I don't have epilepsy, though my sister does (she has taken Keppra and Lamictal in the past) and I have personally been prescribed almost every anti-convulsant there is in the past as well I must admit in order to treat schizoaffective disorder (to treat the bipolar part -- schizoaffective = schizophrenia + bipolar), and I do know quite a bit about psychiatric drugs because I've taken so many in my life and mental illness is very common in my family, except I have never been prescribed phenobarbital. I know that is one of the older anti-convulsants, which isn't used as often anymore (at least in humans). If I were you I'd ask your vet as many questions as you can about which anti-convulsant is the safest for your dog, which is most effective, which has the least side effect profile, what he/she would use if they were in your position, etc. My Grandma was on phenobarbital for several years after she had a brain anyeurism, and if I remember correctly it helped with headaches but made her sleep a lot, again though, don't know if this applies to dogs.

Hope this is helpful. Feel free to email me.