This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Pharmacokinetics of Retapamulin in Pediatric Subjects With Uncomplicated Skin Infections. (NCT00555061), a na phase 4 study. The primary outcome is Number of Participants With Measurable Plasma Concentrations, by Age Group.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00555061 |
| Phase | Phase 4 |
| Condition | Skin Infections, Bacterial |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 60 |
| Arms in the primary outcome | n/a |
| Lead sponsor | GlaxoSmithKline |
| Results posted | Yes |
2. Clinical Question
Population
Children aged 2 to 24 months with uncomplicated skin and skin structure infections. The registry describes secondarily-infected traumatic lesions, secondarily-infected dermatoses, and impetigo, including bullous and non-bullous forms.
Intervention
Topical Retapamulin Ointment, 1%, applied twice daily for 5 days. The study assessed pharmacokinetics, safety, and efficacy.
Comparator
There was no comparison group. The registry describes a single-group, open-label study and lists allocation as not applicable.
Primary question
How many participants, by age group, had measurable retapamulin plasma concentrations in samples collected on Day 3 or Day 4, usually 4 to 8 hours after the first dose of the day?
The primary endpoint concerns whether retapamulin was measurable in plasma at the sampling time. It is not a comparison of treatment with placebo or another medicine, and it does not directly measure improvement in skin infection. The registry also lists clinical success at follow-up by infection type and age, bacteriological success by baseline pathogen, and therapeutic response by age as secondary outcomes.
The registry record reports enrollment of 60 participants but does not report the primary endpoint counts by age group or numerical results for the listed secondary outcomes. It therefore does not show how often concentrations were measurable or how clinical and bacteriological outcomes were distributed. The treatment question can be framed as a pharmacokinetic description in this pediatric population, not as a comparative estimate of treatment effect.
3. Trial Design
This was a Phase 4, completed, open-label, non-comparative study sponsored by GlaxoSmithKline. The registry lists a single treatment group receiving Retapamulin Ointment, 1%. Treatment was topical, twice daily for 5 days. The study enrolled 60 participants, with a stated age range of 2 to 24 months, who had uncomplicated skin and skin structure infections.
The listed infection types include secondarily-infected traumatic lesions, secondarily-infected dermatoses, and impetigo, both bullous and non-bullous. The registry describes the study's aims as evaluating pharmacokinetics, safety, and efficacy. Its primary outcome was the number of participants with measurable plasma concentrations, reported by age group. The stated sampling timeframe was Days 3 to 4, 4 to 8 hours after the first dose of the day.
The design has no randomized allocation, masking, or concurrent control group. Consequently, it is suited to describing observations within the treated group, not estimating a treatment-versus-control contrast. Open-label status means masking was absent, but the registry does not describe how outcome assessment was conducted or whether any specific outcomes were assessed by personnel unaware of treatment.
The registry records a start date of 2007-09, primary completion in 2008-08, and completed status. It does not report the protocol details, the justification for the enrollment target, or the methods used to choose participants for pharmacokinetic sampling beyond stating that samples were collected randomly within the sampling window.
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
| Stage | Retapamulin Ointment, 1% |
|---|---|
| STARTED | 87 |
| COMPLETED | 78 |
| NOT COMPLETED | 9 |
Reasons for not completing this period:
| Reason | Retapamulin Ointment, 1% |
|---|---|
| Adverse Event | 3 |
| Protocol Violation | 1 |
| Lost to Follow-up | 2 |
| Withdrawal by Subject | 2 |
| Participant enrolled, but never treated | 1 |
Analysis population for the primary outcome, as defined in the registry: Pharmacokinetic (PK) Population: all participants who received at least one dose of study medication and who had PK samples taken. Seven participants did not have PK samples collected.
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.
| Characteristic | Unit | Retapamulin Ointment, 1% |
|---|---|---|
| Participants analysed | 86 | |
| Age, Continuous | months | 10.6 (SD 6.89) |
| Gender: Female | Participants | 32 |
| Gender: Male | Participants | 54 |
| Race/Ethnicity, Customized: African American/African Heritage | participants | 46 |
| Race/Ethnicity, Customized: White/Caucasian | participants | 36 |
| Race/Ethnicity, Customized: American Indian or Alaska Native | participants | 1 |
| Race/Ethnicity, Customized: Central/South Asian | participants | 1 |
| Race/Ethnicity, Customized: East Asian | participants | 1 |
| Race/Ethnicity, Customized: Missing | participants | 1 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Participants With Measurable Plasma Concentrations, by Age Group, measured over Days 3 to 4; 4 to 8 hours post-dose of the first dose of the day.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of participants with measurable plasma concentrations of retapamulin, reported by age group. A concentration was considered measurable relative to the assay's lower limit of quantification, which the registry gives as 0.5 ng/mL. This makes the endpoint a count based on whether a sample met a measurement threshold, rather than a continuous summary of the concentration values.
