Mizoribine therapy for patients with lupus nephritis: the association between peak mizoribine concentration and clinical efficacy

The clinical efficacy of mizoribine (MZR; 4-carbamoyl-1-b-d-ribofuranosylimidazolium) in patients with lupus nephritis was investigated. Thirteen Japanese patients with biopsy-proved lupus nephritis were enrolled in this study. A change in global assessments score, total protein (TP) of serum, serum creatinine, creatinine clearance (Ccr), proteinuria, titers of serum anti-ds DNA antibody, C3, C4, and hemolytic complement activity (CH50) were examined. Following MZR treatment, the level of urinary protein decreased (P < 0.05), whereas the level of Ccr increased (P < 0.05). Moreover, the level of TP significantly increased from 5.5 g/dl to 6.3 g/dl (P < 0.01) and the level of C3 increased significantly (P < 0.01). However, there was no change in the levels of both C4 and CH50. The titer of anti-ds DNA antibody significantly decreased (P < 0.05). The dosage of prednisolone could be tapered from 24.8 mg to 14.9 mg daily during the period. The clinical effects associated with MZR concentration in the blood revealed that there was a significant correlation between the peak MZR blood concentration of more than 0.66 µg/ml and clinical improvement (P = 0.021). Our results suggest that an optimal MZR blood concentration was important for the treatment of lupus nephritis.