The establishment of secondary chemical reference substances calibrated against a primary chemical reference substance 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 secondary chemical reference substances (for example, on a regional basis) would reduce the delay in receiving the reference material.

The body which establishes a secondary chemical reference substance for national/regional use should be clearly defined by the competent drug regulatory authority. Clear documentation must exist to establish the relationship between the secondary and the primary chemical reference substance.