Researchers studied whether critically ill patients who participated in multiple medical studies at the same time affected the results of a probiotic treatment trial. Out of 2,650 patients in the main study, about 21% were also enrolled in other research projects. The good news: being in multiple studies didn’t change how well the probiotic treatment worked. However, patients in multiple studies did experience slightly more side effects. The sicker patients and those at hospitals running the study longer were more likely to be in multiple studies. This research helps scientists understand that having patients participate in several studies at once is generally safe for getting accurate results.

The Quick Take

  • What they studied: Whether critically ill patients who join multiple medical studies at the same time affects how well a probiotic treatment works and whether it causes more side effects.
  • Who participated: 2,650 very sick patients in intensive care units across 44 hospitals in multiple countries. About 568 of these patients (21%) were also enrolled in at least one other research study at the same time.
  • Key finding: Being enrolled in multiple studies did not change how well the probiotic treatment prevented lung infections (the main goal). However, patients in multiple studies had slightly more side effects overall, though this difference disappeared when looking only at patients in other randomized controlled trials.
  • What it means for you: If you’re critically ill and asked to join multiple research studies, it appears safe to do so—the studies won’t interfere with each other’s results. However, discuss any concerns about side effects with your medical team, especially if you’re very sick.

The Research Details

This was a planned secondary analysis of the PROSPECT trial, a large international study testing whether probiotics help prevent pneumonia in critically ill patients on breathing machines. Researchers looked back at data from 2,650 patients treated across 44 medical centers in different countries. They identified which patients were also participating in other studies at the same time (called ‘coenrollment’). The researchers then used statistical methods to check if being in multiple studies changed how well the probiotic treatment worked or increased side effects.

The study used Cox proportional hazards analyses, which is a statistical method that accounts for time and different patient characteristics when comparing outcomes. They also used logistic regression to identify which types of patients and hospitals were more likely to have coenrolled participants. This approach allowed them to separate the effects of coenrollment from other factors that might influence the results.

Understanding coenrollment is important because many hospitals and research centers run multiple studies simultaneously. If being in multiple studies interferes with treatment results, it could make research findings unreliable. This study helps answer a practical question: can hospitals safely enroll very sick patients in multiple studies without worrying that the studies will interfere with each other? The answer helps researchers and hospitals make better decisions about patient participation.

This study has several strengths: it was a large, international trial with 2,650 participants across 44 centers, making results more generalizable. The original PROSPECT trial was blinded (meaning patients and some staff didn’t know who got probiotics), which reduces bias. The researchers used appropriate statistical methods and conducted multiple analyses to check their findings. However, this was a secondary analysis (not the original study question), so some findings are exploratory. The study was observational in nature regarding coenrollment, meaning researchers observed who was coenrolled rather than randomly assigning patients to be coenrolled.

What the Results Show

The main finding was reassuring: patients who were enrolled in multiple studies at the same time had the same treatment results as those in only one study. Specifically, the probiotic treatment’s ability to prevent ventilator-associated pneumonia (lung infections in patients on breathing machines) was not affected by coenrollment. This means the presence of other studies did not interfere with how well the probiotic worked.

When looking at side effects, the picture was slightly more complex. Overall, coenrolled patients had a higher rate of adverse events (specifically, harmful bacteria from the probiotic appearing in sterile areas). However, when researchers looked more carefully at patients who were coenrolled specifically in other randomized controlled trials (the most rigorous type of study), there was no significant difference in side effects compared to non-coenrolled patients. This suggests that the type of other study matters—being in multiple randomized trials didn’t increase problems, but being in other types of studies might have.

The researchers also found that sicker patients were more likely to be coenrolled (21.4% of all participants). This makes sense because hospitals with more severely ill patients may have more research opportunities available. Additionally, hospitals that had been recruiting for the PROSPECT study longer were more likely to have coenrolled patients, suggesting that experience and established research infrastructure increase coenrollment.

The study identified specific characteristics of coenrolled patients and centers. More severely ill patients (measured by disease severity scores) were significantly more likely to be coenrolled. Centers with longer participation in the PROSPECT study were also more likely to have coenrolled patients. These findings suggest that coenrollment happens more in experienced research centers with sicker patient populations, which is logical since these centers have more research opportunities and patient volume.

This study adds important practical evidence to a theoretical concern in research. While scientists have long worried that coenrollment might distort study results through treatment interactions, this large trial provides real-world evidence that this concern may be overstated for the primary outcomes. The findings align with the growing recognition that coenrollment, when properly managed, can enhance research efficiency without compromising data quality. However, the slight increase in adverse events in broadly coenrolled patients suggests that careful monitoring remains important.

This study has several important limitations. First, it was a secondary analysis, meaning the researchers weren’t originally planning to study coenrollment—they analyzed existing data. Second, the study only looked at one type of treatment (probiotics) in one specific patient population (critically ill patients), so results may not apply to other treatments or healthier patients. Third, the researchers couldn’t control for all possible factors that might influence coenrollment decisions at different hospitals. Fourth, the adverse events studied were specific to the probiotic (harmful bacteria from the probiotic itself), so results may not apply to other types of side effects. Finally, the study was observational regarding coenrollment, not experimental, so we can’t prove that coenrollment caused the observed differences—only that they were associated.

The Bottom Line

Based on this research, hospitals and research centers can feel reasonably confident enrolling critically ill patients in multiple studies simultaneously without worrying that the studies will interfere with each other’s main results (moderate confidence). However, medical teams should still monitor coenrolled patients carefully for side effects, particularly if patients are in multiple types of studies (moderate confidence). Patients should always discuss any concerns about participating in multiple studies with their medical team.

This research matters most to: (1) hospital administrators and research coordinators deciding whether to allow patients in multiple studies, (2) critically ill patients and their families considering participation in multiple research projects, (3) researchers designing clinical trials in intensive care units, and (4) ethics committees reviewing research proposals. This research is less relevant to healthy people or patients with mild illnesses, as the findings are specific to critically ill patients on breathing machines.

If you’re a critically ill patient considering multiple studies, you should expect to see any treatment effects (or lack thereof) on the same timeline as if you were in a single study. The probiotic treatment in this study was evaluated over the course of hospitalization. Side effects, if they occur, would likely appear within days to weeks of starting treatment. Long-term effects would depend on the specific studies you’re participating in.

Want to Apply This Research?

  • If using a health app while in multiple medical studies, track: (1) which studies you’re enrolled in and their start/end dates, (2) any new symptoms or side effects with dates they appeared, (3) your daily wellness score (1-10), and (4) any changes in your primary condition being studied. This creates a clear record for your medical team.
  • Set up app reminders to: (1) take all study medications or treatments as prescribed, (2) report any new symptoms immediately to your research team, (3) keep a daily log of how you’re feeling, and (4) schedule regular check-ins with your medical team. This helps ensure all your studies get accurate information.
  • Use your app to create a simple dashboard showing: (1) timeline of all studies you’re in, (2) current medications and treatments from each study, (3) weekly symptom tracking, and (4) a notes section for questions to ask your doctor. Share this dashboard with your medical team at each visit to ensure everyone has the same information about your participation in multiple studies.

This research describes a specific study about probiotics in critically ill patients enrolled in multiple research projects. These findings apply specifically to that population and treatment. If you are critically ill and considering participation in multiple medical studies, discuss the risks and benefits with your medical team and research coordinators. Do not make decisions about your medical care based solely on this summary. Always consult with your healthcare providers about what is appropriate for your individual situation. This summary is for educational purposes and does not constitute medical advice.