Study to Assess if ABP 798 is Safe & Effective in Treating Moderate to Severe Rheumatoid Arthritis (RA) Compared to Rituximab: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study to Assess if ABP 798 is Safe & Effective in Treating Moderate to Severe Rheumatoid Arthritis (RA) Compared to Rituximab (NCT02792699), a randomized phase 3 study. The primary outcome is Area Under the Serum Concentration-time Curve From Time 0 to Infinity (AUCinf) After the Second Infusion of the First Dose.

2. Clinical Question

The trial compared ABP 798 with rituximab in people with moderate to severe rheumatoid arthritis. Its primary endpoint was pharmacokinetic: the area under the serum concentration-time curve from time 0 to infinity after the second infusion of the first dose. The registry also describes efficacy and safety as study aims, and posts disease activity and cell-depletion outcomes among its secondary results.

Thus, the central comparison is about serum drug exposure after the initial treatment dose. The trial also permits examination of disease activity, pharmacodynamic response, and adverse events, but these are distinct questions. The primary endpoint alone does not establish whether participants experienced a particular clinical benefit or harm.

3. Trial Design

The study was randomized, quadruple-masked, parallel-group, and phase 3. The registry lists an enrollment of 311. It identifies Amgen as the sponsor and marks the trial completed. The recorded start date is 2016-05-17, and the primary completion date is 2018-10-08. The registry record does not report the actual number of participants included in every endpoint analysis, which can differ from overall enrollment.

Three treatment sequences are described. Participants assigned to ABP 798 / ABP 798 received ABP 798 for the first and second doses. Participants assigned to rituximab (EU) / rituximab (EU) received the EU formulation for both doses. Participants assigned to rituximab (US) / ABP 798 received the US formulation initially and switched to ABP 798 for the second dose. Each dose consisted of two 1000 mg intravenous infusions two weeks apart; the first dose was given on days 1 and 15, and the later dose at weeks 24 and 26.

The primary pharmacokinetic endpoint concerns the second infusion of the first dose, with measurement times spanning day 15, pre-dose, end of infusion, and postdose follow-up through 10 weeks. The registry lists additional pharmacokinetic outcomes, including exposure over other intervals, maximum concentration, time to maximum concentration, terminal elimination measures, and clearance. It also posts secondary outcomes related to disease activity and CD19+ cell depletion.

The record does not report the randomization ratio, allocation-concealment procedure, detailed masking procedures, or a protocol-level explanation for the treatment sequences. Nor does it give a sample-size justification or a full statistical analysis plan. The enrollment figure alone should therefore not be read as evidence of the assumptions or calculations used to choose the planned trial size.

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: Participants were randomized in a 1:1:1 ratio to 1 of 3 groups, stratified by geographic region (North America vs Eastern Europe vs Western Europe), seropositivity (rheumatoid factor \[RF\]-positive and/or cyclic citrullinated peptide \[CCP\]-positive vs RF-negative and CCP-negative), and number of prior biologic therapies used for RA (1 vs \> 1).

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The pharmacokinetic (PK) parameter analysis set (randomized participants who received the full protocol-specified infusion on day 1 and had an evaluable ABP 798 or rituximab serum concentration-time profile) with available AUCinf data. Participants with unreliable terminal elimination rate constant values were excluded.

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: The full analysis set included all randomized participants.

6. Primary Endpoint

The registry lists the primary outcome as Area Under the Serum Concentration-time Curve From Time 0 to Infinity (AUCinf) After the Second Infusion of the First Dose, measured over Day 15, pre-dose, end of infusion, and 3, 6, 24, and 48 hours, and 2, 6, and 10 weeks postdose..

The primary endpoint, AUCinf, represents the area under the serum concentration-time curve from time 0 extrapolated to infinity after the second infusion of the first dose. It summarizes drug exposure over time rather than measuring a single serum concentration. A larger area can reflect greater overall exposure, while the endpoint itself does not specify whether that exposure produces a clinical benefit.

