Gabapentin in Preventing Nausea and Vomiting in Patients Receiving Chemotherapy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Gabapentin in Preventing Nausea and Vomiting in Patients Receiving Chemotherapy (NCT00880191), a randomized phase 3 study. The primary outcome is Comparison of Percentage of Complete Responders.

2. Clinical Question

In general, a randomized comparison is intended to make the groups comparable, on average, with respect to factors that might affect the outcome. Double masking is intended to limit the influence of treatment knowledge on participants’ experiences and on outcome assessment. Those design features describe the study’s structure; they do not substitute for the outcome results.

The study’s stated focus is delayed chemotherapy-induced nausea and vomiting. Its primary endpoint combines emetic episodes with use of rescue therapy into a complete-response classification. This is a question about the proportion of participants meeting that definition, rather than a comparison of the severity of nausea alone. The registry record lists additional outcome measures, including emetic episodes, rescue-agent use, distress questions, satisfaction, and complete-response comparisons across different time windows.

3. Trial Design

The registry record identifies NCT00880191 as a completed phase III randomized, double-blind, parallel-group study sponsored by the Alliance for Clinical Trials in Oncology. Enrollment is recorded as 430. The recorded study start is 2009-04, and primary completion is recorded as 2011-03. The record describes a comparison of gabapentin with placebo for prevention of delayed chemotherapy-induced nausea and vomiting in patients receiving highly emetogenic chemotherapy.

The two arm descriptions share a background regimen involving oral dexamethasone and a 5HT3 receptor antagonist, with gabapentin in one arm and oral placebo in the other. The descriptions state that the study drug or placebo was taken once daily on day 1 and either two or three times daily on days 2 through 5. Dexamethasone is described as twice daily on days 2 through 4, with or without a 5HT3 receptor antagonist. The arm descriptions do not provide complete dosing details, and the doses are not reported in the registry record.

Randomization indicates that participants were assigned to study groups by a random process, while double masking means the record characterizes the study as masked for two parties. Which specific parties were masked, and how masking was implemented, are not reported in the registry record. The record identifies a parallel design, in which the listed groups are compared as separate arms; it does not describe a crossover design.

The registry record lists seven outcome measures and two analyses. It names complete response as a secondary outcome as well as the primary comparison of the percentage of complete responders. Several secondary measures concern alternative time windows, daily responses, emetic episodes, rescue agents, distress, and satisfaction. The detailed statistical analysis plan, the rationale for the enrollment target, and whether any interim analyses were planned are not reported in the registry record.

The study is marked completed, but completion status alone does not provide evidence about the comparative outcome. The registry record does not report numerical primary-outcome results, group response percentages, confidence intervals, or a primary-outcome p-value. As a result, the design can be described, but the size and precision of the primary comparison cannot be assessed from the reported information.

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

Reasons for not completing this period:

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 Comparison of Percentage of Complete Responders, measured over Days 2 through 6.

The primary endpoint is the percentage of participants classified as complete responders during days 2 through 6. The registry definition requires both no emetic episodes and no use of rescue therapy during that period. A participant who does not complete the study or does not provide complete data is assumed to be a non-responder. The endpoint therefore treats missing or incomplete outcome information as failure to meet the complete-response definition, according to the stated rule.

In general, a binary endpoint turns each participant’s experience into one of two categories: meeting or not meeting a specified criterion. Reporting the percentage in each group can make a clinical outcome easier to interpret as a proportion of participants, while combining vomiting episodes and rescue treatment use in this definition captures more than either feature alone. It also means that a participant can fail to meet the endpoint because of either an emetic episode or rescue therapy use, even if the other criterion is absent.

Such a combined endpoint is useful only when its components and assessment period are clear. Here, the record specifies the criteria and the days covered. It does not report the observed percentage of complete responders in either arm or a between-group estimate. Thus, the endpoint definition is available, but the comparative result and its precision are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a randomized comparison contribute?

