Lady has been on phenobarbital for seizures for almost ten years. It is very hard on the liver so you must use milk thistle to protect it. I have used milk thistle almost since day one and it has only been in the past 1.5 years that Lady's liver values have become elevated. I use Marin since milk thistle needs to be given with vitamin E. You only use 1/4 pill for a Yorkie so it is very inexpensive.
Here are some links for you:
Canine Epilepsy - Using Phenobarbital to control seizures in dogs Reducing the risk of liver disease MILK THISTLE Marin for Small to Medium Dogs (30 Tablets)