Pharmacokinetics of progesterone

Pharmacokinetics of Progesterone

Progesterone is a naturally occurring steroid hormone that plays a crucial role in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. The pharmacokinetics of progesterone, which refers to how the body absorbs, distributes, metabolizes, and excretes the hormone, is a complex process that is influenced by various factors.

Absorption

Progesterone can be administered orally, intramuscularly, or transdermally. The absorption of progesterone varies depending on the route of administration. Oral administration results in rapid absorption, with peak plasma concentrations achieved within 2 to 3 hours. However, oral progesterone undergoes extensive first-pass metabolism, which significantly reduces its bioavailability. Transdermal and intramuscular administration bypasses first-pass metabolism, resulting in higher bioavailability.

Distribution

Once absorbed, progesterone is distributed throughout the body. It is highly lipophilic and readily crosses cell membranes, including the blood-brain barrier and the placenta. Progesterone is bound to serum proteins, primarily sex hormone-binding globulin (SHBG) and corticosteroid-binding globulin (CBG), with a small fraction remaining unbound or "free."

Metabolism

Progesterone is primarily metabolized in the liver by the cytochrome P450 enzyme system. The major metabolic pathway involves conversion to pregnanediols and pregnanolones, which are subsequently conjugated with glucuronic acid and excreted in the urine.

Excretion

The metabolites of progesterone are excreted primarily in the urine. A small amount is also excreted in the bile and ultimately ends up in the feces. The elimination half-life of progesterone is approximately 5 minutes in the blood, but its metabolites have a much longer half-life of several hours.

Factors Influencing Pharmacokinetics

The pharmacokinetics of progesterone can be influenced by various factors, including age, body weight, liver function, and concomitant medications. Certain medications, such as rifampin and phenytoin, can induce the metabolism of progesterone and reduce its effectiveness.

See Also

• Pharmacodynamics of progesterone
• Pharmacology of progesterone
• Pharmacokinetics
• Pharmacodynamics

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