Comparative Antimicrobial Efficacy of Two Topical Acne Therapies for the Treatment of Facial Acne: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparative Antimicrobial Efficacy of Two Topical Acne Therapies for the Treatment of Facial Acne (NCT00841776), a randomized phase 4 study. The primary outcome is Median Change in Total Propionibacterium Acne (P.Acne) Counts.

2. Clinical Question

The clinical question focuses on a microbiological measure, not solely on visible acne lesions. Both therapies contain clindamycin, while the other ingredient differs. The registry also lists outcomes concerning clindamycin-resistant and erythromycin-resistant P. acne counts, total acne lesions, inflammatory lesion counts, and noninflammatory acne counts. Those additional measures give the stated comparison a broader scope, but the registry record does not report numerical findings for them.

The stated primary outcome is a median change in total P. acne counts. It is therefore important to distinguish the question about bacterial counts from the secondary questions about resistance and lesion counts. The record does not give a direction of change, a threshold for a clinically meaningful difference, or an estimate comparing the therapies. It also does not identify a particular population subgroup for the primary question.

3. Trial Design

The registry identifies this as a randomized, single-masked, parallel-group Phase 4 study, with enrollment of 54 participants. The two treatment groups are Duac gel and Ziana gel, and the adverse-event summaries list 27 participants at risk in each group. The registry does not specify who was masked, how the random allocation sequence was generated, or whether allocation was concealed before treatment assignment.

Duac is described as a clindamycin and benzoyl peroxide gel; Ziana is described as a clindamycin and tretinoin gel. These descriptions establish the treatment contrast recorded for the study, but details such as dose, application instructions, treatment adherence, and permitted co-interventions are not reported in the registry record. The record does not describe whether any participants discontinued or switched treatment.

The primary outcome is median change in total P. acne counts, assessed at baseline and Weeks 2, 4, 8, 12, and 16. The study purpose is described as determining the development of microbial resistance with use of either topical therapy. The registry lists six outcome measures in total, including the primary measure and secondary measures related to resistant P. acne counts and acne lesion counts.

The study status is completed. Its recorded start is 2007-08 and its primary completion is 2008-11. The sponsor is Stiefel, a GSK Company. Further details about recruitment, sites, participant characteristics, the trial protocol, and the rationale for the enrollment target are not reported in the registry record. The record labels the study design as parallel, but does not provide a more detailed description of how visits, specimen collection, or outcome assessments were conducted.

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 Median Change in Total Propionibacterium Acne (P.Acne) Counts, measured over Baseline, Weeks 2, 4, 8, 12, & 16.

The primary endpoint is the median change in total Propionibacterium acne (P. acne) counts, expressed in P. acne counts. The registry describes counting total colony-forming units and gives the assessment schedule as baseline and Weeks 2, 4, 8, 12, and 16. It identifies the median as the summary measure and the inter-quartile range as the measure of dispersion.

In general, a median describes the middle of an ordered set of measurements and is less influenced by unusually high or low values than a mean. The inter-quartile range describes the spread of the middle portion of those measurements. These are general interpretations of the named statistics; the registry record does not report the actual medians or inter-quartile ranges.

Microbial counts are relevant to the stated study purpose because the study concerns microbial resistance during topical acne treatment. The primary endpoint is total P. acne counts, however, and should not be conflated with the separate secondary outcomes on clindamycin-resistant or erythromycin-resistant P. acne counts. Nor is it the same as the lesion-count outcomes. Each addresses a different aspect of the study question.

The registry gives the assessment schedule and endpoint description but does not report the numerical outcome results, the exact calculation used to define change, or how measurements across the scheduled visits were compared. It also does not report a threshold for interpreting a change as clinically important. Consequently, the endpoint's role can be described, but the size and precision of any treatment contrast cannot be assessed from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The methods that can be described are limited to the design labels and outcome definitions in the registry record. The study is randomized, single-masked, and parallel-group, and the registry identifies it as Phase 4. These labels describe broad features of the design; they do not reveal the operational details of randomization, masking, or statistical analysis. Those details are not reported in the registry record.

What does randomization contribute?

In general, random allocation is intended to make treatment groups comparable with respect to factors that could influence outcomes, including factors that are not measured. It does not guarantee that groups will be identical, especially in a study with a modest enrollment. Randomization alone also cannot rule out bias from losses to follow-up, differences in adherence, outcome measurement, or selective reporting. The sequence-generation and allocation-concealment methods are not reported in the registry record, so their implementation cannot be evaluated.

What does single masking tell readers?

The registry classifies the study as single-masked, but does not identify which people were masked. In general, masking can reduce the influence of treatment knowledge on behavior or assessment. Its relevance depends on who knew assignments and how the outcomes were measured. The registry does not report masking procedures, whether masking was maintained, or whether it could have been apparent from the treatments.

