointestinal toxicity with celecoxib vs nonsteroidal anti-inflammatory drugs for osteoarthritis and rheumatoid arthritis: the CLASS study: a randomized controlled trial. JAMA. 2000;284: 1247–1255. 37. Crofford LJ, Oates JC, McCune WJ, et al. Thrombosis in patients with connective tissue diseases treated with specific cyclooxygenase 2 inhibitors. A report of four cases. Arthritis Rheum. 2000;43:1891–1896. 38. Henry D, Dobson A, Turner C. Variability in the risk of major gastrointestinal complications from nonaspirin nonsteroidal anti-inflammatory drugs. Gastroenterology. 1993;105: 1078 –1088. 39. Kaufman DW, Kelly JP, Sheehan JE, et al. Nonsteroidal anti-inflammatory drug use in relation to major upper gastrointestinal bleeding. Clin Pharmacol Ther. 1993;53:485– 494. 40. Savage RL, Moller PW, Ballantyne CL, Wells JE. Variation in the risk of peptic ulcer complications with nonsteroidal antiinflammatory drug therapy. Arthritis Rheum. 1993;36: 84 –90. 41. Loll PJ, Picot D, Ekabo O, Garavito RM. Synthesis and use of iodinated nonsteroidal antiinflammatory drug analogs as crystallographic probes of the prostaglandin H2 synthase cyclooxygenase active site. Biochemistry. 1996;35:7330 – 7340. 42. Loll PJ, Picot D, Garavito RM. The structural basis of aspirin activity inferred from the crystal structure of inactivated prostaglandin H2 synthase. Nat Struct Biol. 1995;2:637– 643. 43. Merino J, Livio M, Rajtar G, de Gaetano G. Salicylate reverses in vitro aspirin inhibition of rat platelet and vascular prostaglandin generation. Biochem Pharmacol. 1980;29: 1093–1096. 44. Livio M, Del Maschio A, Cerletti C, de Gaetano G. Indomethacin prevents the long-lasting inhibitory effect of aspirin on human platelet cyclo-oxygenase activity. Prostaglandins. 1982;23:787–796. 45. Rao GHR, Johnson GG, Reddy KR, White JG. Ibuprofen protects platelet cyclooxygenase from irreversible inhibition by aspirin. Arteriosclerosis. 1983;3:383–388.
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Cyclooxygenase (COX)-1 and COX-2 catalyze the formation of prothrombotic and antithrombotic eicosanoids, respectively. Aspirin, conventional nonsteroidal anti-inflammatory drugs (NSAIDs), and COX-2– specific inhibitors exhibit different patterns of inhibition of COX-1–mediated thromboxane biosynthesis and COX-2–mediated prostacyclin biosynthesis. The relationship between the pharmacologic inhibition of these vasoactive eicosanoids and the thromboprophylaxis or thrombogenicity exhibited by different therapeutic agents is currently unclear. Future studies are needed to assess the antithrombotic properties of commonly used NSAIDs, the hypothetical thrombogenicity of COX-2–specific inhibitors in high-risk patients, the need for concomitant aspirin with selective versus nonselective COX inhibitors, and the antiplatelet and gastric toxicity of the aspirin/ COX-2–specific inhibitor combination in comparison with the aspirin/conventional NSAID combination. Am J Med. 2001;110(3A):28S–32S. © 2001 by Excerpta Medica, Inc.
ROLE OF THROMBOXANE A2 IN CARDIOVASCULAR CONDITIONS
T
he isozymes cyclooxygenase (COX)-1 and -2 catalyze the conversion of arachidonic acid to eicosanoids, which play an important role in platelet– vessel wall interactions. The eicosanoid thromboxane (Tx)A2 causes irreversible platelet aggregation, vasoconstriction, and smooth muscle proliferation.1 It is the major COX-1 product of arachidonic acid metabolism in platelets, and its biosynthesis is increased in syndromes of platelet activation, such as unstable angina2 and peripheral arterial obstructive disease (PAOD).3–5 In patients with unstable angina, 84% of the episodes of chest pain are associated with phasic increases in the excretion of thromboxane metabolites.2 In patients with PAOD, increased thromboxane generation is associated with a higher risk of major vascular events.6 Inhibition of thromboxane synthesis underlies the efficacy of aspirin in significantly reducing the incidence of cardiovascular death, myocardial infarction, and stroke in high-risk patients.7,8
ANTITHROMBOTIC EFFECT OF PROSTACYCLIN
From the Division of Experimental Therapeutics, University of Pennsylvania, Philadelphia, Pennsylvania, USA (FCL) and the Division of Rheumatology, University of Michigan Medical Center, Ann Arbor, Michigan, USA (LJC). Requests for reprints should be addressed to Francesca Catella-Lawson, MD, University of Pennsylvania, GCRC 160 Dulles Building, 3400 Spruce Street, Philadelphia, Pennsylvania 19014. 28S © 2001 by Excerpta Medica, Inc. All rights reserved.
