The Center for Drug Evaluation and Research (CDER) issued the guidance for Internal Standards (IS) in Chromatography Bioanalysis. CDER is a part of the FDA that monitors the availability of safe and effective over-the-counter and prescription drugs. The FDA issued this in the form of a question and answer format on September 4, 2019.

Who are these recommendations for?
Contract research organizations

What does it deal with?
This guidance deals with the variability of IS response in validation of chromatographic analytical data that is submitted in the following:

New drug applications
Investigational new drug applications
Biologics license applications
Abbreviated new drug applications

This document provides the Agency's views on the potential impact of IS response variability on the precision of analyte concentration measurement. It determines the need for further investigation in case the variability is likely to hamper the data accuracy.

Insights from FDA
The guidance begins by first answering what the internal standards of analytical chemistry and their need in bioanalysis. It further explains the various sources of IS response variability as the sources could have an impact on the accuracy of the analyte concentration measurements.

The guidance identifies the following common sources:
Human error in standards preparation
Issues occurring during the analysis of standards
Matrix effects within the standards

The third question cites two examples where IS response variability probably will not affect the accurateness of the reported data.

When does the IS response not have any impact on the data accuracy?
In the case where in the same analytical run, the IS response of subject samples is similar to that of calibration standards and quality control samples (Cals/QCs).

In case the IS responses for subject samples in question show a repeating pattern or a gradual drift, but the range of IS responses is similar for subject samples as well as Cals/QCs

When can the data accuracy be impacted?
IS responses for certain subject samples differ considerably from the majority of subject samples, and for Cals/QCs, the IS responses have a differing variability pattern

Where amongst the subject samples, there is a gradual increase or decrease that goes beyond the normal range of IS responses, and wherein a run, there are no IS responses for QCs interspersed among the impacted segment.

For each of these variances in IS responses, there are suggested approaches that can be adopted to alleviate the variability.

Where IS responses significantly differ from the responses for Cals/QCs:
Follow the pre-established criteria for repeat analysis
Where IS responses that gradually drift or drifting variance is observed:

Reanalysis of subject samples. The guidance also offers steps to be undertaken based on the reanalysis results.
Consistently higher or lower IS responses as compared to Cals/QCs:

A subset of the subject samples needs to be reanalyzed. Even here, there are further steps enumerated based on the reanalysis results.

This is the gist of the FDA guidance. The recommendations of the guidance aren't legally binding on the biolab but are a source of guidance. This guidance is available on the FDA's website for review.

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