View source for Equilin

{{Short description|Chemical compound}}
{{Distinguish|Equilenin}}
{{Drugbox
| Verifiedfields = verified
| Watchedfields = verified
| verifiedrevid = 461094587
| IUPAC_name = (9''S'',13''S'',14''S'')-3-hydroxy-13-methyl-9,11,12,14,15,16-hexahydro-6''H''-cyclopenta[''a'']phenanthren-17-one
| image = Equilin.svg
| width = 225px

<!--Clinical data-->
| tradename =
| pregnancy_AU = <!-- A / B1 / B2 / B3 / C / D / X -->
| pregnancy_US = <!-- A / B / C / D / X -->
| pregnancy_category =
| legal_AU = <!-- Unscheduled / S2 / S3 / S4 / S5 / S6 / S7 / S8 / S9 -->
| legal_CA =
| legal_UK =
| legal_US =
| legal_status =
| routes_of_administration = [[Oral administration|By mouth]]
| class = [[Estrogen (medication)|Estrogen]]

<!--Pharmacokinetic data-->
| bioavailability =
| protein_bound =
| metabolism =
| elimination_half-life =
| excretion =

<!--Identifiers-->
| CAS_number_Ref = {{cascite|correct|CAS}}
| CAS_number = 474-86-2
| CAS_supplemental =
| ATC_prefix =
| ATC_suffix =
| ATC_supplemental =
| PubChem = 223368
| IUPHAR_ligand =
| DrugBank_Ref = {{drugbankcite|correct|drugbank}}
| DrugBank = DB02187
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 193995
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 08O86EX0J4
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = D04041
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 42309
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 323533
| synonyms = Δ<sup>7</sup>-Estrone; 7-Dehydroestrone; Estra-1,3,5(10),7-tetraen-3-ol-17-one

<!--Chemical data-->
| C=18 | H=20 | O=2
| SMILES = O=C3CC[C@H]4C/2=C/Cc1c(ccc(O)c1)[C@H]\2CC[C@]34C
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C18H20O2/c1-18-9-8-14-13-5-3-12(19)10-11(13)2-4-15(14)16(18)6-7-17(18)20/h3-5,10,14,16,19H,2,6-9H2,1H3/t14-,16+,18+/m1/s1
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = WKRLQDKEXYKHJB-HFTRVMKXSA-N
}}

'''Equilin''' is a [[natural product|naturally occurring]] [[estrogen (medication)|estrogen]] [[sex hormone]] found in [[horse]]s as well as a [[medication]].<ref name="Elks2014">{{cite book|author=J. Elks|title=The Dictionary of Drugs: Chemical Data: Chemical Data, Structures and Bibliographies|url=https://books.google.com/books?id=0vXTBwAAQBAJ&pg=PA298|date=14 November 2014|publisher=Springer|isbn=978-1-4757-2085-3|page=495}}</ref><ref name="pmid16112947">{{cite journal | vauthors = Kuhl H | title = Pharmacology of estrogens and progestogens: influence of different routes of administration | journal = Climacteric | volume = 8 | pages = 3–63 | year = 2005 | issue = Suppl 1 | pmid = 16112947 | doi = 10.1080/13697130500148875 | s2cid = 24616324 | url = http://hormonebalance.org/images/documents/Kuhl%2005%20%20Pharm%20Estro%20Progest%20Climacteric_1313155660.pdf}}</ref><ref name="pmid24176763">{{cite journal | vauthors = Bhavnani BR, Stanczyk FZ | title = Pharmacology of conjugated equine estrogens: efficacy, safety and mechanism of action | journal = J. Steroid Biochem. Mol. Biol. | volume = 142 | pages = 16–29 | date = July 2014 | pmid = 24176763 | doi = 10.1016/j.jsbmb.2013.10.011 | s2cid = 1360563 }}</ref> It is one of the estrogens present in the estrogen [[combination drug]] preparations known as [[conjugated estrogens]] (CEEs; e.g. '''Premarin''') and [[esterified estrogens]] (EEs; e.g. '''Estratab''', '''Menest''').<ref name="pmid16112947" /><ref name="pmid24176763" /> CEEs is the most commonly used form of estrogen medications in [[hormone replacement therapy]] (HRT) for [[menopausal symptoms]] in the [[United States]].<ref name="pmid24176763" /> [[Estrone sulfate (medication)|Estrone sulfate]] is the major estrogen in CEEs (about 50%) while equilin sulfate is the second major estrogen in the formulation, present as about 25% of the total.<ref name="pmid16112947" /><ref name="pmid24176763" />

