indication

For use as a female contraceptive (depot).

pharmacology

Etonogestrel is used as a female contraceptive. Etonogestrel 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. Etonogestrel 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.

mechanism of action

Etonogestrel binds to the progesterone and estrogen receptors. Target cells include the female reproductive tract, the mammary gland, the hypothalamus, and the pituitary. Once bound to the receptor, progestins like etonogestrel will slow the frequency of release of gonadotropin releasing hormone (GnRH) from the hypothalamus and blunt the pre-ovulatory LH (luteinizing hormone) surge.

toxicity

Symptoms of overdose include nausea, vomiting, vaginal bleeding, and other menstrual irregularities.

biotransformation

Hepatic.

half life

25 hours

route of elimination

Excretion of ENG and its metabolites, either as free steroid or as conjugates, is mainly in urine and to a lesser extent in feces.

drug interactions

Artemether: Artemether may decrease the effectiveness of etonogestrel by increasing its metabolism via CYP3A4. Consider an alternate non-hormonal means of contraception during artemether therapy.

Bexarotene: Bexarotene may decrease the serum concentration of Contraceptives (Progestins). Since bexarotene is teratogenic and can lower serum concentrations of etonogestrel, it is advised that women of childbearing potential use two forms of contraception (including at least one non-hormonal form).

Colesevelam: Bile Acid Sequestrants may decrease the serum concentration of Contraceptives (Progestins). Administer oral progestin-containing contraceptives at least 1-4 hours prior to or 4-6 hours after administration of a bile acid sequestrant. Consider alternatives in order to avoid this combination when possible, due to the risk for impaired contraceptive effectiveness.

Thiopental: Thiopental may decrease the effect of Etonogestrel. Contraceptive failure may occur. Alternative nonhomomonal contraception should be used during concomitant therapy.

Tretinoin: Oral Tretinoin may decrease the effect of oral contraceptive, Etonogestrel. An alternate form of contraception should be used during concomitant therapy.

Warfarin: Etonogestrel may alter the anticoagulant effect of warfarin. Concomitant therapy should be avoided. Monitor for changes in coagulation status if etonogestrel is initiated, discontinued or dose changed.