L’essai clinique contrôlé randomisé

Abstract

It is generally agreed that the first comparative clinical trial in history was done by James Lind in 1747, in the treatment of scurvy. The general bases of modern experimental medicine were published by Claude Bernard in 1865. However, it is the development of new drugs and the evolution of methodological concepts that led to the first randomized controlled clinical trial, in 1948, which showed that the effects of streptomycin on pulmonary tuberculosis were significantly different from those of a placebo. Today, "evidence-based" medicine aims to rationalize the medical decision-making process by taking into account, first and foremost, the results of controlled randomized clinical trials, which provide the highest level of evidence. In the second half of the 20th century it became clear that different kinds of clinical trials might not provide the same level of evidence. Practitioners' intimate convictions must be challenged by the results of controlled clinical trials. Take the CAST trial for example, which, in 1989, tested antiarrhythmic drugs versus placebo in patients with myocardial infarction. It was well known that ventricular arrhythmias were a factor of poor prognosis in coronary heart disease, and it was therefore considered self-evident that drug suppression of these ventricular arrhythmias would reduce the mortality rate. In the event, the CAST trial showed the exact opposite, with an almost 3-fold increase in total mortality among patients with coronary heart disease who were treated with antiarrhythmic drugs. These results had a profound impact on the use of antiarrythmic drugs, which became contraindicated after myocardial infarction. A clinical trial has to fulfill certain methodological standards to be accepted as evidence-based medicine. First, a working hypothesis has to be formulated, and then the primary outcome measure must be chosen before beginning the study. An appropriate major endpoint for efficacy must be selected, in keeping with the primary outcome. One may choose either a single endpoint (for instance all-cause mortality; or a composite criterion taking into account various manifestations of the same health disorder (for instance cardiovascular mortality plus non lethal myocardial infarction plus non lethal ischemic stroke). The trial must be controlled, i.e. must compare the intervention with a standard or dummy treatment. A randomization process is used to ensure that the groups are comparable. The patients must be monitored and the results analyzed in double-blind manner The required number of patients is calculated based on the working hypothesis ("superiority" trial or "equivalence" trial), as well as the spontaneous variability of the main endpoint, and the alpha and beta statistical risks. The experimental design (cross-over or parallel groups) is chosen according to the primary outcome measure and the disease characteristics. Finally, the results must be analyzed in an intention-to-treat manner, taking into account all the patients who were initially randomized. The results of these methodologically sound trials form the basis for official therapeutic guidelines, which help physicians to choose the best treatments for their patients. However, extrapolating the results of randomized controlled clinical trials to the general patient population is not always straightforward. For instance, it is well known that patients who participate in clinical trials are highly selected and therefore somewhat unrepresentative. In addition, their numbers are limited and the treatment period is often much shorter than in routine management of a chronic disease. Finally, patients in clinical trials are monitored more closely than in routine practice. This is why we need post-marketing pharmacoepidemiological studies, in which cohorts of patients exposed to the treatment in question are monitored sufficiently long to determine the precise risk-benefit ratio. Controlled clinical trials are lacking in various fields of biomedical research, either because drug companies consider them unprofitable, or because they concern public health issues that are outside the scope of the private sector In such cases, controlled clinical trials must be undertaken and funded by the public sector Today, only North American institutions such as NIH and the National Heart Blood and Lung Institute are capable of sponsoring such trials. This creates a potential problem for extrapolation to European patient populations, which may be different. Large controlled clinical trials must start to be sponsored by public funding in Europe if European practitioners are to receive the evidence-based results they need to rationalize their medical practice.