Raloxifene

Etki Mekanizması

Raloxifene binds to both estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta), producing tissue-dependent agonist or antagonist effects determined by the local complement of coactivator and corepressor proteins. In breast tissue, raloxifene functions as a potent estrogen antagonist, blocking estradiol-mediated proliferative signaling with high selectivity. This strong breast-tissue antagonism underlies its effectiveness for gynecomastia treatment and breast cancer risk reduction. In bone, raloxifene acts as an estrogen agonist, maintaining bone mineral density by inhibiting osteoclast-mediated resorption. Critically, raloxifene is a weaker antagonist at hypothalamic estrogen receptors compared to tamoxifen, which means it produces less disruption of estrogen-driven negative feedback on GnRH secretion. The result is a more modest increase in LH and FSH compared to tamoxifen, limiting its utility as a standalone PCT agent. In the uterus, raloxifene does not exhibit the partial agonist activity seen with tamoxifen, which translates to a substantially lower risk of endometrial hyperplasia and endometrial cancer with long-term use. Raloxifene is metabolized primarily through glucuronidation rather than CYP450-dependent oxidation, which reduces the potential for drug-drug interactions compared to tamoxifen.