Efficacy of PegIntron and Rebetol in Previously Untreated Patients With Chronic Hepatitis C Infected With HCV Genotype 1/4/5/6 (Study P04243): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy of PegIntron and Rebetol in Previously Untreated Patients With Chronic Hepatitis C Infected With HCV Genotype 1/4/5/6 (Study P04243) (NCT00709059), a registered phase not stated study. The primary outcome is Number of Study Participants Who Had a Virological Response (VR) at Week-72.

2. Clinical Question

The clinical question is about response observed during treatment with the combination in a specified population, not a randomized comparison of treatments. The study was a non-interventional Phase IV survey, and the brief summary places it in primary care. The registry record lists chronic hepatitis C as the condition and limits eligibility to previously untreated participants with the specified genotypes.

The primary outcome is a count of participants meeting the virological-response definition at the stated assessment time. The registry record also says that participants who dropped out or were withdrawn from treatment were considered not to respond. However, the posted results do not give the response count, the analyzed count, or results by fibrosis stage. Consequently, the clinical question can be described from the registered objective and endpoint, but its observed answer is not reported in the registry record.

3. Trial Design

The registry record describes PRACTICE, also identified as Study P04243, as a non-interventional Phase IV survey. Its objective was to evaluate the effectiveness of PegIntron plus Rebetol among previously untreated patients with chronic hepatitis C in a primary care setting. Enrollment is recorded as 538, and the study status is completed. The recorded start is 2004-12 and the primary completion is 2009-12.

The intervention is the combination of PegIntron (peginterferon alfa-2b; SCH 54031) and Rebetol (ribavirin; SCH 18908). The listed arm description covers previously untreated participants infected with HCV genotype 1, 4, 5, or 6. The registry record does not describe a separate control arm or state how participants were allocated. It therefore does not support a treatment-versus-control interpretation, and a causal comparison with another treatment cannot be drawn from the listed arm.

The primary outcome measure is the number of participants with a virological response at Treatment Week 72. The registry record defines response as absence of HCV RNA in a qualitative PCR test and says dropouts or participants withdrawn from treatment were considered not to respond. It identifies the Full Analysis Set as the analyzed population, described as the intent-to-treat population with non-missing viral response at Week 72.

The brief summary says the study would also explore whether liver fibrosis stage influenced the chances of sustained virologic response. The registry record does not report a fibrosis-stage analysis or an analysis plan. It lists one outcome measure and zero analyses. The posted results do not report the response count or other outcome estimates, so the completed status and enrollment alone do not establish the observed effectiveness result.

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: Full Analysis Set (FAS)was analyzed. FAS consisted of all participants in the intent-to-treat population wih non-missing viral response at Week 72.

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 Number of Study Participants Who Had a Virological Response (VR) at Week-72, measured over Treatment Week 72.

The primary endpoint is the number of study participants with a virological response at Treatment Week 72. Response is defined as absence of HCV RNA in a qualitative polymerase chain reaction test. The measure is therefore a binary participant-level outcome represented as a count: each participant is classified as having or not having the defined response. The registry record says that participants who dropped out or were withdrawn from treatment were considered not to respond.

Using a virological measure gives the outcome a direct connection to detectable viral RNA at the specified assessment time. In general, an endpoint of this kind can provide a clinically interpretable way to describe the proportion of an analyzed group meeting a defined response criterion. Here, however, the registry record specifies the number, not a proportion, and the posted results do not state the response count or the denominator used for the reported analysis. No proportion or uncertainty estimate can therefore be described from the registry record.

The endpoint is tied to Treatment Week 72; it should not be confused with a result at another visit or with a broader clinical outcome. The study summary also refers to sustained virologic response and to exploring fibrosis stage, but the registry record’s listed primary measure is the Week-72 response count. A distinct sustained-response definition, its assessment timing, and results by fibrosis stage are not reported in the registry record.

In general, endpoint interpretation depends on a clear outcome definition, assessment timing, population, and handling of unavailable assessments. The record supplies the response definition and timing, but the relationship between its nonresponse rule for dropouts and its Full Analysis Set definition is not fully clear. That uncertainty limits interpretation of who contributes to the stated count.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record identifies a count endpoint: the number of participants meeting a defined virological-response criterion at Treatment Week 72. In general, a count records how many observations fall into a category, while a binary outcome distinguishes whether each participant meets that category. A count is interpretable only alongside the population and denominator to which it refers. The registry record does not give the reported response count or analyzed denominator, so a response rate cannot be recovered or described.

What does the endpoint definition mean?

The outcome definition is absence of HCV RNA in a qualitative PCR test. A qualitative test classifies a result rather than reporting a numeric viral-load value. For this endpoint, the registry record treats the response as present when the specified absence is recorded. It also states that participants who dropped out or were withdrawn from treatment were considered not to respond. In general, assigning an outcome to participants without an observed assessment is a missing-data rule, and its consequences depend on how many assessments are unavailable and why. Those details are not reported in the registry record.

Why does the analysis population matter?

