Drug Interactions between dehydroepiandrosterone and fulvestrant

GENERALLY AVOID: Theoretically, high levels of dehydroepiandrosterone (also known as prasterone or DHEA) may negate the pharmacologic effects of selective estrogen receptor modulators (SERMs) like tamoxifen and estrogen receptor antagonists like fulvestrant when they are used to treat estrogen receptor positive cancer. In vitro studies have demonstrated that the sulfate conjugate of DHEA (DHEA-S) is estrogenic in a low-estrogen environment, allowing it to compete with SERMs and estrogen receptor antagonists to bind to the estrogen receptor and promote cell growth in estrogen receptor positive breast cancer cells. The in vitro study that analyzed this potential interaction with tamoxifen found that tamoxifen's ability to inhibit cell growth could be circumvented by DHEA-S at concentrations >= 90 mcg/dL; while the study analyzing DHEA-S with fulvestrant used a concentration of 900 mcg/dL.

MANAGEMENT: The use of dehydroepiandrosterone (also known as prasterone or DHEA) should be generally avoided in patients using SERMs like tamoxifen or estrogen receptor antagonists like fulvestrant. Some authorities consider the use of DHEA to be contraindicated in patients with a known or suspected estrogen dependent tumor as well as in patients with a known or suspected history of breast cancer. Consultation with an oncologist as well as a gynecologist should be considered prior to starting this combination.