1. Introduction

Secondary Stroke Prevention with Antiplatelet Drugs: Have We Reached the Ceiling?

Patients with transient ischemic attack (TIA) or ischemic stroke carry a risk of recurrent stroke of between 5% and 20% per year. In patients with TIA or ischemic stroke of non-cardiac origin, antiplatelet drugs are able to decrease the relative risk of stroke by 11–15% and the risk of stroke, myocardial infarction, and vascular death by 15–22%. Aspirin is the most widely used drug. It is affordable and effective. Low doses of 50–325 mg aspirin are as effective as high doses and cause less gastrointestinal side-effects. The combination of aspirin with slow-release dipyridamole is superior to aspirin alone for stroke prevention but not for the prevention of cardiac events. The risk of major bleeding complications is not increased with the combination, which suggests that dipyridamole might act in another way than as antiplatelet drug. Clopidogrel is not superior to aspirin in unselected stroke patients but is superior in patients at high risk of recurrence. The combination of aspirin plus clopidogrel is not more effective than clopidogrel alone, but carries a higher bleeding risk. The most effective antiplatelet drugs, the GP IIb/IIIa antagonists, are not superior to aspirin and carry a higher risk of bleeding. These results indicate that any antiplatelet therapy with a more potent drug than aspirin will only have a marginally higher efficacy, which might be offset by a higher bleeding rate. Therefore, selection of patients who might benefit from antiplatelet therapy other than aspirin is important.

Data fraud in clinical trials

Highly publicized cases of fabrication or falsification of data in clinical trials have occurred in recent years and it is likely that there are additional undetected or unreported cases. We review the available evidence on the incidence of data fraud in clinical trials, describe several prominent cases, present information on motivation and contributing factors and discuss cost-effective ways of early detection of data fraud as part of routine central statistical monitoring of data quality. Adoption of these clinical trial monitoring procedures can identify potential data fraud not detected by conventional on-site monitoring and can improve overall data quality.

Central statistical monitoring: detecting fraud in clinical trials

BACKGROUND

Central statistical monitoring in multicenter trials could allow trialists to identify centers with problematic data or conduct and intervene while the trial is still ongoing. Currently, there are few published models that can be used for this purpose.

PURPOSE

To develop and validate a series of risk scores to identify fabricated data within a multicenter trial, to be used in central statistical monitoring.

METHODS

We used a database from a multicenter trial in which data from 9 of 109 centers were documented to be fabricated. These data were used to build a series of risk scores to predict fraud at centers. All analyses were performed at the level of the center. Exploratory factor analysis was used to select from 52 possible predictors, chosen from a variety of previously published methods. The final models were selected from a total of 18 independent predictors, based on the factors identified. These models were converted to risk scores for each center.

RESULTS

Five different risk scores were identified, and each had the ability to discriminate well between centers with and without fabricated data (area under the curve values ranged from 0.90 to 0.95). True- and false-positive rates are presented for each risk score to arrive at a recommended cutoff of seven or above (high risk score). We validated these risk scores, using an independent multicenter trial database that contained no data fabrication and found the occurrence of false-positive high scores to be low and comparable to the model-building data set.

LIMITATIONS

These risk score have been validated only for their false-positive rate and require validation within another trial that contains centers that have fabricated data. Validation in noncardiovascular trials is also required to gage the usefulness of these risk scores in central statistical monitoring.

CONCLUSIONS

With further validation, these risk scores could become part of a series of tools that provide evidence-based central statistical monitoring, which in turn can improve the efficiency of trials, and minimize the need for more expensive on-site monitoring.

A statistical approach to central monitoring of data quality in clinical trials

Background

Classical monitoring approaches rely on extensive on-site visits and source data verification. These activities are associated with high cost and a limited contribution to data quality. Central statistical monitoring is of particular interest to address these shortcomings.

Purpose

This article outlines the principles of central statistical monitoring and the challenges of implementing it in actual trials.