How should the primary measure be understood?

The primary measure is median change in total P. acne counts, with inter-quartile range as the named dispersion measure. In general, a median is useful when measurements are skewed or include extreme values, while the inter-quartile range describes variability around the middle of the distribution. These summaries do not by themselves provide a treatment contrast or quantify its uncertainty. The record does not give the observed summary values, an estimate of the difference between groups, or a confidence interval.

The primary measurement schedule includes baseline and Weeks 2, 4, 8, 12, and 16. In general, repeated measurements from the same participant are related, so analyses of multiple visits need to account for that within-participant dependence if they combine observations. The registry does not report whether each visit was analyzed separately, whether a repeated-measures model was used, or which visit was designated for a primary treatment comparison. No statistical model, covariate adjustment, or method for handling baseline values is described.

Why can count data need special care?

In general, count outcomes may be skewed and may show greater variability than a simple model assumes. Over-dispersion means that the observed variability is larger than expected under a basic count model; ignoring it can make uncertainty estimates too small. This is a general statistical consideration, not a claim about the distribution of this study's P. acne counts. The record does not report count distributions, model assumptions, transformations, or a method selected to handle over-dispersion.

What does the record say about planning?

The enrollment recorded for the study is 54, with 27 participants listed at risk in each group in the adverse-event summary. The record does not report a sample-size justification or a planned target effect for the original trial. A planning illustration based on an observed effect is not the same as the trial's original design rationale or an estimate of observed power. The study's own design rationale is not reported in the registry record.

In general, a sample-size calculation depends on assumptions about the effect to detect, outcome variability, significance level, allocation, and analysis. If the effect is uncertain or estimated from the same study, a planning illustration is conditional on that estimate and its assumptions; it does not establish the probability that a completed study detected a true effect. The registry record does not report enough information to evaluate an original sample-size calculation.

The registry lists zero analyses and provides no numerical outcome estimates. Thus, methods such as model choice, confidence-interval construction, handling of missing values, and adjustment for multiple comparisons cannot be evaluated as applied to this trial. General statistical explanations do not fill in those unreported protocol or analysis details.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists six outcome measures: the primary total P. acne count measure and secondary measures concerning clindamycin-resistant P. acne, erythromycin-resistant P. acne, total acne lesions, inflammatory acne lesion counts, and noninflammatory acne counts. The primary measure also has multiple scheduled assessments, from baseline through Week 16. Testing several outcomes or visits can raise a multiplicity concern: in general, the more comparisons considered, the greater the chance that an apparently notable result occurs by chance if no adjustment or prespecified hierarchy is used.

The registry record does not report a multiplicity adjustment, a hierarchy among secondary outcomes, a designated primary visit for the repeated measurements, or an analysis plan specifying which comparisons would be emphasized. It is therefore not possible to determine how the study planned to control interpretation across outcomes and visits. The absence of a reported adjustment does not establish that none was used; the details are not reported in the registry record.

Missing-data methods and analysis populations are also not reported in the registry record. It does not specify whether the primary analysis was intended to include all randomized participants, participants who received treatment, or a subset with evaluable measurements. It does not describe how missing visits, withdrawals, or incomplete specimens were handled. These omissions limit assessment of potential bias and of how closely any analysis would represent the randomized comparison.

The registry lists zero analyses and no numerical outcome results. As a result, there are no reported analysis populations or missing-data procedures to evaluate against the intended study question.

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 1% reporting threshold.

Most frequent non-serious adverse event terms

The adverse-event summary lists 27 participants at risk in each treatment group. It records zero participants with serious adverse events in the Duac group and zero in the Ziana group. The registry also lists five participants with other adverse events in each group. These are group-level counts, not a description of the event types or their severity beyond the serious-versus-other distinction.

The record does not report the nature, timing, duration, or treatment relatedness of the other adverse events. It also does not clarify whether the counts refer to participants experiencing at least one event or to a particular event-counting convention. The listed figures should therefore be read as the registry's adverse-event summary, not as a complete clinical account of safety.

The death figures are not reported in the registry record. A recorded value of zero for serious adverse events is not proof that no events could occur, and the counts alone do not establish equivalence between treatments. In general, safety comparisons depend on the event definitions, observation period, completeness of reporting, and precision of the estimates. The registry does not provide confidence intervals or a comparative safety analysis.

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

The record establishes that a randomized, single-masked, parallel-group study compared Duac gel with Ziana gel in facial acne and specified median change in total P. acne counts as the primary outcome. It also documents the planned assessment schedule and lists secondary measures related to resistant bacteria and acne lesions. These registry entries describe the study's question and structure.

