I am sorry your pet is having to deal with this disorder. There are 2 aspects to consider. There is research in humans that indicates a ketogenic diet can reduce the number and severity of seizures. It is typically used only in children who have failed to respond to a number of different medications. However, there is no indication this diet is effective in dogs. The most common medical condition to address in dogs with phenobarbital treatment is liver damage due to the medication. For that reason we monitor our seizure disorder patients on phenobarbital with laboratory evaluations regularly and add medications to support liver function. These include SAM-e, milk thistle, and hemp oil. There are a number of commercial diets designed to aid liver function. Purina has HP Hepatic diet, Hill’s has I/d Hepatic Care, and Royal Canin has Canine Hepatic Formula.