Drug Interactions between bazedoxifene / conjugated estrogens and fluoroestradiol F 18

GENERALLY AVOID: Coadministration of the radioactive diagnostic agent fluoroestradiol F 18 with drugs that block the estrogen receptor (ER), such as tamoxifen and fulvestrant, may reduce the uptake of fluoroestradiol F 18 into ER-positive tumors. This may therefore reduce its potential to detect ER-positive non-primary breast cancer lesions. Fluoroestradiol F 18 binds to the ER and its uptake in human tumors is dependent on ER density and function in tumors and physiologic issue, including in the liver, ovaries, and uterus. The effect of selective ER modulators such as tamoxifen and ER down-regulators such as fulvestrant may persist for up to 8 and 28 weeks, respectively. In clinical studies, treatment with ER modulators or fulvestrant was discontinued 60 days prior to the administration of fluoroestradiol F 18. However, concurrent use of aromatase inhibitors was permitted in these clinical studies.

MANAGEMENT: Concomitant use of fluoroestradiol F 18 with systemic endocrine therapy that targets estrogen receptors, including estrogen receptor modulators such as tamoxifen and estrogen receptor down-regulators such as fulvestrant is not recommended. Administration of fluoroestradiol F 18 is recommended prior to starting treatment with these drugs. However, the manufacturer advises that treatment with estrogen receptor modulators or down-regulators should not be delayed in order to administer fluoroestradiol F 18.