When FDA is not prepared to approve an NDA or BLA in its current form, it issues a Complete Response Letter describing every deficiency the agency identified. What the CRL itself does not decide is how long FDA's review of the fix will take. That is set separately, under 21 CFR 314.110, by whether the resubmission is classified Class 1 or Class 2 — a distinction that traces back to FDA's November 1997 commitment to Congress during PDUFA reauthorization and is now implemented through CDER's MAPP 6020.4. Sponsors who treat the CRL as a deficiency checklist and the classification as an afterthought are the ones most likely to build a response around a 2-month assumption FDA does not share.
What Class 1 and Class 2 actually mean
The Class 1/Class 2 framework did not originate as a regulation; it started as a policy commitment. In its November 1997 letter to Congress on PDUFA reauthorization, HHS committed FDA to recognizing two categories of CRL resubmission, each with its own review-goal date. That commitment is now codified in 21 CFR 314.110 and implemented operationally through CDER's MAPP 6020.4, "Classifying Resubmissions of Original NDAs, BLAs, and Efficacy Supplements in Response to Complete Response Letters," with a parallel CBER standard operating procedure for biologics. The practical effect: a resubmission is not just a document sponsors send back to FDA. It is a submission that gets sorted into one of two review tracks the moment FDA receives it.
What actually counts as Class 1
MAPP 6020.4 does not leave Class 1 open to interpretation. It names specific categories of deficiency that qualify, because they can be resolved with information FDA can verify quickly rather than material that requires a full substantive review:
- Final printed labeling. Labeling changes that do not depend on new data.
- Draft labeling. Proposed labeling submitted for FDA's review and negotiation.
- Safety updates in the original format. New safety data or tabulations submitted in the same format as the original submission, with changes clearly highlighted.
- Assay validation data or minor reanalysis. Limited, readily available information that does not involve a new dataset.
- Everything else is Class 2 by default — including any item that would require an advisory committee, and by extension any deficiency response built around new clinical or nonclinical studies or a substantial manufacturing change.
A sponsor does not get to keep a Class 1 clock by calling a resubmission Class 1. FDA reviews the substance, and if the scope is really Class 2, the classification changes and the clock restarts from the resubmission date — it does not prorate the difference. Why the classification call is the real risk
Where sponsors get the call wrong
The exposure is not usually a sponsor deliberately mislabeling a resubmission. It is scope creep during response drafting: a labeling-only Class 1 response that picks up an expanded safety analysis along the way, or an assay-validation update that grows into a broader CMC justification because it was already being written. Either change can push the resubmission's actual content past what MAPP 6020.4 treats as Class 1, and FDA's classification determination follows the substance of what was submitted, not the cover letter's characterization of it. Once FDA reclassifies, the review clock resets to 6 months from the resubmission's receipt date — the sponsor does not keep the time already elapsed against the 2-month goal, and internal launch planning built around the shorter clock is now wrong by months, not weeks.
- Separate deficiencies by MAPP 6020.4 category before deciding what classification to target.
- Request a Type A meeting to confirm FDA's read on classification before building the resubmission around an assumption.
- Hold the resubmission's scope to what the target classification actually allows — no folded-in improvements that were not deficiencies.
- Plan resourcing and launch timelines off the classification FDA is likely to apply, not the one the sponsor would prefer.
None of this changes what has to go into the response — the deficiencies in the CRL still have to be resolved on the merits. What it changes is the sequencing: confirming classification before the resubmission is drafted, rather than discovering FDA's view of it after submission, is the difference between a review that runs on the 2-month goal and one that quietly becomes 6. Companies that treat the CRL response the way they treat a Q-Submission — as a scoped, FDA-confirmed interaction rather than a unilateral filing — are the ones who keep the timeline they planned for.
Frequently asked questions
What is the difference between a Class 1 and a Class 2 resubmission?
Under 21 CFR 314.110, a Class 1 resubmission carries a 2-month FDA review goal and is limited to deficiencies addressable with readily available information — final or draft labeling, or safety updates and minor data reanalysis submitted in the same format as the original application. A Class 2 resubmission carries a 6-month review goal and covers everything else, including new clinical or nonclinical studies, major CMC changes, or anything requiring an advisory committee.
Who decides whether a CRL resubmission is Class 1 or Class 2?
The sponsor proposes a classification when it resubmits, but FDA makes the determination. If FDA finds that a sponsor-classified Class 1 resubmission actually contains Class 2-scope content, it reclassifies the resubmission — restarting the clock at 6 months from the resubmission receipt date, not extending the original 2-month goal proportionally.
Can a sponsor request a meeting with FDA before resubmitting after a CRL?
Yes. Sponsors can request a Type A meeting after a Complete Response Letter to align with FDA on the deficiencies, the resubmission's scope, and the classification the agency is likely to apply — before committing resources to a response that FDA may later reclassify.
Sources & further reading
- eCFR. 21 CFR 314.110 — Complete response letter to the applicant. ecfr.gov
- FDA. CDER Manual of Policies & Procedures (MAPP) index, including MAPP 6020.4, Classifying Resubmissions of Original NDAs, BLAs, and Efficacy Supplements in Response to Complete Response Letters. fda.gov
This article is provided for general informational purposes and reflects the regulatory landscape as of its publication date. It is not legal or regulatory advice. Confirm current CRL resubmission classification requirements with FDA or qualified counsel before acting.
