To evaluate the correlation between the efficacy of mizoribine (MZR) and the factors that might effect MZR concentration: renal function and dosage and administration of MZR in patients with rheumatoid arthritis (RA).
The efficacy of MZR treatment was prospectively evaluated in 97 RA regardless of dosage, at the 14 participated institutions. The Disease Activity Score 28-CRP3 was used to assess RA activity. The renal function was evaluated based on the serum creatinine and serum cystatin-C (Cys-C). The patients were followed up for 24 weeks.
The patients with a mean age 66.2 years included 18 male. The renal function assessment showed increased creatinine in 16.4% of patients and increased Cys-C in 54.5%, suggesting the higher sensitivity of Cys-C to detect impaired renal function than creatinine. In patients with good or moderate response according to the European League against Rheumatism classification criteria, the Cys-C was significantly higher compared with those with no response. MZR treatment was significantly more effective in patients with an arithmetic product of the single MZR dose used and Cys-C of 179 or more.
The efficacy of MZR may increase in proportion to its single dose, or increased Cys-C level in patients with impaired renal function.