Expiration Dates and Retesting...
Pharmaceutical ingredients are controlled by cGMP regulations. Users of pharmaceutical materials should be informed regarding when the material can be re-tested for continued use.
ICH Q1A(R2)/FDA Definition:
Expiration date: The date placed on the container/labels of an API designating the time during which the API is expected to remain within established shelf-life specifications if stored under defined conditions and after which it should not be used.
Retest date: The date when a material should be reexamined to ensure that it is still suitable for use.
Retest period: The period of time during which the drug substance is expected to remain within its specification and, therefore, can be used in the manufacture of a given drug product, provided that the drug substance has been stored under the defined conditions. After this period, a batch of drug substance destined for use in the manufacture of a drug product should be retested for compliance with the specification and then used immediately. A batch of drug substance can be retested multiple times and a different portion of the batch used after each retest, as long as it continues to comply with the specification. For biotechnological/biological substances known to be labile, it is more appropriate to establish a shelf-life than a retest period. The same may be true for certain antibiotics.