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 mu g/mL in the responder group and 1.59 +/- 0.82 mu g/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 (EU-LAR) criteria was 56.3% at 24 weeks. The plasma level of MZR which was greater than or equal to 2.12 mu g/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.