Efficacy and Tolerability of Rimegepant for the Prevention of Migraine in Adults With History of Inadequate Response to Oral Preventive Medications: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy and Tolerability of Rimegepant for the Prevention of Migraine in Adults With History of Inadequate Response to Oral Preventive Medications (NCT05518123), a randomized phase 4 study. The primary outcome is Mean Change From Observation Phase (OP) in the Number of Migraine Days Per Month Over the Entire DBT Phase (Weeks 1 to 12).

2. Clinical Question

The clinical question is restricted to adults with a history of inadequate response to oral preventive medications. It does not directly address people outside that population, nor does the primary endpoint assess every aspect of migraine burden. The registry lists additional outcomes concerning migraine-day responses, quality of life, interictal burden, and adverse events. Those outcomes complement the primary comparison but answer different questions.

3. Trial Design

The registry describes NCT05518123 as a phase 4, randomized, quadruple-masked, parallel-group study comparing rimegepant with placebo. Pfizer is listed as the sponsor. The registry records an enrollment of 962 and a status of completed. The recorded study start is 2022-11-07, and the primary completion date is 2025-03-31. These are registry dates and status details; they do not by themselves describe when each participant entered or completed treatment.

The primary endpoint covers the double-blind treatment phase, from the observation phase before randomization through Week 12. Participants assigned to rimegepant were compared with participants assigned to placebo. The primary analysis population was not simply everyone enrolled: the registry defines it as participants randomized only once, who took at least one dose of double-blind study drug, and who had at least 14 days of electronic diary efficacy data in both the observation phase and at least one four-week interval in the double-blind phase. The reported primary arm sizes are 324 for rimegepant and 319 for placebo.

The registry also lists an open-label extension phase and a follow-up phase. The extension adverse-event groups include participants who received rimegepant in the extension after either double-blind assignment. Those phases therefore have different exposure histories from the initial randomized comparison. Their safety counts should not be read as if they were another randomized comparison of rimegepant against placebo throughout.

Randomization is intended to support a comparison between groups while reducing systematic differences in treatment assignment. Masking is intended to limit the influence of treatment knowledge on participants and study conduct. The registry does not report further operational details about how these procedures were 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.

Before assignment: A total of 962 participants signed the informed consent form and were enrolled in the study. Of the enrolled participants, 658 participants were randomized in the study and 304 were not randomized (due to failure to meet eligibility criteria at screening \[282 participants\], withdrawal of consent \[21 participants\], or adverse event \[1 participant\]).

DBT Phase

Reasons for not completing this period:

OLE Phase

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: DBT migraine analysis set: enrolled participants who were randomized only once, took \>=1 dose of DB study drug (rimegepant or placebo), and had \>=14 days of electronic diary (e-diary) efficacy data (not necessarily consecutive) in both OP and \>=1 month (4-week interval) in the DBT Phase.

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: DBT safety analysis set (SAS): enrolled participants who took greater than or equal to (\>=)1 dose of DB study drug (rimegepant or placebo).

6. Primary Endpoint

The registry lists the primary outcome as Mean Change From Observation Phase (OP) in the Number of Migraine Days Per Month Over the Entire DBT Phase (Weeks 1 to 12), measured over Observation phase (28 days prior to randomization), DBT phase (through Month 3 [Week 1 to 12]).

The primary endpoint is the mean change from the observation phase in the number of migraine days per month over the double-blind treatment phase, covering Weeks 1 to 12. A migraine day counted if a participant had a qualified migraine headache or used specified acute migraine-specific medication to treat headache or aura. A qualified headache was defined using headache duration, pain features, and associated symptoms. The registry states that monthly migraine days were prorated to 28 days.

This endpoint captures change in the frequency of migraine days over a fixed treatment period. It is useful for comparing average change between randomized groups, while retaining the meaning of the outcome in days per month. The registry reports least-squares means for each group and a least-squares mean difference from a mixed models analysis. Such model-based means can account for the analysis structure specified by the model, but the registry record does not provide the model specification or its covariates.

