The new england journal of medicine Clopidogrel versus Aspirin and Esomeprazole Francis K.L. Chan, M.D., Jessica Y.L. Ching, M.P.H., Lawrence C.T. Hung, M.D., Vincent W.S. Wong, M.D., Vincent K.S. Leung, M.D., Nelson N.S. Kung, M.D., Aric J. Hui, M.D., Justin C.Y. Wu, M.D., Wai K. Leung, M.D., Vivian W.Y. Lee, Pharm.D., Kenneth K.C. Lee, Ph.D., Yuk T. Lee, M.D., James Y.W. Lau, M.D., Ka F. To, M.D., Henry L.Y. Chan, M.D., S.C. Sydney Chung, M.D., and Joseph J.Y. Sung, M.D., Ph.D.
b a c k g r o u n d
Concurrent therapy with a proton-pump inhibitor is a standard treatment for patients Therapeutics (F.K.L.C., J.Y.L.C., L.C.T.H., receiving aspirin who are at risk for ulcer. Current U.S. guidelines also recommend clo- V.W.S.W., A.J.H., J.C.Y.W., W.K.L., Y.T.L., pidrogel for patients who have major gastrointestinal intolerance of aspirin. We com- H.L.Y.C., J.J.Y.S.), the School of Pharmacy(V.W.Y.L., K.K.C.L.), and the Departments pared clopidogrel with aspirin plus esomeprazole for the prevention of recurrent bleed- of Surgery (J.Y.W.L., S.C.S.C.) and Anatomi- ing from ulcers in high-risk patients.
cal and Cellular Pathology (K.F.T.), Princeof Wales Hospital, Chinese University ofHong Kong; and the Medical Unit, United Christian Hospital (V.K.S.L., N.N.S.K.) — We studied patients who took aspirin to prevent vascular diseases and who presented all in Hong Kong. Address reprint requests with ulcer bleeding. After the ulcers had healed, we randomly assigned patients who to Dr. Francis K.L. Chan at the Departmentof Medicine and Therapeutics, Prince of were negative for Helicobacter pylori to receive either 75 mg of clopidogrel daily plus es- omeprazole placebo twice daily or 80 mg of aspirin daily plus 20 mg of esomeprazole twice daily for 12 months. The end point was recurrent ulcer bleeding.
Hong Kong, China, or at fklchan@cuhk.
We enrolled 320 patients (161 patients assigned to receive clopidogrel and 159 to re- Copyright 2005 Massachusetts Medical Society. ceive aspirin plus esomeprazole). Recurrent ulcer bleeding occurred in 13 patients re-ceiving clopidogrel and 1 receiving aspirin plus esomeprazole. The cumulative inci-dence of recurrent bleeding during the 12-month period was 8.6 percent (95 percentconfidence interval, 4.1 to 13.1 percent) among patients who received clopidogrel and0.7 percent (95 percent confidence interval, 0 to 2.0 percent) among those who re-ceived aspirin plus esomeprazole (difference, 7.9 percentage points; 95 percent confi-dence interval for the difference, 3.4 to 12.4; P=0.001).
c o n c l u s i o n s
Among patients with a history of aspirin-induced ulcer bleeding whose ulcers hadhealed before they received the study treatment, aspirin plus esomeprazole was superi-or to clopidogrel in the prevention of recurrent ulcer bleeding. Our finding does notsupport the current recommendation that patients with major gastrointestinal intoler-ance of aspirin be given clopidogrel.
