PREMPHASE (PREMARIN;CYCRIN 14/14)
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PREMPHASE (PREMARIN;CYCRIN 14/14) (PREMPHASE (PREMARIN;CYCRIN 14/14)).
PREMPHASE combines conjugated estrogens (PREMARIN) and medroxyprogesterone acetate (CYCRIN). Estrogens act by binding to nuclear estrogen receptors (ERα and ERβ), which regulate gene transcription and produce effects in tissues such as the endometrium, breast, and bone. Medroxyprogesterone acetate is a progestin that induces secretory changes in the endometrium and reduces the risk of endometrial hyperplasia associated with estrogen therapy.
| Metabolism | Conjugated estrogens are extensively metabolized in the liver via glucuronidation and sulfation, with enterohepatic recirculation. Medroxyprogesterone acetate is primarily metabolized via hydroxylation and reduction by CYP3A4, forming multiple metabolites. |
| Excretion | Conjugated estrogens and MPA are primarily excreted in urine (∼90% as glucuronide and sulfate conjugates) and feces (∼10% as unabsorbed drug and biliary metabolites). |
| Half-life | Conjugated estrogens: terminal half-life 10–24 h (accumulation with daily dosing). MPA: terminal half-life 12–33 h (mean ∼17 h). |
| Protein binding | Conjugated estrogens: 50–80% bound to albumin and sex hormone-binding globulin (SHBG). MPA: 90–95% bound to albumin, not to SHBG or corticosteroid-binding globulin. |
| Volume of Distribution | Conjugated estrogens: 1–2 L/kg (extensive tissue distribution). MPA: 0.5–1.0 L/kg (moderate distribution into adipose and liver). |
| Bioavailability | Conjugated estrogens: oral, 40–50% (extensive first-pass glucuronidation). MPA: oral, 100% (almost completely absorbed; minimal first-pass effect). |
| Onset of Action | Conjugated estrogens: oral, vasomotor symptom relief within 2–4 weeks. MPA: oral, endometrial transformation within 10–14 days of continuous dosing. |
| Duration of Action | Conjugated estrogens: effects persist for 24 h with daily dosing; steady state reached in 5–7 days. MPA: daily oral dosing maintains endometrial protection; withdrawal bleeding occurs 2–7 days after last dose. |
| Molecular Weight | Premarin: conjugated equine estrogens (MW ~300-400 Da); medroxyprogesterone acetate: 386.55 Da |
One tablet daily (conjugated estrogens 0.625 mg/medroxyprogesterone acetate 5 mg) for 14 days, followed by one tablet daily (conjugated estrogens 0.625 mg) for 14 days; continuous cycling. Oral administration.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment required for renal impairment; use with caution in severe renal disease due to potential fluid retention. |
| Liver impairment | Contraindicated in Child-Pugh class C cirrhosis; in Child-Pugh class A or B, use lowest effective dose and monitor liver function; avoid in acute hepatic disease. |
| Pediatric use | Not indicated for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | Use lowest effective dose for shortest duration; increased risk of thromboembolic events, stroke, and dementia; consider alternative therapies. |
| 1st trimester | Estrogen and progestin exposure during first trimester may be associated with congenital anomalies. Use is contraindicated due to risk of fetal harm. |
| 2nd trimester | Use in second trimester is not recommended; estrogens and progestins can affect fetal development. |
| 3rd trimester | Use in third trimester may be harmful; estrogens can feminize male fetus, and progestins may cause genital abnormalities. |
Clinical note
Comprehensive clinical and safety monograph for PREMPHASE (PREMARIN;CYCRIN 14/14) (PREMPHASE (PREMARIN;CYCRIN 14/14)).
| Placental transfer | Both conjugated estrogens (PREMARIN) and medroxyprogesterone acetate (CYCRIN) cross the placenta. |
| Breastfeeding | Estrogens and progestins are excreted in breast milk and may reduce milk production and quality. Use is not recommended during breastfeeding. |
■ FDA Black Box Warning
Estrogens with or without progestins should not be used to prevent cardiovascular disease or dementia. There is an increased risk of endometrial cancer in a woman with a uterus who uses unopposed estrogens. 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 of age) during 5.6 years of treatment with conjugated equine estrogens (0.625 mg) combined with medroxyprogesterone acetate (2.5 mg) relative to placebo. The WHI Memory Study (WHIMS) reported an increased risk of developing probable dementia in postmenopausal women 65 years of age or older during 4 years of treatment with CE (0.625 mg) combined with MPA (2.5 mg) relative to placebo.
| Serious Effects |
Known or suspected pregnancyUndiagnosed abnormal genital bleedingKnown or suspected breast cancerKnown or suspected estrogen-dependent neoplasiaActive or history of venous thromboembolismActive or history of arterial thromboembolismLiver disease or impaired liver functionHypersensitivity to any ingredient
| Precautions | Cardiovascular disorders: increased risk of stroke, DVT, pulmonary embolism, and myocardial infarction, Malignant neoplasms: increased risk of endometrial cancer (if uterus intact) and breast cancer, Dementia: increased risk of probable dementia in women ≥65 years, Gallbladder disease, Hypercalcemia in patients with breast cancer and bone metastases, Visual abnormalities: retinal vascular thrombosis, Fluid retention, Elevated blood pressure, Hypertriglyceridemia |
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| Lactation Rating | Avoid |
| Teratogenic Risk | First trimester: epidemiological studies suggest a small increased risk of non-cardiac congenital anomalies (e.g., limb defects) and possible neural tube defects from estrogen exposure. Second and third trimesters: exposure may cause urogenital tract abnormalities in male and female offspring (e.g., vaginal adenosis, clear cell adenocarcinoma in females; hypospadias in males). Use is contraindicated in pregnancy. |
| Fetal Monitoring | Monitor for signs of thromboembolism, hypertension, and fluid retention. Assess fetal growth and development if inadvertent exposure occurs. No routine monitoring required as drug is contraindicated. |
| Fertility Effects | May alter menstrual cycle and suppress ovulation. Return to fertility may be delayed after discontinuation. No permanent impairment. |
| Food/Dietary | No specific food interactions; advise consistent intake of calcium and vitamin D (1000-1500 mg calcium/day; 600-800 IU vitamin D/day) for bone health. Avoid grapefruit juice if on concurrent statins or other CYP3A4 substrates (grapefruit may affect estrogen metabolism). |
| Clinical Pearls | Premphase is a cyclic estrogen/progestin regimen for postmenopausal women with an intact uterus. The 14/14 regimen: conjugated estrogens 0.625 mg daily continuously plus medroxyprogesterone acetate 5 mg from days 15–28. Assess endometrial status before starting; annual mammograms and pelvic exams required. Avoid in women with known or suspected pregnancy, breast cancer, or active thromboembolic disease. Consider risk of cardiovascular events, stroke, and dementia with prolonged use. Taper rather than abruptly discontinue to avoid withdrawal bleeding. |
| Patient Advice | Take the pink tablet daily for days 1–14 of each cycle, then the light-blue tablet daily for days 15–28. Bleeding may occur mid-cycle or during placebo days. · Report any abnormal vaginal bleeding, chest pain, leg swelling, severe headache, or vision changes immediately. · Do not use if pregnant or planning pregnancy; use effective contraception if needed. · Smoking increases risk of cardiovascular side effects; avoid smoking. · Annual breast and pelvic exams are mandatory; perform monthly breast self-exams. |