A Study to Learn About the Study Medicine (Called Ritlecitinib) For the Potential Treatment of Severe Alopecia Areata (AA) In Children 6 To Less Than 12 Years of Age: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Learn About the Study Medicine (Called Ritlecitinib) For the Potential Treatment of Severe Alopecia Areata (AA) In Children 6 To Less Than 12 Years of Age (NCT05650333), a na phase 1 study. The primary outcome is Area Under the Plasma Concentration-Time Profile Over the Dosing Interval of 24 Hours, at Steady State (AUC24ss/AUCtau) of Ritlecitinib on Day 7.

2. Clinical Question

The study was designed to describe pharmacokinetics (PK) and pharmacodynamics (PD) in this age group, rather than to compare treatment with a control or establish a clinical treatment effect. The primary endpoint concerns the amount of ritlecitinib measured in plasma over a dosing interval. It is a measure of drug exposure, not a measure of scalp hair growth or change in alopecia areata severity.

The registry also lists secondary PK measures, including maximum observed plasma concentration, time to maximum concentration, apparent oral clearance, apparent volume of distribution, and elimination half-life. PD outcomes include changes from baseline in IP-10 and T- and B-lymphocytes on Day 7. These outcomes address drug disposition and selected biological measures. The registry record does not report numerical results for the primary endpoint or the listed secondary outcomes, so the study's observed PK and PD findings cannot be described from this record.

3. Trial Design

This was an interventional, phase 1, open-label study with a single group and no comparator. The intervention was ritlecitinib 20 mg taken orally once daily. The brief summary specifies dosing for 7 days. Because treatment was open label and there was no comparison group, the design does not provide a concurrent control for separating changes associated with treatment from other influences.

The registry lists 15 participants as enrolled. The brief summary separately states that 12 children would participate. These figures are not reconciled in the registry record, and the number included in any particular analysis may differ from either figure. The primary endpoint description states that participants with evaluable PK data were included and that two participants were not included in that analysis because they lacked evaluable PK data. A fuller account of participant flow is not reported in the registry record.

The study began on 2023-03-02, had primary completion on 2023-08-11, and is listed as completed. The brief summary says that participation lasted about 10 weeks. For PK evaluation, blood samples were collected on Day 7 at pre-dose and at 0.5, 1, 3, 8, and 24 hours, with the pre-dose concentration used as an estimate for the 24-hour post-dose concentration. The brief summary also describes blood collection for PD evaluation at screening and on Day 7.

The stated focus was PK and PD in children with severe alopecia areata. The registry record does not report a randomized allocation, masking, a control arm, or a clinical efficacy comparison. It also does not report a protocol rationale for the sample size or a statistical analysis plan beyond the endpoint-specific information recorded for the primary PK measure.

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: A total of 15 participants, 6 to less than 12 years of age with greater than or equal to (\>=) 50% scalp hair loss due to alopecia areata, were enrolled. Study started from 02 March 2023 and completed on 11 August 2023.

Treatment Period (7 Days)

Reasons for not completing this period:

Follow-up (35 Days After Last Dose)

Analysis population for the primary outcome, as defined in the registry: Pharmacokinetic (PK) parameter analysis population: treated participants who had at least 1 of the PK parameters of primary interest. All participants with evaluable PK were included in the analysis. Two participants weren't included in analysis as they didn't have evaluable PK data (1 discontinued study intervention on Day 3 and the other had the important protocol deviation, PK samples not collected on Day 7). "Number of Participants Analyzed": participants evaluable for the outcome measure.

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: All participants who were enrolled in the study and were assigned to study intervention.

6. Primary Endpoint

The registry lists the primary outcome as Area Under the Plasma Concentration-Time Profile Over the Dosing Interval of 24 Hours, at Steady State (AUC24ss/AUCtau) of Ritlecitinib on Day 7, measured over Day 7: 0 (pre-dose), 0.5, 1, 3, 8 and 24 hours [pre-dose concentration was used as an estimate for the concentration of 24 hours post dose].

The primary endpoint is the area under the plasma concentration-time profile over the 24-hour dosing interval at steady state, identified as AUC24ss/AUCtau for ritlecitinib on Day 7. It summarizes plasma drug exposure across the dosing interval rather than describing a single concentration at one sampling time. The endpoint is reported as a geometric mean, with geometric coefficient of variation as its measure of dispersion. The registry record does not report the numerical estimate or its dispersion.

