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 Ridinilazole Versus Vancomycin Treatment for Clostridium Difficile Infection (NCT03595553), a randomized phase 3 study. The primary outcome is Number of Participants With Sustained Clinical Response (SCR) Defined as Clinical Response and no Recurrence of CDI Through 30 Days Post End of Treatment (EOT)..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03595553 |
| Phase | Phase 3 |
| Condition | Clostridioides Difficile Infection |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Quadruple |
| Enrollment | 759 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Summit Therapeutics |
| Results posted | Yes |
2. Clinical Question
Population
The trial enrolled participants with Clostridioides difficile infection (CDI). Further eligibility details and a description of the primary analysis population are not reported in the registry record.
Intervention
The experimental treatment was ridinilazole 200 mg twice daily for 10 days. The registry describes the study as comparing its efficacy and safety with an active treatment.
Comparator
The active comparator was vancomycin 125 mg four times daily for 10 days. The registry identifies both treatments as drugs and describes a randomized, parallel-group study.
Primary question
The primary outcome was the number of participants with sustained clinical response at Day 40. Sustained response required clinical response and no CDI recurrence through 30 days after the end of treatment. The registry's study rationale was to assess whether ridinilazole could improve sustained response relative to vancomycin, while also comparing safety and tolerability. However, arm-specific primary endpoint counts and an effect estimate are not reported in the registry record, so the comparative outcome cannot be described from these registry entries.
The primary question is clinically framed around both initial response and recurrence after treatment. That distinction matters: the endpoint is not simply whether symptoms improved during treatment, but whether response was sustained without a recurrence during the stated follow-up period. The registry also lists secondary outcomes covering clinical response, clinical cure, later sustained-response time points, and measures of bile acids and gut microbiota. These outcomes broaden the topics assessed, but they do not substitute for missing primary endpoint results.
3. Trial Design
The registry describes a phase 3, randomized, quadruple-masked, parallel-group, active-controlled study. It lists an enrollment of 759 and a completed status. The sponsor is Summit Therapeutics. The recorded study start date is 2019-01-28, and the primary completion date is 2021-11-17.
Participants were assigned to ridinilazole or vancomycin. Ridinilazole was described as 200 mg twice daily for 10 days; vancomycin was described as 125 mg four times daily for 10 days. The registry identifies the study as randomized and reports quadruple masking, but does not specify which individuals or roles were masked. The allocation procedure, including any details about sequence generation or concealment, is not reported in the registry record.
Parallel-group design means the assigned treatment groups are followed alongside one another rather than participants crossing between treatments. In general, random assignment can help make groups comparable at the start of a trial, while masking can reduce the influence of treatment knowledge on care, outcome assessment, or reporting. Those are general design principles; the registry does not provide enough detail to assess how these procedures were implemented.
The primary endpoint was assessed at Day 40, with the outcome description also referring to assessments at D40, D70, and D100. The registry gives the primary timeframe as Day 40 and defines sustained clinical response by the absence of CDI recurrence through 30 days post end of treatment. Specific follow-up procedures beyond the stated assessments are not reported in the registry record.
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 | Ridinilazole | Vancomycin |
|---|---|---|
| STARTED | 370 | 375 |
| COMPLETED | 312 | 327 |
| NOT COMPLETED | 58 | 48 |
Reasons for not completing this period:
| Reason | Ridinilazole | Vancomycin |
|---|---|---|
| Withdrawal by Subject | 20 | 8 |
| Physician Decision | 3 | 2 |
| Adverse Event | 2 | 5 |
| Death | 24 | 22 |
| Lost to Follow-up | 6 | 7 |
| Other as indicated in CSR | 3 | 3 |
| Sponsor Decision | 0 | 1 |
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.
