Pharmacokinetics of Estrogens
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Estrogens are well absorbed orally and transdermally, but natural estrogens are inactive by the oral route due to rapid metabolism in liver. Estradiol esters injected i.m. are slowly absorbed and exert prolonged action.
PHARMACOKINETICS
Estrogens are well
absorbed orally and transdermally, but natural estrogens are inactive by the
oral route due to rapid metabolism in liver. Estradiol esters injected i.m. are
slowly absorbed and exert prolonged action. Natural estrogens in circulation
are largely plasma protein bound—to SHBG as well as to albumin.
Estradiol is converted
to estrone and vice versa in liver.
Estriol is derived from estrone. All three are conjugated with glucuronic acid
and sulfate— excreted in urine and bile. Considerable enterohepatic circulation
occurs due to deconjugation in intestines and reabsorption—ultimate disposal
occurs mostly in urine.
Ethinylestradiol is
metabolized very slowly (t½ 12–24 hours)—orally active and more potent.
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