Nested Randomized Controlled Trials in Large Databases: An Opportunity for Inflammatory Bowel Disease?

Although randomized controlled trials (RCTs) are the gold standard for investigating the efficacy and safety of interventions, they present major operational challenges due to their complexity, time-consuming nature, and high costs. To address some of these difficulties, RCTs nested in cohorts (RCTsNC) have been developed to enable patient enrolment and randomization from existing databases. RCTsNC is an emerging trial design, which has been successfully utilized across several medical disciplines but not inflammatory bowel disease (IBD). This narrative review outlines the principles of RCTsNC and discusses the numerous advantages it affords for IBD, including harnessing longer-term longitudinal data for safety and efficacy assessment, and enhanced recruitment and follow up processes. Leveraging pre-existing cohorts and their organizational structures improves patient acceptance and is more economical compared to traditional randomized trials. Observational data for IBD, derived from research (cohort and case-control studies) and non-research sources (electronic health records and registries), provides access to comprehensive records for a large number of IBD patients. It permits researchers to address knowledge gaps in IBD where traditional RCTs have had a limited role, such as specific sub-populations typically excluded from pivotal trials, or assessing the effect of environmental exposures on disease course. This review also details caveats of this study design that include the risk of selection bias and constraints related to comparisons with placebo. In conclusion, RCTsNC offers a promising opportunity IBD research given the challenges of the current IBD RCT landscape.