Pentoxifylline and Combination Antiretroviral Therapy to Improve Blood Vessel Function in HIV-Infected People: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Pentoxifylline and Combination Antiretroviral Therapy to Improve Blood Vessel Function in HIV-Infected People (NCT00864916), a randomized phase 2 study. The primary outcome is Flow-mediated Dilation of the Brachial Artery.

2. Clinical Question

3. Trial Design

The registry identifies this as a Phase 2 randomized, placebo-controlled trial with a parallel-group model. Participants were assigned to pentoxifylline plus cART or placebo plus cART. The masking designation is quadruple. The record lists enrollment as 19 and status as completed. It names Indiana University as sponsor. The study start is recorded as 2009-03, and primary completion as 2012-12.

The design focuses on the added effect of pentoxifylline in the context of combination antiretroviral therapy. Because both groups received cART, the comparison does not estimate the effect of cART itself. The randomized allocation is intended to make the groups comparable on average, while placebo and masking are design features intended to reduce the influence of expectations and knowledge of assignment. The record does not describe the practical masking procedures or identify which roles were included in the quadruple designation.

The primary outcome was flow-mediated dilation of the brachial artery, assessed at Week 48. Its analysis population is described as participants who completed the Week 48 visit procedures. The posted outcome summaries include 4.0 participants for pentoxifylline plus cART and 5.0 for placebo plus cART. These are the endpoint counts; the registry record does not explain the relationship between those counts and the enrollment figure or provide a participant-flow account.

The registry reports one primary outcome measure and one analysis. No secondary outcomes are posted. Details such as the randomization sequence, allocation concealment, visit schedule beyond the endpoint timeframe, adherence assessment, protocol deviations, and analysis population are not reported in the registry record. The record also does not report a planned sample-size justification or an interim-analysis plan.

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: Numbers of participants who completed the week 48 visit procedures

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: Completed enrollment visit

6. Primary Endpoint

The registry lists the primary outcome as Flow-mediated Dilation of the Brachial Artery, measured over Measured at Week 48.

Flow-mediated dilation measures the change in the diameter of the brachial artery in response to a stimulus that increases blood flow. The result is expressed as percent dilation. It is used as a physiological measure of vascular endothelial function: the endothelium is the inner lining of blood vessels, and its function is relevant to how vessels respond to changes in blood flow. The registry frames the study around endothelial dysfunction, blood-vessel function, and inflammation in people with HIV.

The primary endpoint was the mean flow-mediated dilation measured at Week 48. The reported unit is percent dilation of the brachial artery, and the registry describes the endpoint as a continuous measure summarized by a mean and standard deviation. A continuous outcome retains information about the magnitude of measurements rather than reducing them to event categories. The group summaries therefore describe the average observed dilation and the spread of individual measurements around that average.

The endpoint population is specified as participants who completed the Week 48 visit procedures. The registry does not report how missing measurements were handled or whether any alternative analysis population was used. The outcome is a physiological measure; the record does not establish that a difference in this measure corresponds to a particular clinical outcome. Its interpretation should remain specific to the measured vessel-function endpoint and the time point recorded.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the mean describe?

The mean is the arithmetic average of the measurements in a group. For a continuous outcome such as percent dilation, it gives a concise description of the group’s central value. The posted means are 2.25 for pentoxifylline plus cART and 3.36 for placebo plus cART. A mean is not a description of every participant: individual measurements can lie above or below it, and the average alone does not show the shape of the data.

What does the standard deviation describe?

The standard deviation summarizes the spread of measurements around the mean, in the same measurement units as the outcome. The reported standard deviations are 2.92 and 1.44, respectively. A larger standard deviation indicates greater dispersion around the group mean in the observed data. It is not the standard error of the mean and is not itself a confidence interval. With small endpoint counts, both the mean and the standard deviation may be sensitive to individual observations. The registry does not provide participant-level measurements or distributional plots in the registry record for this interpretation.

What is a mean difference?

A mean difference expresses a contrast between group means in the outcome’s units. The sponsor’s analysis is identified as a linear-regression analysis of mean difference in final values and reports -1.34. Regression can estimate a group contrast within a model; the meaning of a coefficient depends on the model and the order or coding of its groups. The registry does not report covariates, adjustment details, or a full model specification. The posted value should therefore be described as the reported regression estimate, rather than reconstructed from the group summaries.

How should the p-value be read?

The reported p-value is 0.52. In general, a p-value describes the probability, under a specified statistical model and null hypothesis, of obtaining data at least as incompatible with that null as the observed data. It is not the probability that the treatment has no effect, and it does not show whether an observed contrast is important to patients. Its interpretation depends on the model and analysis assumptions. The registry record does not provide enough information to evaluate all those assumptions or reproduce the regression analysis.

Why does a confidence interval matter?

