Safety, Tolerability, and Efficacy Study of rAvPAL-PEG Administered Daily in Subjects With Phenylketonuria (PKU): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety, Tolerability, and Efficacy Study of rAvPAL-PEG Administered Daily in Subjects With Phenylketonuria (PKU) (NCT01212744), a na phase 2 study. The primary outcome is Blood Phenylalanine Concentration.

2. Clinical Question

3. Trial Design

This was a Phase 2, open-label, single-group study of rAvPAL-PEG in subjects with phenylketonuria. The registry record lists 16 enrolled participants. It describes daily subcutaneous administration at varying doses and identifies safety, tolerability, and efficacy as the study aims. The study began in 2011-03, had a primary completion date of 2015-04, and is listed as completed.

Open-label means that treatment assignment was not masked from participants or study personnel, according to the registry record’s masking designation. A single-group design means the listed intervention was assessed without a concurrent control group in the record. Allocation is recorded as not applicable. These features matter when interpreting changes over time: an observed before-and-after difference, if reported, would not by itself separate a treatment effect from other explanations such as changes over time or differences in measurement conditions.

The primary outcome is blood phenylalanine concentration, with baseline and Week 16 listed as time points. The primary outcome description specifies plasma phenylalanine. The record also lists secondary outcomes related to adverse events, drug concentrations, and several antibody measures. It lists 10 outcome measures overall, but no outcome analyses. Consequently, the registry record does not give the outcome values, the number of participants contributing to each measure, or the statistical comparisons used for the outcomes.

The efficacy population is defined as subjects who received any amount of study drug and had post-treatment blood phenylalanine measurements. The number in that population is not reported in the registry record. The enrollment count should therefore not be treated as the number included in the primary outcome analysis.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The efficacy population will consist of all subjects who received any amount of study drug and have post-treatment blood Phe concentration measurements.

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 Blood Phenylalanine Concentration, measured over Baseline, Week 16.

The primary outcome is blood phenylalanine concentration, described as plasma Phe and measured in umol/L at baseline and Week 16. Phenylalanine is the substance named in the study’s stated purpose: evaluating whether daily rAvPAL-PEG is associated with a reduction in blood Phe concentration among subjects with PKU. The registry specifies the mean as the outcome summary and standard deviation as its measure of dispersion.

In general, a mean describes the central value of a continuous measurement across observations. A standard deviation describes how spread out individual measurements are around that mean. They answer different questions: a group mean can indicate the overall level, while the standard deviation indicates variation among the measurements. Neither alone describes the precision of the estimated mean in the way a confidence interval would.

Baseline and Week 16 provide two time points for describing the outcome. To interpret a change, readers would need the actual values at each time point, the number of observations contributing at each time, and an analysis of the within-participant pattern. Those results are not reported in the registry record. The listed endpoint therefore identifies what was intended to be measured, but does not establish the size or precision of any change.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information in the registry record is limited. It identifies a continuous primary outcome, a mean and standard deviation as the planned descriptive summaries, and baseline and Week 16 as time points. It does not report an outcome analysis, an effect estimate, a confidence interval, or a test result. The explanations below are general statistical context, not a description of methods confirmed to have been used in this study.

What do the mean and standard deviation describe?

In general, a mean is the arithmetic average of observed values and summarizes the central level of a continuous outcome. A standard deviation describes the spread of individual values around that mean. A larger standard deviation indicates more variability among the observations; it does not mean that the mean itself is less accurate by the same amount. The standard deviation is a description of participant-level variation, whereas the uncertainty around an estimated mean is commonly conveyed with a standard error or confidence interval.

The record specifies mean and standard deviation for blood phenylalanine concentration, but gives neither at baseline nor at Week 16. It also does not state whether the primary statistical target was a difference between those means, a mean within-participant change, or another contrast. The study purpose refers to reduction, but the stated outcome description alone does not supply an estimate of that reduction.

Why does the single-group design matter?

In general, repeated measurement of the same people can describe how an outcome changes over time. If paired measurements are available, an analysis can account for the fact that measurements from one participant are related to each other. A comparison of two group means that treats all observations as independent would not represent that within-person relationship. The registry record does not identify the analysis method used for baseline and Week 16 measurements, so it is not possible to say how that relationship was handled.

A single-group design has no concurrent control group described in the record. In general, the absence of a control means that a before-and-after pattern cannot distinguish the intervention’s contribution from all other influences that may change over time. This is a design limitation, not a calculation issue. Statistical adjustment cannot create the missing randomized control comparison when the registry record does not describe one.

What can a confidence interval add?

In general, a confidence interval expresses uncertainty around an estimate, using a method with a stated confidence level. Its width reflects both the amount of information and the variability in the data, along with the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval under that method; neither width nor position alone resolves limitations in study design. No confidence interval for the primary outcome is reported in the registry record.

