Title: Elcometrine
CAS Registry Number: 7759-35-5
CAS Name: 17-(Acetyloxy)-16-methylene-19-norpregn-4-ene-3,20-dione
Additional Names: 16-methylene-17a-hydroxy-19-nor-4-pregnene-3,20-dione 17-acetate; 16-methylene-17a-acetoxy-19-norpregn-4-ene-3,20-dione
Manufacturers' Codes: ST-1435
Trademarks: Nestorone (Pop. Council)
Molecular Formula: C23H30O4
Molecular Weight: 370.48
Percent Composition: C 74.56%, H 8.16%, O 17.27%
Literature References: Synthetic, non-orally active progestin. Prepn: V. Schwarz et al., Tetrahedron Lett. 1967, 1925; eidem, Collect. Czech. Chem. Commun. 33, 4337 (1968). Pharmacology: N. Kumar et al., Steroids 65, 629 (2000). Clinical pharmacokinetics: G. Noé et al., Contraception 48, 548 (1993). Metabolism: O. Heikinheimo et al., ibid. 50, 275 (1994). Clinical trial of subdermal implant: S. Diaz et al., ibid. 51, 33 (1995). Clinical trial of vaginal rings delivery system: I. Sivin et al., ibid. 69, 137 (2004); idem et al., ibid. 71, 122 (2005).
Properties: Crystals from methanol, mp 178-179°. [a]D21 -105° (c = 1.2 in chloroform). uv max (methanol): 240 nm (log e 4.21).
Melting point: mp 178-179°
Optical Rotation: [a]D21 -105° (c = 1.2 in chloroform)
Absorption maximum: uv max (methanol): 240 nm (log e 4.21)
Therap-Cat: Progestogen; contraceptive (implantable).
Keywords: Progestogen; Contraceptive (Implantable).
Eledoisin Elenolide Eletriptan Eleutherobin Elgodipine

Systematic (IUPAC) name
(17α)-17-acetyl-16-methylene-3-oxoestr-4-en-17-yl acetate
Clinical data
Legal status Prescription only
Routes Subcutaneous implant, vaginal ring, transdermal patch[1]
Pharmacokinetic data
Bioavailability 10% (oral)[1]
Half-life 1-2 hours (oral)[1]
CAS number 7759-35-5
ATC code None
PubChem CID 108059
ChemSpider 97161
Chemical data
Formula C23H30O4 
Mol. mass 370.482 g/mol

Nestorone (or nesteron), also known as elcometrine and ST-1435,[2] is a 19-norprogesterone derivative and steroidal progestin which is used as a hormonal contraceptive in several South American countries.[1]

Nestorone is only weakly active orally, and is instead given as a subcutaneous implant.[3] It is more than 100-fold times as potent when delivered subcutaneously relative to orally.[1]

Nestorone acts primarily as a high-affinity agonist of the progesterone receptor. It lacks significant affinity for the androgen receptor, and accordingly, does not produce any androgenic or anabolic effects. It does not bind to the estrogen receptor either. Nestorone does however have some affinity for the glucocorticoid receptor, where it appears to act as an agonist, but it does not appear to produce any glucocorticoid side effects unless used at high doses.[1][4] It does not bind to the mineralocorticoid receptor.[5]

Nestorone does not bind to sex hormone-binding globulin, and is instead bound to serum albumin.[1]