Effect of Perioperative Gabapentin on Postoperative Opioid Requirements: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effect of Perioperative Gabapentin on Postoperative Opioid Requirements (NCT05494385), a randomized phase 4 study. The primary outcome is Opioid Prescription at Discharge.

2. Clinical Question

3. Trial Design

This is a Phase 4, randomized, quadruple-masked, parallel-group study sponsored by Indiana University. The registry lists enrollment of 114 participants and marks the study completed. The recorded start date is 2021-07-27, and the primary completion date is 2023-06-17. The design compares preoperative gabapentin followed by postoperative placebo with preoperative gabapentin followed by postoperative gabapentin.

Randomization means that treatment assignment is intended to be determined by chance rather than by a clinician's or participant's preference. In general, this can reduce systematic differences between groups at the point of assignment. The registry does not describe the randomization sequence, allocation concealment, stratification, or the way participants were assigned, so those design details are not reported in the registry record.

Quadruple masking indicates that the record classifies the study as masked at four roles or levels. The specific roles and procedures used to maintain masking are not reported in the registry record. The parallel design means that participants were assigned to a treatment strategy and evaluated within that group, rather than being described as switching between strategies.

The stated clinical context is surgery for pelvic organ prolapse. The registry's brief summary frames the question around pain control, while the primary outcome concerns whether an opioid prescription is issued at discharge. It also lists opioid refill requests, inpatient pain scores, inpatient morphine milligram equivalents, length of stay, nausea, and sedation as secondary outcomes. The record does not provide detailed eligibility criteria, baseline characteristics, actual treatment adherence, or follow-up procedures beyond the primary outcome timeframe.

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.

6. Primary Endpoint

The registry lists the primary outcome as Opioid Prescription at Discharge, measured over Length of postoperative hospital stay (at discharge, an average of 32 hours from time of registration for surgery).

The registered primary endpoint is opioid prescription at discharge, measured as the number or percentage of participants requiring an opioid prescription in each group. The registry states that participants who use 5 or more doses of PRN opioids during the inpatient postoperative course will receive a prescription. The assessment timeframe is discharge after the postoperative hospital stay, described as an average of 32 hours from registration for surgery.

This endpoint captures a care decision linked to recorded inpatient PRN opioid use. In general, a binary endpoint such as receiving or not receiving a prescription can provide a direct group-level comparison of how often an event occurs. It is not a direct measurement of pain intensity, total opioid consumption, or later opioid use. Those concepts are represented separately among the registered secondary outcomes, including inpatient pain scores, inpatient morphine milligram equivalents, and opioid refill requests.

The registry record does not provide the number of participants who received a discharge prescription in either group, a percentage, an effect estimate, or an uncertainty interval. It also does not report further endpoint definitions or adjudication procedures. Accordingly, the stated rule and timeframe describe what was intended to be measured, but the record does not show the observed primary-endpoint comparison.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the trial as randomized and parallel-group, and it specifies a participant-count endpoint. The record does not describe the statistical analysis used for the primary outcome. The following statistical concepts are general explanations of how such data are commonly interpreted; they are not claims about analyses performed in this trial.

What a binary endpoint represents

A binary outcome classifies each participant according to whether an event occurred. For this endpoint, the event is receiving an opioid prescription at discharge. A group count records how many participants experienced the event, while a percentage expresses that count relative to the relevant group denominator. The registry describes the endpoint as a percentage of patients requiring a prescription, but it does not report group-specific counts or percentages.

Comparisons of binary outcomes can be expressed in different ways. A risk difference describes the absolute separation between event proportions, while a risk ratio describes their relative scale. These measures answer different questions and can convey different impressions when event rates are not similar. Neither measure is reported for this primary outcome in the registry record, and no value can be inferred from the stated endpoint definition alone.

What uncertainty intervals contribute

General statistical explanation: a confidence interval describes a range of effect estimates compatible with the observed data under the analysis assumptions. It helps readers assess precision, not merely whether an estimate is on one side of a threshold. A wide interval usually conveys less precision than a narrow interval. For this trial's primary endpoint, the registry record does not report an estimate or confidence interval, so the precision of any group contrast cannot be evaluated.

A p-value, when reported, summarizes how compatible the observed data are with a specified statistical null model. It does not measure the probability that a treatment strategy is beneficial, nor does it by itself establish practical importance. The record reports zero analyses and does not give a primary-outcome p-value. The absence of a reported test should not be interpreted as a nonsignificant result.

How noninferiority is evaluated

General statistical explanation: a noninferiority analysis asks whether the data rule out an unacceptable loss relative to a comparator. It therefore requires a prespecified noninferiority margin, an effect estimate, and an uncertainty interval interpreted in relation to that margin. The margin is a clinical and statistical threshold, not something that can be selected after seeing the results without changing the question. The registry states a noninferiority objective, but the margin and analysis are not reported in the registry record. The objective alone does not show that noninferiority was demonstrated.

