title: Plasma pharmacokinetic characteristics of risperidone and their relationship to saliva concentrations in children with psychiatric or neurodevelopmental disorders.
abstract: BACKGROUND
  Risperidone is a second-generation antipsychotic agent widely used in the treatment of schizophrenia and other psychotic disorders in adults. Risperidone is probably the most frequently used atypical antipsychotic in the pediatric population.
  
  
  OBJECTIVE
  The goals of this study were to estimate the pharmacokinetic parameters of risperidone and its enantiomers in a pediatric population and explore relationships between saliva and plasma concentrations.
  
  
  METHODS
  Eligible patients, between 4 and 15 years of age, included those taking a stable dose of oral risperidone ranging from 0.01 to 0.07 mg/kg BID for > or =4 weeks to treat psychiatric or neurodevelopmental conditions. A trough blood level and predose saliva sample were collected at study initiation; the regular risperidone dose was administered; and paired samples of blood and saliva were collected at 1, 2, 4, and 7 hours postdose. Plasma/saliva concentrations of risperidone and enantiomers of its principal active metabolite, 9-hydroxyrisperidone (9-OH-risperidone), were measured using a chiral liquid chromatography-tandem mass spectrometry assay. Standard pharmacokinetic parameters were calculated. Cytochrome P450 2D6 genotypes of *3,*4,*5 deletion and duplication were determined.
  
  
  RESULTS
  The study included 19 patients (age range, 4 years 2 months to 15 years 11 months). Mean (SD) values for C(max), t(1/2), and AUC 0 to 12 hours for risperidone in plasma were 15.9 (22.2) ng/mL, 3.0 (2.3) h, and 92.1 (200.6) ng x h/mL, respectively. Corresponding values in saliva were 12.0 (21.0) ng/mL, 3.4 (3.2) h, and 27.8 (38.7) ng x h/mL, respectively. Mean (SD) plasma enantiomer values for C(max) and AUC calculated up to the last observation were: (+)-9-OH-risperidone, 13.6 (10.0) ng/mL and 73.6 (52.3) ng x h/mL; (-)-9-OH-risperidone, 4.9 (3.1) ng/mL and 29.3 (19.1) ng x h/mL. Corresponding enantiomer values in saliva were: (+)-9-OH-risperidone, 5.2 (8.8) ng/mL and 15.6 (8.9) ng x h/mL; (-)-9-OH-risperidone, 5.0 (7.9) ng/mL and 15.6 (9.1) ng x h/mL, respectively. Large interindividual variability in risperidone and enantiomer concentrations was noted. A highly significant relationship between predose plasma and predose saliva risperidone concentrations was observed. The logarithmic regression model indicated that the log risperidone saliva concentration = -0.100 + 0.594 x log plasma concentration (R(2) = 0.93 [Spearman]).
  
  
  CONCLUSIONS
  In this preliminary pharmacokinetic study of parameters for risperidone and the enantiomers of 9-OH-risperidone in a pediatric population, mean C(max) and t(1/2) of risperidone were generally similar to those previously described in adults. The highly significant relationship between predose plasma and predose saliva risperidone concentrations suggests that saliva measurements may be a viable alternative to plasma sampling in children.
authors.affiliation: The Nisonger Center, The Ohio State University, Columbus, Ohio 43210, USA. aman.1@osu.edu
authors.forename: Michael G
authors.initials: MG
authors.lastname: Aman
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Vinks
authors.forename: Bart
authors.initials: B
authors.lastname: Remmerie
authors.forename: Erik
authors.initials: E
authors.lastname: Mannaert
authors.forename: Yaser
authors.initials: Y
authors.lastname: Ramadan
authors.forename: Jessica
authors.initials: J
authors.lastname: Masty
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Lindsay
authors.forename: Krista
authors.initials: K
authors.lastname: Malone
mesh_terms: D000293:Adolescent; D014150:Antipsychotic Agents / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use; D019540:Area Under Curve; D002648:Child; D002675:Child, Preschool; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics / Q000378:metabolism; D002658:Developmental Disabilities / Q000188:drug therapy; D005260:Female; D005838:Genotype; D006207:Half-Life; D006801:Humans; D007555:Isoxazoles / Q000737:chemistry / Q000378:metabolism; D008297:Male; D001523:Mental Disorders / Q000188:drug therapy*; D000068882:Paliperidone Palmitate; D011743:Pyrimidines / Q000737:chemistry / Q000378:metabolism; D018967:Risperidone / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use; D012463:Saliva / Q000737:chemistry*