Evaluating the Efficacy of Dextromethorphan/Quinidine in Treating Irritability in Huntington's Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluating the Efficacy of Dextromethorphan/Quinidine in Treating Irritability in Huntington's Disease (NCT03854019), a randomized phase 3 study. The primary outcome is Irritability as Assessed by The Irritability Scale.

2. Clinical Question

3. Trial Design

The registry record describes a phase 3 randomized, quadruple-masked crossover trial sponsored by The University of Texas Health Science Center, Houston. Its stated purpose was to assess the efficacy and safety of dextromethorphan/quinidine 20mg/10mg in patients with irritability due to Huntington's disease. Enrollment was 20, and the record lists the study as completed.

A crossover design means participants receive more than one study condition in a planned sequence, allowing comparison of outcomes under each condition within the trial. The registry record lists a dextromethorphan/quinidine-then-placebo sequence and a placebo-then-dextromethorphan/quinidine sequence. The masking designation is quadruple, but the specific roles of the masked groups are not reported in the registry record.

The posted primary outcome is Irritability Scale total score at 4 weeks. Its results list 18 observations for dextromethorphan/quinidine and 18 for placebo. The comparison is reported as a mean difference, but the registry record does not describe the model used to account for the crossover structure, sequence, period, or within-participant correlation. The unadjusted recalculation accompanying the results treats the posted summary statistics as a simple comparison and should not be confused with a reported crossover-model analysis.

Descriptions of the dosing schedules are posted for the treatment sequences, but washout procedures, period-specific timing, and the rationale for the sequence are not reported in the registry record. The record also does not report the planned sample-size justification, the original statistical analysis plan, or the recruitment and completion flow needed to explain how the enrollment figure relates to the outcome-specific numbers.

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.

First Intervention (4 Weeks)

Washout (1 Week)

Second Intervention (4 Weeks)

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 Irritability as Assessed by The Irritability Scale, measured over 4 weeks.

The primary endpoint is irritability measured with the Irritability Scale. The registry record describes a total score ranging from 0 to 42, with higher scores indicating greater irritability. The outcome is a continuous score, and the posted summary describes the mean and standard deviation for each treatment condition at the 4-week timeframe.

A scale score gives researchers a consistent way to quantify a behavioral feature across participants and study conditions. Analyzing the mean can describe the average score in each condition, while the standard deviation conveys how spread out individual scores are around that average. Comparing these summaries gives a group-level view of the observed difference; it does not show how every participant's score changed.

The registry record names irritability as the principal outcome of interest, making it the most direct posted measure for the study's stated question. Its interpretation depends on the score's direction and range, as well as on the size and precision of the between-condition estimate. The registry record does not report a threshold for a clinically important change, so the clinical meaning of a score difference cannot be established from the posted endpoint description alone.

The stated timeframe is 4 weeks. The record does not provide a more detailed account of how the assessment relates to each crossover period or whether the reported comparison adjusts for period or sequence. Those details matter when interpreting the score contrast in a crossover trial.

7. Results Posted in the Registry

• Dextromethorphan/Quinidine 20mg/10mg (DM/Q 20mg/10mg): mean 18.70 versus 19.90 on control; difference -1.20 (95% CI -7.57 to 5.17), standardized effect d = -0.12; z-test p = 0.712.

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.

Behavioral Symptoms, as Assessed by the Hospital Anxiety and Depression Scale (HADS).

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Dextromethorphan/Quinidine 20mg/10mg (DM/Q 20mg/10mg): mean 10.60 versus 11.10 on control; difference -0.50 (95% CI -5.43 to 4.43), standardized effect d = -0.07; z-test p = 0.842.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Dextromethorphan/Quinidine 20mg/10mg (DM/Q 20mg/10mg) and the control. The interval gives the range of effects that remain compatible with the data.

Behavioral Symptoms, as Assessed by the Neuropsychiatric Inventory-Questionnaire (NPI-Q) - Severity Score.

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Dextromethorphan/Quinidine 20mg/10mg (DM/Q 20mg/10mg): mean 8.20 versus 8.60 on control; difference -0.40 (95% CI -3.94 to 3.14), standardized effect d = -0.07; z-test p = 0.825.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Dextromethorphan/Quinidine 20mg/10mg (DM/Q 20mg/10mg) and the control. The interval gives the range of effects that remain compatible with the data.