A p-value, when used, describes how compatible data are with a specified statistical model and null hypothesis. It is not the probability that the null hypothesis is true, and it does not measure the clinical importance of an effect. The registry record lists no outcome analyses and reports no p-value for the primary outcome. There is therefore no posted inferential result to interpret.

How should the planning assumptions be read?

The record includes planning-illustration assumptions based on an observed effect: a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It describes the target effect as a stated fraction of the observed effect. These are assumptions for a planning illustration, not evidence that the trial itself used a two-arm design. The actual trial is recorded as single-group, with allocation not applicable.

In general, a sample-size calculation estimates how many participants per arm might be needed under specified assumptions to detect a target effect with a chosen probability, if those assumptions hold. The resulting sample sizes are planning illustrations, not observed power. The record does not report the underlying observed effect used for the illustration or the resulting planning values in the registry record for this analysis. It also does not report the trial’s own sample-size justification. These calculations should not be mistaken for an analysis of the completed study or proof that the study could detect a particular effect.

Normal-approximation calculations are general planning methods that rely on assumptions about the distribution of the estimate. When data are highly variable, skewed, or otherwise poorly represented by the assumed model, precision or operating characteristics may differ from the approximation. Whether those concerns apply to the primary outcome cannot be determined without the outcome data and analysis details.

What is not established by the posted statistical record?

The registry record does not report the primary outcome values, the analyzed population size, missing-data methods, confidence intervals, hypothesis tests, or an analysis plan. It does not report interim analyses or the rationale for the selected sample size. It lists secondary outcome categories, but no analyses of them. Thus, statistical methods beyond the descriptive outcome type and the stated planning-illustration assumptions cannot be attributed to this trial from the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists 10 outcome measures, including the primary blood phenylalanine outcome and secondary outcomes concerning adverse events, drug concentrations, and antibody positivity. It lists 0 outcome analyses. A multiplicity strategy—such as a hierarchy of outcomes, an adjustment to account for multiple statistical tests, or a distinction between confirmatory and exploratory analyses—is not reported in the registry record.

In general, when researchers test many outcomes or make many comparisons, the chance of at least one apparently unusual result can increase. A prespecified analysis plan can clarify which comparisons are central and how multiple tests are handled. Without posted analyses or a reported multiplicity approach, there is no basis for judging the statistical status of secondary findings. The listed outcomes identify topics of measurement, but do not establish that results were analyzed or that a particular adjustment was used.

The primary efficacy population is described as subjects who received any amount of study drug and had post-treatment blood Phe measurements. The number meeting that definition is not reported in the registry record. The record also does not give the number with measurements at each time point, reasons for missing measurements, or methods for handling missing data. It is therefore not possible to assess whether the analyzed observations represent all enrolled participants or whether missingness could affect interpretation.

In general, missing-data methods rely on assumptions about why measurements are absent. Different assumptions can lead to different estimates, particularly when missingness is related to outcome values or treatment experience. No imputation approach, sensitivity analysis, or other missing-data procedure is reported in the registry record. The enrollment count should not be treated as the primary outcome analysis denominator.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: angioedema (6.2%).

The registry record reports serious adverse events affecting 1 of 16 participants and other adverse events affecting 16 of 16 participants in the rAvPAL-PEG group. Deaths are listed as 0. Angioedema appears among the serious adverse event terms at 6.2%. These figures describe the safety entries posted for this single-group study; they are not a comparison with a control group.

In general, a serious adverse event classification is distinct from the broader category of adverse events. The categories should not be combined or treated as interchangeable. The registry record also lists study-drug-related adverse events as a secondary outcome, but the summary figures alone do not establish which events were judged related to study drug. Nor do they establish that treatment caused a particular event.

Safety counts are descriptive. With no concurrent control group described, the record does not provide a comparative estimate of event rates. The serious-event term listing does not by itself indicate how many participants experienced that specific term, and the registry record does not give further event-level context. These entries should be read as reported observations in the study, not as a causal or comparative safety conclusion.

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

The registry record establishes that a Phase 2 study evaluated daily, subcutaneous rAvPAL-PEG at varying doses in subjects with phenylketonuria. It identifies blood phenylalanine concentration at baseline and Week 16 as the primary outcome and describes reduction in blood Phe as the study’s purpose. It also lists safety, tolerability, drug concentration, and antibody outcomes.

What the posted record does not establish is the size or direction of the primary outcome change. It reports no blood phenylalanine means, standard deviations, changes, confidence intervals, or outcome analyses. The record therefore cannot support a conclusion about how much concentrations changed or how precisely any change was estimated. A study objective is not a finding, and the absence of posted analyses is not evidence that no change occurred.