In contrast to TxA2, prostacyclin (PGI2) is a potent platelet inhibitor, a vasodilator, and an inhibitor of vascular smooth muscle cell proliferation. It is the major COX-2 product of arachidonic acid metabolism in the macrovascular endothelium in vitro.9 Its effects are mediated by a single membrane G protein coupled receptor,10 and Murata et al11 have reported that inactivation of the prostacyclin receptor gene results in an increased susceptibility to thrombosis in vivo. Although this study provides the first evidence for the homeostatic antithrombotic effect of endogenous prostacyclin in vivo, infusion of exogenous prostacyclin is an effective platelet inhibitor in vivo, albeit limited by gastrointestinal and vasoactive side effects.12,13 These results are consistent with experimental data that demonstrate that the antithrombotic effect of combining thromboxane synthase inhibitors with thromboxane receptor antagonists are largely attributable to augmented prostacyclin formation.14 Fitzgerald et al showed that prostacyclin biosynthesis is increased in syndromes of platelet activation, such as unstable angina.2 In these patients, phasic increases in thromboxane biosynthesis during chest pain are accompanied by a parallel increase in prostacyclin biosynthesis. This probably reflects a local compensatory response by the vascular endothelium stimulated by the platelets during ischemia. 0002-9343/01/$20.00 PII S0002-9343(00)00683-5
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Figure 1. Aspirin, conventional NSAIDs, and COX-2–specific inhibitors exhibit a different pattern of inhibition of COX-1– mediated thromboxane (TxA2) biosynthesis and COX-2–mediated prostacyclin (PGI2) biosynthesis.
Similarly, in patients with PAOD who have accelerated platelet turnover,3–5 prostacyclin biosynthesis is also increased.15 Again, this is compatible with the postulated role of prostacyclin as a local regulator of platelet–vessel wall interactions.
ROLE OF COX-2 IN THE BIOSYNTHESIS OF PROSTACYCLIN Thromboxane A2 is primarily synthesized by platelet COX-1, whereas PGI2 biosynthesis is largely mediated by the COX-2 isoform. This is inferred by our findings that pharmacologic inhibition of COX-2 leads to selective inhibition of prostacyclin biosynthesis.16,17 Catella-Lawson et al assessed the effects of the dual COX-1/COX-2 inhibitor indomethacin, the specific COX-2 inhibitor rofecoxib, and placebo on the biosynthesis of vasoactive eicosanoids.16 COX-1– dependent thromboxane biosynthesis by platelets was assessed by measurement of urinary 11-dehydro-TxB2 (Tx-M), the major metabolite of TxB2.3,5,18 This was decreased by 59.9 ⫾ 16.6% (percent least square mean change ⫾ SEM) by indomethacin, but was not inhibited by rofecoxib (⫹1.74 ⫾ 15.2%), or placebo (⫹11.1 ⫾ 13.8%). Biosynthesis of prostacyclin was assessed by measurement of urinary 6 keto-prostaglandin F1␣ (6-keto-PG F1␣) and 2,3-dinor 6-keto-PGF1␣ (PGIM). Urinary excretion of 6-keto-PGF1␣, which is a hydration product of PGI2, predominantly reflects renal biosynthesis of PGI2.19 Thus, urinary 6-keto-PGF1␣ shows a significant linear correlation with renal function, as assessed by creatinine clearance and the para-aminohippurate clearance rate, in healthy women and patients who have chronic glomerular disease and systemic lupus erythematosus (SLE) with active and inactive renal lesions.20 Also in the same patient population, inhibition of urinary 6-keto-PGF1␣ by a nonsteroidal anti-inflammatory drug (NSAID) correlates with the reduction in renal function associated with NSAID treatment.20 In contrast, urinary excretion of PGI-M largely reflects extra-renal biosynthesis of prostacyclin.18,19 PGI-M is the major enzymatic metabolite of prostacyclin,21 and its excretion rate increases in a concentration-dependent manner in urine collections performed during and after intravenous infusion of PGI2 at three escalating concentra-
