title: Mizoribine requires individual dosing due to variation of bioavailability.
abstract: BACKGROUND
  Mizoribine (MZR) is an immunosuppressant used for the treatment of glomerular diseases, but there are few reports on the pharmacokinetics of MZR in children.
  
  
  METHODS
  First, we performed a pharmacokinetic study on nine childhood-onset glomerular disease patients. The MZR dosages ranged from 1.8 to 14.5 mg/kg/dose. Pharmacokinetic parameters were analyzed using 38 MZR concentration-time curves. Second, nine patients who were newly treated with MZR were enrolled to validate the findings obtained from prior investigation.
  
  
  RESULTS
  In the prior study, peak serum MZR concentration (C(max) ) was dose-dependent in each patient. Although proportionality between dosage and C(max) was observed in each patient, the regression coefficient was in a wide range from 0.075 to 1.04 and was specific to each patient. This variability was likely caused by individual variation of bioavailability. When the optimal time-point to monitor C(max) was investigated, the time-to-reach peak serum MZR concentration (T(max)) was similar among all the patients, which was from 2.5 to 3.5 h after administration of MZR. T(max) was most frequently observed at 3 h and the serum MZR concentration ratio relative to C(max) at 3 h was also highest (0.93 ± 0.07). In the following study, it was validated that monitoring C(3) is reproducible and reliable after adjusting the dosage of MZR to obtain target serum concentration.
  
  
  CONCLUSIONS
  Individual dosing is required to optimize C(max) in childhood-onset glomerular disease patients. The safe dosage of MZR for each patient could be predicted by evaluating the serum MZR concentration 3 h after administration.
authors.affiliation: Department of Hospital Pharmaceutics, School of Pharmacy, Showa University, Tokyo, Japan.
authors.forename: Toshiya
authors.initials: T
authors.lastname: Fuke
authors.forename: Yoshifusa
authors.initials: Y
authors.lastname: Abe
authors.forename: Satoshi
authors.initials: S
authors.lastname: Hibino
authors.forename: Mikawa
authors.initials: M
authors.lastname: Takeshi
authors.forename: Takako
authors.initials: T
authors.lastname: Saito
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Sakurai
authors.forename: Shuichiro
authors.initials: S
authors.lastname: Watanabe
authors.forename: Jun-ichiro
authors.initials: J
authors.lastname: Murayama
authors.forename: Kazuo
authors.initials: K
authors.lastname: Itabashi
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Nakano
mesh_terms: D000293:Adolescent; D001682:Biological Availability; D002648:Child; D002675:Child, Preschool; D004305:Dose-Response Relationship, Drug; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000493:pharmacokinetics; D008181:Lupus Nephritis / Q000097:blood / Q000188:drug therapy*; D008297:Male; D012189:Retrospective Studies; D012263:Ribonucleosides / Q000008:administration & dosage / Q000493:pharmacokinetics*; D016896:Treatment Outcome
chemical_list: D007166:Immunosuppressive Agents; D012263:Ribonucleosides; C010052:mizoribine