A Study of Ixekizumab in Participants With Plaque Psoriasis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study of Ixekizumab in Participants With Plaque Psoriasis (NCT02993471), a non-randomized phase 1 study. The primary outcome is Pharmacokinetics (PK): Maximum Observed Drug Concentration (Cmax) of Cytochrome P450 (CYP450) Substrate-Midazolam.

2. Clinical Question

The study is described as a drug interaction study. It examines blood concentrations of a mixture of commonly used drugs metabolized by cytochrome P450, with the aim of evaluating whether ixekizumab affects their pharmacokinetics. Midazolam is the substrate named in the primary endpoint; the cocktail also includes caffeine, warfarin with vitamin K, omeprazole, and dextromethorphan.

According to the registry summary, participants take the cocktail on three occasions: before ixekizumab treatment and after one and twelve weeks of treatment. The registered primary endpoint focuses on the maximum observed concentration of midazolam. The registry record does not report the corresponding concentration estimates, the size or direction of any change, or a statistical test of the study question. The available record therefore describes what was measured, but does not establish a numerical pharmacokinetic finding.

3. Trial Design

This Phase 1 study is listed as completed, with a non-randomized allocation, no masking, and a single-group model. The registry lists an enrollment of 28 participants. Its summary describes two study periods: an oral drug cocktail in Period 1 before ixekizumab, followed by cocktail doses during Period 2 while participants receive ixekizumab subcutaneously. The cocktail contains caffeine, warfarin plus vitamin K, omeprazole, dextromethorphan, and midazolam.

The cocktail was administered once on day 1 of Period 1 and twice in Period 2, on day 8 and day 85. The summary also describes assessments after one and twelve weeks of ixekizumab treatment. The study was expected to last about 17 weeks, including follow-up. The registry dates the study start as 2016-12-22 and primary completion as 2017-11-21.

Because allocation was non-randomized and the study is recorded as single-group, the Period 1 measurements are not a randomized parallel-group control. The periods provide measurements under different treatment conditions, but the record does not specify the statistical approach used to compare those measurements. The safety listings include 28 participants at risk in the cocktail group and 27 at risk in the cocktail-plus-ixekizumab group. Those groups should not be interpreted as randomized, exchangeable arms.

The registry record does not report detailed eligibility criteria, the number of participants who completed each period, or the reasons for any differences between the listed safety populations. It also does not report the protocol’s sample-size justification, planned interim analyses, or a complete statistical analysis plan. These omissions limit how fully the design and analysis choices can be reconstructed from the registry record.

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: Multicenter, open-label, 2-period, fixed-sequence study.

Period 1 (Drug Cocktail)

Period 2 (Drug Cocktail + Ixekizumab)

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: All enrolled participants who received at least 1 dose of study drug with evaluable PK data.

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 enrolled participants who received at least 1 dose of study drug.

6. Primary Endpoint

The registry lists the primary outcome as Pharmacokinetics (PK): Maximum Observed Drug Concentration (Cmax) of Cytochrome P450 (CYP450) Substrate-Midazolam, measured over Predose, 0.5, 1, 2, 3, 4, 6, 8, 12, and 24 hours postdose.

The primary endpoint is the maximum observed concentration, or Cmax, of midazolam, reported in nanograms per milliliter. Concentration is assessed at predose and at 0.5, 1, 2, 3, 4, 6, 8, 12, and 24 hours after dosing. The endpoint uses the highest observed concentration across the scheduled sampling profile to describe the peak level recorded after a dose.

Pharmacokinetic endpoints are used to characterize how a drug or substrate’s concentration changes in the body over time. As a general statistical concept, Cmax captures a peak in the measured concentration profile; it does not by itself describe the full profile, the time at which the peak occurs, or total exposure. Those are distinct pharmacokinetic features.

The registry specifies a geometric mean as the summary parameter and a geometric coefficient of variation as the dispersion measure. In general, geometric summaries are used for data whose distribution is better described on a multiplicative scale than by an arithmetic average. The registry record does not report the Cmax estimates, their dispersion values, or a comparison between periods. It therefore identifies the measurement and its planned summary form without documenting the observed primary endpoint result.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a geometric mean and geometric coefficient of variation for the primary endpoint. It does not report an inferential analysis, an effect estimate, or a confidence interval. The explanations below describe general statistical concepts; they do not assert that a particular analysis was performed in this study.

What does Cmax represent?

Cmax is the highest concentration observed among the scheduled measurements after a dose. Here, the registered profile includes a predose measurement and postdose measurements through 24 hours. As a general concept, this endpoint reduces a sequence of concentration observations to a peak value. It should not be confused with the timing of the peak or with total exposure over time. The registry record does not report participant-level profiles or the resulting Cmax values.

