Drug Groups

approved; investigational

Description

A synthetic progestational hormone with actions similar to those of progesterone and about twice as potent as its racemic or (+-)-isomer (norgestrel). It is used for contraception, control of menstrual disorders, and treatment of endometriosis. It is usually supplied in a racemic mixture (Norgestrel, 6533-00-2). Only the levonorgestrel isomer is active.

Indication

For the treatment of menopausal and postmenopausal disorders and alone or in combination with other hormones as an oral contraceptive.

Pharmacology

Levonorgestrel is a progestin or a synthetic form of the naturally occurring female sex hormone, progesterone. In a woman's normal menstrual cycle, an egg matures and is released from the ovaries (ovulation). The ovary then produces progesterone, preventing the release of further eggs and priming the lining of the womb for a possible pregnancy. If pregnancy occurs, progesterone levels in the body remain high, maintaining the womb lining. If pregnancy does not occur, progesterone levels in the body fall, resulting in a menstrual period. Levonorgestrel tricks the body processes into thinking that ovulation has already occurred, by maintaining high levels of the synthetic progesterone. This prevents the release of eggs from the ovaries.

Toxicity

LD50 >5000 mg/kg (orally in rats)

Affected Organisms

Biotransformation

Hepatic

Absorption

Levonorgestrel is not subjected to a "first-pass" effect and is virtually 100% bioavailable.

Protein Binding

55%

Elimination

About 45% of levonorgestrel and its metabolites are excreted in the urine and about 32% are excreted in feces, mostly as glucuronide conjugates.

Distribution

* 260 L [Healthy Female Volunteers under Fasting Conditions]
* 1.8 L/kg

Clearance

* 7.7 +/- 2.7 L/h [Healthy Female Volunteers under Fasting Conditions]

References

External Links