Milk Thistle given in conjunction with the Phenobarbitone is supposed to help the liver. There is a very good canine epilepsy support group called the Phyllis Croft Foundation for Canine Epilepsy who I found brilliant when my last Dane was diagnosed as an epileptic.
Don't know if you are insured, if you are unless you have complete faith in your vet I would ask to get referred to a Neurologist. They see more cases of Epilepsy than a normal vet. It is now nearly 3 years since Misty my previous Dane showed symptoms of Epilepsy (she subsequently died of bloat) and we were referred to a Neurologist who did an MRI scan. The scans are to check whether there is any noticable cause for the epilepsy. In the case of Misty there wasn't - this is called ideopathic epilepsy.
Should you have any other questions please do not hesitate to either put another post on or pm or e-mail me.
Hope this helps
Sharon