Applicability of clinical trial results to the individual patient: practice guidelines

Randomized controlled trials (RCTs) constitute the methodological gold standard to generate therapeutic or preventive evidence. Diagnostic or prognostic evidence is given by studies with different designs, rather than RCTs. Given the structural design that a RCT must present to be valid--discussed in previous issues of the Journal--one major question is the applicability of trial results to populations or individual patients that are different from those analyzed in that trial. In other words, how does the cardiologist know whether to apply a specific treatment--whose efficacy and risk profile have been defined in a good quality RCT, i.e. one with valid and important results--to his/her individual patient? The simplest solution would be found in the answer to the question: "Could my patient have been enrolled in the study by satisfying its inclusion and exclusion criteria?" If the answer is "yes", then it would be sound to apply the study results to the patient, so long as it is done carefully. If the answer is "no" (because the patient presents different demographic features or serious comorbidities not found in the trial subjects, for example), then transfer of the therapeutic results from the trial would be seriously compromised. The evaluation of these questions is complex and, due to its importance, deserves a systematic approach. In this article we will present some practical guidelines on whether to reject the applicability of RCT results to patients who are different from those included in the trial.