A Study In Patients With Neuropathic Pain From Diabetic Peripheral Neuropathy (DPN): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study In Patients With Neuropathic Pain From Diabetic Peripheral Neuropathy (DPN) (NCT00643760), a randomized phase 2 study. The primary outcome is Change From Baseline in the Mean 24-hour Average Pain Intensity (API) Score at End of Maintenance Treatment (EOMT) Using Last Observation Carried Forward (LOCF) Data.

2. Clinical Question

The study asked whether GEn was effective in treating neuropathic pain associated with diabetic peripheral neuropathy. Its primary outcome was a continuous pain score, based on participants’ daily ratings of pain over the preceding 24 hours. The registry reports group means and comparisons with placebo at the end of maintenance treatment.

Changes were calculated as the end-of-maintenance score minus the baseline score. As a result, a more negative change represents a greater reduction in the recorded score from baseline; it does not, on its own, establish that a between-group difference is reliable or clinically important. The comparisons and their confidence intervals help assess the size and uncertainty of those differences.

The registry reports 421 participants enrolled overall and lists five treatment groups. It does not report the original sample-size justification or a threshold for a clinically important difference. The question addressed by the statistical comparisons is therefore narrower than whether any observed change would matter to an individual participant.

3. Trial Design

This was a completed Phase 2, randomized, triple-masked, parallel-group study sponsored by XenoPort, Inc. The registry lists 421 participants enrolled and identifies diabetic neuropathy as the condition. The record gives the study start as 2008-03 and primary completion as 2009-02.

Five groups are listed: placebo, GEn 1200 mg/day, GEn 2400 mg/day, GEn 3600 mg/day, and pregabalin 300 mg/day. Pregabalin is described as a positive control. The intervention descriptions specify maintenance treatment for 14 weeks for the active treatment groups. The registry record does not describe the placebo regimen in comparable detail.

The primary endpoint was analysed in the ITT Population. The reported endpoint sample sizes were 120 for placebo, 62 for GEn 1200 mg/day, 56 for GEn 2400 mg/day, 116 for GEn 3600 mg/day, and 66 for pregabalin 300 mg/day. These are the counts associated with the posted primary outcome results, rather than a description of everyone enrolled.

Randomization and masking are features of the design intended to support fair comparisons and reduce the influence of expectations or knowledge of assigned treatment. The registry does not report the randomization procedure, masking roles, allocation ratio, planned duration beyond the described maintenance treatment, or original sample-size justification. Further details of those design choices are not reported in the registry record.

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: 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.

6. Primary Endpoint

The registry lists the primary outcome as Change From Baseline in the Mean 24-hour Average Pain Intensity (API) Score at End of Maintenance Treatment (EOMT) Using Last Observation Carried Forward (LOCF) Data, measured over Baseline and EOMT (representing the earliest date of Week 13 visit/withdrawal visit).

The primary endpoint was change from baseline in mean 24-hour average pain intensity at the end of maintenance treatment, using last observation carried forward data. Baseline was the mean of daily 24-hour average pain intensity scores during the last 7 days before randomization. The end-of-maintenance value used the earliest date of the Week 13 visit, withdrawal visit, or last dose of study drug.

Participants used a hand-held diary to rate pain over the preceding 24 hours on an 11-point Pain Intensity Numerical Rating Scale, from 0 (no pain) to 10 (pain as bad as you can imagine). The change was calculated by subtracting the baseline score from the end-of-maintenance score. Negative group means therefore indicate that the recorded score was lower at the end point than at baseline.

This continuous outcome preserves more information about the amount of change than a simple category such as improved or not improved. Comparing group means can describe the average difference between assigned groups, while confidence intervals show the uncertainty around that estimate. The endpoint is useful for examining average pain-score changes over the study period, but a group mean cannot describe every participant’s experience. The registry record does not state a threshold for interpreting a change as clinically important.

Last observation carried forward was used when a participant provided fewer than 4 days of diary data. That approach fills a missing end-point value using an earlier recorded value; the assumptions and possible consequences of this choice are discussed in the statistical interpretation.

