Key Considerations in Stability Testing

Within the bio/pharmaceutical industry, ascertaining drug substance/product stability is an integral part of the development process and must be performed according to specific regulatory requirements. Rigorous testing methods need to be employed to determine a product’s stability, safety, integrity, and shelf-life under a variety of stipulated conditions.

Rigorous testing for stability is considered to be a pre-requisite for acceptance or approval of any bio/pharmaceutical product submission by the relevant regulatory body. “Stability assessment is potentially the most important aspect of drug product development,” says Stuart Kirbyshire, stability manager, Intertek Pharmaceutical Services. “Any regulatory authority will expect you to have a full and thorough knowledge of your product, and without understanding changes to chemical and physical stability under variations of temperature, humidity, and light, obtaining approval will prove problematic.”

Guidelines, provided by the International Council for Harmonization (ICH), the World Health Organization (WHO), and other agencies, specify that bio/pharmaceutical products need to have an expiration date that has been determined via the most appropriate stability test protocols (1,2). These guidelines take into consideration the climatic zone of the intended market, of which there are four separate classifications for worldwide stability testing (3). 

“It is also key to assess your product across a broad range of climatic conditions to ensure global market reach,” Kirbyshire confers. “Understanding the effects of transportation and temperature cycling is also desirable to prove there will be no unanticipated events during shipping and storage.”

Some of the guidelines provided for stability testing, however, are only applicable to conventional small-molecule drug products/substances and, as guidelines, do not provide specific methodologies for the recommended tests. Therefore, analytical methods and bioassays need to be developed by analysts, which then must be validated. See Table I for an overview of the typical analytical methods employed.

“The analytical techniques employed can vary depending upon the type of molecule, dosage format, and intended therapeutic use,” explains Kirbyshire. “As the primary purpose for conducting stability studies is to determine shelf life, characterization of degradation products, and potency for any pharmaceutical product.” 

“For biologics, driven by their complexity of structure, a more diverse analytical capability is required for a stability study. Therefore, it is important to design stability programmes that incorporate robust analytical approaches,” notes Jordi Trafach, associate director-Biologics, Intertek Pharmaceutical Services. “These analytical approaches should be built on a good scientific understanding of degradation pathways and established stability-indicating methods, which are sensitive and specific to changes in critical quality attributes (CQAs).”

Key aspects relating to biologics 

Biologics are known to be extremely sensitive to environmental factors and susceptible to aggregation and degradation (4). “To reduce the risk of degradation and maintain the biological activity of the product, suitable conditions for storage and shelf life must be established,” emphasizes Trafach. “Understanding potential degradation routes in relation to the storage environment are paramount to establishing which CQAs are more susceptible to change throughout the lifetime of the pharmaceutical or biopharmaceutical. Ultimately, this understanding ensures that the optimal quality control strategy is in place to monitor continued efficacy and safety of a therapeutic.”

As a result of the complex nature of biologics, Trafach states that bespoke, non-compendial methods may be required to monitor all potential and known degradants throughout product development. He stresses that it is also important to consider excipients that are often required in biologic formulations, as these excipients may be susceptible to degradation or may also react with the main biologic product. 

“In cases where a potential degradant is observed at a later development stage, there may be the requirement to retest, which could lead to delays to the study completion, potentially impacting product registration,” Trafach continues. “Stability-indicating methods should be optimized and validated to demonstrate precision, accuracy, and robustness and that method performance is fit for its intended use.” 

Forced degradation studies 

Forced degradation studies are used to determine the degradation products that are formed during accelerated pharmaceutical studies and long-term stability studies (5). These studies are mandated by regulatory bodies for new drug substances and are integral to understanding degradation pathways, and, as such, gaining a comprehensive assessment of biologic stability, Trafach notes.

“Forced degradation studies also drive invaluable information regarding formulation development and process development,” he adds. “A forced degradation study can include factors such as temperature, light, pH, oxidizing agents, mechanical stress, and freeze-thaw cycles. The knowledge from these studies, in conjunction with a detailed understanding of the product and process, help to establish CQAs.”

Planning is prudent

The level of complexity and scientific expertise required to perform stability testing of sufficient quality and efficiency can take a considerable period of time and incur significant costs (6). However, appropriate procedure planning can be helpful, according to Kirbyshire. “With good planning of other activities around long-term studies, supported by bracketing and matrixing of batches, pack types, and strengths, as detailed in ICH Q1D, time pressures can be eased,” he says.

“In addition to planning,” Kirbyshire continues, “testing of a product stored under stress conditions can give an early indication of how the long‑term stability may turn out later down the line. So, it’s key to pay particular attention to the product performance at the early stages of your study at these conditions.”

