A Randomized Placebo-Controlled Study of the Neurokinin-1 (NK1) Receptor Antagonist Serlopitant Prurigo Nodularis (PN): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Randomized Placebo-Controlled Study of the Neurokinin-1 (NK1) Receptor Antagonist Serlopitant Prurigo Nodularis (PN) (NCT02196324), a randomized phase 2 study. The primary outcome is Average Visual Analog Scale at Baseline.

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group, placebo-controlled phase 2 study of serlopitant in subjects with prurigo nodularis. The registry lists the study as completed. The recorded start date is 2014-07-09, and the primary completion date is 2016-05-27. Enrollment is listed as 128. The active arm received serlopitant 5 mg tablets, and the comparator arm received placebo tablets.

The record describes the study as double-blind and identifies quadruple masking. These labels indicate that masking was part of the design, but the registry record does not specify which groups of people were masked, how masking was maintained, or how treatment assignments were generated. The allocation method is identified as randomized; further operational details are not reported in the registry record.

The primary analysis population is described as the Intent-to-treat population consisting of randomized participants who were treated, analyzed according to the treatment to which they were randomized. The primary measure has results for 63 placebo participants and 64 serlopitant participants. The record’s total enrollment and the arm counts for this particular measure refer to different reported quantities; the registry does not explain the difference in their coverage.

The primary measure is average Visual Analog Scale itch severity at baseline. A secondary measure, the Patient Benefit Index for patients with pruritus, is recorded at Week 8 / End of Treatment, with results for 61 placebo participants and 63 serlopitant participants. The registry also lists additional secondary outcomes addressing itch, burning, stinging, global assessment, quality of life, and other symptom measures. Detailed dosing schedules, visit schedules beyond the stated timeframes, and the full protocol are not reported in the registry record.

The study summary describes the purpose as assessing safety and effectiveness relative to placebo. That stated purpose should be distinguished from the specific primary measure posted in the results: a baseline value does not itself quantify a treatment effect. The registry record does not report the original design assumptions, the rationale for the enrollment target, or a full statistical analysis plan.

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: This study consisted of a screening period of up to 4 weeks. All the assessments were done at screening as per the schedule of assessment.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The Intent-to-treat (ITT) population - all randomized participants who were treated. This population was analyzed based upon the treatment to which participants were randomized.

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.

Population: Intent-to-treat (ITT) population - all randomized participants who were treated. This population was analyzed based upon the treatment to which participants were randomized. Of the 128 randomized participants, 127 received study drug (63 placebo, 64 serlopitant) and comprised the ITT population.

6. Primary Endpoint

The registry lists the primary outcome as Average Visual Analog Scale at Baseline, measured over At Baseline.

The primary measure is Average Visual Analog Scale at Baseline. It captures participants’ average itch over the past 24 hours using a 10-cm horizontal line. Participants mark a position between no itch at 0 cm and the worst imaginable itch at 10 cm. The record states that higher values indicate worse outcome. A visual analog scale turns a subjective symptom into a continuous measure that can represent gradations in severity rather than limiting responses to a few categories.

Baseline measurement can describe the symptom burden of the groups at study entry and help readers assess whether the reported groups began with similar average scores. The posted means are 7.92 for placebo and 7.88 for serlopitant, with standard deviations of 1.63 and 1.311, respectively. Those summaries describe variation among participants as well as the group averages.

However, a baseline score is not a follow-up response, a change from baseline, or a comparison of symptom improvement during treatment. For that reason, the primary measure as posted cannot establish whether itch changed after randomization or whether changes differed between groups. The registry record does not report a primary outcome timepoint after treatment or a primary change-from-baseline result. The secondary outcomes include measures recorded later in the study, but they are distinct from this baseline primary measure.

