THEELIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for THEELIN (THEELIN).
Estrogen receptor agonist; binds to estrogen receptors (ERα and ERβ), modulating gene transcription and promoting estrogenic effects.
| Metabolism | Hepatic metabolism via cytochrome P450 (CYP3A4) and conjugation (glucuronidation). |
| Excretion | Renal: ~50% as glucuronide and sulfate conjugates; fecal: ~30% via enterohepatic recirculation; biliary: ~20%. |
| Half-life | Terminal elimination half-life: 13–19 hours (mean 16 h); clinical context: supports once-daily dosing for estrogen replacement. |
| Protein binding | 97–99% bound to albumin and sex hormone-binding globulin (SHBG). |
| Volume of Distribution | 0.5–1.2 L/kg; clinical meaning: moderate tissue distribution, with accumulation in fat and reproductive tissues. |
| Bioavailability | Oral: ~5% due to extensive first-pass metabolism; intramuscular: 100%. |
| Onset of Action | Intravenous: 5–15 minutes; intramuscular: 30 minutes to 2 hours; oral: 2–4 hours (first-pass metabolism delays effect). |
| Duration of Action | Intravenous: 30–60 minutes; intramuscular: 24–48 hours; oral: 12–24 hours; clinical note: duration affected by dosing frequency and formulation. |
Intramuscular: 0.22 to 1.1 mg (220 to 1100 mcg) once weekly for menopausal symptoms; 0.5 to 2 mg (500 to 2000 mcg) once weekly for prostatic carcinoma.
| Dosage form | INJECTABLE |
| Renal impairment | No specific dose adjustment provided; contraindicated in severe renal impairment due to potential fluid retention. Use with caution in patients with renal disease. |
| 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 as clinically indicated. |
| Pediatric use | Not recommended for use in pediatric patients; safety and efficacy not established. For induction of puberty in specific cases (e.g., Turner syndrome): initial 0.2 mg (200 mcg) intramuscular once weekly, titrate upward as needed. |
| Geriatric use | Use lowest effective dose for shortest duration due to increased risk of cardiovascular and thromboembolic events. Dose adjustment not inherently required but monitor for fluid retention and endometrial hyperplasia. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for THEELIN (THEELIN).
| Breastfeeding | Excreted in human breast milk with an M/P ratio of approximately 1.0. May reduce milk production and quality. Not recommended during breastfeeding due to potential adverse effects on the infant, including hormonal disruption. |
| Teratogenic Risk | FDA Pregnancy Category X. First trimester: High risk of fetal harm, including congenital anomalies such as VACTERL association. Second and third trimesters: Continued risk of urogenital tract abnormalities and potential carcinogenicity. Estrogens are contraindicated in pregnancy. |
■ FDA Black Box Warning
Estrogens have been reported to increase the risk of endometrial cancer, cardiovascular disorders, and breast cancer. In postmenopausal women, estrogens with or without progestins should be used at the lowest effective dose and for the shortest duration consistent with treatment goals.
| Serious Effects |
Undiagnosed abnormal genital bleeding, known or suspected pregnancy, known or suspected breast cancer (except in appropriately selected patients), known or suspected estrogen-dependent neoplasia, active or history of venous thromboembolism, active or history of arterial thromboembolism, known or suspected hypersensitivity to estrogens.
| Precautions | Risk of endometrial cancer, cardiovascular disease, breast cancer, venous thromboembolism, dementia, gallbladder disease, visual abnormalities, and hypertriglyceridemia. Use caution in patients with renal impairment, hepatic impairment, or hypothyroidism. |
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| Fetal Monitoring |
| Monitor for signs of thromboembolism, hypertension, and hepatic dysfunction. Fetal ultrasound for anomalies if inadvertent exposure. Assess fetal growth and well-being if used during pregnancy (contraindicated). |
| Fertility Effects | May impair fertility by altering endometrial receptivity and disrupting ovulation. Reversible upon discontinuation. Use in assisted reproductive technology may be adjunctive but not for routine fertility preservation. |