definitely been confirmed as epileptic...sounds like over-medication to me based on this limited info. The Potassium Bromide, which is often rx'd to accompany phenobarb (to lessen the need for so much narcotic)may well be enough to control or stop the seizures (if they are just head-shakes but the dog doesn't collapse, doesn't loose awareness, doesn't pee involuntarily, etc)and I think this dog owner should talk again with the vet, perhaps get a second opinion!

seizures can be caused by many things,,,,but in a very very simple way their casued a short in the electrial impluse of the brain....
if the dosage was to high your friend should of had a blood panel done.... some times the loading dose will knock a dog or person down but then the body adjusts to the meds....
my concern is that sometimes dogs have one or two epsiodes a month...then suddenly they grow closer togeter then their called cluster seizures....this is dangerouse....
so i guess what i am saying...i would have your friend call the vet and discuss the dosing of the dogs meds....seizures can kill if left untreated....