My uncle has stage 4 bladder cancer and renal failure.?

He has refused dialysis. What type of pain drugs are suitable for his condition since most narcotics are excreted via kidney? What would be the least toxic pain drug for him? I have dug through his prescriptions and there were no pain drugs. I need a second opinion before I see his physician.My goal is to just make him feel as much comfortable as possible. Thank you so much for you help.God bless.