Estradiol/estradiol enanthate

{{Short description|Combination drug}}

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| image = Estradiol.svg

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| image2 = Estradiol enanthate.png

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| caption2 = Estradiol (top) and
estradiol enanthate (bottom)

| type = combo

| drug_name = Estradiol/estradiol enanthate

| component1 = Estradiol

| class1 = Estrogen

| component2 = Estradiol enanthate

| class2 = Estrogen

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| routes_of_administration = Intramuscular injection

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| synonyms = E2/E2-EN; E2/EEn

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Estradiol/estradiol enanthate (E2/E2-EN) is an injectable combination formulation of estradiol (E2), a short-acting estrogen, and estradiol enanthate (E2-EN), a long-acting estrogen, which was developed by Boehringer around 1960 for potential medical use but was never marketed.{{cite journal | vauthors = Kaiser R | title = Die Östrogenausscheidung im Zyklus und nach Injektion von Östradiolestern. Ein Beitrag zur Therapie mit Depotöstrogenen | trans-title = Estrogen excretion during the cycle and after injection of estradiol esters. A contribution to therapy with depot estrogens | language = de | journal = Geburtshilfe Frauenheilkd | volume = 21 | pages = 868–78 | date = September 1961 | issn = 0016-5751 | pmid = 13750804 }}{{cite book | last1 = Kaiser | first1 = R | chapter = Über die Oestrogenausscheidung nach Injektion von Oestradiolestern | trans-chapter = Estrogen excretion after injection of estradiol esters | pages = 227–232 | doi = 10.1007/978-3-642-86860-3_24 | title = Gewebs-und Neurohormone: Physiologie des Melanophorenhormons | year = 1962 | trans-title = Tissue and Neurohormones: Physiology of the Melanophore Hormone | language = de | publisher = Springer, Berlin, Heidelberg | isbn = 978-3-540-02909-0}} It contained 1 mg E2 and 9 mg E2-EN in oil solution and was intended for administration by intramuscular injection.

A single intramuscular injection of E2/E2-EN (1 mg/9 mg) has been found to result in a 10-fold increase in estradiol excretion on the 2nd day post-injection (due to the 1 mg short-acting E2 component). Following this, estradiol excretion remained above the menstrual-cycle average for 10 days post-injection and did not return to baseline until the 24th day post-injection (due to the 9 mg long-acting E2-EN component).

E2/E2-EN is similar to estradiol benzoate/estradiol phenylpropionate (brand name Dimenformon Prolongatum), another injectable combination medication of a shorter-acting estrogen (2.5 mg) and a longer-acting estrogen (10 mg). In contrast to E2/E2-EN however, estradiol benzoate/estradiol phenylpropionate was marketed for medical use.