Safety and Efficacy of IDP-123 Lotion to Tazorac® Cream, in the Treatment of Acne Vulgaris: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety and Efficacy of IDP-123 Lotion to Tazorac® Cream, in the Treatment of Acne Vulgaris (NCT02938494), a randomized phase 2 study. The primary outcome is Absolute Change From Baseline in Mean Noninflammatory Lesion Count to Week 12.

2. Clinical Question

The endpoint captures change in facial open and closed comedones, counted together as noninflammatory lesions. The reported comparison is unadjusted and has a confidence interval from -13.11 to -3.895 lesions, with p < 0.001. The numerical results describe this trial's posted data; they do not establish how results would generalize to people who were not enrolled or under different study conditions.

3. Trial Design

The registry record describes a randomized, quadruple-masked, parallel-group Phase 2 study, with a total enrollment of 210. The study status is completed. The record gives a start of 2015-11 and a primary completion of 2016-07. Bausch Health Americas, Inc. is identified as the sponsor. The condition studied was acne vulgaris.

Four groups are listed: IDP-123 Lotion, Tazorac Cream, Vehicle Lotion, and Vehicle Cream. For the primary efficacy comparison, the two vehicle groups were combined as a single comparator, as described in the posted efficacy population. The registry record therefore does not give separate efficacy results for Vehicle Lotion and Vehicle Cream in that analysis. The posted safety results, by contrast, list the two vehicle groups separately.

The primary outcome was absolute change from baseline in mean noninflammatory lesion count to Week 12. The listed endpoint timeframe is Baseline (Day 0), Week 12. The arm summaries include 69 participants for IDP-123 Lotion, 72 for Tazorac Cream, and 69 for the combined vehicle group. The safety groups have their own at-risk counts, which are reported with the safety results.

The masking description indicates quadruple masking, but the identities of the masked roles and operational details are not reported in the registry record. Further details about allocation procedures, eligibility criteria, treatment administration, follow-up beyond the listed endpoint timeframe, and the trial's original sample-size justification are not reported in the registry record. The registry record identifies the trial as randomized and parallel-group but does not give enough detail to infer those additional design features.

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

Analysis population for the primary outcome, as defined in the registry: Efficacy analyses compared IDP-123 Lotion and the combined Vehicle Lotion and Vehicle Cream groups, as pre-specified in the statistical analysis plan. There is no information for separate Vehicle Lotion and Vehicle Cream groups, since the comparator group was pre-specified to be combined Vehicle Lotion and Vehicle Cream.

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 Absolute Change From Baseline in Mean Noninflammatory Lesion Count to Week 12, measured over Baseline (Day 0), Week 12.

The primary endpoint is absolute change from baseline in mean noninflammatory lesion count at Week 12. It counts open comedones, described as blackheads with a dilated or open follicle opening, and closed comedones, described as whiteheads with a small opening at the skin surface. For facial noninflammatory lesions, open and closed comedones were recorded as a single count.

A change endpoint compares a participant's count at follow-up with their baseline count. Negative changes in the posted arm summaries indicate that the mean count decreased over the measurement period. The IDP-123 Lotion mean change was -21.6 lesions, while the combined vehicle mean change was -13.1 lesions. The endpoint is a continuous measure, and the posted arm summaries report means and standard deviations.

Using change from baseline makes the outcome directly describe within-period movement in lesion count, while the between-group comparison assesses how the average changes differed across assigned groups. The endpoint does not, by itself, describe every aspect of acne severity or a participant's experience. The registry record does not report additional primary outcome measures or a separate clinical interpretation threshold for this lesion-count change.

7. Results Posted in the Registry

• IDP-123 Lotion: mean -21.60 versus -13.10 on control; difference -8.50 (95% CI -13.11 to -3.89), standardized effect d = -0.62; z-test p = <0.001.
• Tazorac Cream: mean -20.30 versus -13.10 on control; difference -7.20 (95% CI -11.71 to -2.69), standardized effect d = -0.53; z-test p = 0.002.