Downloaded from www.nejm.org at OLIVE VIEW UCLA MED CTR on February 28, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved. c l o p i d o g r e l v e r s u s a s p i r i n a n d e s o m e p r a z o l e t o p r e v e n t u l c e r b l e e d i n g two decades 50 million Americans have started taking aspirin for the prevention of heart at- study population
tack and stroke.1 However, aspirin doubles the risk The study was conducted at the Prince of Walesof upper gastrointestinal bleeding even at doses as Hospital in Hong Kong. We screened consecutivelow as 75 mg daily.2 A history of upper gastrointes- users of low-dose aspirin (325 mg or less per day)tinal bleeding from an ulcer is the most important who presented with upper gastrointestinal bleed-risk factor for subsequent upper gastrointestinal ing. The patients underwent endoscopy within 24bleeding in patients taking aspirin.3,4 Up to 15 per- hours after presentation to identify the site of thecent of those taking aspirin who have a history of bleeding. During endoscopy, three biopsy speci-bleeding from ulcers had recurrent bleeding within mens were obtained from the antrum and twoone year.5 from the body of the stomach for a rapid urease test Proton-pump inhibitors reduce the risk of as- (CLO, Delta West) and for histologic examination pirin-induced ulcer bleeding,5-7 and combination for Helicobacter pylori with the use of hematoxylintherapy with proton-pump inhibitors has been ad- and eosin stain and Warthin–Starry stain, if neces-vocated for patients at high risk for ulcer bleeding sary. Patients with H. pylori infection were treatedwho are taking aspirin.8,9 However, compliance for one week with a triple-drug regimen that in-with the drug regimen may limit the usefulness of cluded a proton-pump inhibitor. Aspirin was with-the combination therapy, especially among patients held during this period. All patients received proton-who are already receiving multiple drugs.
pump inhibitors to promote the healing of ulcers.
An alternative strategy is to replace aspirin with Follow-up endoscopy was performed eight weeks another antiplatelet drug that does not induce ulcer. after eradication therapy, while the patients wereClopidogrel, which inhibits the platelet adenosine not taking acid-suppressing drugs. H. pylori wasdiphosphate receptor, has been shown to prevent considered to be present if any portion of the spec-ischemic events.10-13 The Food and Drug Adminis- imen was positive; it was considered to be absent ortration has approved clopidogrel for the treatment eradicated when all above-noted test results wereof vascular diseases.14 In healthy volunteers, clopid- negative.
ogrel did not induce gastric damage.15 It was re- Patients were considered eligible for inclusion if ported to be more efficacious and to induce fewer they had endoscopically confirmed ulcer healing,episodes of gastrointestinal bleeding than aspirin.10 negative results on the test for H. pylori or success-Although the combination of clopidogrel and aspi- ful eradication of H. pylori and anticipated regularrin increases the overall risk of bleeding,11 a recent use of antiplatelet therapy for the duration of theanalysis indicated that the excess risk of bleeding trial. The exclusion criteria were concomitant usewas attributed to the dose-dependent ulcerogenic of nonsteroidal antiinflammatory drugs (NSAIDs),effect of aspirin.16 cyclooxygenase-2 inhibitors, anticoagulant agents, The American College of Cardiology–American other antiplatelet drugs, or corticosteroids; a history Heart Association guidelines recommend the use of of gastric surgery other than a patch repair; allergy
clopidogrel for hospitalized patients with a coro- to aspirin or clopidogrel; and the presence of erosive
nary syndrome who are unable to take aspirin be- esophagitis, gastric-outlet obstruction, renal fail-
cause of major gastrointestinal intolerance (class IA ure requiring dialysis, terminal illness, or cancer.
recommendation).17,18 However, there has been no
prospective trial to assess whether clopidogrel is treatment
an alternative to aspirin plus a proton-pump inhib- Eligible patients were randomly assigned to receive
itor for patients at risk for ulcer.
either 75 mg of clopidogrel (Plavix, Sanofi-Synthela- Our study was a 12-month, prospective, ran- bo) daily plus esomeprazole placebo twice daily or domized, double-blind trial that compared clopid- 80 mg of aspirin daily plus 20 mg of esomeprazoleogrel with aspirin plus esomeprazole for patients (Nexium, AstraZeneca) twice daily for 12 months.
who had previous aspirin-induced ulcer bleeding. Randomization was carried out with the use of aWe hypothesized that after the ulcers had healed, computer-generated list of random numbers. An in-clopidogrel would not be inferior to aspirin plus dependent staff member assigned the treatmentsesomeprazole in the prevention of recurrent ulcer according to consecutive numbers that were keptbleeding among these high-risk patients.
