This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Study to Evaluate the Efficacy and Safety of PT20 in Subjects With Hyperphosphataemia and Dialysis Dependent Chronic Kidney Disease (NCT02151643), a randomized phase 2 study. The primary outcome is Change in Serum Phosphate Concentration From Baseline (Visit 7, Day 1) to Visit 11 (Day 29).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02151643 |
| Phase | Phase 2 |
| Condition | Hyperphosphataemia |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Quadruple |
| Enrollment | 153 |
| Arms in the primary outcome | 5 |
| Lead sponsor | Phosphate Therapeutics |
| Results posted | Yes |
2. Clinical Question
Population
Participants had hyperphosphataemia and dialysis-dependent chronic kidney disease. The registry describes the primary analysis population as the Intent-to-Treat population. Enrollment was 153, although the primary endpoint results are reported for smaller groups. The registry record does not explain the difference between enrollment and the endpoint group counts.
Intervention
Participants were assigned to one of four oral PT20 regimens: 400 mg three times daily, 800 mg three times daily, 1600 mg three times daily, or 3200 mg three times daily. Dosing began with the first meal or snack after receipt of study medication on Day 1. The record describes no dose change within each cohort.
Comparator
The comparator was matched oral placebo, administered three times daily. The registry describes five parallel groups and reports the primary endpoint separately for each PT20 dose and placebo.
Primary question
The primary question was whether serum phosphate concentration changed from baseline on Day 1 to Day 29, and how that change varied across the four PT20 dose groups and placebo. The endpoint was measured in mg/dL. The registry also lists analyses of dose response and comparisons, but the posted analysis entries do not consistently identify the exact statistical question tested by each p-value.
3. Trial Design
This was a randomized, quadruple-masked, parallel-group phase 2 study sponsored by Phosphate Therapeutics. It enrolled 153 participants with hyperphosphataemia and dialysis-dependent chronic kidney disease. The registry lists the study as completed; the recorded start date is 2014-05-07 and the primary completion date is 2015-03-18.
Participants were allocated among four PT20 dose groups and a matched-placebo group. PT20 was given orally three times daily at 400 mg, 800 mg, 1600 mg, or 3200 mg per administration. The corresponding daily amounts are listed as 1.2 g/day, 2.4 g/day, 4.8 g/day, and 9.6 g/day. Placebo was also administered orally three times daily. Dosing began with the first meal or snack after receipt of medication on Day 1. The record says dose administration was not to change within each cohort.
The primary endpoint compared serum phosphate concentration at baseline, defined as Visit 7 on Day 1, with Visit 11 on Day 29. Blood samples were collected, processed, and analysed by a central laboratory. The primary population was the Intent-to-Treat population. The registry reports endpoint group counts of 20, 20, 20, 32, and 35 for the four PT20 groups and placebo, respectively.
The record also lists secondary changes in haemoglobin, serum ferritin, transferrin saturation, calcium x phosphate product, and the overall Gastrointestinal Symptom Rating System score over the same visit interval. Details of the randomization procedure, masking implementation, allocation concealment, and the rationale for the planned enrollment are not reported in the registry record. The registry record also does not report the planned duration of treatment beyond the endpoint visit information.
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: Subjects underwent stratified randomisation into 1 of the 4 PT20 dose groups or equivalent placebo group based pre-randomisation serum phosphate level (ratio of 8:8:8:13:13) - serum phosphate \< 7.5 mg/dL were deemed to have a lower level of serum phosphate; serum phosphate ≥ 7.5 mg/dL were deemed to have a higher level of serum phosphate.
Overall Study
| Stage | Group 1 - PT20 400 mg Tid | Group 2 - PT20 800 mg Tid | Group 3 - PT20 1600 mg Tid | Group 4 - PT20 3200 mg Tid | Group 5 - Placebo Tid |
|---|---|---|---|---|---|
| STARTED | 26 | 25 | 25 | 39 | 38 |
| COMPLETED | 20 | 21 | 21 | 32 | 35 |
| NOT COMPLETED | 6 | 4 | 4 | 7 | 3 |
Reasons for not completing this period:
| Reason | Group 1 - PT20 400 mg Tid | Group 2 - PT20 800 mg Tid | Group 3 - PT20 1600 mg Tid | Group 4 - PT20 3200 mg Tid | Group 5 - Placebo Tid |
|---|---|---|---|---|---|
| Adverse Event | 2 | 0 | 1 | 4 | 0 |
| Withdrawal by Subject | 0 | 1 | 1 | 1 | 1 |
| Hyperphosphataemia | 1 | 0 | 0 | 0 | 1 |
| High Ferritin levels | 3 | 3 | 2 | 2 | 1 |
Analysis population for the primary outcome, as defined in the registry: Intent-to-Treat (ITT) population.