Behavioral Symptoms, as Assessed by the Neuropsychiatric Inventory-Questionnaire (NPI-Q) - Caregiver Distress.

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Dextromethorphan/Quinidine 20mg/10mg (DM/Q 20mg/10mg): mean 7.80 versus 11.30 on control; difference -3.50 (95% CI -7.80 to 0.80), standardized effect d = -0.55; z-test p = 0.111.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Dextromethorphan/Quinidine 20mg/10mg (DM/Q 20mg/10mg) and the control. The interval gives the range of effects that remain compatible with the data.

The posted secondary outcomes cover behavioral symptoms assessed with HADS, NPI-Q severity, NPI-Q caregiver distress, and the irritability/aggression subscale of the PBA-s. The record lists 25 secondary outcomes as posted, although the registry record does not provide a reported analysis for the three secondary outcomes included in the numerical comparisons. The wider list of outcomes indicates that the study collected measures beyond the primary Irritability Scale result.

Across the three secondary comparisons with numerical summaries, the estimated mean differences are negative, meaning the posted means are lower in the dextromethorphan/quinidine condition than in the placebo condition. The confidence intervals for these comparisons include zero. The caregiver-distress estimate is larger in magnitude than the other two, but its interval also includes zero. These patterns do not provide a clear, precise secondary signal that changes the interpretation of the primary result.

Secondary outcomes can add context by asking whether related aspects of behavior show patterns consistent with the primary measure. They do not replace the primary outcome, and the measures are not interchangeable: each captures a different construct or reporter perspective. Similar directions across outcomes may be of interest, but correlated measures and multiple comparisons mean that isolated estimates should not be treated as independent confirmation.

The registry record does not report multiplicity adjustments or a hierarchy for interpreting secondary outcomes. Unadjusted results carry less weight because assessing many outcomes increases the opportunity for chance findings. Here, the posted secondary comparisons are descriptive and imprecise; they should be interpreted alongside the primary estimate and the missing analysis details, not as separate proof of a treatment effect.

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

• Behavioral Symptoms, as Assessed by the Hospital Anxiety and Depression Scale (HADS).
• Behavioral Symptoms, as Assessed by the Hospital Anxiety and Depression Scale (HADS).
• Behavioral Symptoms, as Assessed by the Neuropsychiatric Inventory-Questionnaire (NPI-Q) - Severity Score.
• Behavioral Symptoms, as Assessed by the Neuropsychiatric Inventory-Questionnaire (NPI-Q) - Severity Score.
• Behavioral Symptoms, as Assessed by the Neuropsychiatric Inventory-Questionnaire (NPI-Q) - Caregiver Distress.
• Behavioral Symptoms, as Assessed by the Neuropsychiatric Inventory-Questionnaire (NPI-Q) - Caregiver Distress.
• Behavioral Symptoms, as Assessed by the Problem Behaviors Assessment - Short Version (PBA-s). - Irritability/Aggression Subscale
• Behavioral Symptoms, as Assessed by the Problem Behaviors Assessment - Short Version (PBA-s) - Irritability/Aggression Subscale

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous: each observation is a score on a scale, rather than a category or event count. The registry record reports means and standard deviations. A mean describes the average score in a condition, while a standard deviation describes the dispersion of scores around that mean. The mean difference expresses the contrast between the two condition averages; the posted estimate is -1.2 points, calculated as the dextromethorphan/quinidine mean relative to the placebo mean.

What does a confidence interval represent?

General explanation: a confidence interval describes the range of effect estimates reasonably compatible with the observed data and the statistical method used. Its width reflects precision: a narrower interval indicates more precise estimation, while a wider interval indicates greater uncertainty. A confidence interval is not a range containing a known fixed proportion of individual participant scores, and it does not assign a probability to the true effect after the data have been observed. The primary interval runs from -7.574 to 5.174, so it includes zero and values in both directions.

What does the p-value tell the reader?

General explanation: a p-value measures how unusual data at least as discrepant as those observed would be under a specified null model and its assumptions. It is not the probability that the null hypothesis is correct, a measure of clinical importance, or a direct measure of the chance that the result will replicate. The unadjusted p-value posted for the primary comparison is 0.712. It should be considered alongside the estimate, confidence interval, design, and limitations rather than treated as a stand-alone conclusion.