in sealed envelopes. We purchased the drugs and Downloaded from www.nejm.org at OLIVE VIEW UCLA MED CTR on February 28, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved. The new england journal of medicine repackaged them so that clopidogrel and aspirin hemoglobin level of at least 2 g per deciliter in theappeared as identical blue capsules and esomep- presence of endoscopically documented ulcers orrazole and its placebo appeared as identical red bleeding erosions. An ulcer was defined as a circum-capsules, according to the International Good Man- scribed mucosal break at least 0.5 cm in diameterufacturing Practice Guidelines for Pharmaceuti- and with a perceptible depth; a bleeding erosioncals. Consecutively numbered, sealed bottles of the was defined as a flat mucosal break of any size thatstudy drugs were dispensed by a research nurse. An- occurred in the presence of blood in the stomach.
ticoagulant agents, NSAIDs, cyclooxygenase-2 in- Endoscopy was performed in a treatment-blindedhibitors, over-the-counter analgesics (including fashion. Only events that were confirmed by theherbal products), corticosteroids, misoprostol, his- adjudication committee and that occurred duringtamine H -receptor antagonists, sucralfate, anti- treatment or within 28 days after the discontinua- platelet drugs other than the study drugs, and pro- tion of treatment were included in the analysis.
ton-pump inhibitors were prohibited.
The secondary end point was lower gastrointes- tinal bleeding, which was defined by either melena a s s e s s m e n t
or rectal bleeding requiring hospitalization or trans- After random assignment, the patients returned at fusion, with negative results on upper endoscopy,
month 1, month 3, and every three months thereaf- or by a decrease in the hemoglobin level of at least 2 g
ter until the end of the study. At each visit, hemo- per deciliter in association with a positive fecal
globin levels and serum biochemical values were occult blood test and negative results on upper
measured, and drug compliance, the use of other endoscopy. Eligible patients underwent colonos-
medications including over-the-counter drugs, and copy to locate the source of bleeding; those with
safety were assessed. Drug compliance was as- a negative result were considered to have gastro-
sessed with the use of pill counts. We also used a intestinal bleeding of an obscure origin. Extra-
territory-wide electronic prescription database that gastrointestinal bleeding included intracranial
captured all prescriptions written within the public hemorrhage and other bleeding disorders such as
health sector; and we retrieved over-the-counter hematuria leading to hospitalization, hypotension,
drugs and prescriptions from the patients, their the need for transfusion, or the need to discontinue
families, and their primary care doctors in order to the study medication.
identify any concomitant therapy with NSAIDs or
aspirin. The assessment of safety was based on phys- statistical analysis
ical examination, laboratory tests, and observed or We determined the size of the sample on the as-
reported adverse events. A direct telephone line sumptions that about 1.5 percent of patients receiv-
was provided for patients and physicians to use to ing aspirin plus esomeprazole would have recur-
report adverse events that occurred between the rent ulcer bleeding within 12 months9 and that
scheduled visits with the study physicians. Patients clopidogrel would not be inferior to aspirin plus
who discontinued the study drugs prematurely esomeprazole if the upper limit of the 95 percent
were followed until the end of the study, to deter- confidence interval for the difference in the rates of
mine whether gastrointestinal events had occurred. recurrent ulcer bleeding did not exceed 4 percent-
The local ethics committee approved the proto- age points. Accordingly, a sample size of 145 pa- col of the study and monitored the patients’ safety tients in each of the two treatment groups was nec-data. All patients gave written informed consent. essary to give the study a power of 80 percent and aAn independent, blinded adjudication committee 5 percent level of significance with the use of a one-reviewed the data to determine which patients had sided equivalence test of proportions.19 Assumingreached the study end points according to the pre- that 10 percent of patients did not complete follow-specified criteria.
up, a total sample of 319 patients would be required.