General: Random assignment is used to create groups whose measured and unmeasured characteristics are expected to be balanced on average, apart from differences arising by chance. This supports a comparison of outcomes between assigned groups. It does not guarantee that every characteristic is balanced in a particular trial, and it does not itself establish the outcome. The record identifies the study as randomized but does not report the specific randomization sequence, allocation concealment procedures, or any baseline comparison details.

What does double masking mean?

General: Masking is intended to reduce the influence of knowing a participant’s assigned group on experiences, care, reporting, or assessment. The registry record calls the study double-blind. It does not identify which roles were masked or describe how masking was maintained. A label describing masking is therefore informative about the intended design, but does not by itself demonstrate that masking remained effective throughout the study.

How should the binary endpoint be understood?

General: A binary endpoint assigns each participant to a category such as meeting or not meeting a prespecified criterion. The primary endpoint is the percentage of complete responders, with complete response defined by the absence of both emetic episodes and rescue therapy use over days 2 through 6. The registry record says incomplete study participation or incomplete data results in classification as a non-responder. This rule makes the outcome definition explicit, while also making the handling of missing information consequential to the endpoint.

When a binary outcome is compared between groups, the analysis can be expressed using group percentages and a measure of difference or association. The registry record does not report the percentages, a contrast, or the statistical method used for the primary comparison. No particular model, adjustment strategy, or test should therefore be inferred. The exact statistical plan is not reported in the registry record.

What would a confidence interval convey?

General: A confidence interval is a range of values compatible with the observed data under a specified method. It helps readers assess precision as well as the estimated direction and size of an effect. It does not guarantee that the true effect lies within the particular interval, and its interpretation depends on the method and assumptions. The registry record does not report a confidence interval for the primary endpoint, so precision cannot be evaluated from the reported primary results.

What would a p-value convey?

General: A p-value describes how inconsistent the observed data are with a stated null hypothesis, assuming the chosen statistical model and its assumptions. It is not a measure of clinical importance and is not the probability that the null hypothesis is true. A p-value is most interpretable alongside the estimated effect and its uncertainty. The primary-endpoint p-value and the method used to obtain it are not reported in the registry record.

What do the planning assumptions mean?

The record describes a planning illustration based on the observed effect, using a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation. It describes the effect to detect as a stated fraction of the observed effect. Those are planning assumptions, not a report of the trial’s prespecified design rationale. The registry record does not report the trial’s own sample-size justification or the effect size assumed when the trial was designed. Numerical outputs from the planning illustration are not reported in the registry record information.

General: A planning sample size estimates how many participants would be needed under a set of assumptions to target a chosen level of statistical power for a specified effect. It is not an observed result and should not be presented as evidence that a completed trial did or did not have adequate power. Observed power is not a replacement for an effect estimate and confidence interval. The planning assumptions described in the record do not allow the trial’s actual power or adequacy to be inferred.

What is known about multiplicity and the analysis population?

The registry record lists seven outcome measures and two analyses. Multiple outcomes or time windows can create multiple opportunities for statistical testing. General: When many comparisons are made, a prespecified strategy may be used to control the chance of false-positive findings or to distinguish primary from exploratory analyses. The registry record does not report a multiplicity adjustment, a hierarchy among outcomes, or a detailed analysis plan. It is therefore not possible to determine how the listed outcomes were handled statistically.

The endpoint definition states that participants who do not complete the study or lack complete data are non-responders. The record does not report the number of such participants, the full analysis population, or whether additional missing-data analyses were conducted. General: Different analysis populations and missing-data approaches can lead to different interpretations, particularly when outcome information is incomplete. The stated endpoint rule is clear, but the record does not provide enough detail to evaluate its implementation or sensitivity.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists seven outcome measures and two analyses. Alongside the primary percentage of complete responders during days 2 through 6, the record names complete response, comparisons across different time windows, emetic episodes, rescue-agent use, distress questions, satisfaction, and daily complete-response endpoints. It does not report which outcomes were tested in each analysis, whether the analyses were prespecified, or whether any multiplicity procedure was used. These details are not reported in the registry record.

