I'm so sorry to read about this
I know of a dog recently from another group that was in kidney failure with numbers around 177...They put her on iv fluids to flush the kidneys and her BUN came back down to 35, I believe. I'll say a prayer for Cooper. Azodyl and Epatikin are used in dogs with kidney problems/failure.
http://www.vetoquinolusa.com/pages/pdf/AzodylVetBro.pdf http://66.187.129.130/vetoquinol_pdfs/Epakitin.pdf