No interim analysis was performed. The data analy- e n d p o i n t s
sis was carried out exclusively by the data review The primary end point was recurrent ulcer bleed- committee.
ing as defined according to prespecified criteria — We used the Kaplan–Meier method to estimate namely, hematemesis or melena documented by the the likelihood of reaching the end points in the in-admitting physician, with ulcers or bleeding ero- tention-to-treat population,20 which was definedsions confirmed on endoscopy, or a decrease in the as all patients who had taken at least one dose of Downloaded from www.nejm.org at OLIVE VIEW UCLA MED CTR on February 28, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved. c l o p i d o g r e l v e r s u s a s p i r i n a n d e s o m e p r a z o l e t o p r e v e n t u l c e r b l e e d i n g the study medication. The log-rank test was used to recurrent ulcer bleeding, 13 in the clopidogrel groupcompare time-to-event curves for the two groups (6 gastric ulcers, 5 duodenal ulcers, 2 both gastric(SPSS software, version 10.0). Failure to take at and duodenal ulcers) and 1 (duodenal ulcer) in theleast 80 percent of the study drugs or the use of aspirin-plus-esomeprazole group. All the patientsprohibited drugs was considered a violation of the with recurrent bleeding had presented with recur-protocol. All P values and 95 percent confidence in- rent melena, hematemesis, or both, requiring hos-tervals were two-sided.
pitalization. The median diameter of the recurrentulcers was 0.5 cm (range, 0.5 to 3.0 cm). Five pa-tients required endoscopic control of active bleed- ing, and eight required transfusion (median, 3.5 p a t i e n t s
units; range, 1 to 9). In 10 of the 14 patients with re- Between September 2001 and June 2003, we current bleeding (71.4 percent), the ulcers recurredscreened 492 consecutive patients who were taking at their previous locations. None of the 14 patientslow-dose aspirin and who presented with hematem- had recurrent H. pylori infection. Two patients withesis, melena, or both, and we enrolled a total of 320 recurrent ulcer bleeding in the clopidogrel groupof these patients. The reasons for exclusion were ter- used concomitant NSAIDs.
minal illness (in 66 patients), cancer (43), end-stage The cumulative incidence of recurrent ulcer renal failure (17), lower gastrointestinal bleeding bleeding during the 12-month study period was 8.6(4), previous gastric surgery (2), gastric-outlet ob- percent (95 percent confidence interval, 4.1 to 13.1struction (1), erosive esophagitis (1), aspirin allergy percent) among patients who received clopidogrel(1), and concomitant treatment with anticoagulant and 0.7 percent (95 percent confidence interval, 0 toagents (8), NSAIDs (3), or other antiplatelet drugs 2.0 percent) among those who received aspirin plus(1); in addition, 25 patients declined participation. esomeprazole (difference, 7.9 percentage points;The intention-to-treat analysis included all 320 pa- 95 percent confidence interval for the difference,tients: 161 patients were randomly assigned to re- 3.4 to 12.4; P=0.001) (Table 2 and Fig. 1). A per-ceive clopidogrel, and 159 patients to receive aspirin protocol analysis of 293 patients showed that theplus esomeprazole (Table 1). The median follow- cumulative incidence of recurrent bleeding was 7.5up was 12 months (range, 0.3 to 12) in both groups. percent (95 percent confidence interval, 3.0 to 11.9All of the patients in the clopidogrel group and all percent) in the clopidogrel group and 0.7 percentbut three patients in the aspirin-plus-esomepra- (95 percent confidence interval, 0 to 2.2 percent) inzole group completed follow-up.
the aspirin-plus-esomeprazole group (difference, Ninety-four percent of the patients in each group 6.8 percentage points; 95 percent confidence inter- took at least 80 percent of the assigned study val for the difference, 2.3 to 11.3; P=0.005).
