Regulatory Guide to Sample Reanalysis in BA/BE Studies

Introduction: Why Sample Reanalysis Is a Critical Topic

Sample reanalysis is an essential component of bioanalytical integrity in bioavailability and bioequivalence (BA/BE) studies. It ensures the accuracy and reproducibility of drug concentration measurements in biological matrices, often plasma or serum. However, reanalyzing samples is not a casual activity — regulatory agencies have placed stringent controls and expectations around it to prevent selective or biased data reporting.

In this guide, we explore the criteria, scenarios, and documentation requirements for sample reanalysis in BA/BE trials as defined by agencies such as FDA, EMA, and CDSCO (India).

Types of Reanalysis in BA/BE Studies

Sample reanalysis can be broadly categorized into two types:

1. Incurred Sample Reanalysis (ISR): A regulatory requirement to assess the reproducibility of real subject samples.
2. Investigative Reanalysis: Triggered when QC or sample results fall outside predefined acceptance limits or due to analytical anomalies.

While ISR is part of planned study design, investigative reanalysis must follow strict procedural and documentation protocols to avoid regulatory findings.

When Is Sample Reanalysis Justified?

Reanalysis is acceptable under specific conditions only. Examples include:

• Unexpected concentration-time profile deviations
• Chromatographic issues like peak splitting, broadening, or interference
• Out-of-specification QC or calibration curve failures
• Instrument malfunction during injection
• Suspected sample degradation (e.g., due to thawing)

Reanalysis should not be used for adjusting results based on sponsor expectations or outlier removal unless scientifically justified and documented.

Acceptance Criteria for Incurred Sample Reanalysis (ISR)

ISR is the gold standard for evaluating method reproducibility. According to regulatory guidelines:

• Minimum of 10% of study samples (usually from both C_max and elimination phase) must be reanalyzed.
• Acceptance criteria: At least two-thirds of the repeated samples should be within ±20% of the original result.

Example of ISR assessment:

ISR failures may prompt revalidation or further investigation. Agencies may reject studies with systemic ISR failure.

Regulatory Guidance and Key Expectations

• FDA: Emphasizes ISR for assessing reproducibility and prohibits arbitrary sample reanalysis.
• EMA: Requires ISR for all pivotal studies and discourages reanalysis unless justified and documented.
• CDSCO: Requires ISR plans to be pre-approved and deviations must be reported with justifications.

All reanalysis must be pre-defined in bioanalytical SOPs and validation protocols, and any deviation must be recorded as part of the study deviation log.

Investigative Reanalysis and Documentation

Unlike ISR, investigative reanalysis is initiated when data anomalies arise during the course of sample analysis. The analyst must notify QA and follow the reanalysis decision tree described in internal SOPs.

Essential documentation includes:

• Reason for reanalysis (e.g., chromatogram anomaly, instrument alert)
• Approval from bioanalytical lead and QA
• Chromatograms and raw data from both original and reanalyzed runs
• Justification memo and reanalysis report

Any attempt to reanalyze without documented rationale or QA oversight can result in a critical audit finding.

Case Study: ISR Failure Triggers Revalidation

In a pivotal BE study of a BCS Class II antihypertensive drug, ISR showed only 50% of reanalyzed samples within ±20% criteria. Root cause analysis revealed inconsistent autosampler temperatures. A full method revalidation was conducted including revised stability studies. The final report was updated in CTD Module 5.3.1.4 and accepted by the EMA after clarifications.

How to Avoid Regulatory Non-Compliance

To prevent findings related to reanalysis:

• Establish a well-defined SOP on sample reanalysis and ISR
• Include ISR plan in study protocol and method validation report
• Engage QA in every reanalysis decision
• Limit reanalysis to scientifically justified cases only
• Maintain transparency in deviation logs and raw data submissions

Explore additional ISR trends and guidance on EU Clinical Trials Register.

Conclusion: Treat Reanalysis as a Scientific, Not Corrective, Tool

Reanalysis plays a crucial role in ensuring the integrity and reliability of bioanalytical results in BA/BE trials. However, without robust SOPs, justified decision-making, and regulatory alignment, it can quickly become a point of scrutiny. Incurred Sample Reanalysis (ISR) is not a formality—it’s a statistical assurance of your method’s reliability. Similarly, investigative reanalysis must be limited, transparent, and defensible. With proper planning and documentation, reanalysis strengthens your study; without it, it invites regulatory trouble.