Methods

A statistical approach to central monitoring is based on a large number of statistical tests performed on all variables collected in the database, in order to identify centers that differ from the others. The tests generate a high-dimensional matrix of p-values, which can be analyzed by statistical methods and bioinformatic tools to identify extreme centers.

Results

Results from actual trials are provided to illustrate typical findings that can be expected from a central statistical monitoring approach, which detects abnormal patterns that were not (or could not have been) detected by on-site monitoring.

Limitations

Central statistical monitoring can only address problems present in the data. Important aspects of trial conduct such as a lack of informed consent documentation, for instance, require other approaches. The results provided here are empirical examples from a limited number of studies.

Conclusion

Central statistical monitoring can both optimize on-site monitoring and improve data quality and as such provides a cost-effective way of meeting regulatory requirements for clinical trials.

A Framework for Addressing Structural Uncertainty in Decision Models

Decision analytic models used for health technology assessment are subject to uncertainties. These uncertainties can be quantified probabilistically, by placing distributions on model parameters and simulating from these to generate estimates of cost-effectiveness. However, many uncertain model choices, often termed structural assumptions, are usually only explored informally by presenting estimates of cost-effectiveness under alternative scenarios. The authors show how 2 recent research proposals represent parts of a framework to formally account for all common structural uncertainties. First, the model is expanded to include parameters that encompass all possible structural choices. Uncertainty can then arise because these parameters are estimated imprecisely from data, for example, a treatment effect of doubtful significance. Uncertainty can also arise if there are no relevant data. If there are relevant data, uncertainty can be addressed by averaging expected costs and effects generated from probabilistic analysis of the models with and without the parameter. The weights used for averaging are related to the predictive ability of each model, assessed against the data. If there are no data, additional parameters can often be informed by eliciting expert beliefs as probability distributions. These ideas are illustrated in decision models for antiplatelet therapies for vascular disease and new biologic drugs for the treatment of active psoriatic arthritis.

Is there an association between low dose aspirin and anemia (without overt bleeding)? Narrative review

BACKGROUND

Overt bleeding associated with low dose aspirin (LDA) is well-recognized, little attention is given to the possibility of association between LDA and occult bleeding, although this is known to occur in healthy volunteers. LDA is used increasingly in primary and secondary prevention of a number of medical conditions, many of which are common in older people, as is anemia. Anemia in older people is associated with adverse outcomes including disability, morbidity and mortality. The purpose of this study was to review the evidence that LDA might cause anemia without overt bleeding.

METHODS

An extensive narrative review was carried out. Electronic searching (including database links) and reference lists of reports were used to identify studies reporting on use of aspirin ≤325 mg/day and anemia or change in hemoglobin (Hb) without overt bleeding. Data were extracted from reports of trials, adverse drug reactions (ADRs) and prevalence studies of adults aged ≥18 years, published since 1980.

RESULTS

There are few relevant data, with considerable heterogeneity among trial designs, duration, and patient characteristics in studies of LDA. In five randomised trials (n = 5879) in (mostly secondary) prevention, the majority of patients were men without peptic ulcer disease aged 50-70 years and no consistent association between LDA and change in Hb was found. In two smaller studies (n = 609) of primary prevention in healthy patients aged ≥70 years, there was a small but statistically significant fall in Hb with LDA. Observational studies, and data from trials in which use of LDA was not a primary focus of the study, were inconclusive.

CONCLUSIONS

It is not clear whether there is an association between LDA and anemia in the absence of overt bleeding, but there may be an association between LDA and fall in Hb in (a subset of) older patients. The available evidence has significant limitations, which are discussed; studies including more older patients, and publication of individual patient data, would help clarify this important matter.

Aspirin resistance

The development of adverse cardiovascular events despite aspirin use has established an interest in a possible resistance to the drug. Several definitions have been set and various laboratory testing modalities are available. This has led to a wide range of prevalence reports in different clinical entities. The etiologic mechanism has been related to clinical, genetic, and other miscellaneous factors. The clinical implications of this phenomenon are significant and warrant concern. Management strategies are currently limited to dosing alteration and introduction of other anitplatelet agents. However, these measures have not met the expected efficacy or safety.