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 population - consisting of all subjects who received at least one dose of study medication and had at least one subsequent contact with the Investigator.
| Characteristic | Unit | Group 1 - PT20 400 mg Tid | Group 2 - PT20 800 mg Tid | Group 3 - PT20 1600 mg Tid | Group 4 - PT20 3200 mg Tid | Group 5 - Placebo Tid | Total |
|---|---|---|---|---|---|---|---|
| Participants analysed | 24 | 23 | 22 | 36 | 36 | 141 | |
| Age, Continuous | years | 60.4 (26 to 86) | 58.0 (30 to 78) | 60.3 (33 to 84) | 55.9 (26 to 77) | 55.0 (23 to 80) | 57.5 (23 to 86) |
| Sex: Female, Male: Female | Participants | 8 | 9 | 11 | 16 | 14 | 58 |
| Sex: Female, Male: Male | Participants | 16 | 14 | 11 | 20 | 22 | 83 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 9 | 9 | 8 | 14 | 13 | 53 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 15 | 14 | 14 | 22 | 23 | 88 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 | 0 | 0 | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 2 | 0 | 0 | 0 | 0 | 2 |
| Race (NIH/OMB): Asian | Participants | 1 | 1 | 0 | 2 | 1 | 5 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 1 | 2 | 0 | 0 | 0 | 3 |
| Race (NIH/OMB): Black or African American | Participants | 7 | 8 | 9 | 12 | 16 | 52 |
| Race (NIH/OMB): White | Participants | 12 | 11 | 13 | 20 | 16 | 72 |
| Race (NIH/OMB): More than one race | Participants | 0 | 0 | 0 | 0 | 0 | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 1 | 1 | 0 | 2 | 3 | 7 |
| Region of Enrollment: United States | Participants | 24 | 23 | 22 | 36 | 36 | 141 |
| Baseline Serum Phosphate Concentrations: < 7.5 mg/dL | Participants | 13 | 15 | 11 | 20 | 20 | 79 |
| Baseline Serum Phosphate Concentrations: ≥ 7.5 mg/dL | Participants | 11 | 8 | 11 | 16 | 16 | 62 |
6. Primary Endpoint
The registry lists the primary outcome as Change in Serum Phosphate Concentration From Baseline (Visit 7, Day 1) to Visit 11 (Day 29), measured over Day 1 to Day 29.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Full Range |
| Unit | mg/dL |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint was change in serum phosphate concentration from baseline at Visit 7 on Day 1 to Visit 11 on Day 29, measured in mg/dL. Serum phosphate is the laboratory measure named in the study's central efficacy question: the study was designed to assess whether the concentration changed over the treatment interval across the assigned PT20 dose groups and placebo.
Change from baseline uses each participant's starting measurement as the reference for interpreting the later measurement. In general, this can help distinguish the change during follow-up from differences in the measured levels participants had before the endpoint interval. The registry describes the endpoint as a mean change in the Intent-to-Treat population. It does not report the individual-level analysis details or explain how participants without both measurements were handled.
The posted group results give mean changes of -0.4 for PT20 400 mg, -0.59 for PT20 800 mg, -1.29 for PT20 1600 mg, -1.363 for PT20 3200 mg, and -0.165 for placebo. The registry identifies the dispersion as full range; the listed ranges are -3.1 to 3.5, -4.9 to 2.6, -4.6 to 1.5, -5.2 to 4.6, and -2.5 to 2.4, respectively. These are ranges of observed values, not confidence intervals for the means. The registry record does not report a confidence interval for each mean change.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
All five posted primary-endpoint group means represent decreases in serum phosphate over the endpoint interval. The largest numerical decreases are reported in the two higher-dose PT20 groups, while the placebo group mean is closer to zero. These are descriptive group results. They do not, on their own, establish that differences between assigned groups are statistically reliable or identify the size of an adjusted treatment effect.
