Safety and Tolerability of Preservative-free Polyhexamethylene Biguanide (PHMB) Ophthalmic Solution in Healthy Subjects: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety and Tolerability of Preservative-free Polyhexamethylene Biguanide (PHMB) Ophthalmic Solution in Healthy Subjects (NCT02506257), a randomized phase 1 study. The primary outcome is Number of Subjects With Dose-limiting Adverse Events.

2. Clinical Question

The study examined short-term safety and tolerability across three PHMB concentrations and a vehicle group. It was a multiple-center, parallel-group Phase 1 study, with 90 participants enrolled. Its registered question is not whether PHMB treats Acanthamoeba Keratitis: the study population was healthy, and the primary endpoint concerns dose-limiting adverse events. Plasma concentration of PHMB is listed as a secondary outcome, but numerical results for that outcome are not reported in the registry record.

The posted primary counts are 0 participants for 0.04% PHMB, 2 for 0.06% PHMB, 3 for 0.08% PHMB, and 0 for PHMB Vehicle. These are descriptive counts. The registry record does not report a statistical comparison, an effect estimate, or uncertainty intervals for the groups. They should therefore be read as the recorded outcomes in these study groups, not as a definitive estimate of how the concentrations compare.

3. Trial Design

This was a randomized, parallel-group, placebo-controlled Phase 1 study sponsored by SIFI SpA. The registry record gives enrollment as 90. Four groups received 0.04% PHMB, 0.06% PHMB, 0.08% PHMB, or PHMB Vehicle. The active PHMB solutions were preservative-free ophthalmic solutions. The vehicle group served as the placebo comparator.

The scheduled regimen was the same for all four groups: 1 drop 12 times daily for 7 days, followed by 1 drop 6 times daily for additional 7 days. The primary endpoint timeframe extended up to 21 days from date of randomization. The record describes the study as multiple-center and parallel-group. Random allocation is listed, and the structured masking classification is quadruple; the official title describes the study as double-masked. The registry record does not explain which roles were masked or why the labels differ.

The study began in 2015-11, reached primary completion in 2016-04, and is listed as completed. The primary objective was safety and tolerability in healthy subjects, rather than clinical efficacy in people with Acanthamoeba Keratitis. A secondary outcome, plasma concentration of PHMB, is listed, but its numerical findings are not reported in the registry record. Further details about sequence generation, allocation concealment, center-specific enrollment, or the conduct of follow-up are not reported in the registry record.

Group sizes for the primary outcome were 26.0 for 0.04% PHMB, 28.0 for 0.06% PHMB, 27.0 for 0.08% PHMB, and 9.0 for PHMB Vehicle. The uneven group sizes are part of the posted design and should be kept in view when interpreting raw counts. The registry record does not report the intended allocation ratio or the reason for the observed group sizes.

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:

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: Adult healthy volunteers

6. Primary Endpoint

The registry lists the primary outcome as Number of Subjects With Dose-limiting Adverse Events, measured over up to 21 days from date of randomization.

The primary endpoint is the number of subjects with dose-limiting adverse events, measured in participants, up to 21 days from date of randomization. It counts subjects who met the endpoint definition in each group; it is not a measure of event severity, duration, or total number of events. The description does not define what qualified as dose-limiting, and that operational definition is not reported in the registry record.

For an early-phase study focused on safety and tolerability, counting participants with a prespecified dose-limiting event can summarize an important type of safety outcome during the observation period. The count is straightforward to interpret as a number of people, but by itself it does not show the precision of the underlying risk estimate or establish whether groups differ. A confidence interval or a statistical comparison would add information about uncertainty; neither is reported for this primary endpoint.

The posted counts are 0 in the 0.04% PHMB group, 2 in the 0.06% PHMB group, 3 in the 0.08% PHMB group, and 0 in the PHMB Vehicle group. The endpoint should be distinguished from the separate adverse-event summary, which also reports other adverse events. The registry record does not report whether all adverse events were reviewed under the dose-limiting definition, or how endpoint events were adjudicated.

