Comparison of Exparel to Bupivacaine With Dexamethasone in TAP Block: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Exparel to Bupivacaine With Dexamethasone in TAP Block (NCT02179892), a randomized phase 4 study. The primary outcome is Mean Opioid Consumption.

2. Clinical Question

3. Trial Design

The registry describes a Phase 4, randomized, triple-masked, parallel-group trial. Participants were allocated to receive one of the two TAP-block regimens: Exparel, or bupivacaine with dexamethasone. A parallel design assigns participants to a group and compares outcomes between groups, rather than having each participant receive both regimens. Random allocation is intended to make the groups comparable on average, although it cannot guarantee comparability in a small study.

The planned enrollment described in the registry summary was up to 50 subjects, with a goal of at least 22 subjects in each group. The registry’s enrollment field reports 9, and the posted endpoint summaries give 5 participants in the Exparel group and 4 in the bupivacaine-and-dexamethasone group. These are distinct pieces of information: the first describes the planned enrollment, while the latter describe the posted outcome groups. The record marks the study as terminated. A reason for termination is not reported in the registry record.

The study was intended for patients undergoing abdominal surgery at Emory University Hospital and Emory University Hospital Midtown. The registry gives a start date of 2014-07 and a primary completion date of 2015-06-06. Further information about the masking procedures, allocation sequence, concealment, and conduct of the trial is not reported in the registry record. The record also does not explain whether termination affected recruitment, follow-up, or outcome collection.

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 Mean Opioid Consumption, measured over Post Surgery (Up to 72 Hours).

The primary endpoint is mean opioid consumption, measured in milligrams, during the postoperative period up to 72 hours. The registry describes collecting each group’s total opioid consumption over the 72-hour postoperative period and identifies the summary measure as a mean with standard deviation. The posted group summaries are 507.0 milligrams with a standard deviation of 602.0 for Exparel, and 392.0 milligrams with a standard deviation of 133.0 for bupivacaine with dexamethasone.

As a general statistical point, opioid consumption is a measure of medication use during a defined period. It can be studied as an outcome in postoperative pain research, but it does not directly measure pain intensity. Pain scores and medication use capture related but different aspects of a postoperative experience; one cannot be substituted for the other without additional evidence. The registry also lists pain scores at rest and with movement, and time to first opioid use, as secondary outcomes.

The record does not describe how opioid use was converted to the reported milligram measure, how medicines or routes were handled, or how missing observations were treated. Those details matter when interpreting a consumption endpoint, but are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The endpoint is continuous: opioid consumption is recorded as an amount in milligrams, and the registry identifies the primary summary as a mean with standard deviation. A mean describes the arithmetic average of recorded values. A standard deviation describes how spread out those values are around the mean. These summaries answer different questions: the mean describes the group’s central level, while the standard deviation describes within-group variability. Neither one alone gives the uncertainty in a comparison between groups.

What does a confidence interval add?

As a general statistical explanation, a confidence interval describes the precision of an estimated quantity under the analysis assumptions. For a randomized comparison, an interval for the between-group contrast would help show which values remain compatible with the observed data and the statistical procedure. A narrow interval indicates greater precision than a wide interval. The registry does not report a confidence interval for the primary comparison, so the precision of the comparative estimate cannot be evaluated from an interval.

Why is a test result not available?

The record lists no analysis for the outcome and indicates that values were missing or not estimable for a two-arm comparison of the continuous endpoint. Therefore, there is no reported p-value or inferential comparison to interpret. A p-value, in general, measures how unusual data at least as incompatible with a specified null hypothesis would be under the test assumptions. It does not measure the size or clinical importance of an effect, and it cannot replace an estimate with an uncertainty interval. No p-value is reported in the registry record.

Arm-level means and standard deviations can support some unadjusted comparisons when the group sizes and analysis assumptions are appropriate. However, the registry’s stated non-estimability means a recalculated comparison is not presented. The reason is not reported, and it would be inappropriate to infer one. The record does not specify whether the issue involved data completeness, the analysis method, or another consideration.

Why does over-dispersion matter?

