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Feature Articles : Nov 15, 2009 (Vol. 29, No. 20)

Head Start Boosts Value of Stability Testing

Early Data Can Guide Formulation Strategies and Contribute to Regulatory Filings
  • Vicki Glaser

Maximizing and validating the stability of a drug is critical throughout its life cycle, beginning in the development phase of an active pharmaceutical ingredient (API), continuing through the final formulation process, and following commercialization as part of post-marketing product analysis.

The assessment of a compound’s chemical and physical characteristics, potency, activity, solubility, and appearance after storage under a variety of defined conditions can guide decision making on which experimental candidate to take forward, or may signal the need to reengineer a lead compound to enhance its stability before initiating costly preclinical and clinical studies.

The stability of a drug, whether a small molecule or a larger biopharmaceutical such as a protein, is an essential part of analytical testing to ensure the identity and activity of the API, assess the final formulation, and detect degradation products or aggregates that might contribute to increased risk of adverse effects and toxicity.

Two years ago, the ICH Steering Committee endorsed the establishment of a Quality Implementation Working Group to monitor the consistent, global implementation of the Q8 (Pharmaceutical Development), Q9 (Quality Risk Management), and Q10 (Pharmaceutical Quality System) guidelines that were established in 2003. These recommendations represented a departure from traditional approaches to quality guidance and emphasized a quality system built on risk- and science-based strategies.

Stefan Adam, Ph.D., director of analytical development and quality control at LifeCycle Pharma, emphasized the importance of applying ICH Q8, Q9, and Q10 guidelines to the early phases of small molecule drug development in his presentation at Bharat Book’s “Stability Testing” conference held earlier this month in London. The outcomes of early-stage testing, including analysis of a compound’s chemical or physical incompatibility, could then be applied to the selection of excipients for formulating the API into a drug product. This type of risk management-based approach can benefit from close interaction between the analytical, formulations, and manufacturing teams.

Risk management is an important component of a proactive stability program, in Dr. Adam’s view. The ability to predict probability of success by performing sound risk assessment at every step of developmentis a valuable tool that can save companies time, resources, and money. For example, from the beginning a company should perform diligent forced-degradation and excipient-compatibility studies and use the results together with data obtained from bulk stability testing and evaluation of the packaging material to predict early on a long-term stable formulation.

Never Too Early

Waiting to begin stability studies until you have a drug in its final formulation may be a costly approach, warned James Clark, stability team leader in the pharmaceutical development services group at Xcelience, a CRO based in Tampa, FL, that provides formulation development, preformulation, analytical, and clinical trial manufacturing services to companies developing small molecule drugs.

Early stability data can help distinguish between parallel compounds in development, guide formulation strategies, contribute to regulatory filings for early-stage clinical studies, and allow researchers “to go into Phase II or III trials with a lot more confidence,” said Clark.

By applying the principles in the ICH Q8, Q9, and Q10 guidelines, companies will define what the FDA describes as critical quality attributes, based on the outcomes of early-stage analytical studies. These can then be used as measures for assessing a drug product as it moves through pilot and large-scale production. A clear understanding of what effect changes in a drug product’s chemical and/or physical properties over time might have on its bioavailability can help define acceptable and optimal parameters and establish a foundation for interpreting later test results.

Sven Oliver Kruse, Ph.D., managing director at Diapharm, has observed an increase in exploratory testing earlier in development, including the use of accelerated conditions and stress testing to assess product degradation. With this information researchers can begin to determine how to develop a stable formulation of an API and whether the final drug product will be formulated as a liquid—for oral or intravenous administration—or a solid.

At the stability testing meeting, Dr. Kruse discussed the European GMP guidelines and, in particular, the requirement for ongoing stability testing as part of the preparation of an annual product quality report (PQR) for pharmaceutical products already on the market. The PQR calls for continuous stability testing of, typically, one batch of product each year, performed in controlled storage cabinets for a period of not less than the stated shelf life. This requirement applies to every different dosage, pack size, and package type for a given product.

The European Union’s GMP guidelines allow ongoing stability-testing protocols to differ from those required for the initial long-term stability determination conducted before a product receives approval for commercial sale. For example, ongoing testing of a particular parameter can be done less frequently if that parameter has been shown not to be critical to product stability, explained Dr. Kruse.

In some cases, frequency of testing can be reduced by 50% or more, for substantial cost savings, he reported. To prove product stability throughout the labeled shelf-life he recommended retesting of all parameters when a product reaches its expiration date. Companies may also need to apply the full testing protocol to the first batch of product made available for commercial sale in order to generate sufficient data for subsequent trend analyses.

Stability testing is essential for determining a product’s shelf life. ICH guidelines have standardized international protocols for stability testing at storage conditions of 30ºC and 65% humidity. Accelerated testing conditions of 40ºC and 75% humidity are commonly used to predict the effects of long-term storage at room temperature.