The ranges are wide in every group and extend across negative and positive values. A range describes the observed spread of participant-level changes; it does not quantify the uncertainty around the group mean in the way a confidence interval does. Because the registry reports full ranges rather than standard errors or confidence intervals for these means, the precision of each mean cannot be read directly from the range endpoints.
The record includes multiple analyses involving all five groups. These include F-test entries with p-values of 0.784, 0.905, 0.976, and 0.914; a linear model log-dose response entry with slope -0.329 and p < 0.001; and mixed-model entries with p-values of <0.001, 0.436, 0.959, <0.001, and 0.144. Since the entries do not provide enough detail to identify the exact contrast or model term for each result, the p-values should not be treated as interchangeable answers to a single question. The dose-response slope is a distinct result from a direct comparison of each dose with placebo.
The registry also lists final-value mean differences between each PT20 group and placebo, with 97.5% confidence bounds. The comparison for PT20 400 mg is 0.117 with an upper bound of 0.761; for PT20 800 mg it is 0.007 with an upper bound of 0.659; for PT20 1600 mg it is -0.705 with an upper bound of -0.05; and for PT20 3200 mg it is -1.195 with an upper bound of -0.618. Lower bounds are not reported for these entries, and the record does not identify the associated test or explain how these comparisons relate to the change-from-baseline endpoint. They therefore should be read as incomplete reported comparison details, not as complete confidence intervals that can be independently interpreted.
Overall, the descriptive means suggest that the changes differed across the dose groups, while the ranges indicate substantial variation among participants. The registry record does not supply a single fully specified estimate with its uncertainty for each PT20-versus-placebo contrast on the primary change endpoint. Interpretation should therefore keep the descriptive pattern separate from the less fully documented model and comparison results.
9. Statistical Methods Explained
The registry record contains several kinds of statistical output, and they answer different questions. Reading them as if they were one analysis would obscure what the reported numbers can support.
What does a mean change describe?
A mean change is the average of participant-level differences between the endpoint measurement and the baseline measurement. A negative mean indicates that the average endpoint value was lower than baseline; a positive mean indicates that it was higher. This is a general explanation of change scores. The posted primary results give the group means, but do not report a standard deviation or confidence interval for those means. The reported full range gives the lowest and highest observed changes, rather than the uncertainty in the estimated mean.
What does a range tell the reader?
In general, a range records the endpoints of the observed data. It can show that participant changes varied in direction and magnitude, but it is sensitive to the most extreme observations and does not describe how densely observations fall within the interval. A confidence interval has a different purpose: it expresses uncertainty around an estimated quantity under a statistical model. The primary endpoint's full ranges should not be read as confidence intervals.
How should the model results be distinguished?
An F-test generally assesses a model-based hypothesis involving one or more terms, but its interpretation depends on the exact model and the null hypothesis. A dose-response model asks whether the outcome follows a pattern associated with dose, rather than simply whether one dose differs from placebo. The registry lists a log-dose response slope of -0.329 with p < 0.001. It also lists four F-test p-values but does not identify the specific tested terms or hypotheses for those entries.
A mixed model can, in general, account for repeated measurements or other forms of correlated observations, depending on its specification. The registry labels several results as Mixed Models Analysis, but does not report the model formula, covariance structure, estimate associated with each p-value, or which time, group, or interaction term was tested. The posted mixed-model p-values therefore cannot be assigned to a particular treatment contrast from the record alone.
What does a p-value convey?
In general, a p-value describes how incompatible the observed data are with a specified null hypothesis under the assumptions of the test. It is not the probability that the null hypothesis is true, nor does it measure the clinical importance or precision of an effect. Its meaning depends on the hypothesis, model, analysis population, and handling of missing data. Because those details are not reported for every posted analysis, individual p-values need to be interpreted with care.
How should pairwise estimates and confidence bounds be read?
