I have also have the exact same problem as you. I’m taking Topamax 50mg x3 @ bedtime as well. My mouth gets so dry my lips stick to my teeth and my throat sticks together when I swallow so I’m always drinking water. Let me know if you find a solution.
I forgot to add....I just started taking Topamax 20mg 1x at bedtime for migraines about 2 1/2 weeks ago and thats about when I noticed the soda thing. Ears about a week ago. Dr actually has me on 10 mg pills but for the first week she had me take 1 pill at night, after first week she increased it to 2 pills at night so I guess you would say I am taking 20 mg? Maybe this is just one of those weird side effects of it lol.
So glad I found your post! I have been dieting so I haven't really drank many carbonated drinks lately...but I have noticed here recently in the past couple of weeks that sodas seem horribly flat to me. Even beer (major disappointment haha). My ears have been itching like crazy and I just figured it was an allergy or something. But then I read on to see your other couple of comment add ons. I'm kind of glad it makes the sodas this way because it keeps me from drinking them so much, but sometimes you just really crave one and you can't even enjoy it!
I just recently started having the SAME exact problem! I just started taking Topamax a few days ago too! But you said it perfectly, the soda tastes flat when I first take a drink, and then my taste buds "kick in" after a second too. I don't know what's causing it...maybe the Topamax?
Additionally, I only seem to have this problem with carbonated drinks. I tried drinking a beer at a wedding over this past weekend and the same this occured, at first taste it tastes flat, then after a few seconds my taste buds kick in and it feels a bit like pins and needles on my tongue and then I finally taste the flavor of the beer (same with soda), My palatte is perfect with anything else as far as beverages and food goes.
I hope this helps you!
Adding to my post above, I also have noticed that my ears seem to be bothering me a bit more than what I would consider normal.
By that I mean it's as if they are plugged up but it takes a lot of work to get them to pop. Don't know if that has anything to do with that above.