Efficacy of single dose of oral mizoribine pulse therapy two times per week for frequently relapsing nephrotic syndrome.

We assessed the efficacy of a single dose of oral mizoribine (MZB) pulse therapy two times per week for children with frequently relapsing nephrotic syndrome (FRNS). Eleven children with FRNS in remission were treated with oral MZB pulse therapy (daily dose 6 mg/kg; maximum total dose 300 mg). We compared their clinical manifestations before and after oral MZB pulse therapy and examined the changes in serum MZB concentration in each patient on the days when MZB was administered. Eight patients had no subsequent relapses (responders), and prednisolone could be discontinued. Although 2 of the other 3 patients (nonresponders) had one relapse and the remaining patient had two relapses, both the dosages of prednisolone and frequency of relapse after oral MZB pulse therapy were significantly lower than before oral MZB pulse therapy. The peak blood concentration and AUC0-4 of MZB in the responders were higher than in the nonresponders. None of patients had severe adverse effects, such as uricacidemia, leukopenia, liver dysfunction or alopecia. Oral mizoribine pulse therapy consisting of a single dose two days a week may be effective and safe in some FRNS patients.