title: Effects of rifampin-based antituberculosis therapy on plasma efavirenz concentrations in children vary by CYP2B6 genotype.
abstract: OBJECTIVE
  An efavirenz-based antiretroviral therapy (ART) regimen is preferred for children more than 3 years of age with tuberculosis. However, rifampin, a key component of antituberculosis therapy, induces CYP2B6. An increased dose of efavirenz is recommended in adults weighing more than 50 kg who require rifampin, but there is scant information in children being treated for tuberculosis.
  
  
  METHODS
  Plasma efavirenz concentrations were compared in 40 children during concomitant treatment for tuberculosis and HIV-1, after stopping rifampicin, and in a control group of children without tuberculosis. Associations with antituberculosis treatment, metabolizer genotype (based on CYP2B6 516G→T, 983T→C, and 15582C→T), weight, and time after dose were evaluated.
  
  
  RESULTS
  Compared to children with extensive metabolizer genotypes, efavirenz concentrations were increased 1.42-fold (95% confidence interval, CI 0.94–2.15) and 2.85-fold (95% CI 1.80–4.52) in children with intermediate and slow metabolizer genotypes, respectively. Concomitant antituberculosis treatment increased efavirenz concentrations 1.49-fold (95% CI 1.10–2.01) in children with slow metabolizer genotypes, but did not affect efavirenz concentrations in extensive or intermediate metabolizer genotypes. After adjustment for dose/kg, each kilogram of weight was associated with a 2.8% (95% CI 0.9–4.7) decrease in efavirenz concentrations. Despite higher milligram per kilogram doses, a higher proportion of children in the lowest weight band (10–13.9 kg) had efavirenz concentrations less than 1.0 mg/l than larger children.
  
  
  CONCLUSIONS
  Antituberculosis treatment was not associated with reduced efavirenz concentrations in children, which does not support increased efavirenz doses. Children with slow metabolizer genotype have increased efavirenz concentrations during antituberculosis treatment, likely due to isoniazid inhibiting enzymes involved in accessory metabolic pathways for efavirenz.
authors.forename: Helen M
authors.initials: HM
authors.lastname: McIlleron
authors.forename: Michael
authors.initials: M
authors.lastname: Schomaker
authors.forename: Yuan
authors.initials: Y
authors.lastname: Ren
authors.forename: Phumla
authors.initials: P
authors.lastname: Sinxadi
authors.forename: James J C
authors.initials: JJ
authors.lastname: Nuttall
authors.forename: Hermien
authors.initials: H
authors.lastname: Gous
authors.forename: Harry
authors.initials: H
authors.lastname: Moultrie
authors.forename: Brian
authors.initials: B
authors.lastname: Eley
authors.forename: Concepta
authors.initials: C
authors.lastname: Merry
authors.forename: Peter
authors.initials: P
authors.lastname: Smith
authors.forename: David W
authors.initials: DW
authors.lastname: Haas
authors.forename: Gary
authors.initials: G
authors.lastname: Maartens
mesh_terms: D000480:Alkynes; D019380:Anti-HIV Agents / Q000008:administration & dosage / Q000493:pharmacokinetics*; D000995:Antitubercular Agents / Q000627:therapeutic use*; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D048588:Benzoxazines / Q000008:administration & dosage / Q000493:pharmacokinetics*; D002648:Child; D002675:Child, Preschool; D003521:Cyclopropanes; D065702:Cytochrome P-450 CYP2B6; D004347:Drug Interactions; D005260:Female; D005838:Genotype; D015658:HIV Infections / Q000150:complications / Q000188:drug therapy*; D006801:Humans; D008297:Male; D010949:Plasma / Q000737:chemistry; D012293:Rifampin / Q000627:therapeutic use*; D014376:Tuberculosis / Q000150:complications / Q000188:drug therapy*
chemical_list: D000480:Alkynes; D019380:Anti-HIV Agents; D000995:Antitubercular Agents; D048588:Benzoxazines; D003521:Cyclopropanes; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; D065702:Cytochrome P-450 CYP2B6; C098320:efavirenz; D012293:Rifampin