Study on the Safety and Effectiveness of Switching Between Two Forms of Tapentadol in Patients With Chronic Low Back Pain: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study on the Safety and Effectiveness of Switching Between Two Forms of Tapentadol in Patients With Chronic Low Back Pain (NCT00594516), a randomized phase 3 study. The primary outcome is The Difference in the Mean Average Pain Intensity Score on an 11-point Numerical Rating Scale (NRS) During the Last 3 Days of Each Double-blind Treatment Period. (Difference Between Two DB Randomization Treatment Sequences).

2. Clinical Question

The registry’s stated objective was to test whether IR could be converted directly to an approximately equivalent total daily dose of ER, and vice versa, while maintaining equivalent safety and efficacy. That objective is broader than simply asking whether pain scores differ: a claim of equivalence requires an appropriate equivalence framework and prespecified criteria. Those criteria and the analysis results are not reported in the registry record. The available description therefore identifies the clinical question and outcome measure, but does not establish whether the study met its objective.

3. Trial Design

The registry identifies this as a phase 3, randomized, triple-masked, two-period crossover study. The listed enrollment is 117. The title describes direct conversion between immediate-release and extended-release tapentadol in people with moderate-to-severe chronic low back pain. The study is marked completed; its recorded start was 2007-12 and its primary completion was 2008-04.

In a crossover design, participants receive treatments in different periods, and randomized groups follow different treatment sequences. This allows a comparison across treatment periods while accounting for the sequence to which participants were assigned. The registry’s primary outcome title specifically describes a difference between the two double-blind randomization treatment sequences. The arm descriptions refer to an open-label period followed by two double-blind periods, with IR and ER appearing in different orders. The detailed period schedule, transition procedures, and any washout period are not reported in the registry record.

The listed ER doses were 100, 150, 200, or 250 mg tablets twice daily. The arm descriptions are incomplete, so they do not fully establish the dose schedule or the details of each sequence. The registry identifies the formulations as study interventions but does not specify in the available record which roles were masked or how masking was maintained.

The primary outcome was a continuous pain score, analyzed as a least-squares mean, with a 95% confidence interval specified as the measure of dispersion. The timeframe was 14 days for each crossover period, with the score contrast based on the last 3 days of each double-blind period. The primary population was per protocol, with additional eligibility criteria determined before unblinding; those additional criteria are not reported in the registry record. The record lists five outcome measures and one analysis, but does not provide numerical primary results.

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.

Before assignment: The study consisted of screening period (up to 21 days), washout period (from 3 to 7 days), open label (OL) treatment period (3 weeks), followed by a double blind (DB) active treatment period, with crossover design of 2 randomized sequences of tapentadol immediate release (IR) to tapentadol extended release (ER) and tapentadol ER to IR (4 weeks)

Open Label (OL): Tapentadol IR

Reasons for not completing this period:

DB: Tapentadol IR to ER & ER to IR

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Per-protocol set defined as the number of randomized subjects who took at least one dose of study drug during the DB treatment period, and who met additional criteria which were identified prior to unblinding.

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 The Difference in the Mean Average Pain Intensity Score on an 11-point Numerical Rating Scale (NRS) During the Last 3 Days of Each Double-blind Treatment Period. (Difference Between Two DB Randomization Treatment Sequences), measured over 14 days for each cross-over period.

The primary endpoint was the difference in mean average pain intensity score on an 11-point numerical rating scale during the last 3 days of each double-blind treatment period. The registry says participants assessed their average pain over the previous 12 hours twice daily. The scale ranged from 0, meaning “no pain,” to 10, meaning “pain as bad as you can imagine.”

Repeated ratings can describe pain over a treatment period more fully than a single assessment. Focusing on the last 3 days defines the time window used for the primary comparison; it does not, by itself, establish that scores were stable or that earlier measurements were irrelevant. The registry does not report how the repeated ratings were combined into the period-level score, beyond identifying the endpoint as a mean average pain intensity score.

The reported estimand was expressed as a least-squares mean difference between the two randomized treatment sequences. A least-squares mean is an estimate from a statistical model and may account for terms specified in that model. Which model terms were used is not reported in the registry record. The listed 95% confidence interval would ordinarily communicate the range of values compatible with the estimate under the model and its assumptions. Neither the numerical estimate nor its interval is reported in the registry record.

