Common Practices for Analytical Methods Transfer

Introduction

For most products, and especially for a successful one, the transfer of analytical methods during development is inevitable. Method transfers are often needed as a consequence of sequential activities (e.g., methods transferred from discovery to pre-clinical, to clinical manufacturing and finally to commercial manufacturing) or parallel activities (e.g., multiple testing sites including formulation and process development, stability and release testing). As such, methods transfers are a natural part of project progression. It is important that Analytical Methods Transfer Exercises (AMTE) are designed taking into consideration factors such as the development stage of the method and project, type of method and its intended use, and sites involved in the transfer. Table 1 lists key considerations and components for AMTEs.

Table 1 - Key considerations and components of AMTEs

Major goals of methods transfer to a new lab are to avoid release of product that does not meet specifications (safety impact) as well as avoid rejection of good product (economic impact). Because of these potentially high-impact implications, an assay cannot be used by the new lab until transfer is successfully completed.

A transfer exercise is the process of establishing a qualified analytical test procedure that originates in another laboratory. It documents that assay performance is equivalent across testing sites. Since each transfer situation is unique, a planned approach tailored to each project is required.

Figure 1 - A hypothetical example of data trending. The white circles represent AMTE results from the transferring and receiving labs. The difference in results is well within the variability of the assay thus, the AMTE is deemed successful, but if the historical data is analyzed for trends, a shift can be detected. When more data points are collected from the receiving lab, it could be determined if the change is real.

Like validation, methods transfer is an exercise that provides a static picture of the process at a given moment in time. When performing this type of activity, it is necessary to keep in mind that processes are dynamic (i.e., things change over time). For that reason, it is important to revisit and monitor assay performance even after completion of a successful transfer. It is also risky to rely on methods transfer as the sole means to approve method use. AMTEs should be complemented by methods validation (depending on the stage of development this could be ICH validation, qualification or verification), training (including records and protocols) and subsequent monitoring of the assay (continuous monitoring). Post-transfer method changes initiated by the transferring lab should be communicated to the receiving lab. Figure 1 illustrates one of the dangers of transferring assays using a single set of experiments. 

The transfer should result in the generation of regulatory documentation, including training records, transfer study design, data analysis plan with pre-defined acceptance criteria, experimental work, and a report.

Considerations for AMTE Design

When performing methods transfer, the stage of development for both the method and the project should be considered. Obviously, late-stage transfers tend to be more stringent. Thus, an evaluation is recommended to define and identify risk level, the assay history and complexity, method validation status, experience at both transferring and receiving laboratories, etc. Based on the outcome of these evaluations, the approach for methods transfer may vary. The use of the method (e.g., release, stability, characterization, in-process monitoring, raw materials testing, registered or additional tests) should also be considered. As for most aspects of development, a careful evaluation of the ultimate risk to patients must be performed (i.e., the AMTE should be more stringent for assays that may result in higher patient risk).

The type of assay transfer, the experimental design and data analysis options should be adapted to different situations in order to meet regulatory expectations. Some factors that simplify (or eliminate) an AMTE include receiving laboratories with extensive experience in the use of a closely related method, new dosage strengths or dosage forms of the same product, compendial methods, use of a co-validation approach, and a very early stage of product development (e.g., before the start of clinical trials).

The probability of a successful AMTE increases with the degree of understanding of the methods (i.e., know your assay before you transfer). Two method characteristics that complicate transfers are variability and lack of robustness. Besides their effect on obtaining reliable values during normal usage, variability impacts setting meaningful AMTE acceptance criteria and may cause the acceptance criteria limits to be too wide to ensure the assay is working properly in the new laboratory. Lack of robustness jeopardizes success because many of the variables evaluated during validation (e.g., reproducibility, inter-instrument, inter-analyst, inter-day, instrument-to-instrument, sample/reagent stability, etc.) come into play during transfer. To ensure easier methods transfer, it is necessary to minimize assay variability and ensure assay robustness is well understood.