The primary outcome is limited to the stated timeframe. It does not summarize longer-term safety, nor does it measure treatment benefit. No additional primary-outcome analysis population, handling of incomplete endpoint observations, or definition of the analysis denominator is reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

General statistical explanation: A binary endpoint records whether each participant did or did not experience a defined event. The primary outcome is reported as the number of participants with dose-limiting adverse events in each group. A participant count is a useful descriptive summary, but it is not the same as an estimated risk, a comparison between groups, or a measure of statistical uncertainty.

To interpret a binary endpoint comparatively, an analysis can estimate the event probability in each group and then quantify a contrast between groups. That contrast might be expressed on an absolute or relative scale, depending on the analysis plan. A confidence interval describes a range of values compatible with the data and the specified statistical method; it communicates uncertainty as well as the direction and magnitude of an estimate. The registry record does not report such an estimate or interval for the primary outcome, so no comparative effect can be interpreted from the posted endpoint counts alone.

The primary counts are 0, 2, 3, and 0 across the 0.04% PHMB, 0.06% PHMB, 0.08% PHMB, and PHMB Vehicle groups. Their group sizes are 26.0, 28.0, 27.0, and 9.0. These are small group totals with few primary events. In general, when events are sparse, estimates can be sensitive to the method used, and standard approximations may perform poorly. Exact or other sparse-data methods may be considered in an analysis, but the registry record does not state what method was planned or used. No method should be attributed to this study based on the counts alone.

General statistical explanation: Randomization aims to make assigned groups comparable on average, while masking is intended to reduce the influence of knowledge of assignment on aspects of study conduct or outcome assessment. Those design features do not guarantee that every observed group difference represents a treatment effect, especially when outcome counts are limited. The registry record lists random allocation and quadruple masking in its structured design information; the official title says double-masked. It does not explain the masking roles, allocation procedure, or whether outcome assessment was independently adjudicated.

The study is described as parallel-group, so each participant was assigned to one of the four groups rather than crossing between treatment groups. The posted summaries do not describe repeated-measures models or center-adjusted analyses. Whether center or other baseline characteristics were incorporated into any analysis is not reported in the registry record. The record reports zero analyses, so it does not provide a statistical test or model for the primary endpoint.

General statistical explanation: A prespecified endpoint definition and a defined analysis population help ensure that participants are counted consistently. For this outcome, the registry provides a title and timeframe but no detailed definition of dose-limiting adverse events. It also does not describe whether the endpoint was analyzed by randomized assignment, treatment received, or another population. The analysis population is not reported in the registry record. This makes it difficult to determine precisely how the participant counts relate to the randomized groups if eligibility, treatment exposure, or follow-up varied.

Missing outcome data can affect both the denominator and interpretation of an event count. A participant with no recorded event could have completed observation without an event, or could have incomplete follow-up; those situations are not equivalent. General approaches to missing data include analyzing observed outcomes under stated assumptions, using imputation, or conducting sensitivity analyses. These are general methodological possibilities, not methods known to have been used. Missing-data counts and handling are not reported in the registry record.

General statistical explanation: Multiplicity arises when several hypotheses or outcomes are examined, increasing the chance of at least one apparently unusual result if no adjustment is made. A trial with multiple concentrations, a placebo group, and multiple outcomes can raise multiplicity questions. However, the record does not specify a testing hierarchy, adjustment procedure, or confirmatory hypotheses. It is not possible to determine from the posted results whether any multiplicity adjustment was planned or conducted. The primary outcome counts should therefore be read descriptively rather than as a set of formal hypothesis tests.

The registry record does not report the rationale for the group sizes, a sample-size justification, a target power, or a planned statistical analysis. Without a stated design calculation and analysis plan, it is not appropriate to infer why the group sizes were selected or what precision the investigators expected. A calculation based on observed effects would be a planning illustration, not observed power, and cannot replace a prospective design justification. No numerical planning result for the primary comparison is reported in the registry record.