This endpoint is relevant to the stated comparison because it quantifies reported pain intensity during exposure to the two formulations. However, an endpoint value alone would not establish equivalence. Equivalence requires a prespecified acceptable range and an analysis demonstrating that the uncertainty around the treatment contrast fits within that range. Those criteria and results are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical descriptions below distinguish what the registry records from general explanations of the methods named in it. The registry identifies the endpoint as continuous, the reported parameter as a least-squares mean, and the dispersion measure as a 95% confidence interval. It does not provide the numerical estimate or enough detail to reconstruct the model.

What does a least-squares mean represent?

General explanation: a least-squares mean is a model-based estimate of an average. Unlike a simple arithmetic average, it can be adjusted for other terms included in the statistical model. For example, a model in a crossover study might account for period or sequence, but the specific terms depend on the analysis plan. The registry record does not report which terms were included, how the model was fitted, or whether any adjustments were made. It is therefore safest to describe the endpoint as a model-based mean contrast without attributing a particular adjustment to it.

The registry states that the primary contrast was between the two double-blind randomization treatment sequences. That wording matters: it identifies the comparison as reported, but it does not provide enough information to infer the exact coefficient, coding, or direction of subtraction. Without the estimate and its definition, the direction of any numerical contrast cannot be interpreted.

How should a confidence interval be understood?

General explanation: a confidence interval expresses statistical uncertainty around an estimate under the assumptions of the analysis. A narrower interval indicates greater precision than a wider interval, while an interval spanning values in both directions may leave several interpretations compatible with the data. The registry specifies a 95% confidence interval but does not report its limits. Its precision therefore cannot be assessed.

A confidence interval is not a guarantee that the true value lies within the displayed limits, nor does it by itself determine clinical importance. Interpreting it requires the numerical limits, the direction and units of the contrast, and a context for judging which differences matter. For an equivalence question, an interval is generally assessed against prespecified equivalence margins. Those margins are not reported in the registry record.

Why does the crossover design matter?

General explanation: crossover studies expose participants to more than one treatment in separate periods. Measurements from the same person tend to be related, so treating all period observations as independent can give an inappropriate description of uncertainty. The analysis commonly needs to reflect the within-participant structure and may also account for period and sequence. Which approach is appropriate depends on the protocol and data.

The registry describes two double-blind periods and different treatment orders. It does not report a washout interval, the exact timing of transitions, or whether carryover was assessed. Carryover refers generally to an effect of an earlier treatment that persists into a later period. Period effects refer to changes over time that could influence scores regardless of treatment. Without the protocol details and analysis specification, the adequacy of any adjustment or assessment cannot be evaluated.

The title and outcome description refer to a difference between randomization treatment sequences, while the study objective discusses conversion between formulations. These descriptions do not establish how the model translated the sequence comparison into a formulation contrast. The numerical analysis and its precise contrast are not reported in the registry record.

What does the pain scale contribute?

The 11-point numerical rating scale records average pain intensity over the previous 12 hours, with 0 defined as “no pain” and 10 as “pain as bad as you can imagine.” The assessment was twice daily. General explanation: a continuous summary of repeated ratings can capture average experience over a defined period, but its interpretation depends on how observations were aggregated and how missing ratings were handled. The registry gives the time window for the primary score but does not report the detailed aggregation rule, the number of completed ratings, or the handling of incomplete diaries.

Because the endpoint is a mean score, a group-level estimate describes an average contrast. It does not show how every participant’s pain changed, whether responses varied substantially, or how many participants had improvement or worsening. Those individual-level distributions are not reported in the registry record.

What can be said about power and planning?

The registry’s planning description refers to a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It also describes the effect to detect as a stated fraction of the observed effect. These are planning assumptions, not evidence about the trial’s observed result. The registry record does not report numerical participant-per-arm planning estimates or a sample-size justification for the actual crossover design. The sample-size assumptions do not establish observed power, and no post hoc power claim can be inferred from them.

The available primary-result record does not include the observed effect needed to interpret a planning illustration based on a fraction of that effect. General explanation: sample-size planning asks what amount of information may be needed under stated assumptions; it cannot substitute for an estimate and confidence interval from the completed study. The enrollment of 117 is recorded, but enrollment alone does not indicate the precision achieved in the per-protocol primary analysis.