The Full Analysis Set is described as consisting of all participants in the intent-to-treat population with a non-missing viral response at Week 72. The outcome description separately says that dropouts and withdrawals were considered nonresponders. These statements do not fully explain whether participants without a Week-72 measurement were retained as nonresponders or excluded because their response was missing. The number of participants in the Full Analysis Set, the number with missing results, and the operational rule used for each case are not reported in the registry record.

In general, an intent-to-treat approach aims to preserve the groups defined at enrollment or allocation, whereas an analysis restricted to participants with observed outcomes can depend on who remains observed. This study is not described as a randomized comparison, and the record’s Full Analysis Set wording is specific to non-missing Week-72 viral response. It would be inappropriate to assume a particular missing-data method beyond the explicit statement about dropouts and withdrawals.

What can a confidence interval tell a reader?

In general, a confidence interval expresses uncertainty around an estimated quantity under the assumptions of the statistical method. A narrow interval indicates greater statistical precision than a wide interval, while neither width nor location alone removes bias from study design, outcome measurement, or missing data. No confidence interval or other uncertainty estimate for the primary endpoint is reported in the registry record. Without a response count and denominator, there is no posted estimate around which to interpret such an interval.

How should a significance level be understood?

The planning-illustration assumptions describe a two-sided significance level of 0.05. In general, a significance level is a design or testing threshold for evaluating evidence against a specified null hypothesis; it is not the probability that a treatment works, and it does not measure the size or clinical importance of an effect. The registry record does not report an inferential test for the primary endpoint, a p-value, or a hypothesis-testing plan. The planning assumption should not be recast as the study’s statistical analysis plan.

What do the planning assumptions represent?

The planning description says illustrations use equal allocation between two arms, a normal approximation, and an effect to detect set as a stated fraction of the observed effect. It distinguishes participants per arm for non-time-to-event outcomes from total events for time-to-event outcomes. These are planning conventions, not observed study results. The registry record does not describe equal allocation or a two-arm randomized design; it lists one intervention arm and notes that allocation is not stated. The observed effect and the resulting planning counts are not reported in the registry record. Thus the assumptions cannot establish that the trial was designed, conducted, or powered in that manner.

In general, over-dispersion is relevant when count variability exceeds what a simple count model expects. It can make uncertainty estimates too optimistic if a model assumes less variability than the data contain. The listed primary endpoint is a count of participants with a binary response, not a repeated-event count, and the registry record does not report a model or dispersion estimate. No over-dispersion adjustment should be attributed to this study.

The record lists one outcome measure and zero analyses. This does not reveal what analyses may have been conducted outside the registry entry, but it means the posted registry information does not specify an analysis method for the primary endpoint. There is no reported covariate adjustment, subgroup model, handling of repeated measurements, or inferential procedure. General statistical methods can clarify what such procedures mean, but none should be presented as having been used in this study unless the registry record reports it.

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("PegIntron Plus Rebetol")
n      <- c(505)
events <- c(176)
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  PegIntron Plus Rebetol  505  176  34.9  30.7  39.2  30.8  39.1  30.8  39.1

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists one outcome measure and zero analyses. It does not report a statistical analysis plan, a prespecified hierarchy of outcomes, or how multiple tests or subgroup assessments would be handled. The study summary says fibrosis stage would be explored in relation to sustained virologic response, but the record does not describe the number of stage groups, the analyses planned, or any adjustment for multiple comparisons. It is therefore not possible to assess multiplicity control from the posted registry information.

In general, testing multiple outcomes, subgroups, or alternative analyses can increase the chance of a seemingly notable finding occurring by chance. Prespecified methods help readers distinguish confirmatory analyses from exploratory ones. That general concern applies when interpreting any reported subgroup result, but no subgroup result or testing procedure is reported. The fibrosis-stage objective should be treated as an stated area of exploration, not as a reported finding.

The missing-data description is not fully resolved. The outcome definition states that dropouts and participants withdrawn from treatment were considered not to respond. The Full Analysis Set description, however, includes participants in the intent-to-treat population with non-missing Week-72 viral response. The registry record does not explain whether a dropout without a Week-72 test is represented as a nonresponse within that set, or how other missing results were handled. Counts of missing assessments, withdrawals, and exclusions are not reported.

In general, missingness can affect an estimate when the chance of having an observed outcome is related to the outcome itself or to participant characteristics. A rule that assigns nonresponse to some missing outcomes makes an assumption about their classification; it does not reveal how many cases were affected. Since the response count, denominator, and missingness details are absent, neither the impact of missing data nor the robustness of the primary result can be assessed from the registry record.

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

The registry record defines a study of PegIntron plus Rebetol in previously untreated participants with chronic hepatitis C and HCV genotype 1, 4, 5, or 6. It identifies the primary measure as the number with a virological response at Treatment Week 72, based on absence of HCV RNA in a qualitative PCR test. It also states that dropouts or participants withdrawn from treatment were considered not to respond. These registry entries describe what the study set out to assess and how the response was defined.

