BackgroundNephrotic syndrome that is resistant to steroid therapy is termed refractory nephrotic syndrome (RNS), a condition that is associated with an increased risk of end-stage renal disease. Immunosuppressants are used to treat RNS; however, prolonged use may lead to significant adverse effects. Mizoribine (MZR) is a novel agent used in long-term immunosuppressive therapy, which has few adverse effects, but data on its long-term use in patients with RNS are unavailable.ObjectiveWe propose a trial to examine the efficacy and safety of MZR compared with cyclophosphamide (CYC) in Chinese adult patients with RNS.MethodsThis is a multicenter, randomized, controlled interventional study with a screening phase (1 week) and a treatment phase (52 weeks). This study has been reviewed and approved by the Medical Ethics Committees of all 34 medical centers that are participating. Patients with RNS consent to participation, and are enrolled and randomized to an MZR group or a CYC group (1:1 ratio), with each group receiving tapering doses of oral corticosteroids. Participants are assessed for adverse effects, and laboratory results are collected at 8 visits during the treatment phase (weeks 4, 8, 12, 16, 20, 32, 44, and 52 [exit visit]). Participants are able to withdraw voluntarily, and investigators are required to remove patients when there are safety concerns or deviations from the protocol.ResultsThe study started in November 2014 and was completed in March 2019. A total of 239 participants from 34 hospitals in China have been enrolled. Data analysis has been completed. The results are being finalized by the Center for Drug Evaluation.ConclusionsThis study examines the safety and efficacy of MZR as a long-term treatment approach for Chinese adults with RNS. It is the longest lasting and largest randomized controlled trial to examine MZR in Chinese patients. The results can help determine whether RNS should be considered as an additional indication for MZR treatment in China.Trial RegistrationClinicalTrials.gov NCT02257697; https://clinicaltrials.gov/ct2/show/NCT02257697International Registered Report Identifier (IRRID)RR1-10.2196/46101