The registry information does not report numerical results for the primary or secondary outcomes. It therefore does not show whether total P. acne counts changed, how changes compared between groups, or how precise any comparison was. No conclusion about the direction or magnitude of a treatment effect can be drawn from the record as described. The same limitation applies to the outcomes on resistant P. acne counts and acne lesions.

The adverse-event summary reports zero participants with serious adverse events in each group and five participants with other adverse events in each group. Those counts do not replace a comparative analysis and do not describe the event types. Death figures are not reported in the registry record.

In general, a study's design and endpoint can be informative even when results are unavailable, because they clarify what investigators intended to measure. But design labels do not answer whether a treatment difference was observed, whether it was statistically precise, or whether it matters clinically. Those judgments require outcome estimates, uncertainty measures, and sufficient details about analysis and follow-up. Such information is not reported in the registry record.

The record should therefore be read as a description of a completed comparative study rather than evidence for a particular comparative outcome. The missing results do not imply that there was no effect or that the therapies had the same effect; they mean that the registry information does not permit those conclusions.

13. Why This Trial Matters Statistically

This study raises a useful statistical distinction between a clinical outcome and a microbiological outcome. The registry's primary measure is total P. acne counts, while its secondary outcomes include resistant P. acne counts and lesion counts. These measures address connected but nonidentical questions. Keeping them distinct is important when interpreting any eventual results: evidence about bacterial counts would not automatically answer a question about lesion counts or resistant bacteria.

The outcome schedule also illustrates why longitudinal design details matter. Measurements are specified at baseline and Weeks 2, 4, 8, 12, and 16. In general, repeated measurements can show how outcomes evolve over follow-up, but an analysis needs to define whether the focus is a particular visit, a trajectory, or another summary. The registry record does not report which approach was used.

The study compares two formulations that both contain clindamycin, with benzoyl peroxide in Duac and tretinoin in Ziana. That treatment structure makes the comparison specific to the recorded regimens; it is not a comparison of clindamycin with no clindamycin. The registry description alone does not establish how the difference in ingredients relates to any outcome.

Finally, the record illustrates the distinction between a completed study and a fully interpretable result. Enrollment and design information are available, but the registry lists zero analyses and does not report outcome estimates or their precision. For statistical interpretation, a clearly defined estimand, analysis population, handling of repeated measures and missing observations, and comparative uncertainty are all important. Their absence prevents a substantive treatment-effect assessment.

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 immediate limitation is the absence of numerical outcome results. The registry identifies the primary endpoint and several secondary outcomes but does not report estimates, dispersion values, confidence intervals, or p-values. With no reported outcome analysis, the comparative findings cannot be evaluated.

The primary endpoint is scheduled at multiple times, but the registry does not identify a primary visit or describe how the repeated measurements were analyzed. It also does not provide the exact change calculation, a treatment contrast definition, or a model. This prevents assessment of whether the analysis matched the stated endpoint and accounted appropriately for within-participant measurements.

Participant characteristics and eligibility details beyond moderate to moderately severe facial acne vulgaris are not reported in the registry record. The record also does not describe treatment adherence, attrition, missing specimens, concomitant treatments, or analysis populations. These details would be important for judging the comparability of the groups and the applicability of any results.

Although the design is labeled randomized and single-masked, the randomization method, allocation concealment, and identity of the masked parties are not reported. The registry also does not report a protocol, original sample-size justification, statistical analysis plan, or multiplicity strategy. Consequently, it is not possible to assess prespecification or determine how the multiple outcome measures and assessment times were handled.

The adverse-event summary is limited to aggregate counts. Event descriptions, relatedness, timing, duration, and death figures are not reported in the registry record. These omissions further restrict interpretation of the safety information.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Comparative Antimicrobial Efficacy of Two Topical Acne Therapies for the Treatment of Facial Acne — NCT00841776.
• Registry record last updated 2017-05-25; status last verified 2017-05.
• Results first posted 2010-07-23.
• 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

The registry describes a completed Phase 4 randomized, single-masked, parallel-group study of Duac gel and Ziana gel for moderate to moderately severe facial acne vulgaris. Enrollment is 54. The recorded study start is 2007-08 and primary completion is 2008-11. The sponsor is Stiefel, a GSK Company.

The primary outcome is median change in total P. acne counts, with inter-quartile range, assessed at baseline and Weeks 2, 4, 8, 12, and 16. Five secondary outcomes concern resistant P. acne counts and acne lesion counts. The registry lists zero analyses and does not report numerical outcome results, analysis methods, or the original sample-size justification.

The adverse-event summary lists 27 participants at risk in each group, zero with serious adverse events in each group, and five with other adverse events in each group. Death figures are not reported in the registry record. The available information describes the trial's design and intended measures but does not permit an assessment of comparative outcome estimates or their precision.