Manipulating the Gut Microbiome Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Manipulating the Gut Microbiome Study (NCT03181828), a randomized phase 1, phase 2 study. The primary outcome is Atom Percent Excess of 13CO2.

2. Clinical Question

3. Trial Design

The registry describes a phase 1 and phase 2, randomized, unmasked crossover study. Enrollment was 4. The status is terminated, and the recorded start and primary completion dates are 2017-03-24 and 2018-06-05. These dates and status do not establish how many participants completed the study or why it was terminated; that information is not reported in the registry record.

In a crossover design, participants are assigned to treatment sequences and receive each condition at different times. The two sequences named in the record are acetohydroxamic acid followed by no intervention, and no intervention followed by acetohydroxamic acid. The arm descriptions refer to a 4-h study in the fasted state under each condition and a 3-day wash-out between periods. The description for the first sequence specifies a single oral dose of 60 mg/kg acetohydroxamic acid, rounded to the nearest 250 mg. The record does not report whether all planned periods were completed or how sequence assignment was generated.

Randomization can reduce systematic differences between assigned sequences, while an unmasked design means masking is not specified. In a crossover, comparisons may also be affected by changes over time or by effects that persist from one period into another. A wash-out is intended to allow prior treatment effects to diminish, but the record does not report the rationale for the 3-day period or whether carryover was assessed. The exact randomization procedure, protocol details, and statistical analysis plan are not reported in the registry record.

The registry lists the study condition as Urea Cycle Disorder, while the brief objective also refers to healthy control adults. The number in each population and the way they were handled in the analysis are not reported. No inference about the trial's actual composition or completion can be made from the planned sequences alone.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: All the enrolled participants have been healthy adults.

6. Primary Endpoint

The registry lists the primary outcome as Atom Percent Excess of 13CO2, measured over Time +0 minutes, +30 minutes, +60 minutes, +90 minutes, +120 minutes, +180 minutes, and +240 minutes from time of infused [13C] Urea IV.

The primary endpoint is titled “Atom Percent Excess of 13CO2,” with units of Atom % Excess. Its description defines the measure as the difference in carbon-13 enrichment in blood CO2 compared with a baseline measurement, after a single bolus of intravenous [13C]-Urea. Measurements are specified at time +0 minutes, +30 minutes, +60 minutes, +90 minutes, +120 minutes, +180 minutes, and +240 minutes from the time of infused [13C] urea IV.

The endpoint is intended to track the appearance of carbon-13 in blood CO2 after labeled urea is infused. The study objective connects this measure to urea hydrolysis by bacterial urease: the registered question is whether acetohydroxamic acid can inhibit that process. As a general statistical point, repeated measurements can describe how an outcome changes over time and may be more informative than a single measurement when the scientific question concerns a time course. They also require an analysis that accounts for measurements from the same participant being related.

The registry record identifies the endpoint as a mean with standard deviation, but it does not report the observed values, a treatment comparison, or a summary measure across the listed time points. No single primary contrast is reported. The record also lists Blood [13C]-Urea as a secondary outcome, without reporting its results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The design and outcome information can be understood using a few general statistical concepts. The registry record gives some design features, but it does not report the analysis methods used for the primary endpoint. The distinctions below are important because a study's design does not by itself determine how its results should be analyzed.

What does a crossover design imply?

In a crossover study, the same participant receives more than one condition in separate periods. The registry describes two sequences, with each sequence placing acetohydroxamic acid and no intervention in a different order. In general, comparing conditions within the same participant can account for stable participant characteristics that might otherwise differ between separate treatment groups. However, measurements from a participant are not independent. An analysis should recognize the repeated observations and the treatment sequence and period structure when those features are relevant.

Crossover studies also require consideration of time-related changes and carryover. Carryover means an effect of an earlier treatment persists into a later period and influences its outcome. A wash-out interval is intended to reduce this possibility. The record gives a wash-out period of 3 days, but does not report whether carryover was assessed, whether a period effect was modeled, or whether the wash-out was considered sufficient. These details are not reported in the registry record, so it is not possible to tell how the analysis handled them.

How should repeated measurements be understood?

The primary endpoint is measured at multiple scheduled times after infused [13C] urea. In general, measurements taken from the same participant over time are correlated: a participant's values can share characteristics that make them more alike than values from different participants. Statistical methods for repeated measures account for that dependence rather than treating every measurement as unrelated. The choice of method can affect the estimated uncertainty and the interpretation of the treatment comparison.

A sequence of time-specific comparisons and a single summary of the full time course answer different questions. A time-specific comparison asks about a treatment contrast at a chosen measurement time. A summary across times asks about the overall pattern under a defined method. The record lists the measurement times but does not report a primary contrast or a model for combining them. It also does not report whether the analysis treated time as categorical or continuous, or how the repeated measures were modeled.

