My Dog Has Been Taking Phenobarbital For Two Years. She

My dog has been taking phenobarbital for two years. She came in from the field tonight unable to walk on her left hind leg. She will allow me to pull the leg and massage her back. Question is I have a prescription of Robaxin 500 mg which she has taken three years ago for a strained muscle. Will it have a bad interaction with the Phenobarbital which she receives daily for seizures?