Mizoribine as an alternative to azathioprine in pediatric renal transplantation

Chronopharmacology of mizoribine in collagen-induced arthritis rats

We previously reported that higher therapeutic effects were obtained in rheumatoid arthritis (RA) patients and RA model animals when the dosing-times of methotrexate and tacrolimus were chosen according to the 24-h rhythms of the inflammatory response. Mizoribine (MZR) is an immunosuppressive agent and is used against RA in the same manner as methotrexate and tacrolimus. In this study, we examined whether a dosing-time dependency of the therapeutic effect of MZR could be detected in collagen-induced arthritis (CIA) rats. To measure C-reactive protein (CRP) and tumor necrosis factor (TNF)-α levels, blood was collected from CIA rats at different times. MZR was administered at two different dosing-times based on these findings and its effects and toxicity were examined. CRP and TNF-α concentrations in blood showed significant 24-h rhythms. The exacerbation of arthritis and excessive increase in leukocytes in CIA rats were markedly lower in the group treated with MZR at the dark phase than those of the group treated with MZR at the light phase. These findings suggest that the therapeutic index of RA therapy may be improved by administering MZR at a time in the day when the inflammatory reaction begins to activate.

Role of mizoribine in renal transplantation

Renal transplantation is the optimal form of therapy for children and adolescents with end-stage renal disease. Usually histocompatibility differences exist between donor and recipient, so it is necessary to modify or suppress the immune response to enable the recipient to accept a graft. Calcineurin inhibitors (CNI), which include cyclosporin (CsA) and tacrolimus (FK506), give many benefits on the outcome after renal transplantation, but have some toxic effects, especially nephrotoxicity. Therefore, inhibitors of purine synthesis revived as newer generation of more specific inhibitors, mizoribine (MZ) and mycophenolate mofetil (MMF). The Japanese pediatric renal transplantation clinical study group attempted to reduce and then discontinue steroid administration in combination with another three immunosuppressive drugs, CsA, MZ and anti-lymphocyte globulin (ALG). This study showed good clinical results. Mizoribine is an effective immunosuppressive drug in human renal transplantation. However, it is not as popular as other inhibitors of purine synthesis, such as azathioprine (AZA) and MMF, because MZ has been used mainly in Japan and infrequently in other countries. However, MZ is a more useful immunosuppressive drug than AZA, when it is used in combination with CNI.