Randomized Study Comparing Genz-644470, Placebo, and Sevelamer Carbonate in Chronic Kidney Disease Patients on Hemodialysis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Randomized Study Comparing Genz-644470, Placebo, and Sevelamer Carbonate in Chronic Kidney Disease Patients on Hemodialysis (NCT00853242), a randomized phase 2 study. The primary outcome is Change From Baseline in Serum Phosphorus at Day 22 (Genz-644470 vs Placebo).

2. Clinical Question

The study focused on serum phosphorus in a population described as having hyperphosphatemic chronic kidney disease while receiving hemodialysis. Its stated purpose was to compare the effects of Genz-644470 with placebo and sevelamer carbonate on reduction in serum phosphorus. The primary endpoint was the change from baseline in serum phosphorus at Day 22, expressed in mg/dL.

The randomized parallel-group design assigned participants to placebo, one of three Genz-644470 dose groups, or one of three sevelamer carbonate dose groups. The primary outcome title identifies comparisons of Genz-644470 against placebo; sevelamer carbonate appears in the additional serum phosphorus comparison. The registry describes treatment as three weeks of oral dosing with meals.

This is a short-term biomarker question. A change in serum phosphorus describes the measured laboratory outcome over the stated period. It does not by itself establish effects on symptoms, longer-term health outcomes, or the comparative value of treatments beyond the measurements and comparisons reported in the registry record.

3. Trial Design

This was a Phase 2, randomized, double-blind, placebo-controlled, dose-ranging study with a parallel-group model and quadruple masking. The registry reports enrollment of 349 and a completed study. The condition listed is chronic kidney failure. The study began in 2009-02, and primary completion was recorded in 2009-08.

Seven treatment groups are described: matched placebo; Genz-644470 at 2.4 g/day, 4.8 g/day, or 7.2 g/day; and sevelamer carbonate at the same three daily dose levels. Each listed regimen was taken orally three times a day with meals for three weeks. The primary serum phosphorus outcome was assessed at baseline and Day 22.

Randomization is intended to create groups that are comparable, on average, with respect to factors that could affect an outcome. Masking can reduce the influence of expectations on participant experience, care, and outcome assessment. The registry’s quadruple-masking label indicates the stated masking category; which specific roles were masked is not reported in the registry record. The allocation ratio and the randomization procedure are not reported in the registry record.

The primary analysis population is described as the Full Analysis Set. It included participants who received at least one dose of study drug and had a baseline and at least one post-baseline phosphorus measurement no later than three days after the date of the last study drug. The numbers contributing to the reported primary group summaries differ across groups, and the record does not provide a complete explanation for those analysis counts.

The trial’s original sample-size justification, planned statistical analysis plan, interim analyses, and the allocation method are not reported in the registry record. The planning illustrations associated with the posted estimates are separate from the original trial design rationale.

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 670 participants were screened of which 321 were screen failure and 349 participants were randomized. After screening, participants entered a two-week phosphate binder washout period prior to randomization.

Only the first 6 of 7 groups are shown.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Full Analysis Set (FAS) included all participants who received at least one dose of study drug and had baseline and at least one post-baseline phosphorus measure less than or equal to (\<=) 3 days after date of last study drug.

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: Safety Set included all randomized participants who received at least one dose of study drug.

Only the first 6 of 8 groups are shown.

6. Primary Endpoint

The registry lists the primary outcome as Change From Baseline in Serum Phosphorus at Day 22 (Genz-644470 vs Placebo), measured over Baseline, Day 22.

The primary endpoint is change from baseline in serum phosphorus at Day 22, measured in mg/dL. A change score describes how much a participant’s measured value shifted over the study period; a negative group mean indicates a downward average change. The registry reports the endpoint as a mean with standard deviation, a way to present the group’s average change along with the spread of participant-level changes.

Serum phosphorus was selected because the study’s stated purpose was to compare treatment effects on its reduction in people with hyperphosphatemic chronic kidney disease receiving hemodialysis. Measuring change from baseline focuses the comparison on movement during the study rather than only on the final measured value. The placebo group provides a reference for interpreting the observed changes in the Genz-644470 groups.

