I'm a little confused, because from what I'ver read and from talking to my neuro, zonegran is an nueral stablizing med just like all the other meds you listed. Each anticonvulsant works on different receptors though, so in that case, the explanation about tolerances still makes sense. Here is the list of what each one does
Felbamate -- sodium channel blocker, calcium channel blockade, glutamate receptor antagonism, GABA potentiation
Levetiracetam/Keppra -- calcium channel blockade only
Gabapentin/Neurontin -- calcium channel blockade, GABA potentiation
Lamotrigine/Lamictal & oxcarbazepine/trileptal -- sodium channel blocker, calcium channel blockade
Tiagabine/Gabitril - GABA potentiation only
Topiramate/Topamax -- sodium channel blocker, calcium channel blockade, glutamate receptor antagonism, GABA potentiation, carbonic anhydrase inhibition
Zonisamide/Zonegran -- sodium channel blocker, calcium channel blockade, GABA potentiation, carbonic anhydrase inhibition
Topamax is the most broad based, but probably the reason zonegran is being used is it is also more broad based, and has less side effects than topamax. My neuro calls it topamax-lite.
Now what your really wanted to know :-), I did take zonegran, and it did help for me more than topamax did, not as much as depakote did. For me I really did have less side effects than topamax. I became potassium defecient on topamax, got tolerant very fast to it(had to bump up my dosage almost weekly) and it took over 6 months for me to even notice any brain fog. I started at 100 mg, and did end up at 300 mg before I started noticing brain fog and switched again. I think 400 is the max recommended dosage, but one of my neuros uses it higher than that. My neuro said that now that its being used for headache patients more the manufacturer is considering making smaller sized tablets(they only come in 100s now) so that migraineurs can taper slower and that might have helped, so maybe something to look for in the future?
I guess if we could figure out which receptor helped us the most, we could figure out which med to take, now if there was some sort of test for that, I would pay money rather than guess and check!
I'm trying Gabitril now which doesn't have as much data behind it but my neuro has some people responding really well to it. And it suppose to have less side effects too, no miracles but so far so good, improvement at least!
Sorry I babbled on so much, I hope this helps a bit,
AJ