tions in healthy volunteers.22 In addition, urinary excretion of PGI-M increases almost threefold in response to localized trauma of the coronary arteries, such as induced by percutaneous transluminal coronary angioplasty (PTCA).23 Urinary 6-keto-PGF1␣ and PGI-M were similarly inhibited by indomethacin and rofecoxib but were not affected by placebo. The least square mean change from baseline for urinary PGI-M was ⫺64.8 ⫾ 10.8 (P ⬍0.05), ⫺73.6 ⫾ 9.1 (P ⬍0.05), and ⫺0.27 ⫾ 9.1 pg/mg (P ⫽ not significant) creatinine in the indomethacin, rofecoxib, and placebo groups, respectively. No differences were noted between rofecoxib and indomethacin with respect to their inhibitory effects on urinary PGI-M excretion (P ⫽ 0.55). Similarly, the least square mean change from baseline for urinary 6-keto PGF1␣ was ⫺25.3 ⫾ 7.0 (P ⫽ 0.05), ⫺27.1 ⫾ 6.3 (P ⱕ0.05), and ⫹2.03 ⫾ 6.4 pg/mg (P ⫽ not significant) creatinine in the indomethacin, rofecoxib, and placebo groups, respectively.16 McAdam et al assessed the effects of another chemically distinct specific inhibitor of COX-2 (celecoxib) on eicosanoid biosynthesis.17 Celecoxib, like rofecoxib, did not suppress urinary excretion of Tx-M but significantly decreased systemic biosynthesis of prostacyclin, as assessed by the excretion of PGI-M in the urine collections performed 4 to 6 and 6 to 12 hours after dosing. The degree of PGI-M inhibition induced by celecoxib was similar to that induced by the nonspecific COX-1/COX-2 inhibitor, ibuprofen.17
SELECTIVE VERSUS NONSELECTIVE INHIBITION The clinical implications of selective versus nonselective inhibition of vasoactive eicosanoids currently are unclear. Aspirin is a more potent inhibitor of COX-1 than of COX-2, and its antithrombotic efficacy has been clearly demonstrated.7,8 Aspirin induces irreversible inhibition of platelet COX-1 and consequent long-term, complete enzyme blockade without the recovery of activity at trough drug levels exhibited by other NSAIDs.24 In addition, at low doses, aspirin selectively inhibits TxA2 formation without inhibiting basal prostacyclin biosynthesis (Figure 1).23,25 It is unclear which of these two unique
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properties plays a more important role in the cardioprophylactic properties of aspirin. In contrast to aspirin, other NSAIDs inhibit both COX-1– derived TxA2 and COX-2– derived PGI2 with limited selectivity,26 –28 and their cardiovascular protection has not been established. There is limited prospective evidence that some NSAIDs may reduce the risk of thromboembolic complications in high-risk patients.29,30 A retrospective epidemiologic study has recently concluded that chronic use of NSAIDs is not associated with a reduced risk of developing a first myocardial infarction in women.31 COX-2–specific inhibitors, a new subclass of NSAIDs, suppress prostacyclin formation without a concomitant inhibition of thromboxane biosynthesis (Figure 1).16,17 The clinical consequences of these effects currently are unknown. The patient population most likely to use chronic anti-inflammatory therapy, the elderly, is also at highest risk for atherosclerotic disease. In these patients, COX-2–specific inhibitors might lead to loss of the homeostatic platelet inhibition normally induced by prostacyclin and consequently promotion or enhancement of platelet activation. Conventional NSAIDs, which inhibit both prostacyclin and thromboxane, do not pose this theoretical risk (Figure 1). It has been suggested that acetaminophen also selectively inhibits prostacyclin biosynthesis.32 However, lack of inhibition of thromboxane biosynthesis by acetaminophen was based on a very small sample size32,33 and confounded by high variability of urinary Tx-M.32 CatellaLawson et al recently reported that administration of a single dose of acetaminophen 1,000 mg to healthy subjects caused a similar, nonselective inhibition (approximately 40%) of both COX-1 and COX-2 isozymes.34 The speculative thrombogenicity of COX-2–specific inhibitors has not been documented in clinical trials to date. The incidence of myocardial infarction in all controlled arthritis trials of celecoxib was 0.1% in the placebo arm, 0.2% in the celecoxib arm, and 0.1% in the NSAID arm. A vascular event occurred in 7 of 1,864 placebotreated patients (0.4%), 32 of 6,376 celecoxib-treated patients (0.5%), and 16 of 2,768 patients treated with conventional NSAIDs (0.6%). A similar incidence of thromboembolic cardiovascular events was also seen with rofecoxib (3.0% per year; n ⫽ 3,595), placebo (2.9% per year; n ⫽ 783) and NSAID comparators (3.0% per year; n ⫽ 1,565) when the overall rofecoxib osteoarthritis safety database was reviewed.35 In the 6-month osteoarthritis studies, the incidence of thromboembolic events was 0.8% in the placebo arm (n ⫽ 371), and 1.2%, 1.0%, and 1.1% in the rofecoxib 12.5-, 25-, and 50-mg arms, respectively (n ⫽ 490, 879, and 379, respectively); 0.5% in the ibuprofen arm (n ⫽ 377), and 1.8% in the diclofenac arm (n ⫽ 498). However, the total sample size and treatment duration of these phase III trials were not powered 30S February 19, 2001