What do mean and standard deviation describe?

The endpoint is specified as a mean with standard deviation. In general, a mean represents the average observed value, while the standard deviation describes dispersion among observed values. Dispersion is not the same as uncertainty in a treatment effect: an effect estimate's uncertainty depends on the design, the number of analyzed participants, the variability, and the analysis method. A confidence interval, when reported, gives a range of values compatible with the data and method under its assumptions. No confidence interval for the primary endpoint is reported in the registry record.

Some continuous outcomes can show greater variability than a simple model assumes. In general, over-dispersion means the observed variability exceeds what a chosen model allows; ignoring it can make uncertainty estimates unreliable. The record does not report a model, a distributional assessment, or an over-dispersion assessment, so there is no basis for saying whether this issue arose in the study.

What can be said about significance and sample size?

A p-value is a measure, under a specified statistical model, of how compatible the data are with a null hypothesis. It does not state the probability that a treatment works, and it does not describe the size or clinical importance of an effect. The registry record reports no primary endpoint p-value or effect estimate, so statistical significance cannot be assessed from the posted results.

The record describes sample-size planning illustrations based on a stated fraction of an observed effect and assumptions including a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such illustrations are planning scenarios, not observed power and not evidence that the trial was designed to achieve a particular power. No numerical illustration values are reported in the registry record for this account, and the record does not report a trial-specific sample-size justification. Because no primary effect estimate is reported, the illustrations cannot be used to infer the trial's outcome or precision.

What analysis details remain unknown?

The registry record reports no analyses, and does not identify an analysis population, a model, a missing-data method, or multiplicity handling. It does not state how the repeated time points were handled or whether the analysis adjusted for sequence or period. These omissions prevent an independent assessment of whether the methods respected the crossover structure and the endpoint's repeated-measure nature. General statistical principles can describe what such an analysis would need to consider, but they cannot substitute for the unreported trial analysis.

10. Multiplicity, Missing Data and Analysis Populations

The primary endpoint is measured at time +0 minutes, +30 minutes, +60 minutes, +90 minutes, +120 minutes, +180 minutes, and +240 minutes. Testing a treatment contrast separately at many time points creates a multiplicity issue: as a general statistical principle, making multiple inferences can increase the chance of at least one apparently unusual result when there is no true difference. Approaches to address this include defining a primary time point, using an overall repeated-measures test, or adjusting for multiple comparisons. The registry record does not report which approach, if any, was used, and it does not identify one time point as the sole primary contrast.

The record indicates that the primary outcome has several categories or time points and was not reduced to one comparison. It reports no analyses. The record also lists Blood [13C]-Urea as a secondary outcome, but does not provide results or state how the primary and secondary outcomes were considered together. A multiplicity plan is not reported in the registry record.

Missing-data handling is not reported. In a crossover study with repeated measurements, missing observations could affect the number of participants contributing to each period or time point. Without completion counts, reasons for missingness, and the analysis method, it is not possible to assess whether the reported summaries, if any, represent all enrolled participants or a subset.

The analysis population is also not reported. The record does not specify whether results were intended to include all randomized participants, only participants who completed both periods, or another population. It does not describe exclusions or protocol deviations. These details matter for understanding what population a treatment comparison would represent and how robust it might be.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry safety summary lists 4 participants at risk in each named group. Serious adverse events affected 0 of 4 in the acetohydroxamic acid oral tablet group and 0 of 4 in the no-intervention group. Deaths were 0 in both groups. The registry does not list any top serious adverse-event terms.

For other adverse events, the summary reports 4 of 4 affected in the acetohydroxamic acid oral tablet group and 0 of 4 affected in the no-intervention group. These are the registry's reported counts; the record does not give event descriptions, timing, severity details for these other events, or participant-level information. It also does not explain whether an event occurred in a particular treatment period or how events were handled for participants exposed to both conditions in the crossover design.

Zero recorded serious adverse events does not establish that serious events could not occur or that a treatment is free of risk. With enrollment of 4, these figures are a limited descriptive summary, not a precise estimate of event frequency. The safety record also does not report an inferential comparison. The counts should be interpreted as posted registry data rather than as proof that one condition caused or prevented an event.

12. What the Result Does, and Does Not, Mean

The registry record identifies a focused physiological question: whether acetohydroxamic acid can inhibit bacterial urease activity in gut flora, as assessed through carbon-13 enrichment after labeled urea. It also documents a randomized, unmasked crossover design, two treatment orders, the planned fasting study periods, and an endpoint measured over time. These details help explain what the investigators intended to study.