| Characteristic | Unit | Ridinilazole | Vancomycin | Total |
|---|---|---|---|---|
| Participants analysed | 370 | 375 | 745 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 209 | 213 | 422 |
| Age, Categorical: >=65 years | Participants | 161 | 162 | 323 |
| Age, Continuous | years | 59.1 (SD 17.89) | 59.6 (SD 17.42) | 59.4 (SD 17.64) |
| Sex: Female, Male: Female | Participants | 209 | 227 | 436 |
| Sex: Female, Male: Male | Participants | 161 | 148 | 309 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 40 | 60 | 100 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 322 | 305 | 627 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 8 | 10 | 18 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 1 | 0 | 1 |
| Race (NIH/OMB): Asian | Participants | 11 | 10 | 21 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 10 | 16 | 26 |
| Race (NIH/OMB): White | Participants | 333 | 331 | 664 |
| Race (NIH/OMB): More than one race | Participants | 8 | 8 | 16 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 7 | 10 | 17 |
| Region of Enrollment: United States | participants | 81 | 87 | 168 |
| Region of Enrollment: Canada | participants | 12 | 17 | 29 |
| Region of Enrollment: Europe | participants | 229 | 220 | 449 |
| Region of Enrollment: Mexico | participants | 5 | 11 | 16 |
| Region of Enrollment: Brazil | participants | 3 | 10 | 13 |
| Region of Enrollment: Chile | participants | 2 | 3 | 5 |
| Region of Enrollment: Argentina | participants | 1 | 0 | 1 |
| Region of Enrollment: Peru | participants | 1 | 0 | 1 |
| Region of Enrollment: Israel | participants | 17 | 15 | 32 |
| Region of Enrollment: South Korea | participants | 10 | 9 | 19 |
| BMI | kg/m^2 | 26.64 (SD 5.729) | 26.36 (SD 5.732) | 26.54 (SD 5.748) |
6. Primary Endpoint
The registry lists the primary outcome as Number of Participants With Sustained Clinical Response (SCR) Defined as Clinical Response and no Recurrence of CDI Through 30 Days Post End of Treatment (EOT)., measured over Day 40.
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of participants with sustained clinical response (SCR) at Day 40. The registry defines SCR as clinical response with no recurrence of CDI through 30 days after the end of treatment. The investigator or a medically qualified designee was to determine sustained response or recurrence at D40, D70, and D100. The assessment was based on available information, including changes from baseline in unformed bowel movements, CDI signs and symptoms, and the need for CDI medication; the description says the investigator should assess cure or failure in a way that best reflects standard clinical practice.
This endpoint combines response and durability. In general, a response measured only during treatment may not capture whether symptoms return after treatment ends. Including a recurrence condition makes sustained response relevant to both improvement and its persistence over the defined period. The endpoint is recorded as a count of participants, which is a binary-outcome format at the participant level: each participant either meets the stated definition or does not. The registry record does not report the arm-specific counts or the comparative estimate for this primary endpoint, so its observed treatment contrast cannot be interpreted from the endpoint definition alone.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies the trial question and its primary outcome, but the registry entries available for this analysis do not include the primary endpoint results by treatment group. In particular, no ridinilazole or vancomycin count for sustained clinical response, treatment-effect estimate, confidence interval, or test result is reported. The treatment comparison therefore cannot be quantified, and no claim about the direction, size, or precision of a primary-outcome difference can be made from the record details.
This absence is especially important because the primary outcome is a count defined using a clinical-response and recurrence rule. A treatment label, study rationale, or endpoint definition does not establish what happened in either group. The rationale describes the intent to confirm an improvement in sustained response and compare safety and tolerability; it is not a report that an improvement was observed. Similarly, the brief summary's description of a phase 2 study does not provide outcome results for this phase 3 trial.
The available adverse-event figures are descriptive counts for the listed treatment groups. They do not provide a randomized comparison adjusted for follow-up, uncertainty, or other analysis choices. The registry also lists several serious adverse-event terms with percentages, but does not assign those terms to treatment groups in the registry record stated. Those entries should not be treated as a complete comparative safety analysis.
In general, a treatment-effect estimate describes the observed contrast between groups, while its confidence interval conveys the range of values compatible with the data and analysis assumptions. Neither is available for the primary endpoint in the registry entries. A p-value, if reported, would address compatibility with a specified null hypothesis under a statistical model; it would not by itself describe the magnitude or clinical importance of an effect. No primary-outcome p-value is reported.
The completed status and enrollment entry describe the trial record, not its efficacy conclusion. The registry record does not report how missing primary-outcome observations were handled, which population was used for the primary analysis, or whether any prespecified analyses differed from the result ultimately reported. These omissions limit interpretation in addition to the absence of arm-level endpoint results.
9. Statistical Methods Explained
What kind of outcome is this?
The primary outcome is expressed as a number of participants meeting a defined condition. In statistical terms, this is a binary outcome for each participant: sustained response is either recorded or not recorded. A group-level count describes how many participants met the definition, but alone it does not convey the comparative effect unless it is considered alongside the appropriate group denominator and analysis method.
