Bioequivalence Study of Two Oral Nitisinone Formulations to Treat Hereditary Tyrosinemia (HT-1): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Bioequivalence Study of Two Oral Nitisinone Formulations to Treat Hereditary Tyrosinemia (HT-1) (NCT02750345), a randomized phase 1 study. The primary outcome is Maximum Observed Plasma Concentration (Cmax).

2. Clinical Question

3. Trial Design

This completed phase 1 study was randomized and used a crossover model. The official title describes a three-period comparison of two oral nitisinone formulations with Orfadin in healthy subjects under fasting conditions. In a crossover study, each participant receives more than one treatment over different periods, so treatment comparisons can use measurements from the same participant as well as comparisons between participants. This design can be useful for pharmacokinetic questions because stable differences between participants may contribute less to a within-participant comparison.

The registry lists six treatment sequences. They vary the order of Test Product 1, Test Product 2, and the reference product across the periods. The sequence descriptions specify a single 10 mg dose of each assigned formulation under fasting conditions. The record does not report the duration of each period, washout intervals, or how period and sequence effects were handled in the analysis.

Allocation is recorded as randomized, while masking is recorded as none. The registry therefore does not describe masking of participants or study personnel. Enrollment was 24, and the record is marked completed. The study began in 2016-03 and reached primary completion in 2016-05. These dates describe the registry timeline; they do not establish when individual analyses were conducted.

The study addressed pharmacokinetic bioequivalence rather than clinical outcomes in people with hereditary tyrosinemia. Although the condition named in the registry is hereditary tyrosinemia, type I, the study population was healthy subjects. The record does not report a treatment comparison on symptoms, disease control, or other clinical outcomes. Nor does it report details of sequence allocation, sample-size justification, or operational procedures beyond the treatment descriptions.

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.

Intervention 1

Reasons for not completing this period:

Intervention 2

Intervention 3

Analysis population for the primary outcome, as defined in the registry: All subjects for whom the primary pk parameters Cmax and AUC (0-120) could be calculated for at least two treatment periods (where one of which is the reference product), and who had no major protocol deviations thought to impact on the analysis of pk data were included in the statistical pk analysis for the study.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Maximum Observed Plasma Concentration (Cmax), measured over 0 - 120 hours post-dose.

The primary endpoint was maximum observed plasma concentration, or Cmax, measured over 0 - 120 hours post-dose. Cmax is the highest measured concentration of a drug in plasma during the specified observation period. It describes the peak concentration reached in that sampling window, rather than the total amount of drug exposure over time or the time at which the peak occurs.

Pharmacokinetic comparisons commonly use Cmax to assess whether formulations produce similar peak exposure. This is relevant to bioequivalence because a formulation may affect the rate or extent to which a drug becomes available in the body. Cmax is usually considered alongside an exposure measure such as area under the concentration-time curve. The registry lists AUC (0-72) and AUC (0-∞) among the secondary outcomes, as well as Tmax, λz, and t1/2.

The posted primary results are geometric means with geometric coefficients of variation. Those summaries describe the concentration distribution within each treatment group, but do not by themselves quantify the test-to-reference contrast or its precision. The registry does not report the comparative Cmax estimates, confidence intervals, or a conclusion against prespecified bioequivalence criteria. Thus the posted primary endpoint summaries can be described, but they cannot establish the study's bioequivalence conclusion on their own.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The main statistical feature is the crossover design. Rather than assigning each participant to only one formulation, the study randomized participants to treatment sequences in which they received Test Product 1, Test Product 2, and the reference across treatment periods. In general, crossover designs can improve precision when a participant's measurements under different treatments are correlated: stable participant characteristics then contribute less to the within-participant contrast. This benefit depends on suitable conduct and analysis. The registry record does not report the washout schedule, period duration, or model used to account for sequence and period effects.

What does a geometric mean describe?

Pharmacokinetic concentrations are often positively skewed and are frequently analyzed on a logarithmic scale. A geometric mean summarizes the center of such data after accounting for that multiplicative scale. It is not the same as an arithmetic average. The posted Cmax geometric means are 1278.0 ng/mL for Test Product 1, 1272.0 ng/mL for Test Product 2, and 1340.0 ng/mL for the Reference Product. They give a treatment-specific description, not the comparative estimate required to assess bioequivalence.

How should the variability measure be read?

The geometric coefficient of variation describes variability relative to the geometric mean on a multiplicative scale. The posted values are 17.8 for Test Product 1, 16.6 for Test Product 2, and 17.3 for the Reference Product. It is a measure of spread, not a measure of uncertainty in the treatment comparison. A confidence interval, in contrast, describes the range of comparative values compatible with the data and analysis under the method's assumptions. The registry does not report confidence intervals for the primary comparison.

Why is a treatment contrast needed?

