Extension Study to Evaluate Safety and Tolerability of Peginesatide for Long-Term Treatment of Anemia in Participants With CKD (EU): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Extension Study to Evaluate Safety and Tolerability of Peginesatide for Long-Term Treatment of Anemia in Participants With CKD (EU) (NCT00453973), a non-randomized phase 2 study. The primary outcome is Proportion of Participants With Mean Hemoglobin in the Target Range of 10.0-12.0 Grams Per Deciliter (g/dL) After Final Dosing Guideline Change.

2. Clinical Question

The clinical question is therefore about maintenance during continued treatment in people who had already entered peginesatide treatment through earlier studies. It is not a question about starting peginesatide in an unselected population, and the record does not support a causal comparison between the two groups. The group descriptions identify different clinical and treatment histories, which matter when interpreting any difference in their recorded outcomes.

The registry states that the purpose was to evaluate long-term safety and tolerability as well as hemoglobin maintenance. The primary endpoint focuses on a target range for mean hemoglobin after a dosing-guideline change. Although the endpoint definition and timeframe are recorded, the registry does not report a numerator, denominator, percentage, estimate of uncertainty, or analysis result for it.

3. Trial Design

This was a Phase 2, non-randomized, open-label, parallel-group extension study. The registry records enrollment of 114 and lists the study status as terminated. The start is recorded as 2006-11 and primary completion as 2009-09. The sponsor is Affymax. The registry describes the study as evaluating long-term safety and tolerability of peginesatide for maintenance treatment of anemia in participants with chronic kidney disease.

Participants entered the extension from earlier peginesatide studies. The dialysis cohort had been on Epoetin at entry in its prior study and switched to peginesatide. The non-dialysis cohort had not been receiving erythropoiesis-stimulating agents in its prior study and received peginesatide. Both groups therefore had previous exposure to peginesatide; the record does not describe a concurrent untreated or active-comparator group.

Non-randomized allocation means the registry does not describe assignment by chance to comparable treatment groups. Open-label means treatment masking was none. These features are important because differences between the cohorts may reflect their different histories or characteristics, as well as events during the extension. The parallel model identifies groups followed in the study; it does not make them a randomized comparison.

The recorded endpoint timeframe is up to 54 months, but the registry does not describe individual follow-up duration or how duration varied among participants. It also does not report the reason the study was terminated. That status alone does not establish why the study ended or whether the endpoint was completed as planned. Details of the dosing-guideline changes, visit schedule, and specific monitoring procedures are not reported in the registry record.

The registry lists one outcome measure and no analyses. This is distinct from evidence that no analyses were conducted: it means analysis results are not recorded in the registry entry. The record also does not provide a statistical analysis plan or enough information to reconstruct the primary endpoint result.

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: Full Analysis - Number of participants with hemoglobin assessed after dosing guideline change

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 Proportion of Participants With Mean Hemoglobin in the Target Range of 10.0-12.0 Grams Per Deciliter (g/dL) After Final Dosing Guideline Change, measured over Up to 54 months.

The primary endpoint is the proportion of participants whose mean hemoglobin fell within the target range of 10.0-12.0 grams per deciliter after the final dosing-guideline change. Its timeframe is up to 54 months. The listed population is the full analysis population, described as participants with hemoglobin assessed after the dosing-guideline change.

A proportion is a binary summary: each participant either meets the specified target-range definition or does not, and the group result is the share meeting it among those included in the calculation. This type of endpoint gives a direct summary of how often a prespecified state was observed in the assessed population. It does not, by itself, show how close values were to the range boundaries, how much individual readings varied, or how hemoglobin changed over time.

Using a mean focuses the endpoint on an average rather than a single reading, but the registry does not explain how readings were selected or averaged, or how much observation was required for a participant to contribute. The record also does not provide the number assessed, the number meeting the range criterion, the resulting percentage, or an uncertainty interval. Thus, the endpoint's definition is available, but its observed value and precision are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

General: What does a proportion measure? A proportion expresses the number of people who meet a defined condition relative to the number included in that calculation. For this endpoint, the condition is having a mean hemoglobin within the stated target range after the final dosing-guideline change. The endpoint is binary at the participant level: the participant either meets the definition or does not. A proportion is useful for a clinically specified target because it describes the frequency of meeting that target, but it compresses information. It does not show the distribution of all hemoglobin values or whether values just outside the range differ substantially from values far outside it.