Pharmacokinetic sampling was described for Day 3 or Day 4, between 4 and 8 hours after the first daily dose. Samples were collected randomly within that window, with one sample taken at 3 hours and one at 11 hours after dosing. The registry does not report the number of measurable concentrations, the age-group counts, or any concentration summaries.
A threshold-based endpoint can describe whether drug was detectable at a specified time, but it does not by itself describe the full concentration profile, exposure over time, or clinical response. Those questions require additional measurements and analyses. The registry record does not report those details. The endpoint is relevant to the study's pharmacokinetic aim, but its interpretation is limited to the sampled time points and the stated quantification threshold.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The primary outcome is defined clearly enough to understand what was intended to be counted: participants with plasma retapamulin concentrations at or above the assay's stated lower limit of quantification, grouped by age. However, the registry record does not report the resulting counts. It also does not report age-specific denominators or concentration summaries. The primary endpoint's observed frequency and precision therefore cannot be evaluated from the registry information.
The timing matters to interpretation. Samples were taken on Day 3 or Day 4, usually 4 to 8 hours after the first dose of the day, with one sample at 3 hours and one at 11 hours. These observations concern selected post-dose sampling times. They should not be read as a complete description of concentrations throughout a dosing interval or across the full treatment course. The registry does not report individual sampling times, age-group definitions, or an analysis accounting for differences in sampling time.
The trial had one treatment group and no comparator. Any reported count would describe the participants sampled during retapamulin treatment; it would not estimate a contrast against another treatment or against no treatment. The study's non-comparative design also means that clinical outcomes, even if numerically reported, would not by themselves separate treatment-associated change from other influences. In this record, numerical results for the primary and listed secondary outcomes are not reported.
For safety, the registry's adverse-event record lists 1 serious and 11 other adverse events for the retapamulin group. The number of participants at risk for these summaries is not reported in that record, so the event counts cannot be interpreted as rates from the available information. Cough is listed among the serious-event terms at 1.2%. These entries are safety descriptions, not evidence of a causal relationship with treatment.
Overall, the registry record establishes the study question, treatment schedule, sampling threshold, and some design features, but it does not provide the outcome results needed to assess the observed pharmacokinetic or clinical findings. No conclusion about the frequency of measurable concentrations or the size and precision of clinical outcomes can be drawn from the posted results described in the record.
9. Statistical Methods Explained
What does a measurable-concentration count represent?
The primary outcome is a binary classification for each sampled participant: a concentration is either measurable under the stated assay threshold or it is not. The registry gives the lower limit of quantification as 0.5 ng/mL. A count of participants above that threshold is a straightforward descriptive summary, but it discards information about how far concentrations lie above the threshold. It also does not capture concentrations at times when no sample was taken.
In general, a threshold can make results easier to describe when the scientific question concerns whether a substance can be quantified. It also makes the conclusion depend on the assay and its limit. A result below the limit is not the same as a demonstrated absence of the substance; it indicates that the concentration was not quantified at or above that limit under the stated measurement procedure. The registry does not provide individual concentration values or further assay-performance information.
Why does the sampling schedule matter?
Pharmacokinetic measurements vary with the time between dosing and blood collection. The registry specifies sampling on Day 3 or Day 4, usually 4 to 8 hours after the first daily dose. It notes one sample at 3 hours and one at 11 hours. Because these measurements were not all taken at precisely the same stated time, an age-group comparison could be affected by differences in sampling times as well as age. The record does not report whether the analysis adjusted for sampling time or how the two samples outside the usual window were handled.
Random collection within a time window can spread sampling times across that window, but it does not ensure that every age group has the same timing distribution. The registry does not give the selection procedure, the group-specific sampling counts, or the actual timing distribution. These omissions restrict assessment of how representative the sampled concentrations are of the intended window.
What can confidence intervals add?
