Study of Antimicrobial Activity of Omiganan 1% Gel vs. Chlorhexidine 2% for Topical Skin Antisepsis in Healthy Adult Subjects: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study of Antimicrobial Activity of Omiganan 1% Gel vs. Chlorhexidine 2% for Topical Skin Antisepsis in Healthy Adult Subjects (NCT00608959), a non-randomized phase 3 study. The primary outcome is Change in Mean Number of Skin Bacterial Counts From Baseline to 72 Hours.

2. Clinical Question

The study focused on the persistence of antimicrobial activity on the skin, rather than on infection prevention or treatment outcomes. Its stated purpose was to assess the activity and safety of omiganan compared with chlorhexidine for killing bacteria on the skin surface. The registry record lists Infection as a condition, but the described study population was healthy adult subjects.

The comparison needs cautious interpretation. Participants were not randomized, and the record characterizes the arms as not being a like-for-like control comparison. The open-label design also means treatment assignment was not masked. These features limit how confidently differences between groups can be attributed to the treatments rather than to differences in participants, study parts, or other features of conduct.

The registry record does not report the numerical primary endpoint results, such as group means, variability, or a between-group estimate. It therefore does not answer the primary question quantitatively in the posted record. The endpoint definition and design can be described, but the magnitude and precision of any observed change cannot be assessed from the registry record.

3. Trial Design

The registry record identifies this as a Phase 3, parallel-group, non-randomized, open-label study. Its official title describes a single-center study of persistence of antimicrobial activity in healthy adult subjects. The record lists enrollment as 30 and study status as completed. The start and primary completion dates are recorded as 2008-05 and 2008-06.

The two named study treatments were omiganan 1% gel and chlorhexidine 2% solution, both applied topically. The record separates omiganan into Part 1 and Part 2 in its safety group descriptions, with chlorhexidine listed as a separate group. It does not describe how participants were assigned to these groups or explain the relation among the parts. Assignment was non-randomized, so the treatment groups may not be comparable on all factors that could influence bacterial counts.

Open-label means that the study was not masked. The record does not give further information about who knew treatment assignment, how the treatments were administered, or whether outcome assessment was blinded. Those details are not reported in the registry record.

The study’s central measurement was the change in mean skin bacterial counts from before the first application to 72 hours post application. The primary endpoint description specifies a baseline measure derived by pooling samples from 6 sites adjacent to each timepoint, and a single sample per subject per timepoint at 72 hours. The stated analysis population included participants with at least one treatment and data available at 72 hours.

The record does not report the protocol’s rationale for its design, how sample size was chosen, or the allocation process. It also does not describe planned interim analyses or a detailed statistical analysis plan. Those omissions matter because they leave unanswered how the non-randomized comparison was intended to address differences between groups and how the primary endpoint was to be analyzed.

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.

Before assignment: Subjects required screening skin samples ( from an average of 2 samples) containing at least 2.5log10 colony forming units per cm2 (CFU/cm2)

Part 1

Reasons for not completing this period:

Part 2

Analysis population for the primary outcome, as defined in the registry: ITT set consists of all subjects who received at least one study treatment and had data available at 72 hours.

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 Change in Mean Number of Skin Bacterial Counts From Baseline to 72 Hours, measured over Prior to first application (0 hours) to 72 hours post application.

The primary endpoint is the change in mean skin bacterial count from baseline to 72 hours after application, measured in log 10 CFU/cm sq. CFU refers to colony-forming units, a way of expressing viable microorganisms recovered from a sample. The endpoint description defines the change by subtracting the 72-hour log10 CFU/cm2 value from the baseline log10 CFU/cm2 value. With this direction of subtraction, the sign of a change must be interpreted in relation to baseline minus follow-up, not the reverse.

The use of a logarithmic scale is common when microbial counts span a broad range. General statistical explanation: a log scale expresses multiplicative differences on an additive scale, which can make changes in counts easier to summarize and compare. The reported measure is a mean, with standard deviation specified as the dispersion measure. A standard deviation describes how spread out individual measurements are around their group mean; it is not the same as the uncertainty of the estimated mean.

