PREFEST
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PREFEST (PREFEST).
PREFEST combines estradiol (an estrogen) and norgestimate (a progestin). Estrogens act by binding to nuclear estrogen receptors (ERα and ERβ), leading to gene transcription regulation, which promotes proliferation of endometrial tissue and secondary sexual characteristics. Norgestimate, a progestin, suppresses gonadotropin secretion and inhibits ovulation, and also counteracts estrogen-induced endometrial hyperplasia by inducing secretory transformation and reducing mitotic activity.
| Metabolism | Estradiol is metabolized primarily via hydroxylation (CYP3A4, CYP1A2, CYP1B1, CYP2C9, CYP2C19, and CYP2D6) and conjugation (glucuronidation and sulfation). Norgestimate is rapidly metabolized in the liver to its active metabolite, norelgestromin, and to other metabolites, primarily via CYP3A4 and CYP2C9. |
| Excretion | Renal: 50-60% as glucuronide conjugates; fecal: 5-10% as unconjugated metabolites; biliary: minor (<5%) |
| Half-life | Estradiol: 13-16 hours (terminal); estradiol valerate: 12-14 hours (prodrug hydrolysis rate-limiting); clinical context: once-daily dosing achieves steady-state in 5-7 days |
| Protein binding | Estradiol: 98% bound to sex hormone-binding globulin (SHBG) and albumin; estradiol valerate: 98% bound to SHBG and albumin |
| Volume of Distribution | Estradiol: 1.2 L/kg (12 L/kg for unbound fraction); clinical meaning: extensive distribution into estrogen-sensitive tissues (breast, uterus, adipose) |
| Bioavailability | Oral: 5-10% (extensive first-pass metabolism to estrone and conjugates); vaginal: 5-10% (minimal first-pass); transdermal: 10-20% |
| Onset of Action | Oral: 2-4 weeks for vasomotor symptom relief; 3-6 months for endometrial protection (when combined with progestin) |
| Duration of Action | 24 hours (once-daily dosing); clinical notes: symptom recurrence within 1-2 weeks if missed dose |
One tablet (estradiol 2 mg) orally once daily on days 1–3, then one tablet (estradiol 2 mg/norgestimate 0.09 mg) orally once daily on days 4–6; repeat cycle continuously.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment guidelines; use with caution in severe renal impairment (GFR <30 mL/min) due to potential accumulation. |
| Liver impairment | Contraindicated in Child-Pugh Class B or C cirrhosis; no specific dose adjustment for mild impairment (Child-Pugh A) but monitor. |
| Pediatric use | Not indicated for pediatric use; safety and efficacy not established. |
| Geriatric use | Use lowest effective dose; consider increased risk of thromboembolism and cognitive effects in women >65 years; avoid use for dementia prevention. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PREFEST (PREFEST).
| Breastfeeding | Estrogen and progestins are excreted in human milk. M/P ratio not established. Use during breastfeeding is not recommended due to potential adverse effects on infant (e.g., jaundice, breast enlargement). |
| Teratogenic Risk | First trimester: Increased risk of congenital anomalies (e.g., VACTERL, heart defects) with estrogens. Second/third trimester: Fetotoxic effects including reduced placental perfusion, fetal growth restriction, and potential genital tract abnormalities. Avoid during pregnancy (FDA Category X). |
■ FDA Black Box Warning
Estrogen plus progestin therapy should not be used for the prevention of cardiovascular disease or dementia. The Women's Health Initiative (WHI) substudy reported increased risks of myocardial infarction, stroke, invasive breast cancer, pulmonary emboli, and deep vein thrombosis in postmenopausal women (50-79 years) during 5.6 years of treatment with conjugated equine estrogens (0.625 mg) plus medroxyprogesterone acetate (2.5 mg) relative to placebo. The WHI Memory Study (WHIMS) reported an increased risk of probable dementia in postmenopausal women 65 years of age or older during 4 years of treatment with conjugated estrogens plus medroxyprogesterone acetate relative to placebo.
| Serious Effects |
["Undiagnosed abnormal genital bleeding","Known, suspected, or history of breast cancer","Known or suspected estrogen-dependent neoplasia","Active DVT, PE, or history of these conditions","Active arterial thromboembolic disease (e.g., stroke, MI) or history thereof","Known anaphylactic reaction or angioedema to PREFEST","Known liver impairment or disease","Known protein C, protein S, or antithrombin deficiency, or other thrombophilic disorders","Known or suspected pregnancy"]
| Precautions | ["Cardiovascular disorders: Risk of stroke, DVT, pulmonary embolism, myocardial infarction.","Malignant neoplasms: Risk of endometrial cancer, breast cancer, ovarian cancer.","Dementia: Increased risk in women 65 years of age or older.","Gallbladder disease: Increased risk.","Hypercalcemia: May occur in women with breast cancer and bone metastases.","Visual abnormalities: Retinal thrombosis; discontinue if sudden partial or complete loss of vision occurs.","Fluid retention: Caution in conditions that may be exacerbated by fluid retention.","Hypocalcemia: Caution in patients with hypoparathyroidism.","Exacerbation of endometriosis: May occur.","Hereditary angioedema: Exogenous estrogens may induce or exacerbate symptoms.","Chloasma: May occur.","Pre-existing hypertriglyceridemia: May cause pancreatitis.","Hepatic hemangiomas: May enlarge."] |
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| Fetal Monitoring |
| Monitor blood pressure, renal function, and signs of thromboembolism. Fetal ultrasound for growth and anatomy if unintentional exposure. Assess for signs of estrogenic effects in neonate. |
| Fertility Effects | Estrogen-containing medications may inhibit ovulation. Use may delay or reduce fertility. Discontinuation typically restores ovulatory cycles. |