Mepolizumab in Chronic Obstructive Pulmonary Diseases (COPD) With Eosinophilic Bronchitis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Mepolizumab in Chronic Obstructive Pulmonary Diseases (COPD) With Eosinophilic Bronchitis (NCT01463644), a randomized phase 3 study. The primary outcome is Percentage Decrease of Sputum Eosinophils From Baseline to End of Therapy (6 Months).

2. Clinical Question

The central clinical question is whether mepolizumab changes sputum eosinophils in patients with fixed airflow obstruction described as COPD and eosinophilic bronchitis. The registry’s stated hypothesis asks whether mepolizumab decreases sputum eosinophils. The trial compares mepolizumab with placebo, and the primary outcome is the percentage decrease from baseline to the end of therapy at 6 months.

3. Trial Design

The registry describes a randomized, quadruple-masked, parallel-group phase 3 clinical trial of mepolizumab and placebo. Random allocation is intended, in general, to reduce systematic differences between treatment groups at the point of assignment. Masking can reduce the influence of treatment knowledge on participant experiences, care, or outcome assessment; the registry labels the masking as quadruple but does not identify the masked roles in the record. Further details of the randomization or masking procedures are not reported in the registry record.

The stated enrollment was 18. The posted primary outcome lists 8 participants in the mepolizumab group and 10 in the placebo group. These are the group sizes attached to the outcome values, and should not automatically be treated as the size of every analysis population. The record does not explain whether all randomized participants contributed to the primary outcome or how participants were handled if outcome data were unavailable.

The trial status is completed. The record gives a start of 2012-01 and primary completion of 2015-08. The primary outcome timeframe is 6 months, measured from baseline to the end of therapy. These dates and the outcome timeframe describe different aspects of the record; they do not establish how long each participant was followed beyond the stated outcome measurement.

The listed interventions are mepolizumab and placebo. Arm descriptions are blank, so dose, treatment schedule, adherence procedures, and any accompanying care are not reported in the registry record. The record identifies COPD and bronchitis among the conditions and describes the target population as having COPD with eosinophilic bronchitis. It does not report further eligibility criteria, recruitment setting, or participant demographic characteristics.

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: Eligible adult patients were enrolled by baseline post-bronchodilator FEV1/VC\<70% and post bronchodilator FEV1 \<60% predicted), greater than 10 pack years and sputum eosinophils greater than/equal to 3%. Patients were then randomized to either mepolizumab 750 mg every 4 weeks (Q4W) or matched placebo in a 1:1 ratio.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Percentage Decrease of Sputum Eosinophils From Baseline to End of Therapy (6 Months), measured over 6 months.

The primary endpoint is the percentage decrease in sputum eosinophils from baseline to the end of therapy at 6 months. Sputum eosinophils are the measured biological feature of interest: the trial’s hypothesis focuses on whether mepolizumab decreases this measure in patients with COPD and eosinophilic bronchitis. The registry describes the outcome as a mean, with standard deviation as its measure of spread. It also states that a larger number represents a greater reduction in sputum eosinophils.

The posted group means are 11.28 for mepolizumab and 7.07 for placebo. The corresponding standard deviations are 6.6 and 11.49. These values describe the groups separately; the record does not provide an estimable two-arm comparison for this continuous outcome. No confidence interval or inferential test result for the between-group effect is reported in the registry record.

The registry’s title calls the outcome a percentage decrease, while its description refers to absolute changes in percent sputum eosinophil counts from baseline to 6 months. This wording should be kept in mind when interpreting the measure. The outcome is a biological measure at the stated follow-up point, not itself a count of exacerbations or a measure of symptoms, function, or quality of life.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the mean describe?

The primary outcome is recorded as a mean, a summary of the observed values in each group. The posted means are 11.28 for mepolizumab and 7.07 for placebo. The registry defines larger numbers as greater reductions in sputum eosinophils. A group mean provides a compact description of the observations, but it does not show whether individual participants had similar changes or widely varying ones. The standard deviations, 6.6 and 11.49 respectively, describe within-group variability around those means.

General statistical explanation: a standard deviation describes the spread of individual measurements, whereas a standard error or confidence interval describes uncertainty in an estimated quantity. The registry gives standard deviations, not a confidence interval for the difference between groups. A confidence interval for a treatment contrast would ordinarily help readers judge both the direction and precision of that contrast. It is not reported in the registry record.

Why is the two-arm comparison important?

The trial’s question is comparative: it asks whether the outcome differs between mepolizumab and placebo. Group-specific means alone do not provide a complete inferential comparison. A suitable comparison would need to define the effect being estimated and its uncertainty, and would need to account for the analysis population and any unavailable outcome data. The registry flags the continuous two-arm comparison as having values missing or not estimable. The reason for that status and the method intended for the comparison are not reported in the registry record.

General statistical explanation: the choice of comparison method can depend on the outcome’s distribution, the analysis plan, and features such as baseline measurements or repeated observations. If measurements are unusually skewed or contain influential values, assumptions of a simple normal model may be questionable. The record does not report diagnostic checks, transformations, or an adjusted analysis, so none should be presumed.