[Incremental cost-effectiveness of dipyridamole + acetylsalicylic acid in secondary prevention of ischemic noncardioembolic stroke]

BACKGROUND AND PURPOSE

The aim of secondary prevention in stroke is to avoid restrokes. The current standard treatment in Germany is a lifelong therapy with low-dose acetylsalicylic acid (ASA). As the incidence of restrokes remains relatively high from a health-care payer's perspective, the question arises, whether the combination of dipyridamole + acetylsalicylic acid (Dip + ASA) is cost-effective in comparison with a therapy based on ASA only.

METHODS

A decision-analytic cross-sectional epidemiologic steady-state model of the German population compares the effects of two strategies of secondary prevention with Dip + ASA (12 months vs. open end) and with ASA monotherapy.

RESULTS

The model predicts the following estimates: the annual incidence of initial ischemic strokes in Germany is estimated at 130,000 plus an extra 34,000 restrokes (base year 2005). Additionally, there are 580,000 people that experienced a stroke > 12 months earlier, of whom 135,000 had a restroke. Every year, nearly 89,000 Germans die of the consequences of an ischemic stroke. If Dip + ASA would have been the standard therapy in secondary prevention of ischemic stroke, an additional 7,500 persons could have been saved in 2005. Statutory health insurance would have to spend 33,000 Euro for every additional life year gained with Dip + ASA as secondary prevention strategy. If secondary prevention with Dip + ASA would be limited to the first 12 months after an initial stroke, which is the time of the highest risk for a restroke, the incremental cost-effectiveness ratio is about 7,000 Euro per life year gained. The results proved to be robust in sensitivity analyses.

CONCLUSION

Secondary prevention with Dip + ASA is cost-effective in comparison to treatment with ASA in monotherapy, because its incremental cost-effectiveness ratio is within common ranges of social willingness to pay. From the standpoint of the patient as well as the health-care payer, focusing on the first 12 months after the initial incident for intensified preventive drug treatment with Dip + ASA should be valuable from a medical as well as a health-economic perspective.

Ensuring trial validity by data quality assurance and diversification of monitoring methods

Errors in the design, the conduct, the data collection process, and the analysis of a randomized trial have the potential to affect not only the safety of the patients in the trial, but also, through the introduction of bias, the safety of future patients. Trial monitoring, defined broadly to include methods of oversight which begin when the study is designed and continue until it is reported in a publication, has a role to play in eliminating such errors. On-site monitoring can be extremely inefficient for the identification of errors most likely to compromise patient safety or bias study results. However, a variety of other monitoring strategies offer alternatives to on-site monitoring. Each new trial should conduct a risk assessment to identify the optimal means of monitoring, taking into account the likely sources of error, their consequences for patients, the study's validity, and the available resources. Trial management committees should consider central statistical monitoring a key aspect of such monitoring. The systematic application of this approach would be likely to lead to tangible benefits, and resources that are currently wasted on inefficient on-site monitoring could be diverted to increasing trial sample sizes or conducting more trials. Clinical Trials 2008; 5: 49—55. http://ctj.sagepub.com

Dipyridamole and headache

The combination of aspirin and dipyridamole is more effective in secondary stroke prevention than aspirin monotherapy. Headache is a frequent early adverse event in patients treated with dipyridamole. In the European Stroke Prevention Study 2, 8% of patients terminated treatment with dipyridamole due to headache compared with 2.1% with placebo. Dipyridamole induces headache more frequently in persons suffering from migraine than those without a primary headache. One way to reduce headache burden is to titrate dipyridamole slowly. Acetaminophen, however, is not effective in treating dipyridamole-induced headache. The optimal strategy to avoid early treatment termination and increase compliance is patient information about the occurrence and limited duration of headache and dose titration.

