Bioequivalence of 20-mg once-daily tamoxifen relative to 10-mg twice-daily tamoxifen regimens for breast cancer.
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.
Buzdar
A U
AU
Division of Medicine, University of Texas M.D. Anderson Cancer Center, Houston 77030.
Hortobagyi
G N
GN
Frye
D
D
Ho
D
D
Booser
D J
DJ
Valero
V
V
Holmes
F A
FA
Birmingham
B K
BK
Bui
K
K
Yeh
C
C
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
D013629:Tamoxifen; C028787:N-desmethyltamoxifen