FDA · Basic · 12 min lesson

The review process - acceptance review, substantive review, AI requests, MDUFA timelines and why 510(k)s stall

21 CFR 807.100 and 807.87; FDA refuse-to-accept policy for 510(k)s; MDUFA V performance goals; additional information requests; AI-enabled device software and PCCP overview as of 2026

What you will learn

Describe the acceptance (refuse-to-accept) review and the 15 day timing, and prepare an RTA self-check.
Explain the substantive review, the MDUFA V goals, the clock and the additional information (AI) request and hold.
Recognise the common reasons for AI holds and not substantially equivalent decisions, and respond to a deficiency letter with a complete, traceable answer.

Key takeaways

FDA aims to finish the acceptance review within 15 calendar days of receipt; the fee and a valid eCopy must be in place first.
A refuse-to-accept (RTA) is answered under the same number; no response within 180 days of the RTA notice means the 510(k) is treated as withdrawn.
MDUFA V goals for 510(k): Substantive Interaction within 60 calendar days and a decision within 90 FDA days, each for 95 percent of submissions.
FDA days stop while the file is with the submitter, so the calendar time to a decision is longer than 90 days.
An AI letter needs one complete, point by point response inside the response window, with every new test tied to the deficiency.
As of 2026, FDA guidance on AI-enabled device software functions was in draft and PCCP guidance existed in final form; check current status.

Free practice question

Norvik's submission arrives at FDA on a Friday. The fee is paid, the eCopy is valid, but the sterilization section has no report attached. Norvik expects a decision in 90 days.

What will most likely happen first?

It will be cleared early because the fee was paid.

Not quite. Fee payment starts the acceptance review only; section 807.100(a) still requires a substantial equivalence order for clearance.

It will likely be refused to accept because a required section is missing, and the clock will not start.

Correct. The RTA policy refuses files missing required elements, and the review clock starts only once the file is accepted, consistent with section 807.100 of 21 CFR and FDA review practice.

It will go straight to a premarket approval.

Not quite. A missing section does not change the pathway; the file is simply refused under the RTA policy.

Nothing, because FDA does not check completeness.

Not quite. FDA runs an acceptance review within about fifteen calendar days, as the RTA policy sets out, consistent with section 807.100 of 21 CFR and FDA review practice.

Key terms

refuse to accept: FDA's early check that a 510(k) is administratively complete before substantive review starts.
Substantive Interaction: FDA contact, in MDUFA V within 60 calendar days, communicating the review outcome so far, often an AI request.
FDA days: Days the file is with FDA; the count stops while FDA waits for the submitter.
additional information request: A deficiency letter during substantive review that puts the review on hold until the submitter responds.
not substantially equivalent: FDA decision that the device does not meet the criteria of 21 CFR 807.100(b).
PCCP: A plan describing planned device modifications and how they will be validated, which FDA can authorise with the submission.

Official sources

Go further

The full lesson has narrated slides, more scenario questions with explained answers and a simulation.

Open the Academy Watch on YouTube

Illustrative example. Educational only, not legal advice.