title: Bioequivalence of 20-mg once-daily tamoxifen relative to 10-mg twice-daily tamoxifen regimens for breast cancer.
abstract: OBJECTIVE
  We studied the bioequivalence of a new once-daily regimen of tamoxifen citrate relative to the standard twice-daily regimen of tamoxifen citrate, an established antiestrogenic treatment for breast cancer.
  
  
  METHODS
  Of 30 women with breast cancer, 27 completed this open, two-period, crossover randomized trial. During one 3-month period, patients took one standard 10-mg tamoxifen tablet twice daily; during the preceding or following 3-month period, patients took one of the new 20-mg tablets once daily. Pharmacokinetic profiles and safety parameters were assessed at the end of each 3-month treatment period.
  
  
  RESULTS
  Overall, measured concentrations of tamoxifen and its principal active metabolite, N-desmethyltamoxifen, remained relatively constant over the 24-hour sampling periods at the end of each treatment sequence. For both compounds, the percentage differences of the geometric means for all pharmacokinetic parameters indicated bioequivalence of the once-daily regimen of tamoxifen relative to the standard twice-daily regimen. Both treatment sequences were well tolerated; reported adverse events occurred at similar frequencies with the two treatment regimens.
  
  
  CONCLUSIONS
  The 20-mg tamoxifen tablet taken once daily was bioequivalent to the 10-mg tamoxifen tablet taken twice daily, with no difference in relative risk. The once-daily treatment is a simpler regimen and may facilitate compliance, which may enhance therapeutic outcomes during long-term treatment of breast cancer.
authors.affiliation: Division of Medicine, University of Texas M.D. Anderson Cancer Center, Houston 77030.
authors.forename: A U
authors.initials: AU
authors.lastname: Buzdar
authors.forename: G N
authors.initials: GN
authors.lastname: Hortobagyi
authors.forename: D
authors.initials: D
authors.lastname: Frye
authors.forename: D
authors.initials: D
authors.lastname: Ho
authors.forename: D J
authors.initials: DJ
authors.lastname: Booser
authors.forename: V
authors.initials: V
authors.lastname: Valero
authors.forename: F A
authors.initials: FA
authors.lastname: Holmes
authors.forename: B K
authors.initials: BK
authors.lastname: Birmingham
authors.forename: K
authors.initials: K
authors.lastname: Bui
authors.forename: C
authors.initials: C
authors.lastname: Yeh
mesh_terms: D000284:Administration, Oral; D000368:Aged; D000704:Analysis of Variance; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008875:Middle Aged; D013629:Tamoxifen / Q000008:administration & dosage* / Q000031:analogs & derivatives / Q000097:blood / Q000493:pharmacokinetics; D013810:Therapeutic Equivalency
chemical_list: D013629:Tamoxifen; C028787:N-desmethyltamoxifen