As a general concept, over-dispersion means that observations vary more than a model or simple summary procedure would anticipate. High variability can make a mean less precise, especially when a group contains few observations. Here, the standard deviation in the Exparel group is 602.0 milligrams, compared with a mean of 507.0 milligrams; the corresponding standard deviation and mean in the other group are 133.0 and 392.0 milligrams. These summaries signal that variability deserves attention, but they do not reveal the distribution or identify the source of the spread. The registry does not report individual values, distributional checks, or methods to address unusual observations.

How should planning illustrations be read?

The sample-size illustrations use the observed effect as a planning basis, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. They are not the trial’s original design justification. A planning illustration asks what enrollment might be needed under its stated assumptions to detect a specified fraction of the observed effect. It is not observed power and does not repair the uncertainty in the trial’s posted comparison. The registry does not report the trial’s own sample-size justification or design assumptions. The planning illustrations should therefore be understood as hypothetical calculations, not as evidence that the completed study had adequate power.

More broadly, statistical inference depends on both data and methods. The registry identifies randomization and masking but does not report the detailed analysis model, handling of missing endpoint values, or any adjustment for baseline variables. Without those details and a reported comparative analysis, readers should distinguish the descriptive arm summaries from an estimate supported by a specified inferential procedure.

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("Group 1-Exparel", "Group 2-Bupivacaine and Dexamethasone IV")
n   <- c(5, 4)
m   <- c(507, 392)
sp  <- c(602, 133)
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  Group 1-Exparel  5  507.000  602.000  -240.482  1254.482
CARM  Group 2-Bupivacaine and Dexamethasone IV  4  392.000  133.000  180.367  603.633

11. Multiplicity, Missing Data and Analysis Populations

The registry identifies mean opioid consumption as the primary endpoint and lists three secondary outcomes: mean Visual Analogue Scale pain score at rest, mean Visual Analogue Scale pain score with movement, and mean time of first opioid use. It reports four outcome measures in total and lists no analyses. The secondary outcome names do not establish whether each was measured at a single time point or at multiple time points; those details are not reported in the registry record.

Multiplicity is a general statistical concern that arises when several outcomes or comparisons are tested. The more tests conducted, the greater the opportunity for chance findings unless the analysis plan accounts for that process. The record does not report a multiplicity adjustment, a hierarchy among secondary outcomes, or a statistical plan specifying how the outcomes would be interpreted together. It is therefore not possible to determine whether or how multiplicity was addressed.

Information about missing outcome data is also limited. The registry states that a two-arm comparison of the continuous primary endpoint was not estimable because values were missing or not estimable, but does not describe the missingness pattern or the method used to handle it. The analysis population is not reported in the registry record. No information is given about exclusions, withdrawals, adherence, or whether the posted group summaries include all participants assigned to each arm. These omissions limit assessment of how the analyzed data relate to the randomized groups.

12. 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 adverse-event record reports zero serious adverse events among the 5 participants listed as at risk in the Exparel group and zero among the 4 listed as at risk in the bupivacaine-and-dexamethasone group. It also reports zero other adverse events and zero deaths in each group. No serious adverse-event terms are listed.

These figures describe what the registry record reports; they do not show that an event is impossible or that the regimens have equivalent safety. With small at-risk groups, an absence of recorded events provides limited information about the frequency of uncommon harms. The record does not give definitions, event-collection procedures, follow-up completeness, or additional detail about adverse-event severity and timing. Those details are not reported in the registry record, so the event counts should be interpreted narrowly as posted safety summaries rather than as a comprehensive safety assessment.

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

The posted results provide descriptive summaries of mean opioid consumption for the two randomized groups and report adverse-event counts. They do not provide an inferential estimate of the primary between-group comparison. The Exparel group’s posted mean is numerically higher than the comparator group’s posted mean, but the registry gives no confidence interval or statistical test that would quantify uncertainty around that contrast. The summaries therefore do not support a firm conclusion about the comparative effect on opioid consumption.