7. Results Posted in the Registry

• Serlopitant: mean 7.88 versus 7.92 on control; difference -0.04 (95% CI -0.55 to 0.47), standardized effect d = -0.03; z-test p = 0.879.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Patient Benefit Index, Version for Patients With Pruritus (PBI-P)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Serlopitant: mean 1.16 versus 0.81 on control; difference 0.35 (95% CI -0.02 to 0.72), standardized effect d = 0.34; z-test p = 0.061.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Serlopitant and the control. The interval gives the range of effects that remain compatible with the data.

The registry lists secondary outcomes spanning itch severity, burning, stinging, patient global assessment, quality of life, and patient benefit. These measures address related but not identical aspects of prurigo nodularis and patient experience. A pattern across different domains can help describe the range of outcomes assessed, but it should not be reduced to a single claim unless the analysis plan defines how those outcomes are to be combined or prioritized.

The posted Patient Benefit Index result at Week 8 / End of Treatment gives one later study comparison, whereas the primary Visual Analog Scale result is explicitly a baseline measure. These results therefore answer different questions and should not be treated as competing estimates of the same endpoint. The secondary result does not supply the missing post-treatment primary comparison.

Secondary outcomes can provide useful context, but they generally carry less confirmatory weight when there are many outcomes and no reported plan for controlling multiplicity. Testing several outcomes increases the chance that at least one may look notable by chance, even if there is no underlying difference. The registry lists 17 outcome measures and 13 analyses, but does not report whether a prespecified hierarchy, adjustment, or other multiplicity strategy was used. Individual unadjusted secondary results should consequently be treated as exploratory evidence rather than stand-alone confirmation.

Different measures can also vary in their scale, timing, and interpretation. A patient-reported benefit index is not interchangeable with an itch-intensity rating or a quality-of-life measure. Their results can be considered together for coherence, but the record does not report a formal synthesis across endpoints. Nor does the listing of an outcome establish that a result was available for every participant or that every analysis was prespecified.

The overall secondary-outcome pattern should therefore be read alongside the endpoint definitions, timepoints, uncertainty intervals, and missing-data information. These details affect how much weight to give any one result. In the absence of a reported multiplicity plan and fuller analysis documentation, secondary findings can suggest questions for further evaluation but do not resolve the limitations of the primary result recorded at baseline.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Number of Participants With Improvement in Pruritus as Reported on Verbal Rating Scale (VRS) - Pruritus
• Number of Participants With Improvement in Burning as Reported on Verbal Rating Scale (VRS) - Burning
• Number of Participants With Improvement in Stinging as Reported on Verbal Rating Scale (VRS) - Stinging
• Worst Visual Analog Scale (VAS)
• Number of Participants With Improvement in Pruritus as Reported on Patient Global Assessment (PGA)
• Numeric Rating Scale (NRS)
• Dermatology Life Quality Index (DLQI)
• Pruritus-specific Quality of Life (ItchyQoL)

9. Statistical Interpretation

10. Statistical Methods Explained

The primary result is a comparison of means for a continuous outcome. A mean describes the average score in a group, while the standard deviation describes the spread of participant scores around that average. The primary outcome’s scale runs from 0 cm, no itch, to 10 cm, the worst imaginable itch. Higher values indicate worse symptoms. The registry reports a mean and standard deviation for each treatment group at baseline.

What does the mean difference represent?

The unadjusted mean difference is expressed as the serlopitant group mean minus the placebo group mean. For the baseline Visual Analog Scale, the difference is -0.04. A negative value means that the average score was numerically lower in the serlopitant group at baseline; a positive value would mean it was higher. Because the outcome is a baseline measure, this comparison describes the groups’ observed starting values. It is not an estimate of change attributable to treatment.

In a randomized trial, baseline descriptions help readers understand the enrolled groups, but randomization does not turn a baseline contrast into an intervention effect. Treatment effects are usually assessed using a measure collected after treatment begins, a change from baseline, or a model that compares outcomes over time. The registry record does not report such a primary comparison for this measure.

How should the confidence interval be read?

