The Pairing of a Selective Estrogen Receptor Modulator, Bazedoxifene, with Conjugated Estrogens as a New Paradigm for the Treatment of Menopausal Symptoms and Osteoporosis Prevention

The menopausal transition is associated with decreased ovarian function and concomitant decline in estrogen production, which may result in physiological effects such as hot flashes, reduced bone mass, and altered lipid profile. It is well established that these unfavorable changes are effectively offset with estrogen therapy (ET) or, in women with a uterus, estrogens in combination with a progestin (hormone therapy). Selective estrogen receptor (ER) modulators (SERMs), which exhibit both ER agonist and antagonist activities depending on the target tissue, have been regarded as offering the potential to provide the benefits of ET and hormone therapy with an improved safety and tolerability profile. To date, no SERM alone has demonstrated an ideal benefit-risk profile for menopausal therapy. The tissue-selective estrogen complex, or the pairing of a SERM with estrogens, may provide an optimal blend of ER agonist and antagonist activities. We evaluated the physiological profile of this novel therapeutic paradigm by using various in vivo models to assess uterine, vasomotor, lipid, and skeletal responses to a tissue-selective estrogen complex partnering bazedoxifene with conjugated estrogens (CE). Bazedoxifene at 3.0 mg/kg effectively antagonized CE-induced uterine stimulation without reversing the positive effects of CE on vasomotor instability. When paired with CE, bazedoxifene at 3.0 mg/kg reduced total cholesterol levels by up to 20% compared with CE alone and significantly increased total bone density relative to control. These preclinical findings showed that the appropriate dose combination of bazedoxifene/CE exhibits positive vasomotor, lipid, and skeletal responses with minimal uterine stimulation. (Endocrinology 149: 6084-6091, 2008)