Mechanism of Action
Raloxifene belongs to the benzothiophene class of compounds and functions as an estrogen agonist/antagonist 2. The biological actions are mediated through binding to estrogen receptors, resulting in:
- Estrogen agonist effects in bone tissue (decreases bone resorption, increases bone mineral density)
- Estrogen antagonist effects in uterine and breast tissues (lacks estrogen-like stimulation) 2
The agonistic or antagonistic action depends on the extent of recruitment of coactivators and corepressors to estrogen receptor target gene promoters 2.
FDA-Approved Indications
Raloxifene is FDA-approved for 1:
- Prevention and treatment of postmenopausal osteoporosis (60 mg daily)
- Reduction of risk of invasive breast cancer in postmenopausal women with osteoporosis or at high risk of breast cancer
Clinical Context
As a SERM, raloxifene demonstrates tissue-selective effects that distinguish it from other drug classes 3:
- Bone: Acts as estrogen agonist, reducing vertebral fracture risk by 30-50% 4
- Breast: Acts as estrogen antagonist, reducing invasive ER-positive breast cancer risk 5
- Uterus: Acts as estrogen antagonist, no endometrial stimulation (unlike tamoxifen) 6
The tissue-specific actions are related to differential expression of estrogen receptor alpha and beta subtypes across tissues, with varying proportions determining the net agonist or antagonist effect 3.