title: Interferon-beta treatment in patients with multiple sclerosis does not alter CYP2C19 or CYP2D6 activity.
abstract: OBJECTIVE
  To determine CYP2C19 and CYP2D6 activity in patients with multiple sclerosis (MS) before and during interferon (IFN)-beta treatment.
  
  
  METHODS
  CYP2C19 and CYP2D6 activities were assessed using the probe drugs mephenytoin and debrisoquine, respectively. Urinary mephenytoin (S/R) and debrisoquine (debrisoquine/hydroxy-debrisoquine) metabolic ratios (MR) were determined in 10 otherwise healthy Caucasian multiple sclerosis (MS) patients in the initial stage of the disease, prior to and 1 month after commencing treatment with IFN-beta (Avonex, Rebif or Betaferon). In addition, CYP2C19*2, CYP2C19*3, CYP2D6*3, CYP2D6*4, and CYP2D6*5 genotyping was performed.
  
  
  RESULTS
  There was no significant difference in the (S)/(R) mephenytoin ratio (mean difference 0.04; 95% CI -0.03, 0.11) or the debrisoquine MR (mean difference 0.29; 95% CI -0.44, 1.02) before and during regular IFN-beta treatment in extensive metabolizers (EM) (P = 0.5 and P = 0.4 for the respective probe drugs; n = 9 subjects). There were also no differences between the different IFN-beta treatments (P = 0.6 for the (S)/(R) mephenytoin ratio and P = 0.7 for the debrisoquine MR; anova; n = 10).
  
  
  CONCLUSIONS
  IFN-beta treatment did not affect the activity of CYP2C19 or CYP2D6. The results suggest that it is safe to administer CYP2C19 or CYP2D6 substrates, without dose adjustment, to patients treated with IFN-beta.
authors.affiliation: Division of Clinical Pharmacology, Department of Laboratory Medicine, NEUROTEC, Karolinska Institutet at Huddinge University Hospital, S-141 86 Huddinge, Sweden.
authors.forename: Karin
authors.initials: K
authors.lastname: Hellman
authors.forename: Ewa
authors.initials: E
authors.lastname: Roos
authors.forename: Anna
authors.initials: A
authors.lastname: Osterlund
authors.forename: Anneli
authors.initials: A
authors.lastname: Wahlberg
authors.forename: Lars L
authors.initials: LL
authors.lastname: Gustafsson
authors.forename: Leif
authors.initials: L
authors.lastname: Bertilsson
authors.forename: Sten
authors.initials: S
authors.lastname: Fredrikson
mesh_terms: D000328:Adult; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics / Q000378:metabolism*; D065731:Cytochrome P-450 CYP2C19; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005838:Genotype; D006801:Humans; D016899:Interferon-beta / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism*; D009103:Multiple Sclerosis / Q000188:drug therapy* / Q000378:metabolism; D010641:Phenotype
chemical_list: D016899:Interferon-beta; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D019389:Cytochrome P-450 CYP2D6