Oral mizoribine pulse therapy for patients with steroid-resistant and frequently relapsing steroid-dependent nephrotic syndrome

Background. We investigated the efficacy of oral mizoribine pulse therapy (mizoribine-pulse) for cyclosporin (CyA)-dependent, steroid-resistant nephrotic syndrome (SRNS) and frequently relapsing, steroid-dependent nephrotic syndrome (FR-SDNS). Methods. One child with CyA-dependent SRNS and eight children with CyA-dependent FR-SDNS were treated with mizoribine-pulse (daily dose: 10 mg/kg; maximum total dose 500 mg). We compared clinical manifestations before and after mizoribine-pulse, and studied the changes in serum mizoribine concentration in each patient on days when mizoribine was administered. Results. Four patients had no subsequent relapses (responders). Two of the four responders discontinued prednisolone and CyA, the other two discontinued CyA. Although each of the five other patients (non-responders) experienced single subsequent relapses, the dosages of prednisolone and CyA after mizoribine-pulse were decreased significantly compared with before mizoribine-pulse. The peak blood concentration of mizoribine in the responders was higher than in the non-responders (3.6±0.9 vs 1.8±0.4 µg/ml). Conclusions. Mizoribine-pulse may be effective for some patients with CyA-dependent SRNS and FR-SDNS.