The Basic Structure of a Randomized Clinical Trial.

BACKGROUND: According to the Directive 2001/20/EC of the European Union, a clinical trial is any investigation in human subjects intended to (1) discover or verify the clinical, pharmacological, and/or other pharmacodynamic effects of one or more investigational medicinal product(s), (2) identify any adverse reactions to one or more investigational medicinal product(s), (3) and/or study absorption, distribution, metabolism and excretion of one or more investigational medicinal product(s) with the object of ascertaining its (their) safety and/or efficacy.

SUMMARY: The major steps in the planning and conduction of a randomized clinical trial (RCT) include the definition of the study population, the random assignment of treatments, the choice of the measures of treatment effects, the duration of the experiment, the assessment of the tolerability and safety of the treatment, and the choice of alternative design models. In doing this, a constant reference will be made to the peculiarities (and diversities) of neurological disorders.

KEY MESSAGES: An RCT is the best model to test the efficacy, tolerability, and safety of a drug, and reflects the need to disentangle the effects of the treatment from the effects of other prognostic variables. This requires a number of restrictions that are, at the same time, limitations for the application of the study results to the individuals who will receive the treatment in clinical practice.