This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Comparison of Oral Gabapentin and Pregabalin in Postoperative Pain Control After Photorefractive Keratectomy (NCT00954187), a randomized na study. The primary outcome is Decreased Overall Pain Score as Measured by the Visual Analogue Scale.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00954187 |
| Phase | NA |
| Condition | Postoperative Pain |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Double |
| Enrollment | 8 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Loma Linda University |
| Results posted | Yes |
2. Clinical Question
Population
The planned population was patients meeting inclusion criteria who were undergoing photorefractive keratectomy (PRK) in one or both eyes. The record does not report the eligibility criteria in detail. It lists an enrollment of 8, but also describes a plan to enroll 104 patients. The primary outcome record states that no subjects were assigned treatment, so the planned population should not be mistaken for a group that actually contributed outcome data.
Intervention
The intervention was oral gabapentin, described in the planned methods as beginning two hours before surgery. The brief summary also describes gabapentin 300 mg TID for 3 days. These are descriptions of the intended regimen, not evidence that participants received it.
Comparator
The comparator was oral pregabalin, also intended to begin two hours before surgery. The brief summary describes pregabalin 50 mg TID for 3 days. The record identifies the drug arms as Gabapentin and Pregabalin, with Neurontin and Lyrica listed in their arm descriptions.
Primary question
The intended question was whether overall pain after PRK differed between the two medicines, with pain measured using the visual analogue scale (VAS) and the primary outcome specified at one month. The registry record says that no data were collected or analyzed and no study procedures were performed. Consequently, it supplies no treatment comparison for that question.
In the planned study, patients were also expected to record pain at several postoperative intervals, assess somnolence with the Epworth Sleepiness Scale, and record dizziness. Those planned assessments do not constitute observed results. The record does not establish whether either medicine reduced pain, whether their effects differed, or how precisely any difference could have been estimated.
3. Trial Design
The registry describes a prospective, randomized study with a parallel-group design and double masking. The intended comparison was between oral gabapentin and oral pregabalin in patients having PRK. Random allocation is intended to reduce systematic differences between treatment groups, while masking is intended to limit the influence of treatment knowledge on care, reporting, or assessment. These design features describe the plan; the record states that no subjects were assigned treatment and no study procedures were performed.
The brief summary describes a planned enrollment of 104 patients, while the registry enrollment field lists 8. These entries do not establish the number of people who received treatment or contributed data. The primary outcome record explicitly says that no subjects were assigned treatment. The registry status is terminated. The reason for termination is not reported in the registry record.
The planned medication courses were described as gabapentin 300 mg TID for 3 days and pregabalin 50 mg TID for 3 days. The summary says treatment would begin two hours before surgery. After PRK, the planned pain assessments included one hour after surgery, the evening of surgery, and three times each day for three subsequent days. Somnolence and dizziness were also to be assessed during that period, with a postoperative clinic visit on the fourth day and a further assessment one month later. The record does not show that these procedures occurred.
The primary outcome is described as decreased overall pain score measured by VAS at one month. No analysis is listed, and the record does not report outcome values, treatment-effect estimates, confidence intervals, or statistical tests. Details of the randomization sequence, allocation concealment, masking procedures, and analysis plan are not reported in the registry record. The design labels alone cannot establish how those methods would have been implemented.
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
| Stage | Gabapentin | Pregabalin |
|---|---|---|
| STARTED | 0 | 0 |
| COMPLETED | 0 | 0 |
| NOT COMPLETED | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: No subjects were assigned treatment and no study procedures were performed
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: No subjects were randomized and assigned treatment so Baseline Characteristics were not collected
| Characteristic | Unit | Gabapentin | Pregabalin | Total |
|---|---|---|---|---|
| Participants analysed | 0 | 0 | 0 | |
| Gender: Female | — | — | 0 | |
| Gender: Male | — | — | 0 |
6. Primary Endpoint
The registry lists the primary outcome as Decreased Overall Pain Score as Measured by the Visual Analogue Scale, measured over one month.
| Element | Registry entry |
|---|---|
| Result type | N/A |
| Measure of spread | not applicable |
| Unit | not stated |
| Endpoint classification | not reduced to a single comparison |
The stated primary endpoint is decreased overall pain score measured by the visual analogue scale (VAS), with a timeframe of one month. A VAS is a way for a participant to express pain intensity along a scale. In general, such a measure can represent a subjective symptom that may be difficult to capture through a laboratory test or clinical sign. The endpoint’s interpretation depends on how the scale is defined, how participants complete it, and how the scores are summarized. Those details are not reported in the registry record.
