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.
In addition to their lack of affinity for the androgen receptor, norgestimate and norelgestromin have virtually no affinity for SHBG, and therefore do not displace testosterone from this carrier protein (although levonorgestrel does still bind with high affinity to SHBG and hence could increase free testosterone levels via occupation of SHBG). In accordance, clinical trials of norgestimate have observed minimal androgenic side effects in women treated with the medication. As an example, clinical studies have found that norgestimate does not appreciably inhibit the increase in SHBG levels produced by ethinylestradiol. This is of interest because estrogens increase and androgens decrease liver production of SHBG and by extension circulating levels of SHBG.The relative binding affinity of norgestimate and its metabolite norelgestromin for the rat prostatic androgen receptor (AR) are 0.3% and 1.3% of those of dihydrotestosterone (DHT), respectively, whereas the respective values for levonorgestrel and gestodene are 22% and 15%. Based on these findings, the ratios of AR to PR binding are 219 for norgestimate and 48 for norelgestromin, whereas the ratios for progesterone, levonorgestrel, and gestodene are 93, 11, and 28, respectively. As such, norgestimate and norelgestromin would appear to have much lower androgenic potency than other 19-nortestosterone progestins. However, levonorgestrel is an important metabolite of both norgestimate and norelgestromin, and it may serve to increase their androgenic potency to some degree.When norgestimate is combined with ethinylestradiol, which is potently antiandrogenic, there are only antiandrogenic effects overall and the combination is suitable for treatment of hyperandrogenism.