A confidence interval gives a range of values compatible with the observed data under the method’s assumptions. It conveys uncertainty in the estimated difference, rather than giving a probability that the true effect lies in a particular interval. The primary interval, -0.555 to 0.475, includes zero and allows values on either side of no mean difference. Its width reflects the limited precision of the estimate; it does not establish that the groups are exactly equal.

The p-value is another summary of the data under a specified statistical model. The primary unadjusted p-value is 0.879. It is not the probability that the null hypothesis is true, nor does it measure the size or clinical importance of a difference. Here, both the interval and p-value concern the baseline group contrast, so neither provides evidence about a post-treatment effect.

What does unadjusted mean in this context?

An unadjusted comparison uses the posted group summaries without controlling for additional covariates or accounting for other outcomes. This can be useful as a transparent descriptive comparison. It may differ from a trial’s planned model, which could account for baseline values, stratification factors, repeated measurements, or other design features. The registry record does not report a full primary analysis model, adjustment variables, or the original statistical analysis plan. Consequently, the posted unadjusted calculations should not be assumed to reproduce every analysis conducted by the study sponsor.

For the secondary Patient Benefit Index result, the registry reports a two-sided t-test on final values. A t-test compares group means while estimating uncertainty from the groups’ variability and sample sizes. The posted registry analysis reports a mean difference of 0.35, a 95% confidence interval from -0.02 to 0.72, and p = 0.062. The unadjusted recalculation from the posted summary statistics gives a mean difference of 0.35 and an interval from -0.016 to 0.716. These values express the same general uncertainty pattern; the registry’s reported analysis and the summary-statistic recalculation are distinct presentations.

Why can dispersion matter?

Standard deviation describes participant-to-participant variation. When outcomes vary considerably within groups, a difference between group means is harder to estimate precisely unless the study has enough observations. Conversely, less within-group variation can make a given mean difference easier to distinguish from random variation. This is a general statistical principle; it does not imply that a particular source of variability was present in this trial.

Over-dispersion is a general concern when data vary more than a model assumes. It is especially relevant to count outcomes or some categorical models, where the variance may exceed a model’s expected variance and uncertainty can be underestimated. The posted primary outcome is continuous and summarized with means and standard deviations; the registry record does not report an over-dispersion assessment. No conclusion about over-dispersion should be drawn from these summaries.

What is the role of the analysis population?

The record defines the primary population as randomized participants who were treated, analyzed according to randomized assignment. This description identifies the population used for the primary measure, but it is not identical to a statement that every randomized participant contributed a value at every visit. The primary arm counts are 63 and 64. For the secondary Patient Benefit Index at Week 8 / End of Treatment, the arm counts are 61 and 63. The registry record does not explain all reasons for the difference in available counts or describe how missing measurements were handled.

Statistical methods depend on both the outcome and the analysis question. A baseline mean comparison is descriptive of starting values; a final-value comparison addresses a later measurement; and a change-score analysis addresses within-person change and between-group differences in that change. These quantities are not interchangeable. The record’s primary outcome is the baseline Visual Analog Scale, while the Patient Benefit Index result is secondary and recorded at Week 8 / End of Treatment.

The registry lists 17 outcome measures and 13 analyses. The multiplicity plan, including whether a hierarchy or adjustment procedure was specified, is not reported in the registry record. When several outcomes are examined, interpreting individual p-values as if only one test had been done can overstate the strength of evidence. This general concern is one reason secondary findings are usually interpreted in the context of the full set of planned analyses.

11. Confidence Intervals and Precision

Precision concerns how narrowly the data estimate a quantity. For a mean difference, the confidence interval is a useful expression of precision: a narrower interval indicates less uncertainty under the chosen method, while a wider interval permits a broader range of plausible values. Precision is distinct from whether a result is statistically significant or clinically important.