The brief summary describes repeated pain assessments after surgery, but the primary outcome record identifies the one-month timeframe and says no data were collected or analyzed. The record therefore does not give a baseline score, postoperative scores, a definition of “overall” pain, a rule for combining assessments, or a threshold for a clinically meaningful change. Those details are not reported in the registry record.
For an endpoint to support a treatment comparison, scores must be available for participants in the groups being compared, and the analysis must specify how those scores relate to the endpoint. Here the outcome record states that no subjects were assigned treatment and no procedures were performed. No observed VAS values or between-group estimate are reported. The endpoint describes what the study intended to assess, not an observed finding about pain.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record does not contain results for the intended primary comparison. Although it names a primary pain outcome at one month and describes two treatment arms, it explicitly says that no data were collected or analyzed, no subjects were assigned treatment, and no study procedures were performed. There is therefore no observed treatment effect to interpret. The record does not report group-specific pain scores, an estimated difference, a confidence interval, or a p-value.
The enrollment field lists 8, while the planned methods describe 104 patients. These entries refer to different aspects of the record and do not establish that any participants received either medicine. The statement that no subjects were assigned treatment is decisive for interpreting the primary outcome: there is no treated comparison in the posted results. It would be inappropriate to describe either arm as having better pain scores or to infer that the medicines had similar effects.
The adverse-event entries list zero participants at risk and zero affected for serious and other events in both arms; deaths are null. Given the explicit statement that no subjects were assigned treatment and no procedures were performed, these entries do not establish that either treatment is safe or that no adverse events occurred during use. They reflect the absence of a treated study population in the registry outcome record. Death information is not reported in the registry record.
The record’s status is terminated, but the reason is not reported in the registry record. Termination alone does not explain why data are absent, whether recruitment began, or whether any information was collected outside the registry. Such details are not reported in the registry record. The available record supports a description of the planned comparison and the absence of posted trial results, not an efficacy or safety conclusion.
Any planning illustration should be distinguished from observed evidence. Sample-size calculations are planning illustrations, never observed power. The stated assumptions refer to a two-sided significance level 0.05, equal allocation, a normal approximation, and an effect expressed as a fraction of an observed effect. But no primary outcome effect is reported in the registry record. No planning illustration can fill that evidentiary gap or be treated as a result from participants in this trial.
9. Statistical Methods Explained
Randomization is a method for assigning participants to treatment groups by chance. In general, it can help balance both measured and unmeasured participant characteristics across groups, reducing the risk that a group difference is mistaken for a treatment effect. It does not guarantee balance in every trial, and its usefulness depends on actual assignment and follow-up. The record labels the study randomized but states that no subjects were assigned treatment. Thus, randomization describes the intended design and did not generate a posted comparison of outcomes.
A parallel-group design assigns participants to one treatment group and follows each group over the study period. The registry identifies gabapentin and pregabalin as the two arms. The planned comparison would have related outcomes in those arms, but the record does not report treatment assignments or outcome observations. Details such as the random sequence method, allocation concealment, and any stratification are not reported in the registry record. Those methods cannot be inferred from the word “randomized.”
Double masking is intended to keep more than one relevant party unaware of treatment assignment. In general, masking may reduce bias in how treatment is delivered, symptoms are reported, or outcomes are assessed. The registry labels the study double masked, but the specific parties to be masked and the procedures used to maintain masking are not reported in the registry record. Because the record says no subjects were assigned and no procedures were performed, it does not document masking in practice.
