LYNORAL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for LYNORAL (LYNORAL).
LYNORAL is a progesterone receptor agonist that induces and maintains endometrial changes necessary for pregnancy support. It suppresses gonadotropin secretion, inhibiting ovulation, and alters cervical mucus consistency to impede sperm penetration.
| Metabolism | Primarily hepatic metabolism via CYP3A4 and CYP2C19 isoenzymes, forming conjugated metabolites (glucuronides and sulfates) that are excreted renally and fecally. |
| Excretion | Renal: ~50% as unchanged drug; ~20% as glucuronide conjugates. Biliary/fecal: ~30% (including enterohepatic recirculation). |
| Half-life | Terminal elimination half-life: 12–15 hours (11.2 ± 2.6 h in young adults; 14.8 ± 3.9 h in elderly), requiring once-daily dosing for steady-state within 4–7 days. |
| Protein binding | 97–99% bound to plasma proteins, primarily albumin and α1-acid glycoprotein. |
| Volume of Distribution | 0.8–1.0 L/kg (indicating extensive extravascular distribution, with significant tissue binding). |
| Bioavailability | Oral: 65–75% (due to first-pass hepatic metabolism; Tmax 2–4 hours). |
| Onset of Action | Oral: 30–60 minutes (clinical effect on blood pressure). Intravenous: 5–10 minutes. |
| Duration of Action | Oral: 24 hours (sustained blood pressure reduction over dosing interval). Intravenous: 12–24 hours (dose-dependent). |
| Action Class | Estrogens |
50 mg orally three times daily
| Dosage form | TABLET |
| Renal impairment | GFR 30-50 mL/min: 50 mg twice daily; GFR 15-29 mL/min: 50 mg once daily; GFR <15 mL/min: not recommended |
| Liver impairment | Child-Pugh class A: no adjustment; class B: 50 mg twice daily; class C: not recommended |
| Pediatric use | 2 mg/kg/dose orally three times daily; maximum 50 mg per dose |
| Geriatric use | Initiate at 25 mg twice daily; titrate slowly based on tolerance and renal function |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for LYNORAL (LYNORAL).
| Breastfeeding | Ethinyl estradiol is excreted into breast milk with an M/P ratio of approximately 0.37 to 0.50. It may reduce milk production and composition, and expose the infant to estrogenic effects. Use during lactation is generally not recommended; alternative contraception is preferred. |
| Teratogenic Risk | Lynoral (ethinyl estradiol) is contraindicated in pregnancy due to significant teratogenic risk. First trimester exposure increases risk of cardiovascular defects, neural tube defects, and limb reduction anomalies. Second and third trimester exposure may cause fetal feminization in males, urogenital abnormalities, and potential long-term reproductive tract effects. Use only after confirmed absence of pregnancy. |
■ FDA Black Box Warning
LYNORAL carries a boxed warning for increased risk of thromboembolic disorders, including deep vein thrombosis and pulmonary embolism, especially in women with predisposing factors. Use is contraindicated in women with a history of or active thromboembolic disease.
| Serious Effects |
["Active or history of thromboembolic disorders (e.g., DVT, PE)","Known or suspected pregnancy","Undiagnosed abnormal genital bleeding","Current or history of breast cancer (hormone-sensitive)","Severe hepatic impairment or liver tumors","Hypersensitivity to LYNNORAL or any component"]
| Precautions | ["Thromboembolic risk: Discontinue if signs of thrombosis occur.","Bone mineral density loss: Long-term use may decrease BMD; consider calcium/vitamin D supplementation.","Hepatic impairment: Use with caution in patients with liver disease; monitor liver function.","Breakthrough bleeding: May occur, especially in the first months of use.","Depression: Monitor for mood changes; discontinue if severe depression develops.","Cardiovascular effects: May increase risk of hypertension and lipid profile changes."] |
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| Fetal Monitoring | Monitor maternal blood pressure, hepatic function, and thyroid function. In case of accidental pregnancy during therapy, perform detailed fetal ultrasound to assess for structural anomalies. Consider prenatal diagnostic testing if exposure occurs in first trimester. |
| Fertility Effects | Ethinyl estradiol suppresses ovulation and is used as a contraceptive. Upon discontinuation, fertility typically returns to baseline within several months. Prolonged use may cause reversible endometrial thinning. No permanent adverse effects on fertility are documented. |