8. Statistical Interpretation

9. Statistical Methods Explained

The posted endpoint is a continuous outcome: each participant contributes a lesion-count change, and each arm is summarized by a mean and standard deviation. The comparisons report a mean difference, a confidence interval, and an unadjusted p value. The registry record does not provide a detailed statistical analysis plan or an entry describing the sponsor's analysis method, so the posted summary statistics should not be read as evidence of a particular model, covariate adjustment, or missing-data procedure.

What a mean change describes

A mean is the arithmetic average of the measured values in a group. For this endpoint, the measured value is the change from baseline to Week 12 in noninflammatory lesion count. A negative mean change indicates a decrease on average, while the standard deviation describes how spread out individual changes are around that average. The mean is useful for describing the group-level direction and magnitude, but it does not reveal the full distribution. Participants can have outcomes that differ substantially from the group mean.

The arm summaries report mean changes of -21.6 lesions for IDP-123 Lotion, -20.3 lesions for Tazorac Cream, and -13.1 lesions for combined vehicle. Their standard deviations are 13.98, 13.67, and 13.62 lesions, respectively. Those standard deviations are measures of observed variability, not uncertainty in the mean itself. The standard error, by contrast, reflects the precision of a mean estimate and depends on both outcome variability and the number of observations.

Reading a mean difference

A mean difference subtracts one group's average change from the other group's average change, according to the comparison's direction. For IDP-123 Lotion versus combined vehicle, the reported difference is -8.5 lesions. The corresponding confidence interval ranges from -13.11 to -3.895 lesions. In this direction, a negative difference indicates a more negative average change in the IDP-123 Lotion arm. The comparison is unadjusted: it is a straightforward contrast of group summaries and is not described as adjusted for baseline values or other characteristics.

The second posted contrast is Tazorac Cream versus combined vehicle. Its mean difference is -7.2 lesions, with a confidence interval from -11.71 to -2.695 lesions. The primary endpoint description specifies the IDP-123 Lotion and combined vehicle comparison as the prespecified efficacy comparison. The registry record does not explain the inferential status or analysis-plan role of the Tazorac Cream contrast.

What a confidence interval and p value convey

A confidence interval gives a range of values compatible with the data under the method used to construct it. It conveys uncertainty about an estimated contrast and is not a range containing a fixed proportion of individual participant outcomes. A narrower interval indicates greater precision than a wider interval, all else being equal. The posted intervals concern differences in mean lesion-count change, not the range of changes experienced by individual participants.

A p value describes how unusual data at least as incompatible with a specified null hypothesis would be if that null hypothesis and the test's assumptions were correct. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of a difference. The reported p values are unadjusted: p < 0.001 for IDP-123 Lotion versus combined vehicle and 0.002 for Tazorac Cream versus combined vehicle. The registry record does not report whether any multiplicity adjustment was used in an analysis outside the posted record.

Why variability matters

With a continuous outcome, participants' changes can vary widely. Standard deviations help describe that spread and are relevant to the precision of group summaries and comparisons. When variability is larger, it is harder to distinguish a given difference in group means from random variation unless the study has more information. This is a general statistical principle, not a claim about the study's original design calculations. The posted standard deviations show appreciable variation in lesion-count changes, but they do not indicate how the individual outcomes were distributed or whether unusual values affected the means.

Over-dispersion is a general concept that arises when observed variability exceeds what a particular model assumes. It matters because an inappropriate variance model can lead to confidence intervals and tests that are too narrow or too wide. The registry record does not report an over-dispersion assessment or a model that would permit evaluating it. Because the primary endpoint is summarized as a continuous measure with means and standard deviations, there is no basis in the registry record for asserting that an over-dispersion adjustment was or was not needed.

What is not specified

The registry record does not report the trial's original sample-size calculation, its assumed effect size, or any design assumptions for the primary endpoint. The sample-size figures are planning illustrations based on the observed contrast and stated calculation assumptions, rather than the trial's own design rationale. The registry record also does not report interim analyses, a detailed missing-data strategy, baseline-adjusted analyses, or analysis-population definitions. Those omissions limit the extent to which the posted summary results can be used to reconstruct the full statistical conduct of the trial.

