Long-Term Safety Extension Study of ACTIMMUNE® (Interferon γ-1b) in Children and Young Adults With Friedreich's Ataxia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Long-Term Safety Extension Study of ACTIMMUNE® (Interferon γ-1b) in Children and Young Adults With Friedreich's Ataxia (NCT02797080), a na phase 3 study. The primary outcome is Number of Participants With Treatment-Emergent Adverse Events (AEs), Serious Adverse Events (SAEs), and Discontinuations Due to AEs.

2. Clinical Question

3. Trial Design

This was a Phase 3, completed, single-group long-term safety extension study of ACTIMMUNE® (interferon γ-1b) in participants with Friedreich's Ataxia. The registry lists Amgen as the sponsor. Enrollment was 38. The intervention was administered 3 times per week by subcutaneous injection. The study began on 2016-06-28, and primary completion was recorded as 2017-03-31.

The single-group design is central to interpreting the results. The registry records allocation as NA and masking as NONE; it does not describe randomized assignment or blinding. Because there is no concurrent control arm, the participant counts describe adverse events reported among those receiving interferon γ-1b. They cannot, by themselves, separate events associated with treatment from events that might also occur without it, nor do they estimate a between-group treatment effect.

The outcome timeframe starts at Baseline/Day 1, described in relation to the Week 28 Follow-Up Visit for Study HZNP-ACT-302, and continues through the end of this study. The registry reports mean treatment duration of 99.2 days with SD 58.48 days. The defined safety population includes participants who received at least 1 dose after the Baseline Visit for Study HZNP-ACT-303. Details about how many people from an earlier study were eligible, invited, or continued into this extension are not reported in the registry record.

The study's stated purpose was to evaluate long-term safety. The registry lists one primary outcome measure and no statistical analyses. Further details about protocol procedures, the sample-size justification, and any planned interim analyses 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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Safety Population, defined as all participants who received at least 1 dose of study drug after the Baseline Visit for Study HZNP-ACT-303.

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 Number of Participants With Treatment-Emergent Adverse Events (AEs), Serious Adverse Events (SAEs), and Discontinuations Due to AEs, measured over Baseline/Day 1 (Week 28 Follow-Up Visit for Study HZNP-ACT-302 ([NCT02593773]) through end of study; mean (SD) duration of treatment was 99.2 (58.48) days..

The primary outcome is the number of participants with treatment-emergent adverse events, serious adverse events, and discontinuations due to adverse events. It is a participant-count outcome: it describes how many people experienced an event in a category, rather than the total number of event episodes. A participant may have more than one event, so a participant count should not be read as an event count.

The registry defines an adverse event as an untoward medical occurrence, whether or not it is considered related to the investigational product. A treatment-emergent adverse event is an adverse change from baseline, including a laboratory test abnormality judged clinically significant by the investigator, that occurs on or after the first dose administered at home and during the study. The definition does not require the investigator to attribute the event to treatment.

A serious adverse event is defined by outcomes or medical significance, including death, a life-threatening event, persistent or significant disability or incapacity, inpatient hospitalization or its prolongation, a congenital anomaly or birth defect, or another medically important event. Seriousness is therefore a classification based on the event's consequences or importance, not simply on whether an event occurred.

Collecting these categories is useful in a safety extension because it captures both broad adverse-event experience and events meeting a serious-event definition. The registry reports counts in serious and other adverse-event categories. It does not report the number of discontinuations due to adverse events.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a participant count represent?

For an outcome expressed as the number of participants with an event, each participant is classified according to whether the event category occurred during the defined observation period. This is different from counting every episode. One person can have repeated episodes, and a person can potentially meet more than one category. Unless overlap is described, counts across categories should not be added to create a total number of distinct participants. The registry's outcome is explicitly a participant count, and the safety summary lists participants at risk and participants affected in the serious and other adverse-event categories.

What is the distinction between an adverse event and a serious adverse event?

In general, an adverse event is a medical occurrence observed during a study, without requiring a judgment that the investigational product caused it. The registry's definition follows that distinction: an event can qualify whether or not it is considered related to treatment. Seriousness is a separate classification based on specified consequences or medical importance, such as death, life-threatening status, hospitalization, or significant disability. Thus, the other adverse-event category and serious adverse-event category describe different classifications, not a comparison between treatment arms.

How should the observation window be understood?