Bioequivalence is a comparative question: it concerns the relationship between exposure under a test formulation and exposure under the reference. A conventional bioequivalence assessment estimates a test-to-reference contrast and evaluates its confidence interval against prespecified acceptance limits. This approach combines the estimated difference with its uncertainty. Similar-looking group summaries cannot replace that procedure. The record does not report the comparative Cmax estimates, confidence intervals, acceptance limits, or a formal decision, so those elements cannot be reconstructed from the posted means and variability summaries.

What does the analysis population mean?

The primary pharmacokinetic analysis included subjects whose Cmax and AUC (0-120) could be calculated for at least two treatment periods, one of which was the reference, and who had no major protocol deviations thought to affect the pharmacokinetic analysis. This is a defined analysis population, not automatically the same as everyone enrolled or everyone assessed for safety. The registry does not report the number excluded for each reason, individual missingness, or the handling of incomplete periods. The primary treatment summaries each list 23.0 subjects; the safety record has different at-risk counts for the reference treatment.

What information is missing for statistical verification?

The registry records zero analysis records and does not provide the model specification, transformation details, treatment ratios, standard errors, confidence intervals, p-values, or a sponsor conclusion. It also does not report the statistical plan, any interim analyses, or sample-size justification. These omissions prevent an independent check of the comparative analysis and its precision.

General statistical principle: a design's ability to estimate a treatment contrast depends not only on the number of observations but also on variability, within-subject correlation, missingness, and the planned analysis. A planning calculation based on an observed effect is an illustration under stated assumptions, not observed power and not a substitute for the trial's analysis. The registry's stated planning assumptions refer to a two-sided significance level of 0.05, equal allocation, a normal approximation, and effects expressed as a fraction of the observed effect. The registry record does not report the study's own sample-size justification or planning result. No new power estimate can be inferred from the endpoint summaries alone.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists the primary Cmax outcome and secondary outcomes covering AUC (0-72), AUC (0-∞), Tmax, λz, and t1/2. It records seven outcome measures but lists five secondary outcomes. The record does not explain the remaining outcome measures or report results for the listed secondary outcomes. It also does not describe a multiplicity adjustment or a hierarchy for testing outcomes. Without that information, it is not possible to determine how the sponsor handled the risk of chance findings across multiple endpoints or comparisons.

Multiplicity is a general statistical concern when several hypotheses are evaluated. The more comparisons considered, the greater the opportunity for an apparently notable result to arise by chance if each is interpreted independently. Planned outcome priorities and any adjustment method help readers understand the strength of evidence. Neither the statistical plan nor a multiplicity strategy is reported in the registry record. This absence should not be taken as proof that no such plan existed; its details are simply not reported in the registry record.

The primary population description requires calculable pharmacokinetic parameters for at least two periods, including the reference, and excludes major protocol deviations thought to affect pharmacokinetic analysis. The registry does not report participant-level missing data, reasons for incomplete measurements, exclusions by treatment sequence, or methods for handling missing observations. It does not provide a full accounting of the relationship between enrollment and the primary analysis population.

These limitations matter especially in a crossover study, where incomplete treatment periods can affect the within-participant comparison. The record also does not report whether the primary analysis included all randomized participants or how deviations were assessed. The stated primary population criteria are the information available; further assumptions about missingness or analysis populations are not justified.

11. Safety Results

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

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The adverse-event record reports zero serious adverse events for Test Product 1 among 23 at risk, zero for Test Product 2 among 23 at risk, and zero for the Reference Product among 24 at risk. The record does not list any serious adverse-event terms. These are counts recorded for the study treatments, not evidence that the risk of serious events is absent.

For other, non-serious adverse events, the record reports 3 affected participants among 23 at risk for Test Product 1, 1 among 23 for Test Product 2, and 1 among 24 for the Reference Product. These counts should be read as descriptive safety information. The registry does not provide event-level details, timing, severity, relatedness assessments, or comparative statistical analyses in the registry record reported.

Deaths are not reported in the registry record. The at-risk counts differ from the primary pharmacokinetic analysis counts, so they describe a safety accounting rather than the primary endpoint population. The record does not establish whether an event count reflects unique participants across all periods or how events were attributed when a participant received multiple treatments. Because this was a phase 1 study in healthy subjects, these counts do not answer broader safety questions in people with hereditary tyrosinemia.

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

The study was designed to compare the pharmacokinetic profile of two oral nitisinone tablet formulations with Orfadin under fasting conditions. It provides posted geometric mean Cmax values and geometric coefficients of variation for each treatment, along with counts for reported adverse events. Those data describe the observed endpoint summaries and recorded safety counts in this study.

The record does not report comparative Cmax estimates, confidence intervals, prespecified bioequivalence limits, or a formal bioequivalence conclusion. Therefore, the treatment-specific summaries cannot establish whether either test formulation met bioequivalence criteria. Nor can the results establish a clinical benefit or lack of benefit: the primary endpoint was a pharmacokinetic measure, and the participants were healthy subjects rather than patients with hereditary tyrosinemia.