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to identify an increased incidence of major thrombotic events in subjects treated with COX-2–specific inhibitors as compared with NSAID-treated patients. Also, the eligibility criteria, such as the exclusion of patients at risk of cardiovascular events from some pivotal studies, or some concomitant medications, such as aspirin at low doses, which was allowed in some studies, might have precluded the precise assessment of the postulated thrombogenic risk of COX-2–specific inhibitors. More recently, the results of two large, double-blind, randomized, controlled trials of COX-2–specific inhibitors have been released. The Celecoxib Long-term Arthritis Safety Study (CLASS) was designed to determine the safety profile of celecoxib (400 mg twice daily) in comparison with ibuprofen (800 mg three times daily), or diclofenac (75 mg twice daily). A total of 4,573 patients with osteoarthritis or rheumatoid arthritis received treatment for 6 months.36 The Vioxx Gastrointestinal Outcomes Research (VIGOR) study was a 12-month trial comparing the safety of rofecoxib (50 mg once daily) and naproxen (500 mg twice daily) in more than 8,000 patients with rheumatoid arthritis. In the CLASS study no difference was noted in the incidence of cardiovascular events between celecoxib and NSAIDs, whereas in the VIGOR study patients randomized to receive rofecoxib had a statistically significant increase in the incidence of major cardiovascular events, as compared with patients randomized to naproxen. The apparent discrepancy in cardiovascular outcome among the two studies is unlikely to be related to specific pharmacologic properties of the two molecules, which induce a similar selective suppression of systemic prostacyclin without a concomitant inhibition of platelet aggregation. In contrast, the uneven distribution of a very small number of cardiovascular events may reflect a mere play of chance or differences in eligibility criteria, study population, study duration, and active control among the two trials. Cardioprotective doses of aspirin were taken by 20% of the patients enrolled in the CLASS study, whereas concomitant use of low doses of aspirin was an exclusion criterium in the VIGOR study. Also, the percentage of patients with rheumatoid arthritis, a condition known to be associated with a higher risk of cardiovascular complications, was 27% versus 100% in the CLASS and VIGOR studies, respectively. The study duration was 6 months and 12 months in the CLASS and VIGOR studies, respectively. Finally, the two studies used different NSAIDs as control (ibuprofen or diclofenac in the CLASS study and naproxen in the VIGOR study), and neither study included a placebo arm. Therefore, it is possible that a more effective cardioprotection exhibited by naproxen, in comparison to the other NSAIDs, may have led to an apparent increased incidence of cardiovascular events in rofecoxib-treated patients. Increased thrombogenic risk in certain patient populations, if confirmed, is likely to be a class-specific comVolume 110 (3A)