Concentration measurements were scheduled at pre-dose and 0.5, 1, 3, 8, and 24 hours on Day 7. The registry says that the pre-dose concentration on Day 7 was used as an estimate of the concentration 24 hours after the Day 7 dose. It also states that a linear-log trapezoidal method was used to evaluate the area under the profile. This approach uses the sampled concentrations to estimate the area between observations, with the calculation taking account of the concentration-time data as described in the record.

Exposure measures such as AUC are used in PK studies to characterize how much drug is present in circulation over time. That information is distinct from evidence about clinical outcomes. In this study, the primary endpoint does not directly measure hair loss, hair regrowth, symptom change, or quality of life. The registry record does not report a threshold for interpreting the AUC value or a clinical outcome linked to a particular exposure.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information recorded for the primary outcome describes a summary of drug exposure, the data collection times, and the method used to estimate the area under the concentration-time profile. The registry record does not report a fuller statistical analysis plan, so the explanation below distinguishes the recorded endpoint methods from general statistical concepts.

What does the area under the curve represent?

In general, a concentration-time curve traces the measured amount of a drug in plasma across time after dosing. The area under that curve combines information across the sampled interval. It is used in pharmacokinetics because a concentration at a single sampling time cannot by itself describe exposure throughout the dosing interval. AUC24ss/AUCtau is the recorded primary measure for ritlecitinib on Day 7, over the dosing interval of 24 hours, at steady state.

The record gives sampling times of 0 (pre-dose), 0.5, 1, 3, 8, and 24 hours on Day 7. It specifies that the Day 7 pre-dose concentration was used as an estimate for the concentration 24 hours after the dose. That substitution is part of the recorded calculation and should be kept in mind when interpreting the endpoint. The registry does not give the individual concentrations or a numerical AUC estimate, so it is not possible to inspect the curve or independently assess the impact of that estimate.

How does trapezoidal estimation work?

In general, measurements are available only at selected times, rather than continuously. A trapezoidal method estimates the area between adjacent observations by treating the change between observations as a series of segments and combining their areas. The registry specifies a linear-log trapezoidal method. This describes the calculation used for the primary PK endpoint; it does not, on its own, provide the result or its uncertainty.

The endpoint description states that the calculation used the Day 7 pre-dose concentration as the estimate of the concentration 24 hours after the Day 7 dose. The record does not give further detail about handling concentrations below a quantification limit, irregular sampling, or other potential data issues. Those procedures are not reported in the registry record and should not be inferred.

Why report a geometric mean?

In general, concentration and exposure measures can have distributions for which a geometric mean is an appropriate summary. The geometric mean is based on the multiplicative scale of the measurements rather than their arithmetic average. A geometric coefficient of variation describes relative dispersion on that scale. It is a measure of variability among values, not a confidence interval and not a statement about the precision of the estimated geometric mean.

The primary endpoint identifies a geometric mean and geometric coefficient of variation, but the numerical estimates are not reported in the registry record. No confidence interval for the primary endpoint is reported either. A confidence interval, in general, describes uncertainty around an estimate under the assumptions of the analysis. Without the estimate, its interval, and supporting analysis details, the precision of the primary result cannot be evaluated.

What can be learned from the design?

A single-group study collects information from participants receiving the study intervention without a concurrent control arm. In general, this structure can support description of measured PK and PD outcomes in the enrolled participants. It does not support a like-for-like comparison with an untreated or alternative-treatment group. The open-label design means treatment assignment was known, but the main endpoint is a laboratory-based exposure measure. The registry record does not report whether assessors were masked to other information or how outcome data were reviewed.

The registry lists a primary PK analysis population consisting of treated participants with at least one primary-interest PK parameter, and says all participants with evaluable PK were included. It also says two participants were not included in the primary analysis because they did not have evaluable PK data. An analysis population is the set of participants whose data contribute to a specified outcome analysis. Its size and composition matter because they determine which observations contribute to an estimate. The record does not report the full participant-level flow or the handling of missing data beyond this statement.

More generally, small or incomplete analysis sets can make estimates less precise, but no precision estimate is available. The registry lists enrollment of 15 and the brief summary describes 12 children participating; these are not reconciled. The actual number analyzed for the primary endpoint should therefore not be assumed from the enrollment figure alone.

What statistical comparisons are recorded?

