Background: Mizoribine (MZR) is a novel immunosuppressant developed in Japan. As MZR is reported to be less toxic than other cytotoxic drugs, it is frequently used in Japan in the treatment of adult patients with rheumatoid arthritis or lupus nephritis. The objective of this study was to evaluate the efficacy of MZR in children with SLE. Nine female children with lupus nephritis who had undergone renal biopsy before starting MZR, were involved in this study. Their mean disease duration was 4.8 years at the time MZR treatment was initiated. Patients who had received intensive medications, such as methyl-prednisolone pulse therapy, intravenous cyclophosphamide pulse therapy, and/or other immunosuppressants, within the 4 months prior to the start of the study, were excluded.
Methods: Patients treated with 3 mg/kg per day of MZR were monitored every month for up to 1 year. The efficacy of MZR was evaluated by the changes from baseline values of serum C3, serum C4, anti-dsDNA antibody titer, erythrocyte sedimentation rate (ESR), urinary protein, dosage of prednisolone (PSL), and the sum of the scores defined by these parameters.
Results: Favorable changes were observed in C3 and ESR after 2 months and 3 months of MZR therapy, respectively. At 3 months of MZR therapy, the sum of scores defined by the parameters for disease activity indicated that MZR was more effective in non-class IV nephritis patients (n = 5) than in class IV nephritis patients (n = 4) (P = 0.0197). All nine children involved in the study tolerated the MZR therapy well during the study.
Conclusion: MZR was safe in lupus children, but its efficacy was limited in patients with non-class IV nephritis. Further study is necessary, in which higher dosages and/or earlier use of MZR is provided to a larger number of children.