Identification and quantification of medical device extractables and leachables via non-target analysis (NTA); Analytical uncertainty.

Leachables are substances that are leached from a medical device during its clinical use and are important due to the patient health-related effects they may have. Thus, medical devices are profiled for leachables (and/or extractables as probable leachables) to assess their potential impact on patient health and safety. This profiling is accomplished by screening extracts or leachates of the medical device for released organic substances via non-targeted analysis (NTA) employing chromatographic methods coupled with mass spectrometric detection. Chromatographic mass spectral response factors (RFs) for extractables and leachables vary significantly from compound to compound, complicating the quantitation of these compounds and the application of assessment strategies such as the Analytical Evaluation Threshold (AET). The analytical uncertainty resulting from response factor variation can be expressed in terms of an uncertainty factor (UF), which estimates the magnitude of response factor variation. This manuscript discusses the concept and impact of analytical uncertainty and provides best practice recommendations for the calculation and use of the uncertainty factor, UF.

A Practical Derivation of the Uncertainty Factor Applied to Adjust the Extractables/Leachables Analytical Evaluation Threshold (AET) for Response Factor Variation.

The analytical evaluation threshold (AET) establishes which chromatographic peaks, produced during organic extractables/leachables (E&L) screening, require toxicological safety risk assessment because the peaks are associated with compounds of potentially unacceptable toxicity. Thus, the AET protects patient safety as its proper application ensures that all potentially unsafe E&L are necessarily assessed. Generally, application of the AET involves the presumption that all organic E&L have the same detector response factor, an assumption that is not valid for any of the detection methods commonly used in E&L screening. Thus, the AET's ability to be protective is compromised for poorly responding compounds, as they will appear to be below the AET when in fact they are not. This unacceptable outcome is addressed by adjusting the AET with an uncertainty factor (UF) whose value is dictated by the magnitude of response factor variation, with a larger variation resulting in a larger UF and a lower adjusted AET. Although the concept of the UF is straightforward, setting a generally accepted, scientifically valid, and practical value for the UF has been challenging. In this article, a database of relative response factors obtained for nearly 1200 E&L via the most commonly applied chromatographic screening methods (gas chromatography/mass spectrometry [GC/MS], liquid chromatography/mass spectrometry with atmospheric pressure chemical ionization [LC/MS-APCI], and LC/MS with electrospray ionization [LC/MS-ESI]) is used to justify UFs for these methods, individually and as a combined practice, based on the practical principle of "the point of diminishing returns". Using this concept results in nearly 92% of the compounds in the database being properly flagged as above an AET adjusted with a UF = 3. Ninety-five percent (95%) coverage of the compounds can be achieved when a UF of 4 is applied to the combination of GC/MS and LC/MS methods or with other combinations of UF values applied to the various methods individually. Coverage is increased to 97% when a UF of 4 is individually applied to the GC/MS method and a UF of 10 is individually applied to the LC/MS methods. Furthermore, the available data suggest that application of both APCI and ESI ionization in LC/MS screening (as opposed to either method separately) provides the greatest coverage of E&L.

Is Retention Time and/or Structure Matching a Solution to the Challenge of Providing Quantitative Data When Screening for Extractables and Leachables by GC/MS?

Leachables can potentially and adversely affect patient safety. Thus, drug products and medical devices are chromatographically screened for organic leachables (and extractables), establishing these compounds' identity and quantity. Accurate quantitation of extractables and leachables is challenging given compound-to-compound variation in response factors. One proposed means for managing variation and improving quantitation accuracy is the use of retention time (RT) and structure to match analytes with their most relevant quantitation surrogate. Although the scientific basis for relationships between RT and structure versus response is unclear, the use of matching was investigated using databases of response factors (RFs) or relative response factors (RRFs), RTs, and structures for extractables/leachables. Gas chromatography with mass spectrometry (MS) detection was investigated as response variation in this technique is less than with other screening methods such as liquid chromatography with MS detection. The overall RF variation across RT and structure makes it difficult to establish whether RT and response or structure and response can be correlated. Rigorous statistical analysis of the data concludes that there are no discernible relationships between these quantities; however, casual visual examination suggests that subtle relationships might exist. The effect that RT or structure matching could have on quantitation accuracy was considered, presuming that the visual trends were real. Under this presumption, it was estimated that RT matching could at most improve quantitation accuracy by 25%, and that structure matching could improve accuracy by at most 50%. However, these improvements do not address the response variation that is independent of RT or structure, and thus it is concluded that RT or structure matching are not viable solutions to RF variation. Rather, it is recommended that databases of authentic RRFs be aggressively populated to provide accurate quantitation. Compounds for which authentic RRFs cannot be secured are most effectively quantified using the median RRF.

Identifying and Mitigating Errors in Screening for Organic Extractables and Leachables: Part 2-Errors of Inexact Identification and Inaccurate Quantitation.

Patients can be exposed to leachables derived from pharmaceutical manufacturing systems, packages, and/or medical devices during a clinical therapy. These leachables can adversely decrease the therapy's effectiveness and/or adversely impact patient safety. Thus, extracts or drug products are chromatographically screened to discover, identify, and quantify organic extractables or leachables. Although screening methods have achieved a high degree of technical and practical sophistication, they are not without issues in terms of accomplishing these three functions. In this Part 2 of our three-part series, errors of inexact identification and inaccurate quantitation are addressed. An error of inexact identification occurs when a screening method fails to produce an analyte response that can be used to secure the analyte's identity. The error may be that the response contains insufficient information to interpret, in which case the analyte cannot be identified or that the interpretation of the response produces an incorrect identity. In either case, proper use of an internal extractables and leachables database can decrease the frequency of encountering unidentifiable analytes and increase the confidence that identities that are secured are correct. Cases of identification errors are provided, illustrating the use of multidimensional analysis to increase confidence in procured identities. An error of inaccurate quantitation occurs when an analyte's concentration is estimated by correlating the responses of the analyte and an internal standard and arises because of response differences between analytes and internal standards. The use of a database containing relative response factors or relative response functions to secure more accurate analyte quantities is discussed and demonstrated.

Identifying and Mitigating Errors in Screening for Organic Extractables and Leachables: Part 1-Introduction to Errors in Chromatographic Screening for Organic Extractables and Leachables and Discussion of the Errors of Omission.

Substances leached from materials used in pharmaceutical manufacturing systems, packages, and/or medical devices can be administered to a patient as part of a clinical therapy. These leachables can have an undesirable effect on the effectiveness of the therapy and/or patient safety. Thus, relevant samples such as material extracts or drug products are chromatographically screened for foreign organic impurities, where screening is the analytical process of discovering, identifying, and quantifying these unspecified foreign impurities. Although screening methods for organic extractables and leachables have achieved a high degree of technical and practical sophistication, they are not without issues with respect to their ability to accomplish the aforementioned three functions. In this first part of a series of three manuscripts, the process of screening is examined, limitations in screening are identified, and the concept of using an internally developed analytical database to identify, mitigate, or correct these errors is introduced. Furthermore, errors of omission are described, where an error of omission occurs when a screening method fails to produce a recognizable response to an analyte present in the test sample. The error may be that no response is produced ("falling through the cracks") or that a produced response is not recognizable ("failing to see the tree for the forest"). In either case, proper use of a robust internal extractables/leachables database can decrease the frequency with which errors of omission occur. Examples of omission errors, their causes, and their possible resolution are discussed.