In sum, the named statistical terms describe the type of endpoint and uncertainty measure, but not the full analysis. The model, contrast definition, assumptions, missing-data procedures, and numerical output are not reported in the registry record. Those omissions limit independent statistical interpretation.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists five outcome measures and one analysis. The primary outcome is the pain-intensity contrast, while the listed secondary outcomes concern rescue medication during IR and ER treatment and total daily dose during the corresponding periods. The registry record does not report a testing hierarchy, multiplicity adjustment, or whether the secondary outcomes were treated as confirmatory or exploratory.

General explanation: when several outcomes or comparisons are tested, the chance of at least one apparently unusual result can increase if each is evaluated separately. Prespecified prioritization or statistical adjustment can address this issue, but the appropriate strategy depends on the study’s objectives and analysis plan. Since the plan and numerical results are not reported in the registry record, the impact of multiple testing cannot be assessed.

The primary analysis population was defined as the per-protocol set: randomized subjects who took at least one dose during the double-blind treatment period and met additional criteria identified before unblinding. The additional criteria and the number of participants included are not reported in the registry record. The record also does not report an intention-to-treat analysis or explain whether one was conducted.

Missing-data handling is not reported in the registry record. In general, incomplete pain ratings or missing period measurements can affect the analysis, particularly if missingness is related to pain, treatment, or tolerability. The record does not state how missing observations were handled, whether imputation was used, or whether sensitivity analyses were performed. It also does not give participant flow by sequence or reasons for missing data and exclusion.

These gaps do not establish that the study lacked procedures for multiplicity or missing data. They mean only that those procedures and their implications are not reported in the registry record. Without them, the robustness of the primary and secondary analyses cannot be evaluated from the registry information.

11. 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 serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: back pain (0.9%), hip fracture (0.9%).

The registry lists one tapentadol safety group with 116 participants at risk for serious adverse events and 116 at risk for other adverse events. The recorded serious adverse-event count is 2; the other adverse-event count is 98. The listed serious terms are Back Pain at 0.9% and Hip Fracture at 0.9%. The death count is not reported in the registry record.

These are aggregate safety figures. They do not show how events were distributed between the IR and ER periods, treatment sequences, or individual participants. The registry does not report event timing, severity beyond the serious classification, duration, outcome, or an assessment of causal relationship. The number of events should not be assumed to equal the number of people affected unless the record explicitly establishes that distinction.

General explanation: an adverse event occurring during a study is not necessarily caused by the study treatment. A group-level count also does not show comparative risk between formulations unless the results are reported separately with an appropriate comparison. Because the listed safety group combines tapentadol exposure and does not provide formulation-specific estimates, these figures cannot establish a safety difference between IR and ER.

The percentages for the serious terms are quoted as registered and should be read as descriptive entries, not as comparative estimates. The safety data provide a limited account of reported events; they do not by themselves characterize the full safety profile or resolve the study’s stated question about equivalent safety.

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

The record establishes that a randomized, triple-masked, two-period crossover study was conducted to examine conversion between immediate-release and extended-release tapentadol in chronic low back pain. It identifies a primary pain measure, the time window used for that measure, and the intended per-protocol population. These details explain what the trial set out to compare, but they are not evidence of the result.

The primary least-squares mean difference and its 95% confidence interval are not reported in the registry record. Without those values, it is not possible to describe whether the sequence groups had similar or different average scores, how large any contrast was, or how precisely it was estimated. The secondary outcome results are also not reported. Accordingly, the registry information does not establish whether direct conversion achieved the stated objective.

The study objective uses the language of approximate dose equivalence and equivalent safety and efficacy. General statistical principle: equivalence is a specific inferential claim, not simply the absence of a statistically significant difference. It requires a defined range of acceptable differences and evidence that the estimate is sufficiently precise relative to that range. The registry record does not report the equivalence criteria or the results needed to assess them.

The safety summary records adverse-event counts in a tapentadol group, but does not provide a formulation-specific comparison. It therefore cannot answer whether the two forms had equivalent safety. Likewise, enrollment and the existence of a completed study do not reveal the precision or reliability of the primary finding.

