Chemical formula: C₂₀H₂₄O₂ Molecular mass: 296.403 g/mol PubChem compound: 5991
The active ingredient, ethinylestradiol, is chemically and biologically identical to endogenous human oestradiol. It substitutes for the loss of estrogen production in menopausal women, and alleviates menopausal symptoms. Estrogens prevent bone loss following menopause or ovariectomy.
Estrogen deficiency at menopause is associated with an increasing bone turnover and decline in bone mass. The effect of estrogens on the bone mineral density is dose-dependent. Protection appears to be effective for as long as treatment is continued.
After discontinuation of HRT, bone mass is lost at a rate similar to that in untreated women.
Evidence from the WHI trial and meta-analysed trials shows that current use of HRT, alone or in combination with a progestagen – given to predominantly healthy women – reduces the risk of hip, vertebral, and other osteoporotic fractures. HRT may also prevent fractures in women with low bone density and/or established osteoporosis, but the evidence for that is limited.
The main therapeutic use of exogenous estrogens is replacement in deficiency states.
Ethinylestradiol is rapidly and completely absorbed from the gut but it undergoes some first pass metabolism in the gut wall.
Ethinylestradiol is rapidly distributed throughout most body tissues with the largest concentration found in adipose tissue. It distributes into breast milk in low concentrations. More than 80% of ethinylestradiol in serum is conjugated as the sulphate and almost all the conjugated form is bound to albumin.
Ethinylestradiol is metabolised in the liver. Hydroxylation appears to be the main metabolic pathway. 60% of a dose is excreted in the urine and 40% in the faeces. About 30% is excreted in the urine and bile as the glucuronide or sulphate conjugate.
The rate of metabolism of ethinylestradiol is affected by several factors, including enzyme-inducing agents, antibiotics and cigarette smoking.
After oral administration, an initial peak occurs in plasma at 2 to 3 hours, with a secondary peak at about 12 hours after dosing; the second peak is interpreted as evidence for extensive enterohepatic circulation of ethinylestradiol.
The elimination half-life of ethinylestradiol ranges from 5 to 16 hours.
None stated.
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