Noninferiority conclusions can also depend on the analysis population and on how missing outcomes are handled. General explanation: excluding participants or assigning assumptions to missing values can affect an estimate, particularly when the decision depends on whether an interval crosses a specified margin. The registry does not report the analysis population, missing-data methods, or sensitivity analyses for this endpoint. No claim about those procedures is warranted.

Why allocation and masking matter

Random allocation is intended to make treatment groups comparable with respect to both known and unknown characteristics, on average. Masking can reduce the chance that expectations influence care, reporting, or outcome assessment. These are general design principles; they do not guarantee that groups were balanced or that bias was absent. The record labels the trial randomized and quadruple-masked, but it does not describe the implementation details, the roles masked, or checks of masking success.

The parallel design means that the treatment strategies are compared across groups. It does not, by itself, identify which statistical model was used. For a binary endpoint, possible analyses can account for the outcome and study design in different ways, and adjusted and unadjusted estimates need not be identical. The registry does not identify a model, covariates, or a plan for adjusted analysis.

Planning illustrations are not trial findings

General statistical explanation: sample-size calculations address how much information a future or planned study might need under stated assumptions. The registry's description of a planning illustration specifies a two-sided significance level of 0.05, equal allocation, a normal approximation, and an effect defined as a stated fraction of the observed effect. It also says that non-time-to-event illustrations are expressed as participants per arm. Such illustrations are planning exercises, not observed power and not evidence that a treatment effect was present. The registry information does not provide numerical sample-size illustration results for discussion.

Over-dispersion matters for outcomes whose variability exceeds what a basic model assumes; accounting for it can prevent overly optimistic uncertainty estimates. This is a general concept, not a reported feature of the primary endpoint analysis. The endpoint is recorded as participant counts, and the registry does not report use of an over-dispersion adjustment or any model at all. Statistical interpretation should therefore remain tied to the information actually reported: an endpoint definition and study aim, without a reported primary analysis.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists six named secondary outcomes: opioid refill requests, inpatient pain scores, inpatient morphine milligram equivalents, length of stay, nausea, and sedation. It reports seven outcome measures overall and zero analyses. The number of listed outcomes raises a general multiplicity consideration: when many outcomes or comparisons are tested, the chance of at least one apparently unusual result can increase. Whether that issue applied to the trial's analysis, and whether any adjustment or outcome hierarchy was used, is not reported in the registry record.

The primary endpoint is also described as having several categories or time points, and it was not reduced to one comparison in the registry results. The record does not identify which categories or time points were analyzed, how they were combined, or which comparison was designated for inference. The endpoint's stated discharge timeframe is available, but a single primary contrast is not.

Missing-data handling is not reported in the registry record. There is no stated account of missing outcome values, withdrawals, exclusions after randomization, imputation, or sensitivity analyses. The analysis population is also not reported: the record does not say whether analyses were based on all randomized participants, participants who received assigned treatment, or another defined group.

These omissions matter because analysis choices can affect both the estimate and its uncertainty. They are especially relevant to a noninferiority question, for which conclusions depend on the analysis population and the relationship between the estimate, its interval, and a prespecified margin. Since the margin and analysis details are not reported, the registry record does not permit assessment of those choices or their effect on interpretation.

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.

The registry's safety entries list zero serious adverse events and zero deaths in each group. They also list zero other adverse events in the reported safety fields. The corresponding numbers at risk are 59 for preoperative gabapentin followed by postoperative placebo and 55 for preoperative and postoperative gabapentin.

These figures should be read as the events recorded in the registry's listed safety categories and populations. They do not establish that no symptoms or adverse experiences of any kind occurred, and they do not provide a detailed account of how events were defined, collected, or assessed. The record does not list serious-event terms, and the top serious-event terms list is empty.

Zero observed events in a recorded category is not proof that the underlying risk is zero. General statistical explanation: when an event is uncommon, a study can observe no events even though the true event probability is not known with certainty. The number at risk and the way events were monitored influence how informative a zero count is. No safety confidence intervals or comparative safety analysis are reported in the registry record, so the entries do not quantify a difference between groups.

These safety counts are distinct from the primary endpoint. They should not be used to infer the number of participants who received an opioid prescription at discharge or to substitute for the missing primary-outcome comparison.

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

The registry record documents a completed randomized trial comparing two perioperative gabapentin strategies in patients undergoing surgery for pelvic organ prolapse. Its stated objective is to assess whether preoperative gabapentin is noninferior to preoperative and postoperative gabapentin for pain control. The registered primary endpoint is an opioid prescription at discharge, with the prescription rule linked to use of 5 or more PRN opioid doses during the inpatient postoperative course.

What the posted record does not establish is the outcome of that comparison. It provides no group-specific primary-event counts or percentages, no effect estimate, no confidence interval, and no primary-outcome test. It also does not report a noninferiority margin or analysis population. Therefore the direction, magnitude, and precision of any primary-outcome difference cannot be determined from the registry information.

