Effects of Gastric Bypass on Blood Levels of Duloxetine: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effects of Gastric Bypass on Blood Levels of Duloxetine (NCT00989157), a na phase 3 study. The primary outcome is Cmax.

2. Clinical Question

3. Trial Design

The registry record marks the study as completed and classifies it as Phase 3. It lists an enrollment of 20 and a start date of 2009-09, with primary completion in 2012-10. The title describes the work as a preliminary comparison of Roux-en-Y bariatric surgery’s effect on duloxetine blood levels. These labels describe the record, but do not establish further design details.

The model is listed as single group, allocation as not applicable, and masking as none. The arm description says all subjects received drug and identifies a single arm. At the same time, the brief summary and primary-outcome description state that patients after surgery are compared with controls matched for body mass index, age, and gender. The adverse-event record also lists Bariatric and Control groups, with 10 participants at risk in each. How these descriptions relate to one another is not explained in the registry record. In particular, it does not report whether controls were recruited separately, how matching was performed, or how participants were assigned to the groups.

The record lists duloxetine as the intervention and emesis as a secondary outcome. It does not report dosing details, eligibility criteria, recruitment methods, the source of control participants, or a protocol description. Although the record identifies Cmax as the primary outcome, the planned statistical analysis is not reported in the registry record. The listed design features therefore support a descriptive account of the study’s intended comparison, but not a complete reconstruction of its conduct.

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: Available Bariatric surgery candidates and pilot study results.

6. Primary Endpoint

The registry lists the primary outcome as Cmax, measured over 0, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.25, 2.5, 3.5, 4.5, 6.5, 8.5, 10.5, 24, 48. 72.

The primary outcome is Cmax, defined in the registry as a mean continuous measure with standard deviation, in ng/ml. In general, Cmax refers to the maximum measured concentration of a drug in blood or another sampled biological fluid over a measurement period. It is used in pharmacokinetic research because it describes the peak concentration observed under the study’s dosing and sampling conditions. It is distinct from measures that describe total drug exposure over time.

The registry describes the endpoint as a comparison of duloxetine pharmacokinetics between patients nine to fifteen months after Roux-en-Y bariatric surgery and matched controls. It lists multiple measurement times, from 0 through 72, but does not state the time unit for those entries or explain how measurements at different times were used to derive Cmax. The dose and administration schedule are also not reported in the registry record.

To interpret a Cmax comparison, readers would need the group estimates, their variability, the number of participants contributing data, and the analysis method. None of those primary-outcome results are reported in the registry record. The endpoint’s purpose can therefore be described, but its observed value and the precision of any group comparison cannot be assessed from the posted information.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies Cmax as a continuous outcome summarized by a mean and standard deviation. These are descriptive statistics: the mean gives a center for the measured values, while the standard deviation describes their spread around that center. They do not, by themselves, quantify uncertainty in a comparison between groups. For that, a report would ordinarily include an estimated contrast and a measure of its precision, such as a confidence interval. No such primary-outcome estimates are reported in the registry record.

What does a confidence interval communicate?

In general, a confidence interval expresses uncertainty around an estimated quantity under the assumptions of the statistical method. A narrower interval indicates greater precision than a wider interval for the same target quantity, although precision alone does not determine whether a result is important. A confidence interval for a group contrast would help readers see which differences remain compatible with the observed data and analysis. The registry does not report a Cmax contrast or confidence interval, so the precision of the comparison cannot be evaluated.

Why does the design description matter?

The record calls the model single group and describes a single arm in which all subjects received duloxetine. Its objective, however, refers to a comparison with matched controls, and the safety record lists Bariatric and Control groups. Allocation is listed as not applicable. These details do not establish whether the comparison was conducted within one enrolled study, how controls were sourced, or how matching was carried out. In general, a nonrandomized comparison may be affected by differences between groups beyond the characteristics used for matching. Matching can address only the factors and procedures actually used; it does not guarantee that other characteristics are balanced.

The statistical model, tests, covariate adjustments, and treatment of any matched structure are not reported in the registry record. It is therefore not possible to judge whether the analysis accounted for the way the comparison groups were assembled. Nor can readers determine whether the analysis used individual measurements, a derived Cmax for each participant, or another approach. Those details are relevant because repeated concentration measurements and a participant-level summary are not interchangeable analysis units.

How should the repeated times be understood?

The primary outcome’s timeframe lists measurements at 0, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.25, 2.5, 3.5, 4.5, 6.5, 8.5, 10.5, 24, 48, and 72. The record does not state the unit for these times, the amount of data available at each time, or the rule used to select the maximum concentration. In general, sampling schedules affect how well a measured peak can represent the underlying concentration curve. A peak occurring between sample times may not be captured directly. This general issue cannot be quantified for this study from the registry record.

