Prophylactic Antibiotics for Prevention of Wound Complications Following Vulvectomy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Prophylactic Antibiotics for Prevention of Wound Complications Following Vulvectomy (NCT00550290), a randomized phase 4 study. The primary outcome is Wound Complications.

2. Clinical Question

The registry describes this as a randomized, double-masked, parallel study. Its brief summary says it was intended to investigate whether a 24 hour post-operative course of broad-spectrum prophylactic antibiotics, specifically Cefazolin, could prevent wound infection and wound breakdown following vulvectomy. The registered primary outcome, however, is stated more broadly as wound complications. The outcome description says that febrile episodes, elevated WBC counts and exam findings were used to diagnose such complications.

The posted results show 3 participants with wound complications in the 24 Hour Post-operative Course of Cefazolin group, among 10 participants, and 2 in the Pre-operative Single Dose of Cefazolin group, among 8 participants. These are counts, not a registry-reported estimate of the comparative effect. The registry record does not report a statistical test, confidence interval, or adjusted comparison for this outcome. The question can therefore be described from the groups and counts, but the posted results do not establish the precision of a difference between regimens.

3. Trial Design

The registry identifies this as a Phase 4, randomized, double-masked, parallel-group trial. It lists 18 participants as enrolled and the study status as completed. The record gives a start of 2007-10 and primary completion of 2009-04. The sponsor is Aultman Health Foundation. These registry entries describe the study as recorded; they do not explain the conduct of masking or the method used to generate or conceal the random allocation.

The two groups differed in post-operative exposure to Cefazolin. Participants in the 24 Hour Post-operative Course of Cefazolin group received Cefazolin 2 grams intravenously within 30 minutes prior to incision and 1 gram every 8 hours for the first 24 hours post-op. Participants in the Pre-operative Single Dose of Cefazolin group received Cefazolin 2 grams intravenously within 30 minutes prior to incision. Thus, both descriptions include a dose before incision, while only the first describes additional doses after surgery.

The primary outcome was the number of participants experiencing wound complications, with a two-week post-operative timeframe. The efficacy population is described as participants who received their assigned dose of each intervention and completed all study visits. The registry record does not report how many participants were excluded from that population, whether every enrolled participant completed all visits, or whether the analysis followed the randomized assignment regardless of treatment received.

Enrollment was 18, with 10 participants in the post-operative-course group and 8 in the single-dose group in the posted outcome. The record does not report the intended enrollment target, a sample-size justification, detailed eligibility criteria, or a protocol for handling deviations from assigned treatment. The design labels alone do not answer those questions.

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

Analysis population for the primary outcome, as defined in the registry: All participants who received their assigned dose of each intervention and completed all study visits were included in the efficacy analysis.

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 Wound Complications, measured over Two-week post-operative.

The primary endpoint is the number of participants experiencing wound complications following vulvectomy, assessed at two-week post-operative follow-up. It is a participant-level binary outcome: a participant is counted as having the event or not having it. The registry says diagnosis used the presence of febrile episodes, elevated WBC counts and exam findings. It does not describe thresholds, adjudication procedures, or how the different clinical findings were combined to determine an event.

A participant count is useful because it summarizes how many people in each group met the recorded definition during the stated follow-up. It is distinct from a measure of the number of wound events, their severity, or the time until a complication occurred. The outcome description does not report separate results for wound infection and wound breakdown, so the posted primary counts cannot be separated into those components.

In this trial, the registry reports 3 participants with wound complications among 10 in the post-operative-course group and 2 among 8 in the single-dose group. The counts provide a direct description of the observed outcome in each group, but by themselves do not quantify uncertainty about the comparison. The registry record does not report confidence intervals or a statistical test for the primary endpoint. The efficacy population description also limits the stated analysis to participants who received their assigned dose and completed all study visits; the record does not give further detail on outcome ascertainment among participants outside that description.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry gives a binary primary outcome: participants with a wound complication. It reports the number with the outcome and the number in each group, but no inferential analysis. The discussion below explains general statistical ideas relevant to this kind of result; it does not describe procedures that the registry says were actually used.

What does a binary outcome represent?

In general, a binary outcome classifies each participant into one of two states for the defined endpoint: the event occurred, or it did not. Here, the event is a wound complication as described in the registry. The posted group values are counts of participants with an event. Such counts are descriptive. To compare groups statistically, an analysis would usually express the contrast using a prespecified measure and quantify the uncertainty around it. The registry record does not report a measure of comparative effect for this outcome.

What would a confidence interval add?

In general, a confidence interval gives a range of values compatible with a statistical procedure and the observed data, under the assumptions of that procedure. It communicates precision as well as direction and magnitude. A narrow interval generally indicates more precise estimation than a wide interval. An interval may include values representing no difference and still be compatible with effects in either direction. No confidence interval for the primary comparison is reported in the registry record, so precision cannot be read from the posted counts alone.

What would a hypothesis test add?

In general, a hypothesis test evaluates the data against a specified null hypothesis using a chosen statistical method and significance level. A p-value describes how surprising data at least as incompatible with the null would be under that null and the model assumptions. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. The registry record reports no p-value or test for the primary endpoint. It also does not report a statistical analysis plan that would identify the intended hypothesis, test, or significance threshold for the trial analysis.