10. Confidence Intervals and Precision

Precision concerns how tightly the available data estimate a quantity. For the primary IDP-123 Lotion versus combined vehicle comparison, the mean difference was -8.5 lesions, and its 95% confidence interval extended from -13.11 to -3.895 lesions. The interval expresses uncertainty in the estimated difference, rather than the range of responses among individual participants. Its values indicate that the data are compatible with a range of negative average differences under the interval's assumptions.

The Tazorac Cream contrast with combined vehicle was -7.2 lesions, with a 95% confidence interval from -11.71 to -2.695 lesions. Both intervals are estimates for their respective comparisons. Their overlap should not be used as a substitute for a direct statistical test comparing IDP-123 Lotion with Tazorac Cream. The registry record does not post such a direct comparison or its confidence interval.

The arm sizes for the primary comparison were 69 participants for IDP-123 Lotion and 69 for combined vehicle. The corresponding Tazorac Cream and combined vehicle arm sizes were 72 and 69. Precision is influenced by the amount of outcome variation as well as the number of observations. The posted standard deviations are 13.98 lesions for IDP-123 Lotion, 13.67 for Tazorac Cream, and 13.62 for combined vehicle.

A confidence interval does not capture every source of uncertainty. It cannot account for unreported choices in analysis, missing-data handling, or possible differences between the enrolled participants and other populations. The registry record does not report whether estimates were adjusted, how missing measurements were addressed, or the detailed method used to produce the intervals. The displayed precision should therefore be interpreted as uncertainty around the posted contrasts, not as a complete account of all limitations.

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 figures are planning illustrations based on the observed effect, not the original trial design calculation. They give participants per arm for 80% power and participants per arm for 90% power; they are not total event counts. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is the stated fraction of the observed effect.

The 80% power column gives the number of participants per arm estimated to provide an 80% chance of detecting the specified effect under those assumptions, if that effect is the true one. The 90% power column describes the corresponding planning target for a 90% chance. These are design calculations, not guarantees about the result of a future study. They are not observed power.

For the IDP-123 Lotion comparison, the illustration uses the observed contrast against combined vehicle. At 100% of that effect, the estimate is 42 participants per arm for 80% power and 56 for 90% power. At 75% of the observed effect, it is 74 and 99 participants per arm, respectively; at 50%, it is 166 and 222. For the Tazorac Cream comparison, the corresponding figures are 57 and 76 at 100% of the observed effect, 101 and 135 at 75%, and 226 and 302 at 50%.

The pattern illustrates a general planning principle: smaller effects are harder to distinguish from random variation and therefore require more participants to reach the same power target. These calculations use the observed effect as their starting point, so they should not be interpreted as evidence that the trial was originally designed around those assumptions. The trial's original sample-size justification is 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, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -8.500; pooled standard deviation σ = 13.801.
2. n = 2 × (1.96 + 0.842)² × 13.801² / -8.500² = 41.4, rounded up to 42 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 <- -8.5                      # observed difference in means
sigma <- 13.8011738631176                     # 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(2938494)
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 = 42 (80% power), 56 (90% power)
 75% of observed effect: n per arm = 74 (80% power), 99 (90% power)
 50% of observed effect: n per arm = 166 (80% power), 222 (90% power)
power.t.test: 42.4 
Simulated power at n = 42 per arm: 0.795 (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.

13. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when a study conducts several statistical tests or evaluates multiple outcomes. When many hypotheses are tested, the chance of obtaining at least one small p value by chance can increase. Researchers can address this through a prespecified hierarchy, adjustment procedures, or other strategies. The registry record describes the comparison of IDP-123 Lotion with combined vehicle as prespecified in the statistical analysis plan, but it does not report a multiplicity adjustment or a complete testing hierarchy.

The record lists three outcome measures and no posted secondary outcome results. It reports the primary lesion-count endpoint and numerical comparisons for IDP-123 Lotion and Tazorac Cream against combined vehicle. Because the registry record does not fully describe the statistical role of the Tazorac Cream comparison or any family of tests, the unadjusted p values should be read as individual, unadjusted comparisons rather than evidence that multiplicity was addressed. No claim about the broader testing strategy can be made from the posted record.