Why does the crossover design matter?

General explanation: crossover trials compare multiple conditions within participants. Because measurements from the same participant are often related, an analysis may need to account for within-participant correlation and for features such as treatment period or sequence. The registry record identifies this trial as crossover, but the analysis method used for the posted primary outcome is not reported in the registry record. The recalculated comparison uses posted summary statistics in a simple unadjusted calculation. It does not incorporate participant-level pairing or adjust for period and sequence, and therefore is not equivalent to a crossover-model result.

The registry record lists the same number of observations, 18, for each primary treatment condition, but does not state whether all observations are paired or how missing measurements were handled. Equal condition counts alone do not demonstrate that every participant contributed a complete pair. Participant-level data or a detailed analysis report would be needed to assess the paired structure and the effects of missing observations.

Why can over-dispersion matter?

General explanation: over-dispersion arises when observed variability is greater than a statistical model expects. When a model does not allow enough variability, it can make standard errors too small and confidence intervals too narrow, creating an overly confident impression. The primary endpoint is continuous and is summarized with standard deviations, so the relevant issue is whether the chosen model adequately represents the score distribution and repeated-measure structure. The registry record does not report a model diagnostic or an assessment of over-dispersion. This is a general statistical consideration, not a finding that over-dispersion occurred in this trial.

The standard deviations reported for the primary conditions are 10.1 and 9.4. These summaries show that scores varied among observations, but they do not reveal the distribution's shape or the relationship between paired observations. The confidence interval in the recalculated comparison is based on the posted summary statistics, not on a participant-level assessment of the score distribution.

What can be inferred from the absence of posted analyses?

The registry record lists no reported analyses for the primary outcome. Accordingly, the numerical contrast available for interpretation is the posted summary and the unadjusted recalculation, not a documented sponsor analysis with a stated model, covariates, or handling of the crossover design. A recalculation can help readers understand the scale and uncertainty of the posted summaries, but it cannot recover undocumented design or analysis decisions. The record does not report the original sample-size justification, interim analyses, analysis populations, missing-data methods, or multiplicity plan. These items should not be inferred from the outcome summaries.

General explanation: a well-specified analysis plan helps distinguish preplanned questions from analyses chosen after results are known. It can also clarify how multiple outcomes, missing observations, and design features were handled. Without such details in the registry record, the posted estimates can be described, but the full analysis process cannot be independently reconstructed from the record.

11. Confidence Intervals and Precision

The primary mean difference is -1.2 points, with a 95% confidence interval from -7.574 to 5.174. The interval is broad and spans zero, allowing for a range of possible contrasts that includes values favoring either condition as well as no difference. In practical terms, the posted summary does not estimate the direction and magnitude of the difference precisely.

Precision is distinct from whether an estimate is statistically significant. A confidence interval that includes zero does not prove there is no difference, just as a point estimate on one side of zero does not establish a reliable effect. The interval communicates uncertainty around the estimate under the method used. Here, that method is an unadjusted recalculation from posted summary statistics, and the registry record does not report a sponsor analysis that accounts for the crossover design.

The standard deviations are 10.1 for dextromethorphan/quinidine and 9.4 for placebo, with 18 observations in each condition. Variation in scores and the limited number of observations contribute to the difficulty of estimating a precise contrast. The record's enrollment figure is 20, but reasons for the outcome-specific counts are not reported in the registry record.

The interval should not be read as an assessment of clinical importance. The registry record describes the score range and direction but does not report a clinically important difference threshold. It also does not provide enough analysis detail to determine how a paired crossover analysis would change the estimated uncertainty. The posted interval is therefore useful for describing the recalculated comparison, but it does not settle the clinical interpretation of the treatment contrast.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total event counts. They are illustrations based on the observed effect, not a report of the trial's original design assumptions. The record does not report the original sample-size justification. The posted illustration assumes a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is the stated fraction of the observed effect.

The 80% power column indicates the planned number of participants per arm that the illustration estimates would give an 80% chance of detecting the selected effect under those assumptions, if that effect were the true one. The 90% power column describes the corresponding planning target for a 90% chance. These are design calculations, not a guarantee that a future study will detect an effect, and not a measure of the result's importance.