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plication of COX-2–specific inhibitors. Crofford et al recently reported a temporal association between celecoxib treatment and ischemic complications in 4 patients with connective tissue diseases.37 All patients had a history of Raynaud’s phenomenon, as well as elevated anticardiolipin antibodies, lupus anticoagulant, or a history compatible with antiphospholipid syndrome. In addition, they had evidence of ongoing inflammation by elevated erythrocyte sedimentation rate, hypocomplementemia, and/or elevated levels of anti-DNA antibodies. After vascular thrombosis and discontinuation of celecoxib treatment, we measured urinary eicosanoids in 2 of the patients. Urinary excretion of PGI-M was greatly elevated (348 and 472 pg/mg creatinine, respectively, versus 25 and 67 pg/mg creatinine assessed in 2 age-matched healthy women). Urinary Tx-M was 1,890 and 4,110 pg/mg creatinine in the 2 patients and 180 and 520 pg/mg creatinine in the 2 control subjects. These results suggest that in patients with connective tissue diseases platelet activation had led to a compensatory increase of prostacyclin biosynthesis. Celecoxib, by inhibiting prostacyclin, may have suppressed this negative feedback mechanism, contributing to the thrombotic complications of these patients. These reports should be interpreted with caution, because these patients had multiple risk factors for hypercoagulability, and the association between celecoxib treatment and the thrombotic episodes could have been only temporal rather than of causative nature. However, our observations raise the potential of clinically important drug reactions. COX-2–specific inhibitors should be used with caution in patients with underlying prothrombotic states. In these patients use of low-dose aspirin or appropriate anticoagulant treatment should be used as clinically indicated. In patients taking warfarin, the prothrombin time should be reassessed after start of treatment with a COX-2–specific inhibitor.
INTERACTIONS AMONG CYCLOOXYGENASE INHIBITORS Low-dose aspirin prophylaxis in high-risk patients is also recommended when conventional NSAIDs are chronically administered for osteoarthritis or rheumatoid arthritis. This combination is usually prescribed, because the cardiovascular benefit exhibited by conventional NSAIDs has not been established. However, it carries an additive risk of upper gastrointestinal bleeding and perforation.38 – 40 In addition, NSAID binding to COX-1 competes with aspirin binding and subsequent acetylation of Ser-530.41 This is the primary mechanism of aspirin-induced irreversible inactivation of the enzyme on platelets.42 Therefore, concomitant administration of aspirin and other NSAIDs might lead to competitive antagonism, as suggested by studies performed in the early 1980s43– 45 and recently confirmed by our group.34 In contrast, COX-2–specific inhibitors do not bind to plate-
let COX-1, and their administration in conjunction with low doses of aspirin does not lead to a competitive interaction.34 In conclusion, conventional NSAIDs and COX-2–specific NSAIDs differentially inhibit the biosynthesis of vasoactive eicosanoids and may decrease, or increase, respectively, the risk of cardiovascular complications in patients with underlying prothrombotic states. Future investigations of drug interactions will determine the optimum therapeutic combinations for the cardioprophylaxis of patients with arthritis.
REFERENCES 1. Hamberg M, Sevensson J, Samuelsson B. Thromboxanes: a new group of biologically active compounds derived from prostaglandin endoperoxides. Proc Natl Acad Sci USA. 1975;72:2294 –2298. 2. Fitzgerald DJ, Roy L, Catella F, FitzGerald GA. Platelet activation in unstable coronary disease. N Engl J Med. 1986;315:983–989. 3. Catella F, Healy D, Lawson JA, FitzGerald GA. 11-dehydrothromboxane B2: a quantitative index of thromboxane A2 formation in the human circulation. Proc Natl Acad Sci USA. 1986;83:5861–5865. 4. Reilly IAG, Doran JB, Smith B, FitzGerald GA. Increased thromboxane biosynthesis in a human preparation of platelet activation: biochemical and functional consequences of selective inhibition of thromboxane synthase. Circulation. 1986;73:1300 –1309. 5. Catella F, FitzGerald GA. Paired analysis of urinary thromboxane B2 metabolites in humans. Thromb Res. 1987;47: 647– 656. 6. Davi G, Gresele P, Violi F, et al. Diabetes mellitus, hypercholesterolemia and hypertension but not vascular disease per se are associated with persistent platelet activation in vivo. Evidence derived from the study of peripheral arterial disease. Circulation. 1997;96:69 –75. 7. Antiplatelet Trialists’ Collaboration. Secondary prevention of vascular disease by prolonged antiplatelet treatment. BMJ. 1988;296:320 –331. 