Randomised trial of prophylactic daily aspirin in British male doctors

Endothelial, platelet and leukocyte interactions in ischemic heart disease: insights into potential mechanisms and their clinical relevance

Recent investigations of the complex interactions among vascular endothelium, platelets and leukocytes have relevance to the pathogenesis of atherosclerosis and ischemic heart disease. Perturbations in the hemodynamic equilibrium maintained by these cellular elements may lead to vasospasm, in vivo thrombosis and a reduction in blood flow. Recent advances in the understanding of these interactions in health and disease states are summarized. The effect of pharmacologic agents on these cell-cell interactions are discussed to provide the reader with a general understanding of the relevance of these interactions in cardiovascular disease.

Estimation issues in clinical trials and overviews

There is a general move towards greater emphasis on point and interval estimates of treatment effect in reporting of clinical trials, so that significance testing plays a lesser role. In this article we examine a number of issues which affect the use and interpretation of conventional estimation methods. Should we accept or avoid the stereotypes of 95 per cent confidence? Should the abstract of a trial report include confidence intervals for major endpoints? Are frequentist confidence intervals being interpreted correctly, and should Bayesian probability intervals be more widely used in trial reports? Does the timing of publication, such as early stopping because of a large observed treatment difference, lead to exaggerated point and interval estimates? How can we produce realistic estimates from subgroup analyses? Is publication bias seriously affecting our ability to obtain unbiased estimates? Is the emphasis on estimation methods a powerful tool for encouraging larger sample sizes? Can we resolve the controversy concerning fixed or random effects models for estimation in overviews of related trials? Our arguments are illustrated by results from recent trials in cardiovascular disease.

Preliminary report of the Stroke Prevention in Atrial Fibrillation Study

Atrial fibrillation, even in the absence of rheumatic valvular disease, predisposes patients to embolic complications, but the role of antithrombotic therapy in the prevention of such complications has not been fully clarified. We therefore performed a randomized, placebo-controlled trial to evaluate warfarin and aspirin individually as prophylaxis against ischemic stroke and systemic embolism (the primary events) in such patients. Patients eligible to receive warfarin (group 1) were assigned to warfarin (open label), aspirin (325 mg per day), or placebo (aspirin and placebo were given in a doubleblind fashion). Those who were not eligible for warfarin (group 2) received either aspirin or placebo in a double-blind fashion. The placebo arm of group 1 was recently terminated, when evidence emerged that each active agent was superior to placebo. In this paper we report preliminary data on active therapy (with either warfarin or aspirin) as compared with placebo in group 1, and on aspirin as compared with placebo in groups 1 and 2 combined. By November 1989, 1244 patients had been followed for a mean of 1.13 years. The event rates were 1.6 percent per year in the 393 patients who made up the two active treatment arms (warfarin and aspirin) of group 1, and 8.3 percent per year in the 195 patients who made up the placebo arm (P less than 0.00005) (risk reduction, 81 percent; 95 percent confidence interval, 56 to 91). In all 517 patients given aspirin, the rate of primary events (3.2 percent per year) was lower than that in the 528 patients given placebo (6.3 percent per year; P = 0.014) (risk reduction, 49 percent; 95 percent confidence interval, 15 to 69). However, we were unable to show a benefit of aspirin in patients over 75 years of age. These preliminary data indicate that antithrombotic therapy with warfarin or aspirin is effective in the short term in reducing the risk of stroke and systemic embolism in patients with atrial fibrillation due to causes other than rheumatic valvular disease. The relative benefits of aspirin and warfarin remain unclear, and the trial is continuing in order to address this issue.

Antiplatelet treatment prolongs survival after carotid bifurcation endarterectomy. Analysis of the clinical series followed by a controlled trial

To examine the role of antiplatelet drugs in the secondary prevention of arteriosclerotic arterial disease following carotid endarterectomy, a clinical series (n = 252) was analyzed. Based on these results a prospective randomized trial was initiated, comparing the effect of antiplatelet drugs (acetyl-salicylic acid [ASA] 1000 mg/day) versus untreated controls. In both investigations patient survival was the primary end point. A cardiac risk (n = 91) implied a significant reduction in patient survival (p less than 0.019 Breslow, p less than 0.052 Mantel). Antiaggregating drugs prolonged survival in the collective series (p less than 0.0001 Breslow, p less than 0.0002 Mantel) and in the subgroup of patients with cardiac risk (p less than 0.014 Breslow, p less than 0.020 Mantel) as well. In the prospective trial 66 patients were recruited, receiving ASA (n = 32) versus no therapy (n = 34). During follow-up 15 patients died, 4 in the treatment, and 11 in the control group. Between both groups there was a significant difference in the probability of survival (p less than 0.021 Breslow, p less than 0.048 Mantel).