The study has no comparator arm, and the registry lists 0 analyses. No p-value, confidence interval, adjusted estimate, or hypothesis test for the primary endpoint is reported. The secondary outcomes include maximum observed concentration, time to maximum concentration, apparent oral clearance, apparent volume of distribution, elimination half-life, and Day 7 changes from baseline in IP-10 and T- and B-lymphocytes. Their names indicate which measurements were intended, but the registry record does not report their numerical results.

Statistical planning calculations based on an observed effect, where present, are illustrations of possible sample sizes under stated assumptions. In general, such calculations ask what sample size might be needed for a specified power and effect under a particular model. They are not observed power, do not show that the original trial was designed around those assumptions, and do not replace the trial's outcome estimates. The registry record does not report the trial's own sample-size justification, interim analyses, or a complete statistical plan.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 17 outcome measures, including the primary PK endpoint, additional PK measures, and PD changes from baseline. When a study considers multiple outcomes, multiplicity is a general statistical concern: assessing many outcomes can increase the chance that some results appear notable by chance, especially when many formal tests are performed. The record does not report a multiplicity adjustment, a hierarchy among secondary outcomes, or whether any formal hypothesis tests were planned. It also lists 0 analyses, so no testing results or adjustment procedures can be reviewed.

The listed outcomes include maximum observed plasma concentration, time to maximum concentration, apparent oral clearance, apparent volume of distribution, elimination half-life, and changes from baseline in IP-10 and T- and B-lymphocytes on Day 7. These endpoints address different aspects of drug disposition and biological response. Their presence in the registry does not show that results were reported or that the outcomes were treated as confirmatory. Numerical results for them are not reported in the registry record.

Missing-data information is limited. The primary PK outcome description says that all participants with evaluable PK were included and that two participants were not included in the analysis because they did not have evaluable PK data. The record does not describe imputation, sensitivity analyses, or the specific reasons for all missing or unevaluable measurements. It also does not provide participant flow by outcome, so analysis denominators for secondary outcomes cannot be established from this record.

The registry lists 15 enrolled, while the brief summary describes 12 children participating. This discrepancy is not resolved in the record and makes it especially important not to assume that enrollment equals the number analyzed. A fuller account of missingness and analysis populations is not reported in the registry record.

11. 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 0% reporting threshold.

Most frequent non-serious adverse event terms

The adverse-event record lists the ritlecitinib 20 mg QD group with 15 participants at risk for serious adverse events and 0 affected. It also lists 15 participants at risk for other adverse events and 3 affected. The death count is 0. These figures describe the counts recorded for this group; they do not provide event-level details or information about severity beyond the serious-versus-other categorization.

In general, an adverse-event count is a safety observation, not by itself proof that the study medicine caused an event. A group-level count also does not describe timing, duration, recurrence, or clinical course. The registry record lists no serious adverse-event terms, and it does not provide further details about the three participants affected by other adverse events in the registry record recorded. The record also does not report a comparator group, so these counts cannot be interpreted as a comparative safety estimate.

The 15 participants listed at risk in the adverse-event record should not automatically be treated as the denominator for every outcome. The registry separately reports that two participants lacked evaluable PK data and does not reconcile its enrollment figure with the brief summary's participant count. Safety and PK analysis populations can differ, and the record does not provide enough detail to establish the flow for every measure.

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

This study's statistical purpose was to characterize ritlecitinib PK and PD in children aged 6 to <12 years with severe alopecia areata. Its primary endpoint was a Day 7 exposure measure, AUC24ss/AUCtau, summarized as a geometric mean with geometric coefficient of variation. The available registry information explains the endpoint and its calculation but does not report the numerical result. As a result, the estimated exposure and its precision cannot be described.

The study was single group and open label, with participants receiving ritlecitinib 20 mg orally once daily for 7 days. That design does not provide a randomized comparison with another treatment or a control condition. The primary endpoint is pharmacokinetic, not a clinical measure of alopecia areata. The listed PD outcomes concern selected biological measures; the registry record does not report numerical results for those outcomes either.

Nothing in the recorded endpoint description establishes how a particular exposure value relates to clinical benefit or harm. No clinical efficacy result, comparative treatment estimate, or numerical primary result is reported in the registry record. The completed status indicates that the study is listed as completed, but completion alone does not supply evidence about the outcomes.

