Phase 2 Healthy Volunteer Study to Evaluate the Ability of PRT064445 to Reverse the Effects of Several Blood Thinner Drugs on Laboratory Tests (Module 3 of 4): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Phase 2 Healthy Volunteer Study to Evaluate the Ability of PRT064445 to Reverse the Effects of Several Blood Thinner Drugs on Laboratory Tests (Module 3 of 4) (NCT03551730), a randomized phase 2 study. The primary outcome is Efficacy:Percent Change From Baseline in Anti-fXa Activity at 2 Mins Following Andexanet/Placebo Administration Activity.

2. Clinical Question

3. Trial Design

This was a phase 2, randomized, quadruple-masked, parallel study in healthy volunteers. The registry lists enrollment of 27 and a completed study, with a start date of 2012-12 and primary completion in 2015-09. The official title describes intravenous PRT064445 after dosing to steady state with one of four direct or indirect factor Xa inhibitors; the primary-endpoint population description identifies 26 participants who received andexanet or placebo. The listed Module 3 arms concern enoxaparin and three PRT064445 formulations or doses.

The primary-endpoint summaries include 8 participants in the placebo group and 6 in each active group: 210 mg original formulation, 420 mg original formulation, and 210 mg lyophilized formulation. Those group counts total 26, but the registry does not report why one fewer participant appears in the endpoint population than in the overall enrollment. It also does not report the participant-level flow or reasons for any exclusions.

The endpoint was measured immediately before administration and again 2 minutes after the end of andexanet or placebo administration. Anti-fXa activity was measured with a commercial kit identified in the registry as Coamatic Heparin-82 33 9363, DiaPharma. The registry lists eight outcome measures overall, including the primary endpoint and seven secondary outcomes. Those secondary outcomes include thrombin generation and pharmacokinetic measures such as maximum concentration, area under the concentration-time curve, time to maximum concentration, terminal half-life, clearance, and volume of distribution.

The registry does not report the randomization method, allocation concealment procedures, the specific roles covered by quadruple masking, or the schedule and details for the accompanying inhibitor dosing. The posted record identifies randomization and masking but does not provide enough detail to reconstruct how treatment assignment was 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: Enoxaparin was administered subcutaneously at 40 mg once daily for 6 days to steady-state in an open label fashion. Subjects were then randomized to receive study treatment intravenously on Day 6; such that they ended at 3 hours after the last dose of enoxaparin.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: 26 subjects who received andexanet or placebo were included in the pharmacodynamics (PD) analysis

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: 27 subjects were enrolled in Module 3

6. Primary Endpoint

The registry lists the primary outcome as Efficacy:Percent Change From Baseline in Anti-fXa Activity at 2 Mins Following Andexanet/Placebo Administration Activity, measured over Baseline to 2 minutes following the end of andexanet/placebo administration.

The primary endpoint is the percent change from baseline in anti-fXa activity at 2 minutes following the end of andexanet or placebo administration. Anti-fXa activity is a laboratory measure of factor Xa inhibition. The measure was taken immediately before treatment and at the stated post-administration time, so the endpoint focuses on an early change in a laboratory value rather than a clinical event or a longer-term outcome.

Change from baseline can help describe how a measurement shifts after an intervention while accounting for the participant's starting value. Expressing that change as a percentage places it relative to baseline, although interpretation still depends on the measurement scale and the analysis used. The registry reports group means and standard deviations for the endpoint, and describes the primary summary as a mean of a continuous measure.

The registry reports that anti-fXa activity was measured using a commercial kit. It does not report further assay performance characteristics, such as measurement precision, or details about handling values outside the assay's measurable range. Those details matter because laboratory endpoints depend on the assay and its measurement properties.

This endpoint can address whether the groups differed in an early laboratory response under the study conditions. It cannot, by itself, establish how participants would fare on clinical outcomes. The registry outcome description does not present a clinical event endpoint as the primary measure.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: each participant has a percent-change measurement, and the registry summarizes each group by a mean and standard deviation. A mean gives a measure of the group's central value. A standard deviation describes the spread of participant measurements around that mean; it is not a confidence interval and does not directly show the precision of the group mean.

What does ANCOVA do?

