How to Respond to an FDA Additional Information Request for a 510(k)

An Additional Information (AI) request from FDA means the reviewing division needs more information before it can make a substantial equivalence determination. Receiving an AI is not a rejection — it is a pause. How you respond determines whether your 510(k) moves toward clearance or into a second AI cycle that can add months to your timeline.

What an AI request contains

AI requests are issued as a letter from the reviewing division. The letter will include a list of numbered questions or information requests. Each item typically corresponds to a specific section of your submission where FDA needs clarification or additional data.

Common AI request categories:

• Predicate questions — FDA doesn't agree with your predicate selection or needs more justification for a technological difference
• Performance data gaps — a specific test is missing, a test protocol is insufficient, or test results don't cover the full intended use
• Software questions — insufficient documentation of hazard analysis, V&V, or cybersecurity
• Labeling questions — inconsistencies between labeling and Section 1, or missing required labeling elements
• Biocompatibility gaps — missing ISO 10993 endpoints, insufficient justification for literature equivalence

How to structure your response

FDA expects AI responses to be submitted as a complete package through eSTAR. The response must address every item in the AI letter — skipping or partially answering any question will almost certainly generate a second AI on the unanswered items.

Structure your response as follows:

• Cover letter — lists every AI item number and a one-line summary of how it is addressed
• Response document — quote each AI item verbatim, then provide your response directly below it
• Updated eSTAR sections — if your response modifies any section of the original submission, include the updated section as an attachment
• New test reports — if FDA requested additional testing, include complete test reports with protocols, results, and conclusions

The most common AI response mistakes

When to request a meeting with FDA

If an AI item involves a fundamental disagreement about predicate selection or a substantial equivalence question where you believe FDA's position is incorrect, you may request a meeting or teleconference with the reviewing division before submitting your response. This can prevent a back-and-forth that adds months to your timeline.

Meeting requests must be made in writing and may take 2-4 weeks to schedule. Factor this into your response timeline if the AI involves a significant strategic question.

After you respond: what to expect

Once you submit your AI response, FDA's review clock restarts. If your response is complete, clearance typically follows within 30-45 days. If FDA issues a second AI, the process repeats — but second AIs are usually narrower, focused on items that weren't fully addressed in your first response.

A second AI request is not a final rejection. However, if FDA determines that substantial equivalence cannot be demonstrated even after multiple AI exchanges, they will issue a Not Substantially Equivalent (NSE) determination.