The primary mean difference is -0.04, with a confidence interval from -0.555 to 0.475. Because the interval includes zero, the posted data are compatible with no difference in average baseline itch score, as well as with differences in either direction. The interval also shows that the estimate is not precise enough to identify a single value. This interpretation is limited to the baseline comparison and should not be transferred to a treatment effect.

The secondary Patient Benefit Index comparison has a recalculated interval from -0.016 to 0.716. The registry-reported interval is -0.02 to 0.72. Both include zero, so the reported data do not rule out no difference under the corresponding analysis. The interval also allows positive differences, and its width conveys uncertainty about the size of any group contrast. The registry reports a two-sided test for this secondary comparison, but statistical uncertainty remains important even when an estimate is directionally positive.

Confidence intervals do not account automatically for every source of uncertainty. Their interpretation depends on the analysis method, the definition of the outcome, and the completeness of the data. The registry record does not report enough detail to assess all model assumptions or the handling of missing observations. The primary measure’s baseline timing is also a substantive limitation: greater precision in a baseline contrast would still not establish a treatment-period effect.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They are illustrations based on the observed effect, with alternative rows using 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. The curve represents the same planning relationship between the assumed effect and the participant requirement. These are hypothetical planning calculations, not observed power for the completed trial.

The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to the stated fraction of the observed effect. The original trial’s own design assumptions and sample-size justification are not reported in the registry record, so these planning illustrations should not be read as the rationale for its enrollment.

The 80% power column means the estimated number of participants per arm under those assumptions for a design with an 80% chance of detecting the specified effect if that effect is the true one. The 90% power column uses a higher target chance under the same planning framework. Power is a property of a proposed design under assumptions; it is not the probability that the trial conclusion is correct.

Smaller effects are harder to distinguish from random variation and require more participants for the same target power, all else held constant. Since the planning effect is based on the observed effect for a baseline measure, the resulting sample sizes are mathematical illustrations rather than a recommendation or a reconstruction of the trial’s original plan. They do not establish whether the completed trial had adequate power for a treatment effect.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -0.040; pooled standard deviation σ = 1.478.
2. n = 2 × (1.96 + 0.842)² × 1.478² / -0.040² = 21,428.0, rounded up to 21,429 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -0.04                      # observed difference in means
sigma <- 1.47785580622739                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(2196324)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 21,429 (80% power), 28,687 (90% power)
 75% of observed effect: n per arm = 38,095 (80% power), 50,998 (90% power)
 50% of observed effect: n per arm = 85,713 (80% power), 114,745 (90% power)
power.t.test: 21429 
Simulated power at n = 21,429 per arm: 0.801 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when several statistical hypotheses are examined. With more tests, there are more opportunities for a result to appear noteworthy by chance. A study can address this through a prespecified outcome hierarchy, family-wise error control, false-discovery procedures, or another strategy. These approaches answer different goals, and they need to be specified to interpret a collection of results appropriately.

The registry lists 17 outcome measures and 13 analyses. It does not report a multiplicity adjustment plan, an outcome hierarchy, or whether the secondary analyses were designated as confirmatory or exploratory. Therefore, the listed p-values should not automatically be interpreted as if they arose from one isolated test. The unadjusted secondary result is useful as a description of the posted analysis, but it has less confirmatory force when the full testing strategy is unknown.

The registry describes the primary analysis population as randomized participants who were treated and analyzed according to randomized assignment. That definition does not state how missing observations were handled. The record does not report whether analyses used complete cases, imputation, a likelihood-based approach, or another procedure. It also does not describe reasons for missing data or whether missingness differed between groups. Those omissions limit assessment of potential bias and the assumptions underlying the results.

The primary outcome counts are 63 for placebo and 64 for serlopitant. The secondary Patient Benefit Index counts are 61 and 63, respectively. The registry does not explain the differences in available numbers or say whether they reflect missing responses, eligibility for the measure, or another reason. No cause should be inferred from the counts alone.