This distinction is important: a numerical difference between observed means is not, by itself, evidence of a reliable group-level difference. As a general statistical principle, randomized assignment supports a fair comparison when allocation, follow-up, and analysis are properly carried out, but randomization cannot make a small study precise. The record does not provide enough analysis detail to evaluate these aspects fully.

The findings also do not directly answer whether postoperative pain differed. Opioid consumption is the primary endpoint, while pain scores at rest and with movement are listed as secondary outcomes. The registry does not post an analysis of those outcomes. Medication consumption and reported pain are related but distinct measures, and the consumption summaries alone cannot establish a result for pain scores.

The trial is marked terminated, and the enrollment field reports 9 compared with a planned enrollment of up to 50 and a goal of at least 22 per group stated in the study summary. The reason for termination and its implications for data collection are not reported. The posted data should consequently be treated as limited descriptive evidence, with the comparative uncertainty unresolved in the registry record. They neither demonstrate that one regimen is better nor establish that the regimens are equivalent.

14. Why This Trial Matters Statistically

This trial illustrates why a registered randomized design and a completed comparative analysis are not the same thing. The record identifies randomization, triple masking, and parallel groups, features that can help structure a fair comparison. Yet the posted primary outcome is accompanied by arm-level summaries without an inferential analysis of the group contrast. Readers can see the observed means and variability, but cannot assess the precision of a comparative estimate from a confidence interval or test result.

The gap between planned and reported enrollment is also statistically important. The study summary describes a goal of at least 22 participants in each group, while the enrollment field reports 9 and the endpoint summaries list 5 and 4 participants in the respective groups. Sparse data usually produce less precise estimates, and unusually variable observations can have substantial influence on a mean. The registry marks the study terminated but does not explain why, leaving the reason and its effect on the planned analysis unknown.

The record further illustrates the value of transparent outcome reporting. It names a primary endpoint and secondary outcomes, but does not report analysis results for them. Without a stated analysis population, missing-data methods, and a reported between-group estimate, it is difficult to judge how the endpoint summaries relate to the planned question. These are statistical reporting limitations, not evidence in themselves about the direction of a treatment effect.

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 endpoint summaries are based on the small groups listed in the registry: 5 participants for Exparel and 4 for bupivacaine with dexamethasone. The large standard deviation reported for Exparel indicates substantial spread in that group’s consumption values. No individual data or distributional summaries are posted, so the influence of unusually high or low observations cannot be evaluated.

The registry marks the study terminated and reports an enrollment of 9, while its study summary describes a larger planned enrollment. The reason for termination, recruitment history, and consequences for follow-up are not reported in the registry record. The record also does not explain why the primary continuous comparison was marked not estimable despite posting arm-level means and standard deviations.

Further limitations include the absence of a reported confidence interval, p-value, analysis model, and analysis population. The record does not describe missing-data handling or provide results for the listed secondary outcomes. It does not report detailed participant characteristics or explain how opioid consumption was operationalized across medications and routes. The registry’s descriptions of the comparator regimen are not fully consistent: the arm description refers to bupivacaine and dexamethasone via TAP block, while the study summary mentions epinephrine in the planned comparator. These gaps limit interpretation of both the estimand and the observed summaries.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Comparison of Exparel to Bupivacaine With Dexamethasone in TAP Block — NCT02179892.
• Registry record last updated 2017-08-11; status last verified 2017-07.
• Results first posted 2017-08-11.
• 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

NCT02179892 is a Phase 4 randomized, triple-masked, parallel-group trial comparing Exparel with bupivacaine and dexamethasone administered through TAP block for patients undergoing abdominal surgery. The primary outcome is mean opioid consumption in milligrams over the postoperative period up to 72 hours. The registry posts means of 507.0 with a standard deviation of 602.0 for Exparel and 392.0 with a standard deviation of 133.0 for the comparator.

The enrollment field reports 9, and the study status is terminated. The registry reports zero serious adverse events, zero other adverse events, and zero deaths in each group. It does not report an inferential analysis of the primary comparison, and the record indicates that a two-arm comparison was not estimable. The reason for termination and the reason for non-estimability are not reported in the registry record.