Bulldog with Epilepsy

I will try to make a long story short here. When Apollo was about 1 years old he had 2 grand mal seizures. We rushed him to the vet and they put him on 64mg of Phenobarbital twice a day. He was good for a few years and then about a year ago he had another grand mal seizure. They tested his liver levels and raised his Phenobarbital. He had another grand mal seizure a few months later so they started him on Keppra. The grand mal seizures stopped but he started to have focal seizures. They were lasting for 5 minutes or so, but they always came in clusters. One night he had 7 clusters within an hour. So we took him to a neurologist and the doctor added Zonisamide to his list of medications. Now he seems to have them once a month, they are only about 5-10 seconds, but they still always come in clusters. So now when he has one we start him on diazepam for 24 hours. Last month he had two focal seizures within a week so we took him back to the neurologist to test his Zonisamide levels. His Phenobarbital levels are on the high side so they don't want to add to that, but his Zonisamide levels are fine so they want to up that medication.

So my question is this. This is the medication Apollo is on. The neurologist say's it's perfectly normal for dogs to get much higher doses than people, but this seems like a lot. But if it stops the seizures, I don't know if we have any other option. Is anyone else in a similar situation?

AM medication:
Phenobarbital - 96mg
Keppra - 1500mg
Zonisamide - 300mg (just went from 200mg to 300mg today)

PM medication:
Phenobarbital - 64mg
Keppra - 1500mg
Zonisamide - 300mg (just went from 200mg to 300mg today)