In general, binary outcomes can be compared using measures such as a difference in proportions, a relative measure, or a model-based estimate. These approaches answer related but distinct questions and can yield different presentations of the same data. The registry entries do not report an estimate for the primary endpoint, so no such measure can be interpreted for this trial from the stated information.
What does a confidence interval add?
In general, a confidence interval communicates uncertainty around an estimated effect. A narrow interval indicates greater precision under the analysis assumptions; a wide interval indicates less precision. Its interpretation depends on the chosen effect measure, the data, and the method used to construct it. The primary-outcome confidence interval and the method used to calculate one are not reported in the registry record. Without an estimate and interval, it is not possible to assess the precision of a primary comparison.
A significance test and a confidence interval are not interchangeable descriptions. In general, a p-value summarizes how compatible the data are with a null hypothesis under a specified model. It does not measure the probability that the null hypothesis is true, and it does not show whether an effect is important in practice. A confidence interval gives an estimated range, but it also depends on modeling and sampling assumptions. The registry record does not report a primary endpoint test result or its statistical model.
What can the randomization and masking tell us?
The study is described as randomized, quadruple-masked, and parallel-group. In general, randomization is intended to limit systematic differences between groups at assignment. Masking is intended to reduce the possibility that knowledge of treatment influences participant behavior, clinical care, outcome assessment, or reporting. These design features can strengthen a comparison, but their labels alone do not show whether implementation was successful. Details such as the allocation method, masking roles, and procedures for maintaining the treatment code are not reported in the registry record.
What does the endpoint definition imply?
The endpoint includes both clinical response and no recurrence through the specified post-treatment period. This definition makes timing and assessment rules important. The record describes assessments at D40, D70, and D100, while the primary timeframe is Day 40. It also states that investigators assessed cure or failure using available information that could include bowel-movement changes, CDI signs and symptoms, and the need for CDI medication. The exact operational rules for classifying each case, resolving uncertain assessments, and handling unavailable information are not reported in the registry record.
For any outcome based on clinical assessment, consistency in applying the definition matters. In general, if assessors use different thresholds or if information is missing unevenly, the resulting counts may be affected. Masking may help limit some assessment bias, but the registry entries do not establish how adjudication, training, or disagreements were handled.
How should planning calculations be read?
The stated sample-size assumptions describe planning illustrations computed from an observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. Such illustrations are not observed power and are not evidence that an effect was present. They depend on the effect used as their starting point and on their statistical assumptions. The registry entries do not state the trial's own sample-size justification or design assumptions, so the illustration should not be treated as a reconstruction of the original design rationale.
In general, over-dispersion matters when observed variability exceeds what a statistical model assumes. If a model ignores extra variability, uncertainty may be understated and intervals or tests may be unreliable. The primary endpoint is described as a participant count with a binary definition; the registry does not report an over-dispersion model or any specific model for its primary analysis. It would be inappropriate to infer one.
What remains unknown about the analysis?
The registry record does not report the primary analysis population, treatment of missing outcomes, adjustment variables, handling of protocol deviations, or prespecified model. It also does not report an interim-analysis plan or a statistical analysis plan. These are not minor details: they help define which observations contribute to an estimate and how uncertainty is quantified. Without them, the design description can be explained, but the primary statistical result cannot be reconstructed or fully appraised.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists several secondary outcomes in addition to the primary sustained clinical response outcome. They include clinical response, clinical cure, sustained clinical response over 60 days and 90 days, and measures relating to bile acids and gut microbiota. When a study evaluates several outcomes or time points, the chance of obtaining at least one apparently notable result can increase if each is assessed separately without a plan for multiplicity. In general, multiplicity procedures can control or describe this issue, but the registry record does not report a strategy for handling it.
The record does not report how missing outcome data were handled. This matters because participants without an observed outcome may be excluded, classified using a rule, or addressed with a statistical method; each choice can affect interpretation. The registry's endpoint description refers to assessment based on available information, but it does not specify the analysis rule for unavailable or incomplete information. The amount and pattern of missingness are not reported in the registry record.
The primary analysis population is also not reported. The record does not specify whether the primary comparison was planned for all randomized participants, participants who received treatment, or another defined group. Nor does it report how treatment discontinuation, protocol deviations, or changes in follow-up were addressed. These details affect what population an estimate would describe and how closely it reflects the randomized comparison.