The primary outcome is a laboratory measure, not a direct measure of symptoms, functioning, or longer-term clinical events. The registry reports the measurement at baseline and Day 22, following a three-week dosing regimen. It does not report a threshold for a clinically meaningful change, and it does not describe how a particular change should be interpreted for an individual participant.

The registry’s outcome population definition requires a baseline measurement and at least one post-baseline measurement within a specified period after the last study drug. Results therefore describe the participants who met that analysis definition; they should not automatically be read as results for every person enrolled.

7. Results Posted in the Registry

• Genz-644470 2.4 g/Day: mean -0.60 versus -0.00 on control; difference -0.60 (95% CI -1.16 to -0.04), standardized effect d = -0.43; z-test p = 0.035.
• Genz-644470 4.8 g/Day: mean -1.20 versus -0.00 on control; difference -1.20 (95% CI -1.78 to -0.62), standardized effect d = -0.83; z-test p = <0.001.
• Genz-644470 7.2 g/Day: mean -1.80 versus -0.00 on control; difference -1.80 (95% CI -2.46 to -1.14), standardized effect d = -1.11; z-test p = <0.001.

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.

Change From Baseline in Serum Phosphorus at Day 22 (Genz-644470 vs Sevelamer Carbonate)

• 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:
  • Genz-644470 4.8 g/Day: mean -1.20 versus -0.60 on control; difference -0.60 (95% CI -1.22 to 0.02), standardized effect d = -0.39; z-test p = 0.059.
  • Genz-644470 7.2 g/Day: mean -1.80 versus -0.60 on control; difference -1.20 (95% CI -1.89 to -0.51), standardized effect d = -0.70; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Genz-644470 4.8 g/Day and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Genz-644470 7.2 g/Day than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Change From Baseline in Serum Calcium (Albumin-adjusted)-Phosphorus Product at Week 22

• 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:
  • Genz-644470 2.4 g/Day: mean -4.50 versus -0.10 on control; difference -4.40 (95% CI -9.35 to 0.55), standardized effect d = -0.35; z-test p = 0.081.
  • Genz-644470 4.8 g/Day: mean -9.20 versus -0.10 on control; difference -9.10 (95% CI -14.58 to -3.62), standardized effect d = -0.66; z-test p = 0.001.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Genz-644470 2.4 g/Day and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Genz-644470 4.8 g/Day than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Change From Baseline in Total Cholesterol at Day 22

• 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:
  • Genz-644470 2.4 g/Day: mean -13.50 versus -3.80 on control; difference -9.70 (95% CI -17.94 to -1.46), standardized effect d = -0.47; z-test p = 0.021.
  • Genz-644470 4.8 g/Day: mean -11.20 versus -3.80 on control; difference -7.40 (95% CI -15.48 to 0.68), standardized effect d = -0.36; z-test p = 0.073.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Genz-644470 2.4 g/Day than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Genz-644470 4.8 g/Day and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes cover serum phosphorus comparisons against sevelamer carbonate, the albumin-adjusted calcium-phosphorus product, total cholesterol, and LDL cholesterol. The posted group summaries show that changes were not uniform across endpoints or across dose groups. Secondary outcomes therefore add context about the measured laboratory profile but do not form a single consistent measure of treatment effect.

The secondary serum phosphorus outcome addresses an active-comparator question rather than repeating the primary placebo comparison. The sponsor reported rank-sum p-values for the listed comparisons at 2.4 g/day and 4.8 g/day, but a sponsor-reported result for the 7.2 g/day comparison is not reported in the registry record. The recalculated comparisons use different group pairings and a mean-difference approach, so they should not be treated as equivalent to the sponsor’s reported tests.

The albumin-adjusted calcium-phosphorus product and cholesterol outcomes are additional continuous laboratory measures. Their observed group means and variability provide descriptive evidence for these outcomes, but the registry does not report sponsor inferential tests for them. The calcium-phosphorus product outcome title refers to Week 22, while its timeframe is listed as Baseline, Day 22. That timing inconsistency is not resolved in the registry record.

