Safety of Lixivaptan in Subjects Previously Treated With Tolvaptan for Autosomal Dominant Polycystic Kidney Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety of Lixivaptan in Subjects Previously Treated With Tolvaptan for Autosomal Dominant Polycystic Kidney Disease (NCT04152837), a na phase 3 study. The primary outcome is Number of Participants Who Develop Serum Alanine Aminotransferase (ALT) Levels >3 × ULN During the Titration or Maintenance Periods Assessed to be Related to Lixivaptan and Result in Discontinuation of Lixivaptan Treatment.

2. Clinical Question

3. Trial Design

The ALERT study (NCT04152837) was registered as a Phase 3, open-label study of lixivaptan in people with ADPKD who had previously experienced abnormal liver chemistry test results while taking tolvaptan. The registry record describes a single-group model, no masking, and no allocation to competing arms. It lists Palladio Biosciences as the sponsor. The study status is terminated.

The registry record reports an enrollment of 7. The brief summary describes a plan to enroll up to 50 eligible participants and treat them with lixivaptan for 52 weeks after titration to an optimal dose. The reported enrollment is therefore the enrollment recorded for the study, while the planned maximum is part of the study description; they should not be read as the same quantity. The registry record does not report why the study was terminated.

The lixivaptan arm description specifies oral capsules, 100-200 mg twice daily. The primary endpoint timeframe is up to 58 weeks. The record also lists a follow-up period as a separate safety assessment period, but it does not report a comparator group or a randomized treatment contrast. The study dates are 2020-09-02 for start and 2022-07-29 for primary completion.

Because the design has one treatment group, its results can describe what was recorded among participants receiving lixivaptan, but they cannot provide a like-for-like comparison with an untreated group or another treatment group. The registry record does not report a protocol-level statistical plan, a sample-size justification, interim analyses, or a reason for termination.

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.

Baseline Period (No Treatment)

Reasons for not completing this period:

Titration Period

Maintenance Period

Reasons for not completing this period:

Follow-up Period

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 Number of Participants Who Develop Serum Alanine Aminotransferase (ALT) Levels >3 × ULN During the Titration or Maintenance Periods Assessed to be Related to Lixivaptan and Result in Discontinuation of Lixivaptan Treatment, measured over Up to 58 weeks.

The primary endpoint is a count of participants meeting a defined liver-safety event criterion. A participant had to develop serum ALT levels >3 × ULN during titration or maintenance; the independent Hepatic Events Review Committee had to assess the abnormality as at least probably related to lixivaptan; and the event had to result in discontinuation of lixivaptan treatment. The stated timeframe is up to 58 weeks. The normal range for ALT was defined as 0-55 U/L.

This endpoint combines a laboratory threshold with an attribution assessment and a treatment consequence. The threshold identifies a specified degree of ALT elevation, while committee review addresses whether the event was probably related to lixivaptan. Requiring treatment discontinuation makes the endpoint narrower than a count of all ALT elevations: elevations that did not meet the threshold, were not assessed as related, or did not lead to discontinuation would not meet the stated definition.

As a count, the endpoint describes how many participants met all of its criteria. It does not measure the average ALT change, the duration of an elevation, or the rate of events over time. No observed primary endpoint count or endpoint analysis is reported in the registry record, so the result cannot be characterized from the endpoint definition alone.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

General statistical explanation: the study's primary endpoint is binary at the participant level. Each participant either meets the full event definition or does not. The posted primary outcome would therefore be interpretable as a count of participants with the event, alongside a denominator identifying how many participants were assessed. The registry record defines the endpoint but does not report the resulting count or denominator for that analysis.

What does the endpoint count?

The definition requires three elements: serum ALT levels >3 × ULN during titration or maintenance; an assessment by the independent Hepatic Events Review Committee that the abnormality was at least probably related to lixivaptan; and discontinuation of lixivaptan treatment because of the event. The committee's review was described as using demographic, medical and medication history, safety data, and other relevant data. It was to assess probable causality using the Drug-Induced Liver Injury Network probability criteria. The normal range for ALT was defined as 0-55 U/L.

This is a composite rule for classifying an event, not a composite of several efficacy outcomes. A participant who had an ALT elevation but did not meet the attribution or discontinuation conditions would not satisfy the full primary endpoint as written. The registry record does not report how borderline or incomplete event information was handled.

How should a count be interpreted?

General statistical explanation: a count summarizes how many observed participants met a rule. The count alone does not convey its precision; interpretation also depends on the number of participants assessed and on the uncertainty around the estimate. Confidence intervals are one general way to express sampling uncertainty: they describe a range of values compatible with the observed data under a specified statistical method. No confidence interval for the primary endpoint is reported in the registry record.

Counts are especially sensitive to individual observations when the study group is small. The registry reports an enrollment of 7, but the primary endpoint's analyzed population and denominator are not reported. Enrollment cannot automatically be treated as the endpoint denominator, because the record does not state how many participants completed each period or had evaluable endpoint data.