A mean difference describes the estimated difference between two group means, with direction determined by the subtraction convention. A confidence interval generally communicates uncertainty around such an estimate. The registry lists mean differences in final values for each PT20 group versus placebo and labels the bounds as 97.5% confidence limits. Only upper limits are listed; the lower limits are not reported in the registry record. Without both bounds and additional details about the model and contrast, these entries do not provide a complete interval for assessing the estimate's uncertainty.
For the primary endpoint, these final-value comparisons are not explicitly identified as contrasts of change from baseline. The distinction matters: comparing final values and comparing changes are not necessarily the same analysis, particularly if baseline values are incorporated differently. The registry record does not provide enough detail to reconcile the final-value comparisons with the mean change summaries or the mixed-model analyses.
What are the limits of an unadjusted recalculation?
For secondary outcomes, recalculated comparisons use posted group summary statistics to form simple, unadjusted two-group estimates. In general, such a calculation can be useful as a transparent descriptive check, but it does not reproduce an adjusted analysis that uses participant-level data, baseline covariates, repeated measurements, or a prespecified model. These recalculations are not substitutes for the sponsor's own analysis. They also do not account for the fact that many endpoints and comparisons may have been examined.
The sample-size figures are planning illustrations based on observed effects, not observed power and not evidence that the trial was designed with those group sizes. In general, a planning calculation asks what sample size might be needed under stated assumptions to detect a chosen effect with a chosen power. The assumptions listed for these illustrations are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. Observed effects can be unstable, especially when estimated from small groups, so these illustrations should not be read as proof that a future study would achieve the indicated power or reproduce the same effect.
The registry record does not report enough information to verify the full statistical analysis plan, including the exact hypotheses for all primary analyses, the prespecified handling of missing observations, or any adjustment strategy across the many reported analyses. These omissions limit how confidently the listed statistics can be connected to a single confirmatory conclusion.
10. Analyses Reported by the Sponsor
| Method | Estimate | 95% CI | P-value |
|---|---|---|---|
| F-test | not reported | 0.784 | |
| F-test | not reported | 0.905 | |
| F-test | not reported | 0.976 | |
| F-test | not reported | 0.914 | |
| linear model - log (dose) - response | Slope -0.329 | not reported | < 0.001 |
| Mixed Models Analysis | not reported | < 0.001 |
The registry's own primary-endpoint analyses include four F-test entries, a log-dose response model, and mixed-model analyses. The record reports a log-dose response slope of -0.329 with p < 0.001. It also reports mixed-model p-values of <0.001, 0.436, 0.959, <0.001, and 0.144. Because the record does not identify the tested term for each entry or provide the corresponding estimates, these results cannot all be interpreted as direct PT20-versus-placebo comparisons.
The registry additionally reports final-value mean differences versus placebo with 97.5% confidence bounds. The listed upper bounds are 0.761, 0.659, -0.05, and -0.618 for the four successive PT20 dose groups; the lower bounds are not reported. These are not the same presentation as the primary group means and full ranges for change from baseline.
There is no discrepancy flag for the posted results. The simple secondary-outcome recalculations are nevertheless distinct from the sponsor's reported analyses: they are unadjusted two-group calculations from summary statistics, whereas the registry lists ANCOVA analyses for the secondary endpoints. The registry's own analyses should be treated as the sponsor's reported analyses; the recalculations are supplementary and do not override them. The record does not report sufficient model detail to reproduce or fully reconcile every sponsor analysis.
11. Multiplicity, Missing Data and Analysis Populations
The record includes one primary endpoint, five named secondary outcomes, and numerous analyses. For the primary outcome alone, it lists multiple F-test, dose-response, mixed-model, and final-value comparison entries. For secondary outcomes, it includes sponsor-reported ANCOVA analyses and selected recalculated pairwise comparisons. Each additional endpoint, dose contrast, time-related test, or model term can create another opportunity for a result to appear unusual by chance.
In general, multiplicity adjustment is a statistical approach for addressing the increased false-positive risk when a family of hypotheses is tested. Different strategies answer different questions and can affect the interpretation of p-values and confidence intervals. The registry record does not report whether adjustments were used, define any family of hypotheses, or describe an order for testing primary and secondary outcomes. It also does not report whether all listed analyses were prespecified or whether some were exploratory.