The record identifies a randomized, quadruple-masked design but does not report detailed allocation procedures, the identities of masked roles, or the full analysis plan. The original sample-size justification, interim analysis plan, and stopping rules are also not reported in the registry record. Without these details, readers cannot establish which analyses were planned in advance or how all sources of missingness and multiplicity were addressed.

These limitations do not mean that an analysis was necessarily inappropriate; they mean the registry record does not contain enough information to evaluate those aspects. A complete protocol and statistical analysis plan would be needed to assess prespecification, outcome prioritization, multiplicity control, and missing-data assumptions in greater detail.

15. 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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: bradycardia (1.6%), syncope (1.6%), respiratory failure (1.6%), neurodermatitis (1.6%), vertigo (1.6%).

The registry reports serious adverse events for 2 of 63 participants in the placebo group and 3 of 64 in the serlopitant group. It reports zero deaths in each group. These are counts among the participants listed at risk for the serious adverse event summary. They describe events recorded during the study and should not be treated as proof that an event was caused by the assigned treatment.

The record also reports other adverse events for 20 of 63 placebo participants and 31 of 64 serlopitant participants. Serious and other adverse events are separate categories in the registry summary; the counts should not be combined or interpreted as mutually exclusive participants unless the record establishes that. The available summary does not provide event-level timing, severity beyond the serious classification, or attribution assessments for each event.

The listed serious event terms—bradycardia, syncope, respiratory failure, neurodermatitis, vertigo, and dizziness—are each reported at 1.6%. The registry excerpt does not assign each listed term to a treatment group, so they should not be attributed to a particular arm. Rare or serious events require careful context, and counts from a trial of this size cannot by themselves characterize all potential safety risks. This summary describes the registry record and is not medical advice.

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

The primary result describes average itch severity at baseline in two randomized groups. The group means, 7.92 and 7.88, are close, and the posted mean difference is -0.04. The confidence interval includes zero, and the unadjusted p-value is 0.879. Taken together, these values indicate that the posted baseline averages do not show a clear separation between groups. They do not tell whether symptoms improved or worsened during treatment.

The trial’s stated purpose was to assess serlopitant relative to placebo, but the registry’s designated primary measure is recorded at baseline. A baseline comparison cannot be interpreted as evidence that serlopitant does or does not affect itch. The registry record does not report a primary post-treatment itch result or a primary change-from-baseline analysis. This distinction is central to understanding what the posted primary data can support.

The secondary Patient Benefit Index outcome provides a later comparison at Week 8 / End of Treatment. Its estimated group difference is positive, but its confidence interval includes zero, and the registry reports p = 0.062 for the two-sided test. This is an uncertain secondary finding, not a definitive conclusion. It also measures patient benefit rather than the primary baseline itch score. The listed additional outcomes broaden the assessment, but the record does not report a multiplicity plan that would establish how to interpret them collectively.

Statistical significance and clinical importance are different concepts. A p-value does not state whether a difference matters to patients, and a confidence interval does not by itself define a clinically meaningful threshold. The registry record does not report a threshold for meaningful change on the measures discussed. It is therefore not possible to classify the observed group contrasts as clinically important based on these statistics alone.

The record also does not fully document missing-data handling, the original analysis plan, or the sample-size justification. Those unknowns limit assessment of robustness and of whether all planned comparisons are represented. The safety summaries give event counts and listed serious event terms, but they do not establish causation or provide a comprehensive assessment of risks.

In short, the posted primary values characterize baseline itch severity, while the later patient-benefit result is secondary and uncertain. The available data should not be translated into a claim that treatment works or does not work. They identify what was measured and the precision of the reported comparisons, while leaving important questions about treatment-period outcomes and analysis details unanswered.

17. Why This Trial Matters Statistically

This trial illustrates why endpoint timing is as important as endpoint name. Average itch severity measured at baseline is a relevant description of the study groups, but it is not a measure of response to treatment. Readers can be misled if a primary outcome label is assumed to mean that the posted comparison evaluates a treatment-period effect. Checking the stated timeframe is essential for interpreting the estimand—the specific quantity an analysis is intended to estimate.

