Efficacy and safety of mizoribine by one single dose administration for patients with rheumatoid arthritis.

Objective: Mizoribine (MZR) is an immunosuppressant that inhibits nucleic acid metabolism and is a relatively safe disease-modifying anti-rheumatic drug (DMARD). We evaluated the efficacy and safety of one single dose per day for patients with rheumatoid arthritis (RA).
Patients and Methods: In this study 32 patients with RA received MZR therapy. We evaluated the average dose of MZR and prednisolone, response to treatment and peak plasma level of MZR.
Results: The average dose of MZR was 146.1±31.2 (range: 50-200) mg/day. The average dose of prednisolone was 4.63±3.59 (range: 0-14) mg/day. The average plasma level of MZR, measured after 3 hours, was 2.20±0.49 µg/mL in the responder group and 1.59±0.82 µg/mL in the non-responder group (p=0.020). The treatment with MZR for 24 weeks was completed by 71.9% of patients and the proportion of patients who achieved a good and moderate response rate according to the European League Against Rheumatism (EULAR) criteria was 56.3% at 24 weeks. The plasma level of MZR which was greater than or equal to 2.12 µg/mL was significantly correlated with the clinical response (p<0.01). Only one of thirty-two cases discontinued the treatment, because of skin eruption.
Conclusion: This study included patients that could not be treated with other DMARDs and/or biologic agents because of age, interstitial pneumonia and other complications. We show that MZR may be a useful and relatively safe therapy for patients in this group.