Rows describing 100%, 75%, and 50% of the observed effect show how the planning result changes with the assumed effect size. Smaller effects require more participants to detect with the same target power, which is why the required numbers increase as the assumed fraction becomes smaller. A curve based on these calculations should be read as a planning aid showing the relation between assumptions and required sample size, not as observed evidence about treatment performance.

This is not observed power. It is a planning illustration computed from the observed effect using the stated assumptions. Because the observed effect is uncertain, especially with a broad confidence interval, the calculated participant requirements should not be treated as a reliable estimate of the sample size needed for a future study without an independently justified target effect and design.

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 = -1.200; pooled standard deviation σ = 9.756.
2. n = 2 × (1.96 + 0.842)² × 9.756² / -1.200² = 1,037.6, rounded up to 1,038 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 <- -1.2                      # observed difference in means
sigma <- 9.75628002878146                     # 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(3854019)
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 = 1,038 (80% power), 1,390 (90% power)
 75% of observed effect: n per arm = 1,845 (80% power), 2,470 (90% power)
 50% of observed effect: n per arm = 4,151 (80% power), 5,557 (90% power)
power.t.test: 1038.6 
Simulated power at n = 1,038 per arm: 0.804 (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. Multiplicity, Missing Data and Analysis Populations

The registry record lists 27 outcome measures, including the primary outcome and multiple secondary measures, and 0 reported analyses. It does not describe a multiplicity procedure, a hierarchy among outcomes, or a plan for controlling the overall chance of false-positive findings when several outcomes are assessed. Without that information, the role of any one secondary result in confirmatory inference is unclear. The secondary comparisons are best read as descriptive results rather than as a collection of independent tests.

The record does not report the original statistical analysis plan, analysis populations, or whether analyses were intended to follow intention-to-treat, per-protocol, or another approach. It also does not report how missing values were handled, whether participants were excluded from particular outcome analyses, or why the primary results list 18 observations per condition when enrollment was 20. The caregiver-distress comparison lists 17 observations per condition. These counts are descriptive; the record does not give reasons for the differences.

Missing-data methods can affect both the estimate and its precision, especially if the likelihood of having an observed score is related to participant characteristics or outcomes. General explanation: complete-case summaries describe participants with available data, while other approaches may use different assumptions about missing values. The registry record does not identify which approach was used for the posted summaries, so no particular missingness mechanism or method can be inferred.

The crossover design also makes details about paired observations and period-specific data important. The record does not report how within-participant correlation, treatment sequence, period, or possible carryover was addressed in the primary analysis. These omissions prevent a full assessment of whether the reported comparison reflects the design as planned. They are limits of the information in the registry record, not evidence that any specific analysis choice was inappropriate.

15. 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: hospitalization for motorcycle accident (5.0%).

The safety summary lists serious adverse events among 0 of 20 participants in the dextromethorphan/quinidine group and 1 of 20 in the placebo group. It lists 0 deaths in both groups. These counts describe the registry record's serious-event summary; they do not by themselves establish a difference in risk between conditions.

The most frequently listed serious-event term is “Hospitalization for motorcycle accident,” reported as 5.0%. The record does not identify the treatment group associated with that term in the information, so it should not be assigned to a condition. The registry record also lists other adverse events affecting 10 participants in the dextromethorphan/quinidine group and 5 in the placebo group, but those figures are not a comparison of event severity or causality.

Safety counts are difficult to interpret without information about event definitions, exposure time, event attribution, and how events were collected. Those details are not reported in the registry record. The small enrolled population also limits the ability of event counts to characterize uncommon harms. These figures should therefore be read as descriptive registry reports, not as a comprehensive safety assessment.

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

The posted primary results show a mean Irritability Scale score of 18.7 with dextromethorphan/quinidine and 19.9 with placebo at the 4-week timeframe. The mean difference is -1.2 points, with a 95% confidence interval from -7.574 to 5.174. Since higher scores indicate greater irritability, the observed average was lower in the dextromethorphan/quinidine condition. The uncertainty interval includes zero and spans both negative and positive values, so the registry result does not estimate a precise direction or size of difference.

These data do not establish that the treatments are equivalent, nor do they establish that one treatment caused a meaningful change. A nonsignificant p-value is not proof of no effect. Conversely, the direction of the point estimate alone is not proof of benefit. The registry record does not report a threshold defining a clinically important score difference, which makes it impossible to classify the estimate's clinical importance from the posted endpoint description.