The 72-hour measurement addresses persistence of antimicrobial activity after application, which is the question named in the study title. Baseline measurement provides a reference for describing subsequent change. According to the record, baseline was calculated by pooling samples from 6 sites adjacent to each timepoint, while the 72-hour assessment used a single sample per subject per timepoint.

The registry record does not report the numerical mean changes, standard deviations, or a comparative estimate for this endpoint. The endpoint’s definition is available, but its observed magnitude and 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 mean change represent?

The primary endpoint is a continuous measure: the change in mean skin bacterial count on a log scale. A mean summarizes the measurements in a group with one central value. The stated change is calculated as the baseline log10 CFU/cm2 value minus the 72-hour value. It is important to preserve that stated order because reversing the subtraction would reverse the sign. The registry record identifies standard deviation as the measure of dispersion, but does not report the actual means or standard deviations.

General statistical explanation: a mean change condenses repeated measurements into a group-level summary. It does not show the full distribution of individual responses. Participants may have changes that differ substantially from the group mean, and a standard deviation helps describe that spread. A standard deviation does not, by itself, show how precisely the group mean or a between-group difference has been estimated.

What would a between-group estimate show?

A comparison of group means would describe how the average change differed between treatment groups. The usefulness of such an estimate depends on the design and analysis, not just on its numerical value. Here, allocation was non-randomized, and the registry record explicitly warns that the arms are not a like-for-like control comparison. Group differences could therefore reflect differences in participants or study conduct as well as treatment. The record does not report an adjustment strategy or enough group-level information to evaluate this issue.

The primary endpoint description includes an ITT set, defined as participants who received at least one study treatment and had data available at 72 hours. That definition is narrower than simply including every enrolled participant: it requires treatment exposure and an observed 72-hour value. The record does not report the number included in that set or detail how other participants’ data were handled.

How should uncertainty be understood?

General statistical explanation: a confidence interval gives a range of values compatible with the data and the method used to calculate it. A narrow interval indicates greater precision than a wide interval, while neither width nor location alone resolves design limitations such as non-random allocation. A p-value, when reported, describes how compatible the data are with a specified statistical model under a null hypothesis; it is not the probability that a treatment effect is real. Neither a confidence interval nor a p-value for the primary endpoint is reported in the registry record.

Because the primary estimates and their uncertainty are absent, the magnitude and precision of the observed endpoint cannot be assessed from the registry record. Statistical significance cannot be inferred from a study’s phase, completion status, or stated objective.

Why can over-dispersion matter?

General statistical explanation: over-dispersion occurs when observed variability exceeds what a statistical model assumes. If a model underestimates variability, uncertainty may appear smaller than it is, and inferential results can be misleading. The primary endpoint is continuous and the registry record specifies a mean and standard deviation; it does not report an over-dispersion assessment or identify a model for the primary analysis. No conclusion about whether over-dispersion was evaluated is possible from the record.

What do planning illustrations mean?

General statistical explanation: sample-size calculations estimate how many participants might be needed under stated assumptions to detect a specified effect with a chosen error rate and power. The record describes planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation; the target effect is a stated fraction of the observed effect. For non-time-to-event outcomes, such calculations are expressed as participants per arm. These are planning illustrations, not the trial’s original design justification and not observed power. The registry record does not report the study’s own sample-size justification. Because the primary endpoint’s observed effect is not reported in the registry record, the underlying effect size for such illustrations cannot be independently evaluated from the record.

Planning calculations depend on assumptions about the effect, variability, allocation, and analysis. They do not show what happened in the trial, nor do they substitute for the observed estimate and its uncertainty. In particular, a planned or retrospectively illustrated sample size cannot establish that a result is precise or that an analysis is unbiased.

What analysis details are absent?

The registry record gives the endpoint definition, dispersion measure, and a description of the analysis population. It does not report the statistical test or model used for the primary analysis, how the non-randomized groups were compared, whether covariates were considered, or how missing measurements were treated. It also does not report whether assumptions were checked or whether sensitivity analyses were performed. These details are needed to understand precisely how a numerical result would have been produced and what assumptions would support its interpretation.

