Run-in periods and treatment outcomes in asthma trials: A narrative review

The run-in period is an important element of randomized controlled trials, and is often used in respiratory disease trials. The design of the run-in period can greatly impact results and data interpretation, and as such should be designed carefully.

In this review, we describe the design of run-in periods across six phase 3A trials of triple therapy in asthma, and discuss how differences in run-in period design (specifically the duration, treatment, and reporting of run-in results) may have the potential to alter the interpretation of study outcomes.

We found that the duration of run-in periods ranged between 2 and 7 weeks, with some studies including a combination of screening, run-in and stabilization periods, and others including a run-in period only. Run-in treatment also varied, with some studies running in patients on their previous inhaled corticosteroid/long-acting β₂-agonist (ICS/LABA) therapy, and others harmonizing treatment by switching to the same ICS/LABA combination used in the on-treatment phase, or a different ICS/LABA combination entirely. Most of the studies included did not report any changes to study outcomes seen prior to randomization.

We discuss the potential implications associated with the various trial designs, and propose that run-in periods should be consciously designed to meet the goals of the specific study. We also propose that standardized reporting of run-in changes would further allow for differentiation between improvements due to improved adherence and true treatment benefits, and aid with comparing data from different clinical trials.