General: Testing multiple outcomes or time windows can increase the chance of obtaining at least one apparently notable result by chance. A statistical plan may address this through a hierarchy, adjusted significance criteria, or a distinction between confirmatory and exploratory analyses. Without such information, results across multiple measures cannot be interpreted as though each were the sole planned comparison. Since outcome results are not reported in the registry record, no conclusions about multiplicity-adjusted findings can be drawn.

The primary outcome description specifies a rule for incomplete information: participants who do not complete the study or do not provide complete data are treated as non-responders. The number of participants affected by this rule, the numbers included in each analysis, and the reasons for incomplete data are not reported in the registry record. The analysis population definition beyond the stated rule is not reported in the registry record.

General: Missing-data handling matters because an analysis may depend on whether participants with incomplete outcomes are excluded, classified by a rule, or addressed through another method. The record’s non-responder rule makes one aspect of the endpoint definition explicit, but it does not show how often the rule was applied or whether sensitivity analyses examined other assumptions. The detailed statistical analysis plan and any additional missing-data procedures are not reported in the registry record.

11. 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 registry record reports serious adverse events affecting 0 of 207 participants in the gabapentin group and 0 of 206 participants in the placebo group. It also reports other adverse events affecting 95 of 207 participants in the gabapentin group and 96 of 206 participants in the placebo group. These are counts of participants recorded as affected, not counts of individual event episodes.

The serious-event figures indicate that no affected participants are recorded in either group for this category. They do not establish that no serious events occurred outside the record’s reporting scope, and they do not provide a statistical comparison. The other adverse-event counts are close in absolute count, but the counts alone do not establish whether the underlying risks differed. No percentages or comparative effect estimates are reported, and none can be inferred without calculating beyond the registry values.

The record does not identify the specific other adverse events in the figures, their severity, timing, or relationship to study treatment. The listed serious-event terms are absent. Death counts are not reported in the registry record. General: Safety counts are best interpreted with their definitions, observation periods, and event details, as well as with information about the number of participants assessed. The registry record does not provide all of those details, so these figures should be read narrowly as recorded participant counts.

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

The study asks whether gabapentin, used with the described background regimen, changes the percentage of complete responders compared with placebo during days 2 through 6. The registry record defines the endpoint and identifies the randomized, double-blind, parallel-group design. However, it does not report the groups’ complete-response percentages or a comparative estimate. The central efficacy question therefore cannot be answered from the outcome information reported in the registry record.

This missing result does not mean that gabapentin and placebo produced identical outcomes. It also does not show that gabapentin improved or worsened the outcome. Without the observed group values, the estimated difference, and an indication of its precision, neither the direction nor the magnitude of the primary comparison is available. The record’s completion status and enrollment figure do not resolve that uncertainty.

The outcome definition is specific: complete response requires no emetic episodes and no rescue therapy use over days 2 through 6, with incomplete study or outcome data classified as non-response. That definition does not cover every aspect of nausea and vomiting. Other listed outcomes address related experiences, but their results are not reported in the registry record. No broader conclusion about symptom severity, patient satisfaction, or other clinical outcomes can be drawn from their listing alone.

The adverse-event counts are also limited in what they can establish. The record lists no participants affected by serious adverse events in either arm, and it lists other adverse events affecting 95 participants in the gabapentin arm and 96 in the placebo arm. These counts do not identify the events or establish a comparative safety effect. Death counts are not reported in the registry record.

General: A trial design describes how a comparison was intended to be conducted; an outcome estimate describes what the comparison found. Both are necessary for a statistical interpretation. In this record, design and endpoint details are available, but the main comparative outcome results and their uncertainty are not reported. Interpretation should remain limited to those documented features rather than filling the gap with assumptions.

13. Why This Trial Matters Statistically

This trial is statistically notable for the gap between a clearly described binary endpoint and the absence of its comparative results in the registry record. The endpoint definition identifies the event-free and rescue-free conditions required for complete response, specifies the assessment period, and states how incomplete data are classified. These details help readers understand what the intended outcome represents. They cannot, by themselves, show how often participants met the definition in either group.