The registry record lists no analyses in the analysis entry. A complete statistical analysis plan, any interim-analysis plan, and any prespecified multiplicity approach are not reported in the registry record. Consequently, the analysis choices and protections against selective emphasis cannot be assessed from these registry entries.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| RIDINILAZOLE 200 MG | 32 | 374 | 8.6% |
| VANCOMYCIN 125 MG | 30 | 377 | 8.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| RIDINILAZOLE 200 MG | 26 of 374 |
| VANCOMYCIN 125 MG | 24 of 377 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| RIDINILAZOLE 200 MG | 124 of 374 |
| VANCOMYCIN 125 MG | 117 of 377 |
Most frequent serious adverse event terms
| Event term | Organ system | RIDINILAZOLE 200 MG | VANCOMYCIN 125 MG |
|---|---|---|---|
| COVID-19 pneumonia | Infections and infestations | 3 of 374 | 3 of 377 |
| Pneumonia | Infections and infestations | 3 of 374 | 1 of 377 |
| Urosepsis | Infections and infestations | 1 of 374 | 3 of 377 |
| Clostridium difficile infection | Infections and infestations | 1 of 374 | 2 of 377 |
| Pulmonary embolism | Respiratory, thoracic and mediastinal disorders | 1 of 374 | 2 of 377 |
| Cardiac failure | Cardiac disorders | 1 of 374 | 1 of 377 |
| Escherichia sepsis | Infections and infestations | 0 of 374 | 2 of 377 |
| Klebsiella infection | Infections and infestations | 1 of 374 | 1 of 377 |
| Pseudomembranous colitis | Infections and infestations | 1 of 374 | 1 of 377 |
| Urinary tract infection | Infections and infestations | 1 of 374 | 1 of 377 |
Most frequent non-serious adverse event terms
| Event term | Organ system | RIDINILAZOLE 200 MG | VANCOMYCIN 125 MG |
|---|---|---|---|
| Diarrhoea | Gastrointestinal disorders | 21 of 374 | 14 of 377 |
| Abdominal pain | Gastrointestinal disorders | 7 of 374 | 7 of 377 |
| Headache | Nervous system disorders | 5 of 374 | 9 of 377 |
| Nausea | Gastrointestinal disorders | 11 of 374 | 3 of 377 |
| Anaemia | Blood and lymphatic system disorders | 6 of 374 | 6 of 377 |
| Hypokalaemia | Metabolism and nutrition disorders | 7 of 374 | 3 of 377 |
| Pyrexia | General disorders and administration site conditions | 7 of 374 | 3 of 377 |
| Dizziness | Nervous system disorders | 5 of 374 | 4 of 377 |
| Constipation | Gastrointestinal disorders | 5 of 374 | 3 of 377 |
| Hypertension | Vascular disorders | 6 of 374 | 2 of 377 |
Serious events with the highest arm-level rate: covid-19 pneumonia (0.8%), pneumonia (0.8%), urosepsis (0.8%), clostridium difficile infection (0.5%), escherichia sepsis (0.5%).
The registry lists serious adverse event counts of 32 for ridinilazole and 30 for vancomycin. The corresponding at-risk counts are 374 and 377. It also lists other adverse event counts of 124 and 117, respectively, and deaths of 26 and 24, respectively. These are descriptive figures from the registry record; they do not, by themselves, establish whether a treatment caused an event or whether the groups differ in safety.
The registry also lists COVID-19 pneumonia, pneumonia, and urosepsis at 0.8% each, and Clostridium difficile infection, Escherichia sepsis, and pulmonary embolism at 0.5% each, among the top serious terms. The registry entries do not specify a treatment-group assignment for these term percentages. They should therefore be read as listed serious-event terms, not as arm-specific rates.
In general, safety comparisons depend on definitions, observation time, exposure, event ascertainment, and the analysis population. The registry entries do not provide a comparative statistical analysis, uncertainty estimates, or further detail on event duration and severity. Counts should not be interpreted as proof of causation, nor as a complete description of the safety profile.
12. What the Result Does, and Does Not, Mean
The registry record establishes that a randomized, quadruple-masked phase 3 study compared ridinilazole with vancomycin for CDI and identifies sustained clinical response as the primary outcome. It also describes the endpoint definition, treatment regimens, several secondary outcomes, and selected adverse-event figures. These details explain the question the study was designed to address and the kinds of outcomes recorded.