General explanation: Analysis of covariance (ANCOVA) compares group outcomes while adjusting for one or more covariates. In a baseline-adjusted analysis, baseline measurement may be included as a covariate, but the registry does not specify which covariates were included in these ANCOVA models. The method can estimate adjusted group means or contrasts and may account for baseline differences, depending on the model specification. The exact covariates, model assumptions, and handling of model diagnostics are not reported in the registry record.

The registry identifies the reported parameter as a difference in least-squares means. Least-squares means are model-based adjusted means, rather than necessarily the simple arithmetic means printed in the group summaries. A difference between least-squares means is consequently not automatically expected to match a subtraction of the displayed raw group means. The record does not explain the scale or coding used for the reported contrast values, so their numerical interpretation beyond the stated parameter is limited.

How should the p-values be read?

General explanation: A p-value evaluates how compatible the observed data are with a null hypothesis under a specified statistical model. It does not measure the probability that a treatment effect is real, nor does it measure the size or importance of an effect. The reported p-values are < 0.001 for all three ANCOVA comparisons. The registry labels the comparisons as superiority analyses, but does not give confidence intervals alongside the p-values. Without an interval estimate, the range of effect values consistent with the reported model cannot be assessed from the posted comparison results.

A confidence interval, in general, gives a range of estimates produced by a method designed to have a stated coverage property over repeated use. It also helps communicate precision: wider intervals indicate less precision than narrower intervals under the same framework. No confidence limits are reported for the ANCOVA contrasts in this record. The absence of those limits does not change the reported p-values, but it limits how fully the adjusted contrasts can be interpreted.

Why are small groups important?

General explanation: Estimates from small groups can be sensitive to the measurements of individual participants, and estimates of variability may themselves be uncertain. Here, the posted primary-endpoint summaries include 8 participants in placebo and 6 in each active group. Those counts describe the endpoint summaries; the registry does not provide participant-level measurements, which would be needed to independently assess distributions, outliers, or model fit. The listed standard deviations summarize observed spread, but cannot replace an uncertainty interval for a group contrast.

The sample-size illustrations associated with trial results are planning calculations, not observed power. In general, a planning calculation uses assumptions about the target effect, significance level, allocation, and statistical model to estimate a sample size for a future study. The stated assumptions for the illustrations use a two-sided significance level of 0.05, equal allocation, a normal approximation, and effects defined as a fraction of the observed effect. They do not represent the original study's design justification, which is not reported in the registry record. These illustrations should not be interpreted as evidence that the completed trial had a particular probability of detecting an effect.

What does the design imply for interpretation?

General explanation: Randomization is intended to make treatment groups comparable with respect to both measured and unmeasured characteristics on average, though it cannot guarantee balance in any particular small trial. Masking can help reduce some sources of bias in treatment administration and assessment, but the registry's label of quadruple masking does not identify who was masked or how masking was maintained. The parallel design means the registry presents separate groups rather than repeated crossover treatment periods; further design details are not reported.

Over-dispersion is a general concern when observed variability exceeds what a chosen statistical model assumes. For a continuous endpoint, model misspecification can affect standard errors, p-values, and confidence intervals. The registry does not report diagnostics or alternative variance methods, so it is not possible to determine from the record whether over-dispersion was assessed or addressed. This is a general model consideration, not a reported finding about this trial.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Placebo", "Module 3 (210 mg Bolus) Original", "Module 3 (420 mg Bolus) Original", "Module 3 (210 mg) Lyophilized")
n   <- c(8, 6, 6, 6)
m   <- c(-3.57, -70.8, -60.83, -69.85)
sp  <- c(12.8, 6.98, 8.39, 7.46)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Placebo  8  -3.570  12.800  -14.271  7.131
CARM  Module 3 (210 mg Bolus) Original  6  -70.800  6.980  -78.125  -63.475
CARM  Module 3 (420 mg Bolus) Original  6  -60.830  8.390  -69.635  -52.025
CARM  Module 3 (210 mg) Lyophilized  6  -69.850  7.460  -77.679  -62.021

11. Analyses Reported by the Sponsor

The registry reports the sponsor's ANCOVA results as least-squares-mean differences of -0.23, -0.20, and -0.23 for the three active-treatment comparisons with placebo, respectively. Each comparison is labelled as superiority and has a p-value of < 0.001. Confidence limits are not reported, and the registry does not describe the model covariates or the scale behind the contrast values.