Secondary results generally carry less inferential weight than a prespecified primary outcome because multiple outcomes and comparisons increase the opportunity for chance findings. The multiplicity strategy and the status of these secondary comparisons as confirmatory or exploratory are not reported in the registry record. They can inform the overall pattern, but they should not be used to override the primary analysis or to make strong claims based on isolated unadjusted results.

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

• Change From Baseline in Serum Phosphorus at Day 22 (Genz-644470 vs Sevelamer Carbonate)
• Change From Baseline in Serum Calcium (Albumin-adjusted)-Phosphorus Product at Week 22
• Change From Baseline in Total Cholesterol at Day 22
• Change From Baseline in Low Density Lipoprotein (LDL) Cholesterol at Day 22

9. Statistical Interpretation

10. Statistical Methods Explained

What does a mean change describe?

The primary outcome is continuous: it can take a range of measured values rather than being a yes-or-no event. The registry reports the mean change in each group. A mean condenses participant-level changes into an average, while the standard deviation describes how widely those changes varied around the mean. A group mean does not imply that every participant had a change of that size or even the same direction.

For the recalculated comparisons, the mean difference is the difference between the two posted group means. A negative value in these comparisons indicates that the Genz-644470 group mean change was more negative than the placebo group mean change. The recalculation uses the summary statistics posted in the registry, and it is unadjusted. It should be distinguished from an analysis of participant-level data, which is not available in the registry record.

Why are there two kinds of comparison results?

The sponsor-reported primary analyses used Wilcoxon Rank Sum Tests. This rank-based method compares the relative ordering of observations between two groups and does not require the same normal-distribution assumption as a basic mean comparison. It is not an estimate of the arithmetic mean difference. The registry reports a p-value for each listed placebo comparison, but no corresponding effect estimate or confidence interval from that test.

The recalculated results instead estimate unadjusted differences in means and provide confidence intervals based on the posted means, standard deviations, and group counts. These calculations treat the outcome as a continuous measure and use a standard error based on the group variability and the number of observations. Because the estimand and method differ from the reported rank-sum analysis, the p-values can differ without indicating a data discrepancy.

What does a p-value say?

A p-value measures how unusual data at least as incompatible with a stated null hypothesis would be if that hypothesis and the test assumptions were true. It is not the probability that the null hypothesis is true, and it does not measure the probability that the result arose by chance in a broad, assumption-free sense. Smaller p-values indicate greater incompatibility with the null model for that particular test, but they do not show whether a difference matters clinically.

Several doses and several endpoints appear in the registry. When many hypotheses are tested, the chance of at least one apparently notable result can increase. Unless a multiplicity strategy is specified and applied, individual p-values should not be treated as a single confirmatory assessment across all comparisons. The multiplicity approach is not reported in the registry record.

How should standard deviations and confidence intervals be read?

A standard deviation describes the spread of individual measurements around a group mean; it is not the uncertainty in the mean itself. A confidence interval for a mean difference conveys the range of effect estimates reasonably compatible with the data and calculation method, subject to the model’s assumptions. Wider intervals indicate less precision, while narrower intervals indicate more precision. An interval crossing zero includes both a difference in one direction and no difference under the interval’s method; an interval that does not cross zero excludes zero under that method, but does not establish clinical importance.

These interpretations are general statistical explanations. The recalculated intervals are unadjusted, and the registry’s own rank-sum analyses do not include confidence intervals in the posted results. No covariate-adjusted estimates, sensitivity analyses, or model diagnostics are reported in the registry record.

What is the role of the analysis population?

The Full Analysis Set definition includes participants with at least one dose and the required baseline and post-baseline phosphorus measurements in the stated window. Restricting an analysis to people with outcome measurements can affect how representative the results are of all randomized participants, particularly if missing measurements are related to outcome or treatment. The registry does not report the number or reasons for missing outcome measurements, or a method for imputing or otherwise handling missing data beyond the stated population definition.

General statistical interpretation: randomization supports comparison of assigned groups when the analysis preserves the randomized comparison and follow-up is adequately accounted for. The registry record does not provide enough information to determine all details of adherence to assignment, protocol deviations, or the handling of participants without eligible measurements.

