mrsD -

I thank you for your post. It appears you may be correct, although I will see my doctor again on Friday for his reposte. First, I was pretty sure I had heard of quinidine's past use as a tricyclic antidepressant, but looks to be incorrect. My assertion must have been based on something of a false memory on my part.

But I was/am certain of my doctor's comment vis-a-vis blocking the metabolism of memantine. Until I looked it up at your instigation. Turns out that quinidine is an inhibitor of the cytochrome P450 enzyme 2D6, which is what gives it its effect as a potentiator of dextromethorphan. NUEDEXTA™ Full Prescribing Information. That said:

Memantine [Namenda] is predominantly renally eliminated, and drugs that are substrates and/or inhibitors of the CYP450 system are not expected to alter the pharmacokinetics of memantine. A clinical drug-drug interaction study indicated that bupropion did not affect the pharmacokinetics of memantine.

NDA 22525 - NAMENDA XR Full Prescribing Information.

I'll try to clear this up on Friday. Thank you again.

Mike

PS And good point re searching for patterns of known interactions on quinidine, as with any med. And as far as quinidine is concerned, I've come across at least one, but was told that it was dose dependent, and at only 10 mg of quinidine, I shouldn't worry about it.