8. Antiplatelet Trialists’ Collaboration. Collaborative overview of randomised trials of antiplatelet therapy. I: prevention of death, myocardial infarction, and stroke by prolonged antiplatelet therapy in various categories of patients. BMJ. 1994;308:81–106. 9. Weksler BB, Marcus AJ, Jaffe EA. Synthesis of prostaglandin I2 (prostacylin) by cultured human and bovine endothelial cells. Proc Natl Acad Sci USA. 1977;74:3922–3926. 10. Namba T, Oida HO, Sugimoto Y, et al. cDNA cloning of a mouse prostacyclin receptor. Multiple signaling pathways and expression in thymic medulla. J Biol Chem. 1994;269: 9986 –9992. 11. Murata T, Ushikubi F, Matsuoka T, et al. Altered pain perception and inflammatory response in mice lacking prostacyclin receptor. Nature. 1997;388:678 – 682. 12. FitzGerald GA, Friedman LA, Miyamori I, O’Grady J, Lewis PJ. A double-blind placebo-controlled evaluation of prostacyclin in man. Life Sci. 1979;25:665– 672. 13. Belch JJ, Capell HA, Cooke, ED, et al. Oral iloprost as a treatment for Raynaud’s syndrome: a double blind multicentre placebo controlled study. Ann Rheum Dis. 1995;54: 197–200. 14. Fitzgerald DJ, Fragetta J, FitzGerald GA. Prostaglandin en-
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15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
32S
doperoxides modulate the response to thromboxane synthase inhibition during coronary thrombosis. J Clin Invest. 1988;82:1708 –1713. FitzGerald GA, Smith B, Pedersen AK, Brash AR. Increased prostacyclin biosynthesis is increased in patients with severe atherosclerosis and platelet activation. N Engl J Med. 1984;310:1065–1068. Catella-Lawson F, McAdam B, Morrison BW, et al. Effects of selective inhibition of cyclooxygenase II on sodium balance, hemodynamics, and vasoactive eicosanoids. J Pharm Exp Ther. 1999;289:735–741. McAdam BF, Catella-Lawson F, Mardini I, et al. Systemic biosynthesis of prostacyclin by cyclooxygenase (COX)-2: the human pharmacology of a selective inhibitor of COX-2. Proc Natl Acad Sci USA. 1999;96:272–277. FitzGerald GA, Pedersen AK, Patrono C. Analysis of prostacyclin and thromboxane A2 biosynthesis in cardiovascular disease. Circulation. 1983;67:1174 –1177. Catella F, Nowak J, FitzGerald GA. Measurement of renal and nonrenal eicosanoid synthesis. Am J Med. 1986; 81(suppl 2B):23–29. Patrono C, Ciabattoni C, Remuzzi G, et al. Functional significance of renal prostacyclin and thromboxane A2 production in patients with systemic lupus erythematosus. J Clin Invest. 1985;76:1011–1018. Brash AR, Jackson EK, Saggese C, et al. The metabolic disposition of prostacyclin in man. J Pharm Exp Ther. 1983; 266:78 – 87. FitzGerald GA, Brash AR, Falardeau P, Oates JA. Estimated rate of prostacyclin secretion into the circulation of normal man. J Clin Invest. 1981;68:1272–1275. Braden GA, Knapp HR, FitzGerald GA. Suppression of eicosanoid biosynthesis during coronary angioplasty by fish oil and aspirin. Circulation. 1991;84:679 – 685. Patrono C, Ciabattoni G, Patrignani P, et al. Clinical pharmacology of platelet cyclooxygenase inhibition. Circulation. 1985;72:1177–1183. Patrignani P, Filabozzi P, Patrono C. Selective cumulative inhibition of platelet thromboxane production by low-dose aspirin in healthy subjects. J Clin Invest. 1982;69:1366 – 1372. Mitchell JA, Akarasereenont P, Thiemermann C, Flower RF, Vane JR. Selectivity of nonsteroidal antiinflammatory drugs as inhibitors of constitutive and inducible cyclooxygenase. Proc Natl Acad Sci USA. 1994;90:11693–11697. Laneuville O, Breuer DK, DeWitt DL, et al. Differential inhibition of human prostaglandin endoperoxide H synthases-1 and -2 by nonsteroidal anti-inflammatory drugs. J Pharm Exp Ther. 1994;271:927–934. Patrignani P, Panara MR, Greco A, et al. Biochemical and pharmacological characterization of the cyclooxygenase activity of human blood prostaglandin endoperoxide synthases. J Pharm Exp Ther. 1994;271:1706 –1712. Brochier ML. Evaluation of flurbiprofen for prevention of reinfarction and reocclusion after successful thrombolysis or angioplasty in acute myocardial infarction. Eur Heart J. 1993;14:951–957. Fornaro G, Rossi P, Mantica PG, et al. Indobufen in the prevention of thromboembolic complications in patients with heart disease. A randomized, placebo-controlled, double-blind study. Circulation. 1993;87:162–164.
