Objective In 2009, the European Vasculitis Study Group reported the results of CYCLOPS, a randomized controlled trial, in which pulse cyclophosphamide (CYC) was found to be similar to a daily CYC regimen in inducing remission in patients with antineutrophil cytoplasmic antibody-associated vasculitis (AAV). We herein conducted an observational study to describe our experience with Japanese AAV patients treated with pulse CYC according to the CYCLOPS protocol. Methods The inclusion criteria were

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... s follows: 1) granulomatosis with polyangiitis, of either the limited or generalized type; 2) microscopic polyangiitis or renal limited glomerulonephritis with at least one poor prognostic factor; or 3) microscopic polyangiitis with a motor disturbance due to vasculitic neuropathy. The patients were treated with pulse cyclophosphamide and prednisolone according to the CYCLOPS protocol. Results Seven patients were included, all of whom (100%) achieved remission with a median time to remission of three months. After the first remission, two patients experienced relapse during the follow-up period of 14.8 months and both were successfully treated with additional pulse CYC therapy. Regarding safety, infection was observed in all patients, including three patients with respiratory tract infections, although all infectious episodes were successfully treated. Bronchoalveolar carcinoma was diagnosed in one patient. Conclusion The administration of pulse CYC according to the CYCLOPS protocol was found to be effective as remission induction therapy in our seven patients with AAV. With regard to safety, treating Japanese patients with AAV according to this protocol may require close attention for signs of respiratory infection. Our findings suggest that this protocol is therefore a viable option for Japanese patients with AAV.