This is not the same as showing that the groups had equivalent outcomes. A missing estimate is not a finding of no difference, and failure to report a noninferiority analysis is not evidence that noninferiority was or was not achieved. The registry's stated objective describes the research question; it does not answer it by itself.

The listed secondary outcomes suggest that the study also tracked other postoperative measures, including pain scores, inpatient opioid amounts, refill requests, length of stay, nausea, and sedation. However, outcome names are not results. The registry reports zero analyses, so it does not support conclusions about these secondary measures either.

The safety entries report zero serious adverse events, zero other adverse events in the listed fields, and zero deaths in the two groups, among 59 and 55 participants at risk, respectively. Those entries are limited to the registry's recorded categories and do not replace a full safety analysis. Taken together, the record describes the design, intended question, endpoint definition, and limited safety counts, but it does not provide the statistical results needed to judge the central comparison.

13. Why This Trial Matters Statistically

This trial is statistically notable because its stated objective is noninferiority, while its primary outcome is a participant-level event at discharge. These features call for an interpretation that depends on a clear margin and a sufficiently precise estimate, not simply on whether a conventional test finds a difference. The registry record states the objective but does not report the margin, effect estimate, or uncertainty interval needed to evaluate it.

The endpoint also illustrates how a clinical decision rule can shape a statistical outcome. A prescription is issued under the registry's description when inpatient PRN opioid use reaches 5 or more doses. This creates a binary measure tied to a threshold. Such a measure is straightforward to describe as a count or percentage, but it does not fully represent pain intensity, total opioid exposure, or later use. The registry lists separate secondary outcomes for some of these related concepts.

Randomization and quadruple masking are important design features because they are intended to limit systematic differences and expectation-related influences. The record gives these labels, but it does not include the operational details needed to assess how they were implemented. This distinction between design labels and analysis evidence is important in registry interpretation.

The record also demonstrates why a completed status and an enrollment figure do not by themselves answer a trial question. Results require outcome data and an analysis that can be interpreted against the stated estimand and decision framework. With zero analyses reported and no single primary comparison, readers cannot assess the treatment contrast or its precision.

For statistical readers, the central lesson is to distinguish a registered hypothesis from a reported finding. The study's design and endpoint definition are informative, but the key inferential elements for the noninferiority question are not reported in the registry record. That reporting gap limits the conclusions that can be drawn without implying that either strategy was superior, equivalent, or noninferior.

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 important trial-specific limitation in the registry record is the absence of a single primary-outcome comparison. The record indicates that the primary outcome has several categories or time points and was not reduced to one comparison. It therefore does not provide the group counts or percentages for opioid prescription at discharge, an effect estimate, or an uncertainty interval. The intended noninferiority question cannot be evaluated without those results.

The noninferiority margin is not reported in the registry record. Because that margin defines what difference would be considered acceptable for the stated question, its absence prevents assessment of the decision criterion. The statistical analysis plan, model, adjustment variables, analysis population, and missing-data procedures are also not reported.

The endpoint definition is tied to a prescription rule based on 5 or more inpatient PRN opioid doses and an assessment at discharge. The record does not report the detailed operational procedures for recording opioid use or issuing prescriptions, or whether the endpoint was assessed consistently across participants. The average interval to the stated assessment is described as 32 hours from registration for surgery, but individual variation and follow-up after discharge are not described for the primary endpoint.

Although enrollment is reported as 114, the registry does not give outcome-specific denominators or explain how many participants contributed to each analysis. The safety at-risk counts of 59 and 55 do not resolve that uncertainty for the primary endpoint. The record also does not provide participant characteristics or detailed eligibility information, which limits assessment of how broadly the intended population is represented.

Finally, the registry lists secondary outcomes but does not report their analyses. The safety fields contain zero-event entries, but provide no event terms, confidence intervals, or comparative analysis. These limitations concern the available registry reporting; they do not establish that the trial lacked methods or results outside the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Effect of Perioperative Gabapentin on Postoperative Opioid Requirements — NCT05494385.
• Registry record last updated 2024-10-23; status last verified 2024-10.
• Results first posted 2024-10-23.
• 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

NCT05494385 is a completed Phase 4 randomized, quadruple-masked, parallel-group study sponsored by Indiana University, with enrollment of 114. It compares preoperative gabapentin followed by postoperative placebo with preoperative and postoperative gabapentin in patients undergoing surgery for pelvic organ prolapse.

The stated aim is noninferiority for pain control. The primary outcome is opioid prescription at discharge, linked to use of 5 or more PRN opioid doses during the inpatient postoperative course. The assessment is at discharge, described as an average of 32 hours from registration for surgery.

The registry record does not report a single primary-outcome comparison, group-specific event results, a noninferiority margin, or an analysis result. It lists six secondary outcomes and zero analyses. Safety entries report zero serious adverse events, zero other adverse events in the listed fields, and zero deaths among 59 and 55 participants at risk in the respective groups.