Frequently Asked Questions about Method Validation

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These are some frequently asked questions about Method Validation:

Q: What is test method validation?
A: Test method validation is the documented process of ensuring a pharmaceutical test method is suitable for its intended use. This is achieved by performing a series of experiments on the procedure, materials, and equipment that comprise the method being validated. The experimental results undergo statistical analysis, and a series of pre-defined acceptance criteria are applied to the results. These experiments are designed to demonstrate the scientific validity of results produced by the method during routine sample analysis. Establishing that a test method consistently produces reliable analytical results is a critical element of assuring the quality and safety of pharmaceutical products.

A validated test method is one has been documented as selective, accurate, precise, and linear over a stated range. Additional parameters and performance characteristics are often evaluated for methods of greater complexity. These serve to establish the method ruggedness or robustness.

Test method validation is a requirement for entities engaging in the testing of biological samples and pharmaceutical products for the purpose of drug exploration, development, and manufacture for human use. It also of great value for any type of routine testing that requires consistency and accuracy.

Q: What are some examples of test methods?
A: The following are examples of pharmaceutical test methods:

• Content Uniformity Assays
• Disintegration
• Friability
• Gas Chromatography (GC) Assays
• Hardness
• Liquid Chromatography (LC) Assays
• Spectroscopy/Spectrophotometry Assays
• Loss on Drying
• Moisture Content by Karl Fischer titration
• Packaging Integrity
• pH
• Visual Identification
• Weight Uniformity

Q: What methods require validation?
A: Generally, any method used to produce data in support of regulatory (e.g., FDA, EMA) filings or the manufacture of pharmaceuticals for human use must be validated. This includes bioanalytical methods of analysis for bioavailability (BA), bioequivalence (BE), pharmacokinetic (PK), toxicokinetic (TK), and clinical studies, as well as methods used for analytical testing of manufactured drug substances and products.

According to ICH Guidelines, the following four types of methods require validation:

• Identification tests
• Quantitative tests for impurities content
• Limit tests for the control of impurities
• Quantitative tests of the active moiety in samples of drug substance or drug product or other selected component(s) in the drug product

In addition, ICH Guidelines define these four types of methods:

“Identification tests are intended to ensure the identity of an analyte in a sample. This is normally achieved by comparison of a property of the sample (e.g., spectrum, chromatographic behavior, chemical reactivity, etc.) to that of a reference standard.

Testing for impurities can be either a quantitative test or a limit test for the impurity in a sample. Either test is intended to accurately reflect the purity characteristics of the sample. Different validation characteristics are required for a quantitative test than for a limit test.

Assay procedures are intended to measure the analyte present in a given sample. In the context of this document, the assay represents a quantitative measurement of the major component(s) in the drug substance. For the drug product, similar validation characteristics also apply when assaying for the active or other selected component(s). The same validation characteristics may also apply to assays associated with other analytical procedures (e.g., dissolution).”

– From ICH Harmonized Tripartite Guideline “Validation of Analytical Procedures: Text and Methodology” Q2 (R1)

Q: What does method validation entail?
A: Method validation involves conducting a variety of experiments that focus on performance elements of the method to be validated. For instance, with chromatographic assay validation, it is essential to establish the method specificity, accuracy, precision, and linearity over a stated concentration range, as well as the stability properties of the solutions, controls, and sample materials. Additional validation experiments may serve to verify robustness, which is the capacity of the method to perform as intended despite minor variations in sample handling or analytical conditions.

Assay validation parameters vary from method to method, depending on the purpose of the assay, the compounds of interest, and other critical components of the analysis.

Further experiments must be done to re-validate a method that has undergone changes, e.g., to equipment, materials, analytical scope, or the location where it is being used.

Q: What are the benefits of method validation?
A: Method validation assures the scientific veracity of analytical results and is a key component of total quality management. Proper validation of a method provides documented evidence of method performance and prescribes on-going measures to ensure quality monitoring for the life of the method.

Well-documented validation facilitates internal QC/QA review and expedites client, sponsor, and regulatory audits by providing clear links between a validated method and the systems, facilities, and procedures upon which the method is founded.

Regulatory bodies governing the approval of drugs for human use require validated methods for routine testing for that end. Laboratories that make method validation a part of standard operating procedures provide themselves a clear means of successful continued support of drug development and production activities.

Q: Are there different types of method validation?
A: The extent of testing for a given method is driven by its intended purpose. A test for appearance will not require the same validation experiments and supporting data as a chromatographic assay.

Method validations fall into three categories: Full, Partial, and Cross-Validation:

Full validation is needed for new methods or when major changes to an existing method affect the scope or critical components.

Partial validation is performed on a previously-validated method that has undergone minor modification. Changes in equipment, solution composition, quantitation range, or sample preparation merit partial method validation. Fewer validation tests are generally needed compared to a full validation; they are selected based on the potential effects of the new changes on method performance and data integrity.

Cross-validation is a comparison of validation parameters when two or more bioanalytical methods are used to generate data within the same study or across different studies. It can be used as a means of determining inter-method equivalency or assessing inter-laboratory execution of the same method.

Q: What is re-validation? When is re-validation required?
A: Re-validation is needed when a previously-validated method undergoes changes sufficient to merit further validation activities and documentation. It usually involves performing a subset of the original validation experiments. Re-validation can be full or partial, as driven by the extent of the method changes. Examples of such changes would be use of different sample matrix, addition of new analytes, or certain alterations of method parameters.

Q: What about method transfers? Verifications? Qualifications?
A: Not all methods need to be validated. Compendial methods, e.g., as published in the USP-NF, are widely accepted as needing only minimal documentation of fitness for use for a given site. An already-validated method may only require a few experiments to verify it for use. Validation of methods for characterization of compounds may not be practical. There are a number of less-demanding approaches to ensuring a method produces valid results and otherwise exhibits scientific integrity.

Method transfer is the documented evidence that a previously validated method has been verified for use at a location other than where it was originally validated. There are several means of doing so:

• Comparative testing – The originating and receiving laboratories analyze different sets of appropriately equivalent samples. Results are compared to pre-defined transfer acceptance criteria.
• Co-validation – The receiving laboratory participates in the initial method validation activities. This can be in support of establishing method ruggedness through inter-laboratory testing, for instance.
• Method validation or revalidation – Complete or partial (re-)validation is performed on the method by the receiving laboratory.
• Transfer waiver – No experimental confirmation is needed for the transfer of the method. The rationale for this decision is formally documented to approve the method for use at the receiving laboratory. Reasoning may be based on parallel methods already in use, similarity of systems and environment, or prior experience of receiving lab personnel with the method being transferred.

Method verification is the documentation that a compendial or otherwise standard method is suitable for use at a given site. It involves confirmation that the scope of use is the same as the published scope and that parameters are not changed outside of tolerances, and is supported by experimental data assessing critical method performance characteristics.

Method qualification is similar to method validation, but it does not require the method under test to be in a finalized form. Method qualification can, therefore, serve to inform method development activities in the final stages of preparing the method for actual validation. They may, for instance, be used to assign validation acceptance criteria. Data from a method qualification might also be used to support method robustness in the Validation Summary Report.

Additional Resources

Additional information is available on:

• Method Validation
  • Analytical Method Validation
  • Bioanalytical Method Validation
• Software Validation