Finally, the listed secondary outcome is plasma concentration of PHMB, but no numerical result or statistical method for it is reported. Pharmacokinetic measurement and clinical event counting answer different questions: concentration describes measured exposure, whereas the primary endpoint records participants with qualifying safety events. The registry record does not report an analysis connecting plasma concentration with the dose-limiting event outcome.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("0.04% PHMB", "0.06% PHMB", "0.08% PHMB", "PHMB Vehicle")
n      <- c(26, 28, 27, 9)
events <- c(0, 2, 3, 0)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  0.04% PHMB  26  0  0.0  0.0  13.2  0.0  12.9  0.1  12.8
ARM  0.06% PHMB  28  2  7.1  0.9  23.5  2.0  22.6  2.2  22.8
ARM  0.08% PHMB  27  3  11.1  2.4  29.2  3.9  28.1  4.0  28.2
ARM  PHMB Vehicle  9  0  0.0  0.0  33.6  -0.0  29.9  0.3  30.8

11. Multiplicity, Missing Data and Analysis Populations

The record lists a primary safety endpoint and one secondary outcome, plasma concentration of PHMB. It also examines three PHMB concentrations against a vehicle group. Those multiple groups and outcomes raise general questions about how many comparisons were planned and how interpretation would account for them. A testing hierarchy or multiplicity adjustment is not reported in the registry record. The posted primary counts are therefore best treated as descriptive results, not as evidence from a documented family of hypothesis tests.

The registry record does not report a prespecified statistical analysis plan, a primary comparison, the intended analysis population, or the treatment of protocol deviations. It lists zero analyses. Consequently, there is no reported test, model, adjusted estimate, p-value, or confidence interval for the primary endpoint. The record also does not report a sample-size justification, target power, or a reason for the group allocation pattern.

Missing outcome data and follow-up completeness are not described. The record does not state whether every randomized participant contributed to the primary outcome, how participants without a recorded event were handled, or whether any outcomes were imputed. It also does not report sensitivity analyses evaluating alternative assumptions about missing observations. These details matter because event counts depend on who was observed and how incomplete records were classified.

Endpoint adjudication, the operational definition of dose-limiting adverse events, and the analysis population are not reported in the registry record. The same is true for any adjustments for center or baseline characteristics. No assumptions about those procedures can be made from the posted counts. In the absence of a documented analysis plan and missing-data approach, interpretation should remain at the level of the descriptive counts and reported safety summaries.

12. 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 3% reporting threshold.

Most frequent non-serious adverse event terms

The registry record lists zero serious adverse events in each of the four groups: 0.04% PHMB, 0.06% PHMB, 0.08% PHMB, and PHMB Vehicle. The numbers at risk in those groups were 26, 28, 27, and 9, respectively. These are counts observed during the reported safety summary, not estimates showing that serious events could not occur.

A zero count means that no serious adverse event was recorded among the participants represented in that group in the posted summary. It does not establish a zero underlying risk, and it does not show how precise an estimated risk would be. The registry record does not provide confidence intervals, longer-term follow-up results, or details on surveillance and event adjudication. It also does not report death counts as numerical values; deaths are listed as null, which is not equivalent to a reported zero.

The record separately reports other adverse events affecting 11 participants in the 0.04% PHMB group, 23 in the 0.06% PHMB group, 16 in the 0.08% PHMB group, and 5 in the PHMB Vehicle group. Those figures are not the serious-adverse-event counts and are not the primary dose-limiting endpoint. The event types, severity, timing, and relationship to study treatment are not detailed in the posted summary. Counts should not be treated as proof of comparative safety or as a complete account of all possible harms.

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

The primary results show that dose-limiting adverse events were recorded for 0 participants in the 0.04% PHMB group, 2 in the 0.06% PHMB group, 3 in the 0.08% PHMB group, and 0 in the PHMB Vehicle group during the stated timeframe. These are the descriptive results of a randomized Phase 1 study in healthy subjects. They do not establish that one concentration is safer or less safe than another, and the record does not report a statistical comparison.

The absence of an event in a group is not evidence that the event is impossible or that its true risk is zero. With few recorded primary events, uncertainty about the underlying event frequency can remain substantial. No confidence intervals or other uncertainty estimates are reported. Likewise, the fact that two groups have different raw counts does not by itself show that the underlying event rates differ. Group sizes were not identical, and the vehicle group included 9.0 participants compared with 26.0, 28.0, and 27.0 in the active-treatment groups.

The study's scope is limited. Participants were described as healthy subjects, the primary observation period was up to 21 days from randomization, and the objective was safety and tolerability. The findings do not answer whether PHMB is effective for Acanthamoeba Keratitis, whether the solutions are suitable for longer use, or how their effects compare in a patient population. Those questions are not measured by this primary endpoint.