Why use a geometric mean?

For measurements that vary multiplicatively or have a right-skewed distribution, a geometric mean can describe a typical value on a multiplicative scale. In general, it is calculated by transforming values to a logarithmic scale, averaging there, and transforming back. The geometric coefficient of variation describes relative spread on that scale. These are general interpretations of the named summaries; the registry record does not give the exact calculation procedure, transformation, or handling of values below a quantification limit.

A confidence interval, in general, expresses uncertainty around an estimated quantity under a statistical model. A narrow interval would indicate greater precision than a wide one, all else being equal. No confidence interval for the primary endpoint is reported in the registry record, so its precision cannot be evaluated from the posted information. A p-value, in general, measures how compatible data are with a specified null model; it is not a measure of clinical importance. No p-value or tested hypothesis is listed for the primary endpoint.

What does the study structure mean for a comparison?

The study is recorded as non-randomized and single-group. The registry describes a cocktail dose in Period 1 before ixekizumab and later cocktail doses during Period 2 with ixekizumab. In general, measurements made at different times in the same study can be compared, but interpretation depends on the analysis and on how participant-level observations are handled. The registry record does not report whether the primary analysis used paired observations, a model, an unadjusted contrast, or another approach. No method should be presumed from the period descriptions alone.

Random allocation can help balance measured and unmeasured characteristics between treatment groups. That general design advantage is not present in the registry description of this study. The Period 1 condition is a pre-treatment measurement, rather than a randomized parallel control condition. The registry itself indicates that the listed groups are not a like-for-like control comparison. Any estimated difference would require cautious interpretation and details of the analysis that are not reported in the registry record.

How should planning illustrations be read?

The planning illustrations are described as calculations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is defined as a stated fraction of the observed effect. For time-to-event outcomes, the illustration uses a total event count based on the Schoenfeld method; for other outcomes, it gives participants per arm. These are general planning calculations, not observed trial outcomes, and not the trial’s own sample-size justification. They are not observed power. No numerical planning estimates are stated in the registry entries summarized by the record.

Sample-size illustrations depend on their assumptions. A target framed around a fraction of an observed effect is a hypothetical planning scenario, not evidence that the effect is reproducible or clinically important. The assumptions also describe a two-arm equal-allocation framework, whereas this study is recorded as a non-randomized, single-group study. That mismatch reinforces that an illustration should not be treated as a reconstruction of the study design or as an inferential result.

What does over-dispersion mean in general?

For count outcomes, over-dispersion means that observed variability is greater than a model’s assumed variability. If ignored, standard errors and confidence intervals can be miscalibrated. This is a general concept and is not evidence that over-dispersion occurred in this study; the registry record does not report a count-outcome model or an over-dispersion assessment.

More broadly, the record does not describe model diagnostics, covariate adjustment, multiplicity control, or sensitivity analyses. The absence of these details means the statistical procedure cannot be independently assessed from the registry record. The posted design and endpoint definitions clarify what the study set out to measure, but do not substitute for a documented analysis plan or reported numerical results.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 10 outcome measures, while the number of recorded analyses is zero. It does not report which outcomes were considered confirmatory, how the primary endpoint was prioritized in the analysis, or whether adjustment for multiple testing was planned or performed. When many endpoints are tested, the chance of at least one apparently unusual result can rise; multiplicity procedures are one general way to address that issue. No such procedure is reported in the registry record.

Missing-data methods are also not reported. The primary endpoint population is defined as all enrolled participants who received at least one dose of study drug and had evaluable pharmacokinetic data. The number meeting that definition is not reported in the registry record. The record does not explain how incomplete concentration profiles, missed samples, or participants without evaluable pharmacokinetic data were handled, nor does it describe imputation or sensitivity analyses.

The registry does not report whether all scheduled time points were required for inclusion in the Cmax analysis or how a maximum was handled when a scheduled measurement was unavailable. It also does not report an analysis population for each period or the extent of participant overlap between the safety listings. Without those details and without the endpoint results, readers cannot assess the influence of missing measurements or determine how the analysis population differed from enrollment.

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 registry lists serious adverse events for two exposure groups. In the Drug Cocktail group, 0 of 28 participants at risk had a serious adverse event. In the Drug Cocktail + Ixekizumab group, 0 of 27 participants at risk had a serious adverse event. Deaths are listed as 0 in each group. No serious adverse event terms are listed.

Other adverse events are listed for 1 of 28 participants in the Drug Cocktail group and 7 of 27 participants in the Drug Cocktail + Ixekizumab group. These are counts as recorded, not adjusted comparisons. The registry record does not give event descriptions for these entries, exposure-adjusted rates, confidence intervals, or a statistical test comparing groups.

