MENOSTAR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MENOSTAR (MENOSTAR).
Estrogen receptor agonist; binds to estrogen receptors, leading to gene transcription and physiological effects.
| Metabolism | Hepatic via CYP3A4; undergoes enterohepatic recirculation. |
| Excretion | Renal (primarily as glucuronide and sulfate conjugates), ~40-60% of a dose excreted in urine; fecal excretion accounts for approximately 10-20% as unabsorbed drug or metabolites. |
| Half-life | Terminal half-life of estradiol is approximately 12-14 hours; with MENOSTAR (estradiol vaginal ring), systemic absorption is minimal, and the effective half-life for local effects is extended by continuous release over 90 days. |
| Protein binding | Estradiol is approximately 98% bound to sex hormone-binding globulin (SHBG) and albumin. |
| Volume of Distribution | Apparent Vd of estradiol is approximately 1.2 L/kg; this large volume reflects extensive distribution into tissues, but for MENOSTAR, systemic distribution is limited due to low absorption. |
| Bioavailability | Vaginal route: minimal systemic bioavailability (<10% of the dose absorbed systemically due to first-pass hepatic metabolism and local action). |
| Onset of Action | Vaginal administration: Clinically detectable effect on urogenital epithelium within 2-4 weeks of continuous use. |
| Duration of Action | Continuous local effect for the entire 90-day period of ring placement; systemic effects are minimal due to low absorption. |
| Molecular Weight | 270.37 |
One Menostar (estradiol 14 mcg/day) transdermal system applied to the lower abdomen once weekly (every 7 days).
| Dosage form | FILM, EXTENDED RELEASE |
| Renal impairment | No dosage adjustment required for renal impairment; estradiol pharmacokinetics not significantly altered in renal disease. |
| Liver impairment | Contraindicated in patients with impaired liver function or active liver disease; no adjustment guidelines available for Child-Pugh classes. |
| Pediatric use | Not indicated for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | No specific dosage adjustment recommended; however, use the lowest effective dose for the shortest duration due to increased risk of thromboembolic events and malignancy in elderly women. |
| 1st trimester | Estrogens are contraindicated in pregnant women. Use during the first trimester may cause fetal harm. Estrogens have been associated with an increased risk of congenital anomalies, including cardiovascular and limb defects. |
| 2nd trimester | Estrogens should not be used during pregnancy. Exposure in the second trimester may interfere with fetal development. No adequate studies in pregnant women. |
| 3rd trimester | Estrogens are contraindicated in the third trimester. Use may lead to fetal harm, including potential effects on urogenital development and long-term reproductive tract abnormalities. |
Clinical note
Comprehensive clinical and safety monograph for MENOSTAR (MENOSTAR).
| Placental transfer | Estrogens cross the placenta readily. Significant placental transfer occurs, with fetal exposure approximately 5-10% of maternal levels. Binding proteins may influence distribution. |
| Breastfeeding |
■ FDA Black Box Warning
Estrogens increase the risk of endometrial cancer. Unopposed estrogen use increases risk of endometrial hyperplasia and carcinoma. Concomitant progestin therapy is recommended.
| Serious Effects |
Known or suspected pregnancyBreast cancer (current or past)Estrogen-dependent neoplasia (e.g., endometrial cancer)Undiagnosed abnormal genital bleedingActive or history of venous thromboembolic events (e.g., deep vein thrombosis, pulmonary embolism)Active or history of arterial thromboembolic disease (e.g., stroke, myocardial infarction)Known thrombophilic disorders (e.g., protein C, protein S, or antithrombin deficiency, or factor V Leiden mutation)Liver dysfunction or disease as long as liver function tests have not returned to normalHypersensitivity to estrogens or any component of the product
| Precautions | Endometrial hyperplasia and carcinoma, Cardiovascular disorders (e.g., stroke, DVT, PE), Breast cancer risk, Gallbladder disease, Hypertriglyceridemia, Fluid retention, Hereditary angioedema |
| Food/Dietary | Grapefruit and grapefruit juice may increase estradiol systemic absorption via CYP3A4 inhibition; avoid concomitant consumption. No other significant food interactions. |
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| Estrogens are excreted in human milk in small amounts, but there are no reports of adverse effects in nursing infants. However, estrogens may decrease milk production and quality. Use with caution in breastfeeding women, especially during the first few weeks postpartum when milk supply is being established. |
| Lactation Rating | L3 - Moderately Safe |
| Teratogenic Risk | First trimester: Use contraindicated due to risk of urogenital tract abnormalities and cardiovascular defects; second and third trimester: Estrogen exposure associated with increased risk of endometrial adenocarcinoma and other malignancies in female offspring; no adequate studies; use only if clearly needed. |
| Fetal Monitoring | Monitor maternal blood pressure, signs of thromboembolism, hepatic function; fetal surveillance including ultrasound for growth and anatomy if inadvertent exposure occurs. |
| Fertility Effects | Estrogens may suppress ovulation and impair fertility; use as contraceptive at indicated doses; fertility may return upon discontinuation. |
| Clinical Pearls | MENOSTAR (estradiol vaginal ring) delivers low-dose estrogen locally for vulvovaginal atrophy. Systemic absorption minimal due to vaginal route; avoids first-pass metabolism. Insert ring high in vagina; replace every 90 days. Do not use in patients with known or suspected breast cancer, estrogen-dependent neoplasia, undiagnosed abnormal genital bleeding, active DVT/PE, or history of same. Monitor for endometrial hyperplasia in uterus intact women; consider adding progestin if needed. |
| Patient Advice | Insert the ring high into the vagina as directed for 90-day continuous use. · The ring may be removed during intercourse; rinse with lukewarm water and reinsert promptly. · Do not use oils or lubricants containing petroleum jelly which may damage the ring. · Report any unusual vaginal bleeding, pain, or signs of thromboembolism (leg pain, chest pain, shortness of breath). · This medication does not protect against STIs or pregnancy; no systemic contraception provided. |