The registry defines the population as participants with hemoglobin assessed after the guideline change. That definition matters because the denominator for a proportion is the group actually included in the analysis, not necessarily everyone enrolled. The registry does not report the number assessed or the number meeting the target. It also does not specify how many measurements contributed to each participant's mean, how missing measurements affected eligibility, or which time points were used. Those details are not reported in the registry record, so the endpoint cannot be independently reconstructed.

Why does the design affect interpretation?

Random allocation is one way to make treatment groups comparable, on average, with respect to measured and unmeasured characteristics. This study was non-randomized, and the registry explicitly indicates that its groups are not a like-for-like control comparison. The cohorts had different prior treatment and dialysis histories. Consequently, a difference in a recorded outcome between them would be a descriptive difference between these groups, not necessarily an effect caused by peginesatide.

The open-label design means masking was none. In general, knowledge of treatment can affect decisions about care, reporting, assessment, and follow-up. Whether and how those possibilities affected this study is not reported in the registry record. The design still allows a descriptive account of events and endpoint status, but it does not remove the need to consider sources of bias when interpreting those data.

The extension setting also defines the population to which results would apply: participants had already received peginesatide in an earlier study. It does not directly describe people with no prior exposure or people selected under other conditions. The registry summary identifies prior treatment but does not report enough detail to characterize all eligibility criteria or the reasons participants entered or did not enter the extension.

What does precision mean for this endpoint?

General: an estimate is more useful when its uncertainty is also described. A confidence interval communicates the range of values that are reasonably compatible with the observed data under the chosen statistical model. Its width reflects both the amount of information and the variability in the data. The registry does not report a primary endpoint estimate or confidence interval, so the precision of the target-range proportion cannot be assessed.

For a binary endpoint, precision depends in part on the number of participants contributing data and on how the outcomes are distributed. The registry records enrollment of 114, but that figure alone does not establish the endpoint denominator: the listed analysis population is participants with hemoglobin assessed after the dosing-guideline change. The number in that population is not reported. No precision measure should therefore be inferred from enrollment alone.

Why can event counts be misleading without time at risk?

General: a simple count records how many participants experienced an event, whereas a rate also accounts for the amount of time participants were observed or exposed. If follow-up differs, the same count can correspond to different underlying event frequencies over time. The safety record lists numbers at risk and affected for each group, but does not report exposure-adjusted rates or detailed person-time. Its counts should be read as recorded participant counts, not as rates comparable across follow-up durations.

General: serious adverse events and other adverse events are separate categories in the registry listing. The counts do not themselves establish causation. The registry does not provide a randomized comparator, an adjudication method, or comparative statistical testing for these events. The serious-event terms listed with percentages are descriptive entries; the record does not give enough information to treat them as comparative risks or to infer why they occurred.

What do the planning assumptions mean?

The registry describes planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. Such values are hypothetical planning quantities, not the power observed in the trial. They answer a conditional question about sample size under specified assumptions; they do not show that the study had a particular probability of detecting an effect or that an effect was established.

The record also states that planning illustrations use participants per arm for non-time-to-event outcomes. That convention does not change the underlying design: this extension was non-randomized, and its two cohorts were not like-for-like control arms. The registry does not report the study's own sample-size justification or its statistical plan. Those items are not reported in the registry record, so the planning illustration should not be presented as the protocol's design calculation.

What can be inferred from the analysis listing?