The stated primary outcome is a VAS pain score at one month. A treatment-effect estimate would ordinarily summarize the contrast between groups using a specified score or change in score. A confidence interval, in general, describes the range of values compatible with the data and the statistical procedure used. Its width conveys precision: a wider interval indicates less precision than a narrower one. No estimate or confidence interval is reported, so neither the direction nor precision of a possible treatment difference can be assessed.
A p-value, in general, evaluates how compatible data are with a specified statistical model under a null hypothesis. It does not measure the size or clinical importance of an effect, and it is not a substitute for an estimate with a confidence interval. No p-value or statistical test is reported in the registry record. The number of analyses is listed as zero, consistent with the statement that no outcome data were analyzed.
The planned pain assessments were repeated over time. In general, repeated scores from the same participant are correlated rather than independent. Analyses of such data need to account for that correlation, define the relevant time points or summary, and address how incomplete records are handled. The brief summary identifies several intended assessment times, but the primary outcome record gives no observed scores and the registry does not report a repeated-measures model or another method for analyzing the repeated assessments. No model should be attributed to the trial from the assessment schedule alone.
Over-dispersion is a general concern when count data vary more than a chosen model expects; ignoring it can make uncertainty estimates too small. It is not possible to assess whether over-dispersion applies to this pain endpoint, because the record reports no outcome data or statistical model. More generally, model choice depends on the outcome’s scale, distribution, design, and analysis objective. These choices are not reported in the registry record.
The stated sample-size assumptions describe a planning illustration: two-sided significance level 0.05, equal allocation, a normal approximation, and an effect to detect expressed as a stated fraction of the observed effect. Such sample-size figures are planning illustrations, not observed power. They are not evidence that the planned trial achieved a target precision or that a treatment effect was detected. The record does not report an observed primary effect, and it does not report a trial-specific sample-size justification or the basis for the planned enrollment. Those details are not reported in the registry record.
For interpretation, the distinction between a protocol plan and an analysis of collected data is central. The record contains descriptions of intended medication regimens, measurements, and follow-up, but explicitly states that no procedures were performed and no data were collected or analyzed. Statistical methods can describe how a future or completed comparison might be analyzed in general; they cannot recover an estimate from outcomes that are not reported.
10. Multiplicity, Missing Data and Analysis Populations
The planned assessments include pain at several postoperative times, as well as somnolence and dizziness. When many outcomes or time points are tested, multiplicity can increase the chance of obtaining at least one apparently notable result by chance. In general, a statistical plan should identify the primary comparison and explain how secondary outcomes and repeated time points will be interpreted. The record names one primary outcome at one month, but a multiplicity procedure or hierarchy for other assessments is not reported in the registry record.
No data were collected or analyzed, so the record does not describe missing outcome observations in the usual sense of missingness among enrolled and followed participants. It also does not specify an imputation method, a sensitivity analysis, or a rule for incomplete questionnaires. These methods are not reported in the registry record. The absence of reported data should not be recast as complete follow-up or as zero pain.
The analysis population is not reported in the registry record. There is no reported intention-to-treat population, per-protocol population, or definition of who would have been included in an analysis. The primary outcome record says no subjects were assigned treatment. With no analyzed participants or outcomes, the record cannot show how exclusions, adherence, withdrawals, or unavailable assessments would have been handled.
These omissions limit assessment of how the planned outcomes would have been analyzed, but the principal limitation is more basic: the record reports no study procedures or outcome analysis. Multiplicity and missing-data methods therefore cannot be evaluated from observed trial results.
11. What the Result Does, and Does Not, Mean
This registry record is useful for identifying the intended question: a comparison of oral gabapentin and oral pregabalin for pain after PRK, with overall pain measured by VAS at one month. It also describes a randomized, double-masked, parallel-group design and planned assessments of pain, somnolence, and dizziness. Those descriptions document intent, not treatment effects.
The posted results do not establish whether either medicine changed pain, whether the medicines differed from one another, or whether either was associated with adverse events in trial participants. No subjects were assigned treatment, no procedures were performed, and no primary outcome data were collected or analyzed, according to the primary outcome record. There is no estimate of the treatment contrast and no measure of its precision. A conclusion of benefit, lack of benefit, equivalence, or safety would go beyond the record.
