Which analytical methods must be validated?

If you are just approaching the topic of method validation, you may be faced with the question which analytical methods are actually affected by method validation.

To answer this question, we have to clarify which methods are used when and for what purpose.

The first thing that comes to mind are the methods that are used in a pharmaceutical quality control laboratory for release and stability analysis during quality control. This includes methods for the demonstration of identity, for the determination of the content and potency of the active ingredient as well as for determining impurities. The latter can also belong to so called stability-indicating methods, i.e. to those that examine the drug’s stability during stability studies under the aspect of whether or to what extent the content of known impurities, such as degradation products, increases over time. Thinking about the applied methods, this mainly includes HPLC methods, but also spectroscopic methods and, depending on the nature of the analyte, also protein biochemical methods, to name just a few.

In addition, the methods that are used as part of in-process controls (IPC) during production must also be validated. IPC methods to be validated can be, for example, protein determinations or activity determinations. Before starting any production, the excipients which are intended to be used in the upcoming production must be released. The methods, which are used for this purpose, however, have to be verified. This is due to the fact that excipients are usually materials listed in pharmacopoeias, for which the corresponding compendial methods must be applied. Moreover, the methods of environmental monitoring should not be forgotten, which must also be validated or verified, respectively, since they involve, among others, microbiological analyses, such as active and / or passive airborne microbial sampling, methods using contact plates and swabbing methods.

After production, the plants used must be cleaned. Cleaning efficiency must be demonstrated by prior performed cleaning validation. The methods applied for cleaning validation must also be validated. These include, for example, quantitative TOC determinations of swab or rinse samples.

If we now take the time aspect into account, we must of course take a step back. First of all, the drug must be developed as well as the analysis methods to be used in the corresponding studies. If necessary, they must be optimized, too. In the early phases of development, those methods are mainly qualified, but before starting a phase III study, they must be validated according to the ICH Q2(R1) requirements.

Another temporal aspect that can result in method validation is a method transfer. A method transfer can take place, for example, within a company, for example by transferring a method from the development laboratory to the quality control laboratory, but also between two companies, for example in case a pharmaceutical company outsources parts of its production to a contract manufacturing organization (CRO) and the CRO's QC laboratories then perform the quality control. In such a case, depending on the complexity of the method and the experience of the new laboratory, the extend of a method validation to be carried out must be determined.

Compendial methods do not have to be validated, but in most cases (depending on the complexity of the method) they have to be verified, i.e. checked for their applicability in the laboratory. Compendial methods are used in the field of raw material testing (see e.g. excipients above, but also for water analysis), in environmental (utility and facility) monitoring and in release analysis. Compendial methods that are most frequently used in release analysis, depending on the drug product, include, for example, the endotoxin determination applying the LAL test, the demonstration of sterility or the determination of the water content using Karl Fischer titration. Further details on the verification of compendial methods are provided in this article.

In summary, the following analytical methods must be validated:

• All QC methods used for release and stability
• IPC methods
• Methods for environmental monitoring
• Methods applied in cleaning validation
• Newly developed methods (before starting phase III studies)
• Transferred methods