The registry gives a window beginning at Baseline/Day 1 and continuing through the end of the study, with the starting point described in relation to the Week 28 Follow-Up Visit for Study HZNP-ACT-302. It also reports mean treatment duration of 99.2 days with SD 58.48 days. In general, treatment duration and time under observation affect the opportunity to record an event. Participants observed for different lengths of time may have different opportunities for events to be noticed. The registry does not provide participant-level exposure times or event timing, so rates per person-time cannot be interpreted from the posted participant counts.

What does the single-group design allow?

In general, a single-group safety summary is descriptive: it records what happened among the people receiving the intervention. A concurrent comparator would be needed to directly estimate how event experience differed between treatment conditions. This registry lists a single-group model, allocation as NA, and masking as NONE. Consequently, the safety counts do not provide a randomized or blinded contrast. Observed events cannot be attributed to the intervention solely on the basis of their occurrence during the study, and an absence of events in a category does not establish absence of risk.

What is statistical uncertainty?

In general, a confidence interval expresses the range of values compatible with observed data under a specified statistical method. For a participant-count outcome, uncertainty depends on the number observed and on the analysis method. A zero count is still an observation from a finite group, not a direct measurement of a zero underlying event probability. The registry record does not report confidence intervals, a statistical test, or a model-based estimate for the adverse-event counts. No additional numerical estimate should be inferred from the posted counts alone.

What do the planning assumptions mean?

In general, a sample-size calculation describes how many participants a hypothetical study might require under stated assumptions about significance level, allocation, statistical approximation, and effect to detect. The planning assumptions associated with this record specify a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. These assumptions describe a planning illustration, not the design of this single-group extension. They do not make the observed study randomized, and any calculated sample sizes are not observed power or evidence that the study had a particular probability of detecting an effect. The registry does not report its own sample-size justification.

Were inferential analyses reported?

The registry lists one primary outcome measure and no analyses. Therefore, the reported safety results are best interpreted as descriptive participant counts. A prespecified model, adjustment strategy, hypothesis test, or analysis handling repeated events is not reported in the registry record. General statistical methods can help explain how such data might be analyzed, but they should not be mistaken for methods documented as having been used in this study.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure, whose title includes treatment-emergent adverse events, serious adverse events, and discontinuations due to adverse events. It does not report a multiplicity adjustment or explain whether these components were treated as separate tests, a combined endpoint, or descriptive safety summaries. Because no statistical analyses are listed, there is no reported inferential testing framework from which to assess control of false-positive findings across outcomes.

Information about missing outcome data, withdrawals, loss to follow-up, and the handling of incomplete safety observations is not reported in the registry record. The enrollment count is 38, and the adverse-event summary lists 38 participants at risk in each of the serious and other categories. Those figures do not describe the completeness of every individual observation or explain how any missing data were handled.

The registry defines a safety population as all participants who received at least 1 dose after the Baseline Visit for Study HZNP-ACT-303. Further analysis-population details are not reported. In particular, the record does not describe a separate intention-to-treat population, a per-protocol population, or rules for including participants with partial follow-up. No statistical analysis plan, interim-analysis procedure, or missing-data method is reported in the registry record.

11. 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 non-serious adverse event terms

The serious adverse-event summary lists 38 participants at risk and 0 participants with a serious adverse event. It also lists 0 deaths. The other adverse-event category lists 38 participants at risk and 17 participants with an event. These figures count participants, not the number of event episodes. They should not be added across categories unless overlap is known; overlap is not reported in the registry record.

The serious-event definition includes events with specified consequences or medical importance. The fact that no participant was recorded in that category describes the observed study group and follow-up period only. It does not establish that serious events cannot occur. The record does not report a confidence interval or other estimate of uncertainty for this count.

The term “other” identifies the separate category in the safety summary; it does not supply details about event type, severity within that category, timing, duration, or investigator assessment of relatedness. A list of the most frequent serious-event terms is not reported. The primary outcome also includes discontinuations due to adverse events, but their count is not reported in the registry record.

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

The results establish a limited descriptive account of safety observations in a single-group extension. During the reported timeframe, 0 of the 38 participants at risk were listed with a serious adverse event, 17 of the 38 participants at risk were listed in the other adverse-event category, and 0 deaths were reported. The mean treatment duration was 99.2 days with SD 58.48 days. These observations apply to the registry-defined safety population and should not be generalized automatically beyond it.