drugs. The rates of discontinuation, excluding pa- Of the 20 patients who were found on adjudica- tients who reached the primary end point, were tion not to have recurrent ulcer bleeding, 4 weresimilar in the two groups — 11.8 percent in the found to have gastrointestinal cancer (3 had colonclopidogrel group (4.3 percent because of adverse cancer and 1 had cholangiocarcinoma), and 2 hadevents, 1.9 percent because of recurrent ischemic anemia that was not due to gastrointestinal bloodevents, 0.6 percent owing to withdrawal of con- loss. Of 14 patients who met the prespecified crite-sent, and 5.0 percent for other reasons) and 8.8 ria for lower gastrointestinal bleeding, 7 receivedpercent in the aspirin-plus-esomeprazole group clopidogrel (6 had gastrointestinal bleeding of ob-(1.9 percent because of adverse events, 3.8 percent scure origin and 1 had a bleeding rectal ulcer) andowing to withdrawal of consent, and 3.1 percent 7 received aspirin plus esomeprazole (5 had gas-for other reasons). No patient who discontinued trointestinal bleeding of obscure origin, 1 had hem-medications early had recurrent ulcer bleeding or orrhoidal bleeding, and 1 had angiodysplasia). Theanemia within the study period.
cumulative incidence of lower gastrointestinalbleeding was 4.6 percent (95 percent confidence in- g a s t r o i n t e s t i n a l e v e n t s
terval, 1.3 to 7.9 percent) in the clopidogrel group Thirty-four cases of suspected serious gastroin- and 4.6 percent (95 percent confidence interval,testinal events were evaluated by the adjudication 1.3 to 8.0 percent) in the aspirin-plus-esomepra-committee. The committee identified 14 cases of zole group (P=0.98).
Downloaded from www.nejm.org at OLIVE VIEW UCLA MED CTR on February 28, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved. The new england journal of medicine cardial infarction, 7 had unstable angina, and 3 had Table 1. Baseline Characteristics of the 320 Patients.*
Aspirin plus
m o r t a l i t y
Of 12 patients who died, 8 were in the clopidogrel group (1 patient died from myocardial infarction, 1 from an intracranial hemorrhage, 1 from heart failure, 3 from sepsis, and 2 from uncertain caus- es), and 4 were in the aspirin-plus-esomeprazole group (1 patient died from myocardial infarction,1 from cerebrovascular insufficiency, 1 from renal failure, and 1 from uncertain causes).
We tested the hypothesis that clopidogrel would Multiple episodes of ulcer bleeding — no. (%) not be inferior to aspirin plus esomeprazole in the prevention of recurrent ulcer bleeding in high-risk patients. The patients enrolled in this study had Ulcer with active bleeding or nonbleeding multiple risk factors, including a recent history of aspirin-induced ulcer bleeding, advanced age, and coexisting conditions. We found that among these high-risk patients who received clopidogrel after their ulcers had healed, the incidence of recurrent ulcer bleeding was unacceptably high: 8.6 percent of the patients had recurrent bleeding during the 12-month period of the study, as compared withonly 0.7 percent of the patients receiving aspirin Serum creatinine >1.2 mg/dl — no. (%)† plus esomeprazole. This finding is not consistent Previous H. pylori infection — no. (%) with the current American College of Cardiology– * Plus–minus values are means ±SD.
American Heart Association practice guidelines, † To convert the value for creatinine to micromoles per liter, multiply by 88.4.
which recommend the use of clopidogrel as an al-ternative antiplatelet agent for patients who havemajor gastrointestinal intolerance of aspirin.18 e x t r a g a s t r o i n t e s t i n a l b l e e d i n g
Current evidence regarding the gastrointestinal a n d o t h e r a d v e r s e e v e n t s
safety of clopidogrel was derived from a secondary Three patients who received clopidogrel had extra- analysis of studies that did not use prespecified cri-gastrointestinal bleeding: two patients had intra- teria to report gastrointestinal complications.10,11cranial hemorrhage, and one had severe hematuria Although one study found a lower incidence of gas-requiring hospitalization for transfusion. None of trointestinal bleeding among patients receiving clo-the patients who received aspirin plus esomepra- pidogrel than among those receiving aspirin,10 azole had extragastrointestinal bleeding. Other ad- relatively high dose of aspirin (325 mg daily) wasverse events occurred in 9.4 percent of the clopido- used as the comparator.
