The proper design of a stability programme is critical to the successful development of any bio-pharmaceutical product, while stability data supports all marketing applications. In this context, biologicals must be given careful consideration since their molecular conformation and biological activity depends not only on covalent forces, but also on non-covalent forces. Biologicals are thus more sensitive to environmental factors and stringent storage conditions are usually necessary. Primary data should be based on long term, real-time, real-condition stability studies.

Drug substance and product
Stability data of at least three representative batches of bulk material and final product are required for a minimum of six months at the time of submission (where intended storage exceeds six months). For shorter storage periods, a case-by-case decision is mandatory. Data on pilot scale batches may be submitted with a commitment to place the first three manufacturing scale batches into the long-term stability program after approval. Manufacturing, quality, container/closure system and storage of the substance entered into the stability program must be representative of the material used in preclinical/clinical studies and for manufacturing scale.

Sample selection
Where the product is distributed in batches differing in fill volume, unit age or mass, samples for the stability program are selected on the basis of a matrix system and/or by bracketing. In these systems only a representative subset of samples are tested. Designs for such reduced stability studies can only be applied when the documentation provided confirms that the stability of the tested samples represents the stability of all samples.

Stability indicating profile
The dossier accompanying the application for marketing authorization must cover a detailed protocol for the assessment of the stability of the drug substance and drug product. It also must cover protocol for assessing the proposed storage conditions and expiration dating. The manufacturer must propose a stability-indicating profile, rather than a single stability-indicating parameter, which detects changes in the identity, purity and potency. Methods must be validated by the time of submission.

Potency
Potencies tested by different laboratories can be compared if expressed in relation to that of an appropriate reference material calibrated directly or indirectly against a national or international reference standard. In some cases, potency is dependent upon the conjugation of the active ingredient(s) to a carrier. Testing prior to conjugation, assessing the release from the carrier, in vivo tests or a surrogate test should be then considered.

Purity & molecular characterization
Relevant physicochemical, biochemical and immunochemical methodologies must yield a comprehensive characterization of the drug substance and/or drug product and the accurate detection of degradation (i.e. deamidation, oxidation, sulfoxation, aggregation, fragmentation). Purity is typically assessed by more than one method. The values obtained are method dependent and should be reported whenever possible (i.e. degree of purity, individual and total degradation products). Wherever significant changes due to degradation are detected, potential hazards must be considered and the degradation of products should be characterized and quantified. Acceptable limits must be proposed and justified.

Drug product characteristics
Appearance (color and opacity for solutions/suspensions; color, texture and dissolution time for powders), visible particulates, pH and moisture level must be monitored. Sterility testing or container/closure integrity testing should be performed initially and at the end of the proposed shelf life. Additives or excipients may degrade during the dating period and must be monitored if appropriate.

Storage conditions
Temperature and humidity: Expiration date is based on real-time/real-temperature data, yet continuing updates of the initial stability data are possible. Where containers and conditions of storage afford sufficient protection, additional stability tests at high and low humidity can be omitted. The stability of freeze-dried products after reconstitution must be demonstrated for the conditions specified on the label.

Accelerated & stress conditions: Accelerated conditions provide useful support for establishing the expiration date, provide stability information for future product development, assist in validation of analytical methods and help elucidate the degradation profile of the drug substance or drug product. Stress conditions are useful in determining whether accidental exposures (i.e. during transportation) are deleterious to the product and help in evaluating which specific test is the best indicator of product stability. Testing for light exposure is performed on a case-by-case basis.

Container/closure: Where the lack of interaction between the liquid product and the container/closure cannot be excluded, studies must include samples maintained in contact with the closure (i.e. bottom-up), as well as in the upright position. Data for all different containers/ closures must be supplied. Multiple-dose vials must be capable of withstanding the conditions of repeated insertions and withdrawals, such that the product retains its full potency, purity and quality.

Testing frequency
Most biologicals have shelf lives within the range of 0.5 to 5 years. For proposed shelf lives of greater than 1 year, studies should be conducted monthly for the first three months, then at three months interval. For proposed shelf lives of greater than 1 year, studies should be conducted every three months during the first year, every six months during the second year and then annually.

Specifications & labeling
The product should retain its specifications throughout its proposed shelf life within the established limits for safety, purity and potency. For most substances precisely defined storage temperatures are recommended. Specific recommendations for products that cannot tolerate freezing, light and/or humidity should appear on containers, packages and/or package inserts in accordance with the national/regional requirements.

The biochemical analysis group at RCC has a vast experience in the design and performance of stability programs for biologicals, as well as in the validation of the respective assays. The fields of expertise include:
■ Long-term stability studies, accelerated and stress conditions in ICH-compliant stability chambers, matrixing and bracketing
■ Analysis of drug substance and drug product, as well as main additives or excipients, pharmacopoeial analysis., method development and validation
■ Assays for biological activity, potency assays (i.e. in vivo and in vitro EPO bioassay) and cell culture assays (i.e. WISH assay and GCSF assay)
■ Purity and impurity profiling (i.e. PAGE, CE, SEC, GC, LC-MS)
■ Identity tests, biochemical and immuno-chemical characterization of the biological and its degradation products (i.e. IP, ELISA, in vitro activity tests)
■ Physicochemical methods such as appearance/color, turbidimetry, nephelometry, texture, dissolution time, relative density, osmolality, visible and sub-visible particles, pH and moisture levels
■ Sterility testing, endotoxin analysis, container/closure integrity testing

(The author is head of biochemical analysis, Business Unit Pharma)