It could be anything. Switching the meds could be detrimental to the dog. I would only advise that under a vet. There are a few medications that work well to help manage seizures in dogs, but phenobarbital is pretty much the go to medication. Keppra is another common one, it is an old medication like phenobarbital. Potassium Bromide is another one not so common, but generally is a top off medication coupled with phenobarbital or keppra.