It is also important to ensure adequate understanding of the performance of impurity assays by including spiked samples at the lower and upper limits during pre-transfer exercises. As for instruments, equivalent equipment may not be an option (e.g., transfer to national laboratories), thus, if possible, validation of the method prior to transfer using multiple instruments (different vendors) should be considered. Identify “equivalent” instruments and provide correction factors for non-equivalent equipment (to address bias). As for process validation, design of experiments (DOE) and multivariate validation method robustness may uncover links that need to be accounted for during transfer.

Methods and Project Continuity, Selection of Critical Samples

Establishing continuity is a key activity during analytical and general project development and during methods transfers. Continuity is seldom addressed, but when ignored, it can result in serious problems in future project activities. For method continuity, appropriate bridging studies must be performed whenever a method is replaced or heavily modified. This can be achieved by using both the original method and modified method over a period of time to evaluate similarity/equivalence. It is important to include key samples (e.g., analytical reference standard, tox lots, clinical lots) when major method changes are adopted and, if appropriate, run samples side-by-side to minimize assay variability when comparing results. Since it is difficult to predict when new methods may be required, it should be common practice to bank samples by establishing and maintaining a sample retain system. This bank will be more useful if the most stable conditions in addition to preferred storage are used. As a rule, never discard important or representative samples for each stage of project, method, or manufacturing development.

Selecting the appropriate samples for AMTEs is critical. Consider inclusion of samples that cover accuracy and linearity for the main product and impurities when appropriate. When demonstrating quantitation limits (QL) or detection limits (DL) as part of the exercise, keep in mind that QL and DL are often instrument dependent. Samples from method validation forced-degraded samples, as well as purified impurities are all useful for method transfer. As previously mentioned, evaluate the need to use samples that contain relevant impurities.

If clinical or commercial samples are used for AMTEs, Out-of-specifications (OOS) results during methods transfer cannot be dismissed or ignored. Needless to say, if the transfer fails due to a sample OOS result (unless OOS samples were used and identified by pre-acceptance criteria in the protocol) a full OOS investigation should be performed to determine the failure cause. The investigation should determine which set of results is correct. Inclusion of OOS samples should be carefully evaluated (case-by-case basis).

Key Components of an AMTE

Table 1 lists key components of an AMTE, but it does not specify the factors involved in the decision making for defining what is included in each of the components. In the following sections, typical approaches to compendial, internal and external transfers are discussed.

Types of AMTEs

AMTEs can be classified by several characteristics, including method type and origin (e.g., compendial methods and product-specific methods), and transferring and receiving laboratories (e.g., external and internal transfers).

Compendial Methods

For compendial methods, transfer is from the compendia to the “receiving” laboratory. Keep in mind that compendial methods are validated and should not be changed. The most common practice for compendial assays is to verify their performance in the hands of the receiving lab.

When the assay is used in multiple laboratories, an inter-laboratory comparison should be a more common practice. To avoid discrepancies, a gap analysis evaluation should be performed before the initiation of the transfer that includes analyst training and experience, state of the equipment (qualified instruments), information on known issues or product-specific requirements (e.g., sample prep or equipment compatibility), and identification of appropriate samples for the verification exercise.

Product Specific Assays

Two common approaches to AMTEs for product-specific assays are Comparative Testing and Co-Validation.

Comparative testing is performed by comparing results from the analysis of the same samples by the transferring and receiving labs. One of the main advantages of comparative testing is the control and flexibility it allows during methods validation. But, because some of the analyses will be repeated by the receiving laboratory after validation, additional work is needed (i.e., some aspects of validation are repeated by the receiving laboratory).

During Co-Validation the receiving laboratory performs some aspect(s) of method validation (e.g., intermediate precision, QL and accuracy). This results in a reduced amount of work overall, but represents a higher risk that the method validation and transfer may fail. To mitigate risk, it is important to generate pre-validation data, and to ensure a high level of experience by both labs. Co-Validation also requires more coordination to meet validation timelines, making this approach more suitable for internal transfers.

Once again, when deciding on which approach is more appropriate, you should consider the stage of development, type of analytical method, receiving lab capabilities (personnel and equipment), and previous transfer experience.