The record also does not provide detailed event descriptions, the operational definition of dose-limiting events, missing-data handling, or the statistical analysis plan. One secondary outcome, plasma concentration of PHMB, is listed without numerical results. Thus, the posted information supports a narrow descriptive account of recorded short-term events, not broad conclusions about treatment benefit, long-term risk, or comparative safety.

14. Why This Trial Matters Statistically

This trial illustrates a common statistical challenge in early-phase safety research: the outcomes of interest may be uncommon, while each group contains a limited number of participants. A simple count is transparent, but sparse counts do not necessarily distinguish groups reliably. A zero count, in particular, is an observation about the study participants and follow-up, not proof that the underlying event cannot occur.

It also shows why denominators and event definitions matter. The active groups and vehicle group had different group sizes, so raw counts are not directly comparable as if each group had equal exposure. The primary endpoint concerns participants with dose-limiting adverse events, while the adverse-event summary separately reports serious events and other adverse events. These categories answer different questions and should not be conflated.

The registry record documents randomization and masking, but it does not report the analysis plan, endpoint definition details, missing-data procedures, or comparative estimates with uncertainty. Those omissions limit how far statistical interpretation can go. A reader can describe the recorded counts, but cannot assess a formal treatment contrast, the precision of an estimate, or whether a planned analysis was followed.

Finally, the study population and timeframe define the meaning of the results. The study involved healthy subjects and assessed the primary endpoint up to 21 days from randomization. It is therefore a focused early-phase safety and tolerability investigation, not an efficacy trial in patients with the listed condition. Statistically, recognizing this scope helps keep the conclusions aligned with the outcomes and population actually represented by the registry record.

15. 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 posted primary outcome is a count of participants with dose-limiting adverse events, but the registry record does not give the operational definition of a dose-limiting event. Without that definition, readers cannot determine which event characteristics qualified or how consistent classification was ensured. The record also does not describe adjudication procedures or whether assessment was independent of treatment assignment.

The registry record reports no inferential analyses for the primary endpoint. It provides no comparative estimate, confidence interval, p-value, or documented statistical method. Although group sizes and event counts are posted, the record does not give a sample-size justification or explain the allocation pattern. The relatively small vehicle group is an important feature of the observed study design, but the reason for that group size is not reported.

Follow-up for the primary endpoint is described as up to 21 days from randomization. Longer-term safety outcomes are not reported in the registry record. Completeness of follow-up, missing outcome counts, and methods for handling missing observations are also not reported. Therefore, the posted counts cannot be evaluated for possible effects of incomplete observation.

The record describes healthy subjects, limiting direct interpretation for patients with Acanthamoeba Keratitis. While PHMB plasma concentration is listed as a secondary outcome, numerical results are not reported. The safety summary does not provide event-level descriptions for other adverse events, and deaths are represented as null rather than a numerical count. Finally, masking is classified as quadruple in the structured information, while the official title calls the study double-masked; the registry record does not explain this difference or identify which study roles were masked.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Safety and Tolerability of Preservative-free Polyhexamethylene Biguanide (PHMB) Ophthalmic Solution in Healthy Subjects — NCT02506257.
• Registry record last updated 2017-02-09; status last verified 2016-12.
• Results first posted 2016-11-23.
• 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.

19. Record Summary

NCT02506257 is a completed, randomized, parallel-group, placebo-controlled Phase 1 study sponsored by SIFI SpA. It enrolled 90 healthy subjects and compared preservative-free PHMB eye drops at 0.04%, 0.06%, and 0.08% with PHMB Vehicle. The dosing schedule in each group was 1 drop 12 times daily for 7 days, followed by 1 drop 6 times daily for additional 7 days.

The primary endpoint was the number of subjects with dose-limiting adverse events up to 21 days from randomization. Posted counts were 0, 2, 3, and 0 across the three PHMB groups and vehicle group, respectively. The registry record also lists zero serious adverse events in each group and reports counts for other adverse events. Plasma concentration of PHMB is listed as a secondary outcome, but numerical results are not reported in the registry record.

No inferential analyses, comparative estimates, confidence intervals, analysis plan, sample-size justification, or missing-data procedures are reported. The available results are descriptive and concern short-term safety in healthy subjects.