The primary population is identified as Intent-to-Treat. That label indicates the stated analysis population, but the registry record does not explain how it was operationalized for each endpoint, how missing baseline or Day 29 measurements were handled, or whether any participants were excluded from particular analyses. Endpoint group counts differ across outcomes, and the record does not explain the reasons for those differences. It also does not report imputation procedures, sensitivity analyses for missing data, or assumptions about the missingness process.
These gaps matter because the analysis population and missing-data approach can affect estimated group changes and the uncertainty around them. A complete interpretation would require the prespecified statistical plan, the participant flow and reasons for unavailable measurements, and details of the models and multiplicity procedures. Those details are not reported in the registry record, so the posted results should be read as incomplete with respect to these aspects of analysis.
12. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Group 1 - PT20 400 mg Tid | 0 | 24 | 0.0% |
| Group 2 - PT20 800 mg Tid | 1 | 23 | 4.3% |
| Group 3 - PT20 1600 mg Tid | 1 | 22 | 4.5% |
| Group 4 - PT20 3200 mg Tid | 5 | 36 | 13.9% |
| Group 5 - Placebo Tid | 5 | 36 | 13.9% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Group 1 - PT20 400 mg Tid | 0 of 24 |
| Group 2 - PT20 800 mg Tid | 0 of 23 |
| Group 3 - PT20 1600 mg Tid | 0 of 22 |
| Group 4 - PT20 3200 mg Tid | 0 of 36 |
| Group 5 - Placebo Tid | 0 of 36 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 4% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Group 1 - PT20 400 mg Tid | 10 of 24 |
| Group 2 - PT20 800 mg Tid | 11 of 23 |
| Group 3 - PT20 1600 mg Tid | 13 of 22 |
| Group 4 - PT20 3200 mg Tid | 16 of 36 |
| Group 5 - Placebo Tid | 16 of 36 |
Most frequent serious adverse event terms
| Event term | Organ system | Group 1 - PT20 400 mg Tid | Group 2 - PT20 800 mg Tid | Group 3 - PT20 1600 mg Tid | Group 4 - PT20 3200 mg Tid | Group 5 - Placebo Tid |
|---|---|---|---|---|---|---|
| Arthritis bacterial | Infections and infestations | 0 of 24 | 0 of 23 | 0 of 22 | 1 of 36 | 0 of 36 |
| Osteomyelitis | Infections and infestations | 0 of 24 | 0 of 23 | 0 of 22 | 1 of 36 | 0 of 36 |
| Pneumonia | Infections and infestations | 0 of 24 | 0 of 23 | 0 of 22 | 1 of 36 | 0 of 36 |
| Staphylococcal bacteraemia | Infections and infestations | 0 of 24 | 0 of 23 | 0 of 22 | 0 of 36 | 1 of 36 |
| Urinary tract infection | Infections and infestations | 0 of 24 | 0 of 23 | 0 of 22 | 1 of 36 | 0 of 36 |
| Acute coronary syndrome | Cardiac disorders | 0 of 24 | 0 of 23 | 0 of 22 | 0 of 36 | 1 of 36 |
| Lower gastrointestinal haemorrhage | Gastrointestinal disorders | 0 of 24 | 0 of 23 | 0 of 22 | 0 of 36 | 1 of 36 |
| Catheter site pain | General disorders | 0 of 24 | 0 of 23 | 0 of 22 | 1 of 36 | 0 of 36 |
| Road traffic accident | Injury, poisoning and procedural complications | 0 of 24 | 0 of 23 | 1 of 22 | 0 of 36 | 0 of 36 |
| Hypervolaemia | Metabolism and nutrition disorders | 0 of 24 | 0 of 23 | 0 of 22 | 0 of 36 | 1 of 36 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Group 1 - PT20 400 mg Tid | Group 2 - PT20 800 mg Tid | Group 3 - PT20 1600 mg Tid | Group 4 - PT20 3200 mg Tid | Group 5 - Placebo Tid |
|---|---|---|---|---|---|---|
| Diarrhoea | Gastrointestinal disorders | 3 of 24 | 3 of 23 | 4 of 22 | 6 of 36 | 2 of 36 |
| Faeces discoloured | Gastrointestinal disorders | 2 of 24 | 3 of 23 | 5 of 22 | 1 of 36 | 0 of 36 |
| Constipation | Gastrointestinal disorders | 0 of 24 | 0 of 23 | 0 of 22 | 1 of 36 | 4 of 36 |
| Nausea | Gastrointestinal disorders | 2 of 24 | 2 of 23 | 0 of 22 | 1 of 36 | 0 of 36 |
| Vomiting | Gastrointestinal disorders | 0 of 24 | 1 of 23 | 0 of 22 | 3 of 36 | 0 of 36 |
| Upper respiratory tract infection | Infections and infestations | 0 of 24 | 0 of 23 | 2 of 22 | 2 of 36 | 0 of 36 |