The randomized, double-blind, parallel-group design is also relevant to interpretation. General: Randomization and masking are design strategies intended to support a fair comparison by limiting systematic differences and the influence of treatment knowledge. They strengthen the rationale for a comparison but do not remove the need to report effect estimates, uncertainty, and analysis details. Here, the record does not report the primary outcome estimate or its precision.

The outcome list also illustrates why analysis plans matter. The registry record names several related outcomes and time windows, while the detailed analysis plan and any approach to multiple comparisons are not reported in the registry record. General: Prespecified priorities help readers distinguish a principal confirmatory question from additional analyses. Without those details and the results, readers cannot assess the statistical role of the secondary measures.

The record includes an endpoint rule for incomplete outcomes, but does not report how many participants were affected or which analysis population was used. That makes the rule visible while leaving its practical impact uncertain. The planning assumptions described in the record likewise should be distinguished from the trial’s own design justification and from observed outcome findings.

For clinical researchers and biostatisticians, the example underscores a basic interpretive principle: design features, endpoint definitions, safety counts, and planning assumptions are different kinds of evidence. They should not be substituted for a reported comparative estimate. A transparent result would include group outcomes, an effect estimate, and an account of uncertainty and analysis choices; those items are not reported in the registry record.

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 primary limitation for interpretation is that the registry record does not report the primary outcome results. There are no group percentages for complete response, comparative effect estimate, confidence interval, or primary-outcome p-value. Consequently, the direction, size, and precision of the primary comparison cannot be assessed. The listed study design and endpoint definition do not remedy this lack of outcome data.

The record identifies the study as randomized and double-blind but does not describe the randomization procedure, allocation concealment, which parties were masked, or how masking was maintained. These details are not reported in the registry record. The arm descriptions also provide only a partial regimen description, and dose quantities are not reported in the registry record.

The endpoint rule classifies participants without complete study or outcome data as non-responders, but the number of participants affected and the analysis population are not reported in the registry record. Additional missing-data procedures and sensitivity analyses are also not reported in the registry record. This limits assessment of how incomplete outcome data may have influenced the endpoint comparison.

The record lists seven outcome measures and two analyses, but does not report the detailed statistical analysis plan, the relationship between analyses and outcomes, or any multiplicity strategy. It also does not report the trial’s own sample-size rationale or whether interim analyses were planned. The planning assumptions described in the record are illustrations, not evidence about the trial’s original design decisions or observed power.

Safety reporting is limited to participant counts for serious and other adverse events. Specific events, their severity and timing, treatment attribution, and death counts are not reported in the registry record. These limitations constrain interpretation of both efficacy and safety and should be kept distinct from any conclusion about the treatments themselves.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Gabapentin in Preventing Nausea and Vomiting in Patients Receiving Chemotherapy — NCT00880191.
• Registry record last updated 2016-07-06; status last verified 2016-07.
• Results first posted 2015-05-21.
• 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

NCT00880191 is recorded as a completed randomized, double-blind, phase III, parallel-group study sponsored by the Alliance for Clinical Trials in Oncology. The study compared gabapentin with placebo alongside a described dexamethasone and 5HT3 receptor antagonist regimen in patients receiving highly emetogenic chemotherapy. Enrollment is recorded as 430, with study start in 2009-04 and primary completion in 2011-03.

The primary endpoint was the percentage of complete responders during days 2 through 6, defined as no emetic episodes and no rescue therapy use. Participants who did not complete the study or provide complete data were classified as non-responders. The registry record does not report the primary outcome percentages, comparative estimate, confidence interval, or p-value. It lists 0 serious adverse events affecting participants in each arm and other adverse events affecting 95 participants in the gabapentin arm and 96 in the placebo arm. Death counts are not reported in the registry record.

The record lists seven outcome measures and two analyses. The detailed statistical analysis plan, multiplicity approach, trial-specific sample-size justification, and additional missing-data procedures are not reported in the registry record.