yes. could easily be.

i suppose the Zonegran brand may actually be pharmacologically slightly LESS active than the particular generic that was working for him. in that case the dose probably needs adjusting and then you will be straight because it will reliably be the same. occasionally a too-high dose of AED will produce more seizures - similarly resolvable with a dose adjustment.

another possible factor - but i think unlikely because you are onto this stuff -

... has he been on any other medication that he does not normally take? (eg. an antibiotic?)

... or similarly, has he been eating or drinking unusual quantities of any specific food or drink... or what about herbal teas?

where i am going with this is if he could be taking anything that might be inducing one of the hepatic enzymes which metabolizes the Zonegran. An inducer would lower his drug level.

The reason he can't have grapefruit juice is the opposite - it inhibits the primary enzyme pathway involved (CYP3A4) - it would raise Zonegran levels. BTW, lime (but not lemon), bergamot and sour orange also have these properties to a lesser degree.

i hope he feels better soon.

~ waves ~