The participant figures also need cautious reading. The registry lists 15 enrolled, while the brief summary describes 12 children participating, and the primary PK description says two participants were not included because their PK data were not evaluable. The record does not reconcile these statements or give full analysis denominators. Therefore, enrollment should not be assumed to be the number contributing to the primary estimate.

Any planning illustrations based on an observed effect are hypothetical calculations under their stated assumptions. They are not observed power, do not establish that the original study was designed with those assumptions, and cannot compensate for missing results. The record supports a description of the study question and measurement approach, but not a conclusion about a treatment effect or a quantitative account of drug exposure.

13. Why This Trial Matters Statistically

The study is statistically informative as an example of a PK-focused investigation in a narrowly defined pediatric age group. Its question differs from a conventional treatment-effect comparison: it centers on drug exposure over a dosing interval and selected PD measures. Understanding that distinction helps readers avoid treating a PK endpoint as though it were a direct measure of clinical improvement.

The primary outcome is described with a specific summary scale, collection schedule, and calculation method. The geometric mean and geometric coefficient of variation communicate the intended way to summarize exposure and variability. The sampling schedule and use of a Day 7 pre-dose concentration to estimate the 24-hour concentration are also material to understanding how the endpoint was constructed. These methodological details give context for interpreting a result if numerical results become available.

The record also illustrates why analysis populations and participant flow matter. Enrollment is listed as 15, the brief summary describes 12 children participating, and two participants are stated to lack evaluable PK data for the primary analysis. Since those figures are not reconciled, readers cannot infer the primary analysis denominator from enrollment alone. Clear participant accounting is important to judge how broadly an estimate represents those enrolled.

Finally, the absence of numerical endpoint results limits the statistical conclusions that can be drawn. The study is listed as completed, and several secondary outcomes are named, but estimates and uncertainty measures are not reported in the registry record. This highlights the difference between a registered measurement plan and interpretable outcome reporting. Sample-size illustrations, if consulted, are planning aids rather than observed power or evidence that the study's findings are precise.

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 direct limitation of the registry record is that it does not report a numerical result for the primary AUC24ss/AUCtau endpoint. It also does not report numerical results for the listed secondary PK and PD outcomes. Without estimates and measures of uncertainty, the observed exposure, its variability, and the precision of the endpoint cannot be evaluated.

The trial had a single group and no comparator. It was open label, and the registry does not describe masking of outcome assessment. This design is appropriate to describe the recorded PK and PD questions, but it does not supply a concurrent control comparison. No comparative estimate or formal test is reported.

Participant accounting is unclear. The registry lists enrollment of 15, whereas the brief summary describes 12 children participating. The primary PK description says two participants were excluded because their PK data were not evaluable. The record does not reconcile these counts, explain the full flow, or provide analysis denominators for each outcome. It does not report detailed missing-data methods or sensitivity analyses.

The record lists 17 outcome measures but 0 analyses. It does not report a multiplicity strategy, interim analyses, the trial's sample-size justification, or a complete statistical analysis plan. The primary endpoint method is described as linear-log trapezoidal estimation, including use of the pre-dose Day 7 concentration as the estimate at 24 hours, but the underlying concentration data and numerical AUC are not reported. These limitations restrict both independent statistical review and interpretation of the study's findings.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Study to Learn About the Study Medicine (Called Ritlecitinib) For the Potential Treatment of Severe Alopecia Areata (AA) In Children 6 To Less Than 12 Years of Age — NCT05650333.
• Registry record last updated 2024-10-08; status last verified 2024-06.
• Results first posted 2024-10-08.
• 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

NCT05650333 is listed as a completed, interventional, phase 1, open-label, single-group study of ritlecitinib in children with severe alopecia areata. The regimen was 20 mg orally once daily for 7 days. The primary endpoint was the Day 7 area under the plasma concentration-time profile over a 24-hour dosing interval at steady state, summarized as a geometric mean with geometric coefficient of variation and evaluated using a linear-log trapezoidal method.

The registry lists enrollment of 15, while the brief summary describes 12 children participating. The primary PK description states that two participants lacked evaluable PK data and were not included in that analysis. The record does not reconcile participant counts. It lists 17 outcome measures and 0 analyses, and does not report numerical results for the primary endpoint. The adverse-event record lists 0 serious adverse events, 3 participants affected by other adverse events, and 0 deaths among the 15 participants at risk in the ritlecitinib group.