Why might methods differ for a binary outcome?

In general, a binary outcome can be analyzed with methods that compare event probabilities or with a regression model that adjusts for selected factors. The choice can depend on the design, sample size, analysis population, and prespecified estimand. Some approaches rely on approximations that may be less dependable when group counts are limited or outcome counts are sparse; exact methods or carefully specified models may be considered in such settings. These are general methodological options, not methods reported as used in this study. The registry does not report a test, model, covariate adjustment, or other comparative procedure.

In general, over-dispersion is relevant when observed variability exceeds what a model assumes. It is often discussed for count outcomes and clustered or repeated observations, rather than a simple participant-level binary outcome. A model that ignores extra variability may give uncertainty estimates that are too small. The registry does not report an over-dispersion assessment, and the posted endpoint is a participant count rather than a repeated-event count. This general concept should not be read as evidence that over-dispersion was present or assessed.

How should the analysis population be understood?

The registry says the efficacy analysis included participants who received their assigned dose of each intervention and completed all study visits. In general, an analysis restricted by treatment received and completion can differ from an analysis that retains every randomized participant in the group to which they were assigned. The choice affects what question the analysis answers and may affect comparability if exclusions are related to outcome or treatment. The registry record does not report participant flow, the number not included in the efficacy population, or a separate intention-to-treat analysis. Therefore, the exact extent and consequences of any exclusions cannot be assessed from this record.

What do the planning illustrations mean?

In general, sample-size calculations depend on assumptions about the effect to detect, statistical significance level, allocation, analysis method, and outcome variability. The planning illustrations accompanying this page are not the trial's own design justification. Their stated framework uses a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation, with the effect to detect expressed as a stated fraction of the observed effect. Such calculations are scenarios for planning future studies, not observed power and not a retrospective measure of whether this trial could establish a difference. The registry record does not report the trial's own sample-size rationale, target effect, or design assumptions.

For binary outcomes, a planning illustration may report participants per arm for a specified power. The displayed planning values should be interpreted in the context of their assumptions and the observed effect used in the calculation. They do not change the underlying limitation that the trial enrolled 18 participants, and they do not constitute evidence about an effect beyond the posted outcome. No new comparative estimate or inferential result is reported because none is included in the registry record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("24 Hour Post-operative Course of Cefazolin", "Pre-operative Single Dose of Cefazolin.")
n      <- c(10, 8)
events <- c(3, 2)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  24 Hour Post-operative Course of Cefazolin  10  3  30.0  6.7  65.2  10.8  60.3  10.9  61.0
ARM  Pre-operative Single Dose of Cefazolin.  8  2  25.0  3.2  65.1  7.1  59.1  7.5  60.0

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure and no secondary outcomes posted. It also lists zero analyses. The primary measure is wound complications at two-week post-operative follow-up. The registry record does not report a statistical analysis plan, a hierarchy of hypotheses, or a procedure for controlling multiplicity. With no posted inferential analyses, it is not possible to determine how multiple statistical tests, if any, were planned or handled. The absence of posted secondary outcomes should not be taken to mean that no other outcomes were collected; their status is not reported in the registry record.

For the primary outcome, the stated efficacy population consists of participants who received their assigned dose of each intervention and completed all study visits. The record does not report how many participants were randomized, how many completed each visit, or whether any enrolled participants were excluded from the reported efficacy analysis. The posted groups include 10 participants in the post-operative-course arm and 8 in the single-dose arm. How these numbers relate to randomized assignment and completion is not further described.

The registry does not report the number of missing outcome observations, the reasons for missingness, or any imputation or sensitivity analysis. It also does not say how a participant with incomplete diagnostic information would have been classified. In general, missing-data methods can affect results when the probability of missingness is related to participant characteristics or outcome status. Without a description of missingness and its handling, the robustness of the outcome counts to incomplete follow-up cannot be evaluated.

The record also does not report whether the primary analysis was based on assigned group regardless of treatment received, or whether any participants changed or did not complete their assigned regimen. These details matter when interpreting randomized studies, but no further information is reported in the registry record.

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 posted safety figures list 0 serious adverse events among 10 participants at risk in the 24 Hour Post-operative Course of Cefazolin group, and 0 among 8 participants at risk in the Pre-operative Single Dose of Cefazolin group. The record also lists 0 other adverse events among 10 and 0 among 8, respectively, and 0 deaths in each group. These are registry counts for the groups shown; they are not the primary wound-complication outcome.

A count of zero means no event was recorded in the listed category and group in the posted results. It does not prove that an event could not occur, establish that all possible harms were measured, or quantify the precision of the safety comparison. The registry record does not report a comparative safety analysis, confidence intervals, event-specific details, or the time period over which adverse events were collected. No serious adverse event terms are listed. The figures should therefore be read as a concise report of recorded counts, not as proof of no risk or as a complete description of safety.

