The establishment of reference materials that have been correlated with the International Chemical Reference Substances may be desirable for various practical reasons, e.g. the latter may not be available in adequate quantities to supply all local needs. Moreover, the availability of such reference materials (for example, on a regional basis) should result in a reduction of the time between ordering and receiving the materials.
The authority to establish a reference substance for national or regional use should be clearly defined by the appropriate drug regulatory body. If an International Chemical Reference Substance exists, it is desirable that all corresponding reference substances should be correlated with it in order to obviate the proliferation of possibly dissimilar reference substances. The first step in establishing such a derived material would be to form an estimate of the amount that might be needed for a period of perhaps three to five years (the duration of storage would depend on the known stability characteristics of the material in question), to define the intended use of the substance, and to determine the extent and nature of testing that is required to evaluate it.
Once the material has been obtained, its identity should first be verified (for example, by infrared spectrophotometry in comparison with the International Chemical Reference Substance) and it should be examined by an appropriate stability-indicating procedure so as to provide a starting point for routine stability monitoring. If the material is to be used as a quantitative assay standard, it and the International Chemical Reference Substance should be subjected to a collaborative test following a strictly defined protocol with the participation of at least three laboratories. From the results so obtained, a value for the content of the assayed component should be assigned. Additionally, the substance should be shown to comply with all the requirements of its specification and it should be confirmed that it is suitable for its intended use.
Once established, the material should be packed in an appropriate way (as nearly as possible in the same way as the corresponding International Chemical Reference Substance) and it should be regularly monitored, in comparison with the primary reference material, to confirm that unacceptable deterioration is not occurring.