The endpoint is an average, so it does not describe every participant’s experience or show how responses varied across individuals. The primary analysis also depends on the registry-defined analysis population and electronic diary observations. It is a measure of migraine-day frequency, not a direct measure of all symptoms, functioning, treatment burden, or safety.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary result comes from a mixed models analysis, with least-squares means and a least-squares mean difference reported by the sponsor. General: a mixed model represents the outcome using both fixed terms and a model for dependence or variation in the observations. In repeated-measures settings, this can allow the analysis to use observations across time while accounting for their structure. The registry identifies the method but does not report the model formula, covariance structure, covariates, or details of how incomplete observations entered the analysis. Those details should not be inferred from the method label alone.

What does the least-squares mean represent?

General: a least-squares mean is a model-based estimate of a group mean, often adjusted for terms included in the model. It is not necessarily the same as a simple arithmetic average of the observed values. The registry reports -2.1 for the rimegepant group and -0.5 for the placebo group, along with the estimated difference of -1.6. Since the model specification is not reported in the registry record, the adjustments behind these estimates cannot be described more specifically.

How should the confidence interval be read?

General: a confidence interval gives a range of estimates compatible with the observed data under the analysis and its assumptions. A narrower interval indicates greater precision than a wider interval on the same scale. The primary between-group interval runs from -2.13 to -1.15 at the 95% confidence level. This range concerns the model’s estimated difference in mean change, not the range of individual participant outcomes. The group-specific intervals are also estimates of group means, not individual response ranges.

What does the p-value say?

General: a p-value measures how unusual data at least as incompatible with a specified null hypothesis would be if that hypothesis and the analysis assumptions held. It is not the probability that the null is correct, a measure of effect size, or a measure of the value of the result to an individual. The sponsor reports p < 0.001 for the primary comparison. The registry does not report whether this test was adjusted for other outcomes or analyses.

Why use a between-group comparison?

General: change within one group alone cannot separate treatment-period change from changes that may also occur without the intervention. A randomized comparator supplies a reference for assessing the difference between groups over the same period. Random assignment supports this comparison by reducing systematic differences in allocation, while masking can limit some influences of treatment knowledge. These design features do not eliminate uncertainty or guarantee that every aspect of study conduct was free of bias.

What can be learned from the planning illustrations?

General: sample-size calculations describe how many participants might be needed under specified assumptions to detect a chosen effect with a chosen power. They are planning illustrations, not observed power and not a retrospective measure of whether the trial “had enough power.” The posted illustrations use a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect set to a stated fraction of the observed effect. They are not the trial’s own design justification. The registry record does not report the trial’s sample-size justification or assumptions used in its original planning.

For binary outcomes, general considerations include the expected event frequency and the size of the difference one wishes to detect. Sparse events can produce imprecise estimates, and the sample size needed to detect a difference can be large when events are uncommon. The planning illustrations should not be treated as evidence that an observed comparison is conclusive. For continuous outcomes, general considerations include outcome variability and the target difference. No dispersion estimate is reported for the primary endpoint in the record’s posted arm results, and a two-arm recalculation is not estimable from those posted summary statistics.

General: over-dispersion occurs when observed variability exceeds what a simple model assumes. If present and unaccounted for, standard errors and intervals may be too optimistic. It is not possible to determine from the registry record whether over-dispersion was assessed or relevant to the primary model. Likewise, the record does not provide enough detail to assess model diagnostics, sensitivity analyses, or the robustness of results under alternative assumptions.

10. Analyses Reported by the Sponsor

The sponsor’s reported primary analysis is a mixed models analysis of the least-squares mean difference. It gives a difference of -1.6 migraine days per month, a 95% confidence interval from -2.13 to -1.15, and p < 0.001. The group-specific least-squares mean changes are also reported. These sponsor estimates form the inferential result for the primary endpoint.

A simple unadjusted recalculation is not available for this continuous endpoint from the posted summary statistics: the registry record marks the required two-arm comparison as not estimable because the necessary values are missing or not estimable. That is not a competing estimate, and it does not imply that the sponsor’s result is incorrect. The registry records no discrepancy between the sponsor analysis and a recalculation.

General: a model-based analysis and an unadjusted calculation can differ because they may use different information and assumptions. If a recalculated estimate conflicts with a sponsor’s own analysis, the sponsor’s analysis takes precedence for the reported trial result. In this case there is no recalculated primary estimate to set against the sponsor analysis. The reported model result should therefore be interpreted on its own terms, with the limits on model detail and missing-data information.

