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PubMed1992

The impact of stopping rules on heterogeneity of results in overviews of clinical trials.

This paper explores the extent to which application of statistical stopping rules in clinical trials can create an artificial heterogeneity of treatment effects in overviews (meta-analyses) of related trials. For illustration, we concentrate on overviews of identically designed group sequential trials, using either fixed nominal or O'Brien and Fleming two-sided boundaries. Some analytic results are obtained for two-group designs and simulation studies are otherwise used, with the following overall findings. The use of stopping rules leads to biased estimates of treatment effect so that the assessment of heterogeneity of results in an overview of trials, some of which have used stopping rules, is confounded by this bias. If the true treatment effect being studied is small, as is often the case, then artificial heterogeneity is introduced, thus increasing the Type I error rate in the test of homogeneity. This could lead to erroneous use of a random effects model, producing exaggerated estimates and confidence intervals. However, if the true mean effect is large, then between-trial heterogeneity may be underestimated. When undertaking or interpreting overviews, one should ascertain whether stopping rules have been used (either formally or informally) and should consider whether their use might account for any heterogeneity found.

Analysis of Variance↗

PubMed1992

Directory of registries of clinical trials.

Registries of clinical trials are a potentially useful resource for the planning of new studies, the promotion of communication and collaboration between researchers, the conduct of meta-analyses, and the facilitation of patient access and recruitment to trials. However, many physicians and researchers are unaware of their existence, and as a result they remain underused. A directory of registries of clinical trials has been developed as a result of an international survey of 63 organizations and 51 individuals in 13 different countries to identify the existence of such registries. This is intended as a resource to keep physicians, researchers, trial organizers, funding bodies and government agencies abreast of the growing number of registries available, and to assist in the planning of future registries. Twenty-four current and six planned registries of clinical trials have been identified. Most focus on AIDS or oncology, but such diverse areas as neurosurgery, cardiovascular disease, dentistry and perinatology are also represented. This paper presents a descriptive profile on each registry and discusses the relative merits of their different organizational features. Recommendations are given for the establishment of future registries.

Clinical Protocols↗

PubMed1991

[Class I anti-arrhythmia agents and prevention of sudden death following myocardial infarction].

The results of therapeutic trials of Class I antiarrhythmic agents after myocardial infarction are not identical or always compatible with those of the CAST. It is important to determine the reason for this disparity in order to try and identify the patients who should not be given these drugs and those in whom they could be beneficial, providing these benefits are clearly demonstrated. Meta-analyses of controlled therapeutic trials of Class I antiarrhythmics after myocardial infarction have been performed. Depending on the study protocol used, the results of the CAST are compatible or incompatible with those of other trials. A possible reason for this apparent discordance from meta-analysis could be the particularly low cardiac risk in the CAST patients.

Anti-Arrhythmia Agents↗

PubMed1991

Treatment of hypertension: a clinical epidemiologist's view.

The majority of deaths attributable to hypertension are coronary artery disease (CAD) deaths and, consequently, the prevention of CAD should be the primary aim of hypertension management. Recent meta-analyses confirm the results of the individual hypertension intervention trials, which demonstrated a disappointing shortfall in the observed prevention of CAD events and mortality from lowering blood pressure compared with the expected benefits. These trial results, rather than challenging the validity of the causal nature of the association between hypertension and CAD may be interpreted to suggest that the management of hypertension in the trials was suboptimal. The drugs used in the trials were almost exclusively thiazide diuretics and to a lesser extent beta-blockers. Both of these drug groups have been shown to have adverse effects on lipid profiles--a pivotal risk factor for CAD. In addition to the effects on lipids, diuretics also adversely affect potassium, uric acid, glucose metabolism, and insulin resistance, all of which directly or indirectly affect the incidence of CAD. In the face of a major shortfall in the overall benefit from managing hypertension with diuretics and to a lesser extent beta-blockers, it therefore seems more logical to recommend for the management of hypertension the use of agents with a more metabolic-friendly profile.

Coronary Disease↗

PubMed1991

Treatment with verapamil during and after an acute myocardial infarction: a review based on the Danish Verapamil Infarction Trials I and II. The Danish Study Group on Verapamil in Myocardial Infarction.