What does randomization contribute?

The record identifies the trial as randomized. In general, random allocation aims to create treatment groups that are comparable in expectation with respect to measured and unmeasured characteristics. It does not guarantee exact balance in a particular trial, especially when the enrollment is 18. The registry does not provide baseline characteristics or a detailed account of the allocation procedure, so the achieved balance cannot be assessed from the posted record. The trial is also described as parallel-group and quadruple-masked. The roles masked and the operational details are not reported in the registry record.

How should planning calculations be read?

The registry’s planning illustration is described as using the observed effect, a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. The record distinguishes this illustration from the trial’s own design. Any sample sizes generated by such an illustration are planning scenarios, not evidence about the number of participants actually enrolled or the probability that the completed trial detected an effect. They are not observed power. The registry does not report the trial’s original sample-size justification or design assumptions.

General statistical explanation: planning calculations depend on assumptions about the target effect, variability, allocation, and analysis method. If those assumptions differ from the eventual data or intended analysis, the calculation may not describe the study’s design or its achieved precision. The illustration should therefore be understood as a hypothetical planning exercise, not as a substitute for an inferential result.

What can be inferred from the posted summaries?

The means and standard deviations permit a descriptive reading of each group’s outcome summary. They do not permit a defensible reconstruction of the sponsor’s intended comparison when the record says that comparison is not estimable. General statistical explanation: an unadjusted recalculation from summary statistics, when one is explicitly available, can differ from an analysis that accounts for the trial’s prespecified methods or data structure. No recalculated comparison is posted for this endpoint, and the sponsor’s own analysis is not reported in the registry record. The displayed descriptive statistics should not be converted into a standalone claim of efficacy or lack of efficacy.

The secondary outcome, proportion of patients with a major exacerbation, is listed without a posted result. The number of analyses is recorded as 0. The statistical model, handling of missing observations, analysis population, and approach to multiplicity are not reported in the registry record. These omissions prevent readers from assessing whether the primary and secondary questions were analyzed under a common plan or how uncertainty across outcomes was handled.

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("Mepolizumab", "Placebo")
n   <- c(8, 10)
m   <- c(11.28, 7.07)
sp  <- c(6.6, 11.49)
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  Mepolizumab  8  11.280  6.600  5.762  16.798
CARM  Placebo  10  7.070  11.490  -1.149  15.289

11. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary sputum eosinophil outcome and one secondary outcome, the proportion of patients with a major exacerbation. It does not report a multiplicity strategy, such as whether the primary outcome was treated as the sole confirmatory test or whether any adjustment across outcomes or analyses was planned. The number of analyses is recorded as 0. The analysis plan and its relationship to the listed outcomes are not reported in the registry record.

The continuous primary comparison is flagged as having values missing or not estimable for a two-arm comparison. That statement establishes that the comparison is unavailable in the registry record, but does not explain whether the issue arose from missing observations, a calculation problem, or another cause. The group means and standard deviations are posted, yet the record does not give the number contributing to each summary beyond the listed group sizes, nor does it describe how unavailable outcomes were handled.

The analysis population is not reported in the registry record. It is therefore unclear whether the outcome summaries represent all randomized participants, participants with observed endpoint data, or another defined group. The record also does not describe imputation, sensitivity analyses, exclusions after randomization, or a missing-data assumption. These details matter because conclusions can depend on which participants are included and how unavailable measurements are treated.

No result for the listed secondary outcome is posted. Without a result and a stated multiplicity plan, readers cannot evaluate that outcome’s estimate or its inferential status in relation to the primary question. The absence of these analysis details should not be filled in by assuming standard trial practice.

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 3% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: myocardial infarction (12.5%), c3 distal humeral fracture with a left trochlear fracture (12.5%), copd exacerbation - hospital admission (10.0%).

The registry reports serious adverse event figures separately for the two groups. In the mepolizumab group, 2 participants were affected among 8 at risk; in the placebo group, 1 was affected among 10 at risk. Other adverse events affected 4 participants among 8 at risk in the mepolizumab group and 4 among 10 at risk in the placebo group. No deaths are reported in either group.

The serious-event terms listed include myocardial infarction at 12.5%, C3 distal humeral fracture with a left trochlear fracture at 12.5%, and COPD exacerbation with hospital admission at 10.0%. The registry record does not explain the denominator or counting convention behind each term’s percentage, so those percentages should not be interpreted as participant-level risks without further information. The list also does not establish whether a term occurred once or more than once, or whether events overlap within participants.

These figures are descriptive safety summaries. The record does not provide a comparative statistical analysis, detailed event narratives, timing, attribution, or a complete discussion of severity and recurrence. Counts from groups of this size cannot by themselves establish whether an event was caused by an intervention or whether the groups differ reliably in safety. The registry record does not report further interpretive analysis of these events.

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

The record documents a randomized comparison of mepolizumab and placebo in COPD with eosinophilic bronchitis, with sputum eosinophils as the primary biological outcome. It reports mean decreases of 11.28 and 7.07, respectively, at the stated 6-month endpoint, and gives a standard deviation for each group. Under the registry’s definition, a larger number represents a greater reduction. These summaries describe the posted group values and their within-group spread.