The study's crossover design means the most relevant comparison would account for the repeated treatment observations within participants and the treatment sequence. The separate geometric means and variability values do not contain enough information to reproduce that analysis. The record also does not report the model, the handling of incomplete periods, or comparative results for the secondary pharmacokinetic outcomes.

The adverse-event counts are limited descriptive observations. Zero serious adverse events were reported for each treatment group, and other adverse events were reported as counts. These findings do not demonstrate that serious events cannot occur or define safety in other populations, settings, or durations of use. The registry record does not report deaths, detailed event descriptions, or a statistical comparison of safety outcomes.

In short, the registry supports a description of the study design, endpoint summaries, and recorded event counts. It does not support a definitive independent judgment about bioequivalence or clinical outcomes. The absent comparative analysis and its uncertainty are central to interpreting what this record can establish.

13. Why This Trial Matters Statistically

This trial illustrates a key distinction in bioequivalence reporting: treatment-specific averages are not the same as the comparative estimate that answers the scientific question. The posted Cmax geometric means provide a useful description of each formulation's observed concentration summary. A formal bioequivalence assessment, however, depends on the test-to-reference contrast and the uncertainty around it, considered against prespecified limits.

The crossover design also makes the statistical structure important. Participants received treatments in randomized sequences, so an appropriate comparison should account for repeated measurements within participants. Separate group summaries do not show how observations from the same participant relate to one another. That relationship can influence the precision of the treatment contrast, and cannot be recovered from the reported means and coefficients of variation alone.

The record is useful for distinguishing study design information from analysis information. It identifies the population, treatments, endpoint, and some descriptive results, but does not report comparative estimates, confidence intervals, the statistical model, or a formal conclusion. This makes clear why endpoint summaries alone should not be treated as a complete inferential result.

It also demonstrates the importance of keeping pharmacokinetic and clinical questions separate. Cmax and the listed secondary endpoints concern drug concentration and disposition. They are not direct measures of disease control or patient experience, and the study enrolled healthy subjects. The record's safety counts likewise have a narrow scope and should not be generalized beyond the study context.

For biostatisticians and clinical researchers, the central lesson is to look for the estimand, analysis population, comparative method, and uncertainty measures that correspond to the stated objective. Where these are absent from the registry record, the appropriate interpretation is descriptive and limited rather than a reconstruction of an unreported analysis.

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 principal limitation for interpreting the primary result is that only treatment-specific Cmax summaries are reported. The registry record does not report the test-to-reference estimates, confidence intervals, formal bioequivalence limits, or sponsor conclusion. These missing elements prevent an independent assessment of whether the primary objective was met.

The record does not describe the statistical model used for this crossover comparison, including how treatment, period, and sequence were handled. It does not report washout intervals or period duration. These design and analysis details matter when interpreting repeated pharmacokinetic measurements, but cannot be inferred from the sequence descriptions.

The analysis population is described by eligibility criteria, but the registry does not report reasons for exclusion, incomplete treatment periods, or the handling of missing pharmacokinetic measurements. The posted primary summaries list 23.0 subjects for each treatment, while safety counts use a different at-risk count for the reference. The record does not provide further reconciliation of those counts.

Although secondary pharmacokinetic outcomes are listed, their results are not reported in the registry record recorded. The registry also does not report a statistical plan, multiplicity strategy, sample-size justification, interim analysis details, or the rationale for the enrollment target. The completed status and enrollment count do not substitute for these methodological details.

Finally, the study was conducted in healthy subjects and focused on pharmacokinetic outcomes under fasting conditions. Its endpoint and population do not directly answer clinical effectiveness questions in hereditary tyrosinemia. Safety reporting is also limited to adverse-event counts, without detailed event descriptions or comparative analyses. These limitations define the scope of conclusions that can be drawn from the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Bioequivalence Study of Two Oral Nitisinone Formulations to Treat Hereditary Tyrosinemia (HT-1) — NCT02750345.
• Registry record last updated 2017-06-14; status last verified 2017-05.
• Results first posted 2016-10-17.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

NCT02750345 is a completed randomized phase 1 crossover study sponsored by Cycle Pharmaceuticals Ltd. It enrolled 24 healthy subjects and compared Nitisinone 10 mg Tablets and Nitisinone 10 mg Tablets baked for 6 months at 40°C/75% RH with Orfadin 10 mg hard capsules under fasting conditions.

The primary endpoint was Cmax from 0 - 120 hours post-dose. Posted geometric means were 1278.0 ng/mL for Test Product 1, 1272.0 ng/mL for Test Product 2, and 1340.0 ng/mL for the reference, with geometric coefficients of variation of 17.8, 16.6, and 17.3, respectively. The registry does not report comparative estimates, confidence intervals, or a bioequivalence conclusion.

Zero serious adverse events were reported for each treatment group. Other adverse-event counts were 3 for Test Product 1, 1 for Test Product 2, and 1 for the reference. Further analysis details, secondary outcome results, and deaths are not reported in the registry record.