grel group (7.5 percent of patients had dyspepsia, Our results raise doubt about the gastrointesti- and 1.9 percent had allergy) and in 4.4 percent of nal safety of clopidogrel even in the absence of ac-the aspirin-plus-esomeprazole group (2.5 percent tive ulcers. Although all the patients had confirmedof patients had dyspepsia and 1.9 percent had aller- ulcer healing before undergoing randomization,gy). Recurrent ischemic events occurred in 9 pa- those in whom upper gastrointestinal bleeding re-tients in the clopidogrel group (1 patient had myo- curred actually had bleeding from recurrent ulcers.
cardial infarction, 6 had unstable angina, and 2 had None had recurrent H. pylori infection. Only twocerebrovascular insufficiency) and in 11 patients in patients with recurrent bleeding used concomitantthe aspirin-plus-esomeprazole group (1 had myo- NSAIDs. This finding was consistent with a retro- Downloaded from www.nejm.org at OLIVE VIEW UCLA MED CTR on February 28, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved. c l o p i d o g r e l v e r s u s a s p i r i n a n d e s o m e p r a z o l e t o p r e v e n t u l c e r b l e e d i n g spective study that reported that 12 percent of pa-tients with a history of ulcer who took clopidogrel Table 2. Kaplan–Meier Estimates of the Likelihood of Recurrent Ulcer Bleeding
and Lower Gastrointestinal (GI) Bleeding at 12 Months.

The mechanisms leading to recurrent ulcer Type of Bleeding
Probability of Bleeding (95% CI)*
bleeding among patients receiving clopidogrel are unknown. Studies in animals have shown that plate- let adenosine diphosphate–receptor antagonists impair the healing of gastric ulcers by suppressing the release of platelet-derived growth factors.22 We speculate that clopidogrel may induce recurrent ul- cers in the previously damaged gastric mucosal barrier, as suggested by the high rate of recurrence at the previous location (71.4 percent) in our study.
Alternatively, patients who have major coexisting * CI denotes confidence interval.
conditions may have a predisposition to the devel-opment of ulcers even in the absence of H. pylori in-fection or the use of NSAIDs.23 Clopidogrel proba-bly provoked bleeding from recurrent ulcers in these The optimal dose of proton-pump inhibitors for patients at high risk from the use of aspirin re-mains undefined. One study showed that among aspirin users with a history of ulcer bleeding whoreceived lansoprazole at 30 mg once daily, the inci- dence of recurrent bleeding over 12 months was Ulcer Bleeding (%)
1.6 percent. However, the upper limit of the 95 per- cent confidence interval was as high as 9.0 per- Cumulative Incidence of Recurrent
cent.5 We used a twice-daily dose of a proton- pump inhibitor to provide better acid control than Follow-up (months)
Our study has several limitations. First, the risk No. at Risk
reduction achieved by clopidogrel or aspirin plus esomeprazole could not be determined, because we did not include a group of patients with a histo-ry of ulcer bleeding who used aspirin without pro- Figure 1. Cumulative Incidence of Recurrent Ulcer Bleeding in the Group
phylaxis. A previous study reported that about 15 Receiving Clopidogrel and the Group Receiving Aspirin plus Esomeprazole.
percent of patients with a history of ulcer bleeding The difference between the groups was significant (P=0.001 by the log-rank who used aspirin had recurrent bleeding within one year.5 It would therefore be unethical to pre-scribe aspirin without prophylaxis for high-riskpatients. Second, whether genetic variation in the vention of recurrent bleeding. Our observations dometabolism of aspirin and proton-pump inhibi- not support the current recommendation that clo-tors among racial and ethnic groups has any effect pidogrel be used for patients who have major gas-on the risk of bleeding and the efficacy of treatment trointestinal intolerance of aspirin.
remains unknown. Third, because the study drugs Supported by a grant from the Division of Gastroenterology and were repackaged from the form available commer- Hepatology at the Chinese University of Hong Kong.
cially, there may have been differences in uptake Dr. Chan reports having received consulting fees from Pfizer and TAP Pharmaceutical Products, and Dr. J. Sung consulting fees from and absorption that changed the therapeutic effi- TAP Pharmaceutical Products.
cacy of the drugs or had adverse effects.
