Outlining the Key Steps to Method Development

Thought and foresight into method development stages can ensure costly errors and delays are avoided later on.

Method development is a critical and continuous process that, if optimized, ensures successful progression of a drug product through its life cycle to commercialization. “Method development consists of three main stages: feasibility—where you determine if the method will work with your sample; development—where you optimize the method; and validation—where the optimized method is validated to the relevant regulatory requirements,” explains Vincent Thibon, technical development lead, RSSL. “Developing a robust method will ensure that routine testing occurs smoothly and limits the amount of testing required.”

Step one—feasibility

“First of all, it is crucial to collect as much background information as possible on the API to understand its characteristics or what development challenges it poses,” says Anders Mörtberg, analytical chemist at Recipharm. “It is also important to check the established literature for analytical methods for compounds with similar profiles.”

In addition to gathering all the relevant data, it is important to define the objective of the method development, asserts Amanda Curson, head of Analytical Development, Tredegar, PCI Pharma Services. “At the beginning, an analytical target profile should be prepared that clearly outlines the requirements of the method, so that all involved understand and know what needs to be achieved with developing that method,” she notes. “The timelines, costs, and client expectations must be defined.”

Curson highlights that some useful questions to ask during these initial phases are as follows: What is the objective? Do you want the method to be suitable for drug substance (DS) initially, but maybe potentially further down the line for drug product (DP)? What is the basic chemistry of the DS? Is there any information on degradation products? Is there any information on chemical, solubility, molecular structure, stability?

Then after searching pharmacopeial methods for any existing information that can be used for the method development project, the phase of the development of the product, which impacts the amount of work required, should be assessed. Defining the phase of development early on is important, Curson emphasizes.

“In order to develop an accurate, reproducible, and reliable method, there must be an understanding of the final purpose of the method. This purpose should be the driving principle behind the research and development stages,” adds Emma Leishman, manager, Advanced Analytics, Avomeen.

However, Leishman notes that there are some starting considerations for any method development, regardless of the final purpose. “First, there is consideration of the analyte itself, as this can determine suitable instrumentation. Some analytes are inherently more difficult. Platform methods or templates may exist for the analyte or close structural analogues, or it might be that a method needs to be developed from scratch using published literature as a starting point,” she says. “Analytes might also be unknowns belonging to broader categories of chemicals, which require a different approach compared to a targeted method for a known compound.”

Step two—development

The next stage is about minimizing the complexity of the methods to ensure they are user-friendly for routine use, Curson continues. “[A method] will be used by different analysts and may be transferred between different labs,” she says. “When it comes to sample preparation and standardization, you want to ensure you can extract the API, which has a pharmacological effect when it gets into the body, from the sample matrix.”

Analyte matrix considerations can highlight some of the hurdles that need to be overcome, adds Leishman. “More challenging matrixes, like oral syrups or topical formulations, may require some creative sample preparation techniques for partial purification, such as solid-phase extraction, liquid-liquid extraction, and centrifugal filters,” she emphasizes. “Some instrumentation is more prone to matrix effects than other techniques, but standard addition curves can be useful for quantitation when matrix effects are present.”

“Developers need to select an appropriate solvent system for dissolving the sample and they should also choose a suitable separation mode, such as reversed phase chromatography or hydrophilic interaction chromatography (HILIC),” states Mörtberg. “A detection principle should also be chosen—for example, for [ultraviolet] UV or visible light, an appropriate detection wavelength should be selected. UV detection is preferred if the analytes contain a UV chromophore due to the widespread availability of UV detectors in [quality control] QC laboratories.”

Sample preparation is also an essential part of method development, Mörtberg continues. “Early on in the development process, suitable sample preparation conditions ensuring quantitative recovery of the analytes should be tested,” he says. “Sample preparation should provide reproducible and homogeneous sample solutions that are compatible with the mobile phase system. Sample preparation techniques are dependent on the nature of the drug product (solid, semi-solid, liquid etc).”

Step three—validation/optimization

Finally, the specificity and sensitivity of the method should be considered, continues Leishman. “The analyte may be a primary component of the matrix, or it might be an impurity present at trace levels. Instrumentation and sample preparation approaches may change if trace level sensitivity is required,” she reveals. “Regulatory guidelines and a knowledge of toxicology are especially important for impurity methods, as these often dictate the permissible limits. Given the trend for increasingly tight regulatory limits, such as for nitrosamines, then it might be prudent to develop a method with sensitivity beyond the minimum requirements in case regulatory authorities decide to lower limits in the future and to fully understand the risk to the consumer.”

“With optimization, you want to make sure your initial method is compatible with the sample matrix,” confirms Curson. “To meet the industry standard, we subject the product to harsh, acidic or basic conditions, oxidation, temperature, and heat so that we are forcing degradation products to be produced, the method must be capable of showing the degradation products and that they do not interfere with the active product potency.”

Once all the relevant screening of the mobile and stationary phases are completed, which should include the samples from forced degradation, further optimization of the chromatographic system should be performed to determine the most appropriate column temperature, as well as optimal solvent gradient or solvent composition, adds Mörtberg. “To streamline the experimentation phase, a design of experiment setup or a method-development-aiding computer program is highly useful. If planned and documented correctly, the data can be used for a later robustness test included in any later method validation,” he says.

“Prior to formal validation of the analytical test procedure, pre-validation experiments using final method conditions should be conducted,” Mörtberg continues. “This will provide an assessment whether the method is ‘validatable’ and a basis for setting relevant acceptance limits for the validation characteristics.”

Ultimately, the method must be transferable between scientists and equipment, irrespective of any potential slight changes in method conditions that may arise, emphasizes Curson. A transferable method is a robust one that will be applicable for future development requirements.

Final remarks

“Without solid analytical methods, it is impossible to make evidence-based conclusions on the safety and efficacy of a product or process,” concludes Leishman. “Strong analytical methodology provides clarity and focus to any scientific endeavor. Costly delays may arise when methods fail during routine analysis, which can be avoided by devoting more resources and thought into the development stages.”

About the Author

Felicity Thomas is the European editor for Pharmaceutical Technology Group.