Efficacy and Safety Study of Moxidectin in Adults With Scabies: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy and Safety Study of Moxidectin in Adults With Scabies (NCT05875441), a randomized phase 2 study. The primary outcome is Percentage of Index Subjects Achieving Complete Cure (Efficacy).

2. Clinical Question

The clinical question has two linked parts. The efficacy part concerns complete cure by the specified follow-up time, not improvement in only one sign or symptom. Cure requires all described clinical signs and symptoms to resolve, including burrows, lesions, and pruritus, and also requires examination evidence that mites, eggs, and/or scybala are absent and dermoscopy is negative for burrows. The safety part concerns adverse events after a single administration of each dose.

The registry lists scabies as the condition and identifies adults as the study population. It describes moxidectin as not approved to treat scabies in humans and states that the effective dose for scabies was not known. The trial therefore compares three dose levels with placebo rather than evaluating an established dose against another active treatment. The posted results can describe the observed outcomes in these randomized groups, but do not on their own establish how results apply to people outside the enrolled study population.

3. Trial Design

This was a phase 2, randomized, placebo-controlled, double-blind, dose-ranging study with a parallel-group model. The registry lists quadruple masking. It records enrollment of 200 and a completed study. The listed study start was 2023-11-23 and the primary completion date was 2024-11-27.

Participants were assigned to one of four groups: moxidectin 8 mg, moxidectin 16 mg, moxidectin 32 mg, or placebo. Each group was described as receiving a single administration on Day 0. For the 8 mg and 16 mg groups, the record describes over-encapsulated moxidectin tablets and placebo capsules used to keep the number of capsules the same. For the 32 mg group it describes a single dose, and for placebo it describes 16 capsules. These are registry descriptions of the assigned interventions; additional operational details are not reported in the registry record.

The primary outcome was complete cure at 28 Days. The primary outcome population was the Full Analysis Set, defined as all randomized index subjects who received study drug and were analyzed according to their randomized treatment group. The arm counts posted for this outcome are 50 for 8 mg, 49 for 16 mg, 51 for 32 mg, and 49 for placebo. The registry’s enrollment figure and these outcome-specific arm counts describe different record entries; additional explanation of their relationship is not reported in the registry record.

The record includes five outcome measures but posts no secondary outcome results in the results summarized for this analysis. Details such as the randomization procedure, allocation concealment, the identity of the groups included in quadruple masking, and the trial’s original statistical design assumptions are not reported in the registry record. Those details should not be inferred from the labels for randomization and masking.

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: The Full Analysis Set defined as all randomized index subjects receiving study drug and analyzed according to the treatment group to which they were randomized.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: A total of 200 index subjects were randomized in the study. 199 (99.5%) randomized index subjects were included in the analysis population (Full Analysis Set and Safety Analysis Set). Only one subject was excluded from these analysis sets as they withdrew prior to IP administration.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Index Subjects Achieving Complete Cure (Efficacy), measured over 28 Days.

The primary endpoint is the percentage of index subjects achieving complete cure at 28 Days. The outcome is reported as counts of participants, with the number meeting the definition assessed against the number in each treatment group. The Full Analysis Set includes randomized index subjects who received study drug and are analyzed in their randomized group.

Complete cure is a combined clinical and examination-based outcome. Clinical cure requires complete resolution of all signs and symptoms, including burrows, inflammatory and noninflammatory lesions, and pruritus. The second part requires microscopic or dermatoscopic cure: absence of mites, eggs, and/or scybala, together with negative dermoscopy for burrows. Thus, the endpoint is stricter than an outcome based on symptom improvement alone. A participant must meet both components to count as completely cured.

A combined endpoint can be useful when the clinical question concerns both how a condition appears and whether examination finds evidence of infestation. It gives a clear, prespecified status at a defined follow-up time, although it does not show the separate contribution of each component unless those component results are also reported. The registry record does not report separate counts for clinical cure and microscopic or dermatoscopic cure, so the posted primary outcome cannot identify which component most often determined whether a participant met the complete-cure definition.