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31. Garcı´a Rodrı´guez LA, Varas C, Patrono C. Differential effects of aspirin and non-aspirin nonsteroidal antiinflammatory drugs in the primary prevention of myocardial infarction in postmenopausal women. Epidemiology. 2000;11:382– 387. 32. Green K, Drvota V, Vesterqvist O. Pronounced reduction of in vivo prostacyclin synthesis in humans by acetaminophen (paracetamol). Prostaglandins. 1989;37:311–315. 33. Green K, Vesterqvist O. Urinary excretion of 2,3-dinorthromboxane B2 in man under normal conditions, following drugs and during some pathological conditions. Prostaglandins. 1984;27:627– 643. 34. Catella-Lawson F, Kapoor S, Reilly MP, De Marco S, FitzGerald GA. Ibuprofen, but not rofecoxib or acetaminophen, antagonizes the irreversible anti-platelet effect of aspirin [abstract]. Arthritis Rheum. 2000;43:S298. 35. Daniels B, Seidenberg B. Cardiovascular safety profile of rofecoxib in controlled clinical trials [abstract]. Arthritis Rheum. 1999;42:435. 36. Silverstein FE, Faich G, Goldstein JL, et al. Gastrointestinal toxicity with celecoxib vs nonsteroidal anti-inflammatory drugs for osteoarthritis and rheumatoid arthritis: the CLASS study: a randomized controlled trial. JAMA. 2000;284: 1247–1255. 37. Crofford LJ, Oates JC, McCune WJ, et al. Thrombosis in patients with connective tissue diseases treated with specific cyclooxygenase 2 inhibitors. A report of four cases. Arthritis Rheum. 2000;43:1891–1896. 38. Henry D, Dobson A, Turner C. Variability in the risk of major gastrointestinal complications from nonaspirin nonsteroidal anti-inflammatory drugs. Gastroenterology. 1993;105: 1078 –1088. 39. Kaufman DW, Kelly JP, Sheehan JE, et al. Nonsteroidal anti-inflammatory drug use in relation to major upper gastrointestinal bleeding. Clin Pharmacol Ther. 1993;53:485– 494. 40. Savage RL, Moller PW, Ballantyne CL, Wells JE. Variation in the risk of peptic ulcer complications with nonsteroidal antiinflammatory drug therapy. Arthritis Rheum. 1993;36: 84 –90. 41. Loll PJ, Picot D, Ekabo O, Garavito RM. Synthesis and use of iodinated nonsteroidal antiinflammatory drug analogs as crystallographic probes of the prostaglandin H2 synthase cyclooxygenase active site. Biochemistry. 1996;35:7330 – 7340. 42. Loll PJ, Picot D, Garavito RM. The structural basis of aspirin activity inferred from the crystal structure of inactivated prostaglandin H2 synthase. Nat Struct Biol. 1995;2:637– 643. 43. Merino J, Livio M, Rajtar G, de Gaetano G. Salicylate reverses in vitro aspirin inhibition of rat platelet and vascular prostaglandin generation. Biochem Pharmacol. 1980;29: 1093–1096. 44. Livio M, Del Maschio A, Cerletti C, de Gaetano G. Indomethacin prevents the long-lasting inhibitory effect of aspirin on human platelet cyclo-oxygenase activity. Prostaglandins. 1982;23:787–796. 45. Rao GHR, Johnson GG, Reddy KR, White JG. Ibuprofen protects platelet cyclooxygenase from irreversible inhibition by aspirin. Arteriosclerosis. 1983;3:383–388.
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