The record lists a mean and standard deviation, but does not provide evidence about the distribution of Cmax values. In general, strongly skewed data or influential observations can make a mean and standard deviation less informative as a summary. A transformation or another statistical approach might sometimes be considered, but the planned method is not reported in the registry record, so no claim can be made about whether any such approach was used.

What is missing from the analysis record?

The registry lists zero analysis entries. It does not report a hypothesis test, p-value, confidence interval, adjusted or unadjusted estimate, or analysis population for the primary outcome. It also does not report missing-data methods, participant flow, or the number with evaluable measurements. These omissions prevent an independent reading of the primary comparison and its uncertainty.

In general, over-dispersion means that observed variability is greater than a model assumes. It can make model-based uncertainty estimates unreliable if the analysis does not account for it. For a continuous pharmacokinetic measure, the registry would need to describe the data and analysis before readers could assess whether this issue arose or mattered. The posted record provides no such assessment.

Any sample-size figures based on an observed effect are planning illustrations, not observed power and not evidence about the trial’s original design rationale. The record’s planning assumptions specify a two-sided significance level of 0.05, equal allocation, and a normal approximation, with effects expressed as a fraction of an observed effect. The protocol’s sample-size justification is not reported in the registry record. Since the primary outcome estimates are also absent, those assumptions cannot substitute for a reported result or clarify the actual analysis.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Bariatric", "Control")
n   <- c(10, 10)
m   <- c(51.04, 61.41)
sp  <- c(11.88, 34.93)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Bariatric  10  51.040  11.880  42.542  59.538
CARM  Control  10  61.410  34.930  36.423  86.397

11. Multiplicity, Missing Data and Analysis Populations

The registry lists Cmax as the primary outcome and emesis as a secondary outcome. It also reports five outcome measures in total, but does not identify the other measures in the information available for this record. The statistical plan does not describe which comparisons were confirmatory, whether testing was planned across multiple outcomes or time points, or whether any adjustment for multiple testing was intended. These details are not reported in the registry record.

In general, when several hypotheses are tested, the chance of at least one apparently unusual result can increase if each test is interpreted in isolation. Methods for handling multiplicity can include identifying a primary outcome in advance, setting a testing sequence, or adjusting inference across a family of tests. Which approach is appropriate depends on the study’s objectives and plan. No approach can be attributed to this study from the registry record.

The record lists multiple concentration measurement times, but does not explain whether each time was tested separately or whether they were used to derive one participant-level Cmax value. These are different analytical strategies, with different implications for multiplicity and interpretation. The analysis entries are absent, so the use of time points cannot be established.

Missing-data handling and analysis populations are also not reported in the registry record. There is no account of how many participants contributed Cmax measurements, whether any scheduled samples were unavailable, how incomplete profiles were handled, or whether participants were excluded from an analysis. The enrollment count and the safety denominators do not resolve these questions. Without a participant flow description and outcome-specific denominators, the extent and possible consequences of missing measurements cannot be assessed.

In general, transparent reporting of prespecified outcomes, analysis populations, and missing-data procedures helps readers distinguish planned analyses from exploratory ones and understand which observations support an estimate. The record does not provide those details for the primary comparison. This absence does not establish that analyses or procedures were not performed; it means they are not reported in the registry record.

12. Safety Results

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

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 safety record lists serious adverse events for the Bariatric and Control groups. In each group, 10 participants are listed as at risk and zero as affected by a serious adverse event. These are the posted serious-event counts. No serious adverse-event terms are listed among the top serious terms.

The record separately lists other adverse events: 2 affected participants among 10 at risk in the Bariatric group and 3 among 10 at risk in the Control group. These figures are distinct from the serious-event counts and should not be treated as serious events. The record does not provide event descriptions or explain whether participants could contribute more than one event.

Deaths are shown as null for both groups. Null does not establish that no deaths occurred; the death information is not reported in the registry record. The safety entries also do not establish which participants were included in the primary Cmax analysis, or how long participants were observed for safety. These event counts describe what the registry posts, not a complete safety profile or a comparison adjusted for study design.

In general, a zero count in a group of this size does not demonstrate that an event is impossible or that risk is absent. Safety counts are most interpretable with clear definitions, observation periods, event-level details, and denominators. Those additional details are not reported in the registry record. No safety conclusion about duloxetine or surgery should be drawn from these counts alone.

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

The record establishes that the study was intended to examine duloxetine pharmacokinetics after Roux-en-Y bariatric surgery, with matched controls named as the comparator, and that Cmax was the primary outcome. It also records an enrollment of 20, a completed status, and measurement times for the outcome. These details describe the research question and some aspects of its registry design.