We are indebted to Dr. S.K. Lo, University of Sydney, for advice on In summary, among patients with a history of the statistical analysis; to Bing-yee Suen, Priscilla Siu, M.Y. Yung, Jessica Leung, Franco Lai, and the Team Two surgical colleagues; aspirin-induced ulcer bleeding, aspirin plus eso- and to the nursing staff of the Endoscopy Center at the Prince ofmeprazole was superior to clopidogrel for the pre- Wales Hospital.
Downloaded from www.nejm.org at OLIVE VIEW UCLA MED CTR on February 28, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved. c l o p i d o g r e l v e r s u s a s p i r i n a n d e s o m e p r a z o l e t o p r e v e n t u l c e r b l e e d i n g r e f e r e n c e s
11. The Clopidogrel in Unstable Angina to
nal haemorrhage with long term use of aspi- Prevent Recurrent Events Trial Investiga- rin: meta-analysis. BMJ 2000;321:1183-7.
tors. Effects of clopidogrel in addition to as- gina). Circulation 2002;106:1893-900.
Weil J, Colin-Jones D, Langman M, et al.
pirin in patients with acute coronary syn- 18. ACC/AHA 2002 guideline update for
Prophylactic aspirin and risk of peptic ulcer dromes without ST-segment elevation.
per gastrointestinal bleeding and perforation 12. Mehta SR, Yusuf S, Peters RJ, et al. Ef-
27, 2004, at http://www.acc.org/clinical/ fects of pretreatment with clopidogrel and guidelines/unstable/III_hospital.htm#III_ anti-inflammatory drugs. Lancet 1994;343: aspirin followed by long-term therapy in pa- 19. Roebruck P, Kuhn A. Comparison of
Lanas A, Bajador E, Serrano P, et al. Ni- tests and sample-size formulae for proving therapeutic equivalence based on the differ- 13. Steinhubl SR, Berger PB, Mann JT III, et
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al. Early and sustained dual oral antiplatelet 20. Kaplan EL, Meier P. Nonparametric esti-
intervention: a randomized controlled trial.
mation from incomplete observations. J Am prazole for the prevention of recurrences of 21. Ng FH, Wong SY, Chang CM, et al. High
14. Center for Drug Evaluation and Research.
incidence of clopidogrel-associated gastro- intestinal bleeding in patients with previous 20-839/SE1-019 (Plavix). (Accessed Decem- ondary prevention of upper gastrointestinal ber 27, 2004, at http://www.fda.gov/cder/ bleeding associated with maintenance acid- 22. Ma L, Elliott SN, Cirino G, Buret A, Ig-
suppressing treatment in patients with pep- narro LJ, Wallace JL. Platelets modulate gas- tic ulcer bleed. Epidemiology 1999;10:228- 15. Fork FT, Lafolie P, Toth E, Lindgarde F.
tric ulcer healing: role of endostatin and vas- Gastroduodenal tolerance of 75 mg clopid- cular endothelial growth factor release. Proc ogrel versus 325 mg aspirin in healthy vol- unteers: a gastroscopic study. Scand J Gas- 23. Chan HL, Wu JC, Chan FK, et al. Is non-
bleeding in patients with Helicobacter pylori Helicobacter pylori, non-NSAID peptic ulcer a infection who are taking low-dose aspirin or 16. Peters RJ, Mehta SR, Fox KA, et al. Ef-
common cause of upper GI bleeding? A pro- naproxen. N Engl J Med 2001;344:967-73.
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