Characterizing Current Registration of Phase 3 Crossover Trials on ClinicalTrials.gov

Background: ClinicalTrials.gov is the primary registry for federally and privately funded clinical trials conducted in the United States. Unlike the more commonly used parallel design, in which each participant is randomized to a certain treatment, in a crossover design, each participant is randomized to a sequence of treatments and each participant serves as his/her own control in estimating treatment effect. This distinct feature makes the design and registration of crossover trials different from that of parallel trials. Objective: To characterize Phase 3 crossover trials registered on ClinicalTrials.gov; to identify registration issues using current system; to inform the development of practical guidance to improve registration of crossover trials on ClinicalTrials.gov. Method: We searched ClinicalTrials.gov on Sep 15, 2014 for trials labeled ‘Crossover Assignment’ in the intervention model, randomized, phase 3, and having results registered and citation provided. Two reviewers independently assessed the eligibility and extracted data on study design details, reporting groups, primary outcomes and adverse events to an electronic form developed on Systematic Review Data Repository. We tabulated the numbers of trials with specified characteristics and described issues in the definitions, instructions, and in using the registration template. Results: Registration of crossover trials was mixed. Only three quarters of included Phase 3 studies (75%, 54/72) labeled as ‘’Crossover Assignment’ trials were real randomized, crossover trials. We found variations of registration format for different sections. Majority of the trials (81.5%, 44/54) presented the outcome following a parallel instead of crossover structure. We proposed guidance for table creation with examples for registering arms/interventions, participant flow, baseline characteristics, outcome and adverse events respectively, to help improve the registration of crossover trials on ClinicalTrials.gov. Conclusion: Many of studies labeled as ‘Phase 3 Crossover Assignment’ have problems in registration on ClinicalTrials.gov The proposed strategy has the potential to improve registration of the design, results and analysis of crossover trials on ClinicalTrials.gov