What the record does not establish is the result of the primary comparison. No outcome values, effect estimate, confidence interval, or p-value are reported for atom percent excess of 13CO2. Accordingly, the posted results do not quantify the size or direction of a difference between acetohydroxamic acid and no intervention, and they do not show how precisely such a difference was estimated. The secondary outcome is named but its findings are also not reported.

The distinction between a stated objective and a reported result is essential. A biological rationale and a measured endpoint do not by themselves demonstrate that an intervention changed the endpoint. Similarly, the record's safety counts do not answer the primary physiological question. The status “terminated” does not explain whether or why the study stopped, and does not show whether the planned data collection was completed.

Enrollment of 4 limits the amount of information available, but the record does not report a primary estimate from which to quantify uncertainty. It would therefore be inappropriate to infer that a treatment effect was present, absent, or clinically important. The registry record supports a description of the design and question; it does not support a conclusion about the primary endpoint's outcome.

More generally, a result should be interpreted in light of its estimate, uncertainty, analysis population, and design. Here, those primary analysis details are not reported in the registry record. The appropriate statistical reading is that the study's intended comparison is identifiable, while its primary result and precision are not available in the posted results.

13. Why This Trial Matters Statistically

This study is statistically notable because its design and endpoint require careful alignment between the scientific question and the analysis. The crossover structure means each participant is intended to experience both conditions, while the outcome is measured repeatedly over time. These features create within-participant dependence that a suitable analysis would need to address. A simple comparison that treated all observations as unrelated would not reflect the design's structure.

The record also illustrates why a list of measurement times is not the same as a prespecified summary of the treatment effect. A time course can be analyzed in several ways, and each answers a somewhat different question. If separate comparisons are made at multiple times, multiplicity needs consideration. If an overall contrast is intended, the summary or model should be clear. The registry record does not report the chosen approach or a single contrast.

Enrollment of 4 makes transparent reporting of participant flow, completion, and uncertainty especially important for understanding what the data can support. Yet analyzed numbers, outcome values, and inferential results are not reported. The record's termination status and sparse outcome reporting make it particularly important not to confuse a study objective or design description with a result.

Finally, the listed sample-size assumptions are planning illustrations rather than the study's own design justification. In general, planning calculations depend on assumptions about the effect to detect and the variability; they do not demonstrate that a completed study had adequate precision. Without a reported treatment estimate and uncertainty, those calculations cannot clarify what the trial found. The record is useful for understanding the question and methodological issues, but its missing analysis leaves the core statistical result unresolved.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The most consequential limitation for interpreting the study is that the registry record reports no primary outcome analysis. The endpoint is specified, but no results, estimate, confidence interval, or p-value are available. The record lists no analyses, so the treatment comparison and its precision cannot be assessed.

Enrollment was 4, and the record does not report how many participants completed each treatment period or contributed data at each scheduled time. The reason for termination is not reported in the registry record. Missing data, withdrawals, and exclusions are also not described. These gaps prevent assessment of participant flow and the completeness of the repeated measurements.

The population is not fully characterized. The objective refers to healthy control adults and adults with urea cycle disorders, while the listed condition is Urea Cycle Disorder. The number in each population and any population-specific findings are not reported. It is also unclear from the record how the two populations were represented in the analysis.

Although the record describes randomization, it does not report the sequence-generation procedure or allocation details. It names a 3-day wash-out but does not report an evaluation of carryover or period effects. The method for handling repeated measurements and multiplicity is not reported. These are important design-specific considerations for a crossover study.

The safety summary gives event counts but lacks descriptions and timing, and does not explain how events were attributed across crossover periods. Finally, the registry record does not report a trial-specific sample-size justification or the primary analysis methods. Together, these limitations mean that the study's intended question is clear, but the strength, precision, and scope of any outcome conclusion cannot be judged from the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Manipulating the Gut Microbiome Study — NCT03181828.
• Registry record last updated 2021-12-15; status last verified 2021-11.
• Results first posted 2021-12-15.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The registry record describes NCT03181828, titled “Manipulating the Gut Microbiome Study,” as a phase 1 and phase 2 randomized, unmasked crossover study with enrollment of 4. Its status is terminated. The recorded start date is 2017-03-24, and the primary completion date is 2018-06-05.

The study objective concerns acetohydroxamic acid and bacterial urease in gut flora. The intervention is a single oral dose of acetohydroxamic acid; the comparator is no intervention. The primary endpoint is atom percent excess of 13CO2 measured at sequential times after infused [13C] urea. Blood [13C]-Urea is listed as a secondary outcome.

The record does not report primary outcome analyses, outcome estimates, confidence intervals, or p-values. It also does not report the analysis population, missing-data approach, multiplicity handling, or reason for termination. The posted information therefore describes the study question and design, but does not provide a result for the primary endpoint.