Aspirin and dipyridamole and their limitations in the therapy of coronary artery disease

We have reviewed some of the voluminous literature on the effects of aspirin combined with dipyridamole on coronary thrombosis. There is clear evidence that aspirin is partially effective in preventing platelet aggregation and subsequent thrombosis in experimental constricted and damaged coronary arteries of dogs. Clinical studies show a clear reduction in myocardial infarction in male human subjects who are given aspirin as therapy for unstable angina, or as prophylaxis in asymptomatic individuals. In many studies aspirin and dipyridamole have been combined and are effective. We have not found dipyridamole to be effective in the dog with coronary artery constriction and find no substantial evidence that it is effective in preventing myocardial infarction in man. Until definitive studies show that combining dipyridamole with aspirin is more effective than aspirin alone, we do not recommend its use for prevention of coronary thrombosis.

Surgery offers no more than medical treatment in the management of transient ischaemic attack

This paper debates the motion that 'Surgery offers no more than medical treatment in the management of transient ischaemic attack' (TIA). The arguments in support of this motion are that surgical treatment has a high morbidity and mortality, and that even the investigation of patients by angiography prior to surgery entails a risk of stroke; that TIA is a marker of generalised vascular disease, and that medical treatment can reduce the incidence of stroke after TIA. The counter arguments are that TIA is associated with an increased risk of stroke and this risk can be reduced by surgery; that recent surgical results show an acceptable complication rate, and that modern methods of investigation permit accurate non-invasive assessment of patients at risk of stroke.

Antithrombotic therapy in historical perspective

The history of antithrombotic therapy is traced over the past 5 decades, with a focus on the treatment of 2 major disorders: venous thromboembolism and acute myocardial infarction. Five subjects pertinent to clinical management decisions are discussed: (1) theories of thrombosis and coagulation, (2) tests of coagulation, (3) the availability of therapeutic interventions, (4) techniques for the diagnosis of vascular obstruction, and (5) the use and misuse of clinical trials.

Antithrombotic therapy in cardiac disease: an approach based on pathogenesis and risk stratification

An approach to the management of thrombosis and embolism in various cardiovascular disorders is discussed. This approach is based on current knowledge of pathogenesis and risk of thromboembolism. Rational therapeutic guidelines are formulated along the lines of anatomic location (arterial circulation, cardiac chambers or prosthetic valves), pathophysiology (activation of platelets or the coagulation system, or both), and degree of thromboembolic risk. With clear understanding of these factors, it may be possible to determine the most suitable platelet inhibitor or anticoagulant regimen for the individual patient, and whether these agents should be given singly or in combination.

Low-dose warfarin and low-dose aspirin in the primary prevention of ischemic heart disease

The thrombotic component in ischemic heart disease (IHD) is now universally recognized. It is therefore logical to consider modifying both fibrin formation and platelet function in primary (as well as secondary) prevention. The scientific case for evaluating lower-dose warfarin in primary prevention rests on the implications of the secondary prevention trials, increasing evidence of an association between the level of factor VII coagulant activity, VIIc, and the incidence of IHD, and the results of short-term lower-dose trials for the prevention of venous thrombosis and thromboembolism. The general case for considering aspirin in primary prevention is well known, but the potential value of low-dose aspirin in men at high risk needs to be established. Currently available evidence suggests that the combination of lower doses of both warfarin and aspirin in primary prevention may be effective and safe. The objective of the factorial Thrombosis Prevention Trial is to demonstrate a reduction in the incidence of IHD in men at high risk attributable to low-dose warfarin or low-dose aspirin, or both, with 1 group receiving both active treatments. The feasibility of this trial has been demonstrated. An International Normalized Ratio of about 1.5, achieved with an average daily dose of 4.6 mg warfarin, has resulted in no increase in the number of men ever reporting minor bleeding episodes, although rectal bleeding occurs more frequently in those men who do report this symptom.