Missing data can also affect estimates. If participants lack a Week 12 measurement, the analysis must decide how to use the available information or otherwise handle the missing outcome. Different approaches can produce different estimates, particularly if missingness is related to participant outcomes. The registry record does not report how many primary endpoint measurements were missing, why any measurements were missing, or how missing data were handled.

The posted arm sample sizes are 69 for IDP-123 Lotion, 72 for Tazorac Cream, and 69 for combined vehicle. The registry record does not specify whether these are the full analysis populations for the primary endpoint, nor does it define an intention-to-treat, per-protocol, or other analysis set. It also does not report whether participants were excluded from efficacy analyses or how exclusions, if any, were managed. These details matter when assessing how closely the reported estimates represent the randomized groups.

The registry record does not describe interim analyses, stopping rules, adjustment for baseline characteristics, or sensitivity analyses. Absence of such information in the record is not evidence that a procedure was or was not used; it means those details are not reported in the registry record. The posted summaries support interpretation of the reported arm means and contrasts, but do not allow a full audit of the analysis plan's implementation.

14. 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 non-serious adverse event terms

The serious adverse event results report zero affected participants in each listed safety group: IDP-123 Lotion, Tazorac Cream, Vehicle Lotion, and Vehicle Cream. The respective numbers at risk were 68, 71, 34, and 33. These are counts of participants with reported serious adverse events and the numbers at risk in each group.

A zero count means that no serious adverse events were recorded for the group in the posted result. It does not establish that an event is impossible or that a treatment has no safety risks. Rare events may not appear in a study of this size, and the registry record does not provide detail about the duration or completeness of safety follow-up. The record also does not list serious adverse event terms.

The safety groups keep Vehicle Lotion and Vehicle Cream separate, unlike the primary efficacy comparison, which combines the two vehicle groups. Other adverse events are also reported in the registry record, but the serious-event counts should not be interpreted as counts of all adverse events. Deaths are not reported in the registry record.

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

The posted primary endpoint results show that mean noninflammatory lesion count decreased from baseline to Week 12 in all three efficacy summaries: -21.6 lesions for IDP-123 Lotion, -20.3 lesions for Tazorac Cream, and -13.1 lesions for combined vehicle. The principal prespecified efficacy comparison was IDP-123 Lotion versus combined vehicle. Its unadjusted mean difference was -8.5 lesions, with a 95% confidence interval from -13.11 to -3.895 and p < 0.001.

These numbers describe average changes in a specific lesion-count outcome over the stated timeframe. They do not describe every participant's outcome, every feature of acne, or outcomes beyond Week 12. A group mean cannot show how many participants improved, stayed similar, or had an increase, because those distributions are not reported. The registry record also does not provide a clinical threshold for deciding what size of lesion-count difference is important to participants.

The Tazorac Cream arm had a mean change of -20.3 lesions and an unadjusted difference of -7.2 lesions compared with combined vehicle. That comparison has its own confidence interval and p value, but the registry record does not establish its role in the testing hierarchy. The reported contrasts do not constitute a direct comparison between IDP-123 Lotion and Tazorac Cream.

The numerical results are specific to a randomized Phase 2 study with an enrollment of 210. The registry record does not report detailed eligibility criteria, baseline characteristics, missing-data handling, or analysis-population definitions. These omissions constrain interpretation and generalization. The results do not establish outcomes in populations or settings not represented by the trial, and the registry record does not provide enough detail to assess all potential sources of bias.

The reported serious adverse event counts are zero in each safety group, but that observation does not prove the absence of risk. Safety interpretation depends on the number of people observed, the length and completeness of follow-up, and the kinds of events monitored. Details needed to fully characterize those matters are not reported in the registry record. The findings are statistical descriptions of posted results, not medical advice or a determination of treatment benefit or harm.