A confidence interval is an interval estimate intended to represent uncertainty around an effect estimate under a statistical procedure. Its width conveys precision: a wider interval indicates less precise estimation than a narrower interval, all else equal. It also shows which effect sizes remain compatible with the analysis at the stated confidence level. Neither interval limits nor a confidence level are reported for the sponsor’s result. Consequently, the p-value and point estimate do not provide the same information as an interval, and the precision of the reported difference cannot be described using a confidence interval.

What is the role of the endpoint counts?

The endpoint counts are the numbers used for the Week 48 outcome summaries: 4.0 in the pentoxifylline group and 5.0 in the placebo group. The outcome definition says these are participants who completed the Week 48 visit procedures. They are not interchangeable with the enrollment count of 19. Without a participant-flow account or an analysis-population description, the registry does not establish why the endpoint counts differ from enrollment, or how participants who did not contribute a Week 48 result were handled.

What do planning illustrations mean?

Sample-size calculations are prospective planning tools, not summaries of what a trial observed. The stated planning assumptions use a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. Any resulting sample-size figures are illustrations based on those assumptions; they are not observed power and do not change the interpretation of the trial’s results. The registry does not report the trial’s own sample-size justification. A recalculated two-arm comparison is marked as not estimable because values were missing or not estimable for that calculation, so no recalculated effect should be inferred from the planning assumptions.

More generally, statistical analyses of small groups can be imprecise, and estimates may be sensitive to observations or modeling choices. A confidence interval, a transparent model specification, and clear reporting of the analysis population would help readers evaluate precision and assumptions. Those details are not reported in the registry record. The distinction between descriptive summaries, the sponsor’s inferential analysis, and hypothetical planning calculations is therefore essential when reading this result.

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("PTX+cART", "Placebo+cART")
n   <- c(4, 5)
m   <- c(2.25, 3.36)
sp  <- c(2.92, 1.44)
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  PTX+cART  4  2.250  2.920  -2.396  6.896
CARM  Placebo+cART  5  3.360  1.440  1.572  5.148

11. Analyses Reported by the Sponsor

The sponsor’s posted analysis is a linear-regression comparison of final values. It reports a mean difference of -1.34 and p = 0.52. The registry does not report a confidence interval, confidence level, or enough model details to reproduce that analysis. The reported result is therefore the available inferential comparison for the endpoint.

A recalculated two-arm comparison is not estimable in the posted output because values are noted as missing or not estimable for that calculation. The group means and standard deviations do not replace the sponsor’s analysis, and no new difference or interval should be derived from them in this interpretation. The registry marks discrepancy as false, so there is no stated conflict between a recalculation and the sponsor result. The sponsor’s analysis takes precedence when a discrepancy is flagged; that condition is not flagged.

The distinction is between the sponsor’s model-based result and an unavailable recalculation, not between two competing estimates. Readers can interpret the reported point estimate and p-value as the registry’s inferential result, while recognizing that its precision and model assumptions cannot be fully assessed from the record.

12. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure and one reported analysis, and no secondary outcomes are posted. That is a description of what appears in the record, not evidence that the study had no other planned outcomes or analyses. A protocol, statistical analysis plan, and multiplicity strategy are not reported in the registry record. It is therefore not possible to determine whether other outcomes or analyses were planned, whether any adjustments for multiple testing were considered, or whether the posted analysis was the only analysis conducted.

The primary outcome is defined at Week 48, and its population is participants who completed the Week 48 visit procedures. The endpoint counts are 4.0 for pentoxifylline plus cART and 5.0 for placebo plus cART, while enrollment is recorded as 19. The record does not provide a flow of participants through the study, reasons for missing measurements, or a detailed account of which participants were included in each analysis. It does not report an intention-to-treat population, a per-protocol population, or a missing-data method. No particular explanation for the difference between enrollment and the outcome counts can be inferred.

Missing outcome data can affect both the precision and interpretation of a comparison, especially when the analysis is limited to participants with completed endpoint procedures. The extent and direction of any such effect depend on why data are absent and how the analysis handles them. Those details are not reported, so the impact of missing endpoint information cannot be assessed from the registry record.

The record also does not report interim analyses, stopping rules, or a prespecified statistical analysis plan. Their absence from the record should not be read as proof that none existed. These reporting gaps limit evaluation of analysis choices and the potential for selective emphasis among outcomes or models.

13. 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 adverse-event record reports serious adverse events in 0 of 10 participants at risk in the pentoxifylline plus cART group and 0 of 9 participants at risk in the placebo plus cART group. The record lists no serious-event terms. These are the registry’s reported counts; they do not establish that no events occurred outside the record’s definitions or reporting period.

For other adverse events, the record reports 6 of 10 participants at risk in the pentoxifylline group and 2 of 9 in the placebo group as affected. These figures are counts of participants affected, not counts of individual event episodes. The registry does not provide the event terms, severity breakdown, timing, or an analysis comparing adverse-event risks. Death counts are not reported in the registry record.

The safety figures should be read separately from the primary efficacy endpoint. The group sizes at risk are small, and the adverse-event counts alone do not establish a treatment-related cause or a reliable difference between groups. The registry record does not report a formal safety analysis or enough detail to assess the completeness of event collection.