Acetylsalicylic acid and the balance between prostacyclin and thromboxane A2

Arachidonic acid is metabolized in endothelial cells to antiaggregatory, vasodilatory prostacyclin (PGI2), and in platelets to aggregatory, vasoconstrictory thromboxane A2 (TxA2). The balance of these two prostanoids is supposed to be involved with thrombogenesis and atherogenesis. Acetylsalicylic acid (ASA) inhibits irreversibly the key enzyme of the synthesis of these prostanoids, i.e. cyclo-oxygenase. Platelets do not synthetize new protein, but endothelial cells do. Because of this, and certain pharmacokinetic characteristics of ASA, it should be possible to shift the balance between PGI2 and TxA2 to the dominance of the former with the proper dose of this drug. Altogether more than 50,000 subjects have volunteered for studies on the effect of ASA in the primary or secondary prevention of myocardial infarction or ischemic stroke. The results show that it is possible to reduce vascular attacks by ASA. Furthermore, ASA has also found to prevent pre-eclampsia. Conclusions on the effect of ASA on the PGI2/TxA2-balance are hampered by uncertainties concerning the measurement PGI2 and TxA2 productions in vivo. It is, however, evident that the doses of ASA used in most trials have been high enough to inhibit partly also the production of PGI2. Whether smaller doses or less frequent administration would be more efficient, remains to be studied.

Cost and efficiency in clinical trials: the U.S. Physicians' Health Study

The U.S. Physicians' Health Study, a primary prevention trial of low-dose aspirin in the reduction of cardiovascular disease and of beta-carotene in lowering cancer risk, implemented a number of design strategies to decrease costs and increase efficiency. These included the choice of physicians as the study population, use of a factorial design, implementation of a pre-randomization run-in phase, and the collection of pre-randomization blood specimens. The use of these strategies enabled us to enroll 22,071 subjects and maintain high compliance and long-term follow-up at a fraction of the usual cost of large-scale trials of primary prevention.

Role of platelet inhibitor therapy in myocardial infarction

Atherosclerotic plaque disruption is the predominant pathogenetic mechanism underlying the acute coronary syndromes. Plaque rupture leads to the exposure of collagen and vessel media, resulting in platelet and clotting activation, and occlusive thrombus formation. While drugs that interfere with platelet activation and function have been available for years, more powerful agents with novel mechanisms of action are being developed. Of the available platelet inhibitor drugs, only aspirin, sulfinpyrazone, and dipyridamole have undergone extensive clinical testing in patients with cardiovascular disease. More recently ticlopidine, a new and potent platelet inhibitor, has been successfully tested in patients with coronary and vascular disease. In acute myocardial infarction, aspirin significantly reduces cardiovascular mortality and reinfarction. Furthermore, the combination of aspirin and a thrombolytic agent produces maximal benefit. A role for heparin in the prevention of early mortality and reinfarction is emerging. This drug is effective for the prevention of left ventricular thrombosis in patients with anterior myocardial infarction. In the secondary prevention of reinfarction and cardiovascular mortality, available data support the use of a platelet inhibitor. Trials have shown that aspirin is as effective alone as in combination with dipyridamole, and is probably more effective than sulfinpyrazone. Long-term anticoagulant therapy also appears to be beneficial, but is associated with a high cost, need for extensive monitoring, and potential for hemorrhagic side effects. The role of aspirin in primary prevention is controversial. It may be indicated for patients at high risk for coronary disease in whom the benefit of therapy may outweigh the potential risk of cerebral bleeding. Coronary atherosclerotic plaque rupture, associated with thrombus formation, is fundamental to the development of acute myocardial infarction. Based on this concept, the role of antithrombotic therapy for the prevention or treatment of ischemic events in patients with coronary artery disease has stimulated enormous interest among clinicians and basic investigators. In this review we will examine: a) the pathogenesis of coronary thrombosis, b) the pharmacology of platelet-inhibitor agents, and c) their role in the management of patients with acute myocardial infarction and in primary and secondary prevention of cardiovascular disease. Platelets interact with both the coagulation and fibrinolytic systems in the pathogenesis of thrombosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Treatment of ischemic stroke. Lessons from clinical trials

The tools and methods of epidemiology, particularly the clinical trial, help guide the clinical practice of medicine. Dr Gorelick reviews the results of major clinical trials for prevention of transient cerebral ischemia and atherothrombotic stroke and assesses the effect of these findings on treatment.

