Cytoxin vs Cellcept??

I have CIDP and in the last few months my pain in my feet and hands have gotten unbearable. I was using Vicodin and it was only lasting 3 to 4 hours. I do not have a loss of weakness in legs or arms. I can walk and use a cane for balance when my pain is bad. I take IVIG once monthly and it has kept the progression of numbness away. I saw my neuro today for the pain and he prescribed Ultram (he says it has been proven that Ultram works better for nerve pain than Vicodin) 50 mg 1-2 every 4-6 hours and Nortriptyline for bedtime. I pray this works. He wants to do a skin biopsy to try and see what is going on. He thinks I could have vasculitis. He says that if I do, he will prescribe Cellcept or Cytoxin. My question is which one works better between the two and which one is less toxic (if possible). If anyone has tried one or the other or both could you let me know please. This pain is driving me CRAZY. I have done nothing in the last month except lay around and cry. I told my husband the other day the only way to get away from this pain is to kill myself :(. I would not do that and it is a stupid idea, but sometimes this pain can get you sooooo frustrated, especially when you can’t find relief. I am very grateful to be alive and very blessed to have other things in my life that have made this disease bearable. (good husband, great daughter(teen), I do not have to work anymore, I have God, have insurance and am able to get IVIG and meds, my husband’s job is good, etc, etc.) God has been good :).
God bless all of you and I pray for all on this board.
Clare in Michigan