The endpoint addresses the study’s stated efficacy question at 28 Days after a single administration. It does not, by itself, describe the timing of cure within that period, persistence beyond the assessment, or outcomes at other follow-up times.

7. Results Posted in the Registry

• Moxidectin 8mg: 56.0% (28/50) versus 2.0% (1/49) on control; risk difference 54.0 percentage points (95% CI 39.6 to 68.3), risk ratio 27.44 (3.88–193.90); unadjusted two-proportion z-test p = <0.001.
• Moxidectin 16mg: 63.3% (31/49) versus 2.0% (1/49) on control; risk difference 61.2 percentage points (95% CI 47.2 to 75.3), risk ratio 31.00 (4.40–218.23); unadjusted two-proportion z-test p = <0.001.
• Moxidectin 32mg: 62.7% (32/51) versus 2.0% (1/49) on control; risk difference 60.7 percentage points (95% CI 46.9 to 74.6), risk ratio 30.75 (4.37–216.39); unadjusted two-proportion z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary: each participant either met the complete-cure definition at 28 Days or did not. For a binary outcome, the basic group summary is the number of participants with the event and the number assessed. The record posts those counts for each randomized group. A proportion can be estimated from such counts, but this explanation does not add a recalculated proportion beyond the registry’s reported comparative results.

What does a risk difference describe?

The risk difference compares the event proportions in two groups by subtracting the comparator proportion from the intervention proportion. It is an absolute contrast, expressed on the probability scale. A positive risk difference in these comparisons means that complete cure was observed more often in the moxidectin group than in placebo. The posted estimates are positive for all three dose comparisons, and their confidence intervals have positive bounds. Absolute contrasts are often useful for understanding how far apart the group outcomes are on the original outcome scale.

A risk difference is tied to the outcome and follow-up definition used in the analysis. Here, it concerns complete cure at 28 Days, not a different definition of response or another time point. Its precision depends in part on the number of participants and the event counts in both groups. The relatively small placebo event count is important context for interpreting all comparisons.

How do relative measures differ?

A risk ratio compares the event proportion in one group with the event proportion in another. An odds ratio compares the odds of the event between groups. Both describe relative rather than absolute contrasts, and neither has the same scale as a risk difference. In this trial, the registry reports risk ratios and odds ratios alongside their confidence intervals. Because complete cure was uncommon in placebo, the relative estimates are large. When the comparator event count is very low, relative measures can be especially sensitive to small changes in event counts and may have wide intervals. Reading them together with the raw participant counts and absolute contrast helps prevent a large relative estimate from obscuring the amount of information in the data.

What does a p-value contribute?

The posted p-values for the three comparisons are unadjusted and each is < 0.001. In general, a p-value describes how compatible the observed data are with a specified null hypothesis under the assumptions of a statistical test. A small p-value is not the probability that the null hypothesis is true, and it does not quantify the probability that a finding will reproduce. It also does not say how large or important the effect is. The registry record does not report the precise test specification or whether the sponsor used another analysis for its conclusions, so the p-values should be understood as the unadjusted values attached to the posted comparisons.

Why use confidence intervals?

A confidence interval expresses uncertainty around an estimated contrast. In general, its endpoints are compatible values for the underlying effect under the method’s assumptions. A narrower interval gives a more precise estimate than a wider interval, while neither interval width nor exclusion of a null value removes uncertainty. For each posted risk difference, the interval is entirely on the positive side of zero. The relative-measure intervals are broad, which makes the exact size of those ratios less certain than their direction alone may suggest. Confidence intervals do not incorporate every source of uncertainty, such as possible bias from missing data or unreported design and analysis decisions.

What is not specified about the analysis?

The record defines the Full Analysis Set as randomized index subjects who received study drug and were analyzed according to randomized assignment. This describes the stated population for the primary result. It does not, by itself, explain how participants with missing or unevaluable endpoint assessments were handled. Such handling, the exact statistical tests, any covariate adjustment, and the sponsor’s original statistical analysis plan are not reported in the registry record. The registry record lists no analysis entries, although it does post the outcome counts and comparisons considered in this statistical interpretation. No specific model, correction, or imputation procedure should be assumed from the available details.