Practical problems in interim analyses, with particular regard to estimation

This article considers some of the practical problems inherent in interim analyses and stopping rules for randomized clinical trials. Topics covered include group sequential designs, trials with unplanned interim analyses, estimation problems in clinical trials with planned interim analyses, and the balance between individual and collective ethics. Particular attention is paid to the fact that clinical trials that stop early are prone to exaggerate the magnitude of treatment effect. Accordingly, a Bayesian "shrinkage" method of analysis is proposed to help quantify the extent to which surprisingly large point and interval estimates of treatment difference in clinical trials that stop early should be moderated.

Aspirin use and chronic diseases: a cohort study of the elderly

OBJECTIVE

To evaluate the associations between the use of aspirin and the incidences of cardiovascular diseases, cancers, and other chronic diseases.

DESIGN

Postal questionnaire survey to elicit details of aspirin use.

SETTING

Californian retirement community.

SUBJECTS

All 22,781 residents of the community (white, affluent, and well educated) were sent a questionnaire that included questions on medical history and the use of drugs such as analgesics, laxatives, and vitamin supplements. In all 61% responded (13,987, 8881 women and 5106 men; median age 73). They formed the cohort that was followed up for 6 1/2 years using discharge summaries from three hospitals serving the area and death certificates from the health department. Only 13 respondents were lost to follow up but seemed not to have died.

MAIN OUTCOME MEASURES

Incidences of cardiovascular diseases, cancers, gastrointestinal bleeding, ulcers, and cataracts were compared in participants who did and did not take aspirin daily.

RESULTS

Age adjusted incidences were computed with an internal standard and five age groups. By 1 January 1988 there had been 25 incident cases of kidney cancer among all participants; 341 incident cases of stroke, 253 of acute myocardial infarction, 220 of ischaemic heart disease, and 317 of other heart disease were reported among respondents without a reported history of angina, myocardial infarction, or stroke. The incidence of kidney cancer was raised among those who took aspirin daily compared with those who did not take it, although the increase was significant only in men (relative risks = 6.3, 95% confidence interval 2.2 to 17, for men and 2.1, 0.53 to 8.5, for women). Those who took aspirin daily showed no increased risk of any other cancer, except colon cancer for both sexes combined (relative risk = 1.5, 1.1 to 2.2). The risk of acute myocardial infarction was reduced slightly among regular users of aspirin in men but not women. The risk of ischaemic heart disease was almost doubled in those who took aspirin daily compared with non-users (relative risks = 1.9, 1.1 to 3.1, for men and 1.7, 1.1 to 2.7, for women). Small, non-significant increased risks of stroke were observed in both sexes.

CONCLUSION

The daily use of aspirin increased the risk of kidney cancer and ischaemic heart disease.

Enhanced gastric mucosal bleeding with doses of aspirin used for prophylaxis and its reduction by ranitidine

1. We evaluated injury to the human gastric mucosa caused by low doses of aspirin and its prophylaxis by ranitidine. On two separate occasions, 30 subjects took aspirin 300 mg daily for 12 days either with or without ranitidine 150 mg, 30 min before aspirin. This dose of aspirin caused more than a 5 fold increase in gastric bleeding, from control values of 0.5 microliters 10 min-1 (95% confidence limits 0.3-0.8 microliters 10 min-1) to 2.8 microliters 10 min-1 (1.9-4.1 microliters 10 min-1, P less than 0.01) after 5 days of aspirin. Adaptation did not occur and the gastric bleeding rates remained elevated at 3.4 microliters 10 min-1 (1.9-6.1 microliters 10 min-1) after 12 days of aspirin consumption (P less than 0.01). 2. Coadministration of ranitidine significantly raised intragastric pH and reduced aspirin induced bleeding to 1.5 microliters 10 min-1 (1.0-2.3 microliters 10 min-1) after 5 days and 1.6 (1.0-2.5 microliters 10 min-1) after 12 days (P less than 0.05). 3. Although these values were higher than control levels our results raise the possibility that coadministration of ranitidine may reduce the incidence of peptic ulceration and gastrointestinal haemorrhage which is increasingly reported in some subjects taking low dose aspirin for vascular prophylaxis.