The results also demonstrate the difference between a numerical estimate and the certainty around it. The baseline mean difference is close to zero, but its confidence interval covers values on both sides of zero. The p-value does not prove equality, and the interval does not establish a treatment effect. Reporting both the estimate and its uncertainty gives more information than treating a p-value as a verdict.

The secondary Patient Benefit Index result illustrates another important issue: multiple outcome measures can describe different parts of a condition, but multiple testing complicates interpretation. Without a reported multiplicity strategy, an isolated secondary result should not be promoted as a definitive finding. The measure’s timing and construct also matter; patient benefit at the end of treatment is not interchangeable with baseline itch intensity.

Finally, this record shows the value of transparent registration and the limits of a registry summary. It provides design labels, group summaries, a secondary analysis, and adverse-event counts, yet does not report several details needed for a complete appraisal, including the original analysis plan, missing-data procedures, and sample-size justification. Statistical interpretation depends not only on calculations but also on knowing what was planned, what was measured, and how incomplete information was handled.

18. 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 efficacy is that the posted primary measure is Average Visual Analog Scale at Baseline. It describes starting itch severity rather than a post-treatment outcome or change. The study summary frames the trial as a comparison of serlopitant and placebo, but the registry record does not report a primary treatment-period itch comparison. Consequently, the primary result cannot answer the central treatment-effect question on its own.

The available analysis details are limited. The registry does not report the original statistical analysis plan, the primary inferential model, the sample-size justification, or whether interim analyses were planned. It also does not state how missing data were handled. Counts differ between the primary measure and the secondary Patient Benefit Index, but the record does not explain why. These gaps restrict assessment of prespecification and robustness.

The multiplicity strategy for the many listed outcomes is not reported. This makes individual unadjusted secondary findings harder to interpret as confirmatory evidence. The registry lists a patient-benefit result at Week 8 / End of Treatment, but it remains a secondary measure, and its confidence interval includes zero. The record does not provide a reported threshold for clinically meaningful change on this measure.

Some design details are also not described beyond the labels. The record identifies randomization and quadruple masking but does not report how the sequence was generated, how allocation was concealed, or which roles were masked. The listed enrollment is 128, while the primary measure has arm-specific counts of 63 and 64; the record does not explain the difference in coverage. These points do not establish flaws, but they leave questions that cannot be settled from the registry summary alone.

Safety interpretation is similarly limited by summary-level reporting. The record gives serious and other adverse-event counts, deaths, and several serious event terms, but does not provide full event narratives, timing, attribution, or all relevant denominators for each term. The results are therefore descriptive and should not be treated as a complete safety profile.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: A Randomized Placebo-Controlled Study of the Neurokinin-1 (NK1) Receptor Antagonist Serlopitant Prurigo Nodularis (PN) — NCT02196324.
• Registry record last updated 2021-05-20; status last verified 2021-05.
• Results first posted 2021-02-02.
• 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.

22. Record Summary

The registry describes a completed randomized, double-blind, placebo-controlled phase 2 parallel-group study of serlopitant 5 mg tablets in subjects with prurigo nodularis. Placebo tablets were the comparator, and the study is identified as quadruple-masked. Enrollment is listed as 128.

The designated primary measure is average itch severity on a 10-cm Visual Analog Scale at baseline. The reported means were 7.92 for placebo and 7.88 for serlopitant, with an unadjusted mean difference of -0.04 and a confidence interval from -0.555 to 0.475. This is a baseline comparison, not a treatment-period result. A secondary Patient Benefit Index comparison is recorded at Week 8 / End of Treatment; its reported two-sided test has p = 0.062.

The registry lists multiple secondary outcomes and reports adverse-event summaries, but does not report the original sample-size justification, multiplicity plan, or missing-data methods. The posted primary data describe starting group values and do not establish a treatment effect.