16. Why This Trial Matters Statistically

This trial illustrates how a prespecified efficacy comparison can differ from the list of randomized arms. The study lists two vehicle groups, but its stated primary efficacy comparison combines Vehicle Lotion and Vehicle Cream. That distinction matters: the posted primary contrast uses a combined comparator, while the safety outcomes retain separate vehicle-group counts. Readers should not treat those as identical analytic groupings.

The endpoint is a change in a continuous measure, summarized through group means and standard deviations. This makes the direction of the mean change straightforward to describe, while the confidence interval helps convey uncertainty in the between-group contrast. The primary unadjusted estimate is -8.5 lesions, with a 95% confidence interval from -13.11 to -3.895. The standard deviations, around 14 lesions in each efficacy group, also show why a group average should not be mistaken for an individual participant's response.

The record demonstrates the importance of distinguishing statistical evidence from study-design information. The unadjusted p value for the primary contrast is <0.001, but the registry record does not include a detailed analysis plan, multiplicity procedure, missing-data method, or original sample-size justification. The planning illustrations are based on the observed effect and stated assumptions; they cannot reveal what assumptions informed the trial's original enrollment target.

Finally, the safety record reports no serious adverse events in the listed groups, but event counts need context and do not establish absence of risk. The trial's Phase 2 setting, the posted at-risk counts, and the limited detail available on safety follow-up all matter when interpreting rare or unreported events. Together, these features make the study useful for understanding how outcome definitions, comparator construction, uncertainty, and reporting completeness shape interpretation of a clinical trial record.

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 registry record gives limited information about who could enter the study, participant characteristics at baseline, and how treatment was administered. Those details are important for judging how comparable the randomized groups were and how well the findings may apply to other populations. The registry record also does not report the original sample-size justification, so the enrollment cannot be evaluated against the trial's planned assumptions from this record alone.

The primary endpoint comparison is described as prespecified, but detailed statistical methods are not reported. The record does not specify the model, any covariate adjustment, multiplicity handling, interim analyses, or sensitivity analyses. It also does not report how missing Week 12 measurements were handled or define the analysis population. These gaps limit assessment of whether the reported estimates are robust to alternative analysis choices.

The efficacy comparison combines the Vehicle Lotion and Vehicle Cream arms, and separate efficacy results for those groups are not reported. The Tazorac Cream comparison with combined vehicle is posted numerically, but its place in the testing hierarchy is not reported. There is no posted direct comparison of IDP-123 Lotion with Tazorac Cream. The registry record lists three outcome measures but no secondary outcome results.

Precision is limited by the finite group sizes and observed variation. The confidence intervals quantify uncertainty under their underlying methods, but the record does not detail those methods. The mean changes do not show individual-level outcome distributions or the proportion of participants with particular patterns of change. A clinical threshold for interpreting the size of the lesion-count difference is also not reported in the registry record.

For safety, serious adverse event counts are listed, but event terms and detailed follow-up information are not reported. Zero recorded serious events does not rule out uncommon harms. These reporting limitations do not invalidate the posted summaries, but they narrow the questions those summaries can answer.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Safety and Efficacy of IDP-123 Lotion to Tazorac® Cream, in the Treatment of Acne Vulgaris — NCT02938494.
• Registry record last updated 2020-09-23; status last verified 2020-09.
• Results first posted 2020-09-23.
• 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, randomized, quadruple-masked, parallel-group Phase 2 study of IDP-123 Lotion, Tazorac Cream, Vehicle Lotion, and Vehicle Cream for acne vulgaris. Enrollment was 210. The recorded study start was 2015-11, and primary completion was 2016-07.

The primary endpoint was absolute change from baseline in mean noninflammatory lesion count at Week 12. The stated prespecified efficacy comparison was IDP-123 Lotion versus combined Vehicle Lotion and Vehicle Cream. The posted mean changes were -21.6 lesions for IDP-123 Lotion, -20.3 for Tazorac Cream, and -13.1 for combined vehicle. The unadjusted primary contrast was -8.5 lesions, with a 95% confidence interval from -13.11 to -3.895 and p < 0.001.

Zero serious adverse events were reported in each safety group. The registry record does not report detailed analysis methods, missing-data handling, multiplicity procedures, the trial's original sample-size justification, or secondary outcome results.