High GGT with Dilantin use

The generic brand of dilantin has caused me to have seizures in the past; so I've continued to take the brand dilantin for 30 years.  My GGT was recently 318, but a liver US was negative.  Due to the high possibility of seizure, I've been very reluctant to try other meds; but I'm wondering at what point does it become necessary?  What would be your next recommendation?  Thank you very much.