The trial is identified as randomized, quadruple-masked, and crossover, but the record does not report the analysis model used for the primary result. The unadjusted recalculation does not account for the potential pairing of repeated observations in a crossover trial. Without a reported crossover analysis, the estimate should be interpreted as a descriptive contrast based on the posted summaries rather than a complete model-based treatment effect.

The secondary summaries are also imprecise and do not resolve the primary uncertainty. The safety summary reports few serious events, but the event counts and incomplete contextual detail do not support broad conclusions about comparative safety. Overall, the registry record provides a limited account of observed scores and events, not a definitive judgment about efficacy or safety.

17. Why This Trial Matters Statistically

This trial is statistically notable because it asks a behavioral outcome question in a randomized crossover design. A crossover design can make within-participant comparisons informative, but only when the analysis and reporting address repeated observations, period, sequence, and other design features. The registry record identifies the design without providing the model details needed to evaluate those features in the posted primary comparison.

The main estimate is modest in magnitude relative to the spread of the scores, and its confidence interval is broad. This is a useful reminder that a point estimate alone can give an incomplete picture: the interval conveys that the data are compatible with a range of possible contrasts. The unadjusted p-value does not replace that interval or establish equivalence.

The study also illustrates the distinction between enrollment and outcome-specific data. Enrollment was 20, whereas the primary outcome lists 18 observations per condition and a secondary comparison lists 17 per condition. The registry record does not explain these counts. Clear accounting of participant flow and missing observations is important for judging the representativeness and precision of results.

Finally, multiple secondary measures can provide a broader descriptive view, but absent a reported multiplicity plan, they should not be treated as a set of independent confirmations. The record's limited analysis detail makes it especially important to distinguish posted descriptive summaries from a fully reported, design-aware statistical analysis.

18. 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 primary statistical limitation is that the registry record identifies a crossover design but does not report whether the primary comparison accounts for the within-participant structure. The posted recalculation is unadjusted and cannot represent a full crossover analysis without participant-level paired data. Period and sequence effects, and any carryover considerations, are not discussed in the registry record.

The primary outcome lists 18 observations in each condition despite enrollment of 20. A secondary outcome lists 17 per condition. The reasons for these counts, the number of participants with complete paired data, and the handling of missing observations are not reported in the registry record. This prevents assessment of whether missingness could affect the comparisons.

The reported summaries do not include a sponsor analysis, and the record lists no reported analyses. The original statistical analysis plan, sample-size rationale, analysis populations, and planned multiplicity approach are not reported in the registry record. These gaps limit assessment of whether the posted estimates correspond to preplanned methods.

The primary confidence interval is broad, and the record does not provide a clinically important difference threshold for the Irritability Scale. Consequently, the precision and clinical relevance of the estimated contrast cannot be fully judged. The reported standard deviations also do not provide the individual-level distribution or within-participant correlation necessary to evaluate the crossover comparison directly.

Safety reporting is descriptive and limited in context. The record does not give exposure-adjusted rates, detailed event attribution, or further information on the serious-event term. With enrollment of 20, the safety figures cannot characterize uncommon events with precision. These limitations apply to interpretation of the registry record and do not establish that unreported procedures or analyses were absent from the conduct of the trial.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Evaluating the Efficacy of Dextromethorphan/Quinidine in Treating Irritability in Huntington's Disease — NCT03854019.
• Registry record last updated 2024-01-05; status last verified 2024-01.
• Results first posted 2024-01-05.
• 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.

22. Record Summary

The registry record describes a completed, randomized, quadruple-masked phase 3 crossover study sponsored by The University of Texas Health Science Center, Houston. It enrolled 20 participants and assessed dextromethorphan/quinidine 20mg/10mg against placebo for irritability associated with Huntington's disease.

The primary outcome was Irritability Scale total score at 4 weeks, ranging from 0 to 42, with higher scores indicating greater irritability. The posted means were 18.7 with dextromethorphan/quinidine and 19.9 with placebo. The mean difference was -1.2, with a 95% confidence interval from -7.574 to 5.174 and an unadjusted p-value of 0.712. The interval is broad and includes zero.

The record lists secondary behavioral outcomes and descriptive adverse-event counts, but no reported analyses. It does not report the trial's original sample-size justification, detailed missing-data methods, or the model used for the crossover comparison. These omissions limit interpretation beyond the posted summaries.