A recalculated, unadjusted two-arm comparison cannot be interpreted from the posted summaries: the registry record identifies values as missing or not estimable for a two-arm comparison of this continuous endpoint. Accordingly, there is no independent recalculated contrast to set against the ANCOVA result. The unadjusted group means and standard deviations remain useful descriptions, but they are not replacements for the sponsor's adjusted analysis.

The record does not flag a discrepancy between the reported analysis and a recalculation. This is not evidence that the ANCOVA model can be independently reproduced; the information needed to reconstruct it is not reported. The posted sponsor analysis is therefore the available inferential result, with its limits in interpretation noted above.

12. Multiplicity, Missing Data and Analysis Populations

The registry reports three primary-outcome ANCOVA comparisons: each of the three active-treatment groups versus placebo. It does not report whether or how multiplicity across these comparisons was handled. When multiple hypotheses are tested, the chance of at least one false-positive result can increase if no adjustment or other prespecified strategy is used. That is a general statistical concern; the record does not establish whether any adjustment was made. The reported p-values should be read as presented, without assuming a particular multiplicity procedure.

The record lists eight outcome measures overall and seven secondary outcomes. These include a thrombin-generation measure and several pharmacokinetic measures. It does not report how many analyses were planned for each outcome, whether outcomes or time points were selected after looking at the data, or how multiplicity across outcomes was addressed. Those details are not reported in the registry record, so the overall inferential context cannot be reconstructed from the posted information.

The registry identifies 26 participants who received andexanet or placebo as the pharmacodynamics analysis population. Endpoint group counts are 8 for placebo and 6 for each active arm. Overall enrollment is 27. The record does not explain the difference between enrollment and the analysis population, or specify whether analysis followed an intention-to-treat, per-protocol, or other principle. It also does not report the number of missing measurements by group, reasons for missingness, imputation methods, or sensitivity analyses.

Missing-data handling matters because an analysis based only on participants with available measurements can be biased if availability is related to treatment or outcome. This is a general consideration, not a claim that missingness occurred or caused bias in this trial. The posted record does not provide enough information to assess that possibility. Likewise, the registry does not report interim analyses or a statistical analysis plan. No assumptions about those procedures can be made from the posted results.

13. 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 3% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists no serious adverse events among the 8 participants in the placebo group or among the 6 participants in each of the three active-treatment groups. This is a count of observed serious adverse events in the recorded groups, not proof that serious events cannot occur. The groups are small, and the record does not provide confidence intervals or additional detail about the observation period for adverse events.

Other adverse events are reported for 5 of 8 placebo participants, 4 of 6 participants in the 210 mg original-formulation group, 4 of 6 participants in the 420 mg original-formulation group, and 5 of 6 participants in the 210 mg lyophilized-formulation group. These are participant counts reported as affected, not counts of all event occurrences. The registry does not list the most frequent serious adverse-event terms; no serious-event terms are listed. Death counts are not reported in the registry record.

These figures describe events recorded during this study and should not be treated as a comparative safety estimate with high precision. In general, adverse-event comparisons depend on definitions, follow-up, ascertainment, and the number of participants observed. The registry's posted figures do not provide enough detail to assess all those aspects, and the small group sizes limit the information conveyed by zero serious events.

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

The results describe the short-term change in a laboratory measure after andexanet or placebo administration among healthy volunteers in this study. The primary summaries show negative mean percent changes in the three active groups and a mean closer to zero in the placebo group. The registry also reports ANCOVA comparisons labelled as superiority, each with p < 0.001. This supports describing the posted data as showing statistically significant adjusted comparisons under the reported analyses, while recognizing that the contrast scale and model details are not explained.

The results do not establish a clinical benefit or harm. Anti-fXa activity is a laboratory endpoint, and the primary outcome is measured 2 minutes after administration. The registry does not report a primary clinical event outcome. A change in a laboratory measure cannot on its own determine whether a participant experiences a meaningful health outcome.

The study was conducted in healthy volunteers, and the primary endpoint analysis included 26 participants. These findings should not be assumed to apply to other populations or clinical settings. The registry does not supply evidence about longer-term outcomes, and the outcome's stated measurement time is limited to the early post-administration assessment.