7. Results Posted in the Registry

• GEn 1200 mg/Day: mean -2.43 versus -2.08 on control; difference -0.35 (95% CI -1.01 to 0.31), standardized effect d = -0.16; z-test p = 0.299.
• GEn 2400 mg/Day: mean -2.10 versus -2.08 on control; difference -0.02 (95% CI -0.70 to 0.66), standardized effect d = -0.01; z-test p = 0.954.
• GEn 3600 mg/Day: mean -2.63 versus -2.08 on control; difference -0.55 (95% CI -1.10 to 0.00), standardized effect d = -0.25; z-test p = 0.051.
• PGB 300 mg/Day: mean -1.65 versus -2.08 on control; difference 0.43 (95% CI -0.22 to 1.08), standardized effect d = 0.20; z-test p = 0.193.

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 the Mean Day-time Average Pain Intensity (API) Score at EOMT Using LOCF Data

• 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 errors.
• Result:
  • GEn 1200 mg/Day: mean -2.35 versus -2.07 on control; difference -0.28 (95% CI -0.94 to 0.38), standardized effect d = -0.13; z-test p = 0.403.
  • GEn 2400 mg/Day: mean -2.06 versus -2.07 on control; difference 0.01 (95% CI -0.67 to 0.69), standardized effect d = 0.00; z-test p = 0.977.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between GEn 1200 mg/Day and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between GEn 2400 mg/Day and the control. The interval gives the range of effects that remain compatible with the data.

Change From Baseline in the Mean Night-time Average Pain Intensity (API) Score at EOMT Using LOCF Data

• 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 errors.
• Result:
  • GEn 1200 mg/Day: mean -2.15 versus -1.99 on control; difference -0.16 (95% CI -0.84 to 0.52), standardized effect d = -0.07; z-test p = 0.645.
  • GEn 2400 mg/Day: mean -2.04 versus -1.99 on control; difference -0.05 (95% CI -0.76 to 0.66), standardized effect d = -0.02; z-test p = 0.890.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between GEn 1200 mg/Day and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between GEn 2400 mg/Day and the control. The interval gives the range of effects that remain compatible with the data.

Change From Baseline in the Mean Current (Morning) Pain Intensity Score at EOMT Using LOCF Data

• 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 errors.
• Result:
  • GEn 1200 mg/Day: mean -2.08 versus -1.90 on control; difference -0.18 (95% CI -0.83 to 0.47), standardized effect d = -0.09; z-test p = 0.585.
  • GEn 2400 mg/Day: mean -1.95 versus -1.90 on control; difference -0.05 (95% CI -0.72 to 0.62), standardized effect d = -0.02; z-test p = 0.883.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between GEn 1200 mg/Day and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between GEn 2400 mg/Day and the control. The interval gives the range of effects that remain compatible with the data.

The registry lists secondary measures covering daytime and nighttime average pain, current morning and evening pain, worst pain during day and night, sleep interference, and rescue medication dose. The posted secondary outcomes also include changes in these measures from baseline at the end of maintenance treatment, using last observation carried forward for the named outcomes. Together, they broaden the description beyond the primary 24-hour average pain score.

In the posted secondary summaries with group results and recalculated comparisons, mean changes are generally negative across placebo and active groups. The comparisons for the reported daytime average pain, nighttime average pain, and current morning pain outcomes do not show a clear separation from placebo in the recalculated estimates: their intervals include zero. Those patterns are broadly consistent with the primary result, where the sponsor-reported GEn comparisons also have intervals that include zero. They should not be treated as independent confirmation, since the outcomes are related measures of pain and share participants and study conditions.

Secondary findings carry less weight when many outcomes and treatment comparisons are examined, particularly when no multiplicity adjustment is reported. A collection of unadjusted tests increases the chance that at least one result may appear notable by chance. The registry record does not report a multiplicity strategy for the secondary analyses, and sponsor-reported adjusted analyses for these outcomes are not listed in the posted summary. The secondary results are therefore best read as descriptive and exploratory evidence about related symptom measures, rather than as a separate confirmatory test of the primary question.

The registry reports 18 posted secondary outcomes, but detailed group results and comparisons are not present for every measure in the listed outcomes. Where results are not posted, a pattern or direction should not be inferred from the outcome title alone.