A movement in the industry toward building quality into a drug compound from the earliest stages of development, sometimes called quality by design, would, in theory, eliminate or greatly reduce the need for end-product testing, including for stability. The theory holds that if you develop and test a product correctly throughout its life cycle and ensure a high level of quality control along the developmental pipeline, then assessment of the final product before release would be redundant. However, it will likely take quite a bit of confirmatory data to convince companies to forgo long-standing release testing.

Targeting Key Parameters

BASi is a contract research services provider that offers preclinical and bioanalytical services, large molecule bioanalysis, method development, and pharmaceutical analysis. The company’s pharmaceutical analysis group primarily fields requests to analyze small molecule drug compounds and also works with proteins and other large molecules.

For stability testing the main focus is on potency and purity analysis, as well as physical characterization (such as moisture content and tablet hardness or dissolution), according to Josef Ludwig, director of pharmaceutical analysis. Studies to assess a compound’s stability typically begin early in development. “They may start even before toxicology studies,” Ludwig said.

Stability testing on an API can give companies an idea of how long they can work with a batch of material before they need to reproduce it. For smaller biotech companies looking to license a compound, information on its stability adds to the database they can provide to potential development partners.

Ludwig described increasing demand for analysis of experimental samples given to animals during toxicology testing. These samples have often been frozen for several months, he noted, and after tox studies are complete, BASi may be asked to assess the stability of simulated samples to show that material maintained at a defined concentration in a given matrix and stored under specified conditions would not have degraded, lost potency, or undergone changes in its physical or chemical properties.

Potency and purity are the biggest concerns, Clark agreed. Appearance is also important—does the product change color over time, for example, even if its potency does not change? The presence of moisture is a key issue as well. If a compound is hydrophilic it is important to know how it will react in the presence of water. Clark emphasized the value of integrated data evaluation and trending analysis, putting together the various components of stability analysis to see the big picture.

Ludwig advised companies to establish robust analytical methodologies early on. In his view, the biggest mistake companies make is to rely on quick-and-dirty methods that may not capture an accurate and precise potency or complete degradation profile.

Too often young companies “do not have an overall stability platform plan” detailing what they will do at each stage, what they are looking for, and how much material they will need, said Barry Rosenblatt, director of technology development for the biopharmaceutical services North America division of Charles River Laboratories.

Technology Challenges

HPLC is the standard analytical tool used to validate the identity and quantity of a compound. Ultra-high pressure liquid chromatography (UPLC) is gaining momentum as a higher-throughput alternative that can accelerate testing and enable higher-resolution analysis. Binding assays are used to assess potency, and functional assays to evaluate activity. Nuclear magnetic resonance imaging may be used to evaluate the identity and proper folding and tertiary structure of proteins and other complex compounds.

Analyzing larger, more complex molecules such as proteins for stability may require additional testing beyond determination of the amount of a chemical entity or the amount of degradants in a sample. “You also have to confirm activity,” said Ludwig. A compound may be present, but it may have reduced or no activity due to changes in its tertiary structure.

Selecting analytical tools for stability studies, especially for larger biopharmaceuticals, is a continuing challenge, particularly because of the variability inherent in available cell-based potency assays, according to Rosenblatt. “The holy grail is to find an in vitro, clinically relevant potency assay,” he said, one that can be validated and yields a reliable stability indication.

Some molecules will form aggregates during stability testing and may exhibit super-activity, explained Rosenblatt. In some cases, aggregates can have greater potency than the monomeric form of the molecule. Aggregation has been associated with increased risk for immunogenicity as well as drug resistance.

“People are concentrating on particulates, and especially ‘sub-visible’ particulates”—a new buzzword being used to describe small, aggregated products that are “invisible in terms of the nascent activity of the molecules and are more of an issue from a safety standpoint” due to their propensity to cause adverse reactions, Rosenblatt explained.

Light scattering is one technique being used to detect and quantify these sub-visible particles. Rosenblatt expects a variety of laser-based imaging tools to become available that will enable visualization of particulates. To support ongoing PAT initiatives, these will likely be microfluidics-based instruments that will allow for real-time analysis of samples as they come off a HPLC instrument.

One of the challenges these new technologies will introduce relates to interpretation of the findings, he said. For example, is the researcher seeing something truly new, or something that has been there all along but can now be detected?

In the future, Clark envisions a growing emphasis on detecting impurities in final formulations (and determining their toxicologic profile) as new and more complex compounds move through development. Analytical methods will rely on a broader menu of technologies, including, for example, mass spectrometry. “UPLC will be used almost exclusively,” replacing HPLC, Clark predicted, especially for highly potent compounds dosed at very low concentrations (sub-milligram to 1 mg).