The effect of verapamil on death and reinfarction after an acute myocardial infarction was studied in two double-blind, randomized, placebo-controlled multicenter trials, the Danish Verapamil Infarction Trials I and II (DAVIT I and II). The studies demonstrated that verapamil 360 mg/day from the 2nd week after an acute myocardial infarction, prevented death and reinfarction. Meta-analyses of the results of DAVITs I and II resulted in a reduction of pooled ratios of 22% (95% confidence limits 1-37, p = 0.04) for death, 21% (5-35, p = 0.02) for first major events (first reinfarction or death), and 27% (6-43, p = 0.02) for first reinfarctions. The effect of verapamil was to prevent myocardial ischemia and reduce sudden death and reinfarction. It is concluded that long-term treatment with verapamil after an acute myocardial infarction may be recommended with the object of reducing overall mortality, major events and reinfarction.

Arrhythmias, Cardiac↗

PubMed1991

Prophylaxis of deep venous thrombosis and pulmonary embolism.

Clinically silent deep venous thrombosis (DVT) develops in up to 25% of patients who undergo general surgical procedures. Approximately 10% of these thromboses are complicated by potentially fatal pulmonary embolism. Two recent meta-analyses of more than 70 published trials of DVT prophylaxis in general surgery have demonstrated conclusively that prophylaxis significantly reduces rates of DVT and fatal pulmonary embolism and results in improved overall survival. Physical methods of prophylaxis, including compression stockings and intermittent pneumatic compression, are as effective as pharmacologic prophylaxis (the most common regimen being heparin, 5000 units subcutaneously ever 8 to 12 hours). Bleeding complications are increased with the use of heparin, although they are clinically minor. Deep venous thrombosis prophylaxis should be routinely instituted for all general surgical patients who undergo major operative procedures.

Heparin↗

PubMed1991

[Rehabilitation following myocardial infarct].

Today rehabilitation after myocardial-infarction is a routine measure in most countries, yet its effectiveness is still under discussion. Rehabilitation aims at ameliorating the quality of life and at preventing a cardiovascular reevent, in other words at prolonging life. The latter "hard" endpoints is best amenable to quantification. Only recent meta-analyses of pooled data were able to show that rehabilitation in fact does prolong life. The relative importance of physical exercise in mostly complex rehabilitation programs is even less clear. This analyses implies a benefit, yet the exact proof is still missing. If rehabilitation could be shown to improve quality of life, its application would, of course, be justified even if it did fail to prolong life. Important open questions relate to the optimizing of rehabilitation: duration, frequency, intensity as well as age and sex of responders. Answering these will be a challenge for tomorrow's rehabilitation medicine.

Combined Modality Therapy↗

PubMed1991

Aspirin in transient ischemic attacks and minor stroke: a meta-analysis.

An overview analysis of seven randomized controlled trials testing the effectiveness of aspirin in the treatment of patients with transient ischemic attacks and minor strokes was performed. A total of 6409 patients from the seven trials was entered in the analysis; 2182 patients received only aspirin; 1598 patients received an aspirin-combination regimen with either sulfinpyrazone or dipyridamole; and 2629 subjects received a placebo. Aspirin alone produced an 18% decrease in all strokes and cardiovascular deaths. The pooling of studies examining aspirin-combination regimens and the larger grouping of studies of aspirin and aspirin-combination regimens led to more striking results. Indeed, significant risk reductions were observed for three of the four outcomes, namely, total deaths, total strokes, and total strokes and cardiovascular deaths, with odds ratios ranging from 0.59 to 0.78. Suggestive, albeit more modest, results were obtained when examining the impact of these regimens on total cardiovascular mortality. The same tendencies have also been observed in three previously published meta-analyses.

Adult↗

PubMed1991

[The role of surgery in portal hypertension].

Following a historical review of the treatment of portal hypertension, the evaluation of the patient with bleeding esophageal varices is discussed. The aim of preoperative evaluation is to determine the best option for either emergency or elective treatment of bleeding esophageal varices. The most recent medical and surgical randomized studies with meta-analyses are discussed.

Esophageal and Gastric Varices↗

PubMed1990

Secondary prevention of death and reinfarction with verapamil after an acute myocardial infarction. The Danish Study Group on Verapamil in Myocardial Infarction.