What can a single-group design estimate?

General statistical explanation: a single-group study can describe outcomes observed among people receiving the study intervention. Without a concurrent comparator, it cannot separate outcomes associated with the intervention from outcomes that might also occur because of the underlying condition, prior treatment, other exposures, or chance. This limitation is particularly important when the outcome is an adverse event and the endpoint depends on clinical review and treatment decisions. The registry record does not report a randomized or otherwise comparable control group.

The study is open-label, and masking is listed as none. General statistical explanation: when treatment assignment is known, expectations or knowledge of treatment can potentially influence reporting, clinical decisions, or outcome assessment. The independent committee's role in reviewing liver abnormalities is part of the endpoint definition, but the registry record does not describe all procedures used to reduce assessment or reporting bias.

What do the planning illustrations mean?

General statistical explanation: a sample-size calculation for a future or hypothetical comparison asks how many participants might be needed under stated assumptions to detect a specified effect with a chosen statistical approach. The planning assumptions described for the 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. For time-to-event outcomes, the stated convention is a total number of events; for other outcomes, it is participants per arm.

Those illustrations are planning calculations, not a report of the trial's actual design or an estimate of its observed power. The ALERT study is described as single-group, so the two-arm assumptions in a planning illustration do not turn it into a randomized comparison. The registry record does not report the trial's own sample-size justification or the numerical planning results in the study information. No new sample-size estimate can be inferred from the enrollment alone.

What statistical analyses are reported?

The registry record lists no analysis entries. It does not report a statistical model, an adjusted analysis, a hypothesis test, a p-value, an uncertainty interval, or a treatment-effect estimate for the primary endpoint. The endpoint description itself is not an analysis result. The absence of a reported analysis also means that readers cannot determine from the registry record whether any planned analysis differed from the posted outcome definitions.

General statistical explanation: analysis choices should match the outcome and design. A binary participant outcome can be described by a count and a proportion, while any comparison requires a suitable comparator and a clearly specified estimand. For a single-group safety study, descriptive reporting can document observed events, but it does not provide the same evidence as a controlled treatment contrast. No proportion or comparative estimate is calculated because the primary endpoint result is not reported.

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("Lixivaptan: Titration and Maintenance Periods")
n      <- c(6)
events <- c(1)
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  Lixivaptan: Titration and Maintenance Periods  6  1  16.7  0.4  64.1  3.0  56.4  3.7  57.9

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists 8 outcome measures: the primary liver-safety endpoint and secondary outcomes covering additional ALT-related events, treatment-emergent adverse events, potentially clinically important laboratory, vital-sign, and ECG findings, and change in eGFR from baseline to final assessment. The record does not report a multiplicity strategy, such as a hierarchy among outcomes or an adjustment for testing several outcomes. It also does not report hypothesis-test results for these outcomes.

General statistical explanation: when several outcomes are examined, the chance of at least one apparently notable result can increase if each is assessed independently. A prespecified hierarchy or multiplicity adjustment can address that issue for confirmatory testing. Because no such strategy is reported, the registry record does not establish which outcomes, if any, were intended to support formal confirmatory claims. The reported endpoint definitions should therefore be read as descriptions of planned measurements, not as evidence that each was analyzed or met a statistical criterion.

Methods for missing data are not reported in the registry record. The analysis populations are also not reported: it is not stated which participants were included in each outcome analysis, how participants who stopped treatment were handled for follow-up outcomes, or how unavailable measurements were treated. The registry reports an enrollment of 7, but that number alone does not identify the denominator for every endpoint. No imputation approach, sensitivity analysis for missing observations, or completeness summary is reported. These omissions limit assessment of how representative the analyzed observations may be of all enrolled participants.

12. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: bacteraemia (16.7%), alanine aminotransferase increased (16.7%), aspartate aminotransferase increased (16.7%).

The registry reports adverse-event counts by period. During titration and maintenance, 6 participants were at risk; 2 were recorded with serious adverse events, 6 with other adverse events, and 0 deaths. During follow-up, 6 participants were at risk; 0 were recorded with serious adverse events, 1 with other adverse events, and 0 deaths. These are participant counts in the registry's categories, not a comparison between treatment arms.

The listed serious adverse-event terms are Bacteraemia, Alanine aminotransferase increased, and Aspartate aminotransferase increased, each reported as 16.7%. The registry record does not report whether participants had more than one serious term, so those percentages should not be added or treated as mutually exclusive categories. It also does not provide participant-level details linking these terms to the primary endpoint's full requirements.

General statistical explanation: an adverse-event count describes events recorded under the registry's reporting rules; by itself, it does not establish causation. The primary endpoint is more specific than the serious-event listing because it requires the ALT threshold, committee assessment of relatedness, and treatment discontinuation. The record does not report enough detail to equate the serious-event terms with primary endpoint cases.