| Dyspnoea | Respiratory, thoracic and mediastinal disorders | 2 of 24 | 0 of 23 | 0 of 22 | 1 of 36 | 1 of 36 |
| Abdominal discomfort | Gastrointestinal disorders | 0 of 24 | 0 of 23 | 1 of 22 | 1 of 36 | 1 of 36 |
| Abdominal pain upper | Gastrointestinal disorders | 1 of 24 | 0 of 23 | 2 of 22 | 0 of 36 | 0 of 36 |
| Dyspepsia | Gastrointestinal disorders | 1 of 24 | 1 of 23 | 0 of 22 | 0 of 36 | 1 of 36 |
Serious events with the highest arm-level rate: road traffic accident (4.5%), neck pain (4.3%), arthritis bacterial (2.8%), osteomyelitis (2.8%), pneumonia (2.8%).
The posted safety summaries report serious adverse events among participants at risk in each group. The groups are listed with 24 participants at risk and 0 affected for PT20 400 mg; 23 and 1 for PT20 800 mg; 22 and 1 for PT20 1600 mg; 36 and 5 for PT20 3200 mg; and 36 and 5 for placebo. Deaths are reported as 0 in every group. These are group-level counts, not estimates adjusted for exposure time or other differences between participants.
The record also lists serious adverse event terms and percentages: Road traffic accident, 4.5%; Neck pain, 4.3%; Arthritis bacterial, 2.8%; Osteomyelitis, 2.8%; Pneumonia, 2.8%; and Staphylococcal bacteraemia, 2.8%. The posted summary does not give group-specific counts for each listed term or explain whether participants could contribute more than one event.
In general, adverse-event counts describe events observed during the recorded follow-up and do not by themselves determine causation. Comparisons are also limited when group sizes and exposure differ. The registry record does not report event-level timing, treatment relatedness, exposure-adjusted rates, or detailed definitions and follow-up for these summaries. The figures should therefore be read as descriptive safety reporting, not as proof of equivalence or a causal comparison.
13. What the Result Does, and Does Not, Mean
The primary results describe average changes in serum phosphate from Day 1 to Day 29 in four PT20 groups and a placebo group. The group means are negative, and the numerical pattern includes larger decreases in the higher-dose groups than in placebo. The record also reports a negative slope in a log-dose response analysis with p < 0.001. Together, these entries show that the posted summaries and at least one reported model analysis display a dose-related pattern, but the registry does not provide enough model detail to establish exactly what hypothesis the slope test addresses or how it should be reconciled with the other analyses.
The group means do not show how precise each mean estimate is. The listed full ranges describe observed participant variation, not confidence intervals. The registry's final-value comparisons have only upper confidence bounds reported and are not explicitly described as comparisons of change from baseline. Thus, the posted results do not offer a complete, directly comparable set of treatment-effect estimates and uncertainty intervals for every dose versus placebo on the primary endpoint.
These results do not establish that PT20 does or does not have a clinical effect. The record does not report a minimum clinically important difference, a clear primary contrast with a complete uncertainty interval, or the details needed to assess all model assumptions and missing-data handling. Statistical evidence, even when a p-value is small, does not by itself indicate the magnitude, precision, or practical importance of an effect.
The findings also pertain to the enrolled study population and the recorded Day 1 to Day 29 interval. The registry record does not report enough detail to assess how broadly the results apply beyond this trial. Secondary outcomes and safety counts add context, but the limitations in multiplicity, analysis detail, and follow-up mean that they should not be treated as conclusive confirmation of the primary pattern.
