Background: Mizoribine (MZR), isolated from culture medium of the mold, is a novel immunosuppressant developed in Japan. It has been used in patients with renal transplantation, lupus nephritis, nephrotic syndrome and rheumatoid arthritis (RA). Objectives: To review MZR in regards to mechanism of action, pharmacokinetics, efficacy and safety in the treatment of rheumatoid RA and juvenile idiopathic arthritis (JIA). Results: The drug MZR inhibits both humoral and cellular immunity in RA patients, It is completely excreted in the urine within 24 h, which contributes to the safety of MZR. A series of multicenter studies indicated that MZR was effective and safe in the treatment of RA. In JIA, however, there are only a few case reports reporting its efficacy and safety. Conclusion: A double-blinded multicenter study is needed to establish the efficacy, safety and indication of MZR in the treatment of JIA.