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists multiple outcomes and analyses, but it does not report a multiplicity-control procedure for the primary and secondary tests. Multiplicity matters because the more hypotheses tested, the greater the chance of at least one apparently positive result even when no underlying effects are present. General: procedures such as a prespecified hierarchy or adjusted significance thresholds can manage that issue, but the registry record does not say whether such a strategy was used. The reported p-values should therefore be interpreted with that documentation gap in mind, especially for secondary outcomes.

The primary analysis population is defined using randomization, treatment exposure, and electronic diary completeness requirements. That definition clarifies who contributed to the primary endpoint, but the registry record does not report the number of participants excluded under each criterion or a comparison of included and excluded participants. It also does not report the amount or pattern of missing diary data, the model’s specific missing-data assumptions, or sensitivity analyses addressing missingness.

General: missing data can affect an estimate if the probability of an observation being missing is related to its outcome or to other participant characteristics. Different assumptions about why data are missing can lead to different analyses. A mixed model may use incomplete repeated observations under particular assumptions, but the method label alone does not establish which assumptions were used or whether they are plausible for this study. The registry record does not report enough detail to assess that issue.

The record also does not report an interim-analysis plan, stopping rules, a protocol-level statistical analysis plan, or the sample-size justification. These matters should not be inferred from the completed status or from the posted results. The available information supports interpretation of the reported primary estimate, but it does not allow a full audit of prespecification, multiplicity handling, or missing-data robustness.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

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: immune thrombocytopenia (0.3%), meningitis (0.3%), iiird nerve paralysis (0.3%), migraine (0.3%), pneumonia pneumococcal (0.3%).

During the double-blind treatment phase, the registry lists serious adverse events in 1 participant in the rimegepant group and 5 participants in the placebo group. The corresponding groups at risk are 328 and 324. During the open-label extension phase, serious adverse events are listed for 2 participants in the group that received rimegepant during both phases and 4 participants in the group that received placebo during the double-blind phase followed by rimegepant in the extension. The extension groups at risk are 301 and 294. The registry lists no deaths in the reported double-blind, extension, and follow-up groups.

These are counts from different phases and group definitions. The open-label extension is not a continued randomized comparison of rimegepant against placebo, because both extension groups received rimegepant during that phase. Counts alone do not establish whether a difference is statistically meaningful or attributable to treatment. Serious adverse events are uncommon in the posted groups, so estimates based on them can be uncertain. The registry also lists other adverse-event counts, but the serious-event counts should not be read as a complete description of tolerability or risk.

General: safety interpretation depends on event type, timing, severity, exposure, and follow-up, as well as the number of participants observed. A count of zero deaths in the listed groups does not establish that a risk is absent. The registry record does not report a formal comparative analysis of serious adverse events.

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

The primary result estimates an average difference between randomized groups in change from the observation phase in monthly migraine days over the double-blind treatment phase. The sponsor-reported estimate is -1.6, with a 95% confidence interval from -2.13 to -1.15. The interval and p-value describe statistical uncertainty under the reported model; they do not measure how each participant responded or guarantee that the effect will be the same in other settings.

The result does not mean that every participant experienced fewer migraine days, that all people with migraine would have the same outcome, or that the estimated difference is important to every individual. The registry record does not report a threshold for clinical importance for this primary difference. The outcome captures migraine-day frequency, not the full experience of migraine, daily functioning, all symptoms, or every potential benefit and harm.

The primary analysis pertains to a defined population with a history of inadequate response to oral preventive medications and with the diary and treatment data required for the analysis set. It should not automatically be generalized to populations not described by those eligibility and analysis criteria. The record’s enrollment figure alone does not mean every enrolled participant contributed to the primary estimate.

Nor does statistical significance settle questions about long-term outcomes, comparative performance against other active treatments, or how results would vary across subgroups. The primary endpoint covers the double-blind treatment phase through Week 12; the registry also lists an open-label extension, but that phase does not preserve the initial placebo comparison. These limits distinguish what the posted result estimates from broader questions that the registry record does not answer.

General: statistical evidence is one part of interpreting a clinical trial. Effect size, uncertainty, endpoint relevance, study conduct, and the completeness of reporting all matter. The registry provides a clear primary estimate and its interval, but does not provide all details needed to assess the model, missing-data assumptions, multiplicity strategy, or original sample-size rationale.

