Related Substances

[Kimico]

Happy TGIF for all:

Where could I find a glossary or an explanation for the term "related substances". I am kind of unfamiliar with this term and I would like to gain an understanding of it. Thank you.

[Rob Burgess]

I take it to mean the following: any substances "related" to a known (e.g. drug substance) compound.

Thus related could be:

1) Process and/or synthetic precursor impurities
2) Degradation products from stability (stress) studies
3) Compounds that are closely related in structure to the compound of interest but are not degradation products or manufacturing by-products e.g. codeine and heroin

From a pharmaceutiucal analysis perspective we are predominantly concerned about 1) and 2)