N-acetylcysteine to Reduce Oxidative Stress and Improve Endothelial Function in HIV-infected Older Adults: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for N-acetylcysteine to Reduce Oxidative Stress and Improve Endothelial Function in HIV-infected Older Adults (NCT01962961), a randomized phase 1, phase 2 study. The primary outcome is Change in Circulating Malondialdehyde Levels.

2. Clinical Question

3. Trial Design

This completed study was a randomized, placebo-controlled pilot trial with a parallel-group design and quadruple masking. The registry lists it as Phase 1 and Phase 2. The reported enrollment was 24. Indiana University was the sponsor. The study start is recorded as 2013-10, and primary completion as 2015-06.

The intervention arms were PharmaNAC 1800 mg and PharmaNAC 3600 mg, with a matching-placebo arm. The lower-dose arm received PharmaNAC 900 mg orally twice daily for 8 weeks; the higher-dose arm received 1800 mg orally twice daily for 8 weeks. Placebo pills were given twice daily for 8 weeks. Participants were described as older adults with HIV who were already receiving stable antiretroviral therapy. The registry record does not report the age threshold used to define older adults or more detailed eligibility criteria.

A parallel design assigns participants to a study group and compares outcomes across groups rather than switching each participant between study treatments. Randomization is intended to reduce systematic differences between groups at assignment. Masking is intended to limit the influence of knowledge about assignment on trial conduct or outcome assessment; the registry's term quadruple does not, by itself, identify every role that was masked.

The primary endpoint was change in circulating malondialdehyde levels, measured in micromolar, from baseline to 8 weeks. The endpoint analysis population was restricted to participants who completed the 8 week trial and had both measurements available. The registry record does not report the randomization procedure, the exact roles covered by masking, or a sample-size justification.

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: Analysis population includes those who completed the 8 week trial and had both baseline and week 8 values available.

5. Baseline Characteristics

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

6. Primary Endpoint

The registry lists the primary outcome as Change in Circulating Malondialdehyde Levels, measured over Baseline and 8 weeks.

The primary endpoint is change in circulating malondialdehyde levels between baseline and 8 weeks, reported in micromolar. The registry describes malondialdehyde as a measure of oxidative stress. The endpoint therefore addresses a biochemical measure related to the study's stated interest in oxidative stress; it is not itself a direct measurement of vascular function.

Using a change from baseline focuses the analysis on how the measured level differs between the start and end of the treatment period. Reporting the mean describes the average observed change in each analysis group. The standard deviation describes how spread out individual changes are around that mean. These are different features: a group mean near zero does not imply that every participant had little or no change, and a mean alone does not show how variable individual results were.

Oxidative stress and endothelial function are distinct concepts in the study description. Malondialdehyde was selected as the primary measure of oxidative stress, while the trial's broader goal also refers to vascular function. The registry record lists three outcome measures, but does not report secondary outcome results in the information summarized for this analysis. The primary endpoint should therefore be interpreted on its own terms, without treating it as evidence of a change in every aspect of vascular function.

The endpoint was assessed among participants who completed the trial and had both baseline and week 8 values. This makes the reported mean a summary of that defined analysis population, rather than automatically a summary of everyone enrolled or assigned. The registry record does not report additional details about how the measurements were collected or how missing endpoint values were handled.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: it records a measured quantity on a numerical scale, with change in circulating malondialdehyde reported in micromolar. For a continuous endpoint, a mean gives the average measured change in a group. A standard deviation describes the spread of observations around that group mean. The registry identifies the reported parameter as a mean and the measure of dispersion as a standard deviation.

What does a group mean tell us?

A group mean compresses observations into a summary. It can describe the average direction and size of change in the analysis population, but it does not show the full distribution of participant-level changes. A mean may be influenced by particularly large or small observations. The standard deviation gives additional information about variability, but it is not a confidence interval and does not directly quantify uncertainty about the group mean or about a difference between groups.

For this trial, the posted means are 0.17 micromolar for PharmaNAC 1800 mg, -0.12 micromolar for PharmaNAC 3600 mg, and -0.0 micromolar for placebo. The corresponding standard deviations are 1.74, 0.054, and 0.56. These summaries are not adjusted comparisons. No adjusted analysis or other inferential result is reported in the registry record.

Why is a between-group estimate important?

A treatment comparison asks how the outcome in an assigned intervention group differs from the outcome in a comparator group. The group means alone do not provide the uncertainty around that difference. A confidence interval, in general, describes a range of values compatible with the data and the assumptions of the analysis. A p-value, in general, measures how inconsistent the data are with a specified null hypothesis under the test's assumptions. Neither measure can be interpreted for this trial's primary two-arm comparison because the registry record does not report an estimable comparison, a confidence interval, or a p-value.

The registry record specifically notes that values were missing or not estimable for a two-arm comparison of the continuous endpoint. This does not erase the posted descriptive summaries, but it limits what can be concluded from them. It is not appropriate to construct a new comparison by subtracting the group means or to infer a test result from the summaries. The reported record does not identify a statistical test or explain why the comparative estimate was unavailable.

How should variability be considered?