The registry lists one outcome measure and zero analyses. This describes what is entered in the registry, not necessarily every analysis performed by investigators. No primary endpoint estimate, test, model, confidence interval, or treatment-group comparison is included. A statistical interpretation should therefore distinguish between the endpoint that was defined and results that were actually posted. Here, the endpoint definition is recorded, while its numerical result and inferential analysis are not reported in the registry record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Maintenance Switch in Dialysis Participants", "Treatment Initiation in Non-Dialysis Participants")
n      <- c(28, 40)
events <- c(0, 0)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Maintenance Switch in Dialysis Participants  28  0  0.0  0.0  12.3  0.0  12.1  0.1  11.9
ARM  Treatment Initiation in Non-Dialysis Participants  40  0  0.0  0.0  8.8  0.0  8.8  0.1  8.6

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure and no analyses. It does not report a statistical analysis plan, a hierarchy of outcomes, or a procedure for controlling multiplicity. With no analysis results listed, it is not possible to determine whether multiple comparisons were performed or how they were handled. The record does not state whether any interim analyses took place; that information is not reported in the registry record.

The primary endpoint population is described as participants with hemoglobin assessed after the dosing-guideline change. The registry does not give the number in that population, the number with missing hemoglobin assessments, or the number excluded from the endpoint calculation. It does not explain how missing measurements were handled, whether participants were included according to an intention-to-treat principle, or how discontinuation or incomplete follow-up affected the analysis. These details are not reported in the registry record.

The phrase “Full Analysis” appears in the endpoint population description, but the record does not define its operational rules. It is therefore not possible to determine from the entry which enrolled participants were included, or how the analysis population related to the participants at risk in the safety listings. The enrollment figure should not be substituted for the endpoint denominator.

These omissions limit reproducibility and interpretation. Without the analysis population, missing-data approach, and statistical plan, the endpoint result cannot be reconstructed or assessed for sensitivity to alternative assumptions. The absence of registry-listed analyses should not be interpreted as proof that the investigators performed none; it means the registry record does not report them.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

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: hyperkalaemia (4.8%), atrial fibrillation (3.9%), acute coronary syndrome (3.2%), acute myocardial infarction (3.2%), cardiac arrest (3.2%).

The registry lists serious and other adverse-event counts separately for each cohort. In the Maintenance Switch in Dialysis Participants group, 51 participants were listed as at risk for serious events and 10 as affected; 51 were listed as at risk for other events and 46 as affected. In the Treatment Initiation in Non-Dialysis Participants group, the corresponding serious-event figures are 63 at risk and 31 affected, and the other-event figures are 63 at risk and 55 affected. These are registry counts, not a randomized comparison.

The serious-event terms with the largest listed percentages include Hyperkalaemia at 4.8%, Atrial fibrillation at 3.9%, and Acute coronary syndrome, Acute myocardial infarction, Cardiac arrest, and Catheter related complication at 3.2% each. The record does not give a comparative analysis for these terms or establish that peginesatide caused them. The terms and percentages are descriptive, and their interpretation is limited by the non-randomized design.

The registry does not report exposure-adjusted rates, detailed follow-up time for each participant, or a definition of how the listed event categories were counted. Counts alone do not show the rate over time. Deaths are not reported in the listed safety data.

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

The record describes an extension study intended to evaluate long-term safety and tolerability of peginesatide and maintenance of hemoglobin in participants with chronic kidney disease who had already received peginesatide in an earlier study. It defines a primary endpoint based on mean hemoglobin falling within the 10.0-12.0 grams per deciliter target range after the final dosing-guideline change. It also records safety counts and serious-event terms for two cohorts with different histories.

Those details do not establish the observed primary endpoint result. The registry does not report the proportion meeting the target, the number assessed, or an uncertainty interval. It therefore cannot show from the posted primary outcome whether the target was met frequently or infrequently, or how precisely any estimate was determined.

The study is not a randomized comparison. Its two groups entered from different prior studies and had different dialysis and treatment histories. They should not be interpreted as equivalent groups differing only in treatment. Any observed difference between them would be descriptive and could reflect factors other than treatment. The record does not support a causal conclusion about peginesatide.

The safety counts provide a record of affected participants within the listed cohorts, but they are not exposure-adjusted rates and are not accompanied by comparative statistical testing. The serious-event terms and percentages do not by themselves establish a treatment relationship. The registry also does not report a reason for the terminated status, so that status cannot be used to infer a safety finding or a particular study outcome.