Internal and External AMTEs

AMTEs can also be classified as internal and external depending on the relationship between the transferring and receiving laboratories. Internal transfers are performed within a single company. These include transfers from Research to Development, Development to Commercial QC, from one site to a new site or duplicated QC lab, etc. AMTEs may be required even if the labs are within the same site or building. External transfers involve more than one company. This includes transfer to an external site such as manufacturer’s site to a contract site, a CMO, or a regulatory lab, or from an external lab to the manufacturer’s facility, or from one external lab to another. Since external transfers include more than one company, there is an increased possibility of finding unexpected problems due to difference in equipment, systems, experience, or training. For this reason, external transfers can be more intensive and extensive.

Statistical Considerations for Transfer

Statistical design allows one to more clearly define the AMTE in terms of acceptance criteria (e.g., how much variation/bias is acceptable) and experiments required (e.g., number of repeats) to achieve success. The use of this approach usually results in a larger number of runs to power statistical conclusions.

A pre-AMTE evaluation should be performed to identify risks associated with transfer and mechanisms to control or minimize the identified risks. The amount of change/variability in assay results that is tolerable and still keeps the product within specifications should be statistically decided (i.e., the acceptance criteria) taking into consideration assay development experience, history, etc. and delineating validation issues from transfer issues and equipment qualification.

The acceptance criteria should take into consideration the risk that an acceptable transfer fails (i.e., acceptance criteria too tight), or an unacceptable transfer succeeds (i.e., acceptance criteria too loose). After the AMTE, the data should be analyzed for shifts and define if there is a systematic bias (analyze and trend historical data) or if the difference can be explained by assay variability.

A good risk assessment should minimize the common transfer mistakes such as not including enough samples, the collection of insufficient data (or wrong data) to support transfer claims, inadequate acceptance criteria (excessively wide limits), data bias, etc.

Points of Contact and Pre-transfer Work

For both internal and external transfers, responsible individuals should be clearly identified and their roles should be clearly defined. At a minimum, there should be an AMTE coordinator (preferably from the transferring laboratory), a transferring laboratory point of contact, a receiving laboratory point of contact, and, for each method, a transferring and receiving laboratory analyst or subject matter expert.

There are many activities that pre-date the actual AMTE experiments. Some of them can be started while the planning is on-going. For example, it is a good idea to provide SOPs, method development reports, validation protocols and reports to the receiving lab as soon as possible. This helps the lab identify training or expertise gaps, critical instrumentation, reagents and/or samples, documentation systems, and other differences between transferring and receiving laboratories. It is also critical to ensure there are sufficient resources to execute, troubleshoot and repeat assays if needed (this includes personnel and samples). The timing of the transfer is also important. ASAP is not always ideal as it may result in long times between the training and the actual use of the methods. This, in turn, results in a need to retrain. On the other hand, waiting too long for methods transfer may result in unnecessary rushing; thus increasing the likelihood of failure. When the AMTE is part of an overall Technology Transfer, coordinate the AMTE so the methods are in place to support process transfer, pilot or engineering batches.

Conclusion

Analytical method transfer exercises are commonly required during BioPharmaceutical product development. The appropriate approach to transfer depends on many factors, including type of method, stage of method validation, stage of product development, receiving lab experience. Key components of the AMTE include study design (including risk assessment and data analysis strategy), training, method knowledge, strategic sample choice, and documentation are key components of a successful method transfer.

Acknowledgments

The authors wish to acknowledge Pfizer colleagues in the Analytical Development and Biological Characterization Group, Quality Control Group, Analytical Group at Commercial Manufacturing Facility in SBY for their continuous work on methods validation and transfer and Dr. Laura Bass for her critical review of this manuscript.

This article was printed in the July/August 2010 issue of Pharmaceutical Outsourcing, Volume 11, Issue 4. Copyright rests with the publisher. For more information about Pharmaceutical Outsourcing and to read similar articles, visit www.pharmoutsourcing.com and subscribe for free.