Efficacy and safety of single-dose mizoribine for patients with rheumatoid arthritis: results at 6 months after switching from a multiple-dose regimen without a change in total daily dose.

To determine the efficacy and safety of single-dose mizoribine (MZR) for patients with rheumatoid arthritis (RA), a 6-month, single-arm, open-label, prospective observation study was performed. In patients who had been taking MZR at 100-150 mg/day in 2-3 divided portions continuously for at least 3 months, and who had shown a lack of clinical response, or escape (defined as a lack of response at the time of switching, even if some form of response had been shown before that), multiple-dose administration was switched to single-dose administration without changing the total daily dose. Efficacy was assessed in terms of the disease activity score, using the 28-joint count and erythrocyte sedimentation rate (DAS 28-ESR). Of the 34 enrolled patients, 28 met all the eligibility criteria and were assessed for efficacy, and finally 26 patients were able to receive the single-dose regimen throughout the full 6 months. The DAS28-ESR showed a significant decrease from 2 months after switching, and 46.4% of the 28 patients finally achieved a good or moderate response (3 and 10 patients, respectively). With regard to safety, no serious adverse events were observed. In conclusion, the administration of MZR at 100 or 150 mg in a single dose is thought to be a useful alternative form of MZR therapy.