The results do not show a treatment effect relative to a control condition. There was no concurrent comparator, and the registry lists no statistical analyses. Counts observed during treatment cannot by themselves establish that treatment caused an event or prevented one. Likewise, the absence of a serious event in the observed group is not proof that the true risk is absent.

The posted results do not provide event-level descriptions, judgments of relatedness, a count of discontinuations due to adverse events, confidence intervals, or details about missing observations. They also do not report the protocol's sample-size justification or interim analyses. Those omissions limit what can be concluded about the completeness, precision, and broader context of the safety summary.

Planning calculations based on assumptions about two-arm comparisons should be distinguished from the actual study design. Any such illustration is not a report of observed power and does not change the descriptive nature of the extension results. The most defensible reading is to treat the counts as observations in the defined safety group over the reported period, while recognizing that comparative effects and several details needed for deeper safety characterization are not reported in the registry record.

13. Why This Trial Matters Statistically

Safety extensions address a different statistical question from a controlled efficacy comparison. Their descriptive focus is the occurrence of adverse events during continued exposure and follow-up. This record makes that focus explicit through its primary outcome, which counts participants with treatment-emergent adverse events, serious adverse events, and discontinuations due to adverse events.

The statistical distinction between an event count and a participant count matters. Counts of affected participants indicate how many people experienced an event category, but do not reveal the number of episodes, recurrence, timing, or duration. Likewise, separating serious from other adverse events makes clear that event classification depends on specified criteria. The reported 0 serious events and 17 participants in the other category are useful descriptions, but they do not contain all the information needed to characterize each event.

The single-group structure also matters. Without a concurrent control condition, these data describe observed safety experience rather than a comparative effect. This is an important limitation to keep visible when interpreting counts, particularly when the event definition does not require a judgment that the event was caused by treatment.

Finally, statistical transparency affects how precisely findings can be interpreted. The registry reports no analyses, confidence intervals, missing-data procedures, or sample-size justification. The record therefore supports a straightforward account of the observed counts, but not claims about comparative risk or statistical significance. Making these boundaries explicit helps keep descriptive safety evidence distinct from conclusions that would require additional design or analysis information.

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 main limitation for interpreting this trial is its single-group design. There is no concurrent control group, and the registry records allocation as NA and masking as NONE. The results therefore cannot provide a direct comparison of adverse-event experience under different treatment conditions. The registry also does not report statistical analyses or uncertainty intervals, so the precision of the event counts is not quantified.

The safety summary is limited to participant counts in serious and other adverse-event categories. It does not report event-level terms, event frequency, timing, duration, severity within the other category, or treatment-relatedness assessments. Although the primary outcome includes discontinuations due to adverse events, that count is not reported. The record also does not report missing-data handling or the number of participants with incomplete follow-up.

The reported mean treatment duration is 99.2 days with SD 58.48 days, but individual follow-up and exposure information is not reported. The registry-defined safety population is described, but additional details about participant characteristics and selection into the extension are not reported in the registry record. As a result, the extent to which these observations represent other people with Friedreich's Ataxia cannot be determined from the record alone.

Finally, the record does not report a protocol-based sample-size justification, interim analyses, or a detailed statistical analysis plan. Planning assumptions associated with a two-arm illustration should not be interpreted as the design or observed power of this single-group study.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Long-Term Safety Extension Study of ACTIMMUNE® (Interferon γ-1b) in Children and Young Adults With Friedreich's Ataxia — NCT02797080.
• Registry record last updated 2024-12-10; status last verified 2024-12.
• Results first posted 2018-05-01.
• 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

NCT02797080 is a completed Phase 3, single-group long-term safety extension study of ACTIMMUNE® (interferon γ-1b) in participants with Friedreich's Ataxia. The registry lists enrollment of 38, with treatment administered 3 times per week by subcutaneous injection. The safety population includes participants who received at least 1 dose after the Baseline Visit for Study HZNP-ACT-303.

The primary outcome concerns the number of participants with treatment-emergent adverse events, serious adverse events, and discontinuations due to adverse events. The posted safety counts are 0 participants with serious adverse events, 17 participants in the other adverse-event category, and 0 deaths. A discontinuation count is not reported in the registry record. No statistical analyses are listed, and the single-group results are descriptive rather than a comparison with a control group.