Mycophenolate Mofetil for Treatment of Relapses of Wegener's Disease or Microscopic Polyangiitis (MPA)

The purpose of this study is to determine the efficacy and safety of a new drug, mycophenolate mofetil, for the treatment of relapses of ANCA-associated vasculitis (Wegener's granulomatosis or microscopic polyangiitis). Therefore, we compare the standard therapy with cyclophosphamide to mycophenolate mofetil. The investigators expect mycophenolate mofetil to be less toxic and almost equally effective as cyclophosphamide.