The outcome is a participant count, not a time-to-event measure. The posted comparison is therefore interpreted as a contrast in the probability of meeting the endpoint by the fixed assessment time. General statistical concepts in this explanation clarify the meaning of the reported measures; they do not imply that an unreported sponsor procedure was used.

10. Confidence Intervals and Precision

The registry reports confidence intervals for the risk differences and for the relative measures in each moxidectin-versus-placebo comparison. A confidence interval is a range of effect values compatible with the observed data under the interval method’s assumptions. It is not a guarantee that the true value lies within that particular range, and it does not describe uncertainty from every possible source, including bias or missing outcomes.

All three risk-difference estimates are positive, and each reported risk-difference interval has positive lower and upper bounds. This means the intervals do not include zero, the value representing no absolute difference between groups. The reported unadjusted p-values are also < 0.001 for each comparison. These features describe the statistical evidence in the posted comparisons; they do not establish the size of an effect with high precision or answer whether the doses differ from one another.

The intervals for the relative measures are broad. In particular, a relative measure can be unstable when the comparator group has only one participant meeting the endpoint. As a result, the large relative point estimates should not be read as precise measures of how many times more likely complete cure is in one group. The absolute counts and risk-difference intervals provide complementary context and are more directly tied to the observed difference in proportions.

The number of participants in each outcome group is limited, and the event count in placebo is especially small. Those data features constrain precision, even when a p-value is small. The posted intervals describe sampling uncertainty under their statistical assumptions; they do not address whether the study population represents other settings, whether endpoint assessments were complete, or whether the analysis plan anticipated the comparisons. The original statistical methods and missing-data approach are not reported in the registry record, so these are additional uncertainties around interpretation.

11. 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 displays are planning illustrations based on the observed effect, not the trial’s original design calculations. For these binary-outcome comparisons, figures mean participants per arm. The assumptions listed for the illustrations are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. The trial’s own original sample-size assumptions and justification are not reported in the registry record.

For a planning scenario using 100% of the observed effect, the figures for the 8 mg comparison are 10 participants per arm for 80% power and 13 participants per arm for 90% power. For 16 mg, the corresponding figures are 8 and 11; for 32 mg, they are 9 and 11. For a scenario using 75% of the observed effect, the figures are 16 and 21 for 8 mg, 13 and 17 for 16 mg, and 13 and 17 for 32 mg. For a scenario using 50% of the observed effect, they are 28 and 36 for 8 mg, 23 and 31 for 16 mg, and 24 and 31 for 32 mg.

The 80% power column gives the illustrative participants per arm under the stated assumptions for a design with an 80% chance of detecting the chosen effect if that effect is real. The 90% power column describes the corresponding target with a 90% chance. These are design-planning probabilities, not probabilities that the trial result is correct. Smaller effects need more participants to detect under otherwise unchanged assumptions. The figures are planning illustrations, not observed power.

Curves based on the same planning setup should be read as showing how the illustrative participant requirement changes as the effect to detect changes. Their values do not replace a design-specific justification; the true trial assumptions and any planned allowance for incomplete observations are not reported in the registry record.

12. 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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.020; treatment proportion p₁ = 0.560; average p̄ = 0.290.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6418 = 1.2580.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5161 = 0.4344.
4. n = (1.2580 + 0.4344)² / (0.5396)² = 9.8, rounded up to 10 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
p0 <- 0.0204081632653061                          # control proportion
p1 <- 0.56                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(5875441)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 10 (80% power), 13 (90% power)
 75% of observed effect: n per arm = 16 (80% power), 21 (90% power)
 50% of observed effect: n per arm = 28 (80% power), 36 (90% power)
power.prop.test: 9.8 
Simulated power at n = 10 per arm: 0.833 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-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.