The posted results do not report how many participants met that definition, how many contributed to the analysis, or an estimate of uncertainty. Therefore, the registry record does not establish the observed response level or its precision. The completed status and enrollment entry do not fill that gap. The absence of a reported result should not be interpreted as a zero response count, nor as evidence for or against an effect.

The study is described as non-interventional, with allocation not stated and no like-for-like control comparison. Any outcome count from the intervention arm, if available elsewhere, would describe that group and setting. Without a suitable comparison, it would not by itself show what would have occurred under another treatment or without the combination. The registry record does not report an adjusted comparative estimate.

The brief summary states that the study would explore the influence of liver fibrosis stage on the chance of sustained virologic response. No stage-specific result or analysis is reported in the registry record. The primary endpoint named in the record is the Week-72 response count; it should not be conflated with a separately defined sustained virologic response outcome.

In general, an endpoint can be useful while still providing an incomplete picture of a study’s findings. Its interpretation depends on the reported estimate, population, missing-data handling, and design. Here, the endpoint definition is available, but key result and analysis details are not. No medical conclusion or comparative claim follows from the registry information alone.

13. Why This Trial Matters Statistically

This trial is statistically informative as an example of why an endpoint definition and an outcome result are different kinds of information. The registry record identifies a concrete virological criterion and assessment time, but it does not report the response count or denominator. Readers can understand what was intended to be measured without being able to quantify the observed result. The distinction prevents an enrollment figure from being mistaken for the number analyzed or for the number who responded.

The record also illustrates how population definitions and missing-data rules need to be read together. It says dropouts and withdrawals were treated as nonresponders, while defining the Full Analysis Set through a non-missing Week-72 viral response. Without clarification of how those descriptions were reconciled, the handling of unavailable outcomes remains uncertain. This matters because the analytic population and treatment of missing outcomes can change the meaning of a count-based endpoint.

Study design is equally important to the interpretation of effectiveness. The registry describes a non-interventional survey, does not state allocation, and does not list a like-for-like control comparison. The primary outcome can therefore be framed as a response measure among participants receiving the combination, not as a randomized estimate of comparative benefit. The distinction is essential when a study’s objective uses the language of effectiveness.

Finally, the record’s interest in fibrosis stage does not amount to evidence of a stage-related effect. The summary describes that objective, but no analysis or result is reported. Separating the stated question from the available result is a core statistical practice: it keeps exploratory aims, design assumptions, and observed findings from being treated as interchangeable.

14. 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 this specific registry entry is that it does not report the primary endpoint result. Although the endpoint definition and assessment time are stated, the response count, analyzed denominator, estimate, and uncertainty are absent. The enrollment entry alone cannot substitute for these missing outcome details.

The analysis-population description and the nonresponse rule for dropouts or withdrawals are not fully reconciled. The registry record does not state how many participants lacked a Week-72 assessment, how many withdrew, or how those cases entered the Full Analysis Set. This prevents assessment of the possible effect of missing outcomes on the endpoint.

The study is explicitly described as non-interventional, and allocation is not stated. The listed intervention arm does not provide a like-for-like control comparison. As a result, the registry entry does not support a randomized comparative interpretation. It also does not report adjustment methods that might address differences between participants or other sources of confounding.

The stated interest in liver fibrosis stage is not accompanied by stage-specific results or an analysis description. The registry record does not report how fibrosis stage was categorized, whether analyses were prespecified, or how multiple comparisons were handled. The posted information therefore cannot answer whether response differed by stage.

Safety information is also limited in the record. It lists no serious-event terms; the death count is not reported in the registry record. The adverse-event fields recorded as 0 do not provide enough context to infer a complete safety profile. More generally, the registry entry does not report an analysis plan or statistical methods for the primary endpoint. These limitations concern what the registry record documents and should not be taken as proof that additional information was never collected.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Efficacy of PegIntron and Rebetol in Previously Untreated Patients With Chronic Hepatitis C Infected With HCV Genotype 1/4/5/6 (Study P04243) — NCT00709059.
• Registry record last updated 2015-11-04; status last verified 2015-11.
• Results first posted 2011-01-10.
• 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.

18. Record Summary

The registry record describes NCT00709059, Study P04243, also named PRACTICE, as a non-interventional Phase IV survey. The sponsor is Merck Sharp & Dohme LLC. It concerns previously untreated participants with chronic hepatitis C infected with HCV genotype 1, 4, 5, or 6, receiving PegIntron plus Rebetol. The stated objective was to assess effectiveness in a primary care setting and explore the influence of liver fibrosis stage.

Enrollment is recorded as 538; the study is marked completed, with a start of 2004-12 and primary completion of 2009-12. The primary outcome is the number of participants with a virological response at Treatment Week 72, defined as absence of HCV RNA in a qualitative PCR test. Dropouts and participants withdrawn from treatment were considered not to respond.

The registry record lists one outcome measure and zero analyses. It does not report the primary response result, a comparator, allocation, or a fibrosis-stage result. The Full Analysis Set is described as the intent-to-treat population with non-missing Week-72 viral response, but its relationship to the stated dropout rule is not clarified.