They do not establish the size or precision of a treatment-versus-placebo effect. The registry says a two-arm comparison for the continuous outcome is missing or not estimable, and no confidence interval or inferential test result is reported. The descriptive ordering of the means should not be treated as proof that one intervention changed the outcome more than the other in the population of interest. Nor does the record support a conclusion that the interventions are equivalent.

The primary measure concerns sputum eosinophils. It is not a direct result for symptoms, lung function, exacerbation frequency, hospitalization, or quality of life. Although the record lists the proportion of patients with a major exacerbation as a secondary outcome, it does not post a result for that outcome. The study rationale discusses exacerbations, but that description cannot replace outcome data.

The safety counts provide a limited descriptive account of serious and other adverse events, along with several listed serious-event terms. They do not, on their own, establish causation or a reliable comparative safety profile. The record lacks details that would be needed to understand the percentages attached to the event terms and does not provide an inferential safety comparison.

Accordingly, the registry supports a description of the trial design, endpoint, group summaries, and reported adverse-event counts. It does not support a firm conclusion about the comparative effect of mepolizumab on the primary endpoint or the secondary exacerbation outcome. The absence of an estimable primary comparison and the limited analysis details are central to interpreting what the posted results can establish.

14. Why This Trial Matters Statistically

This trial is statistically informative as an example of the difference between reporting group summaries and reporting a usable comparative estimate. The primary endpoint has a mean and standard deviation for each group, but the registry marks the two-arm continuous comparison as missing or not estimable. Without that comparison, readers lack the estimate and uncertainty most directly connected to the randomized question.

The distinction matters because a clinical trial is designed to compare assigned groups, not merely to describe each one separately. Randomization can support a causal comparison when the trial’s allocation, follow-up, outcome measurement, and analysis are appropriately handled. The registry identifies randomization and masking, but does not report enough analytic detail to judge how the primary contrast was formed or why it is unavailable.

The record also illustrates why an endpoint’s definition and direction should be read carefully. The outcome is described as a percentage decrease in sputum eosinophils, and the registry says larger values indicate greater reduction. That convention gives descriptive direction to the means, but does not supply evidence about precision or clinical importance. The secondary outcome of major exacerbation is listed without a result, so the rationale concerning exacerbations should not be confused with a posted finding.

Finally, the record demonstrates the limits of small-group safety summaries. It reports participants affected by serious and other adverse events and lists selected serious-event terms, but does not provide detailed event-level context or inferential comparisons. A transparent statistical interpretation keeps those descriptive details separate from conclusions that the record cannot establish.

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 registry reports enrollment of 18, with primary outcome group sizes of 8 for mepolizumab and 10 for placebo. Those figures limit the amount of information available for assessing variability and comparative precision. The record does not provide a confidence interval or an inferential test for the primary outcome, and it explicitly flags the two-arm comparison as missing or not estimable. The reason for that status is not reported in the registry record.

The trial’s population is described broadly as COPD with eosinophilic bronchitis and fixed airflow obstruction. Further eligibility criteria and participant characteristics are not reported in the registry record. This limits assessment of how closely the participants reflect other populations with COPD. Arm descriptions are blank, and treatment dose, schedule, adherence, and related treatment details are not reported.

The outcome description has a wording distinction: the title refers to a percentage decrease, while the description refers to absolute changes in percent sputum eosinophil counts. The record says a larger number represents a greater reduction, but provides no further clarification of the calculation or scale. Baseline group summaries and individual observations are also not reported, so the underlying distributions and baseline comparability cannot be assessed.

The secondary major-exacerbation outcome has no posted result. The analysis population, statistical model, missing-data approach, multiplicity plan, and original sample-size justification are not reported in the registry record. Safety reporting is limited to group counts and selected event terms; detailed timing, attribution, recurrence, and interpretation are not reported. These limitations restrict both efficacy and safety conclusions from the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Mepolizumab in Chronic Obstructive Pulmonary Diseases (COPD) With Eosinophilic Bronchitis — NCT01463644.
• Registry record last updated 2025-09-24; status last verified 2024-11.
• Results first posted 2025-09-24.
• 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 describes a completed, randomized, quadruple-masked, parallel-group phase 3 trial of mepolizumab versus placebo in COPD with eosinophilic bronchitis. Enrollment was 18, and the primary outcome was the mean percentage decrease in sputum eosinophils from baseline to 6 months.

The posted means were 11.28 for mepolizumab and 7.07 for placebo, with standard deviations of 6.6 and 11.49. The registry marks the continuous two-arm comparison as missing or not estimable, and reports no confidence interval or inferential test result. The listed secondary outcome, proportion of patients with a major exacerbation, has no posted result.

Serious and other adverse-event counts are reported by group, with no deaths reported. The registry does not provide the analysis plan, analysis population, missing-data method, or multiplicity strategy. The available record therefore supports descriptive reporting but does not establish a precise comparative effect for the primary question.