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

The study's purpose was to assess lixivaptan in participants with ADPKD who had previously experienced liver chemistry abnormalities on tolvaptan and were permanently discontinued from it. The primary endpoint was designed to identify a particular liver-safety event during titration or maintenance: an ALT elevation exceeding 3 × ULN, assessed as at least probably related to lixivaptan by an independent committee, and resulting in treatment discontinuation. The endpoint design makes clear what event the study was intended to track.

The registry record does not report the observed primary endpoint count, so it does not establish how many participants met that definition. It also does not report an analysis of efficacy or a comparative estimate. The adverse-event counts are descriptive and arise from a single-group, open-label study. They should not be interpreted as evidence that lixivaptan caused or prevented any event, nor as evidence of a difference from another treatment.

General statistical explanation: a result is more informative when its estimate is accompanied by an indication of uncertainty and a clear denominator. For this study, the registry record does not report a primary endpoint estimate, confidence interval, or analysis population. The small reported enrollment of 7 further means that the available registry counts represent a limited amount of participant experience; they cannot establish how frequently a less common event would occur in a broader population.

The record also cannot establish how the findings apply to people with ADPKD who did not have prior tolvaptan-associated liver chemistry abnormalities, because the enrolled population was defined by that history. The single-group design does not allow a like-for-like comparison. The appropriate interpretation is therefore limited to the registered design and the adverse-event counts that are reported, with the primary result and several analysis details not reported in the registry record.

14. Why This Trial Matters Statistically

This study raises a focused statistical question: how to describe a safety outcome in a group selected because of a prior liver-chemistry concern with another treatment. The endpoint is not simply any ALT elevation. It combines a laboratory threshold, an independent committee's assessment of probable relation to lixivaptan, and discontinuation of study treatment. That specificity can make an endpoint more clinically interpretable, while also making its result dependent on consistent measurement, review, and documentation.

The design matters for the strength of conclusions. An open-label, single-group study can describe observed events in the treated participants, but it does not supply a concurrent control for separating treatment-associated events from other causes. The registry-reported enrollment of 7 makes precision an important consideration, yet the primary endpoint result and its uncertainty are not reported. A reader therefore cannot assess the frequency of the primary event or how precisely it was estimated from the registry record.

The distinction between endpoint definitions and endpoint findings is also important. Detailed outcome criteria do not establish that an event occurred, and adverse-event terms cannot substitute for the primary endpoint without information confirming all its criteria. Similarly, planning calculations based on two-arm assumptions are not evidence that this single-group study had a comparative design or achieved a particular level of power.

For biostatistical interpretation, the record illustrates why design, denominator, outcome definition, analysis population, and uncertainty all matter alongside event counts. Here, several of those elements are not reported in the registry record, so the information supports a careful description of the study rather than a comparative treatment conclusion.

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 registry record reports an enrollment of 7, while the study description says up to 50 eligible participants were planned. The reason for the difference between the planned maximum and recorded enrollment is not reported in the registry record. The reason the study was terminated is also not reported, so termination should not be assigned a cause based on the available information.

The design is open-label and single-group, with no like-for-like control comparison. The population was selected for prior liver chemistry abnormalities while receiving tolvaptan and permanent discontinuation for that reason. Findings from this group would not automatically describe people with ADPKD who do not share that treatment history. The registry record does not report detailed baseline characteristics that would help assess the composition of the enrolled group.

The primary endpoint result, its analysis denominator, and any estimate of precision are not reported in the registry record. Nor are the analysis populations, missing-data procedures, multiplicity approach, or detailed statistical methods. The record does not report why the study ended or whether follow-up and outcome collection were complete for all enrolled participants.

The adverse-event data are presented as counts by period and as serious-event terms with percentages, but the registry record does not report participant-level overlap among terms or enough detail to map each serious term to the primary endpoint definition. The listed adverse events do not provide a comparator-based estimate of risk. Together, these limitations restrict interpretation to the registered study description and the descriptive safety counts, rather than supporting a causal or comparative conclusion.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Safety of Lixivaptan in Subjects Previously Treated With Tolvaptan for Autosomal Dominant Polycystic Kidney Disease — NCT04152837.
• Registry record last updated 2023-04-10; status last verified 2023-03.
• Results first posted 2023-04-10.
• 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

NCT04152837, the ALERT study, was a Phase 3, open-label, single-group study of lixivaptan in participants with ADPKD who previously experienced liver chemistry abnormalities while receiving tolvaptan and were permanently discontinued from it for that reason. The sponsor listed in the registry record is Palladio Biosciences. Lixivaptan was administered as oral capsules, 100-200 mg twice daily. The study description planned treatment for 52 weeks after titration; the primary endpoint timeframe was up to 58 weeks.

The registry reports enrollment of 7 and study status as terminated. The primary endpoint counted participants with serum ALT levels >3 × ULN, assessed as at least probably related to lixivaptan by the independent Hepatic Events Review Committee, that resulted in treatment discontinuation. The primary endpoint result and its analysis are not reported in the registry record. Adverse-event counts are reported for titration and maintenance and for follow-up, but there is no comparator group or posted analysis establishing a treatment contrast.