Re: Reply requirements to satisfy 820.198(e)
21CFR820.198(e)(8) does say that if you do respond, you must keep a record of the response. Other than that, there is no requirement in 21CFR820.198 to respond to the filer of a complaint.
However, it's notable that you have had enough complaints to be able to characterize ~90% of them as due to doctor misuse. The FDA, it seems to me, is very clear in the overall context of the QSR that device makers are obligated to take action in response to complaints about adverse events in such a manner as to cause fewer adverse events in the future, whatever the basis for the complaints. See for instance
Chapter 15 "Complaints" of "Medical Device Quality Systems Manual: A Small Entity Guide", which capsulizes the FDA's guidance stance.
Based on the sparse description of the situation that you've given us, my inference would be that in some manner, your Instructions for Use--which you describe as very thorough--are nonetheless not effective.
It's conceivable that at some point an adverse event might be reported to the FDA as a complaint, and they might decide to inspect you and review your complaint records...and perhaps based on numbers of complaints, your analyses of each one, and whatever changes have or haven't been made to change the factors found in your analyses to have been responsible, it's conceivable that they might deem your
device to be not effective. Effectiveness of course is a cardinal mandate for devices, so that would lead to bad things.
Thus I would suggest that, while you aren't legally required to respond to doctors who complain to you, you might want to make changes and then do some documented A/B clinicals, iterating until you achieve a substantive improvement, so that you have evidence that you've addressed the situation.
(I'm also surprised that your sales/marketing people aren't screaming that something needs to be done to avoid future adverse event complaints and unhappy doctors, but that's an off-topic direction in this forum.)