Precision depends on more than the mean. It is influenced by the number of observations, the variability in those observations, and the analysis approach. Greater variability generally makes a group mean or a contrast less precise when other conditions are comparable. This is a general statistical principle, not a claim that a particular feature caused the spread seen in this trial. The posted standard deviations differ across groups, and the endpoint analysis counts are 9, 7, and 6 for PharmaNAC 1800 mg, PharmaNAC 3600 mg, and placebo, respectively.

When continuous data are more variable than a model expects, a model may represent uncertainty poorly. Over-dispersion is a general term for variability exceeding what a statistical model anticipates. It matters because standard errors and confidence intervals depend on assumptions about variability. The registry record does not report that an over-dispersion problem was assessed or that a particular model was used. The posted endpoint is summarized as a mean with standard deviation, so no model-specific conclusion should be assumed.

What role do randomization and masking play?

Random allocation is intended to create groups that are comparable on average with respect to measured and unmeasured characteristics, though randomization does not guarantee exact balance in a small trial. It supports causal comparison when the allocation is maintained and the analysis is appropriate, but it cannot compensate for an unavailable treatment-effect estimate. The record says the trial was randomized; it does not describe the sequence-generation or allocation-concealment procedures.

Masking can reduce the chance that expectations influence treatment delivery, participant behavior, or outcome assessment. The registry labels the trial quadruple-masked. That label is part of the recorded design, but the record does not say which roles were masked or how masking was maintained. The effect of masking cannot be assessed from the label alone.

How should planning calculations be read?

The registry's stated planning assumptions describe illustrations based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is defined as a stated fraction of the observed effect. Such calculations are planning illustrations; they are not the trial's original design justification and are not observed power. The registry record does not report a sample-size justification for the trial. Any planning figure should be understood as conditional on its assumptions, rather than as a result observed among trial participants.

Planning calculations depend on assumptions about the outcome, variability, target effect, allocation, and analysis. If those assumptions differ from what a future study encounters, the planning result may not describe that study's operating characteristics. Because the registry record does not provide a formal statistical plan or a reported comparison estimate, a reader should not treat a planning illustration as evidence that this pilot had a particular ability to detect an effect.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("PharmaNAC 1800 mg", "PharmaNAC 3600 mg", "Placebo")
n   <- c(9, 7, 6)
m   <- c(0.17, -0.12, -0)
sp  <- c(1.74, 0.054, 0.56)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  PharmaNAC 1800 mg  9  0.170  1.740  -1.167  1.507
CARM  PharmaNAC 3600 mg  7  -0.120  0.054  -0.170  -0.070
CARM  Placebo  6  -0.000  0.560  -0.588  0.588

11. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures, but reports no posted secondary outcome results in the information summarized for this analysis. It does not describe a multiplicity strategy, such as how conclusions would be adjusted when examining several outcomes or comparisons. The presence of multiple outcome measures makes it important to know which endpoint was designated primary and how other results were to be interpreted; the record identifies change in circulating malondialdehyde as the primary endpoint, but does not provide a fuller statistical plan.

The stated primary analysis population includes participants who completed the 8 week trial and had both baseline and week 8 values available. This is a complete-case definition for the primary endpoint as described in the record. The registry does not report how many enrolled or assigned participants lacked either measurement, why measurements might be missing, or whether any method was used to account for missing outcomes. It also does not report an intention-to-treat analysis or another analysis population beyond the stated endpoint population.

Endpoint counts are 9 for PharmaNAC 1800 mg, 7 for PharmaNAC 3600 mg, and 6 for placebo. The safety records list different at-risk counts. The registry record does not explain the difference, so it should not be interpreted as a specific pattern of withdrawal, noncompletion, or missingness.

The record does not report interim analyses, stopping rules, or a prespecified multiplicity procedure. Those details are not reported in the registry record, and their absence from the posted information should not be filled in by assumption. The absence of a reported secondary result also means that the primary endpoint should not be taken as a complete account of every outcome considered during the study.

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 0% reporting threshold.

Most frequent non-serious adverse event terms

The safety record lists zero serious adverse events among the participants at risk in each group: 9 for PharmaNAC 1800 mg, 8 for PharmaNAC 3600 mg, and 7 for placebo. These are group-specific counts as recorded, not estimates of comparative safety. The registry record lists no serious adverse event terms. Death counts are not reported in the registry record.

The record also lists other, non-serious adverse events affecting 6 participants in each group. These counts are separate from the serious-event counts and should not be combined with them. The safety at-risk counts differ from the endpoint analysis counts; the registry does not explain why, so the difference should not be assigned a cause.

A zero serious-event count in a group means that no serious events were recorded for the listed at-risk group in this registry entry. It does not establish that the risk of a serious event is absent, nor does it establish equivalence between groups. Event counts in a pilot study are descriptive, and the registry does not report a formal comparative safety analysis or confidence intervals for these counts. The posted counts should therefore be read as a record of events, not as a precise estimate of relative risk.