In the future, Kirbyshire believes that there will be increased focus on the benefits of accelerated stability assessment programmes (ASAP) during early stage development, which have the potential to expand into later-stage assessments. “The ASAP strategy is based on the robust methods for forced degradation, where the products are submitted to high temperature and humidity conditions, and the time points reduced to 14 days,” he explains. “This is sufficient enough to cause a suitable increase in degradation, which can be used to predict the potential long-term stability effects.”

Despite some success being witnessed in the small-molecule arena, however, Kirbyshire stresses that suitability for physical stability testing or large-molecule assessment is not currently proven. “With increased use of the technique, further advances will be made establishing ASAP as a reliable and cost-effective method of determining product stability,” he says.

Considering the finished product

Stability of a bio/pharmaceutical product will have a dependency upon the dosage form and packaging-closure system chosen for commercial deployment (7). “The anticipated shelf life and in-use storage of your product once commercially available will strongly influence the approach to stability testing during development,” confirms Kirbyshire. (Figure 1)

For example, parenteral solutions can have greater susceptibility to extremes of temperature and light, which usually leads to a storage temperature range of 2–8 °C being targeted, he explains. “Therefore, 12 months storage at 2–8 °C and six months accelerated at 25 °C/60% relative humidity (RH) is sufficient to establish shelf life,” he notes.

In the cases of dry powder inhalers (DPIs) and oral solid doses, humidity is the key attribute to assess, Kirbyshire emphasizes. “Long-term studies at high humidity conditions (e.g., 30 °C/75% RH and 40 °C/75% RH) are required,” he says. “A critical test at all time points is the assessment of aerodynamic particle size distribution for DPIs and dissolution for oral solid doses, which will confirm continued efficacy. Any reduction in performance may be improved by the use of effective packaging and potentially the addition of desiccant materials. Stability studies are key to determining these.”

Outsourcing stability testing

The decision to outsource stability studies can have a significant impact, either positive or negative, on the success of the overall drug development programme. If due diligence is not performed when choosing a partner, the sponsor’s decision could turn out to be costly (8).

“When assessing any outsourcing stability partner, there are many things to consider,” reveals Kirbyshire. “They must have an expert understanding of the key regulatory guidance, ICH Q1A R2 but must also show compliance with [International Organization for Standardization] ISO 9001 to give full confidence in the quality systems and data integrity.”

Some other important aspects to consider when choosing an outsourcing partner for stability testing are the qualification and maintenance schedules of the storage facility and associated monitoring systems, Kirbyshire continues. “The integrity of the study is only as good as the reliability and robustness of the equipment and control strategies utilized by the provider,” he adds. “Excursions from storage conditions can have an unpredictable and severely detrimental effect to any study, be it a short-term assessment of API stability, through to a full registration stability programme extending up to five years.”

Of course, there are noteworthy benefits of partnering with an outsourcing service provider. “As pharmaceutical development has become an increasingly global partnering process, selecting a provider with knowledge and experience of import/export requirements is strongly recommended particularly for some of the more challenging markets,” Kirbyshire adds.

Significant improvements

Over the years, there have been significant improvements in the reliability of equipment and monitoring systems, including real-time feedback of potential excursions, according to Kirbyshire. These technological improvements have given rise to accelerated and efficient decisions to be taken regarding the next stage of product development. 

“Regulatory decisions are routinely changing based on currently available data and justified strategies of stability assessment,” he summarizes. “Through harmonization of this information, companies developing medicines can make informed decisions on the best approach to adopt for their products.”

References

1. ICH, Q1A–Q1F Stability, ICH Quality Guidelines.
2. WHO, “Annex 2: Stability Testing of Active Pharmaceutical Ingredients and Finished Pharmaceutical Products,” WHO Technical Report Series, No. 953 (Geneva, Switzerland, 2009).
3. H.U. Bhuyian, et al., Eu. J. Biomed. Pharm. Sci. 2 (6) 30–40 (2015).
4. T. Morrow and L. Felcone, Biotechnol. Healthc. 1 (4) 24–26, 28–29 (2004).
5. F. Iram, et al., J. Anal. Pharm. Res. 3 (6) 00073. DOI: 10.15406/japlr.2016.03.00073.
6. S. Bajaj, D. Singla, and N. Sakhuja, J. Appl. Pharm. Sci. 2 (3) 129–138 (2012).
7. WHO, “WHO Expert Committee on Specifications for Pharmaceutical Preparations,” WHO Technical Report Series, No. 863-Thirty-fourth Report (Geneva, Switzerland 1996).
8. D. Browne, Outsourcing Resources, Supplement to Pharm. Tech. Volume 33 (8) (August 2009). 

Article Details 

Pharmaceutical Technology
Vol. 43, No. 3
March 2019
Pages: 52–56

Citation 

When referring to this article, please cite it as F. Thomas, “Key Considerations in Stability Testing," Pharmaceutical Technology 43 (3) 2019.