Serum concentrations of ABP 798 and rituximab were quantified using a validated electrochemiluminescent method. The registry says AUCinf was estimated using the linear trapezoidal rule. Measurements were scheduled around the day 15 infusion and at follow-up times through 10 weeks postdose. The primary endpoint is reported as a geometric mean with a geometric coefficient of variation for each group. Geometric summaries are commonly used for pharmacokinetic measures that are analyzed on a multiplicative scale; they describe typical exposure while accounting for skewed distributions.

The registry reports pairwise geometric mean ratios with 90% confidence intervals for ABP 798 versus each rituximab formulation and for the two rituximab formulations against one another. A ratio near 1 indicates similar estimated geometric means, while the confidence interval describes uncertainty in the ratio. These statistics address comparative exposure. They do not, by themselves, answer the separate clinical question of whether rheumatoid arthritis disease activity changes similarly over time.

The analysis population is described as randomized participants who received the full protocol-specified infusion on day 1, had an evaluable serum concentration-time profile, and had available AUCinf data. The rest of the registry’s population description is incomplete, so further exclusions or handling of unusable pharmacokinetic profiles are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Different statistical summaries answer different questions in this trial. The primary endpoint is continuous and pharmacokinetic. Its group summaries are geometric means, and the main pairwise results are geometric mean ratios. Secondary outcomes include continuous measures and a binary percentage. Because outcome types and estimands differ, one statistical method cannot be assumed to apply to every result.

What does a geometric mean ratio express?

A geometric mean ratio compares typical values on a multiplicative scale. A ratio of 1 corresponds to equal geometric means; a ratio below 1 means the numerator group’s estimated geometric mean is lower, and a ratio above 1 means it is higher. The reported 90% confidence interval expresses uncertainty in that ratio. If an interval includes 1, the data are compatible with a ratio of 1 under the interval’s assumptions. If the interval excludes 1, it does not alone establish a clinically important difference or satisfy an equivalence criterion. Equivalence requires a prespecified acceptable range, and the relevant margin is not reported in the registry record.

The geometric coefficient of variation describes relative variability around the geometric summary. It is not the same quantity as a standard deviation on the original scale. Pharmacokinetic data can be right-skewed, so analysis on a logarithmic scale and reporting geometric summaries are common approaches. The registry reports geometric coefficients of variation for the primary endpoint, but the detailed model and transformations used for the sponsor’s analysis are not reported in the registry record.

How should confidence intervals and p-values be read?

A confidence interval gives a range of estimates compatible with the observed data under a specified statistical procedure. Its width conveys precision: wider intervals indicate less precise estimates than narrower intervals, all else equal. A confidence interval is not a guarantee that the true value lies in the particular interval, and it does not describe the probability that a treatment is effective. The primary comparison uses 90% intervals in the registry. The unadjusted re-calculations for selected secondary endpoints report their own intervals and p-values; those should be distinguished from the sponsor’s reported analyses.

A p-value measures how incompatible the observed data are with a specified null model, conditional on the model’s assumptions. A p-value does not measure effect size, clinical importance, or the probability that the null hypothesis is true. It also does not correct for examining multiple outcomes. Because the registry record does not report a multiplicity strategy, unadjusted p-values for secondary comparisons are exploratory evidence rather than definitive tests of a single prespecified claim.

What do the secondary endpoint calculations represent?

For change in disease activity, the re-calculated contrast is an unadjusted difference between reported group means. The reported mean estimates are least-squares means, accompanied by standard errors. The re-calculation approximates standard deviations from those standard errors and sample sizes, then uses a pooled standard deviation for a standardized effect measure. This is a summary-statistic calculation, not a reconstruction of the trial’s full fitted model. The registry’s adjusted LS mean comparisons are separate sponsor analyses and should not be conflated with the unadjusted re-calculations.