The effect of verapamil on death, reinfarctions, and major events i.e. reinfarction or death, has been investigated in two Danish double-blind, placebo-controlled verapamil infarction trials DAVIT I and II. DAVIT I, which was an early intervention trial, demonstrated that after six months there was a statistically non-significant reduction of mortality and reinfarction. DAVIT II demonstrated a non-significant reduction of mortality rate (P = 0.11, hazard ratio 0.80, 95% confidence limits 0.61-1.05), a significant reduction of reinfarction rate (P = 0.04, 0.77, 0.58-1.03), and major event rate (P = 0.03, 0.80, 0.64-0.99) in the verapamil group compared with the placebo group. Meta-analyses of DAVIT I (including only patients alive on day eight) and of DAVIT II showed a statistically significant reduction of odds ratio of mortality of 22% (P = 0.04), of reinfarctions of 27% (P = 0.02), and of major events of 21% (P = 0.02). It is concluded that long-term treatment with verapamil after an acute myocardial infarction is associated with a significant reduction in overall mortality, major events, and reinfarction rates.

Anti-Arrhythmia Agents↗

PubMed1989

Is it possible to reduce the risk of cardiovascular events in subjects suffering from intermittent claudication of the lower limbs?

This study meta-analysed randomized, double-blind, placebo controlled trials in patients with intermittent claudication of the lower limbs comparing ticlopidine to placebo in order to test the hypothesis that the drug, a pure antiplatelet agent, is able to reduce the incidence of thrombotic cardio-vascular events on atherosclerotic arteries in these patients. A highly significant reduction, from 9% to 3% (p ranging from 0.006 to 0.002), was observed for fatal or non-fatal cardio-vascular events in a total of 611 patients (301 with ticlopidine, 310 with placebo). The duration of follow-up ranged from 6 to 12 months. Side-effects, defined as withdrawal from study medication for any reason but death, cardio-vascular events or cancer, were 2.4 times more frequent in the ticlopidine treated patients as compared to placebo. We concluded that in this high risk population, prevention of cardio-vascular events is likely to be effective.

Cardiovascular Diseases↗

PubMedDate not supplied

Meta-analysis of cancer trials: a new approach to the assessment of treatment.

Meta-analysis of clinical trials offers the opportunity to pool results from a number of randomised studies so increasing the statistical ability to detect the value of treatment. More accurate estimates of the likely size of such effects can also be obtained. Subset analysis, which is seldom reliable in individual clinical trials, can be made more trustworthy. Meta-analysis of randomised trials of adjuvant therapy in early breast cancer illustrates the value of such analyses. These have helped not only routine clinical practice but also thrown light upon biological mechanisms and directed future research. Meta-analyses or overviews are playing an increasingly prominent role in cancer research. They offer the opportunity to maximise the use of information about a given treatment by combining the results from multiple randomised trials in a meaningful way. Whilst data from studies examining the same issue cannot simply be combined (due to trial heterogeneity), summation of the treatment effect across trials can be performed. It is reasonably assumed that differences between studies are differences in magnitude rather than differences in direction. The net result of such a process is to produce a result which is more accurate in its estimate of treatment benefit than its component parts.

Breast Neoplasms↗

PubMedDate not supplied

Critical reading of the meta-analysis of clinical trials.

In this paper we shall present the general principles of meta-analysis and will then discuss the various factors needed to evaluate a meta-analysis: description of the problem; definition of the outcome(s) (primary and secondary); methods for identifying and selecting trials for inclusion; statistical methods used; and the presentation and discussion of the results. We shall then examine other problems such as the detection of bias, the validity of the information provided by the meta-analysis, the problem of heterogeneity, the sensitivity and robustness of the meta-analysis, quality criteria for a meta-analysis, and how to locate published meta-analyses. Finally we present a decision algorithm which should help answer the question: should and can the results from the meta-analysis be integrated into clinical practice?

Bias↗

PubMedDate not supplied

A meta-analytical approach examining the potential relationship between talc exposure and ovarian cancer.

The concern that use of talc or talc-containing substances in the perineal region of women may subject them to an increased risk for ovarian cancer has become an important issue in the study of ovarian cancer. The purpose of this paper is to examine whether this concern, heightened by several epidemiological studies purporting to show an increased risk, is valid. Epidemiological studies examining the possibility of this relationship are reviewed, and meta-analyses of their results are performed. The conclusion reached herein is that the evidence regarding the risk of ovarian cancer associated with talc exposure is equivocal, and further examination of the relationship is required before a sound conclusion can be made.

