PREMPRO (PREMARIN;CYCRIN)
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PREMPRO (PREMARIN;CYCRIN) (PREMPRO (PREMARIN;CYCRIN)).
PREMPRO combines conjugated estrogens (PREMARIN) and medroxyprogesterone acetate (CYCRIN). Estrogens bind to estrogen receptors (ERα and ERβ), activating gene transcription involved in cell growth, differentiation, and function. Progestins like medroxyprogesterone acetate bind to progesterone receptors, antagonizing estrogen-induced endometrial proliferation and reducing risk of endometrial hyperplasia.
| Metabolism | Conjugated estrogens are hydrolyzed in the liver and extensively metabolized via glucuronidation and sulfation. Medroxyprogesterone acetate is metabolized in the liver via hydroxylation and conjugation, primarily by CYP3A4. |
| Excretion | Conjugated estrogens and medroxyprogesterone acetate are primarily excreted in urine as glucuronide and sulfate conjugates; about 10% excreted in feces via bile. |
| Half-life | Conjugated estrogens: 10-24 hours (terminal); medroxyprogesterone acetate: 12-17 hours. Clinical context: steady-state reached after 5-7 days. |
| Protein binding | Conjugated estrogens: 50-80% bound to albumin and sex hormone-binding globulin (SHBG); Medroxyprogesterone acetate: 90% bound to albumin. |
| Volume of Distribution | Conjugated estrogens: ~10 L/kg; medroxyprogesterone acetate: ~4 L/kg. Clinical meaning: extensive tissue distribution, including reproductive tissues. |
| Bioavailability | Oral: 40-60% for conjugated estrogens (first-pass metabolism); medroxyprogesterone acetate: 100% (oral) due to minimal first-pass effect. |
| Onset of Action | Oral: symptom relief within 2-4 weeks for vasomotor symptoms; maximal effect may take 8-12 weeks. |
| Duration of Action | Duration: 24 hours for daily dosing; clinical effects persist with continuous therapy. Withdrawal bleeding may occur during placebo week if cyclic regimen used. |
| Molecular Weight | Premarin (conjugated estrogens): average 338 Da (range 270-400 Da). Cycrin (medroxyprogesterone acetate): 386.5 Da. |
One tablet (0.625 mg conjugated estrogens/2.5 mg medroxyprogesterone acetate or 0.625 mg/5 mg) orally once daily.
| Dosage form | TABLET |
| Renal impairment | No specific GFR-based dose adjustment recommended; use with caution in severe renal impairment. |
| Liver impairment | Contraindicated in severe hepatic disease (Child-Pugh C); use with caution in mild to moderate impairment (Child-Pugh A or B) with monitoring. |
| Pediatric use | Not indicated for use in pediatric patients. |
| Geriatric use | Use lowest effective dose for shortest duration; increased risk of dementia, stroke, and thromboembolism; consider non-hormonal alternatives. |
| 1st trimester | Known teratogen. Estrogens and progestins are associated with congenital anomalies including cardiac defects and limb reduction. Use contraindicated during pregnancy. |
| 2nd trimester | Continued risk of fetal harm. Associated with VACTERL association. Use contraindicated. |
| 3rd trimester | May cause delayed delivery, prolonged labor, and fetal harm. Use contraindicated. |
Clinical note
Comprehensive clinical and safety monograph for PREMPRO (PREMARIN;CYCRIN) (PREMPRO (PREMARIN;CYCRIN)).
| Placental transfer | Both conjugated estrogens (PREMARIN) and medroxyprogesterone acetate (CYCRIN) cross the placenta. Estrogens are detected in fetal tissues. Progestins achieve fetal serum levels approximately 50% of maternal levels. |
| Breastfeeding | Estrogens and progestins are excreted in human milk. Can reduce milk production and composition. Use only if clearly needed, with caution. |
■ FDA Black Box Warning
Estrogens plus progestin 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. The WHI Memory Study (WHIMS) reported increased risk of probable dementia in postmenopausal women aged 65 years and older.