Acetylsalicylic acid 100 mg and 1000 mg daily in acute myocardial infarction suspects: a placebo-controlled trial

Of 1078 patients admitted to the coronary care unit with acute chest pain, 293 who had possible acute myocardial infarction and symptoms of median 4 h duration were randomized to treatment with acetylsalicylic acid (ASA) 100 mg daily, 1000 mg daily or placebo for 3 months. During hospitalization, the combined incidence of cardiac death and non-fatal myocardial infarction on-treatment (withdrawals not included) was significantly lower (P less than 0.02) in the 100 mg group (7.1%) than in both the 1000 mg group (20.8%) and the placebo group (19.7%). During later time periods of treatment and at all time periods analysed according to the intention-to-treat principle (withdrawals included), data suggested the same trend, but differences were not statistically significant. Collagen-induced platelet aggregation and serum thromboxane B2 were reduced to the same degree in the two ASA groups and were normal in the placebo group. The data suggest that low-dose ASA could be cheap and safe as first-aid therapy in myocardial infarction suspects.

Pharmacology of a potent, new antithrombotic agent, 1,3-dihydro-7,8-dimethyl-2H-imidazo[4,5-b]quinolin-2-one (BMY-20844)

The effects of 1,3-dihydro-7,8-dimethyl-2H-imidazo[4,5-b]quinolin-2-one (BMY-20844) on platelet function and experimental thrombosis were evaluated in a series of in vitro, ex vivo and in vivo experiments. The compound inhibited platelet aggregation in vitro in platelet rich plasma obtained from humans, rats and rabbits with EC50s of less than 1 microgram/ml when aggregation was induced by ADP, collagen or thrombin. Supra-additive interaction against ADP aggregation was also observed when BMY-20844 was combined with prostacyclin. BMY-20844 was orally active with an ex vivo ED50 in the rat of 3.2 mg/kg vs ADP. Significant antithrombotic activity was observed in two animal models (laser induced thrombosis in the microcirculation of the rabbit ear and coronary artery thrombosis in the dog). Inhibitions of 52% at 3 mg/kg p.o. in the laser model and 100% at 1 mg/kg i.d. in the coronary artery thrombosis model were obtained. Modest inotropic and hemodynamic effects were observed in ferrets and dogs. BMY-20844 was found to be a potent, specific inhibitor of platelet low Km cyclic AMP phosphodiesterase.

Differential effect of aspirin on thromboxane and prostaglandin biosynthesis in man

1. Effects of a single intravenous dose of aspirin (600 mg) on bradykinin-stimulated prostaglandin (PG) and on thromboxane (TX) biosynthesis were determined in nine healthy male volunteers. Plasma concentrations of 6-oxo-PGF1 alpha and 13,14-dihydro-15-oxo-PGF2 alpha were measured in samples obtained during repeated 10 min intravenous infusions of bradykinin before and up to 6 h after the dose of aspirin. TXB2 was measured in serum from blood allowed to clot at 37 degrees C. 2. Aspirin inhibited bradykinin stimulated PG and platelet TX biosynthesis 0.5 h after the dose. Serum TXB2 remained low, whereas PG synthesis recovered within 6 h. 3. Effects of intravenous sodium salicylate (600 mg) were studied identically in eight subjects. Prostanoid biosynthesis was not inhibited. 4. Biosynthesis of prostacyclin and TXA2 under basal conditions was studied in eight subjects by measuring 2,3-dinor-6-oxo-PGF1 alpha and 2,3-dinor-TXB2 in hourly urine samples obtained during and after intravenous infusion of aspirin and, on a separate occasion, of vehicle. 5. Aspirin infusion reduced urinary excretion of both metabolites greater than 90%, but excretion of 2,3-dinor-6-oxo-PGF1 alpha recovered more rapidly than did that of 2,3-dinor-TXB2. 6. We conclude that cyclo-oxygenase is rapidly synthesised in bradykinin-responsive tissues in vivo and that this reflects similarly rapid enzyme biosynthesis in tissues that produce PGI2 under basal conditions.