[Guidelines given by the DSG and DGN concerning stroke therapy--new therapeutic aspects]

Surgeries of symptomatic carotid stenose should not be operated on later than 14 days after stroke; until the operation inhibitors of platelet aggregation have to be administered (Table 1). The application of anticoagulants like warfarin or phenprocoumon in case of intracranial stenoses is no longer recommended. Instead 100-300 mg aspirin should prophylactically be given. The risk of suffering a stroke is significantly reduced by the application of antihypertensives. Patients with focal cerebral ischemia should be given 40 mg of Simvastatin which leads to a significant decrease of vascular risk. After the first cerebral ischemic incidenz patients with open foramen ovale of the heart should be given 100-300 mg aspirin. In case of aspirin relapse an oral anticoagulation has to be carried out with an INR of 2.0 up to 3 for at least one year.

Dipyridamole may induce migraine in patients with migraine without aura

Dipyridamole inhibits phosphodiesterase 5 (PDE5) and adenosine re-uptake. The most prominent side-effect is headache. We examined the migraine-generating effects of dipyridamole as well as the cerebral blood velocity response in a single-blind study, including 10 patients with migraine without aura and 10 healthy subjects. Dipyridamole 0.142 mg/kg per min was administered intravenously. Headache intensity was scored on a verbal rating scale along with pain characteristics and accompanying symptoms. Blood velocity in the middle cerebral artery (V(mca)), blood pressure and heart rate were recorded repeatedly. Headache was induced in all migraine patients and in eight of 10 healthy subjects (P = 0.47) with no significant difference in headache intensity (P = 0.53). However, five patients but only one healthy subject experienced the symptoms of migraine without aura, according to ICHD-2 criteria, within 12 h (P = 0.14). Four patients reported photophobia after dipyridamole compared with no healthy subjects (P = 0.087). V(mca) decreased (P < 0.001) during and after dipyridamole infusion with no difference between groups (P = 0.15) coinciding with initiation, but not cessation of immediate headache. Thus, dipyridamole induces symptoms of migraine and an initial decrease in V(mca) in migraine patients, but not significantly more than in healthy subjects. This relatively low frequency of migraine induction, compared with nitric oxide donors and sildenafil, is probably due to the less specific action of dipyridamole on the cGMP signalling pathway as well as a possible bidirectional effect of adenosine on migraine induction.

[Anticoagulation for secondary prevention: which drug in which situation?]

Thromboembolic events are a major complication of cardiovascular diseases. Secondary prevention of thromboembolic complications can be achieved by anticoagulation with heparin or vitamin-K-antagonists. A new class of direct thrombin inhibitors has been recently introduced into clinical medicine. Clinical studies have demonstrated theses agents to be comparable in efficacy for prophylaxis of venous thromboembolism. However, the results of ongoing trials are awaited in helping to define the place of direct thrombin inhibitors in secondary prevention. Antiplatelet therapy constitutes the cornerstone in the management of patients with acute coronary syndromes and generally high-risk patients with atherothrombosis. Until recently, long-term antiplatelet therapy for the treatment and prevention of atherothrombotic disease was traditionally limited to aspirin. The availability of the thienopyridines and glycoprotein IIb/IIIa inhibitors represents an important addition to the physician's armamentarium. Due to the increased risk of major bleeding, for each patient the decision of anticoagulation and antiplatelet therapy must be tightly correlated to the individual benefit-risk ratio.

Inhibition of platelet activation and aggregation

It has recently been established that platelets are involved at all stages of atherosclerotic disease. A major platelet mediated process is the acute vessel closure at the site of atherosclerotic plaque rupture and there is emerging evidence for platelet adhesion to endothelial cells in the early stage of atherosclerotic disease. This, through engagement of other cells, leads to the development of the atherosclerotic plaque. Beside dietary, cholesterol- and lipid-lowering, and other pharmaceutical approaches antiplatelet therapy plays an important part in the treatment of atherosclerosis and its multifarious clinical manifestations. Antiplatelet therapy and the currently approved substances for oral (acetylsalicylic acid, dipyridamole, cilostazol, ticlopidin and clopidogrel) and parenteral (acetylsalicylic acid, abciximab, eptifibatide and tirofiban) administration are discussed in the following section. Attention is given to each single agent and its mechanism of action. Differences in pharmacodynamic and pharmacokinetic properties are elucidated and outlook on future antiplatelet strategies is discussed.