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("Omiganan 1% Gel (Part 2)", "Chlorhexidine 2%(Part 1)")
n   <- c(25, 24)
m   <- c(-1.91, -1.87)
sp  <- c(1.563, 1.656)
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  Omiganan 1% Gel (Part 2)  25  -1.910  1.563  -2.555  -1.265
CARM  Chlorhexidine 2%(Part 1)  24  -1.870  1.656  -2.569  -1.171

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists 3 outcome measures and 2 analyses, but does not provide enough detail to identify all the hypotheses tested or how they were related. It does not report whether the primary endpoint was the only confirmatory test, whether secondary outcomes were tested formally, or whether any adjustment for multiple comparisons was planned or used. A multiplicity strategy is therefore not reported in the registry record.

General statistical explanation: when several outcomes, timepoints, or comparisons are tested, the chance of obtaining at least one apparently unusual result can increase. Methods for addressing multiplicity can control that risk, but the appropriate approach depends on the analysis plan and the roles of the outcomes. Without the named outcomes and analysis details, it is not possible to determine whether multiplicity was a practical issue or how it was handled.

The stated primary analysis population consists of participants who received at least one study treatment and had data available at 72 hours. This definition makes availability of the 72-hour measurement part of inclusion in that population. The record does not report how many participants lacked such data, why measurements might be missing, or whether the analysis used imputation, a sensitivity analysis, or another missing-data approach. Those details are not reported in the registry record.

General statistical explanation: missing outcome data can affect both the precision of an estimate and its interpretation, particularly when missingness is related to participants’ outcomes or other characteristics. Restricting an analysis to participants with observed measurements does not, on its own, establish that missing data are harmless. The record does not provide enough information to assess the potential effect of missingness.

The record also does not report the number analyzed for the primary endpoint. The listed enrollment and safety-group counts do not establish that number, because the endpoint population has its own treatment-and-data requirements.

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 registry record lists three safety groups: Omiganan 1% Gel (Part 1), Chlorhexidine, and Omiganan 1% (Part 2). Each group has 25 participants at risk for serious adverse events, with 0 affected in each group. For other adverse events, each group also has 25 at risk; the recorded affected counts are 0, 7, and 8, respectively.

These entries are descriptive counts. The registry record does not provide further definitions for the categories in these entries, nor does it report a statistical comparison of the groups. Because the study was non-randomized and the record cautions that the arms are not a like-for-like control comparison, the counts should not be interpreted as an unconfounded estimate of relative safety. The record’s separate Part 1 and Part 2 labels also should not be collapsed into a single omiganan group without additional information.

Deaths are not reported in the registry record. The absence of a reported death count is not the same as a documented zero. The safety entries also do not provide event descriptions, timing, severity details beyond the serious/non-serious distinction, or follow-up information. These limits prevent a fuller interpretation of the observed safety counts.

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

The registry record establishes that a completed Phase 3 study was designed to examine persistence of antimicrobial activity on the skin after topical omiganan 1% gel or chlorhexidine 2%. It defines the primary endpoint as the change in mean skin bacterial count from baseline to 72 hours and describes the population intended for that analysis. It also gives limited safety counts for three labeled groups.

The record does not report numerical results for the primary endpoint. It therefore does not show the observed mean change in either treatment group, the difference between groups, or the uncertainty around any comparison. Without those results, it is not possible to characterize the magnitude or precision of the primary finding from the registry record. Completion of the study and a stated study purpose do not supply those missing outcome estimates.

Even if a numerical comparison were available, the non-randomized allocation and the record’s warning that arms are not like-for-like would remain important. A group contrast in this design could reflect differences between groups beyond treatment. The open-label status is also relevant, although the record does not say whether outcome assessors were masked or describe the laboratory procedures in sufficient detail to evaluate possible measurement effects.

The endpoint concerns bacterial counts on the skin at a specified timepoint. It is not itself a measure of infection prevention, infection treatment, or a clinical benefit to participants. The registry record’s condition label does not change the endpoint into a clinical infection outcome. The study’s objective and the laboratory endpoint should be interpreted within the scope of the measurements actually described.

The safety counts show no serious adverse events recorded among the listed participants at risk, alongside other adverse event counts in two of the groups. Those entries are not enough to establish comparative safety, particularly given the design and the absence of further event details. Death figures are not reported in the registry record.

