If the API manufacturer must retain a sample of each batch – and so must the drug product manufacturer under 21 CFR 211, – can the API manufacturers retained sample satisfy both requirements?

The purpose of the retained sample for the API manufacturer is to retain an authentic sample of
the material representing its quality at the time it was shipped out. The purpose of the retained
sample for the drug product manufacturer is to retain a sample of the material as it was received.
In most cases it is unlikely that the API manufacturers sample can satisfy both. On the other
hand, there could be a plant in which APIs are made in one half of the plant; drug products are
made in the other. In that situation, one retained sample could be enough.