The safety groups arise in a non-randomized, single-group study and should not be treated as balanced control arms. Their denominators differ, and the registry does not explain the difference in the listed numbers at risk. Zero recorded serious events means none are listed for these groups in the registry record; it does not by itself establish the absence of risk. The counts are descriptive and should be read alongside the study’s design and the limits of the recorded safety information.

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

The record shows that the study was designed to characterize the pharmacokinetics of cytochrome P450 substrates in participants receiving ixekizumab, with midazolam Cmax as the primary endpoint. It records the dosing periods, sampling times, summary measures, enrollment, and safety counts. These details clarify the intended measurement, but the primary endpoint’s observed values are not reported in the registry record.

Without the geometric mean estimates, variability, a comparison estimate, or an uncertainty interval, the record cannot show how large or precise a difference in midazolam Cmax may have been. No conclusion about the direction or statistical significance of a pharmacokinetic change can be drawn from the endpoint definition alone. The registry’s lack of recorded analyses also means the method used to evaluate the primary question is not available.

The non-randomized, single-group design matters. The pre-treatment cocktail period and the later periods during ixekizumab are different treatment conditions, but the registry does not describe a randomized control comparison. The result, even if reported elsewhere, would need to be understood in terms of the study sequence and the analysis method rather than read as a randomized treatment contrast.

The safety entries document zero serious adverse events and zero deaths in both listed groups, alongside other adverse event counts. These observations describe the registry listings; they are not a controlled estimate of comparative safety. Overall, the available record supports a careful account of what was measured and which safety counts were recorded, but it does not report the primary numerical result needed to answer the pharmacokinetic question.

13. Why This Trial Matters Statistically

This study illustrates a distinction that is central to biostatistics: an endpoint definition is not the same as a reported endpoint result. The registry identifies midazolam Cmax, its sampling schedule, and the geometric summaries intended for description. Without the numerical estimates and their uncertainty, readers can understand the measurement but cannot judge the size or precision of the finding.

It also illustrates why design labels matter. A non-randomized, single-group study with measurements before and during treatment does not have the same comparison structure as a randomized parallel-group trial. The treatment periods and safety listings should be interpreted in that context. Design information guides what kinds of conclusions an analysis might support, while the absent statistical methods prevent readers from evaluating how the primary comparison was made.

The record further shows why safety counts need denominators and design context. Counts of serious and other adverse events are useful descriptive information, but they do not automatically provide a comparative estimate. Differences in listed participants at risk and the non-randomized structure constrain interpretation.

Finally, planning illustrations and observed findings answer different questions. A planning calculation explores assumptions about a future or hypothetical study; it is not a result from the participants enrolled in this study and is not observed power. Separating endpoint definitions, study design, safety counts, analyses, and planning assumptions helps prevent an incomplete registry entry from being read as a complete statistical report.

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 registry record has no reported primary pharmacokinetic estimates or analyses, despite naming midazolam Cmax as the primary endpoint. It therefore does not allow readers to assess the direction, magnitude, or precision of the primary result. The record also does not report confidence intervals, p-values, or the method used to compare measurements across periods.

The non-randomized, single-group design limits the interpretation of contrasts between the pre-treatment and treatment periods. The registry does not report an adjustment strategy for period effects or other potential influences, and no such strategy should be assumed. Detailed eligibility criteria, participant completion by period, and reasons for the difference between the safety-group denominators are not reported in the registry record.

Missing-data handling, the number of participants with evaluable pharmacokinetic data, and the treatment of incomplete concentration profiles are also not reported. The registry lists 10 outcome measures but gives no recorded analyses, and it does not describe multiplicity control or sensitivity analyses. Safety information is limited to the listed counts; adverse event descriptions beyond the serious-event terms are not given in the record. The protocol’s sample-size justification and interim-analysis plan are not reported.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Study of Ixekizumab in Participants With Plaque Psoriasis — NCT02993471.
• Registry record last updated 2019-03-12; status last verified 2017-12.
• Results first posted 2019-03-12.
• 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

This completed Phase 1 study enrolled 28 participants with plaque psoriasis and examined ixekizumab alongside a cocktail of cytochrome P450 substrates. The registry describes non-randomized allocation, no masking, and a single-group model. The primary endpoint is midazolam Cmax, summarized as a geometric mean with geometric coefficient of variation over a specified postdose sampling profile.

The registry record does not report the primary endpoint values or any analyses. It lists zero serious adverse events and zero deaths in each safety group, with other adverse events listed for 1 of 28 participants in the Drug Cocktail group and 7 of 27 in the Drug Cocktail + Ixekizumab group. These counts are descriptive and do not form a randomized comparison.