==Pharmacology==

===Pharmacodynamics===
Equilin is an estrogen, or an [[agonist]] of the [[estrogen receptor]]s (ERs), the [[ERα]] and [[ERβ]].<ref name="pmid16112947" /> In terms of [[relative binding affinity]] for the ERs, equilin has about 13% and 49% of that of estradiol for the ERα and ERβ, respectively.<ref name="pmid16112947" /> Analogously to the reversible transformation of [[estrone (medication)|estrone]] into [[estradiol (medication)|estradiol]] by [[17β-hydroxysteroid dehydrogenase]], equilin can be converted into the more potent estrogen [[17β-dihydroequilin]] in the body.<ref name="pmid16112947" /><ref name="pmid24176763" /> This estrogen has about 113% and 108% of the relative binding affinities of estradiol for the ERα and ERβ, respectively.<ref name="pmid16112947" /><ref name="pmid24176763" /> Equilin is present in CEEs in the form of equilin sulfate, which itself is inactive and acts as a [[prodrug]] of equilin via [[steroid sulfatase]].<ref name="pmid16112947" /><ref name="pmid24176763" />

Similarly to [[synthetic compound|synthetic]] estrogens like [[ethinylestradiol]], equilin and CEEs have disproportionate effects in certain [[tissue (biology)|tissue]]s such as the [[liver]] and [[uterus]] relative to [[bioidentical]] human estrogens like estradiol and estrone.<ref name="pmid16112947" /> Because of their disproportionate potency in the liver, equilin and CEEs have relatively increased effects on [[liver protein synthesis]] compared to estradiol.<ref name="pmid16112947" />

A dosage of 0.25&nbsp;mg/day equilin sulfate is equivalent to 0.625&nbsp;mg/day CEEs in terms of relief from [[hot flash]]es.<ref name="pmid16112947" /> At a dosage of 0.625&nbsp;mg/day equilin sulfate, the increases in circulating levels of [[sex hormone-binding globulin]] (SHBG), [[corticosteroid-binding globulin]], and [[angiotensinogen]] were 1.5 to 8&nbsp;times those observed with [[estrone sulfate (medication)|estrone sulfate]].<ref name="pmid16112947" /> Equilin has about 42% of the relative potency of CEEs in the [[vagina]] and 80% of the relative potency of CEEs in the [[uterus]], while its more active form, 17β-dihydroequilin, has about 83% of the relative potency of CEEs in the vagina and 200% of the relative potency of CEEs in the uterus.<ref name="pmid16112947" />

{{Relative oral potencies of estrogens}}

===Pharmacokinetics===
Equilin has about 8% of the [[relative binding affinity]] of [[testosterone]] for SHBG, relative to 12% in the case of [[estrone (medication)|estrone]].<ref name="pmid16112947" /> In terms of [[plasma protein binding]], it is bound 26% to SHBG and 13% to [[human serum albumin|albumin]].<ref name="pmid16112947" /> The [[metabolic clearance rate]]s of equilin and equilin sulfate are 2,640&nbsp;L/day/m<sup>2</sup> and 175&nbsp;L/day/m<sup>2</sup>, respectively.<ref name="pmid16112947" /> In accordance, the [[biological half-life]] of equilin sulfate is substantially longer than that of equilin.<ref name="pmid16112947" /> Equilin is converted into [[17β-dihydroequilin]] in the [[liver]] and in other [[tissue (biology)|tissue]]s.<ref name="pmid16112947" /><ref name="pmid24176763" /> Equilin and 17β-dihydroequilin can also be transformed into [[equilenin]] and [[17β-dihydroequilenin]].<ref name="pmid16112947" /><ref name="pmid24176763" /> Equilin is [[excretion|excreted]] in the form of [[glucuronide]] conjugates.<ref name="pmid16112947" />

==Chemistry==
{{See also|List of estrogens#Equine estrogens}}

Equilin, also known as δ<sup>7</sup>-estrone or as 7-dehydroestrone, as well as estra-1,3,5(10),7-tetraen-3-ol-17-one, is a [[natural product|naturally occurring]] [[estrane]] [[steroid]] and an [[structural analog|analogue]] of [[estrone (medication)|estrone]].<ref name="pmid16112947" /><ref name="pmid24176763" /> In terms of [[chemical structure]] and [[pharmacology]], equilin is to [[17β-dihydroequilin]] (δ<sup>7</sup>-17β-estradiol) as estrone is to [[estradiol (medication)|estradiol]].<ref name="pmid16112947" /><ref name="pmid24176763" />

==References==
{{Reflist}}

{{Estrogens and antiestrogens}}
{{Estrogen receptor modulators}}

[[Category:Sterols]]
[[Category:Hydroxyarenes]]
[[Category:Estranes]]
[[Category:Estrogens]]
[[Category:Human drug metabolites]]
[[Category:Ketones]]
[[Category:Prodrugs]]