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

The central result is descriptive: the registry reports mean changes in circulating malondialdehyde and standard deviations for the primary analysis population. The reported mean changes are 0.17 micromolar for PharmaNAC 1800 mg, -0.12 micromolar for PharmaNAC 3600 mg, and -0.0 micromolar for placebo. The endpoint measures oxidative stress according to the registry description.

The posted results do not include an estimable two-arm comparison for this continuous endpoint. They do not provide a treatment-effect estimate with a confidence interval or a p-value. As a result, the means cannot establish that either PharmaNAC dose differed from placebo. Nor do they establish whether any apparent separation among group summaries reflects a real difference, random variation, or other factors.

The endpoint is a measure of oxidative stress, while the trial's broader stated goal included vascular function. A result for circulating malondialdehyde alone should not be treated as a direct result for endothelial function or every aspect of vascular health. The registry record does not report a posted secondary outcome result that would allow those broader questions to be assessed.

The endpoint analysis was limited to participants who completed the 8 week trial and had measurements at baseline and week 8. Thus, the summaries describe that analysis population, not automatically everyone enrolled or assigned. The registry record does not report how missing endpoint information was handled beyond defining the population with both measurements available.

These results do not support medical advice or a conclusion about treatment use. They also do not show that N-acetylcysteine does or does not work. The study's randomized, placebo-controlled design is relevant to a causal comparison, but the record does not provide an estimable primary between-group result. A cautious interpretation keeps the observed group summaries separate from claims about comparative effects.

14. Why This Trial Matters Statistically

This trial illustrates why descriptive summaries and comparative estimates answer different statistical questions. A mean change describes the average within-group result among participants included in the endpoint analysis. A treatment comparison asks whether the observed change differs between an intervention group and placebo, while also quantifying uncertainty. The registry reports the group means and standard deviations but notes that values were missing or not estimable for a two-arm comparison.

The distinction matters especially in a pilot trial. The registry reports enrollment of 24 and identifies the study as Phase 1 and Phase 2. A pilot's summaries can characterize observed measurements and variation, but they do not automatically establish the evidence needed for a treatment-effect conclusion. No sample-size justification or formal analysis plan is reported in the registry record.

The endpoint also illustrates the importance of keeping a measured biomarker distinct from the broader clinical question. Malondialdehyde is described as a measure of oxidative stress, whereas the stated study goal also includes vascular function. Statistical interpretation should remain tied to the endpoint actually reported rather than extending a result to a different construct.

Finally, the record demonstrates why analysis populations and denominators deserve attention. The primary outcome uses participants who completed the trial and had both measurements available, while the safety records list different at-risk counts. Those records do not explain the differences. Recognizing that limitation is more informative than assuming that all counts represent the same population or that the differences have a known cause.

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 main limitation for interpreting the primary result is that the registry does not report an estimable two-arm comparison for the continuous endpoint. The group summaries are available, but no comparative effect estimate, confidence interval, or p-value is reported. The registry also does not explain why the comparison was not estimable.

The primary endpoint analysis included participants who completed the 8 week trial and had both baseline and week 8 measurements. The record does not report how missing measurements were handled, how many participants were excluded from this analysis, or whether results were evaluated in another analysis population. Endpoint counts and safety at-risk counts differ, and the reason is not reported.

The registry identifies three outcome measures but reports no secondary outcome results in the information summarized for this analysis. It does not describe a multiplicity plan or a full statistical analysis plan. The method used for any formal comparison, if planned, is not reported. The record also does not report how randomization was generated, which roles were covered by quadruple masking, or how masking was maintained.

The trial is described as a pilot and reports enrollment of 24, but no sample-size justification is reported. The registry does not provide enough information to assess whether the observed standard deviations or endpoint analysis population were anticipated in the design. The scope of generalization is also limited by the population described in the record: HIV-infected older adults receiving stable antiretroviral therapy. The age threshold and more detailed eligibility criteria are not reported.

Finally, the primary endpoint concerns circulating malondialdehyde, described as a measure of oxidative stress. It does not directly report endothelial function. The record therefore does not provide grounds to extend the primary result to the study's broader vascular-function objective.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: N-acetylcysteine to Reduce Oxidative Stress and Improve Endothelial Function in HIV-infected Older Adults — NCT01962961.
• Registry record last updated 2016-02-08; status last verified 2015-12.
• Results first posted 2016-02-08.
• 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

This completed randomized, placebo-controlled pilot trial studied PharmaNAC, a form of N-acetylcysteine, in HIV-infected older adults receiving stable antiretroviral therapy. It used a parallel-group design and was described as quadruple-masked. The registry lists Phase 1 and Phase 2 and enrollment of 24.

The treatment groups received PharmaNAC 1800 mg or PharmaNAC 3600 mg, each given orally twice daily for 8 weeks at the stated dose, or matching placebo pills twice daily for 8 weeks. The primary endpoint was change in circulating malondialdehyde levels from baseline to 8 weeks, reported as a mean and standard deviation among participants who completed the trial and had both measurements.

The registry reports group summaries but states that values were missing or not estimable for a two-arm comparison of the continuous endpoint. It does not report a comparative effect estimate, confidence interval, or p-value. The safety record lists zero serious adverse events in each group, while deaths are not reported in the registry record.