Epsom salts and kidney problems

Although he doesn't know it yet, I want my husband to start doing some liver flushes. He has Multiple Myeloma, and had a stem cell transplant several months ago with high dose chemo. He runs a higher risk of kidney failure because of the cancer, and wondered if the Epsom Salts would be safe for him? Or would the other magnesium solution (? mag. citrate) would be safer. He currently does not have any kidney problems.

Thanks in advance for any advice!