Lack of effects of S-equol-containing supplement on the pharmacokinetics of oral hormone therapy drugs for breast cancer.

purposeS-equol is an intestinal bacterial metabolite of soy isoflavones. S-equol-containing supplements have been demonstrated to alleviate menopausal symptoms, including hot flashes and joint pain, because of decreasing estrogen levels. Hence, some patients with hot flashes and joint pain induced by hormone therapy drugs are taking S-equol-containing supplements with expectation of reducing their symptoms. However, there is little information of pharmacokinetic interaction between S-equol and drugs. Therefore, we investigated the potential of S-equol to affect the pharmacokinetics of hormone therapy drugs.

methodsThis open-label, crossover study was performed at a single center. Twenty-four healthy postmenopausal women were enrolled and divided into four groups containing six subjects (three equol-producers and three equol-nonproducers). Each group received either anastrozole, letrozole, exemestane, or tamoxifen at standard doses on days 1 and 15. All subjects received S-equol-containing supplement at a standard dose of 10 mg on days 9-15. Blood samples for pharmacokinetic assessment were drawn at predefined time points.

resultsNo significant differences were observed in the geometric mean area under the concentration-time curve from 0 h to 24 h of anastrozole (269.0 vs. 289.3 ng‧h/mL; P = 0.14), letrozole (496.5 vs. 523.5 ng‧h/mL; P = 0.07), exemestane (54.1 vs. 53.8 ng‧h/mL; P = 0.69), and tamoxifen (638.4 vs. 578.8 ng‧h/mL; P = 0.22) without and with S-equol-containing supplement on days 1 and 15.

conclusionS-equol-containing supplement has no clinically significant effects on the exposure of oral hormone therapy drugs for breast cancer. TRIAL REGISTRATION NUMBER AND DATE OF REGISTRATION: jRCTs031200084, August 13th, 2020.