The record also does not permit a firm interpretation of the relative performance of the three active regimens. Their group means differ, but there are no posted direct comparisons among those groups. The ANCOVA comparisons are each against placebo, and their estimates are reported without confidence intervals. The reported p-values do not describe the precision or practical importance of the treatment contrasts.

Finally, the absence of serious adverse events in these small groups is a description of the observed record, not a guarantee of safety. The other-adverse-event counts show that such events were recorded in every group. The registry does not provide sufficient detail to characterize the full range, severity, or timing of those events. The most defensible reading is limited to the recorded laboratory summaries, adjusted comparisons, and adverse-event counts under the study conditions.

15. Why This Trial Matters Statistically

This trial illustrates why statistical interpretation requires both descriptive summaries and model-based comparisons. The group means and standard deviations show the observed endpoint values and spread, while the ANCOVA results address adjusted comparisons. Those quantities answer related but different questions and need not match numerically. In this record, the contrast values are not explained on a scale that can be directly related to the raw group summaries, which makes clarity about model output especially important.

The study also highlights the importance of precision estimates. Small p-values are reported, but confidence intervals for the adjusted contrasts are absent. Without those intervals, readers cannot assess the range of contrast values compatible with the reported analysis. This matters even when the p-values are small: statistical evidence against a null hypothesis is not the same as a precise estimate of effect magnitude.

Three active regimens are compared with a shared placebo group, and the endpoint population is small. That structure raises general questions about multiplicity, direct treatment comparisons, and the stability of estimates. The registry does not report how multiplicity was addressed and does not report direct comparisons among active groups. The listed sample-size illustrations are planning aids based on assumptions, not observed power and not evidence about the study's original design rationale.

Finally, the primary measure is an early laboratory outcome in healthy volunteers. Clear distinctions among laboratory change, adjusted statistical contrasts, and clinical outcomes are essential. The record offers information about the first two, but the primary endpoint does not answer a clinical-event question. This is a useful example of how statistical significance, precision, study population, and outcome relevance each shape interpretation.

16. 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 registry record leaves several details unavailable for independent interpretation. It does not explain the covariates in the ANCOVA model, the scale or coding for the least-squares-mean differences, or the reasons confidence intervals are absent. The analysis cannot be reproduced from the posted summaries, and the recalculated unadjusted two-arm comparisons are identified as missing or not estimable.

Information about missing data and analysis populations is limited. The record states that 26 participants were included in the pharmacodynamics analysis, while overall enrollment was 27, but does not explain the difference. It does not report endpoint availability by participant, reasons for exclusions or missing measurements, or a missing-data strategy. The registry also does not identify an intention-to-treat or other analysis principle.

The record does not report multiplicity handling across the three comparisons, across the eight outcome measures, or across any additional analyses. It also does not report an analysis plan, interim analyses, or the study's sample-size justification. These omissions mean that the intended inferential framework cannot be fully assessed from the registry entry alone.

The endpoint is an early laboratory measurement, and the primary analysis population consists of healthy volunteers. The record does not provide clinical-event results as the primary outcome or information about longer-term consequences. Group sizes are limited, and the adverse-event counts therefore describe what was observed without establishing the frequency of uncommon events. Details of adverse-event follow-up, severity, and ascertainment are not reported in the registry record.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Phase 2 Healthy Volunteer Study to Evaluate the Ability of PRT064445 to Reverse the Effects of Several Blood Thinner Drugs on Laboratory Tests (Module 3 of 4) — NCT03551730.
• Registry record last updated 2023-02-22; status last verified 2023-02.
• Results first posted 2018-08-13.
• 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.

20. Record Summary

This completed phase 2 randomized, quadruple-masked, parallel study enrolled 27 healthy volunteers. The primary endpoint was percent change from baseline in anti-fXa activity 2 minutes after the end of andexanet or placebo administration. The pharmacodynamics analysis included 26 participants: 8 in the placebo group and 6 in each of three active-treatment groups.

The registry reports group means and standard deviations, plus three ANCOVA comparisons against placebo. Each comparison is labelled as superiority, with p < 0.001; confidence intervals are not reported. The record lists seven secondary outcomes and reports no serious adverse events in any group. It does not report the model covariates, multiplicity procedure, missing-data handling, or a direct comparison among the active groups. Results concern an early laboratory endpoint in healthy volunteers and should be interpreted within that scope.