In general, a confidence interval expresses the uncertainty around an estimate under the assumptions of the analysis. For a proportion or count-based outcome, an interval can show how much uncertainty remains when the number of observations is limited. It does not guarantee that the estimate is free from bias, and it does not address missing measurements or design limitations by itself.
The registry record does not report a confidence interval or an inferential analysis for the primary endpoint. Without the age-specific event counts and denominators, the estimate and its precision cannot be reconstructed. The registry lists no analyses. No particular interval method, hypothesis test, or covariate-adjustment strategy is reported.
How should the single-group design be understood?
A single-group study can describe outcomes observed among participants receiving the study treatment. It cannot directly estimate a between-group treatment effect because no comparison group is present. General comparisons with external experience would require compatible populations, outcome definitions, and measurement procedures; the registry does not report such a comparison. The study is explicitly non-comparative, so the central statistical task is descriptive rather than a randomized treatment contrast.
The sample-size assumptions listed for planning illustrations describe a hypothetical two-arm calculation: a two-sided significance level of 0.05, equal allocation, a normal approximation, and an effect defined as a fraction of the observed effect. Those assumptions are not the design of this single-group study, and the record does not state that they were used to choose its enrollment. Such illustrations are planning exercises, not observed power, and cannot substitute for an analysis of the actual endpoint results.
Why are multiple outcomes and age groups relevant?
The registry lists 4 outcome measures, including the primary pharmacokinetic count and secondary clinical and bacteriological outcomes. Looking at multiple outcomes or subgroups can create multiple opportunities to notice apparently unusual patterns. In general, a statistical plan may address this through prespecified priorities, adjusted testing, or a cautious emphasis on estimation. The registry does not report a multiplicity strategy, a detailed analysis plan, or numerical outcome results. It is therefore not possible to determine how any multiplicity concerns were handled.
Age-group reporting is part of the primary outcome definition, but the record does not identify the age bands or report their counts. Subgroup estimates can be less precise when observations are divided among groups. Without group denominators, estimates, or intervals, neither the amount of uncertainty nor the consistency of results across age groups can be assessed.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists 4 outcome measures: the primary count of participants with measurable plasma concentrations by age group and secondary outcomes concerning clinical success, bacteriological success, and therapeutic response. It does not report a multiplicity plan, such as a hierarchy of tests or an adjustment for examining several outcomes or age groups. The registry also lists no analyses. As a result, the record does not show whether outcomes were treated as descriptive, whether formal hypothesis tests were planned, or how any multiplicity was addressed.
The pharmacokinetic population is defined as participants who received at least one dose and had pharmacokinetic samples taken. The registry states that 7 participants did not have pharmacokinetic samples collected. The reasons are not reported in the registry record. Since the primary endpoint depends on a sample, those participants cannot contribute a measured concentration under the stated population definition. The number included in the pharmacokinetic population and the endpoint denominators by age group are not reported.
The record does not describe how missing clinical or bacteriological outcome data were handled, whether other data were incomplete, or whether any sensitivity analyses were conducted. It also does not report an intention-to-treat analysis or other analysis-population definitions for those outcomes. These omissions matter because missingness can affect both the denominator and the interpretation of an observed count. The reported pharmacokinetic population definition clarifies who was eligible for that analysis, but it does not explain the missing samples or establish how missing outcomes were handled.
11. What the Result Does, and Does Not, Mean
The study asks a descriptive pharmacokinetic question in children aged 2 to 24 months receiving topical retapamulin. Its primary outcome is whether a sampled plasma concentration was measurable at the stated threshold and sampling times. The registry record gives the endpoint definition, but not the counts or concentration results. It therefore does not establish how many participants had measurable concentrations or how results varied by age.
The design also does not answer a comparative efficacy question. With one treatment group and no control arm, the study cannot estimate a treatment-versus-comparator difference. The registry lists clinical and bacteriological outcomes, but their numerical results are not reported in the registry record. No conclusion about comparative clinical benefit can be drawn from the information recorded.
Measurable plasma concentrations are not equivalent to clinical success, and the listed clinical outcomes are not substitutes for concentration measurements. Each outcome addresses a different question. The threshold-based pharmacokinetic endpoint does not describe the full concentration-time profile, and a concentration result alone would not establish a clinical outcome.