The listed enrollment of 8 should not be read as evidence that 8 participants completed treatment or posted outcome measurements. The brief summary describes a plan for 104 patients, but the record does not resolve the difference between that plan and the enrollment field. It explicitly states that no subjects were assigned treatment. The reason for termination and any explanation for the discrepancy are not reported in the registry record.
Likewise, zero participants at risk or affected in the adverse-event entries cannot be interpreted as evidence of no harms when the record reports no treated participants. Null death entries do not provide a mortality result. The registry record can support statements about the planned study and its lack of reported data, but it cannot answer the clinical comparison it set out to address.
12. Why This Trial Matters Statistically
This record illustrates why design descriptions and outcome evidence must be kept separate. Randomization, masking, and a defined primary endpoint are features of a planned comparison, but they do not by themselves provide an estimate of treatment effect. That estimate requires observed outcomes from participants assigned to the groups. The registry states that no subjects were assigned treatment and no data were collected or analyzed.
The distinction between intended enrollment and analyzed participants also matters. The brief summary describes a planned enrollment of 104, while the enrollment field lists 8. Neither entry should be treated as the size of an outcome analysis. The primary outcome record says no subjects were assigned treatment, so there are no posted group results to interpret. This avoids confusing registry metadata with evidence from participants.
Statistical precision cannot be assessed without an estimate and its uncertainty. A sample-size illustration is not observed power and cannot stand in for an outcome analysis. Likewise, a zero count in an adverse-event record is not reassuring evidence about treatment exposure when the record says no subjects were treated. The meaning of a count depends on the population at risk and whether the study procedures occurred.
For clinical researchers, the central statistical lesson is that an attractive design description cannot overcome absent data. The record identifies an important planned comparison and outcome, but leaves unanswered the treatment effect, its precision, and the handling of repeated outcomes. The posted information is therefore informative about the registry record’s status and limitations, not about comparative clinical performance.
13. 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 limitation is the explicit lack of study conduct and outcome data. The record states that no subjects were assigned treatment, no study procedures were performed, and no data were collected or analyzed. The endpoint therefore has no observed values, and no treatment contrast or uncertainty estimate can be assessed.
There is also a discrepancy between the enrollment field, which lists 8, and the planned enrollment of 104 described in the brief summary. The record does not explain the difference. The enrollment field should not be interpreted as the number treated or analyzed, particularly because the primary outcome record says there were no treatment assignments.
The reason the study was terminated is not reported in the registry record. The record does not explain whether recruitment began, what led to termination, or whether information exists outside the registry. Eligibility criteria, randomization procedures, masking details, and a detailed statistical analysis plan are also not reported in the registry record.
The primary outcome label does not specify how “overall” pain was defined or how the VAS assessments would have been combined. The summary describes several planned assessment times and additional symptom measures, but no analysis plan for those repeated outcomes is reported in the registry record. Missing-data procedures and analysis populations are not reported either. These limitations prevent assessment of both the planned methods in detail and any treatment result; the absence of results is not evidence of no effect.
14. Related Tutorials
15. Related Statistical Calculators
16. Sources
- ClinicalTrials.gov: Comparison of Oral Gabapentin and Pregabalin in Postoperative Pain Control After Photorefractive Keratectomy — NCT00954187.
- Registry record last updated 2017-01-09; status last verified 2016-11.
- Results first posted 2014-09-25.
- 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.
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17. Record Summary
The registry describes a prospective, randomized, double-masked, parallel-group comparison of oral gabapentin and pregabalin for postoperative pain after PRK. The planned primary outcome was decreased overall pain score measured by VAS at one month. The brief summary describes planned pain, somnolence, and dizziness assessments and gives medication schedules for the two arms.
The record lists enrollment of 8 and describes a planned enrollment of 104. It is marked terminated. The primary outcome record states that no subjects were assigned treatment, no study procedures were performed, and no data were collected or analyzed. No primary outcome estimate, confidence interval, statistical test, or analyzed population is reported. The reason for termination and the explanation for the enrollment discrepancy are not reported in the registry record. The posted information describes the intended trial but supplies no comparative efficacy or safety result.