The record does not report numerical Cmax results. It therefore does not show whether the measured peak concentration was higher, lower, or similar between the stated groups. There is no estimated difference, confidence interval, or hypothesis-test result from which to assess the magnitude or precision of the comparison. The absence of a result is not a finding of no difference.

Even if a group difference were reported, interpretation would depend on the analysis method, data completeness, dosing conditions, and how the control group was selected and matched. The registry does not report those details. In general, a measured pharmacokinetic outcome describes drug concentration under the conditions studied; it is not, by itself, a measure of clinical benefit or harm. The posted information does not support a treatment recommendation or a conclusion about clinical outcomes.

The safety record reports zero serious adverse events among 10 participants at risk in each named group, and other adverse events among 2 and 3 participants, respectively. Death information is not reported in the registry record. These counts are limited observations and do not replace a detailed safety analysis. Overall, the record permits readers to identify the study question and selected design and safety details, but does not provide the primary outcome results needed to answer the pharmacokinetic comparison.

14. Why This Trial Matters Statistically

This study poses a statistically focused question: whether a pharmacokinetic measure of duloxetine differs in patients after Roux-en-Y bariatric surgery compared with matched controls. Cmax is a direct summary of peak measured concentration, and a clear comparison could help characterize how concentrations observed under the study conditions vary between the named groups. The registry’s stated objective makes this a relevant example of a continuous-outcome comparison in a clinical population.

The record also illustrates why design labels and outcome reporting must be read together. It describes a single-group model and one arm, yet names matched controls in its objective and lists two groups in its safety information. Allocation is not applicable, and the record does not explain the relationship between these descriptions. This makes the distinction between a randomized trial and a nonrandomized comparison important: the stated matching factors do not establish that all sources of group differences were addressed.

Statistically, an outcome name and summary format are not enough to evaluate evidence. Readers need group estimates, an estimate of the contrast, its uncertainty, outcome-specific denominators, and a description of the analysis. Those primary-result details are not reported in the registry record. This absence makes the record useful for identifying reporting gaps as well as for understanding the intended question.

The study is also a reminder that a concentration profile depends on the measurement schedule and the definition of the derived endpoint. The record lists repeated times but does not specify the time unit or explain how those readings yielded Cmax. Without the result and analysis description, the clinical question remains identifiable, but its statistical answer cannot be assessed from the posted record.

15. 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 principal limitation of the posted information is that it contains no numerical primary-outcome result. The Cmax mean, standard deviation, group contrast, uncertainty interval, and test result are not reported in the registry record. Consequently, the direction, magnitude, and precision of the intended comparison cannot be assessed.

The study structure is also not fully clear. The record labels the model single group and describes one single arm in which all subjects received drug. Its objective refers to matched controls, while safety information names Bariatric and Control groups. Allocation is not applicable. The record does not explain how these accounts fit together, how controls were recruited, or how matching was carried out. It is therefore not possible to characterize the comparison as randomized or to evaluate the matching procedure.

The enrollment is 20, but the record does not state the number contributing data to the primary endpoint. It gives no participant flow, outcome-specific denominator, missing-measurement account, or analysis population. The time unit for the listed measurement times is not reported in the registry record. Nor are dosing details, eligibility criteria, or the statistical analysis plan reported. These gaps limit reproducibility and interpretation.

The registry lists five outcome measures but does not give the full set of measures or a multiplicity strategy. It reports zero analysis entries. Safety information is limited to group counts; event descriptions and death information are not reported in the registry record. These limitations concern the completeness of the posted record and do not establish what was or was not done outside it.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Effects of Gastric Bypass on Blood Levels of Duloxetine — NCT00989157.
• Registry record last updated 2014-08-11; status last verified 2014-07.
• Results first posted 2014-08-11.
• 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.

19. Record Summary

The registry record identifies a completed Phase 3 study with enrollment of 20, a start date of 2009-09, and primary completion in 2012-10. Its stated aim is to compare duloxetine pharmacokinetics in patients nine to fifteen months after Roux-en-Y bariatric surgery with controls matched for body mass index, age, and gender. Duloxetine is listed as the intervention, Cmax in ng/ml as the primary outcome, and emesis as a secondary outcome.

The design is labeled single group, allocation is not applicable, and masking is none, although the record also refers to matched controls and lists Bariatric and Control safety groups. Numerical Cmax results, analysis details, and missing-data methods are not reported in the registry record. The posted safety counts include zero serious adverse events among 10 participants at risk in each group and other adverse events in 2 and 3 participants, respectively. Death information is not reported in the registry record.