RESUMEN
Head to head trials have been proposed as an alternative to the ethical and methodological concerns related to placebo-controlled trials. While those studies may be particularly informative from the clinical and cost-effectiveness point-of-view, avoiding placebo poses several regulatory concerns: for superiority designs, the choice of the trial population, outcomes, dose and escalation of the comparator, as well as the comparator itself may be an issue; for non-inferiority studies, issues related to uncertain assay sensitivity and exposure of large samples to potentially ineffective or unsafe drugs make them inappropriate, in the absence of a previous positive superiority trial, for regulatory purposes. The inclusion of active comparators in regulatory trials should not be seen as an alternative, but as a useful complement to the information that can be obtained from placebo-controlled studies.