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

• Change From Baseline in the Mean Day-time Average Pain Intensity (API) Score at EOMT Using LOCF Data
• Change From Baseline in the Mean Night-time Average Pain Intensity (API) Score at EOMT Using LOCF Data
• Change From Baseline in the Mean Current (Morning) Pain Intensity Score at EOMT Using LOCF Data
• Change From Baseline in the Mean Current (Evening) Pain Intensity Score at EOMT Using LOCF Data
• Change From Baseline in the Mean Day-time Worst Pain Intensity Score at EOMT Using LOCF Data
• Change From Baseline in the Mean Night-time Worst Pain Intensity Score at EOMT Using LOCF Data
• Change From Baseline in the Mean Sleep Interference Score at EOMT Using LOCF Data
• Change From Baseline in the Mean Daily Dose of Rescue Medication at EOMT Using LOCF Data

9. Statistical Interpretation

10. Statistical Methods Explained

The primary endpoint is continuous: it records a score and its change from baseline, rather than whether an event occurred. The registry reports least-squares means and standard errors for the groups. A least-squares mean is a model-based group estimate; the reported adjusted comparisons use ANCOVA. Standard errors describe the sampling uncertainty of estimates, while confidence intervals give a range of values compatible with the data and model assumptions.

What does ANCOVA contribute?

ANCOVA is a model for comparing group outcomes while adjusting for specified covariates. In a randomized trial, such adjustment can account for baseline measures or other variables included in the model, and can produce an adjusted comparison rather than simply subtracting the posted group means. The registry gives the method and adjusted contrasts for the three GEn comparisons, but the covariates, model specification, and handling of other analysis details are not reported in the registry record. The adjusted results should therefore be read as the sponsor’s reported analysis, not reconstructed from the group summaries.

Why are there recalculated comparisons?

The recalculated contrasts are simple unadjusted comparisons based on posted means, sample sizes, and estimated variability. The pooled standard deviations are approximate, because they were derived from reported standard errors and group sizes. These calculations provide a transparent descriptive check, but they do not reproduce ANCOVA. They also do not incorporate any adjustment for multiple comparisons. Where the recalculated result differs from the sponsor’s analysis, the sponsor’s own analysis takes precedence.

A mean difference is expressed in the outcome’s score units. A negative estimate for a GEn group versus placebo indicates a lower mean change in that group, in the direction of a greater reduction from baseline. The interpretation must be paired with its interval: an estimate alone does not show how precisely the difference has been estimated.

What do confidence intervals and p-values convey?

A confidence interval expresses uncertainty around an estimate under the analysis assumptions. A wide interval indicates that a range of effects remains compatible with the observed data; an interval spanning zero includes both directions of difference as well as no difference. A p-value measures how incompatible the data are with a specified null hypothesis under the model. It is not the probability that the null hypothesis is true, nor a measure of the size or clinical importance of an effect.

Statistical significance is commonly judged using a threshold, but the registry’s reported p-values should be interpreted alongside the interval estimates and the study’s multiple comparisons. The record does not state whether the reported comparisons were adjusted for multiplicity. Without that information, a single p-value does not capture the broader uncertainty created by evaluating multiple doses and outcomes.

How should last observation carried forward be understood?

For the primary outcome, the registry states that last observation carried forward was used if fewer than 4 days of diary data were provided. This means an earlier observation can stand in for a later value that is unavailable. The method is straightforward to describe, but it assumes that the carried-forward value is a reasonable substitute for the missing end-point measurement. If pain changes after the last observed diary entry, that assumption may not hold. The registry does not report sensitivity analyses comparing this approach with other missing-data methods.

The primary analysis population is identified as ITT, a label generally associated with analysing participants according to their randomized assignment. The registry does not provide a detailed definition of which participants or measurements were included in that population, or how deviations from assigned treatment were handled.

What does the parallel randomized structure imply?

In a parallel-group design, participants are assigned to a treatment group and comparisons are made across groups. Randomization supports comparability on average, while masking is intended to limit influences related to knowing assignment. The registry identifies the study as randomized, triple-masked, and parallel, but does not report the randomization method, masking roles, or allocation concealment details. These design labels describe the broad structure, not every operational safeguard.