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

The result establishes a limited descriptive fact: the registry reports wound complications for 3 participants in the 24 Hour Post-operative Course of Cefazolin group and 2 participants in the Pre-operative Single Dose of Cefazolin group. The respective groups contain 10 and 8 participants in the posted outcome. The reported endpoint was assessed two-week post-operatively and used febrile episodes, elevated WBC counts and exam findings to diagnose wound complications.

The result does not establish that one regimen is better or worse than the other. The record provides no statistical test, confidence interval, or comparative effect estimate. Without those, the reader cannot assess the statistical uncertainty around a between-group contrast using the registry analysis. The counts also do not distinguish wound infection from wound breakdown, despite both being mentioned in the brief study summary as concerns.

The comparison is between two Cefazolin regimens, one of which includes post-operative doses and one described as a single pre-operative dose. It is not a comparison with no prophylactic antibiotic. The posted counts cannot establish what would have happened under an unrepresented treatment regimen, and they should not be generalized beyond the population and follow-up described without further evidence.

The efficacy population was defined as participants who received their assigned dose and completed all study visits. The registry does not report enough participant-flow or missing-data detail to determine whether this population included all randomized participants. It also does not report the protocol's statistical plan or a sample-size justification. Those absences limit assessment of how the posted result relates to the trial's original analytic intentions.

Planning calculations are not findings from the trial. They are hypothetical illustrations based on assumptions and the observed effect, and should not be interpreted as observed power or as evidence that a treatment effect has been demonstrated. The overall meaning of the posted result is therefore descriptive: it records the observed group counts, while leaving the comparative effect and its precision unreported.

14. Why This Trial Matters Statistically

This study illustrates a distinction that is important in clinical-trial reporting: descriptive event counts are not the same as a statistical comparison. The registry reports the number of participants with wound complications in each group, but does not report a test, an effect estimate, or a confidence interval. A reader can see what was observed, but cannot use the registry record to assess the precision of a formal comparison.

The small enrollment is also central to statistical interpretation. With 18 participants enrolled and the posted outcome groups containing 10 and 8 participants, the event counts are a limited basis for estimating a broader pattern. In general, estimates from small groups can be imprecise, and a lack of a reported statistical result should not be mistaken for evidence of equivalence. Conversely, the observed counts alone do not establish a meaningful difference.

The design has a clearly described clinical contrast: both groups received a pre-incision Cefazolin dose, while one group also received post-operative doses during the first 24 hours. A good analysis would need to make clear which population and treatment contrast it targets, how incomplete follow-up is handled, and what effect measure is used. The registry record provides only part of that information.

The record also demonstrates why planning illustrations should be kept separate from trial findings. A calculation based on an observed effect can help show the assumptions behind a future planning scenario, but it cannot substitute for a prespecified sample-size rationale or recover missing inferential reporting. The registry does not report its own sample-size justification.

Statistically, the most useful takeaway is the boundary between what the posted data show and what they leave unresolved. The group counts are visible and interpretable as observations. The uncertainty, analysis population details, and comparative conclusion are not reported in the registry 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 primary limitation for interpretation is the absence of a reported comparative analysis. The registry lists zero analyses and provides no confidence interval, p-value, or effect estimate for wound complications. The count data describe the groups but do not quantify the uncertainty of a contrast between them.

Enrollment was 18, and the posted outcome includes 10 participants in the post-operative-course group and 8 in the single-dose group. The registry does not explain the relationship between enrollment, randomization, and inclusion in the efficacy analysis beyond stating that participants had to receive their assigned dose and complete all study visits. Participant flow and any exclusions are not reported in the registry record.

The endpoint definition is only partly specified. The record names febrile episodes, elevated WBC counts and exam findings as diagnostic information, but does not describe thresholds, adjudication, or whether the criteria had to occur together. The posted result does not separate wound infection from wound breakdown or report component-specific counts. The outcome timeframe is stated as two-week post-operative, with no further detail about assessment timing.

The registry record does not report the trial's sample-size justification, detailed statistical plan, handling of missing observations, or multiplicity procedure. It also does not describe allocation concealment or how masking was implemented. The safety counts have no reported comparative analysis or detailed adverse-event observation period. These omissions do not show that procedures were absent; they mean that their details are not reported in the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Prophylactic Antibiotics for Prevention of Wound Complications Following Vulvectomy — NCT00550290.
• Registry record last updated 2018-10-17; status last verified 2018-09.
• Results first posted 2018-09-18.
• 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

This completed Phase 4 study is listed as randomized, double-masked and parallel, with enrollment of 18. It compared a pre-operative single dose of Cefazolin with a regimen that included the pre-incision dose plus Cefazolin every 8 hours for the first 24 hours post-op.

The primary outcome was the number of participants with wound complications at two-week post-operative follow-up. The registry reports 3 participants with complications among 10 in the post-operative-course group and 2 among 8 in the single-dose group. It reports no statistical analyses for this outcome.

The registry also lists 0 serious adverse events, 0 other adverse events and 0 deaths in each group. It does not report a comparative safety analysis. The efficacy population is described as participants who received their assigned dose and completed all study visits; further participant-flow, missing-data, and analysis-plan details are not reported in the registry record.