Brief Answer:
In theory should be just as good

Detailed Answer:
I read your question carefully and I understand your concern.

There are many generic forms of Dilantin (or Phenytoin which is the name of the drug itself). They vary among different countries, several forms exist in the US, the most widely spread is Phenytek produced by Mylan, but other companies manufacture generic forms as well such as Wockhart, Actavis, Taro pharmaceuticals, Apotheca etc.

In theory there shouldn't be any difference between generics and the original product they should be exact copies, just as good. That should be guaranteed by national regulators like FDA in the US which should exercise strict control on generics to guarantee equivalency with the original product. Whether that is what happens in reality...not always, in some patients when they switch from the original to generic there may be a change. Only in some though in most cases efficacy and tolerability is the same.

As for the why you never get Dilantin, the answer is easy, because it costs more. Since in theory they are identical insurance pays for the cheaper version.

Whether the fact you suffer seizures is due to it being a generic version it's hard to say unless you have tried both and noticed a clear difference. There are many antiepileptics out there some work better for certain patients, if you are having seizures despite that high dose perhaps your doctor should consider trying another antiepileptic drug.

I remain at your disposal for other question.

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