The recalculated planning illustrations use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect set to a stated fraction of the observed effect. They are not reconstructions of the trial’s original design plan. The original assumptions and sample-size justification are not reported in the registry record.

11. Confidence Intervals and Precision

Precision is best judged from the confidence interval, not from the point estimate alone. The sponsor-reported 95% confidence intervals for the three GEn comparisons all extend across zero. For GEn 1200 mg/day, the interval is -1.02 to 0.31; for GEn 2400 mg/day, it is -0.71 to 0.66; and for GEn 3600 mg/day, it is -1.10 to 0.01. These ranges include values on both sides of no difference, so the posted estimates do not tightly determine the direction of the adjusted comparison.

The point estimates range from -0.02 to -0.55 across the three GEn doses. Each interval also includes differences that are larger in magnitude than its point estimate. This uncertainty means that the estimates should not be read as exact effects. The interval for GEn 3600 mg/day comes closest to excluding zero, but its reported upper limit is 0.01 and the sponsor-reported p-value is 0.105. The recalculated unadjusted interval has a slightly positive upper end as well, but its associated test is not the sponsor’s adjusted analysis.

The pregabalin comparison has a reported 95% confidence interval from -0.22 to 1.08. Its interval also spans zero. The registry does not report a p-value or analysis method for that comparison, which limits direct comparison with the reported ANCOVA analyses.

Confidence intervals describe uncertainty under the analysis model; they do not show the full range of individual participant responses, and they do not determine clinical importance. The registry does not report a minimally important difference for the pain score. Thus, even a more precise estimate would need a clinically justified threshold to support judgments about importance. The intervals should also be considered in the context of the several doses and outcomes evaluated, since multiplicity can make isolated intervals or p-values less conclusive.

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 sample-size figures are planning illustrations based on the observed effect, not the trial’s original design assumptions. For these continuous outcomes, the listed figures are participants per arm, not total events. The calculations assume a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. They use the stated fraction of the observed effect as the effect to detect. The original sample-size justification is not reported in the registry record.

The 80% power column gives the planned number of participants per arm under those assumptions for an 80% chance of detecting the specified effect, if that effect and the assumptions are correct. The 90% power column gives the corresponding per-arm number for a 90% chance. These are planning probabilities under a hypothetical design, not probabilities that the observed trial result is true.

Rows that plan for 75% or 50% of the observed effect represent progressively smaller target differences. Smaller effects are harder to distinguish from random variation, so they require more participants per arm to reach the same target power. This relationship can be especially striking when the observed contrast is close to zero: the planning numbers become very large because a very small difference is difficult to detect.

These calculations are illustrations, not observed power. They should not be used to infer whether the completed trial was capable of detecting an effect other than the specific hypothetical effects and assumptions used in each row. In particular, they do not replace the trial’s unavailable design justification or account for the sponsor’s adjusted analysis.

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 = -0.350; pooled standard deviation σ = 2.151.
2. n = 2 × (1.96 + 0.842)² × 2.151² / -0.350² = 592.7, rounded up to 593 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 <- -0.35                      # observed difference in means
sigma <- 2.1506044524996                     # 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(643760)
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 = 593 (80% power), 794 (90% power)
 75% of observed effect: n per arm = 1,054 (80% power), 1,411 (90% power)
 50% of observed effect: n per arm = 2,371 (80% power), 3,174 (90% power)
power.t.test: 593.6 
Simulated power at n = 593 per arm: 0.799 (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 sponsor-reported analyses should be distinguished from the recalculated comparisons. For the GEn doses, the sponsor reports adjusted mean differences versus placebo from ANCOVA, with 95% confidence intervals and p-values. The recalculations use the posted group means, sample sizes, and approximate pooled variability to form unadjusted comparisons. They are not a reproduction of the ANCOVA model.

The discrepancy is clearest for GEn 3600 mg/day: the recalculated unadjusted p-value is 0.051, while the sponsor-reported ANCOVA p-value is 0.105. The recalculated contrast is -0.55, and the reported adjusted contrast is also -0.55, but the uncertainty and test results differ. The sponsor’s own analysis takes precedence because it is the trial’s reported analysis; the recalculation is supplementary and should not replace it.