14. Why This Trial Matters Statistically

This trial illustrates why the estimated difference between randomized groups is more informative than either group’s change viewed alone. The placebo group provides a concurrent comparison during the same double-blind period, while randomization is intended to make the groups comparable on average. The primary finding is expressed in the endpoint’s own units, monthly migraine days, which makes the magnitude and uncertainty interpretable without converting it into another measure.

It also illustrates the distinction between a model-based result and a simple calculation from summary statistics. The sponsor reports a mixed models estimate, but the posted summaries do not support a two-arm recalculation for this continuous endpoint. Recognizing that boundary avoids treating a missing recalculation as evidence against the sponsor result, or presenting an unsupported calculation as a check on it.

Several statistical questions remain important even when a primary p-value is small. The confidence interval conveys precision; the analysis population defines who contributed; diary completeness and missing-data handling may affect the estimate; and many secondary outcomes raise multiplicity concerns. The registry does not report all the details needed to answer those questions fully.

The secondary measures also show why outcomes must be read according to their definitions. A threshold-based responder outcome, a mean change in migraine days, a quality-of-life score, and a serious adverse-event count are not the same estimand. Their results may add context, but they do not replace the primary comparison or necessarily receive equal evidential weight.

For biostatisticians and clinical researchers, the record is a useful example of balancing a clearly reported primary estimate against incomplete reporting of analysis details. It shows what can be interpreted from the estimate, interval, test, and analysis-set definition, while marking the limits on broader statistical conclusions.

15. 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 statistical method is identified as mixed models analysis, but the registry record does not report its formula, covariates, covariance structure, or diagnostic checks. It is therefore not possible to determine precisely how the model was specified or to reproduce its estimate from the posted summary statistics. The record does not provide a usable two-arm recalculation for the continuous primary endpoint.

The registry defines the primary analysis set through treatment exposure and electronic diary data requirements. It does not report participant flow by analysis criterion, the amount and pattern of missing diary data, or sensitivity analyses under alternative missing-data assumptions. These omissions limit assessment of how the analysis population and incomplete observations may influence the estimate.

The record does not report the trial’s sample-size justification, interim-analysis plan, protocol-level statistical analysis plan, or multiplicity strategy. The posted planning illustrations are based on observed effects and stated assumptions rather than the original design rationale. They cannot establish the trial’s observed power or substitute for an original prospective calculation.

The reported primary estimate applies to the defined analysis population and the double-blind treatment period through Week 12. The registry record does not provide a threshold for clinical importance of the estimated difference. It also does not report subgroup estimates or enough detail to assess consistency across participant characteristics.

Safety interpretation is limited by the reported event counts and different phase-specific group definitions. Extension-phase participants had different exposure histories, and both extension groups received rimegepant. The record does not report a formal comparative analysis of serious adverse events. These limitations do not negate the posted findings, but they restrict how far they can be extended beyond the endpoint, analysis population, period, and comparisons actually reported.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Efficacy and Tolerability of Rimegepant for the Prevention of Migraine in Adults With History of Inadequate Response to Oral Preventive Medications — NCT05518123.
• Registry record last updated 2026-05-22; status last verified 2026-04.
• Results first posted 2026-05-22.
• 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.

19. Record Summary

NCT05518123 is a completed phase 4 randomized, quadruple-masked, parallel-group study of rimegepant 75 mg versus placebo in adults with migraine and a history of inadequate response to oral preventive medications. The registry lists an enrollment of 962, with a recorded start date of 2022-11-07 and primary completion date of 2025-03-31.

The primary endpoint was mean change from the observation phase in monthly migraine days over the double-blind treatment phase through Week 12. The sponsor-reported mixed models estimate was a least-squares mean difference of -1.6, with a 95% confidence interval from -2.13 to -1.15 and p < 0.001. The primary analysis set included 324 participants assigned to rimegepant and 319 assigned to placebo.

The registry lists additional efficacy, quality-of-life, burden, and safety outcomes, including an open-label extension. Important analysis details—including multiplicity handling, missing-data assumptions, and the original sample-size rationale—are not reported in the registry record.