Adult↗

PubMedDate not supplied

[Effectiveness of psychotherapy in asthma: meta-analysis].

Various works have been done to find the efficiency of different psychotherapies of asthma. The results are sceptical and sometimes contradictory; this contradiction probably is due to the multiple methods or also to the various variables linked to the illness. The results of our meta-analyses on 74 hypotheses chosen by specific criteria show the efficiencies of all these psychotherapies in asthma; however, these results are largely dependent on the 8 variables taken into account.

Asthma↗

PubMed1995

Role of Helicobacter pylori in gastrointestinal disease: implications for primary care of a revolution in management of dyspepsia.

The majority of patients with dyspepsia are managed in general practice. However, most of the literature on Helicobacter pylori and its association with gastrointestinal disease has originated from secondary care. This review summarizes the role of H pylori in dyspepsia from the perspective of primary care and suggests a new strategy for the management of dyspeptic patients in this setting. Recent meta-analyses and consensus statements have supported the use of eradication therapy as first-line treatment of peptic ulceration. Studies from primary care have supported the use of eradication therapy in patients who have H pylori related peptic ulcer disease and require long-term H2-antagonist medication, on both clinical benefit and cost-effectiveness grounds. Of the many regimens proposed for the eradication of H pylori, the best evidence supports a triple combination of bismuth, metronidazole and tetracycline. Regimens using proton pump inhibitors may be more acceptable to patients but lack good evidence from trials. Use of a positive serum enzyme-linked immunoabsorbent assay for H pylori antibodies as a criterion for endoscopic investigation has been shown to result in a 23% reduction in endoscopic workload. Further research should answer questions of importance to general practitioners, such as the role of eradication therapy in patients with nonulcer dyspepsia and the effectiveness of eradication of H pylori in the prevention of gastric cancer.

Dyspepsia↗

PubMed1994

Cardiovascular structural changes and calcium antagonist therapy in patients with hypertension.

Regression of cardiovascular structural changes is a main goal of antihypertensive treatment. Two recent meta-analyses of relatively small noncomparative studies have suggested that angiotensin-converting enzyme (ACE) inhibitors may be more effective than other classes of drugs in inducing regression of left ventricular hypertrophy (LVH). The effect of different antihypertensive drugs on arteriolar structural changes has not yet been properly investigated. The aim of this study was to evaluate the effect of 6 months of treatment with amlodipine (5-10 mg o.d.) or enalapril (10-20 mg o.d.) on blood pressure (BP) (ambulatory monitoring), heart rate (HR), LV mass and function (M-mode echo, two-dimensionally guided), forearm minimal vascular resistance (min VR = BP/max blood flow-venous occlusion plethysmography, taken as an index of vascular structural changes) in 24 hypertensive patients in a comparative single-blind, randomized study, with blind reading of echocardiograms and plethysmographic tracings. After 6 months of treatment with amlodipine 5-10 mg o.d., significant reductions in LV mass index (p = 0.004) and forearm min VR (p = 0.02) were observed. Before and during treatment, LV systolic function, both at rest and during stress (handgrip test), evaluated by fractional shortening as related to end-systolic stress, was in every case within 95% confidence limits calculated in normal subjects. Similar results were observed with enalapril. No significant differences were observed for Doppler indices of diastolic filling after 6 months of treatment with either drug. These results indicate that a significant regression of structural changes in the heart and in the small resistance vessels can be observed after long-term treatment with amlodipine in essential hypertensive patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

The management of menopausal symptoms in women with breast cancer.

The symptomatic postmenopausal woman with breast cancer presents the clinician with a difficult task with respect to hormone replacement therapy (HRT). All of the published meta-analyses have been consistent in showing that there is a slightly increased risk of developing breast cancer in those patients using postmenopausal estrogens for greater than 10 years. However, there have been no published placebo-controlled clinical trials on the effects of HRT in women with a history of breast cancer. Quality of life must be balanced against the theoretical risk of tumor promotion. Assessment of osteoporotic and cardiac risk factors (i.e., smoking, hypertension, family history, hyperlipidemia) should influence the decision. Valid alternatives to estrogen replacement include low-dose progesterones such as Bellergal or vitamin E for hot flashes, and biphosphonates, calcium, anabolic steroids, and calcitonin for osteoporosis.

Breast Neoplasms↗