Clinical Trial of Ezogabine (Retigabine) in ALS Subjects: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Clinical Trial of Ezogabine (Retigabine) in ALS Subjects (NCT02450552), a randomized phase 2 study. The primary outcome is Change in Short-interval Intracortical Inhibition (SICI) Measured by Transcranial Magnetic Stimulation (TMS).

2. Clinical Question

The study focused on neuronal excitability, assessed through electrophysiologic measures rather than a clinical outcome such as daily function. SICI is a TMS-based measure of cortical inhibition, expressed as a unitless ratio. The trial also listed changes in other measures of motor-system excitability and muscle cramping frequency as secondary outcomes.

The registry record identifies the comparison and measurement schedule, but it does not report the estimated changes, uncertainty intervals or statistical test results for the primary endpoint. Consequently, the record does not establish the direction or precision of any difference between either dose and placebo.

3. Trial Design

This was a randomized, quadruple-masked, parallel-group phase 2 trial of ezogabine in people with amyotrophic lateral sclerosis. The registry record lists enrollment of 65. Participants were assigned to oral ezogabine 600 mg/day, oral ezogabine 900 mg/day, or placebo. It describes the placebo as matched oral placebo, but does not provide further details about allocation procedures or the masking of specific roles.

The stated total study duration was approximately 14 weeks, and participants were to take study drug for approximately 10 weeks. The primary endpoint was change in short-interval intracortical inhibition (SICI), measured by transcranial magnetic stimulation (TMS). The listed assessment times were screening, baseline, Week 6 and Week 8. The primary-outcome population was defined in relation to electrophysiologic data quality: good-quality data depended on the central reader’s evaluation. The registry record does not give the decision rules or the number of participants whose data met that definition.

Secondary outcomes included resting motor evoked potential threshold, identified as a prespecified secondary outcome of primary importance, as well as MEP amplitude, duration of cortical silent period, intracortical facilitation, electrotonus, strength-duration time constant, recovery cycle and muscle cramping frequency. The record lists 12 outcome measures overall. It does not give numerical results for the primary endpoint in the information available for this account.

The record marks the study as completed and lists its start as 2015-06 and primary completion as 2018-01. It does not report the method used to generate the randomization sequence, allocation concealment procedures, or a detailed protocol for handling deviations from assigned treatment. Those details should not be inferred from the design labels alone.

4. Participant Flow and Accounting

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

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: As a result of electrophysiologic response, good quality data was defined based on the central reader's evaluation.

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 Change in Short-interval Intracortical Inhibition (SICI) Measured by Transcranial Magnetic Stimulation (TMS), measured over Screening, Baseline, Week 6, Week 8.

The primary endpoint was change in short-interval intracortical inhibition (SICI), measured by transcranial magnetic stimulation (TMS). The registry describes SICI as a ratio based on the motor evoked potential (MEP) response when a conditioning pulse is delivered before a signaling pulse. The conditioning pulse is set at 80% of resting motor threshold and precedes the signaling pulse by 3 ms. The outcome is unitless and was to be summarized as a mean with standard deviation.

TMS is a neurophysiologic test used to assess upper motor neuron function. SICI is relevant to this trial because the study question concerned neuronal excitability in ALS. The measure offers a way to examine a physiologic response under the trial conditions; it is not itself a direct measure of symptoms, daily functioning or disease progression. A change in this measure would therefore describe a change in the recorded electrophysiologic endpoint, not by itself establish a change in broader clinical status.

The registry lists screening, baseline, Week 6 and Week 8 as assessment times. It describes comparison of ezogabine at 600 mg/day or 900 mg/day with matched oral placebo. The primary-outcome population was limited to data judged to be good quality by a central reader. The specific quality criteria are not reported in the registry record.

Most importantly for interpretation, numerical estimates of change, between-group contrasts and uncertainty measures for this primary endpoint are not reported in the registry record. The endpoint definition clarifies what the trial intended to measure, but it does not reveal the observed treatment differences.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean and standard deviation describe?

The primary outcome is a continuous, unitless measure. A mean describes the central value of a set of measurements, while a standard deviation describes how dispersed individual measurements are around that mean. These summaries answer different questions: the mean characterizes the group’s average, whereas the standard deviation describes variation among measurements. Neither summary alone gives the uncertainty in a comparison between randomized groups.

For a treatment comparison, an estimated difference between groups would describe the contrast in average outcome under the analysis used. A confidence interval would communicate the range of values compatible with the data and the statistical method, under its assumptions. A narrower interval indicates greater precision than a wider interval. The registry record does not report a primary contrast or confidence interval for SICI, so the effect and its precision cannot be assessed from the record.

Why does the randomized comparison matter?

Random assignment is intended to make treatment groups comparable, on average, with respect to characteristics known and unknown at assignment. Comparing assigned groups can therefore support an estimate of the effect of assignment to the trial interventions, provided the analysis is appropriate and follow-up and outcome measurement are handled adequately. The record labels the study randomized and parallel-group, but does not report the detailed randomization or analysis procedures. Those methods should not be assumed from the design label.