13. Multiplicity, Missing Data and Analysis Populations

The registry posts three primary comparisons, one for each moxidectin dose against placebo. Their p-values are explicitly unadjusted and are all < 0.001. If a study tests several hypotheses, the chance of at least one false-positive result across the set can increase. Multiplicity procedures can address this issue, but whether any adjustment was prespecified or used in the sponsor’s analysis is not reported in the registry record. The reported p-values should therefore be read as nominal values for the individual comparisons, not as documented multiplicity-adjusted results.

No direct statistical comparison between the three moxidectin dose groups is posted. The fact that each dose is compared with placebo does not answer whether one dose differs from another. Nor does the similarity of the observed complete-cure counts establish dose equivalence. The registry record does not report an analysis of dose trend or a formal dose-selection procedure.

The stated primary analysis population is the Full Analysis Set: randomized index subjects who received study drug, analyzed according to their randomized group. This definition retains randomized assignment for those included, but it is not the same as a complete description of the handling of all randomized participants. The record does not state how many participants did not receive study drug, had missing endpoint assessments, or were excluded from the Full Analysis Set, nor does it describe imputation or other missing-data methods. The relationship between the enrollment figure and outcome-specific counts is not explained in the registry record.

The registry lists five outcome measures but posts no secondary outcome results for this record. No analysis entries are listed, and the detailed statistical analysis plan is not reported. These gaps mean it is not possible to assess from the registry record whether the posted comparisons follow a prespecified hierarchy, how missing primary outcomes were addressed, or whether analyses of other outcomes affect interpretation. The absence of those details does not invalidate the posted counts, but it limits assessment of analysis choices and the broader evidence base within this trial record.

14. 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 1% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports serious adverse-event counts separately from other adverse events. It lists zero serious adverse events in each group: moxidectin 8 mg, 0 among 50 at risk; moxidectin 16 mg, 0 among 48 at risk; moxidectin 32 mg, 0 among 52 at risk; and placebo, 0 among 49 at risk. Deaths are reported as zero in every group. These are observed counts during the safety reporting period described in the record; the duration and detailed event-collection procedures are not reported in the registry record.

For other adverse events, the record lists 9 among 50 at risk in the 8 mg group, 5 among 48 in the 16 mg group, 11 among 52 in the 32 mg group, and 8 among 49 in placebo. These are participant counts and should not be interpreted as counts of distinct event types. The registry does not provide serious adverse-event terms because no serious events are listed.

Zero serious events observed does not establish that a risk is absent. The groups are limited in size, and the record does not provide enough detail to assess event severity beyond the serious-versus-other categorization, timing, relatedness, or completeness of follow-up. The counts describe what was reported, not a basis for medical advice or a broad safety conclusion.

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

The posted primary results show that complete cure at 28 Days was observed in each moxidectin group and in the placebo group, with the group counts reported as 28 of 50 for 8 mg, 31 of 49 for 16 mg, 32 of 51 for 32 mg, and 1 of 49 for placebo. The three posted comparisons against placebo have positive risk-difference estimates and unadjusted p-values of < 0.001. These statistics describe the observed data and uncertainty under the analyses attached to the comparisons.

They do not establish that the three moxidectin doses have equal effects, that one dose is best, or that a dose-response relationship has been demonstrated. The registry does not report direct dose-to-dose comparisons or a formal dose-trend analysis. Nor do these results establish a benefit or risk for people outside the studied adult population, at other follow-up times, or under different treatment conditions.

The endpoint is a combined clinical and examination-based definition at a fixed time. The primary counts do not reveal which component contributed to each outcome, how quickly participants reached cure, or whether cure persisted after Day 28. The registry record does not report these details. The single-dose design also does not answer questions about repeated dosing or alternative schedules.

The safety data show zero reported serious adverse events and zero deaths in each group, alongside reported counts of other adverse events. These observations should not be taken to prove that serious harms cannot occur. A trial with limited group sizes may not characterize uncommon events, and the record does not report detailed event terms or the safety follow-up period.