Protection against cataract by aspirin, paracetamol and ibuprofen

Results of a case-control of 423 cataract patients and 608 controls in Oxfordshire shows that the protective effect against cataract associated with consumption of aspirin-like analgesics (aspirin, paracetamol and ibuprofen family) is manifest even at low doses. Less than 150 g total dose was associated with a halving of the risk of cataract extraction.

Platelet inhibitor agents in cardiovascular disease: an update

Platelets interact with the coagulation and fibrinolytic systems in the maintenance of hemostasis. However, these physiologic mechanisms may become pathologic, requiring prevention and treatment. In this review, the following clinical developments are analyzed: 1) the role of platelets in thrombogenesis; 2) the pharmacology of platelet inhibitory agents; and, most important, 3) the results of recent randomized trials of platelet inhibitor agents in different cardiovascular disorders. Aspirin reduces mortality and infarction rates in unstable angina and significantly decreases vascular mortality in acute myocardial infarction. Platelet inhibitors decrease mortality and recurrent cardiovascular events in the chronic phase after myocardial infarction. They also decrease vein graft occlusion rates after coronary bypass surgery. Although platelet inhibitors are beneficial in preventing acute vessel occlusion during coronary angioplasty, they are ineffective in preventing chronic restenosis. Antiplatelet agents, combined with warfarin, reduce thromboembolic events in patients with a mechanical prosthesis. Platelet inhibitors are also effective in secondary prevention of vascular events in patients with cerebrovascular disease. Finally, the use of aspirin for primary prevention of cardiovascular disease is still evolving, particularly in individuals at high risk. In conclusion, platelet inhibitors are effective in patients with a variety of cardiovascular disorders. The best studied, most inexpensive and least toxic agent is aspirin at a daily dose of 160 to 325 mg. Studies using new platelet inhibitor agents with different mechanisms of action are currently underway.

Use of microbleeding and an ultrathin endoscope to assess gastric mucosal protection by famotidine

We have developed an ultrathin endoscope for repeated endoscopy in unsedated subjects and used it with assessment of bleeding rates to investigate aspirin-induced gastric mucosal injury and its prevention by famotidine. Compared with placebo, 900 mg of aspirin b.i.d. taken for 48 h caused significant endoscopic injury (median grade 3.5, interquartile range 2-4, modified Lanza scale, p less than 0.01), with an increase in mucosal bleeding from 2.0 (geometric mean; 95% confidence limits, 1.1-3.9) microliters/12 min, to 8.3 (2.4-28.8) microliters/12 min (p less than 0.05). Famotidine (20 mg b.i.d.) raised intragastric pH and reduced endoscopic antral injury (median 1.5, interquartile range 0.5-2, p less than 0.05) and bleeding [3.1 (1.2-8.3) microliters/12 min, p less than 0.01] to levels not significantly different from placebo [1 (0-1) and 2.0 (1.1-3.9) microliters/12 min, respectively]. By contrast, 2 mg of famotidine b.i.d. had no significant effect on intragastric pH endoscopic injury or bleeding rates. The two assessments of gastric mucosal injury correlated strongly (r = 0.71, p less than 0.01). The reduction in bleeding with famotidine tended to be higher, the greater the intragastric pH (r = 0.66, p = 0.057). Ultrathin endoscopy is a simple technique that validates gastric mucosal bleeding as a measure of acute gastric mucosal injury in humans. Acid suppression is an effective method of ameliorating this injury.

V.A. Cooperative Study of antiplatelet agents in diabetic patients after amputation for gangrene: unobserved, sudden, and unexpected deaths

We report on unobserved, sudden, and unexpected deaths that occurred in a randomized multicenter trial. The long-term effects of aspirin plus dipyridamole on major vascular outcome variables were studied in 231 non insulin-dependent diabetic men with either a recent amputation for gangrene or active gangrene. Depending upon the definition of sudden death used, there were 14, 22, or 17 deaths in the drug group versus 6, 6, or 3 deaths in the placebo group (p = 0.04, 0.001, or 0.001, respectively). Total deaths from atherosclerotic vascular disease or deaths from all causes did not differ in the two treatment groups. Since this finding of a secondary end point is found only after multiple analyses of the data, it must be interpreted with caution. However, it is suggested that further studies on effects of antiplatelet agents on sudden deaths should be performed.