The design constrains interpretation as well. This was a single-group, open-label study, not a randomized comparison described against a control group. In general, an outcome pattern over time in one group can be informative descriptively, but cannot alone determine what would have happened under a different condition. The registry record does not describe an allocation method or masking that would address those limitations.

The safety figures document reported events in the study, including serious adverse events affecting 1 of 16 participants, other adverse events affecting 16 of 16 participants, and 0 deaths. They do not provide a treatment-versus-control comparison or establish causation. Angioedema is listed among serious adverse event terms at 6.2%, but the record does not make that entry a comparative risk estimate.

In general, statistical evidence should be interpreted through its estimate, precision, analysis population, and design—not through the study aim or a single summary alone. Since the outcome analyses and analysis details are not reported in the registry record, the appropriate interpretation is limited to the study’s design, intended measurements, and posted safety counts.

13. Why This Trial Matters Statistically

This trial is statistically informative as an example of how the design and reporting record shape the conclusions available to readers. Its central outcome is a continuous measure, blood phenylalanine concentration, with baseline and Week 16 specified. The record also specifies mean and standard deviation, which identify useful descriptive summaries. But those summaries are not accompanied by outcome values or analyses, so the intended statistical question cannot be answered numerically from the registry record.

The single-group design is also central to interpretation. In general, within-group measurements can describe a trajectory, but a control group helps distinguish changes associated with the intervention from changes that might have occurred over time for other reasons. Here, no like-for-like control comparison is described. This difference between describing change and attributing change is a core issue in clinical trial interpretation.

The record’s efficacy-population definition highlights another important point: enrollment and analysis populations need not be identical. Requiring both receipt of study drug and a post-treatment measurement defines who would contribute to the stated efficacy population, but the number meeting the criteria is not reported. Without that count and details about missing measurements, readers cannot assess how much information supports the primary outcome.

Finally, the registry record lists 10 outcome measures and no outcome analyses. In general, multiple outcomes make clear reporting of the analysis plan and multiplicity approach valuable, since readers need to know which questions were primary and how secondary results were interpreted. The posted record makes the intended measurement areas visible, while leaving the numerical efficacy analysis and its statistical uncertainty unreported.

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.

Several trial-specific limitations affect interpretation. The registry record describes a single-group, open-label study with allocation recorded as not applicable. It does not describe a concurrent control group, so there is no like-for-like comparison in the record. This limits the ability to distinguish a change over time from a change attributable to the intervention. Open-label status also means the record does not report masking.

The primary outcome is identified, but its results are not. Blood phenylalanine concentration is specified at baseline and Week 16, with mean and standard deviation as summaries; the registry record does not report the values, a change estimate, a confidence interval, or a test result. No outcome analyses are listed. The direction, magnitude, and precision of any change therefore remain unknown from the registry record.

The efficacy population requires receipt of any amount of study drug and a post-treatment blood Phe measurement. Its size is not reported, nor are the numbers with measurements at each time point. Missing-data patterns and handling methods are also not reported. The listed enrollment count cannot substitute for those analysis details.

The study used varying doses, but the record does not provide dose-specific outcome results or analyses. It also does not report the statistical plan, sample-size justification, interim analyses, or a multiplicity approach. Although several secondary outcome topics are listed, their analyses are not reported. These gaps prevent assessment of dose patterns, secondary findings, and the robustness of statistical conclusions.

The safety summaries are descriptive and lack a concurrent control comparison. They do not establish that events were caused by treatment. Taken together, these limitations mean the registry record describes the question and study structure more fully than it reports the evidence needed to quantify efficacy or compare safety.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Safety, Tolerability, and Efficacy Study of rAvPAL-PEG Administered Daily in Subjects With Phenylketonuria (PKU) — NCT01212744.
• Registry record last updated 2019-02-26; status last verified 2019-02.
• Results first posted 2019-02-26.
• 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

NCT01212744 is a completed Phase 2, open-label, single-group study of daily subcutaneous rAvPAL-PEG at varying doses in subjects with phenylketonuria. The registry record lists 16 enrolled participants and identifies blood phenylalanine concentration at baseline and Week 16 as the primary outcome, summarized by mean and standard deviation. The stated purpose was to evaluate reduction in blood Phe concentration.

The record lists 10 outcome measures and 0 outcome analyses. It does not report the primary outcome values, an analysis estimate, or its precision. The stated efficacy population requires receipt of any amount of study drug and a post-treatment blood Phe measurement, but the number meeting that definition is not reported.

Safety entries include serious adverse events affecting 1 of 16 participants, other adverse events affecting 16 of 16 participants, and 0 deaths. Angioedema is listed among serious adverse event terms at 6.2%. Because the study is single-group and no outcome analyses are posted, the registry record supports description of the design and reported counts, but not a numerical efficacy conclusion or a comparative safety conclusion.