The parallel-group structure means the assigned groups are followed as separate groups rather than each participant receiving every intervention in sequence. The trial compares oral ezogabine at 600 mg/day and 900 mg/day with placebo. The registry does not give numerical SICI results for either comparison. A complete interpretation would ordinarily need the group summaries, the between-group estimates, uncertainty intervals and the analysis population.

What is the role of masking?

The record identifies the trial as quadruple-masked. Masking is intended to reduce the influence of treatment knowledge on care, outcome measurement, participant reporting or other study processes. Which individuals were masked, and how masking was maintained, are not reported in the registry record. The label alone does not demonstrate that masking was successful.

How should repeated assessments be understood?

SICI was scheduled at screening, baseline, Week 6 and Week 8. Repeated measurements can describe how an outcome changes over time and can help distinguish a follow-up value from a change relative to baseline. Statistical analysis of repeated measurements must account for the fact that observations from the same participant are related; they are not independent observations. General statistical methods may model time, treatment group and their relationship, but the registry record does not identify the model used for this endpoint. No particular model or contrast should be attributed to the trial without that information.

Change scores and follow-up scores adjusted for baseline are both possible approaches in clinical research, but the registry record does not state which approach was used. It also does not report whether every scheduled measurement was available for each participant. As a result, the timing listed for the outcome should not be mistaken for a complete account of the analysis.

Why is outcome quality relevant?

The primary-outcome population depended on a central reader’s evaluation of electrophysiologic data quality. Central review can apply a consistent assessment across groups, but its interpretation depends on prespecified and reproducible criteria. The record does not describe those criteria, the handling of readings that did not meet them, or whether reviewers were masked to assignment. These omissions limit assessment of how the analysis population was formed.

What can a planning illustration tell a reader?

General statistical explanation: a sample-size calculation is a planning exercise based on assumptions about the effect to detect, variability, significance level, allocation and analysis method. It is not a measure of the probability that a completed study found a real effect. The record’s stated planning assumptions use a two-sided significance level of 0.05, equal allocation between two arms and a normal approximation, with the target effect described as a fraction of an observed effect. These are described as planning assumptions, not as the trial’s original design justification. The registry record does not report that justification, and no numerical planning estimate is reported in the information.

Over-dispersion is a general concern when observed variability exceeds what an assumed statistical model allows. If a model understates variability, its uncertainty estimates may be too small and its tests may appear more decisive than warranted. The registry record does not say that over-dispersion was present or identify a model for the primary endpoint; this concept is general and should not be read as a finding about this trial.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists a primary endpoint and multiple secondary outcomes. It identifies change in resting motor evoked potential threshold as a prespecified secondary outcome of primary importance. Testing several outcomes or time points can raise a multiplicity issue: when many statistical hypotheses are examined, the chance of at least one apparently unusual result can increase if each is assessed without accounting for the others. This is a general statistical concern, not a claim that a particular analysis was performed in this trial.

The registry record does not report a multiplicity adjustment, a hierarchy for testing outcomes, or a detailed statistical analysis plan. It also does not report numerical primary-outcome results or the results for the listed secondary measures. The record’s analysis count is zero, so the available information does not document outcome analyses. It would be inappropriate to assume that an unreported adjustment was or was not used in a separate analysis.

Missing-data handling is also not reported in the registry record. The primary population was defined by central-reader assessment of electrophysiologic data quality, but the record does not state how many measurements were excluded, why data might be unavailable, or how incomplete repeated measurements were handled. It does not identify an imputation method or provide sensitivity analyses.

The record does not specify whether the primary comparison followed an intention-to-treat principle, a per-protocol approach, or another analysis population. Enrollment and safety denominators should not be taken as the number included in the SICI analysis. Without the analysis population, missing-data methods and results, readers cannot assess the extent to which exclusions or incomplete follow-up may affect interpretation.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: depressed level of consciousness (5.3%), influenza (4.3%), pneumonia (4.3%), cerebrovascular accident (4.3%).

The registry reports serious adverse events and other adverse events separately. For serious adverse events, the 900 mg/day ezogabine group had 1 affected participant among 19 at risk; the 600 mg/day group had 2 among 23 at risk; and the placebo group had 0 among 23 at risk. Deaths were reported as 0 in each group. These are descriptive counts from the registry record, not estimates adjusted for differences in follow-up or other factors.

The record also lists serious adverse-event terms with percentages: Depressed Level of Consciousness, 5.3%; Influenza, 4.3%; Pneumonia, 4.3%; and Cerebrovascular Accident, 4.3%. The record does not provide the corresponding event counts or explain the denominator for these percentages in the information. They should therefore be read as listed, without deriving additional counts or assigning them to a specific group.

Serious adverse-event counts do not summarize every adverse event, its duration or severity, or the uncertainty around between-group differences. Small descriptive counts can be difficult to compare, and these figures alone do not establish a causal relationship or comparative safety. The primary SICI endpoint is a separate efficacy measure; the safety counts do not answer that endpoint’s treatment-effect question.