In short, the registry supports a careful description of the design, endpoint definition, and recorded adverse-event figures. It does not supply enough outcome or analysis information to estimate the primary endpoint, quantify its precision, or determine a treatment effect. These limits are especially important when reading a long-term extension that enrolled participants with prior treatment exposure and lacked a like-for-like control group.

14. Why This Trial Matters Statistically

This study is statistically informative as an example of the distinction between a long-term extension and a controlled efficacy comparison. Participants had prior peginesatide exposure, and the two cohorts came from different prior studies with different clinical and treatment histories. The non-randomized design can describe what was recorded among these participants, but it does not isolate a treatment effect in the way a randomized, comparable control group could.

The endpoint also illustrates why a clear definition is only one part of a usable result. The target range and assessment timing are specified, and the analysis population is described as participants with hemoglobin assessed after the dosing-guideline change. Yet the registry does not report the numerator, denominator, estimate, or uncertainty. Without those pieces, readers cannot evaluate either the observed target-range frequency or its precision.

The safety record demonstrates another important distinction: counts of affected participants are not the same as event rates over time, and neither is automatically a causal treatment comparison. Follow-up duration and exposure-adjusted rates are not reported. The cohorts are also not directly comparable, so differences in recorded safety counts should be interpreted descriptively.

Finally, registry completeness matters. The entry records an endpoint and safety listings but no analyses, and it does not report the analysis plan, missing-data handling, or reason for termination. Recognizing these omissions prevents a study's design description from being mistaken for its results. The record can inform readers about what was intended and what adverse-event data were entered, while leaving key questions about endpoint estimation and statistical inference unanswered.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The principal limitation is that the primary endpoint result is not reported in the registry record. Although the target-range definition and timeframe are listed, the number assessed, the number meeting the definition, the percentage, and any uncertainty measure are absent. The endpoint therefore cannot be quantitatively interpreted or reproduced from this entry.

The study was non-randomized, open-label, and explicitly did not have like-for-like control arms. The cohorts had different prior study settings and treatment histories: the dialysis group had been receiving Epoetin before switching to peginesatide, while the non-dialysis group had not been receiving erythropoiesis-stimulating agents before peginesatide. This limits direct comparisons between their outcomes and restricts causal interpretation.

The registry does not report the reason for termination, the statistical analysis plan, the sample-size justification, interim analyses, missing-data methods, or the operational definition of the full analysis population. It also does not provide individual follow-up duration, exposure-adjusted adverse-event rates, or details sufficient to reconstruct how hemoglobin measurements were averaged. These items are not reported in the registry record.

Enrollment of 114 does not establish how many participants contributed to the primary endpoint or how completely outcomes were observed. Safety counts are presented without exposure adjustment, and the record does not provide a comparative analysis. The listing of serious-event terms and percentages is informative as a descriptive registry entry, but it does not establish causality or comparative risk.

These limitations concern the information recorded and the study design; they do not imply that unreported analyses or procedures did not occur. They do mean that the registry entry alone cannot support a precise estimate of the primary endpoint or a controlled treatment-effect conclusion.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Extension Study to Evaluate Safety and Tolerability of Peginesatide for Long-Term Treatment of Anemia in Participants With CKD (EU) — NCT00453973.
• Registry record last updated 2012-06-29; status last verified 2012-06.
• Results first posted 2012-05-28.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

This Phase 2 extension study evaluated peginesatide for long-term maintenance treatment of anemia in participants with chronic kidney disease who had previously received peginesatide. The registry records enrollment of 114, non-randomized allocation, no masking, a parallel model, and terminated status. Its primary endpoint was the proportion with mean hemoglobin in the 10.0-12.0 grams per deciliter target range after the final dosing-guideline change, over up to 54 months.

The study included a dialysis cohort with prior Epoetin treatment and a non-dialysis cohort that had not been receiving erythropoiesis-stimulating agents. The registry records serious and other adverse-event counts and selected serious-event terms, but no primary endpoint analysis. The endpoint result, statistical analysis plan, missing-data methods, and reason for termination are not reported in the registry record. The two cohorts are not a like-for-like control comparison, so their data are descriptive rather than a randomized estimate of treatment effect.