With respect to the re-test date of the drug substances, we have the stability data of a drug substance for up to 24 months at real time stability condition. The re-test period is assigned up to 24 months. According to the “Evaluation of Stability Data – ICH Q1E”, 2.4.1.1(the proposed retest period or shelf life can be up to twice, but should not be more than 12 months beyond, the period covered by long-term data), the retest period can be assigned up to 36 months. Can we assign the retest period up 36 months? If yes, does it require retesting of the active pharmaceutical ingredient (API) at 24 months?

Retest period and expiry date for APIs should be based on stability data. If an expiry date has been
assigned to an API then its batches cannot be used after the expiry period. However, if a retest period has
been assigned to the API, then after the retest period is over the API batch can be tested and used immediately
(e.g., within one month of the testing). In the scenario presented above extrapolation of expiry date beyond
24 months should be based on stability data both at long-term and accelerated storage conditions. If the test
results are satisfactory the retest period can be extended to a period not exceeding 36 months. Once the retest
period of the API has been extended to 36 months, testing batches at the 24 months time point would be part
of the ongoing stability protocol (it will not be considered retest). For further guidance on retest period and
expiry period please consult Stability Testing of New Drug Substances – ICH Q1 A (R2).