11. Confidence Intervals and Precision

Precision concerns how closely an estimate is likely to locate the underlying group difference, given the data and the analysis assumptions. The recalculated primary mean differences have confidence intervals that quantify uncertainty around those unadjusted estimates. For Genz-644470 2.4 g/day versus placebo, the estimate was -0.6 mg/dL with a confidence interval from -1.157 to -0.043. For 4.8 g/day, the estimate was -1.2 mg/dL with a confidence interval from -1.782 to -0.618. For 7.2 g/day, the estimate was -1.8 mg/dL with a confidence interval from -2.457 to -1.143.

Each interval lies on the negative side of zero under the recalculation, but the interval widths show that the exact mean difference remains uncertain. The interval for the 2.4 g/day comparison reaches closer to zero than the other intervals. That feature reflects less separation from zero in the estimate relative to its uncertainty; it does not on its own determine clinical relevance. The registry does not supply a threshold for a meaningful change in serum phosphorus.

Confidence intervals are not guarantees that the true value lies within a particular interval, and they do not address biases not represented by the calculation. These intervals use the posted group summaries and are not adjusted for multiple comparisons. They should not be confused with the sponsor’s rank-sum test results, for which intervals are not reported in the registry record.

Group standard deviations are substantial relative to the observed mean changes, indicating variability in participant-level change. The mean and interval therefore describe group-level evidence, not an expected change for every participant. Precision is also affected by the analysis population counts, which are smaller than the registry enrollment and differ across treatment groups. Reasons for those differences are not reported in the registry record.

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 illustrative calculations based on the observed effect in a comparison and are not the trial’s original sample-size justification. The stated calculation assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and an effect to detect set to the stated fraction of the observed effect.

The 80% power column describes the number of participants per arm that the planning calculation estimates would be needed to have an 80% chance of detecting the specified effect under those assumptions, if that effect and model were correct. The 90% power column uses a higher target chance of detection, so its participant requirement is larger for the same assumed effect. These are planning targets, not guarantees about the result of a future study.

Rows for smaller fractions of the observed effect require more participants per arm. This is because a smaller difference is harder to distinguish from ordinary variability at the same significance level and target power. The estimates also depend on the observed variability used in the calculation; if that differs in another study, the planning requirements can change.

These figures are not observed power. They are not a retrospective measure of whether the completed trial had a sufficient chance to detect its findings, and they should not be interpreted as evidence that a result is reliable or unreliable. The original trial’s design assumptions, including its own sample-size rationale, are not reported in the registry record.

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 = -0.600; pooled standard deviation σ = 1.401.
2. n = 2 × (1.96 + 0.842)² × 1.401² / -0.600² = 85.6, rounded up to 86 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 <- -0.6                      # observed difference in means
sigma <- 1.40148730521067                     # 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(853242)
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 = 86 (80% power), 115 (90% power)
 75% of observed effect: n per arm = 153 (80% power), 204 (90% power)
 50% of observed effect: n per arm = 343 (80% power), 459 (90% power)
power.t.test: 86.6 
Simulated power at n = 86 per arm: 0.797 (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. Analyses Reported by the Sponsor

The registry’s reported primary analyses compare each Genz-644470 group with placebo using Wilcoxon Rank Sum Tests. The reported p-values are 0.025 for 2.4 g/day, < 0.001 for 4.8 g/day, and < 0.001 for 7.2 g/day. The registry does not provide rank-sum effect estimates or confidence intervals alongside those tests.

The recalculated results use the posted group means and standard deviations to estimate unadjusted mean differences and confidence intervals. They produce mean differences of -0.6 mg/dL, -1.2 mg/dL, and -1.8 mg/dL, respectively, with recalculated p-values of 0.035, <0.001, and <0.001. The recalculation and sponsor analysis are not identical statistical procedures: one targets a difference in means, while the reported rank-sum test compares the ordering of observations.

The p-values need not match because the analyses use different statistics and assumptions. There is no indication in the registry record that the underlying posted summaries conflict with the reported tests, and the discrepancy flag is false. The sponsor’s analysis should be understood as the analysis reported in the registry; the recalculation is an additional, unadjusted summary-based perspective, not a replacement for participant-level analysis or the sponsor’s test.

