Other activities
Norgestimate and its active metabolites do not bind to other steroid hormone receptors besides the progesterone and androgen receptors and hence have no other off-target hormonal activity. This includes estrogenic, glucocorticoid, antimineralocorticoid, and neurosteroid activity. However, levonorgestrel has been found to inhibit 5α-reductase and hepatic cytochrome P450 enzymes in vitro to some extent. Pharmacokinetics
Norgestimate is rapidly and almost completely metabolized into its active metabolites, mainly norelgestromin (the primary active metabolite) and to a lesser extent levonorgestrel, upon oral ingestion. As a result, only very low concentrations (70 pg/mL) of norgestimate itself are detectable in the circulation, and only for about 6 hours after an oral dose. The oral bioavailability of norgestimate is unknown. This is due to the rapid and extensive metabolism of norgestimate, which makes determination of overall bioavailability difficult and necessitates methods other than area-under-the-curve (AUC) to do so. Peak levels of norelgestromin (3,500 pg/mL) are reached at approximately 2 hours following administration of norgestimate. Co-administration of norgestimate with a high-fat meal has been found to significantly decrease peak levels of norelgestromin, although the area-under-the-curve levels of norelgestromin are not significantly altered by food. Steady-state levels of norelgestromin and levonorgestrel are reached within 21 days of treatment with norgestimate. There is an approximate 2-fold accumulation in levels of norelgestromin and a non-linear approximate 8-fold accumulation in levels of levonorgestrel with continuous administration of norgestimate. The accumulation of levonorgestrel is thought to be a result of its high affinity for SHBG, which limits its biological activity.
Overdose
Interactions
Pharmacology
Pharmacodynamics
Norgestimate is a rapidly and completely converted prodrug, mainly of norelgestromin (17β-deacetylnorgestimate or levonorgestrel 3-oxime), but also of levonorgestrel (3-keto-17β-deacetylnorgestimate) to a lesser extent (22 ± 6% of an administered dose or about 40–70 µg) and of levonorgestrel acetate (levonorgestrel 17β-acetate) in very small amounts. Via its active metabolites, norgestimate has progestogenic activity, antigonadotropic effects, very weak androgenic activity, and no other important hormonal activity. Progestogenic activity
Norgestimate is a progestogen, or an agonist of the progesterone receptor. The relative binding affinities of norgestimate and its active metabolites for the progesterone receptor compared to promegestone (100%) are 15% for norgestimate, 10% for norelgestromin, 150% for levonorgestrel, and 135% for levonorgestrel acetate. Because of their low concentrations, norgestimate and levonorgestrel acetate are not thought to contribute significantly to the biological activity of norgestimate. In addition, although levonorgestrel binds to the progesterone receptor with much higher affinity than norelgestromin, levonorgestrel has high affinity for sex hormone-binding globulin (SHBG) (87% of that of testosterone), which may limit its activity, whereas norelgestromin does not bind to SHBG. The ovulation-inhibiting dosage of norgestimate is 200 µg/day. Androgenic activity
In addition to its progestogenic activity, norgestimate has weak androgenic activity. However, the medication shows less androgenic activity than related 19-nortestosterone progestins like levonorgestrel and norethisterone. Norgestimate and norelgestromin have negligible affinity for the androgen receptor (both 0% of the affinity of metribolone), while levonorgestrel has considerable affinity for the androgen receptor (45% of that of metribolone).