PREMARIN

Indications

• Menopausal symptoms
• Vulvar and vaginal atrophy
• Prevention of osteoporosis in postmenopausal women
• Hypoestrogenism due to hypogonadism or castration

Dosage

Children: Conjugated estrogens are not typically indicated for use in the pediatric population. Refer to specialized resources for any off-label use.

Adults: Refer to the BNF for specific dosing guidelines, as doses may vary based on the indication and patient-specific factors.

Mechanism of action

Conjugated estrogens exert their effects primarily through binding to estrogen receptors, leading to the activation of estrogen-responsive genes. This binding triggers a cascade of biological responses that promote the development and maintenance of female reproductive tissues, regulation of the menstrual cycle, and other systemic effects such as bone density maintenance and modulation of cholesterol levels.

Pharmacodynamics

The pharmacodynamics of conjugated estrogens involve their role in modulating gene expression within estrogen-responsive tissues. They help to alleviate symptoms associated with menopause, such as hot flashes and vaginal dryness, and play a critical role in bone health by inhibiting osteoclast activity, thus reducing bone resorption and helping to prevent osteoporosis.

Pharmacokinetics

Following oral administration, conjugated estrogens are absorbed through the gastrointestinal tract. They undergo first-pass metabolism in the liver, which can affect their bioavailability. The half-life of conjugated estrogens varies, but they generally have a half-life of several hours. They are metabolized primarily in the liver and excreted in urine. The pharmacokinetics can be influenced by factors such as age, liver function, and concurrent medications.

Contra-indications

• Known hypersensitivity to conjugated estrogens or any of the excipients
• Estrogen-dependent neoplasms, including breast cancer
• Undiagnosed abnormal genital bleeding
• Active or past venous thromboembolic disorders
• Severe liver dysfunction or disease
• Pregnancy

Adverse effects

• Nausea
• Headache
• Breast tenderness
• Abdominal cramps
• Bloating
• Mood changes
• Increased risk of thromboembolic events
• Hypertension
• Cholestatic jaundice
• Gallbladder disease

Interactions

• Anticoagulants may have altered effects
• Certain anticonvulsants may reduce efficacy of estrogen therapy
• Rifampicin and other enzyme inducers may decrease effectiveness
• St. John's Wort may decrease hormone levels

Precautions

• Monitor patients for signs of thromboembolic disorders
• Assess risk factors for cardiovascular disease
• Evaluate liver function before and during treatment
• Consider individual patient history of breast cancer or other estrogen-sensitive conditions

Pregnancy

Conjugated estrogens are contraindicated in pregnancy due to risk of fetal harm.

Breast-feeding

Conjugated estrogens may be excreted in breast milk; use with caution in breastfeeding women.

Storage

Store at room temperature, away from light and moisture. Keep out of reach of children.

Formulations

• Oral tablets
• Injectable forms

Indications

• Hormone replacement therapy in menopausal women
• Contraception in combination with progestins
• Management of estrogen receptor-positive breast cancer
• Treatment of hypogonadism in women

Mechanism of action

Oestrogens exert their effects by binding to oestrogen receptors (ERα and ERβ) located in various tissues, including reproductive organs, bones, and the cardiovascular system. Upon binding, the oestrogen-receptor complex translocates to the nucleus, where it regulates the transcription of target genes involved in cell growth, differentiation, and metabolism. This action influences various physiological processes such as menstrual cycle regulation, bone density maintenance, and lipid metabolism.

Pharmacodynamics

Oestrogens have multiple effects on different tissues. In the reproductive system, they promote the growth and maturation of the endometrium, regulate ovulation, and maintain pregnancy. In bone tissue, oestrogens inhibit osteoclast activity, reducing bone resorption and helping to maintain bone density. They also have a positive effect on lipid profiles by increasing high-density lipoprotein (HDL) and decreasing low-density lipoprotein (LDL) levels, thus providing cardiovascular protection.

Pharmacokinetics

Oestrogens are absorbed well after oral administration, with peak plasma concentrations occurring within a few hours. They undergo extensive first-pass metabolism in the liver, resulting in variable bioavailability. Oestrogens are primarily metabolized in the liver through conjugation, forming glucuronides and sulfates, which are then excreted in the urine. The elimination half-life varies depending on the specific oestrogen used, but typically ranges from a few hours to a day. Oestrogens can also be administered via transdermal patches, intramuscular injections, or vaginal routes to bypass first-pass metabolism.

Contra-indications

• Known or suspected pregnancy
• Active or past history of thromboembolic disorders
• Severe liver disorders
• Estrogen-dependent tumors
• Uncontrolled hypertension
• Undiagnosed vaginal bleeding
• History of stroke or myocardial infarction

Adverse effects

• Nausea
• Headache
• Breast tenderness
• Mood changes
• Weight gain
• Increased risk of thromboembolic events
• Hypertension
• Chloasma
• Gastrointestinal disturbances

Interactions

• Anticonvulsants (e.g., phenobarbital, phenytoin) which may decrease estrogen levels
• Antibiotics (e.g., rifampicin) that can reduce the efficacy of estrogen
• Corticosteroids which may have altered metabolism when used with estrogens
• Certain herbal supplements (e.g., St. John's Wort) that may affect estrogen activity

Precautions

• Monitor for signs of thromboembolic events
• Consider risk factors for cardiovascular disease
• Assess liver function before and during therapy
• Evaluate the risk of estrogen-dependent tumors
• Use with caution in patients with a history of depression

Pregnancy

Estrogens should not be used during pregnancy as they may cause harm to the fetus.

Breast-feeding

Estrogens can be excreted in breast milk; caution is advised when used during breastfeeding.

Storage

Store in a cool, dry place away from light, at room temperature.

Formulations

• Tablets
• Transdermal patches
• Injectable formulations
• Topical gels or creams