Antithrombotic Secondary Prevention After Stroke

In patients with transient ischemic attack (TIA) or ischemic stroke of noncardiac origin, antiplatelet drugs are able to decrease the risk of stroke by 11% to 15%, and decrease the risk of stroke, myocardial infarction (MI), and vascular death by 15% to 22%. Aspirin leads to a moderate but significant reduction of stroke, MI, and vascular death in patients with TIA and ischemic stroke. Low doses are as effective as high doses, but are better tolerated in terms of gastrointestinal side effects. The recommended aspirin dose, therefore, is between 50 and 325 mg. Bleeding complications are not dose-dependent, and also occur with the lowest doses. The combination of aspirin (25 mg twice daily) with slow-release dipyridamole (200 mg twice daily) is superior compared with aspirin alone for stroke prevention. Ticlopidine is effective in secondary stroke prevention in patients with TIA and stroke. For some end points, it is superior to aspirin. Due to its side-effect profile (neutropenia, thrombotic thrombocytopenic purpura ), ticlopidine should be given to patients who are intolerant of aspirin. Prospective trials have not indicated whether ticlopidine is suggested for patients who have recurrent cerebrovascular events while on aspirin. Clopidogrel has a better safety profile than ticlopidine. Although not investigated in patients with TIA, clopidogrel should also be effective in these patients assuming the same pathophysiology than in patients with stroke. Clopidogrel is second-line treatment in patients intolerant for aspirin, and first-line treatment for patients with stroke and peripheral arterial disease or MI. A frequent clinical problem is patients who are already on aspirin because of coronary heart disease or a prior cerebral ischemic event, and then suffer a first or recurrent TIA or stroke. No single clinical trial has investigated this problem. Therefore, recommendations are not evidence-based. Possible strategies include the following: continue aspirin, add dipyridamole, add clopidogrel, switch to ticlopidine or clopidogrel, or switch to anticoagulation with an International Normalized Ratio (INR) of 2.0 to 3.0. The combination of low-dose warfarin and aspirin was never studied in the secondary prevention of stroke. In patients with a cardiac source of embolism, anticoagulation is recommended with an INR of 2.0 to 3.0. At the present time, anticoagulation with an INR between 3.0 and 4.5 cannot be recommended for patients with noncardiac TIA or stroke. Anticoagulation with an INR between 3.0 and 4.5 carries a high bleeding risk. Whether anticoagulation with lower INR is safe and effective is not yet known. Treatment of vascular risk factors should also be performed in secondary stroke prevention.

Rationale for the use of platelet aggregation inhibitors in PAD patients

Peripheral arterial disease (PAD) is a major risk marker for systemic ischaemic events. The understanding of PAD has moved from PAD as an organ-specific disease to PAD as the lower-limb localization of a multifocal disease, i.e. atherothrombosis. Blood platelet activation and aggregation is a common denominator in atherothrombotic events, and use of antiplatelet agents in patients with PAD can inhibit thrombus formation and reduce the occurrence of myocardial infarction (MI), ischaemic stroke (IS) and vascular death. Many studies have investigated various antiplatelet regimens for preventing acute cardiovascular events in patients with a prior ischaemic event, although many of these studies had a number of limitations. The Antiplatelet Trialists' Collaboration performed a meta-analysis of 23 stroke trials and found an average odds risk reduction of 25% for a combined endpoint of stroke, MI or vascular death. The concept of atherothrombosis as a multifocal disease was challenged by the Clopidogrel versus Aspirin in Patients at Risk of Ischaemic Events (CAPRIE) trial. This study showed an 8.7% decrease in the relative risk reduction for further atherothrombotic events with clopidogrel over aspirin (p = 0.043) for the overall population, in terms of the combined endpoint of IS, Ml or vascular death.