For the GEn 1200 mg/day comparison, the reported sponsor p-value is 0.295 and the recalculated unadjusted p-value is 0.299. For GEn 2400 mg/day, those values are 0.946 and 0.954, respectively. Small differences are expected when methods and adjustment differ. For pregabalin, the registry posts an adjusted mean difference and confidence interval, but its analysis method and p-value are not reported in the registry record. No parallel recalculated-versus-reported p-value comparison can be made for that group.

15. Multiplicity, Missing Data and Analysis Populations

The study compares three GEn doses with placebo on the primary outcome, includes a pregabalin positive-control group, and lists numerous secondary outcomes. Testing several doses and outcomes creates a multiplicity issue: even if no true difference exists, the chance of at least one apparently unusual result increases as more comparisons are made. A prespecified procedure can address this, for example by adjusting significance thresholds or using a hierarchical testing plan.

The registry record does not report whether the primary comparisons were adjusted for multiplicity, how the three dose comparisons were ordered, or whether secondary analyses were confirmatory or exploratory. It also does not report a complete statistical analysis plan. Consequently, the reported p-values should be read as posted results rather than assumed to have family-wise error control. This is particularly relevant when considering a value close to a conventional threshold or scanning across many outcomes for an isolated finding.

Missing data are handled for the primary endpoint with last observation carried forward when fewer than 4 days of diary data were provided. The endpoint description identifies this rule, but the registry does not report the number of participants affected, the amount or reasons for missingness, or sensitivity analyses under alternative assumptions. Carrying an earlier pain score forward may fail to reflect a participant’s later experience if the outcome changes after the recorded observation.

The primary analysis population is identified as ITT Population, but detailed inclusion rules and the handling of missing outcome data within that population are not reported. The registry also does not report interim analyses, stopping rules, or the original sample-size justification. These omissions do not invalidate the posted numerical results, but they limit assessment of the prespecification, robustness, and multiplicity control of the analyses.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: partial seizures (1.8%), diabetic ketoacidosis (1.8%), hyperkalaemia (1.8%), ankle fracture (1.8%), renal failure (1.8%).

The registry reports serious adverse events and other adverse events by group. Serious adverse events were recorded for 6 participants in the placebo group, 3 in the GEn 1200 mg/day group, 4 in the GEn 2400 mg/day group, 5 in the GEn 3600 mg/day group, and 2 in the pregabalin 300 mg/day group. The at-risk counts shown for these groups are 120, 62, 56, 116, and 66, respectively.

The other adverse event counts were 50 for placebo, 34 for GEn 1200 mg/day, 25 for GEn 2400 mg/day, 62 for GEn 3600 mg/day, and 32 for pregabalin 300 mg/day. These counts should be read with their group sizes and the registry’s event definitions in mind. They are not, by themselves, a comparison of event severity, duration, or causation.

The registry lists serious-event terms including partial seizures, diabetic ketoacidosis, hyperkalaemia, ankle fracture, renal failure, and respiratory failure, each at 1.8%. The posted summary does not identify the treatment group for each term, so those terms should not be assigned to a particular group. Death counts are not reported in the registry record. These safety figures describe reported counts and do not establish that an event was caused by a study treatment.

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

The posted results describe changes in average pain scores from baseline and comparisons between randomized groups. Mean 24-hour average pain intensity decreased from baseline in each listed group. The sponsor-reported adjusted comparisons between each GEn dose and placebo have confidence intervals that include zero. This means the data, under the reported analysis, do not precisely distinguish those adjusted differences from no difference.

That interpretation is not the same as proving that all treatments had identical effects. The intervals also include nonzero differences, so uncertainty remains about the size and direction of the comparisons. Nor do the estimates show what every individual experienced: group means can conceal substantial variation among participants. The registry does not report a threshold for a clinically important difference, so statistical estimates cannot by themselves answer whether any difference would matter to patients.

The study includes a pregabalin positive-control group, but the posted comparison has no reported p-value or method. The available result should not be used to make an unsupported conclusion about that group. Similarly, the secondary outcomes provide related symptom information, but unadjusted analyses across many measures carry additional uncertainty.