For the binary cell-depletion outcome, the unadjusted contrast is a difference in observed proportions. Its confidence interval reflects uncertainty in that contrast under the calculation approach. A risk difference is expressed on the absolute proportion scale, while a risk ratio or odds ratio expresses a relative comparison. These measures need not look numerically alike, especially when the outcome is common. The registry also reports its own risk-difference estimates and 90% confidence intervals. The exact inferential methods behind those sponsor estimates are not stated in the registry record.

Why can over-dispersion matter?

Over-dispersion is a general statistical issue that arises when observed variability is greater than a model assumes. For count or binary data, an overly restrictive model can produce confidence intervals that are too narrow and p-values that are too small. Methods that account for extra variability can give more cautious uncertainty estimates. The registry information does not establish whether over-dispersion was relevant to these analyses or which procedures were used to address it. This is a general consideration, not a claim about the trial’s specific data.

What do the planning illustrations mean?

The planning illustrations use observed effects to show hypothetical participants per arm for 80% power and participants per arm for 90% power at a two-sided significance level of 0.05, with equal allocation and a normal approximation. They vary the effect to detect as a stated fraction of the observed effect. These are not observed power calculations and do not document the trial’s own sample-size design. The trial’s sample-size assumptions and justification are not reported in the registry record. Because the observed effect itself is uncertain, planning based on it is illustrative rather than a reliable forecast of the size needed for a future study.

Overall, the reported sponsor analyses, unadjusted re-calculations, and hypothetical planning illustrations have different purposes. The sponsor analyses are the trial’s own posted inferential results. Re-calculations provide transparent descriptive comparisons from summary statistics, but do not reproduce unreported modeling choices. Planning illustrations explore hypothetical study sizes and are not evidence about the strength or success of the completed trial.

10. Analyses Reported by the Sponsor

For the primary pharmacokinetic endpoint, the registry reports sponsor analyses as least-squares geometric means and geometric mean ratios, with 90% confidence intervals for the pairwise comparisons. The posted ratio for ABP 798 versus rituximab (US) is 0.957, with a 90% confidence interval of 0.887 to 1.032. For ABP 798 versus rituximab (EU), the reported ratio is 0.885, with a 90% confidence interval of 0.820 to 0.954. The registry also reports the rituximab formulation comparison.

For selected secondary outcomes, sponsor-reported analyses are available alongside unadjusted re-calculations from summary statistics. For change in disease activity, the sponsor gives LS mean differences and 90% confidence intervals for comparisons involving ABP 798. For complete CD19+ cell depletion, it reports risk differences and 90% confidence intervals. These estimates may differ from simple re-calculations because they can reflect analysis choices or models not recoverable from the posted group summaries. The registry record does not provide enough detail to reconstruct those choices fully.

No discrepancy is flagged between the posted sponsor results and the calculations included with these summaries. Where sponsor and re-calculated estimates appear together, the sponsor’s own analysis is the relevant trial analysis; a summary-statistic re-calculation is supplementary and unadjusted. Neither should be interpreted without its estimand, analysis population, and uncertainty interval. The record does not report the complete statistical analysis plan, so the relationship between each posted estimate and any prespecified testing hierarchy cannot be confirmed.

11. Multiplicity, Missing Data and Analysis Populations

The registry record does not report whether the trial used a formal multiplicity adjustment, a testing hierarchy, or a prespecified strategy for interpreting the many outcomes and comparisons. With multiple statistical tests, chance alone can produce apparently notable results. Adjustments or an ordered testing plan can limit that risk, but neither should be assumed. The posted secondary analyses should therefore be interpreted as separate results with their own uncertainty, not as a collection of independent confirmatory tests.

Missing-data handling is also not reported in sufficient detail. For the primary pharmacokinetic analysis, the registry defines a population requiring an evaluable concentration-time profile and available AUCinf data. It does not fully specify how missing samples, unevaluable profiles, or unreliable terminal elimination estimates affected inclusion. For secondary outcomes, the record gives endpoint-specific analysis counts, but the general missing-data assumptions, imputation procedures, and sensitivity analyses are not reported in the registry record.