The appropriate conclusion is limited: the registry describes the design and planned outcomes, while the key numerical efficacy results and important analysis details are not reported in the registry record. No conclusion about treatment benefit, lack of benefit, or equivalence follows from the design description alone.

13. Why This Trial Matters Statistically

This trial raises several statistical issues that are central to interpreting formulation-conversion studies. The crossover structure makes treatment sequence, period, and within-participant dependence relevant. A contrast based on repeated periods can be informative, but its meaning depends on how the model represents those features and how the transition between formulations was managed. The registry describes two double-blind periods and randomized sequences, but does not report the analysis model or transition details.

The stated objective also highlights the difference between testing for a difference and assessing equivalence. A conventional difference test asks whether the data are inconsistent with a zero contrast under a specified model. Equivalence instead asks whether the plausible contrast is contained within a prespecified acceptable range. General statistical explanation: a confidence interval is useful for this purpose because it displays uncertainty, but the interval must be compared with a clinically justified margin. Neither the margin nor the primary confidence interval is reported in the registry record.

The endpoint is a repeated patient-reported pain measure summarized as a mean. Its interpretation depends on the scoring window, aggregation procedure, completeness of ratings, and analysis population. The registry supplies the scale anchors and assessment frequency, but does not describe all of these analytic details. The per-protocol definition also matters because exclusions after randomization can change the population represented by the result.

Finally, the registry’s aggregate safety figures do not support a direct IR-versus-ER comparison, and the listed secondary outcomes do not have numerical results. These limitations illustrate why a trial’s design, endpoint definitions, analysis choices, and actual estimates all need to be considered together. In this record, the design is described more fully than the numerical evidence needed to evaluate the objective.

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 most direct limitation is that the registry record does not report the primary estimate or its 95% confidence interval. The size, direction, and precision of the pain-score contrast therefore cannot be assessed. Secondary outcome results are also not reported, leaving rescue medication use and total daily dose findings unavailable.

The analysis description is incomplete for evaluating a crossover study. The record does not report the statistical model, its terms, the exact contrast coding, or whether period and sequence effects were addressed. It does not describe a washout interval or report whether carryover was considered. These details are important to understanding what the sequence comparison estimates and whether the assumptions behind it are plausible.

The primary population is defined as per protocol, but the additional pre-unblinding criteria, analysis sample size, participant flow, and reasons for exclusion are not reported in the registry record. Missing-data methods, sensitivity analyses, and any intention-to-treat analysis are also not reported. Consequently, the effect of incomplete measurements or post-randomization exclusions cannot be evaluated.

The stated objective concerns approximate equivalence, yet the registry does not report equivalence margins, a decision rule, or a sample-size justification tied to those criteria. The listed planning assumptions refer to a normal approximation, equal allocation, and a two-sided significance level of 0.05, but numerical planning estimates are not reported in the registry record. Those assumptions alone do not establish that the study was planned or analyzed to demonstrate equivalence.

Safety information is aggregated across tapentadol and does not distinguish IR from ER exposure. The registry does not report deaths, event timing, causal assessment, or detailed event outcomes. These limitations restrict interpretation of both the efficacy objective and comparative safety.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Study on the Safety and Effectiveness of Switching Between Two Forms of Tapentadol in Patients With Chronic Low Back Pain — NCT00594516.
• Registry record last updated 2015-04-15; status last verified 2015-03.
• Results first posted 2010-07-26.
• 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 identifies NCT00594516 as a completed phase 3 randomized, triple-masked, two-period crossover study of immediate-release and extended-release tapentadol in people with chronic low back pain. Enrollment was 117. The primary endpoint was a least-squares mean difference in average pain intensity on an 11-point numerical rating scale, comparing randomized treatment sequences during the last 3 days of each 14-day crossover period.

The primary population was per protocol. The registry lists five outcome measures and one analysis. Its safety summary records 2 serious adverse events and 98 other adverse events among 116 at risk in the tapentadol group; the serious-event terms listed are Back Pain and Hip Fracture, each at 0.9%.

The numerical primary outcome, confidence interval, secondary results, model details, equivalence criteria, and missing-data procedures are not reported in the registry record. The available record therefore describes the trial question and design but does not permit assessment of whether the conversion objective was met.