Raloxifene: Action as a selective estrogen receptor modulator
Raloxifene (brand names Evista and generics) is a selective estrogen receptor modulator (SERM) used for the prevention and treatment of postmenopausal osteoporosis and to reduce the risk of invasive breast cancer in postmenopausal women with increased risk. Raloxifene has tissue-specific action: in bone and lipid metabolism it acts agonistically like an estrogen, whereas in breast tissue and the endometrium it acts antagonistically like an antiestrogen. This dual action makes raloxifene an attractive therapeutic option for postmenopausal women who desire bone protection without increasing the risk of hormone-dependent tumors.
Raloxifene was approved in 1998 for osteoporosis treatment and in 2007 for breast cancer prevention. Compared to classical hormone replacement therapy, raloxifene has the advantage that it does not cause vaginal bleeding or endometrial hyperplasia. In the large studies MORE (Multiple Outcomes of Raloxifene Evaluation) and CORE, raloxifene was shown to significantly reduce the risk of vertebral fractures and reduce the risk of breast cancer. Therapy is an alternative or supplement to bisphosphonates and denosumab.
Mechanism of action
Raloxifene is a benzothiophene derivative and acts by binding to estrogen receptors (ERα and ERβ). Unlike estradiol, raloxifene induces different conformational changes at the receptor depending on the tissue and co-activator, leading to agonistic or antagonistic effects. In bone cells, liver cells, and the cardiovascular system, raloxifene acts as an estrogen agonist and mediates estrogen-like protective effects. In breast tissue cells and the endometrium it acts as an estrogen antagonist and blocks estrogen-stimulated cell proliferation.
The agonistic action on bone is mediated by binding to osteoblasts and osteocytes, which reduces osteoclast activity and slows bone resorption. This results in an increase in bone density, especially in the spine, and a reduction in vertebral fracture risk. In lipid metabolism, raloxifene leads to a reduction in LDL and lipoprotein a without significantly affecting HDL.
Pharmacokinetically, raloxifene is rapidly absorbed after oral administration but exhibits pronounced first-pass metabolism. Absolute bioavailability is approximately 2 percent because a large portion is metabolized in the intestine and liver to glucuronides. The elimination half-life is approximately 27.7 hours, so once-daily administration is sufficient. Elimination occurs predominantly via feces, to a lesser extent renally.
Areas of application
- Treatment of postmenopausal osteoporosis to reduce the risk of vertebral fractures
- Prevention of postmenopausal osteoporosis in women with increased fracture risk
- Reduction of breast cancer risk in postmenopausal women with increased risk (approved in the USA, in Europe as an additional indication)
Raloxifene is not indicated for the treatment of menopausal symptoms such as hot flashes; in fact, hot flashes may occur or be intensified under raloxifene. Also not for primary treatment of existing breast cancer; tamoxifen or aromatase inhibitors are established for this purpose.
Dosage and administration
Adult postmenopausal women: 60 mg raloxifene once daily orally.
Start of therapy: when indicated, earliest after the onset of menopause.
Duration of treatment: long-term, typically several years, annual re-evaluation of indication and risks.
Administration: take with water, independent of meals. Preferably at the same time each day.
Missed tablet: take as soon as remembered. If the next dose is due soon, skip the missed tablet and continue the normal schedule.
Calcium and vitamin D: substitution recommended if intake is low, as raloxifene develops its effects optimally only with adequate calcium and vitamin D supply.
Renal insufficiency: use with caution in moderate to severe impairment, not recommended in severe renal insufficiency. Hepatic insufficiency: contraindicated in moderate to severe impairment.
Important: during prolonged immobilization (such as major surgery, hospitalization, bed rest), interrupt therapy due to increased thrombosis risk.
Side effects
Very common: hot flashes (especially at the beginning of therapy), flu-like symptoms, leg cramps, peripheral edema.
Common: headaches, dizziness, gastrointestinal complaints, rash, blood pressure changes, fatigue.
Uncommon: deep vein thrombosis, pulmonary embolism, visual disturbances, mastalgia (breast sensitivity), migraine.
Rare to very rare: retinal vein thrombosis, ischemic stroke (especially in women with cardiovascular risk profile or pre-existing conditions, RUTH study), severe allergic reactions, skin reactions including Stevens Johnson syndrome (very rare).
Thrombosis risk: significantly increased (approximately 2 to 3 fold), especially in the first months of therapy. In patients with risk profile (obesity, smoking, previous thrombosis history) raloxifene should not be used.
In the RUTH study, a slightly increased risk of fatal stroke was observed in women with cardiovascular risk factors or established coronary heart disease, so the cardiovascular history must be considered before starting therapy.
Drug interactions
- Coumarins such as phenprocoumon, warfarin: Raloxifene may slightly reduce anticoagulant effect. Monitor INR when starting or stopping raloxifene therapy.