The registry gives a total enrollment of 311, but the analysis populations vary across outcomes. For example, the primary pharmacokinetic groups include 94, 96, and 94 participants, while the disease activity and cell-depletion outcomes have their own group counts. Differences in denominators can arise from eligibility for a particular analysis or unavailable measurements; the specific reasons are not fully reported. A reader should not treat overall enrollment as the denominator for every outcome.

Interim analyses, stopping rules, the randomization ratio, sample-size justification, and the full statistical analysis plan are not reported in the registry record. The planning illustrations based on observed effects are not a substitute for the trial’s original design calculations. Without the prespecified analysis details, it is not possible to determine from the registry alone which outcomes were intended as formal tests, how family-wise error was controlled, or how protocol deviations and missing values were handled.

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: pneumonia (1.9%), back pain (1.9%), cardiac failure chronic (1.0%), abdominal pain (1.0%), rectal haemorrhage (1.0%).

The registry reports serious and other adverse events over weeks 1-24, and for treatment sequences over weeks 1-48. For weeks 1-24, the serious-event counts are 4 of 104 for ABP 798, 5 of 104 for rituximab (EU), and 5 of 103 for rituximab (US). For the weeks 1-48 sequences, the serious-event counts are 8 of 104 for ABP 798 / ABP 798, 8 of 104 for rituximab (EU) / rituximab (EU), and 8 of 103 for rituximab (US) / ABP 798. No deaths are reported in any of these listed groups.

These are counts of participants affected, not counts of every event, and the observation periods and treatment sequences differ. The groups’ adverse-event counts should not be treated as a formal comparative safety analysis. The registry does not report adjusted comparisons, confidence intervals, or a detailed account of event ascertainment in this record. The listed serious-event terms include pneumonia and back pain at 1.9% each, alongside terms listed at 1.0%.

Adverse-event counts describe what was reported during the specified follow-up; they do not establish that a medicine caused an event or that groups have equivalent safety. Longer follow-up, event definitions, participant-level context, and comparative uncertainty all matter. No medical conclusion should be drawn from these counts alone.

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

The primary result describes estimated serum drug exposure after the second infusion of the first dose. The reported geometric mean ratios and their 90% confidence intervals quantify how exposure compared between ABP 798 and the rituximab formulations in the analyzed pharmacokinetic population. They do not directly measure symptoms, function, or disease control, and they do not establish that one treatment is preferable.

The registry labels the primary comparisons as equivalence analyses. Whether an interval meets an equivalence criterion depends on a prespecified margin and an appropriate analysis population. The margin and its justification are not reported in the registry record. Therefore, the interval estimates can be described, but the full basis for an equivalence conclusion cannot be checked from this record alone.

Secondary disease activity and cell-depletion results address other dimensions of the study, but they do not convert the primary pharmacokinetic endpoint into a clinical efficacy endpoint. Nor does a secondary estimate that is not statistically distinguishable from zero prove that the groups are the same. An interval may still include effects that could matter, and the record does not give a clinical threshold for interpreting these contrasts.

Likewise, posted adverse-event counts are descriptive. They do not determine causality, rule out uncommon events, or establish comparative safety. The record’s analysis populations, missing-data procedures, multiplicity approach, and detailed statistical plan are incomplete or not reported. Those omissions limit how firmly the results can be interpreted as confirmatory.

The most defensible reading is narrow: the registry reports a completed randomized, masked, parallel-group comparison with pharmacokinetic, secondary clinical and pharmacodynamic, and safety results. Each result should be interpreted according to its endpoint, population, time frame, and uncertainty. The record supports description of these estimates, but does not resolve every clinical question about efficacy, equivalence, or safety.

