Melengestrol acetate

Not to be confused with Megestrol acetate.

Melengestrol acetate (MLGA), sold under the brand names Heifermax and MGA among others, is a progestin medication which is used in animal reproduction.^[1][2] It is not approved for use in humans, and is instead used as an implantable contraceptive for captive animals in zoos and other refuges,^[3] and is also used as a feed additive to promote growth in cattle, a purpose it is licensed for in the United States and Canada.^[4]

Melengestrol acetate

Clinical data
Trade names	Heifermax, MGA
Other names	MGA; MLA; MLGA; Melengesterol acetate; Methylsuperlutin; U-21240; BDH-1921; 17α-Acetoxy-16-methylene-6-methyl-6-dehydroprogesterone; 17α-Acetoxy-16-methylene-6-methylpregna-4,6-diene-3,20-dione
Drug class	Progestogen; Progestin; Progestogen ester
ATC code	None
Identifiers
IUPAC name [(8R,9S,10R,13S,14S,17R)-17-acetyl-6,10,13-trimethyl-16-methylidene-3-oxo-1,2,8,9,11,12,14,15-octahydrocyclopenta[a]phenanthren-17-yl] acetate
CAS Number	2919-66-6
PubChem CID	250948
DrugBank	DB14659
ChemSpider	219803
UNII	4W5HDS3936
KEGG	D04900
CompTox Dashboard (EPA)	DTXSID5048184
ECHA InfoCard	100.018.964
Chemical and physical data
Formula	C25H32O4
Molar mass	396.527 g·mol−1
3D model (JSmol)	Interactive image
SMILES O=C4\C=C3\C(=C/[C@@H]1[C@H](CC[C@@]2([C@](OC(=O)C)(C(=C)\C[C@@H]12)C(=O)C)C)[C@@]3(C)CC4)C
InChI InChI=1S/C25H32O4/c1-14-11-19-20(23(5)9-7-18(28)13-21(14)23)8-10-24(6)22(19)12-15(2)25(24,16(3)26)29-17(4)27/h11,13,19-20,22H,2,7-10,12H2,1,3-6H3/t19-,20+,22+,23-,24+,25+/m1/s1 Key:UDKABVSQKJNZBH-DWNQPYOZSA-N

Uses

Animal reproduction

MLGA is used in animal reproduction.^[3][4]

Pharmacology

Pharmacodynamics

MLGA is a progestogen, and hence is an agonist of the progesterone receptor.^[5] It has been found to possess 73% of the affinity of progesterone for the progesterone receptor in rhesus monkey uterus.^[5]

Chemistry

See also: List of progestogens, Progestogen ester, and List of progestogen esters

MLGA, also known as 17α-acetoxy-16-methylene-6-dehydro-6-methylprogesterone or as 17α-acetoxy-16-methylene-6-methylpregna-4,6-diene-3,20-dione, is a synthetic pregnane steroid and a derivative of progesterone.^[1][2] It is specifically a derivative of 17α-hydroxyprogesterone with a methyl group at the C6 position, a methylene group at the C16 position, a double bond between the C6 and C7 positions, and an acetate ester at the C17α position.^[1][2] As such, it is also a derivative of 16-methylene-17α-hydroxyprogesterone acetate. MLGA is the acetate ester of melengestrol, which in contrast, has never been marketed.^[1] Analogues of MLGA include other 17α-hydroxyprogesterone derivatives such as chlormadinone acetate, chlormethenmadinone acetate, cyproterone acetate, delmadinone acetate, hydroxyprogesterone caproate, medroxyprogesterone acetate, megestrol acetate, methenmadinone acetate, and osaterone acetate.^[1] The only structural difference between MLGA and megestrol acetate is the presence of the C16 methylene group in the former.^[1]

Society and culture

Legal status

In November 2024, the FDA approved melengestrol acetate Type A liquid medicated article (brand name MEL 500) for increased rate of weight gain, improved feed efficiency and suppression of estrus (heat) in heifers fed in confinement for slaughter; and for suppression of estrus (heat) in heifers intended for breeding.^[6][7]

Generic names

Melengestrol acetate is the generic name of the drug and its USANTooltip United States Adopted Name and USPTooltip United States Pharmacopeia.^[1][2] Melengestrol is the INNTooltip International Nonproprietary Name and BANTooltip British Approved Name of the unesterified free alcohol form.^[1][2]

Brand names

MLGA is marketed under the brand names Heifermax and MGA among others.^[1][2]