In short, the posted record identifies what the study set out to measure, but it does not report the primary numerical results needed to evaluate the observed comparison. It supports a description of study methods and recorded safety entries, not a quantitative conclusion about the primary endpoint.

14. Why This Trial Matters Statistically

This trial illustrates why a clearly defined endpoint is only one part of statistical interpretation. The registry record specifies a mean change in log-scale skin bacterial counts and identifies the sampling times and analysis population. Those details clarify the intended measurement, but without the numerical endpoint results they cannot establish the observed size or precision of the comparison.

Its non-randomized allocation is especially important for clinical researchers reading comparative evidence. Random assignment is one method for making groups comparable in expectation; this study did not use it. The registry record itself cautions that the arms are not a like-for-like control comparison. A difference between groups, if reported, would need to be read alongside the possibility that group composition or other features contributed to it. The record does not describe an adjustment method that would address this concern.

The study also distinguishes between a laboratory measure and a clinical outcome. Skin bacterial counts can describe antimicrobial activity on the skin, while the endpoint as registered does not directly measure infections or their consequences. Keeping that distinction clear helps prevent claims from extending beyond the outcome assessed.

The record’s safety group entries demonstrate another interpretive point: event counts need context. Participants at risk, event definitions, follow-up, and study design all affect what can be concluded from counts. Here, serious adverse event counts are recorded for the three labeled groups, but deaths and detailed event information are not reported in the registry record.

Finally, the entry shows the limits of a registry record as an account of statistical evidence. It includes the endpoint definition and selected design information, but does not report the primary estimates or detailed analysis methods. A completed status does not replace those results. Recognizing what is documented and what remains unreported is essential to a careful evidence assessment.

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 most important limitation for interpreting the primary outcome is that its numerical results are not reported in the registry record. Group means, standard deviations, comparative estimates, confidence intervals, and p-values are not available in the record. As a result, the direction, magnitude, and precision of the primary comparison cannot be assessed.

The study was non-randomized, and the registry record explicitly warns that the arms are not a like-for-like control comparison. The record does not explain the assignment process or describe any adjustment for potential group differences. It is therefore not possible to determine from the record whether observed group differences could be separated from differences in participants or study conduct.

The design was open-label. Further masking details, including whether outcome assessors were blinded, are not reported in the registry record. The record also does not describe laboratory procedures or quality control in detail beyond its sampling description. These omissions limit assessment of how the bacterial-count measurements were obtained and handled.

The stated analysis population requires treatment exposure and data at 72 hours, but the number meeting that definition and the handling of missing data are not reported. The relation between enrollment of 30 and 25 participants at risk in each of the listed safety groups is also not explained in the registry record. The record does not provide enough information to reconcile those entries or establish the primary analysis sample size.

Other limitations include the absence of a reported statistical test or model, a detailed multiplicity plan, interim-analysis information, and the trial’s own sample-size justification. Death figures, detailed adverse event descriptions, and fuller follow-up information are not reported in the registry record. These gaps constrain interpretation of both efficacy-related and safety-related evidence.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Study of Antimicrobial Activity of Omiganan 1% Gel vs. Chlorhexidine 2% for Topical Skin Antisepsis in Healthy Adult Subjects — NCT00608959.
• Registry record last updated 2010-01-26; status last verified 2010-01.
• Results first posted 2010-01-25.
• 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 NCT00608959 as a completed Phase 3, parallel, non-randomized, open-label study. Its official title describes a single-center comparison of omiganan 1% gel and chlorhexidine 2% for topical skin antisepsis in healthy adult subjects. Enrollment is listed as 30, with start and primary completion dates recorded as 2008-05 and 2008-06.

The primary endpoint is change in mean skin bacterial counts from baseline to 72 hours, measured in log 10 CFU/cm sq. The stated analysis population includes participants who received at least one treatment and had data available at 72 hours. Numerical primary endpoint results and detailed analysis methods are not reported in the registry record.

Safety entries list 25 at risk in each of three groups and zero serious adverse events in each. Other adverse event counts are 0, 7, and 8. Deaths are not reported in the registry record. The record cautions that the non-randomized arms are not a like-for-like control comparison.