Antiplatelet agents for secondary prevention of ischemic stroke

OBJECTIVE

To review and summarize the efficacy, mechanisms of action, and cost of the options available when choosing antiplatelet agents for secondary stroke prevention.

DATA SOURCES

This article is based on a review of the literature found with MEDLINE, CINAHL, and Cochrane Reviews (1980-June 2000) and abstracts from relevant international scientific meetings. We searched for the terms aspirin, ticlopidine, dipyridamole, antiplatelet, and clopidogrel.

STUDY SELECTION

English-language articles, both reviews and original studies, were evaluated, and all information considered relevant was included in this review. In addition, guidelines from the American Heart Association are included.

DATA SYNTHESIS

Aspirin is a relatively inexpensive and effective agent for secondary stroke prevention, and lower doses of aspirin appear as effective as higher doses. Ticlopidine has been used alone or in combination with aspirin, but serious adverse effects have limited its use. Clopidogrel has emerged as a safe and effective alternative to ticlopidine and lacks some of the serious adverse effects associated with ticlopicine, but is not superior to aspirin in secondary stroke prevention. Unlike previous studies, one recent trial showed that dipyridamole in combination with aspirin is superior to aspirin alone.

CONCLUSIONS

Antiplatelet therapy is a key component of secondary prevention strategies in ischemic stroke. While aspirin has been the cornerstone in the management of stroke, other classes of antiplatelet drugs present new opportunities to optimize antiplatelet therapy.

Aggrenox: an aspirin and extended-release dipyridamole combination

Stroke is one of the leading causes of death in the United States. The risk of experiencing a recurrent stroke remains elevated for several years after an initial stroke or a transient ischemic attack (TIA), therefore secondary prevention is crucial in reducing the risk of stroke and the complications and costs associated with stroke. Aggrenox, a combination of low-dose aspirin and extended-release dipyridamole, is a new agent that is effective in the secondary prevention of stroke and transient ischemia of the brain. The clinical effect of its two antiplatelet agents are additive and significantly better than either aspirin or dipyridamole alone, although it has not been shown to be more effective than aspirin alone in preventing death. Aggrenox is much more expensive than aspirin alone but has been shown to be more cost-effective. At this point, much of the pharmacologic information concerning this combination agent is based on previous data about aspirin and immediate-release dipyridamole. This combination of aspirin and extended-release dipyridamole may play a significant role in secondary stroke and TIA prevention.

Antithrombotic Secondary Prevention After Stroke

In patients with transient ischemic attack (TIA) or ischemic stroke of noncardiac origin, antiplatelet drugs are able to decrease the risk of stroke by 11% to 15%, and decrease the risk of stroke, myocardial infarction (MI), and vascular death by 15% to 22%. Aspirin leads to a moderate but significant reduction of stroke, MI, and vascular death in patients with TIA and ischemic stroke. Low doses are as effective as high doses, but are better tolerated in term of gastrointestinal side effects. The recommended aspirin dose, therefore, is between 50 and 325 mg. Bleeding complications are not dose-dependent, and also occur with the lowest doses. The combination of aspirin (25 mg twice daily) with slow release dipyridamole (200 mg twice daily) is superior compared with aspirin alone for stroke prevention. Ticlopidine is effective in secondary stroke prevention in patients with TIA and stroke. For some endpoints, it is superior to aspirin. Due to its side effect profile (neutropenia, thrombotic thrombocytopenic purpura ), ticlopidine should be given to patients who are intolerant of aspirin. Prospective trials have not indicated whether ticlopidine is suggested for patients who have recurrent cerebrovascular events while on aspirin. Clopidogrel has a better safety profile than ticlopidine. Although not investigated in patients with TIA, clopidogrel should also be effective in these patients assuming the same pathophysiology than in patients with stroke. Clopidogrel is second-line treatment in patients intolerant for aspirin, and first-line treatment for patients with stroke and peripheral arterial disease or MI. A frequent clinical problem is patients who are already on aspirin because of coronary heart disease or a prior cerebral ischemic event, and then suffer a first or recurrent TIA or stroke. No single clinical trial has investigated this problem. Therefore, recommendations are not evidence-based. Possible strategies include the following: continue aspirin, add dipyridamole, add clopidogrel, switch to ticlopidine or clopidogrel, or switch to anticoagulation with an International Normalized Ratio (INR) of 2.0 to 3.0. The combination of low-dose warfarin and aspirin was never studied in the secondary prevention of stroke. In patients with a cardiac source of embolism, anticoagulation is recommended with an INR of 2.0 to 3.0. At the present time, anticoagulation with an INR between 3.0 and 4.5 can not be recommended for patients with noncardiac TIA or stroke. Anticoagulation with an INR between 3.0 and 4.5 carries a high bleeding risk. Whether anticoagulation with lower INR is safe and effective is not yet known. Treatment of vascular risk factors should also be performed in secondary stroke prevention.