A randomized trial comparing ticlopidine hydrochloride with aspirin for the prevention of stroke in high-risk patients. Ticlopidine Aspirin Stroke Study Group

We report the results of the Ticlopidine Aspirin Stroke Study, a blinded trial at 56 North American centers that compared the effects of ticlopidine hydrochloride (500 mg daily) with those of aspirin (1300 mg daily) on the risk of stroke or death. The medications were randomly assigned to 3069 patients with recent transient or mild persistent focal cerebral or retinal ischemia. Follow-up lasted for two to six years. The three-year event rate for nonfatal stroke or death from any cause was 17 percent for ticlopidine and 19 percent for aspirin--a 12 percent risk reduction (95 percent confidence interval, -2 to 26 percent) with ticlopidine (P = 0.048 for cumulative Kaplan-Meier estimates). The rates of fatal and nonfatal stroke at three years were 10 percent for ticlopidine and 13 percent for aspirin--a 21 percent risk reduction (95 percent confidence interval, 4 to 38 percent) with ticlopidine (P = 0.024 for cumulative Kaplan-Meier estimates). Ticlopidine was more effective than aspirin in both sexes. The adverse effects of aspirin included diarrhea (10 percent), rash (5.5 percent), peptic ulceration (3 percent), gastritis (2 percent), and gastrointestinal bleeding (1 percent). With ticlopidine, diarrhea (20 percent), skin rash (14 percent), and severe but reversible neutropenia (less than 1 percent) were noted. The mean increase in total cholesterol level was 9 percent with ticlopidine and 2 percent with aspirin (P less than 0.01). The ratios of high-density lipoprotein and low-density lipoprotein to total cholesterol were similar in both treatment groups. We conclude that ticlopidine was somewhat more effective than aspirin in preventing strokes in this population, although the risks of side effects were greater.

Final report on the aspirin component of the ongoing Physicians' Health Study

The Physicians' Health Study is a randomized, double-blind, placebo-controlled trial designed to determine whether low-dose aspirin (325 mg every other day) decreases cardiovascular mortality and whether beta carotene reduces the incidence of cancer. The aspirin component was terminated earlier than scheduled, and the preliminary findings were published. We now present detailed analyses of the cardiovascular component for 22,071 participants, at an average follow-up time of 60.2 months. There was a 44 percent reduction in the risk of myocardial infarction (relative risk, 0.56; 95 percent confidence interval, 0.45 to 0.70; P less than 0.00001) in the aspirin group (254.8 per 100,000 per year as compared with 439.7 in the placebo group). A slightly increased risk of stroke among those taking aspirin was not statistically significant; this trend was observed primarily in the subgroup with hemorrhagic stroke (relative risk, 2.14; 95 percent confidence interval, 0.96 to 4.77; P = 0.06). No reduction in mortality from all cardiovascular causes was associated with aspirin (relative risk, 0.96; 95 percent confidence interval, 0.60 to 1.54). Further analyses showed that the reduction in the risk of myocardial infarction was apparent only among those who were 50 years of age and older. The benefit was present at all levels of cholesterol, but appeared greatest at low levels. The relative risk of ulcer in the aspirin group was 1.22 (169 in the aspirin group as compared with 138 in the placebo group; 95 percent confidence interval, 0.98 to 1.53; P = 0.08), and the relative risk of requiring a blood transfusion was 1.71. This trial of aspirin for the primary prevention of cardiovascular disease demonstrates a conclusive reduction in the risk of myocardial infarction, but the evidence concerning stroke and total cardiovascular deaths remains inconclusive because of the inadequate numbers of physicians with these end points.

