ESTINYL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ESTINYL (ESTINYL).
Estinyl (ethinyl estradiol) is a synthetic estrogen that binds to estrogen receptors, leading to increased synthesis of DNA, RNA, and various proteins in target tissues. It suppresses gonadotropin release, modulating the hypothalamic-pituitary-ovarian axis.
| Metabolism | Primarily hepatic via CYP3A4; undergoes first-pass metabolism; conjugates with glucuronic acid and sulfate; enterohepatic recirculation occurs. |
| Excretion | Renal excretion of metabolites (approximately 40-50% as ethinyl estradiol glucuronide and sulfate conjugates) and fecal excretion (approximately 20-30% as conjugates and minor metabolites); <10% excreted unchanged in urine. |
| Half-life | Terminal elimination half-life is approximately 13-27 hours (mean ~17 hours); enterohepatic recirculation contributes to variability; steady-state achieved within 3-5 days. |
| Protein binding | Highly bound to serum albumin (~97-98%); also binds to sex hormone-binding globulin (SHBG) with lower affinity. |
| Volume of Distribution | Apparent volume of distribution is approximately 2.5-5.5 L/kg (mean ~3 L/kg), indicating extensive extravascular distribution and tissue binding. |
| Bioavailability | Oral bioavailability is approximately 40-45% due to first-pass metabolism in the gut wall and liver; substantial interindividual variability (range 20-65%). |
| Onset of Action | Oral: Onset of clinical effect (e.g., contraceptive efficacy) occurs within 3-7 days of initiation; effects on endometrium and pituitary-ovarian axis require continuous dosing. |
| Duration of Action | Duration of action persists for 24 hours with daily dosing; contraceptive protection is maintained with consistent daily intake; after discontinuation, ovulation may resume within 2-3 weeks. |
| Molecular Weight | 296.4 |
0.01-0.05 mg orally once daily for contraception or 2.5-10 mg orally 3-4 times daily for 5-10 days for hemostasis in dysfunctional uterine bleeding. Route: oral. Frequency: daily for contraception; multiple daily doses for acute bleeding.
| Dosage form | TABLET |
| Renal impairment | No specific GFR-based dose adjustments are established. Use with caution in patients with renal impairment due to potential fluid retention. |
| Liver impairment | Contraindicated in severe hepatic disease (Child-Pugh class C). In mild to moderate impairment (Child-Pugh A or B), use with caution and reduce dose by 50% if necessary. |
| Pediatric use | For contraception in postmenarchal adolescents: same as adult dosing (0.01-0.05 mg orally once daily). For other indications, use lowest effective dose; no standard weight-based guidelines available. |
| Geriatric use | Not typically indicated for postmenopausal women. If used, start at lowest effective dose due to increased risk of thromboembolism, fluid retention, and cardiovascular events. |
| 1st trimester | Ethinyl estradiol is contraindicated in pregnancy. Use during first trimester associated with congenital anomalies (e.g., heart defects, limb reduction). Increased risk of fetal harm, including VACTERL association. Avoid use in pregnancy. |
| 2nd trimester | Contraindicated in pregnancy. Potential for adverse effects on fetal development, including urogenital abnormalities and other malformations. No indication for use during second trimester. |
| 3rd trimester | Contraindicated in pregnancy. May cause fetal harm, including reproductive tract anomalies and potential long-term effects. Use only if clearly needed for life-threatening conditions, though alternative therapies preferred. |
Clinical note
Comprehensive clinical and safety monograph for ESTINYL (ESTINYL).
| Placental transfer | Ethinyl estradiol crosses the placenta. Studies demonstrate measurable fetal serum concentrations. In animal studies, placental transfer results in fetal exposure, with potential for teratogenicity. Human data limited but consistent with fetal exposure. |
■ FDA Black Box Warning
Cigarette smoking increases the risk of serious cardiovascular side effects from estrogen-containing products. This risk increases with age and with heavy smoking (15 or more cigarettes per day) and is quite marked in women over 35 years of age. Women taking estrogens should not smoke.
| Serious Effects |
Known or suspected pregnancyUndiagnosed abnormal genital bleedingKnown or suspected estrogen-dependent neoplasia (e.g., breast cancer)Active venous thromboembolism or history of VTE (e.g., deep vein thrombosis, pulmonary embolism)Active arterial thromboembolic disease (e.g., stroke, myocardial infarction) or prothrombotic conditionsSevere hepatic impairment or acute liver disease (e.g., hepatitis, cirrhosis, liver tumors)Hypersensitivity to ethinyl estradiol or any componentUse with Hepatitis C drug combinations containing ombitasvir/paritaprevir/ritonavir ± dasabuvir (increased ALT elevations)
| Precautions | Increased risk of thromboembolic disorders, myocardial infarction, stroke, hepatic adenoma, gallbladder disease, hypertension, hypercalcemia in breast cancer patients; potential for fluid retention; glucose intolerance; worsening of endometriosis; uterine leiomyoma growth; hereditary angioedema; cholestatic jaundice; lactation suppression. |
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| Breastfeeding |
| Ethinyl estradiol is excreted into breast milk in small amounts. Combined oral contraceptives containing ethinyl estradiol may reduce milk production and alter milk composition, especially in early postpartum period. Use with caution in breastfeeding women; low-dose progestin-only contraceptives are preferred. Monitor infant for gynecomastia or other estrogenic effects. |
| Lactation Rating | L3 (Moderately safe; use with caution, potential for adverse effects on lactation and infant) |
| Teratogenic Risk | FDA Pregnancy Category X. First trimester: Increased risk of congenital anomalies including cardiovascular and limb defects from estrogenic effects. Second and third trimesters: Associated with fetal harm (urogenital abnormalities, vaginal adenosis, clear cell adenocarcinoma in female offspring) due to diethylstilbestrol (DES) component. Contraindicated in pregnancy. |
| Fetal Monitoring | Prior to initiation: Exclude pregnancy with sensitive test. During use: Monitor for thrombotic events (DVT, PE), hypertension, hepatic dysfunction, and glucose intolerance. Fetal monitoring not indicated as drug is contraindicated in pregnancy. Perform pregnancy test if pregnancy suspected. |
| Fertility Effects | Used for hormone replacement in hypogonadism to induce puberty and fertility. High doses may suppress ovulation and endometrial development. Reversible effect on fertility upon discontinuation. |
| Food/Dietary |
| Grapefruit juice may increase ethinyl estradiol levels. No other significant food interactions. |
| Clinical Pearls | ESTINYL (ethinyl estradiol) is an estrogen component in combination oral contraceptives. Monitor for thromboembolic events, especially in smokers over 35. Avoid in women with history of DVT/PE, stroke, or breast cancer. Use with caution in hypertension, diabetes, and migraine with aura. Consider CYP3A4 inducers (e.g., rifampin) reducing contraceptive efficacy. |
| Patient Advice | Take at the same time daily to maintain contraceptive efficacy. · Report severe headache, chest pain, leg swelling, or visual disturbances immediately. · Smoking increases risk of serious cardiovascular side effects, especially over age 35. · Use backup contraception if vomiting or severe diarrhea occurs within 4 hours of dosing. · Do not stop without medical advice; withdrawal bleeding may not be immediate. |