Finally, the posted results do not provide the original analysis plan, a missing-data approach, or multiplicity procedures. These matters affect how confidently the statistical comparisons can be interpreted as confirmatory. The appropriate reading is descriptive: the registry reports higher observed complete-cure counts in the moxidectin groups than in placebo, with uncertainty and analysis limitations that remain relevant.

16. Why This Trial Matters Statistically

This trial is statistically informative because it places three dose levels in a randomized comparison with placebo and defines a specific binary endpoint at a fixed follow-up time. A parallel-group comparison can estimate how often participants met the same complete-cure definition across assigned groups. The inclusion of both absolute and relative comparative measures also illustrates why no single statistic should carry the entire interpretation.

The placebo group had one participant meeting the primary endpoint, while each moxidectin group had more observed complete cures. This makes the context of the comparator especially important: relative estimates can become large when the reference event count is very small, while absolute contrasts remain expressed as differences in outcome proportions. Confidence intervals add a view of uncertainty that the point estimates and p-values cannot provide alone.

The study also illustrates a common distinction between observing similar outcomes across dose groups and demonstrating equivalence among doses. The posted analyses compare each dose with placebo, rather than directly comparing doses. Similar counts are useful descriptive information, but do not establish that dose effects are the same or identify an optimal dose.

Finally, the record highlights why registry reporting details matter. Clear information about analysis populations, missing outcomes, multiplicity, and the original analysis plan helps readers assess whether results are confirmatory and how broadly they can be interpreted. Several of those details are not reported in the registry record, so the statistical conclusions should remain tied closely to the posted endpoint, groups, and comparisons.

17. 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 result is based on a single assessment at 28 Days and a combined complete-cure definition. The registry does not post separate results for the clinical and microscopic or dermatoscopic components, so the source of endpoint failures cannot be examined. Results at other follow-up times and durability beyond the primary assessment are not reported in the registry record.

Although the study is described as randomized and quadruple-masked, the registry record does not provide the randomization method, concealment details, or which parties were masked. It does not report further participant eligibility characteristics, site information, or the study’s geographic setting. These omissions limit assessment of how the enrolled population and trial conduct may relate to other contexts.

The primary analysis population excludes randomized index subjects who did not receive study drug under its stated definition. The number excluded, the reasons for exclusion, and the handling of missing or unevaluable assessments are not reported in the registry record. The record’s enrollment figure is 200, while the outcome arm counts are 50, 49, 51, and 49; the relationship between these entries is not explained.

The posted p-values are unadjusted, and multiplicity procedures are not reported. There are no posted direct comparisons among dose groups. The original sample-size justification, planned statistical tests, covariate adjustments, and analysis plan are also not reported in the registry record. These issues make it difficult to judge whether the posted comparisons were prespecified and how robust they are to analytical choices.

Safety reporting is limited to counts of serious and other adverse events and deaths. Event descriptions, relatedness assessments, timing, and detailed follow-up are not reported. Zero serious events in the listed groups therefore describes the posted observations but cannot rule out uncommon harms.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Efficacy and Safety Study of Moxidectin in Adults With Scabies — NCT05875441.
• Registry record last updated 2026-06-16; status last verified 2025-05.
• Results first posted 2026-06-16.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

21. Record Summary

The registry record describes a completed phase 2 randomized, placebo-controlled, double-blind, dose-ranging study of single-dose oral moxidectin in adults with scabies. Enrollment is listed as 200. The primary endpoint was complete cure at 28 Days, requiring both complete clinical resolution and microscopic or dermatoscopic cure.

Complete cure was recorded for 28 of 50 participants in the 8 mg group, 31 of 49 in the 16 mg group, 32 of 51 in the 32 mg group, and 1 of 49 in placebo. Each posted moxidectin-versus-placebo comparison has an unadjusted p-value of < 0.001. The record lists zero serious adverse events and zero deaths in each group.

The registry does not report the original analysis plan, missing-data procedures, multiplicity adjustment, or direct comparisons among dose groups. Interpretation should remain focused on the posted 28-Day outcomes and their reported uncertainty.