The safety record lists 1 serious and 11 other adverse events for the treatment group, while the number at risk is not reported. Cough is listed among serious-event terms at 1.2%. These entries describe what the registry records; they do not establish whether an event was caused by treatment. More broadly, the absence of a comparator and the missing outcome denominators limit interpretation of safety counts.
Thus, the registry record provides useful details about the study population, treatment schedule, endpoint definition, and sampling window, but does not provide enough outcome data to quantify the observed results or their precision. That is a limitation of what can be concluded from this record, not evidence for or against a treatment effect.
12. Why This Trial Matters Statistically
This trial is statistically notable for the distinction between measuring drug exposure and evaluating a clinical treatment effect. Its primary endpoint is a count based on a quantification threshold, while the study has no comparison group. Those features call for descriptive interpretation: the endpoint concerns measurable plasma concentrations in sampled participants, not a randomized contrast or a direct measure of infection resolution.
The sampling window is also central. Concentrations depend on when samples are taken relative to dosing, and the registry records sampling on Day 3 or Day 4, usually 4 to 8 hours after the first dose of the day. It also notes samples at 3 hours and 11 hours. Describing the time window is essential to defining what the result would represent; it cannot be treated as a measurement at one uniform time without further information.
The record demonstrates why endpoint definitions and analysis populations need to be read together. The pharmacokinetic population requires both treatment exposure and sample collection, while 7 participants had no pharmacokinetic samples collected. Yet the registry does not report the resulting analysis denominator or the primary outcome counts. Even a precisely defined endpoint cannot be interpreted quantitatively without its observed numerator and denominator.
Finally, planning calculations need to match the actual design. The listed planning assumptions describe an illustrative two-arm calculation, whereas the study itself is single-group and non-comparative. Such illustrations do not constitute observed power, nor do they show how the original enrollment target was justified. The registry record does not report that justification. These distinctions help prevent hypothetical planning quantities from being mistaken for results or for evidence of a treatment comparison.
13. 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 main limitation for interpreting the registry results is that numerical results for the primary endpoint are not reported. Age-specific counts, denominators, concentration summaries, and measures of precision are absent. Although 60 participants were enrolled, the registry states that 7 had no pharmacokinetic samples collected and does not report the number analyzed for the primary endpoint. The reasons for missing samples are not reported in the registry record.
The study has a single treatment group, no masking, and no comparator. It can describe observations in the treated group but cannot provide a randomized comparison. The record does not report the protocol, a statistical analysis plan, an enrollment-target justification, interim analyses, or the handling of missing clinical outcome data. It also does not provide numerical results for the listed clinical and bacteriological outcomes or describe how multiple outcomes and age groups were handled analytically.
For the primary endpoint, sampling was scheduled on Day 3 or Day 4 within a post-dose window, but actual timing distributions and age-group definitions are not reported. The two noted samples outside the usual 4 to 8 hour window may have different timing contexts; the record does not describe their handling. The threshold-based outcome also does not provide a full concentration profile.
The safety entries lack reported denominators for participants at risk. Accordingly, the recorded event counts cannot be interpreted as rates from the information available. These limitations concern the details and results reported in the registry; they should not be filled by assumptions about the study's conduct or analysis.
14. Related Tutorials
15. Related Statistical Calculators
16. Sources
- ClinicalTrials.gov: Pharmacokinetics of Retapamulin in Pediatric Subjects With Uncomplicated Skin Infections. — NCT00555061.
- Registry record last updated 2016-12-28; status last verified 2016-11.
- Results first posted 2010-04-30.
- 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.
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17. Record Summary
This completed Phase 4 study enrolled 60 children aged 2 to 24 months with uncomplicated skin and skin structure infections. It was open-label, non-comparative, and single-group, with treatment using topical Retapamulin Ointment, 1%, twice daily for 5 days. The registry records a start date of 2007-09 and primary completion in 2008-08.
The primary outcome was the number of participants with measurable plasma concentrations by age group. Samples were collected on Day 3 or Day 4, usually 4 to 8 hours after the first dose of the day; the stated lower limit of quantification was 0.5 ng/mL. Seven participants did not have pharmacokinetic samples collected.
The registry does not report the primary endpoint counts, age-group denominators, concentration summaries, or numerical results for the listed secondary outcomes. It also does not report the analysis plan, multiplicity handling, or reasons for missing samples. The available record therefore describes the design and endpoint but does not support quantitative interpretation of the study's outcome results.