Interactions in clinical trials: Protocol and statistical analysis plan for an explorative study of four randomized ICU trials on use of pantoprazole, oxygenation targets, haloperidol and intravenous fluids

Background: Intensive care unit (ICU) patients receive numerous interventions, but knowledge about potential interactions between these interventions is limited. Co-enrolment in randomized clinical trials represents a unique opportunity to investigate any such interactions. We aim to assess interactions in four randomized clinical trials with overlap in inclusion periods and patient populations. Methods: This protocol and statistical analysis plan describes a secondary explorative analysis of interactions in four international ICU trials on pantoprazole, oxygenations targets, haloperidol and intravenous fluids, respectively. The primary outcome will be 90-day all-cause mortality. The secondary outcome will be days alive and out of hospital in 90 days after randomization. All patients included in the intention-to-treat populations of the four trials will be included. Four co-primary analyses will be conducted, one with each of the included trials as reference using a logistic regression model adjusted for the reference trial's stratification variables and for the co-interventions with interactions terms. The primary analytical measure of interest will be the analyses’ tests of interaction. A p-value below.05 will be considered statically significant. The stratification variable- and co-intervention-adjusted effect estimates will be reported with 95% confidence intervals without adjustments for multiplicity. Conclusion: This exploratory analysis will investigate the presence of any interactions between pantoprazole, oxygenation targets, haloperidol and amount of intravenous fluids in four international ICU trials using co-enrolment. Assessment of possible interactions represents valuable information to guide the design, statistical powering and conduct of future trials.