Reference standards (RS) are critically important for the execution of bioassays to determine the potency of biopharmaceuticals. Potency of the drug product or drug substance is determined relative to that of the RS and for a valid relative potency measurement, the RS must show the same dose-response characteristics as the drug sample in the bioassay being used. In most drug development programs, a succession of RS is required. Ensuring stability of the RS and continuity of potency measurements throughout the life-cycle of a drug represents a major investment of resources. Timely development of a RS program is essential to avoid costly delays during drug development.  Regulatory requirements for the RS become increasingly stringent as the drug development program proceeds.

To examine issues encountered in the development of in-house RS for use in bioassays, BEBPA formed a focus group. The results of their discussions have now been published as a scientific white paper “Reference Standards for Potency Assays” which can be found through the link below. This presents an overview of current practices common in the biopharmaceutical industry, highlighting common issues encountered and the ways in which some organizations address these.

A number of general principles apply throughout the RS development program. Usually, and ideally, the same RS is used for the potency assay and other analytical techniques but some analytical techniques may require a special preparation or formulation of the RS.  Keeping retention samples of all RS is important. Replacement RS should be prepared while there is still sufficient stock of the previous RS for comparison in the bridging studies required whenever a RS is replaced.  Data from physicochemical analyses must be used in combination with potency data in selecting a RS that is representative of the product as currently manufactured and in monitoring stability.

As soon as development of a biological assay is started, a RS should be selected.  This first RS is referred to in this paper as  Development RS (DRS).  Later, during clinical development, the DRS is succeeded by the interim RS (IRS) representative of the current clinical product. The first IRS may need to be replaced with a second (third, . . . ) IRS if stocks run low or if the characteristics of the clinical product change, (impurity profiles improve, formulations change, etc.). The tests for the required characterization of the first, and any subsequent, IRS are discussed in detail.

Release of commercial products typically requires a two-tier reference system consisting of a primary RS (PRS) and a working RS (WRS), also called a secondary RS. The First PRS should be of sufficient quantity to last for as long as possible, preferably the entire commercial life of the product, though if stock of the PRS runs low or it is insufficiently stable, it becomes necessary to establish a replacement PRS.

Major concerns in the RS program are stability of the RS and potency assignment. Measures to promote stability are discussed in detail as are various means of monitoring the stability. Potency assignment is discussed with statistical considerations covered in an appendix.

Case studies of replacement of RS are presented and two special cases are considered: biosimilar products, where the originator product is available to serve as a reference material until development of an in-house RS and the case of transitioning from an older, single tier, RS program to a two-tier system.

The scientific white paper “Reference Standards for Potency Assays” is available through the link below.  It contains a plethora of approaches and common practices surrounding many aspects of establishing and maintaining a RS program throughout the development and commercialization of a drug product. The focus is on RS for potency assays and includes discussion about the many common hurdles many firms face.