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

The trial addresses a focused physiologic question: whether SICI measured by TMS changed after treatment with ezogabine at 600 mg/day or 900 mg/day compared with placebo. Its randomized, quadruple-masked, parallel-group design is relevant to that comparison, and the registry gives a defined outcome schedule and an outcome-quality criterion based on central review.

However, the registry record does not report numerical results for the primary endpoint. It therefore does not show the observed change in any group, the difference between either dose and placebo, or the precision of those comparisons. The record cannot support a conclusion about the direction or size of a primary treatment effect. The endpoint definition and trial design describe what was intended to be assessed, not what the analysis found.

Even if a difference in SICI were reported, that would be a result for a neurophysiologic measure. It would not by itself demonstrate a change in symptoms, function or disease progression. Likewise, the listed secondary outcomes are measures and questions, not evidence of results; numerical findings for them are not reported in the registry record.

The safety section gives serious adverse-event counts and selected event-term percentages. These should be interpreted descriptively and separately from efficacy. They do not, by themselves, establish that one group was safer or that an event was caused by treatment.

In short, the registry record allows readers to understand the trial’s stated design, intervention groups, primary endpoint and selected safety counts. It does not provide the primary outcome estimates needed to judge the result statistically. No treatment conclusion should be drawn from the study question, planned assessments or absence of posted primary results.

13. Why This Trial Matters Statistically

This trial is statistically notable for the way it connects a mechanistic research question with a defined physiologic endpoint. SICI measured by TMS is a continuous, unitless measure, and the record specifies a mean and standard deviation as its summary. The comparison is organized across two active doses and placebo in a randomized, masked, parallel-group study.

At the same time, the example shows why a precise endpoint definition is not a substitute for results reporting. Assessment times and a population-quality rule help describe the intended measurement, but readers also need numerical estimates, uncertainty and analysis details to interpret the comparison. Without those, the trial’s primary statistical question remains unanswered in the registry record.

The central-reader criterion for good-quality electrophysiologic data is another important statistical feature. Decisions about which measurements qualify can affect the analysis population and the interpretation of results. Transparent reporting of criteria, exclusions and missing-data handling would help readers understand how the intended sample relates to the analyzed data.

The registry also lists multiple secondary outcomes, including one described as a prespecified secondary outcome of primary importance. This highlights the need for clear reporting of outcome priorities and any approach to multiplicity. Without that information and outcome estimates, readers cannot evaluate how secondary findings relate to the primary question.

Finally, the serious adverse-event counts illustrate the distinction between descriptive safety reporting and comparative inference. Counts are useful for describing what was recorded, but do not replace analysis of uncertainty or context. Taken together, the record is useful for understanding the design and measurement strategy while also illustrating the limits of interpretation when numerical efficacy results and analysis methods are not reported.

14. Limitations

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

The main limitation for statistical interpretation is that numerical results for the primary SICI endpoint are not reported in the registry record. No group means, changes, between-group estimates, confidence intervals or p-values are available in the record. The primary effect and its precision therefore cannot be assessed.

The analysis population is only partly characterized. Good-quality electrophysiologic data depended on central-reader evaluation, but the criteria, exclusions and number of qualifying observations are not reported. The enrollment figure does not establish how many participants contributed data to the primary analysis. The record also does not describe missing-data handling or sensitivity analyses.

The registry does not report the statistical model used for repeated measurements, the specific primary contrast, or whether results were adjusted for baseline. It does not provide the randomization procedure or allocation-concealment details. Although the study is labeled quadruple-masked, it does not identify the masked roles or report an assessment of masking.

Multiple secondary outcomes are listed, but the registry record does not report a multiplicity strategy or numerical results for those outcomes. The record does not provide the trial’s sample-size justification or interim-analysis plan. These details cannot be inferred from the planning assumptions listed for an illustrative calculation.

Safety information is limited to group-level counts and selected serious-event terms with percentages. The record does not give further context for the percentages in the information. These limitations mean the posted information supports description of the trial design and selected safety counts, but not a full statistical assessment of efficacy or comparative safety.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Clinical Trial of Ezogabine (Retigabine) in ALS Subjects — NCT02450552.
• Registry record last updated 2019-08-28; status last verified 2019-08.
• Results first posted 2019-08-28.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The registry record describes a completed randomized, quadruple-masked, parallel-group phase 2 trial of ezogabine in people with amyotrophic lateral sclerosis. The assigned interventions were oral ezogabine 600 mg/day, oral ezogabine 900 mg/day and matched oral placebo. Study drug was taken for approximately 10 weeks, within a total study duration of approximately 14 weeks.

The primary endpoint was change in unitless SICI measured by TMS, with assessment scheduled at screening, baseline, Week 6 and Week 8. Primary-outcome data were subject to a central-reader quality assessment. The record lists multiple secondary outcomes and serious adverse-event counts by group.

Numerical primary-outcome results and key analysis details are not reported in the registry record. The available information therefore describes the trial question and design but does not establish the direction or precision of the primary treatment comparison.