The record does not report whether the rank-sum comparisons were adjusted for the multiple dose comparisons, nor does it report a complete analysis plan. Neither set of p-values alone establishes the clinical meaning of the observed changes.

15. Multiplicity, Missing Data and Analysis Populations

The registry lists multiple dose comparisons for the primary serum phosphorus outcome, additional comparisons involving sevelamer carbonate, and several secondary laboratory outcomes. Testing multiple hypotheses creates a multiplicity concern: even if no true differences existed, the chance of obtaining one or more low p-values across a large set of tests could be higher than for a single prespecified test. Statistical procedures can control this issue, but the method depends on the analysis plan and the questions being treated as a family.

A multiplicity adjustment, a hierarchy of hypotheses, or another strategy for controlling the overall error rate is not reported in the registry record. The reported p-values should therefore be read as unadjusted evidence for their individual comparisons, not as proof that the complete set of outcomes met a study-wide criterion. The registry does not identify which secondary findings, if any, were intended to be confirmatory.

The record defines the Full Analysis Set for the primary endpoint by dose received and availability of baseline and post-baseline serum phosphorus measurements within the specified window. This is useful information about who contributed to the primary outcome analysis, but it does not fully describe missing-data handling. The number of participants excluded from the analysis, the reasons for missing measurements, and any imputation or sensitivity analyses are not reported in the registry record.

Enrollment and outcome-analysis counts are not interchangeable. The posted group summaries show the participants contributing to each outcome, while enrollment refers to the trial’s reported enrollment. The registry does not explain all differences between those counts or report a complete accounting of randomized participants by analysis population.

The randomization procedure, allocation ratio, protocol deviations, and analysis plan are not reported in the registry record. Interim analyses are also not reported in the registry record. Without those details, it is not possible to assess fully whether all analyses followed a prespecified plan or how missing information and multiple testing were addressed.

16. 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 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: coronary artery disease (2.1%), myocardial infarction (2.1%), appendicitis (2.1%), catheter bacteraemia (2.1%), arteriovenous graft thrombosis (2.1%).

The adverse-event summary reports serious adverse events by treatment group as counts among those at risk. The serious-event figures were 4 of 50 for placebo; 2 of 49 for Genz-644470 2.4 g/day; 6 of 48 for 4.8 g/day; and 6 of 50 for 7.2 g/day. For sevelamer carbonate, the figures were 8 of 50 at 2.4 g/day, 5 of 51 at 4.8 g/day, and 5 of 48 at 7.2 g/day. These are descriptive counts, not adjusted comparisons of risk.

The registry also reports other adverse events by group, but the counts do not establish that an event was caused by a study drug. The listed serious-event terms each have a reported frequency of 2.1%; the record does not give an arm-level breakdown for those terms. Death counts are not reported in the registry record.

These summaries do not by themselves show whether treatment groups differ reliably in safety. The study was short, and the registry does not report a statistical comparison of serious adverse events or detailed event-level timing and attribution. Small differences in counts should not be interpreted as evidence of a causal treatment effect.

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

The central statistical finding is that the posted mean serum phosphorus change was more negative in each Genz-644470 dose group than in the placebo group, with increasingly negative group means across the listed doses. The registry’s rank-sum tests report p-values for each placebo comparison, and the recalculated mean-difference estimates have confidence intervals on the negative side of zero. These results describe short-term laboratory measurements in the analysis population defined by the registry.

The findings do not establish the clinical importance of the observed changes. The registry does not report a minimum clinically important difference, longer-term outcomes, or how the biomarker changes relate to symptoms or other health outcomes. Nor do the results establish that the measured pattern would persist beyond the three-week regimen and Day 22 assessment.

The study included sevelamer carbonate groups, but the primary outcome is framed as Genz-644470 versus placebo. The registry’s secondary active-comparator results are limited and use differing analytic presentations. The available record does not justify a broad conclusion about the relative clinical merits of the treatments.

Statistical significance is not proof that a treatment works, and a nonsignificant result would not establish equivalence or absence of an effect. The p-values, estimates, and confidence intervals address particular comparisons under particular assumptions. They do not eliminate uncertainty about participant selection, missing measurements, multiplicity, or the relevance of a laboratory outcome to clinical outcomes.

