PREMARIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PREMARIN (PREMARIN).
Estrogen replacement therapy. Estrogens act by binding to nuclear estrogen receptors (ERα and ERβ) in target tissues, regulating gene transcription and protein synthesis. Conjugated equine estrogens contain multiple estrogenic compounds, primarily estrone sulfate and equilin sulfate.
| Metabolism | Metabolized in the liver via phase 1 (oxidation by CYP450 enzymes, primarily CYP1A2 and CYP3A4) and phase 2 (conjugation with glucuronide and sulfate). Conjugated estrogens are hydrolyzed to active estrogens, which undergo enterohepatic recirculation. Major metabolites include estrone, estradiol, and equilin, as well as their sulfate and glucuronide conjugates. |
| Excretion | Primarily renal as conjugated metabolites (estrone sulfate, estradiol glucuronide), with ~60-80% excreted in urine; ~10-20% in feces via biliary elimination |
| Half-life | Mean terminal elimination half-life of total estrogens is 10-24 hours (estrone ~17h, equilin ~13h). Clinical context: Once-daily dosing yields steady-state within 5-7 days |
| Protein binding | 50-80% bound primarily to sex hormone-binding globulin (SHBG) and albumin |
| Volume of Distribution | Apparent Vd ~1.1 L/kg (range 0.8-1.5 L/kg). Clinical meaning: extensive distribution into tissues, including breast, uterine, and adipose tissue |
| Bioavailability | Oral: 40-70% (extensive first-pass metabolism). Vaginal: ~50-100% (varies by formulation, higher with vaginal rings). Transdermal: ~100% (bypasses first-pass metabolism) |
| Onset of Action | Oral: 2-4 weeks for symptomatic relief (vasomotor symptoms); vaginal cream: 2-4 weeks for urogenital atrophy; intravenous: minutes for hemostatic effects |
| Duration of Action | Oral: 24 hours (once-daily dosing maintains effect); vaginal: 24-48 hours; duration depends on dose and indication; withdrawal bleeding may occur 2-3 days after discontinuing cyclic regimen |
| Molecular Weight | 272.38 |
| Action Class | Estrogens |
| Brand Substitutes | Conjugase Tablet, Conjya 0.625mg Tablet, Espauz 0.625mg Tablet |
0.3-1.25 mg orally once daily for 21 days followed by 7 days off; or continuous daily 0.3-0.625 mg. Conjugated estrogens 0.625-1.25 mg/day intravaginally for atrophic vaginitis.
| Dosage form | CREAM |
| Renal impairment | No specific dosage adjustment recommended; use with caution in severe renal impairment. |
| Liver impairment | Contraindicated in severe hepatic disease (Child-Pugh class C). In mild-to-moderate impairment (Child-Pugh A or B), use with caution; no specific dose reduction guidelines. |
| Pediatric use | For moderate to severe vasomotor symptoms: 0.3-1.25 mg orally once daily cyclically or continuously; for female hypogonadism: 0.3-0.625 mg orally once daily for 21 days, then 7 days off; for pubertal induction: 0.3 mg orally daily initially, titrate upward. |
| Geriatric use | Use lowest effective dose for shortest duration; increased risk of stroke, dementia, and breast cancer. Consider alternative therapies. |
| 1st trimester | Contraindicated. Estrogens are associated with fetal harm, including congenital anomalies, and use during the first trimester is not recommended. |
| 2nd trimester | Contraindicated. Estrogens may cause fetal harm; avoid use during the second trimester unless clearly needed. |
| 3rd trimester | Contraindicated. Estrogens are associated with genitourinary tract anomalies and other adverse effects; use during the third trimester is contraindicated. |
Clinical note
Comprehensive clinical and safety monograph for PREMARIN (PREMARIN).
| Placental transfer | Crosses the placenta; evidence of significant transfer to fetal circulation. |
| Breastfeeding | Excreted in human breast milk. Estrogens may reduce milk quantity and quality. Use during breastfeeding is not recommended due to potential adverse effects on the infant. |
■ FDA Black Box Warning
Estrogens increase the risk of endometrial cancer. Unopposed estrogen therapy increases the risk of endometrial hyperplasia and carcinoma. Use a progestin in women with an intact uterus. Estrogens should not be used to prevent cardiovascular disease or dementia. The Women's Health Initiative (WHI) study reported increased risks of myocardial infarction, stroke, invasive breast cancer, pulmonary emboli, and deep vein thrombosis in postmenopausal women (50–79 years of age) during 5 years of treatment with conjugated equine estrogens (0.625 mg) plus medroxyprogesterone acetate (2.5 mg) relative to placebo.
| Serious Effects |
Undiagnosed abnormal genital bleedingKnown or suspected pregnancyKnown or suspected breast cancer (except in selected patients)Known or suspected estrogen-dependent neoplasiaActive or past history of venous thromboembolism (e.g., deep vein thrombosis, pulmonary embolism)Active or past history of arterial thromboembolism (e.g., stroke, myocardial infarction)Known protein C, protein S, or antithrombin deficiency or other thrombophilic disordersKnown liver dysfunction or diseaseHypersensitivity to conjugated estrogens or any component of the formulation
| Precautions | Cardiovascular disorders: Increased risk of stroke, DVT, PE, and myocardial infarction. Discontinue if thrombotic events occur., Malignant neoplasms: Risk of endometrial cancer (use progestin if uterus intact), breast cancer (especially with combined therapy), and ovarian cancer., Gallbladder disease: Increased risk requiring surgery., Hypertriglyceridemia: May cause pancreatitis if severely elevated., Hepatic impairment: Contraindicated in acute or chronic liver disease., Fluid retention: Monitor patients with cardiac or renal dysfunction., Hypocalcemia: May occur in patients with hypoparathyroidism., Endometriosis: Exacerbation possible., Angioedema: Risk in women with hereditary angioedema., Visual abnormalities: Discontinue if sudden partial or complete loss of vision occurs., Pregnancy: Should not be used during pregnancy. |
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| Lactation Rating | L4 (Possibly Hazardous) |
| Teratogenic Risk | Use of PREMARIN (conjugated estrogens) during pregnancy is contraindicated. First trimester exposure is associated with a risk of congenital anomalies including cardiovascular defects and limb reduction defects. Second and third trimester exposure may increase risk of urogenital tract abnormalities in female offspring and potential long-term reproductive effects. Estrogens are not recommended for use in pregnancy. |
| Fetal Monitoring | PREMARIN is contraindicated in pregnancy. If inadvertent exposure occurs, monitor fetal growth and development via ultrasound. Assess for congenital anomalies. No routine monitoring is required in non-pregnant patients. |
| Fertility Effects | Estrogens can suppress gonadotropin release, potentially inhibiting ovulation and reducing fertility. Effects are reversible upon discontinuation. Long-term use may impact endometrial receptivity and ovarian function. |
| Food/Dietary | Avoid grapefruit and grapefruit juice; may increase estrogen levels. No other significant food interactions. Limit alcohol intake as it may worsen side effects. |
| Clinical Pearls | Monitor for venous thromboembolism risk; avoid in patients with history of breast cancer or liver disease; use lowest effective dose for shortest duration; progestin needed in women with intact uterus to prevent endometrial hyperplasia. |
| Patient Advice | Take exactly as prescribed; do not skip doses or stop without consulting your doctor. · Report any unusual vaginal bleeding, chest pain, shortness of breath, or vision changes immediately. · Avoid grapefruit products as they may affect hormone levels. · Do not smoke while taking this medication; smoking increases risk of serious side effects. · You may experience nausea, breast tenderness, or mood changes; inform your provider if bothersome. |