14. Why This Trial Matters Statistically

This trial illustrates why a study’s primary endpoint must be kept distinct from its broader aims. The primary measure is AUCinf, a pharmacokinetic summary of drug exposure. The registry also describes efficacy and safety questions and posts disease activity, cell-depletion, and adverse-event results. Those outcomes add context, but they are not interchangeable with the primary endpoint.

It also demonstrates the importance of distinguishing a ratio from a clinical conclusion. A geometric mean ratio summarizes relative exposure, and a confidence interval describes its precision. An equivalence label alone is not enough to assess the decision: the acceptable margin and its prespecified rationale are necessary. When those details are not reported, the estimates remain informative but a reader cannot independently assess the full equivalence framework.

The multiple treatment sequences are statistically relevant. The trial includes ABP 798 and two rituximab formulations, with the US-formulation sequence switching to ABP 798 for the second dose. Comparisons therefore need to be read in the context of which formulation participants received and at what point. Treating every group as a simple, unchanged exposure to one medicine would misstate the design.

Finally, the record illustrates the difference between sponsor analyses and summary-statistic re-calculations. Re-calculations can make assumptions visible and offer an unadjusted comparison, but cannot recover every feature of a fitted model or the original analysis plan. Planning illustrations derived from observed effects are likewise not evidence of observed power or a record of the planned sample-size justification. These distinctions help keep statistical description proportional to what the registry reports.

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 registry record leaves important design and analysis details unavailable. It does not report the full statistical analysis plan, sample-size justification, multiplicity strategy, interim analyses, or missing-data procedures. These omissions limit assessment of which outcomes were prespecified as confirmatory and how the trial handled incomplete measurements or repeated testing.

The primary endpoint is pharmacokinetic rather than a direct clinical measure. While exposure is central to the stated comparison, the primary result alone does not establish comparative disease control or safety. The registry also labels the primary analyses as equivalence analyses without reporting the equivalence margin. That prevents an independent assessment of the interval estimates against the intended acceptance criteria.

The primary analysis population requires evaluable concentration-time data and available AUCinf data, but its registry description ends mid-sentence after referring to an unreliable terminal elimination rate constant. Detailed exclusion rules and the impact of exclusions are therefore unclear. Secondary outcome denominators also vary, and the record does not explain all differences in analysis populations.

The treatment sequences require careful interpretation because the US rituximab group transitions to ABP 798 for the second dose, whereas the other sequences continue the same study medicine. Safety summaries cover different follow-up spans and regimes, so they are not direct matched comparisons across an identical exposure period. The record does not provide formal comparative safety estimates.

Finally, several secondary outcomes and analyses are posted. Without a reported multiplicity plan or a clear hierarchy, isolated unadjusted results should not be treated as definitive. Re-calculations based on summary statistics also rely on approximations and cannot reproduce unreported model specifications. These limits do not invalidate the posted estimates, but they narrow the conclusions that can be supported by the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Study to Assess if ABP 798 is Safe & Effective in Treating Moderate to Severe Rheumatoid Arthritis (RA) Compared to Rituximab — NCT02792699.
• Registry record last updated 2020-10-06; status last verified 2020-10.
• Results first posted 2019-10-23.
• 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

NCT02792699 is a completed phase 3 randomized, quadruple-masked, parallel-group trial sponsored by Amgen. It enrolled 311 participants with moderate to severe rheumatoid arthritis. The registry records a start date of 2016-05-17 and a primary completion date of 2018-10-08.

The primary endpoint was AUCinf after the second infusion of the first dose, comparing ABP 798 with rituximab formulations. The study also posted pharmacokinetic, disease activity, CD19+ cell-depletion, and safety outcomes. The primary results are geometric mean ratios with 90% confidence intervals; secondary results include sponsor analyses and, for selected outcomes, unadjusted re-calculations.

The registry does not report the full statistical plan, multiplicity strategy, sample-size justification, or detailed missing-data approach. The posted estimates should therefore be read as endpoint-specific results with their stated populations and uncertainty, rather than as a complete resolution of clinical efficacy, equivalence, and safety questions.