Interpretation should therefore remain bounded: the reported data show group-level changes in serum phosphorus over the stated short-term period, with uncertainty around the mean differences and variability among participants. They do not support individualized predictions or medical decisions.

18. Why This Trial Matters Statistically

This trial illustrates why a statistical result should be read through its estimand and method, rather than through a p-value alone. The primary reported tests are Wilcoxon Rank Sum Tests, while the recalculated summaries estimate unadjusted differences in means. Both describe the same general comparison but answer statistical questions in different ways, so their p-values are not expected to be identical.

The dose-ranging structure also makes the pattern across groups relevant, but a sequence of group means is descriptive evidence rather than a formal dose-response analysis. The registry does not report a prespecified trend model or a multiplicity plan. Recognizing those omissions helps distinguish a visible pattern from a separately tested claim.

Precision matters as well as direction. The recalculated confidence intervals communicate uncertainty about the mean differences, while the group standard deviations show that individual changes varied. These are distinct features: uncertainty about an average is not the same as variation among participants.

Finally, the endpoint is a laboratory biomarker measured over a short period. Statistical evidence about a measured change does not automatically answer questions about clinical outcomes or durability. This record is useful for examining how randomized group comparisons, rank-based tests, mean differences, confidence intervals, and multiple outcomes should be interpreted together, while remaining attentive to what the registry does not report.

19. 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 leaves important design and analysis details unspecified. The original sample-size justification, allocation ratio, randomization procedure, and full statistical analysis plan are not reported. The record also does not describe interim analyses, adjustment for multiple comparisons, or sensitivity analyses. These omissions limit assessment of how the analyses were planned and how robust the findings are to alternative assumptions.

The primary analysis uses the Full Analysis Set definition, which requires eligible serum phosphorus measurements after treatment initiation. The registry does not provide a full explanation of missing measurements, exclusions, protocol deviations, or how those factors may have affected the analysis population. Analysis group counts vary across outcomes, and the reasons are not reported in the registry record.

The trial assessed a short-term laboratory endpoint after a three-week regimen. Longer-term follow-up results are not reported in the registry record. The record also does not define a clinically meaningful change in serum phosphorus, and it does not link the reported biomarker change to clinical outcomes.

The sponsor-reported primary tests are rank-based, while recalculated mean differences use posted summary statistics and are unadjusted. The latter cannot reproduce an analysis of participant-level data or account for features not present in the summaries. The registry does not provide confidence intervals for the sponsor’s reported tests.

There is also a timing-label difference for the calcium-phosphorus product outcome: its title says Week 22, while the timeframe says Baseline, Day 22. The registry record does not clarify that discrepancy. These limitations counsel against extending the results beyond the recorded comparisons and measurement period.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: Randomized Study Comparing Genz-644470, Placebo, and Sevelamer Carbonate in Chronic Kidney Disease Patients on Hemodialysis — NCT00853242.
• Registry record last updated 2015-05-01; status last verified 2015-04.
• Results first posted 2015-05-01.
• 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.

23. Record Summary

NCT00853242 is a completed Phase 2 randomized, double-blind, placebo-controlled, dose-ranging study in people with hyperphosphatemic chronic kidney disease receiving hemodialysis. Enrollment was 349. The trial compared three daily doses of Genz-644470 with matched placebo and included three corresponding sevelamer carbonate dose groups.

The primary outcome was change in serum phosphorus from baseline to Day 22. Group mean changes were -0.0 mg/dL with placebo and -0.6 mg/dL, -1.2 mg/dL, and -1.8 mg/dL with Genz-644470 at 2.4 g/day, 4.8 g/day, and 7.2 g/day, respectively. The registry reports Wilcoxon Rank Sum Test p-values for the placebo comparisons; separate unadjusted mean-difference recalculations include confidence intervals.

The record lists additional laboratory outcomes and adverse-event counts. Multiplicity handling, the original sample-size rationale, detailed missing-data procedures, and several elements of the statistical plan are not reported in the registry record. The posted evidence concerns short-term group-level measurements and should be interpreted within those limits.