MMF Versus CTX in the Induction Treatment of ANCA Associated Vasculitis

Inclusion Criteria: 1. A new diagnosis of ANCA associated vasculitis (eg. MPA or Wegener granulomatous, or renal limited vasculitis) proved by histology and serology. 2. Renal involvement attributable to active ANCA associated vasculitis with at least one of the following: * Elevated serum creatinine between 150 and 500 umol/l - renal biopsy * Demonstrating paucin -immune necrotizing glomerulonephritis * Red cell casts * Haematuria with \> 30 red blood cells/HPF and proteinuria \> 1g/24h 3. Serum ANCA positive by indirect immunofluorescence (IIF) and positivity in the anti-PR3 or anti-MPO by ELISA 4. Age 18\~65 years Exclusion Criteria: 1. More than two weeks treatment with cyclophosphamide (CYC) or other cytotoxic drug within previous 6 months or with oral corticosteroids (OCS) for more than 4 weeks 2. Co-existence of another multisystem autoimmune disease, e.g. SLE 3. Serum creatinine \> 500umol/l 4. Severe viral infection(HBV, HCV, CMV) within 3 months of first randomization or known HIV infection 5. Congenial or acquired immunodeficiency 6. Immediately life-threatening organ manifestations (e.g. lung haemorrhage or dialysis dependence) 7. Previous malignancy 8. Pregnancy or inadequate contraception if female 9. Anti-GBM antibody positivity 10. Cerebral infarction due to vasculitis 11. Rapidly progressive optic neuropathy or retinal vasculitis or orbital pseudotumour 12. Massive gastro-intestinal bleeding 13. Heart failure due to pericarditis or myocarditis 14. Liver dysfunction measured on at least 2 separate occasions 15. Age \< 18y or Age \> 65y