14. Why This Trial Matters Statistically
This trial is statistically informative because it compares several PT20 dose levels with placebo and reports both group-level changes and analyses of dose response. A multi-dose design can distinguish a simple treatment-versus-control question from a question about whether outcomes vary with dose. Those are related but different statistical questions, and the registry's collection of several analysis types makes that distinction especially important.
The primary results also illustrate why descriptive means, ranges, model p-values, and confidence intervals should not be treated as interchangeable. The means show the average direction and size of change in each group. The full ranges show observed participant spread. A dose-response p-value tests a model-based pattern, while a treatment contrast estimates a difference between groups. Each needs a clearly stated estimand and uncertainty measure to support a precise interpretation.
The record's incomplete reporting of some model details and confidence bounds is consequential. Readers cannot confidently map every p-value to a specific hypothesis, or independently judge precision for each dose-versus-placebo effect on change from baseline. That is a reporting limitation, not evidence that the analysis was necessarily inappropriate. It identifies what further documentation would make the results easier to assess.
Finally, the number of outcomes and analyses makes multiplicity relevant. Clear specification of the primary contrast, secondary hypothesis status, missing-data approach, and any adjustment strategy would help separate confirmatory evidence from exploratory patterns. The trial therefore serves as a useful example of how a registry can contain substantial numerical output while still leaving key questions about interpretation and reproducibility unresolved.
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.
A central limitation is the incomplete statistical detail attached to the primary results. The registry reports mean changes and full ranges, but does not report confidence intervals for the group means. It also lists several analysis p-values without specifying the exact term or contrast tested by each. This prevents a complete reconstruction of the primary inferential analysis from the registry record alone.
The final-value mean differences are reported with 97.5% confidence bounds, but only upper bounds are listed. The record does not explain why the lower bounds are absent or clearly connect these comparisons to the primary change-from-baseline estimand. Consequently, they cannot be treated as complete confidence intervals for the primary treatment effects.
Group counts vary across the posted primary and secondary endpoint results. The registry does not state why measurements are unavailable for some participants, how missing data were handled, or whether exclusions differed by group. Although the primary population is called Intent-to-Treat, the record does not give enough detail to assess how that population was implemented for each analysis.
The registry record also does not report the full statistical analysis plan, multiplicity procedures, randomization details, or the model specifications needed to reproduce the sponsor's analyses. The secondary recalculations are simple unadjusted comparisons and are not substitutes for the sponsor's ANCOVA results. The sample-size illustrations are based on observed effects and stated planning assumptions, not on the trial's documented design justification.
Finally, the primary endpoint covers the interval from Day 1 to Day 29. The record does not provide further outcome follow-up in the posted results, so interpretation is limited to the reported interval. These reporting and design-context limitations should be kept distinct from the numerical findings themselves.
16. Related Tutorials
17. Related Statistical Calculators
18. Sources
- ClinicalTrials.gov: Study to Evaluate the Efficacy and Safety of PT20 in Subjects With Hyperphosphataemia and Dialysis Dependent Chronic Kidney Disease — NCT02151643.
- Registry record last updated 2018-01-16; status last verified 2017-12.
- Results first posted 2018-01-16.
- 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.
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19. Record Summary
NCT02151643 is a completed randomized, quadruple-masked, parallel phase 2 study sponsored by Phosphate Therapeutics. It enrolled 153 participants with hyperphosphataemia and dialysis-dependent chronic kidney disease. Four oral PT20 dose regimens were compared with matched placebo.
The primary endpoint was mean change in serum phosphate concentration from Day 1 to Day 29 in the Intent-to-Treat population. The reported group means were negative in all groups, with a negative log-dose response slope reported at p < 0.001. The primary group dispersion is presented as full ranges rather than confidence intervals, and several model results are not linked to clearly identified hypotheses in the registry record.
Secondary outcomes include haemoglobin, serum ferritin, transferrin saturation, calcium x phosphate product, and gastrointestinal symptom scores. Safety summaries report serious adverse events and no deaths in the listed groups. Important details about multiplicity, missing-data handling, model specification, and some confidence bounds are not reported in the registry record.