| Serious Effects |
PregnancyUndiagnosed abnormal genital bleedingKnown or suspected breast cancerKnown or suspected estrogen-dependent neoplasiaActive or history of venous thromboembolismActive or history of arterial thromboembolism (e.g., stroke, MI)Known thrombophilic disorders (e.g., protein C, S, or antithrombin deficiency)Hypersensitivity to any componentLiver disease or impaired liver functionUse in men with prostate cancer (progestin component)
| Precautions | Cardiovascular disorders: Increased risk of stroke and DVT, Malignant neoplasms: Increased risk of endometrial cancer (unopposed estrogen) and breast cancer (estrogen plus progestin), Gallbladder disease: Increased risk, Hypercalcemia: May occur in patients with breast cancer and bone metastases, Visual abnormalities: Retinal vascular thrombosis; discontinue if sudden vision loss occurs, Hereditary angioedema: Exogenous estrogens may exacerbate symptoms, Pre-existing hypertriglyceridemia: May cause pancreatitis, Hepatic impairment: Use caution, Hypothyroidism: Estrogens may increase thyroid-binding globulin, requiring increased thyroid hormone dose, Fluid retention: Caution in cardiac or renal dysfunction, Hypocalcemia: Caution in hypoparathyroidism, Exacerbation of endometriosis: May induce malignant changes, Exacerbation of other conditions: Asthma, diabetes, migraine, porphyria, SLE, hepatic hemangiomas |
Loading safety data…
| Lactation Rating | L4 (Possibly Hazardous) |
| Teratogenic Risk | PREMARIN (conjugated estrogens) and CYCRIN (medroxyprogesterone acetate) are contraindicated in pregnancy. Estrogens are associated with an increased risk of vaginal adenosis, clear cell adenocarcinoma of the cervix/vagina in female offspring, and congenital anomalies in male/female reproductive organs when used during the first trimester. Exposure during the second and third trimesters may increase risk of urogenital abnormalities and potential neurobehavioral effects. Use in pregnancy is not indicated. |
| Fetal Monitoring | Monitor pregnancy status (negative pregnancy test before initiation). During use, if pregnancy occurs, perform fetal ultrasound to assess for anomalies. Monitor for signs of thromboembolism, hypertension, and glucose intolerance. No specific fetal monitoring required beyond standard prenatal care. |
| Fertility Effects | PREMPRO suppresses ovulation and endometrial proliferation, reducing fertility. Upon discontinuation, fertility may return but can be delayed. Long-term use may alter menstrual cycle regularity and endometrial receptivity. |
| Food/Dietary | Avoid grapefruit and grapefruit juice as they may increase estrogen levels. Maintain adequate calcium and vitamin D intake for osteoporosis benefit. No significant dietary restrictions; alcohol may increase risk of breast cancer and should be limited. |
| Clinical Pearls | Prempro contains conjugated estrogens (PREMARIN) and medroxyprogesterone acetate (CYCRIN). It is indicated for menopausal symptoms and osteoporosis prevention in women with an intact uterus. Use the lowest effective dose for the shortest duration. Avoid in women with a history of breast cancer, active DVT/PE, or coronary artery disease. Baseline mammogram and pelvic exam required. Monitor for abnormal vaginal bleeding; consider endometrial biopsy if bleeding persists. Risk of dementia increases in women >65 years when used for more than 4 years. |
| Patient Advice | Take exactly as prescribed; do not skip doses or stop without consulting your doctor. · Report any unusual vaginal bleeding, chest pain, shortness of breath, leg swelling, or vision changes immediately. · This medication does not prevent pregnancy and may increase risk of blood clots, stroke, and certain cancers. · Smoking increases the risk of cardiovascular side effects; avoid smoking. · Store at room temperature away from moisture and heat; protect from light. · Have regular check-ups including mammograms and pelvic exams as recommended. · Inform all healthcare providers that you are taking Prempro before any surgery or lab tests. |