On a quick scan, I don't see any such cases documented in literature. And drugs.com shows only "moderate" interaction, with each possibly raising levels of the other, very common with drugs that address the same condition and basically saying stop if you don't tolerate the combination (like if your heart starts fluttering). Nuedexta has 460 moderate interactions listed.
In fact, the combination that makes up Nuedexta itself has a major warning behind it, because of that one drug amps up another thing (potentiation). The same for the combo that makes up Relyvrio.
Type your current drugs into drugs.com and see what comes up. I am not saying to ignore drug interactions, but PK data are lacking on that particular combination, as with many. For legal reasons, mfrs list all possible interactions.
If either mfr, both aware of the other's development program, thought there was a significant likelihood of serious interaction when using both, there would be PK data out of someone's lab by now.
Of course, one is always more cautious in starting new drugs if someone has pre-existing cardiovascular issues.
I'd be interested to see the ms or case reports or bulletin your neuro is going by.
