It depends upon the level of the final product and the probability of the API yielding toxic degradants.
If the active ingredient is in a topical product, then maybe not have to identify all degradants. When I validated a stability indicating assay where the API was in a teat dip, I did not have to identify the degradants.
When the final product was a GMP manufactured injectable; then, I had to make efforts to identify the degradants. For example, I had a project where I had to convert a HPLC assay to a LC/MS compatible assay in order to elucidate probable degradant structures. I fraction collected the degradants from the original HPLC assay, then analyzed the fractions by the LC/MS compatible assay.
In another instance, the API was in a GMP injectable final product, and there were no literature references on the degradation pathways. I contacted the manufacturer, who could not find literature references either. So, I did 'chemistry.' I wrote out the equations to figure out possible degradant structures.
Then, I scoured through literature and vendor websites to find these structures. In the end, I found a few of the possible degradant compounds through commercial sources. I also used the 'related compounds' approach, wherein I purchased compounds that were closely related in structure and characteristics to the possible degradant structures. I, then, analyzed all these possible degradants and related compounds to show specificity and stability indication of the assay.
