According to FDA regulations, if an applicant wishes to pursue approval of its Abbreviated New Drug Application (ANDA), applicant must submit all materials required to fully address all shortcomings in the Complete Response Letter (CRL) within one year of the CRL’s issuance. The applicant must submit a request for an extension on or before the due date for the CRL response.

The Possible scenarios while dealing with CRL

1. Failure to Respond to a CRL Within 1 Year
2. Failure to Respond to a CRL Within the Extended Time Period Granted by FDA
3. Submitting a Request for an Extension of Time to Respond to a CRL
4. Evaluation of a Request for an Extension to Respond to a CRL
5. Withdrawal of an ANDA

Conclusion: Following FDA’s written communication to the applicant, the applicant will have 30 days to justify why the ANDA should not be withdrawn and to ask for an extension of time to remedy all CRL defects.

These are a few examples of the exceptions the FDA might consider when determining whether or not an applicant’s request for an extension of time to reply to a CRL is acceptable.

• A national or international public health emergency (such as COVID-19) postponed the start of investigations required to rectify flaws found in the CRL.
• The ANDA applicant and/or active pharmaceutical ingredient (API) manufacturer are conducting an ongoing risk assessment for impurities in the drug product and/or API.
• The ANDA applicant is conducting an ongoing analytical assessment of extractables/leachable.
• The ANDA applicant is unable to procure the API from the API manufacturer.
• The ANDA applicant is unable to obtain the RLD and is attempting to procure the product samples under CREATES.
• The RLD has been reformulated, necessitating additional bioequivalence (BE) studies from the ANDA applicant. Based on the deficiencies identified in the CRL, the ANDA applicant decides to conduct new BE studies
• The ANDA applicant is transferring production to a new manufacturing facility.
• The ANDA applicant is still addressing the issues found during a recent facility inspection.

Detailed reference document from
https://www.fda.gov/regulatory-information/search-fda-guidance-documents/failure-respond-anda-complete-response-letter-within-regulatory-timeframe-guidance-industry