Rationale for a non-inferiority clinical trial design focused on subpopulations

Although double-blind, placebo-controlled clinical trials are utilized extensively to characterize the efficacy and safety of new treatment options, the characteristics of the trial participants often do not reflect those of the wider patient population. In most cases, one or more patient subgroups (whether defined by race, ethnicity, co-morbidity, concomitant medication, age, or gender) will be under-represented. Understanding treatment responses in these subpopulations is a vital component of the overall therapeutic profile of a medication. Several different approaches to subgroup analyses within a single trial have been described. In addition, meta-analytic and data pooling approaches utilize results from multiple clinical trials of similar design to increase the number of patients within a targeted subgroup. If the results from exploratory analyses are suggestive of a clinically relevant difference in treatment response for a particular subgroup, then implementation of a prospectively designed clinical trial may be warranted. In this commentary, we discuss the design and results of various studies that include subgroup analyses. In addition, we describe a novel study design with a non-inferiority subpopulation analysis (NISA) that may provide new insights with respect to subgroup analyses. The NISA study design relies on characterization of the dominant group of patients recruited to date in placebo-controlled trials. In the NISA study, the group of patients with those same characteristics is referred to as the Core group. The other key features of the NISA design include non-inferiority analyses comparing subgroups to the Core group and study conditions closely aligned with routine clinical practice (heterogeneous study population and open-label drug administration without placebo). Limitations of the NISA design include the requirement of previously conducted placebo-controlled trials, the inability to compare treatment response to placebo, and that NISA has yet to be validated in practice. We also describe the implementation of the NISA study design in two ongoing clinical trials. After completion of these two studies, the practical value of the NISA design can be more thoroughly evaluated.