- Cholestyramine: reduces raloxifene absorption, maintain minimum 12-hour interval from intake.
- Other estrogens or hormone preparations: not recommended due to pharmacodynamic interaction.
- Live vaccines: no special precaution required.
- Anticonvulsants: theoretical effects on absorption, clinically usually not relevant.
- Thyroid hormones: usually no relevant interaction.
Special precautions
Pregnancy and breastfeeding: contraindicated because raloxifene can be embryotoxic and teratogenic.
Premenopausal women: not approved and not sufficiently studied.
Children: not approved.
Contraindications: pregnancy, breastfeeding, premenopausal women, active or past thromboembolic events (deep vein thrombosis, pulmonary embolism, retinal vein thrombosis), prolonged immobilization, unexplained vaginal bleeding, severe hepatic insufficiency, severe renal insufficiency, endometrial or breast cancer in active treatment, known hypersensitivity.
Before therapy: detailed history of thrombosis risk, cardiovascular pre-existing conditions, breast cancer history, gynecological examination with mammography, bone density measurement (DXA), calcium and vitamin D status, liver and kidney values.
During therapy: annual gynecological check-up with mammography, re-evaluation of thrombosis risk, bone density measurement every 1 to 2 years, monitoring of cardiovascular symptoms.
During prolonged immobilization (such as major surgery, hospitalizations, travel over 4 hours): interrupt therapy 72 hours before and for several days after the immobilization period, resume after mobilization.
Lifestyle: balanced diet with sufficient calcium (1000 to 1200 mg per day) and vitamin D (800 IU per day), regular physical activity, no smoking, moderate alcohol consumption, fall prevention in at-risk patients.
Driving ability: usually not impaired; use caution if dizziness or visual disturbances occur.
You may also be interested in
- Alendronic acid, bisphosphonate for osteoporosis
- Risedronic acid, another bisphosphonate
- Denosumab, RANKL antibody for osteoporosis
- Teriparatide, anabolic agent for severe osteoporosis
- Tamoxifen, SERM in breast cancer therapy
- Tibolone, alternative hormone therapy in postmenopause
Frequently asked questions
What is a SERM and how does raloxifene differ from tamoxifen?
SERM stands for selective estrogen receptor modulator. These substances act like an estrogen or antiestrogen depending on the tissue. Raloxifene acts as an estrogen agonist on bone (protection against osteoporosis) and as an antagonist in the breast (reduction of breast cancer risk). Tamoxifen also acts as a SERM but has a different focus of action with primary application in adjuvant therapy of hormone-sensitive breast cancer. Both substances increase thrombosis risk; tamoxifen additionally increases endometrial cancer risk, which is not observed with raloxifene.
Does raloxifene protect against all fractures or only vertebral fractures?
The MORE study demonstrated that raloxifene significantly reduces the risk of vertebral (spine) fractures. For non-vertebral fractures, particularly at the femoral neck, the effect in the studies was not statistically significant. Therefore, raloxifene is primarily considered therapy for women with increased risk of vertebral fractures. In very high fracture risk at other locations, bisphosphonates, denosumab, or teriparatide are preferred.
Why do I get hot flashes while taking raloxifene?
Raloxifene acts as an estrogen antagonist in the central nervous system and can thereby intensify or newly trigger menopausal symptoms such as hot flashes. This side effect occurs especially at the beginning of therapy and often decreases during continued use. Therefore, raloxifene is not suitable for women with pronounced menopausal symptoms who also seek relief from hot flashes.
How high is the thrombosis risk with raloxifene?
The thrombosis risk with raloxifene is approximately 2 to 3 fold increased compared to women without therapy. In absolute numbers, this corresponds in postmenopausal women to an increase of approximately 1 additional thrombosis per 1000 women per year. In patients with risk profile including obesity, smoking, prior thromboses, or family history of thrombosis, the risk is significantly higher and raloxifene is usually not used. Interrupt therapy during prolonged immobilization periods.
Sources
- Gelbe Liste, Raloxifene active ingredient profile
- BfArM, Federal Institute for Drugs and Medical Devices
- Umbrella Association for Osteology (DVO)
- AWMF S3 Guideline for Prevention, Diagnosis and Treatment of Osteoporosis
- European Medicines Agency, EPAR Evista
Legal notices and liability disclaimer
The information provided on this page serves exclusively general informational purposes and does not constitute medical advice, diagnosis, or treatment recommendation. It does not replace the advice of a licensed physician or pharmacist. Raloxifene is a prescription drug and should be used under medical supervision, particularly in patients with cardiovascular risk factors or thrombosis history. All information is based on expert information and recognized scientific sources published at the time of creation; the currently valid product information of the manufacturer is always decisive. Sanoliste assumes no liability for completeness, timeliness, or accuracy of the information presented. In a medical emergency, call emergency number 112.