The Workbench · Craft
Substantive Interaction decides where a review clock stops
This blog has already covered why MDUFA's review-time figures are performance goals FDA negotiates with industry, not deadlines a submission can enforce, and the earlier completeness check a submission has to clear before that clock starts counting at all. Once a 510(k) or PMA is past that gate and under substantive review, FDA's own 2014 guidance on communication during device review draws a line most submission trackers never draw: some of what FDA sends back leaves the MDUFA clock running, and some of it stops it cold. The two look similar in an inbox. They are not similar in what they do to the calendar.
Four named types of communication, not an inbox of emails
The guidance — which superseded FDA's 2008 interactive-review policy — sets out staged communications for 510(k)s, original PMAs, Panel-Track PMA supplements, and Pre-Submissions: an Acceptance Review Communication at the completeness stage, a Substantive Interaction decision once technical review is underway, ongoing Interactive Review where warranted, and a Missed MDUFA Decision Communication if FDA runs past its own goal date. Each of those is a defined term in the guidance, not a label a tracker can apply loosely to whatever FDA happened to send.
Substantive Interaction is the fork in the road
By a set point in the review — the specific goal day has shifted across MDUFA cycles, but the mechanism hasn't — the lead reviewer has to decide how any outstanding questions get resolved. If they can be closed within the remaining MDUFA timeframe without a formal hold, the reviewer proceeds by Interactive Review. If they can't, FDA issues a formal Additional Information request instead, and the submission goes on hold. That single decision is what actually determines which of the next two paths a filing is on — not the tone or format of whatever email arrives.
Interactive Review doesn't pause anything
Interactive Review can happen by phone, fax, or email, doesn't require a review-cycle-ending letter, and — this is the part a naive tracker misses — has no effect on the MDUFA review clock. FDA's own guidance is explicit that time spent in Interactive Review counts as FDA time, not sponsor time. A submission fielding an Interactive Review question isn't “on hold” in any sense the calendar recognizes, even though it feels, from the sponsor's side, exactly like being asked for something and having to answer.
An Additional Information request is a different instrument
An AI request (a Major Deficiency Letter, in a PMA's terms) formally closes the current review cycle and places the submission on hold; the days between FDA sending it and the sponsor's complete response don't count as FDA review time at all. That's the mechanism generating the number a sponsor sees on a decision-summary letter months later — not the number of days that passed, but the number of days FDA was actually the party holding the file.
The same fork, different terms, across submission types
The guidance draws this line for 510(k)s, original PMAs, Panel-Track PMA supplements, and Pre-Submissions, but a PMA's own supplement structure adds another wrinkle a tracker built only around 510(k) vocabulary will miss: a 180-Day PMA Supplement gets its own Substantive Interaction communication, while other PMA supplement types don't necessarily follow the same staged path at all. A single “review communication” template copied across submission types will apply a fork that doesn't exist for the type actually in front of it.
Where this meets the file
A submission tracker that logs “FDA responded” on a single date, without recording whether that response was Interactive Review or a formal AI hold, can't tell you whether the MDUFA clock is running or stopped — which means it can't tell you, either, whether a quiet stretch afterward is normal or worth escalating. The fix is a status field that borrows the guidance's own vocabulary rather than inventing a simpler one. A Q-Submission and review-communication tracker built on that distinction is previewed in the launch catalog. If your team logs these communications differently, the shelf takes that correction directly.
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