Antithrombotic therapy in the primary prevention of acute myocardial infarction

The high factor VII coagulant (VIIc) activity in men at high risk of coronary heart disease suggests that restoring normal hemostatic activity with appropriate oral anticoagulants might constitute effective primary prevention. A pilot study was therefore undertaken of a randomized, double-blind, placebo-controlled trial of long-term, low-dose warfarin therapy. Middle-aged men at high risk (mean VIIc 120% of standard) but without clinical coronary heart disease or contraindications to anticoagulants were randomized to warfarin or placebo. The initial warfarin dose (2.5 mg/day) was increased at intervals to lower VIIc to 70% of standard and increase the prothrombin time international normalized ratio to 1.6. The control participants received the same dose sequence of placebo. The pilot study confirmed the feasibility of the design, the absence of any increased risk of serious bleeding, and the high compliance and low withdrawal rate from randomized treatment. Accordingly, a full-scale thrombosis prevention trial has been launched, which, in addition to low-dose warfarin, includes a low-dose aspirin regimen (75 mg/day) in a factorial design. The aim of this trial is to produce a 30% reduction in coronary heart disease in 6,000 high-risk men aged 45 to 69 years. The men will receive either separate or combined therapy and will be followed up for 5 years. Evidence so far indicates that the risk of bleeding in those receiving combined therapy will be no higher than that in those taking aspirin alone.

Trial of low-dose aspirin plus dipyridamole versus anticoagulants for prevention of aortocoronary vein graft occlusion

In a prospective randomised trial, 249 patients who had aortocoronary vein bypass surgery were assigned either to a platelet inhibitory drug regimen or to standard anticoagulant therapy. Treatment was replaced by placebo in half of the patients in each group after 3 months. The platelet inhibitory drug regimen--very low-dose aspirin combined with dipyridamole--was as effective as standard anticoagulant therapy to prevent early and late graft occlusion. Death, myocardial infarction, and severe bleeding occurred significantly more often in patients receiving anticoagulants, whereas mild drug-related gastrointestinal and cerebral side-effects were more common in patients taking platelet inhibitory drugs. Antithrombotic treatment should be continued for at least 1 year after coronary artery bypass graft surgery.

Prevention of the formation of arterial thrombi using different antiplatelet drugs: experimental study in dogs

We have induced the formation of arterial thrombosis in dogs by means of an intima lesion produced by continuous current. The platelets were labeled with 111-In-oxine. Groups of 7 mongrel dogs received treatment for 7 days prior to the trial: Group I, control; Group II, 5 mg/kg body weight/day acetylsalicylic acid; Group III, 20 mg/kg body wt/day acetylsalicylic acid; Group IV, 15 mg/kg body wt/day triflusal + 5 mg/kg body wt/day dipyridamole; Group V, 15 mg/kg body wt/day triflusal; and Group VI, 5 mg/kg body wt/day acetylsalicylic acid + 5 mg/kg body wt/day dipyridamole. The only effective treatment for arterial thrombosis prevention was that employed in Group II (p less than 0.05).

Human gastric mucosal bleeding induced by low dose aspirin, but not warfarin

OBJECTIVE

To investigate the suitability of treatment with low dose aspirin or warfarin, or both, as possible prophylaxis against cardiovascular disease by determining the effect on gastric mucosal bleeding.

DESIGN

Randomised crossover trial.

SETTING

Academic department of therapeutics.

SUBJECTS

Twenty healthy male volunteers aged 19-22.

INTERVENTIONS

On separate occasions and in randomised order all subjects received aspirin 75 mg, warfarin, or aspirin 75 mg combined with warfarin. Each treatment was given for 12 days or (when warfarin was used) for longer if necessary until the international normalised ratio of the prothrombin time was stable at 1.4-1.6.

END POINT

Loss of blood over 10 minutes into gastric washings.

MEASUREMENTS AND MAIN RESULTS

Bleeding over 10 minutes into gastric washings under baseline conditions and after five days, and at end of each regimen of treatment. Aspirin 75 mg increased bleeding from 0.60 (95% confidence interval 0.36 to 0.99) microliters/10 minutes to 1.26 (0.71 to 2.25) microliters/10 minutes at five days, with no evidence of either progressive change or adaptation thereafter. Warfarin had no effect on bleeding either alone or when combined with aspirin.

CONCLUSIONS

Aspirin 75 mg causes gastric mucosal bleeding. Low dose warfarin neither induces gastric mucosal bleeding nor enhances that caused by aspirin.