title: Adaptive dosing approaches to the individualization of 13-cis-retinoic acid (isotretinoin) treatment for children with high-risk neuroblastoma.
abstract: OBJECTIVE
  To investigate the feasibility of adaptive dosing and the impact of pharmacogenetic variation on 13-cis-retinoic acid (13-cisRA) disposition in high-risk patients with neuroblastoma.
  
  
  METHODS
  13-cisRA (160 mg/m(2) or 5.33 mg/kg/d) was administered to 103 patients ages 21 years or less and plasma concentrations of 13-cisRA and 4-oxo-13-cisRA quantitated on day 14 of treatment. Seventy-one patients were recruited to a dose adjustment group, targeting a 13-cisRA C(max) of 2 μmol/L, with dose increases of 25% to 50% implemented for patients with C(max) values less than 2 μmol/L. A population pharmacokinetic model was applied and polymorphisms in relevant cytochrome P450 genes analyzed.
  
  
  RESULTS
  13-cisRA C(max) values ranged from 0.42 to 11.2 μmol/L, with 34 of 103 (33%) patients failing to achieve a C(max) more than 2 μmol/L. Dose increases carried out in 20 patients in the dose adjustment study group led to concentrations more than 2 μmol/L in 18 patients (90%). Eight of 11 (73%) patients less than 12 kg, receiving a dose of 5.33 mg/kg, failed to achieve a C(max) of 2 μmol/L or more. Significantly, lower C(max) values were observed for patients treated with 5.33 mg/kg versus 160 mg/m(2) (1.9 ± 1.2 vs. 3.1 ± 2.0 μmol/L; mean ± SD; P = 0.023). C(max) was higher in patients who swallowed 13-cisRA capsules as compared with receiving the drug extracted from capsules (4.0 ± 2.2 vs. 2.6 ± 1.8 μmol/L; P = 0.0012). The target C(max) was achieved by 93% (25/27) versus 55% (42/76) of patients in these 2 groups, respectively. No clear relationships were found between genetic variants and 13-cisRA pharmacokinetic parameters.
  
  
  CONCLUSIONS
  Dosing regimen and method of administration have a marked influence on 13-cisRA plasma concentrations. Body weight-based dosing should not be implemented for children less than 12 kg and pharmacologic data support higher doses for children unable to swallow 13-cisRA capsules.
authors.affiliation: Northern Institute for Cancer Research and Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK. G.J.Veal@ncl.ac.uk
authors.forename: Gareth J
authors.initials: GJ
authors.lastname: Veal
authors.forename: Julie
authors.initials: J
authors.lastname: Errington
authors.forename: Sophie E
authors.initials: SE
authors.lastname: Rowbotham
authors.forename: Nicola A
authors.initials: NA
authors.lastname: Illingworth
authors.forename: Ghada
authors.initials: G
authors.lastname: Malik
authors.forename: Michael
authors.initials: M
authors.lastname: Cole
authors.forename: Ann K
authors.initials: AK
authors.lastname: Daly
authors.forename: Andrew D J
authors.initials: AD
authors.lastname: Pearson
authors.forename: Alan V
authors.initials: AV
authors.lastname: Boddy
mesh_terms: D000293:Adolescent; D000970:Antineoplastic Agents / Q000008:administration & dosage* / Q000009:adverse effects / Q000493:pharmacokinetics; D001835:Body Weight / Q000187:drug effects; D002648:Child; D002675:Child, Preschool; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D005260:Female; D005838:Genotype; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D015474:Isotretinoin / Q000008:administration & dosage* / Q000009:adverse effects / Q000493:pharmacokinetics; D008297:Male; D009447:Neuroblastoma / Q000097:blood / Q000188:drug therapy* / Q000235:genetics; D016896:Treatment Outcome
chemical_list: D000970:Antineoplastic Agents; D003577:Cytochrome P-450 Enzyme System; D015474:Isotretinoin