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

The result describes flow-mediated dilation of the brachial artery at Week 48 among participants who completed the visit procedures. The observed group means were 2.25 for pentoxifylline plus cART and 3.36 for placebo plus cART. The sponsor’s regression analysis reports a mean difference of -1.34 and p = 0.52. A confidence interval is not reported, and a recalculated two-arm comparison is not estimable in the posted output.

These results do not establish that the treatments are equivalent, nor do they establish that a difference is absent. A p-value does not quantify the probability that a treatment has no effect, and a point estimate without an interval does not show the range of effects compatible with the analysis. The small endpoint counts further limit how precisely the outcome can be characterized. The posted summaries describe the observed data; they are not a substitute for a complete account of missing observations, analysis populations, and model assumptions.

The outcome is a physiological measure of vessel dilation, not a direct report of cardiovascular events or a broad measure of health. The registry’s description links the study rationale to vascular function and inflammation, but the posted primary result concerns only the specified Week 48 flow-mediated dilation measure. No secondary outcomes are posted, and no broader clinical outcomes can be inferred from this result.

The findings also concern the particular comparison in the record: pentoxifylline added to cART versus placebo added to cART. They do not address cART versus no cART. The record’s design and outcome reporting cannot by themselves establish effects in other populations, at other time points, or on outcomes not reported. The appropriate reading is narrow: these are the posted results for this endpoint and study population, with substantial limits on precision and interpretation.

15. Why This Trial Matters Statistically

This trial is statistically informative as an example of why a reported point estimate should be read alongside its uncertainty and analysis population. The registry gives group means, standard deviations, endpoint counts, and a regression-based mean difference with a p-value. It does not give a confidence interval for the mean difference. Those omissions matter because the estimate’s precision cannot be evaluated from the p-value alone.

The outcome counts are also important context. The record reports enrollment of 19, but defines the primary outcome population by completion of Week 48 visit procedures and lists outcome counts of 4.0 and 5.0. Without participant flow or missing-data details, readers cannot establish how the endpoint population arose or whether the analysis represents a broader randomized population. Clear reporting of those details would support a more complete assessment of the result.

The record illustrates a further distinction between a sponsor’s analysis and recalculation from summary statistics. The sponsor’s regression result is reported, whereas a recalculated comparison is not estimable in the posted output. Treating those as interchangeable could create a misleading impression of independent confirmation. Likewise, hypothetical sample-size calculations are planning illustrations, not evidence of observed power.

Finally, the study’s narrow primary endpoint and absence of posted secondary outcomes constrain interpretation. A physiological measure can address a focused research question, but it should not be treated as a direct result for unreported clinical outcomes. Careful separation of the endpoint, model-based estimate, uncertainty, safety counts, and missing-data information is central to reading the registry record accurately.

16. 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 outcome counts are limited to participants who completed the Week 48 visit procedures: 4.0 in the pentoxifylline plus cART group and 5.0 in the placebo plus cART group. Although enrollment is recorded as 19, the registry does not provide participant flow or explain how the endpoint counts relate to enrollment. Reasons for missing Week 48 measurements and the method used to handle missing data are not reported.

The sponsor’s analysis reports a mean difference of -1.34 and p = 0.52, but no confidence interval is reported. The registry also lacks details of the linear-regression model, including any covariates or adjustment choices. A recalculated two-arm comparison is not estimable in the posted output. These gaps limit independent assessment of the estimate, its precision, and the assumptions behind the analysis.

The registry reports one primary outcome measure, one analysis, and no posted secondary outcomes, but does not provide a statistical analysis plan or multiplicity strategy. It does not report the trial’s own sample-size justification, interim analyses, or stopping rules. Their absence from the registry record does not establish whether they existed outside the record.

The outcome is a Week 48 physiological measure, and the registry entries do not establish how it relates to unreported clinical outcomes. The adverse-event record provides participant counts but limited detail on event terms and timing; death counts are not reported in the registry record. These reporting limitations call for a narrow interpretation of the posted results.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Pentoxifylline and Combination Antiretroviral Therapy to Improve Blood Vessel Function in HIV-Infected People — NCT00864916.
• Registry record last updated 2014-05-12; status last verified 2014-04.
• Results first posted 2014-04-16.
• 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.

20. Record Summary

The registry describes a completed Phase 2 randomized, placebo-controlled, quadruple-masked, parallel-group trial sponsored by Indiana University. It compares pentoxifylline plus cART with placebo plus cART in people with HIV. Enrollment is recorded as 19.

The primary endpoint is mean flow-mediated dilation of the brachial artery at Week 48, among participants completing the visit procedures. The posted endpoint counts are 4.0 and 5.0. The reported group means are 2.25 and 3.36, with standard deviations of 2.92 and 1.44. The sponsor’s linear-regression analysis reports a final-value mean difference of -1.34 and p = 0.52; a confidence interval is not reported. No secondary outcomes are posted, and a recalculated comparison is not estimable in the registry output.