Antithrombotic drugs for secondary stroke prophylaxis

Stroke is the third most common cause of adult mortality in the United States. Antithrombotic agents form the mainstay of stroke prevention. Aspirin produces a modest reduction in the risk of second stroke and is widely recommended for initial therapy. The thienopyridines ticlopidine and clopidogrel are alternatives for secondary prevention in patients who do not respond to or cannot take aspirin. They are no more effective than aspirin and have been associated with thrombotic thrombocytopenic purpura. The combination of aspirin and extended-release dipyridamole has several mechanisms of action and an additive effect on reducing stroke risk compared with either agent alone. A 2-fold increase in risk reduction and favorable safety profile suggest that the combination can serve as first-line prophylaxis against a second stroke.

The role of biostatistics in the prevention, detection and treatment of fraud in clinical trials

Recent cases of fraud in clinical trials have attracted considerable media attention, but relatively little reaction from the biostatistical community. In this paper we argue that biostatisticians should be involved in preventing fraud (as well as unintentional errors), detecting it, and quantifying its impact on the outcome of clinical trials. We use the term 'fraud' specifically to refer to data fabrication (making up data values) and falsification (changing data values). Reported cases of such fraud involve cheating on inclusion criteria so that ineligible patients can enter the trial, and fabricating data so that no requested data are missing. Such types of fraud are partially preventable through a simplification of the eligibility criteria and through a reduction in the amount of data requested. These two measures are feasible and desirable in a surprisingly large number of clinical trials, and neither of them in any way jeopardizes the validity of the trial results. With regards to detection of fraud, a brute force approach has traditionally been used, whereby the participating centres undergo extensive monitoring involving up to 100 per cent verification of their case records. The cost-effectiveness of this approach seems highly debatable, since one could implement quality control through random sampling schemes, as is done in fields other than clinical medicine. Moreover, there are statistical techniques available (but insufficiently used) to detect 'strange' patterns in the data including, but no limited to, techniques for studying outliers, inliers, overdispersion, underdispersion and correlations or lack thereof. These techniques all rest upon the premise that it is quite difficult to invent plausible data, particularly highly dimensional multivariate data. The multicentric nature of clinical trials also offers an opportunity to check the plausibility of the data submitted by one centre by comparing them with the data from all other centres. Finally, with fraud detected, it is essential to quantify its likely impact upon the outcome of the clinical trial. Many instances of fraud in clinical trials, although morally reprehensible, have a negligible impact on the trial's scientific conclusions.

Antiplatelet therapy for secondary stroke prevention

The precise role of antiplatelet therapy in secondary stroke prevention remains a matter of some debate. Although specific antiplatelet agents (notably aspirin, ticlopidine, dipyridamole, and clopidogrel) have been shown to be active in the prevention of secondary stroke, questions remain about the effective dose of these agents and their potential efficacy in combined therapeutic regimens. In addition, haematological and gastrointestinal side-effects of antiplatelet agents remain a significant clinical concern for patients and prescribing physicians. This review article examines research on both monotherapy and combination antiplatelet therapy for secondary stroke prevention, with an emphasis on lessons learned about dosage schedules, treatment protocols, and side-effect profiles.