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NorethisteroneNoretisteron memiliki waktu paruh eliminasi 5,2 hingga 12,8 jam, dengan waktu paruh eliminasi rata-rata 8,0 jam.[1]<ref name="pmid12215716" /> Metabolisme norethisterone sangat mirip dengan testosteron (dan nandrolone) dan terutama melalui reduksi ikatan rangkap Δ4Δ<sup>4</sup> menjadi 5α- dan 5β-dihydronorethisterone, yang diikuti dengan reduksi gugus keto C3 menjadi empat isomer 3. ,5-tetrahidronorethisteron.[3]<ref name="pmid16112947" /> Transformasi ini dikatalisis oleh 5α- dan 5β-reduktase serta 3α- dan 3β-hidroksisteroid dehidrogenase baik di hati maupun di jaringan ekstrahepatik seperti kelenjar pituitari, rahim, kelenjar prostat, vagina, dan payudara.<ref name="pmid11162927">{{cite journal | vauthors = Schoonen WG, Deckers GH, de Gooijer ME, de Ries R, Kloosterboer HJ | title = Hormonal properties of norethisterone, 7alpha-methyl-norethisterone and their derivatives | journal = The Journal of Steroid Biochemistry and Molecular Biology | volume = 74 | issue = 4 | pages = 213–22 | date = November 2000 | pmid = 11162927 | doi = 10.1016/s0960-0760(00)00125-4 | quote = [95...] several mono- and disulphated as well as mono- and diglucuronidated metabolites of NET have been detected in urine from NET treated women [16,17]. In unconjugated form these NET (or MeNET) metabolites are represented by 5α- and 5β-reduced NET (5α-NET or 5β-NET) and by 3α- and 3β-hydrogenated 5α-NET and 5β-NET, leading to 3α,5α-NET, 3β,5α-NET, 3α,5β-NET and 3β,5β-NET or their corresponding MeNET metabolites (Figs. 1 and 2). These steroid conversions of NET or MeNET may take place in the liver, but also in the pituitary, endometrium, prostate, vagina and breast. The enzymes involved in these metabolic processes are 5α- and 5β-reductase as well as 3α- and 3β-hydroxysteroid dehydrogenase (HSD). | s2cid = 19797254}}</ref> Dengan pengecualian 3α,5α- dan 3β,5α-tetrahydronorethisterone, yang memiliki afinitas signifikan terhadap ER dan bersifat estrogenik sampai tingkat tertentu, metabolit 3,5-tetrahydro dari norethisterone tidak aktif dalam hal afinitas terhadap reseptor steroid seks (khususnya , PR, AR, dan ER).[96][97][98]<ref name="pmid3871879">{{cite journal | vauthors = Chávez BA, Vilchis F, Pérez AE, García GA, Grillasca I, Pérez-Palacios G | title = Stereospecificity of the intracellular binding of norethisterone and its A-ring reduced metabolites | journal = Journal of Steroid Biochemistry | volume = 22 | issue = 1 | pages = 121–6 | date = January 1985 | pmid = 3871879 | doi = 10.1016/0022-4731(85)90151-7| doi-access = free }}</ref><ref name="pmid3090814">{{cite journal | vauthors = Garza-Flores J, Vilchis F, García GA, Menjívar M, Pérez-Palacios G | title = A-ring reduction enhances the antigonadotropic potency of norethisterone | journal = Acta Endocrinologica | volume = 112 | issue = 2 | pages = 278–83 | date = June 1986 | pmid = 3090814 | doi = 10.1530/acta.0.1120278 }}</ref><ref name="pmid19008332">{{cite journal | vauthors = Lemus AE, Enríquez J, Hernández A, Santillán R, Pérez-Palacios G | title = Bioconversion of norethisterone, a progesterone receptor agonist into estrogen receptor agonists in osteoblastic cells | journal = The Journal of Endocrinology | volume = 200 | issue = 2 | pages = 199–206 | date = February 2009 | pmid = 19008332 | doi = 10.1677/JOE-08-0166 | doi-access = free }}</ref> Sejumlah kecil norethisterone juga diubah oleh aromatase menjadi EE.<ref name="pmid12215716" /><ref name="pmid16112947" /><ref name="pmid17341557" /> Norethisterone juga dimetabolisme di hati melalui hidroksilasi, terutama oleh CYP3A4.[4]<ref name="pmid18356043"/> Beberapa konjugasi (termasuk glukuronidasi dan sulfasi)<ref [95]name="pmid11162927" [99]/><ref name="ScarsiDarin2016">{{cite journal | vauthors = Scarsi KK, Darin KM, Chappell CA, Nitz SM, Lamorde M | title = Drug-Drug Interactions, Effectiveness, and Safety of Hormonal Contraceptives in Women Living with HIV | journal = Drug Safety | volume = 39 | issue = 11 | pages = 1053–1072 | date = November 2016 | pmid = 27562873 | pmc = 5048570 | doi = 10.1007/s40264-016-0452-7 }}</ref> norethisterone dan metabolitnya terjadi meskipun ada hambatan sterik oleh gugus etil di C17α. [3] Kelompok etinil norethisterone disimpan di sekitar 90% dari seluruh metabolitnya.[3]<ref name="pmid16112947" />
Norethisterone digunakan dalam pil KB, berlawanan dengan progesteron itu sendiri, karena tidak dimetabolisme secepat progesteron bila dikonsumsi secara oral. Ketika progesteron dikonsumsi secara oral, ia dengan cepat dimetabolisme di saluran pencernaan dan hati, dan dipecah menjadi banyak metabolit berbeda. Padahal, norethisterone tidak dimetabolisme dengan cepat sehingga memungkinkan norethisterone hadir dalam jumlah yang lebih tinggi sehingga memungkinkannya bersaing secara lebih efektif untuk tempat pengikatan reseptor progesteron.[3]<ref name="pmid16112947" />
====Eliminasi====
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