The record does not provide the complete analysis plan, original sample-size justification, multiplicity procedures, or sensitivity analyses for missing data. Those absences limit how fully the robustness of the conclusions can be assessed. The study’s results are therefore best understood as estimates from this trial and its reported analysis, not as definitive evidence for every patient group, dose, or treatment setting.

No treatment recommendation follows from these statistical summaries. They report the observed and estimated group-level results, together with their uncertainty, without establishing a clinical decision for an individual.

18. Why This Trial Matters Statistically

This trial illustrates why a treatment comparison cannot be interpreted from group averages alone. All reported groups had negative mean changes in the primary pain score, but the relevant evidence is the difference between each active group and placebo, alongside its uncertainty. This distinction is central in clinical research because improvement over time within a group does not isolate the contribution of the assigned treatment.

The reported ANCOVA estimates and confidence intervals also show why a point estimate near a conventional significance boundary should not be treated as a decisive result. For GEn 3600 mg/day, the sponsor-reported interval extends to 0.01 and the p-value is 0.105, while the unadjusted recalculation yields a different p-value. The gap reinforces the importance of identifying which analysis produced a result and giving precedence to the sponsor-reported model rather than treating recalculations as interchangeable.

The study also provides a practical example of multiplicity. Several doses, a positive control, and a range of secondary outcomes create many potential comparisons. Without a reported adjustment strategy, isolated unadjusted findings deserve caution. Similarly, last observation carried forward is a clear but assumption-dependent way to address some missing diary data; the absence of sensitivity analyses leaves uncertainty about how those assumptions affect results.

Finally, sample-size illustrations based on observed effects are useful for understanding how harder-to-detect differences demand larger groups, but they are not evidence about the trial’s original planning or its observed power. Separating design assumptions, reported analyses, recalculations, and exploratory results is essential for a statistically careful reading of a clinical trial record.

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.

Several trial-specific reporting gaps constrain interpretation. The registry identifies randomization, triple masking, and a parallel design, but it does not describe the randomization procedure, masking roles, allocation concealment, or detailed model specification. The covariates used in the reported ANCOVA analyses are not reported in the registry record.

The record gives group sizes for the primary endpoint, but does not explain the difference between total enrollment and the outcome analysis counts. It does not report detailed participant flow, reasons for withdrawal, the number with incomplete diary data, or the extent to which last observation carried forward affected the endpoint. Alternative missing-data analyses are not reported.

The original sample-size justification and target effect are not reported. The planning illustrations based on observed effects are separate from the trial’s own design and cannot fill that gap. Multiplicity procedures for the primary dose comparisons and the many secondary outcomes are also not reported, which limits interpretation of isolated p-values.

There is incomplete reporting for some comparisons: the pregabalin comparison lacks a posted method and p-value, and sponsor-reported ANCOVA results are not listed for the secondary outcomes described in the results summaries. A clinical-importance threshold for the pain scale is not reported. Finally, the available record does not provide enough information to evaluate the full safety profile or attribute listed serious events to treatment. These limitations concern the scope and detail of the registry reporting; they do not change the reported estimates themselves.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: A Study In Patients With Neuropathic Pain From Diabetic Peripheral Neuropathy (DPN) — NCT00643760.
• Registry record last updated 2013-07-22; status last verified 2013-01.
• Results first posted 2011-05-11.
• 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

The registry record describes a completed randomized, triple-masked, parallel-group Phase 2 study of GEn at three daily doses versus placebo, with pregabalin 300 mg/day as a positive control. The study enrolled 421 participants with neuropathic pain associated with diabetic peripheral neuropathy.

The primary outcome was change from baseline in mean 24-hour average pain intensity at the end of maintenance treatment, using last observation carried forward data. Sponsor-reported ANCOVA comparisons for the three GEn doses have 95% confidence intervals that include zero. Recalculated unadjusted results are supplementary and do not replace the sponsor’s reported analysis.

The registry also lists secondary pain and related outcomes and reports adverse-event counts. Multiplicity procedures, the original sample-size justification, detailed missing-data sensitivity analyses, and some comparison details are not reported in the registry record. The posted estimates should therefore be read with attention to their uncertainty and the limits of the available analysis details.