of levonorgestrel is thought to be a result of its high affinity for SHBG, which limits its biological activity. The plasma protein binding of norelgestromin is approximately 99% and it is bound to albumin but not to SHBG. Conversely, levonorgestrel is approximately 98% bound to plasma proteins and is bound to both albumin and SHBG. Norgestimate is extensively metabolized into its active metabolites during first-pass metabolism in the liver and intestines. The major metabolite of norgestimate is norelgestromin and is formed from norgestimate via deacetylation in the liver and intestines. A more minor metabolite of norgestimate is levonorgestrel, which accounts for 20 to 25% (22 ± 6%) of an administered dose or about 40 to 70 µg norgestimate, and a very minor metabolite of norgestimate is levonorgestrel 17β-acetate. Both of these metabolites are active similarly to norgelstromin. With a typical oral contraceptive dosage of norgestimate of 200 to 250 µg/day, an amount of 50 to 60 µg/day levonorgestrel may be produced. This is similar to the ovulation-inhibiting dosage of levonorgestrel, and suggests that norgestimate may act in considerable part as a prodrug specifically of levonorgestrel. Following their formation, the active metabolites of norgestimate are inactivated via reduction, hydroxylation, and conjugation into levonorgestrel metabolites. The terminal half-life of norelgestromin is between 17 and 37 hours and of levonorgestrel is between 24 and 32 hours. The metabolites of norgestimate are eliminated 47% in urine and 37% in feces. Unchanged norgestimate is undetectable in urine. Chemistry Norgestimate, also known as 17α-ethynyl-18-methyl-19-nortestosterone 3-oxime 17β-acetate or as 17α-ethynyl-18-methylestr-4-en-17β-ol-3-one 3-oxime 17β-acetate, is a synthetic estrane steroid and a derivative of testosterone. It is a racemic mixture of E and Z isomers. Norgestimate is more specifically a derivative of norethisterone (17α-ethynyl-19-nortestosterone) and is a member of the gonane (18-methylestrane) subgroup of the 19-nortestosterone family of progestins. It is the C3 oxime and C17β acetate ester of levonorgestrel and is also known as levonorgestrel acetate oxime. A related compound is norethisterone acetate oxime (norethisterone-3-oxime 17β-acetate). History Norgestimate was introduced as a component of combined oral contraceptives in 1986. Based on its year of introduction, norgestimate is sometimes described as a "third-generation" progestin. Norgestimate was approved in combination with estradiol for use in menopausal hormone therapy in 1999 in the United States, and a generic version of this preparation became available in this country in 2005. Society and culture Generic names Norgestimate is the generic name of the drug