They do not establish the primary treatment result. Arm-specific sustained-response counts, an effect estimate, a confidence interval, and a primary-outcome test result are not reported in the registry record. It is therefore not possible to state from these registry entries whether observed sustained response was higher in either group, how large any difference was, or how precise an estimate might be. The stated study rationale is an objective, not a result.
The safety counts likewise do not establish that either treatment is safer. They are descriptive entries without a reported comparative analysis or uncertainty estimate. The serious-event terms and percentages are not assigned to treatment groups in the registry record stated. Any interpretation beyond those recorded counts would require additional information.
In general, a trial's design can support a causal comparison when conduct and analysis are appropriate, but a design description alone does not supply the comparison's outcome. A complete interpretation would require arm-level results and details of the analysis, including how missing observations and analysis populations were handled. Those details are not reported in the registry record. The record can therefore be used to understand the planned clinical question and some safety reporting, but not to determine the magnitude, precision, or statistical significance of the primary treatment contrast.
13. Why This Trial Matters Statistically
This trial is statistically notable for a primary endpoint that combines clinical response with the absence of recurrence after treatment. In general, that kind of outcome differs from a measure focused only on response during therapy: it incorporates persistence over a defined follow-up period. The result depends on how both response and recurrence are assessed, making the endpoint definition and follow-up procedures important to interpretation.
The randomized, quadruple-masked, active-controlled design identifies a framework intended to compare two treatments while limiting some sources of bias. The phase 3 designation and completed status describe the study, but do not themselves indicate what the comparison found. Statistical conclusions require the outcome data and analysis, not the design label alone.
The registry also lists outcomes at multiple time points and outcomes involving clinical cure, bile acids, and gut microbiota. In general, a range of outcomes can provide a broader view of treatment effects, while raising questions about multiplicity and how findings are prioritized. The registry record does not report a multiplicity strategy or the primary statistical analysis details.
Most importantly, the primary arm-level results and comparative estimate are not reported in the registry entries. That absence illustrates a central distinction in clinical-trial interpretation: knowing the question and design is not the same as knowing the result. Without the outcome contrast and its uncertainty, neither the size nor the precision of the primary comparison can be evaluated.
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 consequential limitation for statistical interpretation is that the registry record does not report arm-specific counts for the primary endpoint or a treatment-effect estimate. Without these, the direction, magnitude, and precision of the primary comparison cannot be assessed. The endpoint definition is detailed, but its observed outcome is not included in the registry record.
Key analysis details are also not reported in the registry record. These include the primary analysis population, statistical model, handling of missing outcomes, treatment of protocol deviations, and any adjustment variables. The registry does not report an interim-analysis plan or a multiplicity strategy despite listing multiple secondary outcomes and time points. These omissions make it difficult to assess the robustness and scope of any potential findings.
The primary endpoint description refers to investigator assessment using available information and allows assessment in a way that best reflects standard clinical practice. The registry entries do not report further operational detail on consistency of assessment, adjudication, or how incomplete information was classified. Although quadruple masking is reported, the roles masked and procedures used are not specified.
The available adverse-event entries are limited descriptive figures. The record does not provide comparative estimates, uncertainty, or enough detail to interpret the serious-event term percentages by treatment group. The trial's own sample-size justification is not reported; the stated assumptions concern planning illustrations and do not establish observed power or the basis for the trial's design. These limitations restrict interpretation of both efficacy and safety from the registry entries alone.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Comparison of Ridinilazole Versus Vancomycin Treatment for Clostridium Difficile Infection — NCT03595553.
- Registry record last updated 2026-10-09; status last verified 2026-10.
- Results first posted 2023-03-03.
- 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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18. Record Summary
NCT03595553 is a completed, randomized, quadruple-masked, parallel-group phase 3 study sponsored by Summit Therapeutics. It enrolled 759 participants with Clostridioides difficile infection and compared ridinilazole 200 mg twice daily for 10 days with vancomycin 125 mg four times daily for 10 days. The recorded study start date is 2019-01-28, and the primary completion date is 2021-11-17.
The primary outcome was the number of participants with sustained clinical response at Day 40, defined as clinical response without CDI recurrence through 30 days after the end of treatment. The registry also lists clinical, safety, and microbiome-related outcomes. Arm-specific primary endpoint results and a comparative effect estimate are not reported in the registry record. The adverse-event section lists serious adverse event counts, other adverse event counts, deaths, and selected serious-event terms, but does not provide a full comparative statistical analysis.