Damaged kidneys will be put under much greater stress with phenobarb, which will cause a rapid deterioration in the kidney
disease. Right now, stabilizing the kidney
disease is a greater priority, as it will help your dog survive AND stop the seizures.
Bear in mind the kidneys (along with the liver) are directly responsible for removing excess phenobarbital from the canine body, so with the kidneys being impaired, this will not be happening as it should.