Absorption, Distribution and Excretion
Femring's drug release rate is rapid in the first hour after administration, and then remains relatively constant over the remaining 3-month dosing interval. Estradiol acetate is rapidly hydrolyzed to estradiol and absorbed via the vaginal mucosa, as evidenced by the average time to reach maximum estradiol concentration (tmax) of approximately 1 hour (range 0.25 to 1.5 hours). After reaching maximum concentration (Cmax = 1129 pg/mL), serum estradiol concentrations rapidly decline and remain relatively stable over the 3-month dosing interval within 24 to 48 hours after administration. Estradiol, estrone, and estriol, as well as glucuronide and sulfate conjugates, are all excreted in the urine. The distribution of exogenous estrogens is similar to that of endogenous estrogens. Estrogens are widely distributed throughout the body, typically at higher concentrations in sex hormone target organs.

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Metabolism / Metabolites
The metabolic mechanism of exogenous estrogen is the same as that of endogenous estrogen. Estradiol is reversibly converted to estrone, and both can be converted to estriol, the latter being the main urinary metabolite. Estrogen can also undergo enterohepatic circulation via sulfate and glucuronic acid conjugation in the liver. The conjugates are secreted into the intestine via bile and are hydrolyzed and reabsorbed in the intestine. In postmenopausal women, a significant portion of circulating estrogen exists in the form of sulfate conjugates, especially estrone sulfate, which serves as a circulating reserve for the synthesis of more potent estrogens. Known human metabolites of estradiol acetate include 6-[(3-acetoxy-13-methyl-6,7,8,9,11,12,14,15,16,17-decahydrocyclopenta[a]phenanthrene-17-yl)oxy]-3,4,5-trihydroxyoxetane-2-carboxylic acid.

Protein Binding
Estrogen circulates in the blood and is primarily (>95%) bound to sex hormone-binding globulin (SHBG) and albumin.

[1]. Comparative controlled trial of a novel oral estrogen therapy, estradiol acetate, for relief of menopause symptoms. Menopause. 2005 Nov-Dec;12(6):708-15.

[2]. Efficacy of a new, oral estradiol acetate formulation for relief of menopause symptoms. Menopause. 2006 May-Jun;13(3):442-50.

Estradiol Acetate is a steroidal ester. Estradiol acetate is a prodrug ester of [DB00783], a naturally occurring hormone in the human body. Estradiol is the most potent form of estrogen steroids in all mammals and is the primary female sex hormone. As a prodrug of estradiol, estradiol acetate produces the same downstream effects as estradiol in vivo by binding to estrogen receptors (ER). Estrogen receptors include ERα and ERβ subtypes and are distributed in various tissues, such as the mammary glands, uterus, ovaries, skin, prostate, bone, fat, and brain. [DB00783] typically has an ester side chain because the oral bioavailability of endogenous estradiol itself is very low (2-10%). Estradiol molecules are rapidly degraded by first-pass metabolism in the intestines and liver before entering systemic circulation to exert their estrogenic effects. Esterol esterification aims to improve absorption and bioavailability after oral administration (e.g., estradiol valerate) by increasing lipophilicity, or by enhancing the release of intramuscularly administered sustained-release formulations (e.g., estradiol cyclopentadiene propionate). Upon absorption, the ester group is cleaved, releasing endogenous estradiol or 17β-estradiol. Therefore, estradiol ester prodrugs are considered biocompatible estrogens. Estradiol acetate, marketed under the brand name Femring, is a vaginal ring used to treat moderate to severe vasomotor symptoms and postmenopausal vulvovaginal atrophy. In adult women with normal menstrual cycles, the primary source of estrogen is the ovarian follicle, which secretes 70 to 500 micrograms of estradiol daily, depending on the stage of the menstrual cycle. However, postmenopausal women generate most endogenous estrogen through the conversion of androstenedione secreted by the adrenal cortex into estrone in peripheral tissues. Therefore, estrone and its sulfate conjugate—estrone sulfate—are the most abundant forms of circulating estrogen in postmenopausal women. Although circulating estrogens are in a state of dynamic equilibrium through metabolic transformation, estradiol is the dominant intracellular estrogen and is far more potent at receptor levels than its metabolites estrone and estriol. Due to the difference in potency between estradiol and estrone, menopause (and the shift of the dominant hormone from estradiol to estrone) is accompanied by a range of symptoms associated with decreased potency and diminished estrogen effects. These symptoms include hot flashes, vaginal dryness, mood swings, menstrual irregularities, cold intolerance, and sleep disturbances. Taking synthetic or biocompatible estrogens, such as estradiol acetate, has been shown to improve these menopausal symptoms. Estradiol acetate is the acetate form of estradiol, the most potent natural estrogen. Estradiol acetate diffuses across cell membranes and binds to nuclear estrogen receptors present in the reproductive tract, mammary glands, pituitary gland, hypothalamus, liver, and bones, thereby activating these receptors. The activated complex binds to estrogen-responsive elements on DNA, activating gene transcription involved in female reproductive system function and secondary sexual characteristic development. See also: Estradiol (with active moiety).

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Drug Indication
Femring is indicated for the treatment of menopausal vasomotor and genitourinary symptoms. Studies have shown that Femring (estradiol acetate) can improve symptoms caused by vaginal atrophy (such as dryness, burning, itching, and dyspareunia) and/or lower urinary tract atrophy (urinary urgency and difficulty urinating).
FDA label

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Mechanism of Action
Estradiol can freely enter target cells (e.g., female organs, breasts, hypothalamus, pituitary gland) and interact with target cell receptors. Once the estrogen receptor binds to its ligand, it enters the target cell nucleus, regulating gene transcription and producing messenger RNA (mRNA). The mRNA interacts with ribosomes to produce specific proteins that express the effects of estradiol on target cells. Estrogen can increase the synthesis of sex hormone-binding globulin (SHBG), thyroid-binding globulin (TBG), and other serum proteins in the liver, and inhibit the secretion of follicle-stimulating hormone (FSH) from the anterior pituitary gland. This enhanced downstream effect of estrogen receptor binding can reverse some menopausal symptoms, which are primarily caused by the loss of estrogen activity.

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Pharmacodynamics
Estrogen exerts its effects throughout the body by potently activating estrogen receptors (ER). Estrogen receptors are distributed in various tissues, including the breast, uterus, ovaries, skin, prostate, bone, fat, and brain. Estradiol can bind to two subtypes of the estrogen receptor: estrogen receptor α (ERα) and estrogen receptor β (ERβ). Estradiol is also a potent agonist of the G protein-coupled estrogen receptor (GPER), which has recently been identified as a major mediator of estradiol's rapid cellular effects.

C20H26O3

314.42

314.188

4245-41-4

9818306

Typically exists as solids at room temperature

1

2

23

476

5

CC(=O)OC1=CC2=C(C=C1)[C@H]3CC[C@]4([C@H]([C@@H]3CC2)CC[C@@H]4O)C

FHXBMXJMKMWVRG-SLHNCBLASA-N

InChI=1S/C20H26O3/c1-12(21)23-14-4-6-15-13(11-14)3-5-17-16(15)9-10-20(2)18(17)7-8-19(20)22/h4,6,11,16-19,22H,3,5,7-10H2,1-2H3/t16-,17-,18+,19+,20+/m1/s1

[(8R,9S,13S,14S,17S)-17-hydroxy-13-methyl-6,7,8,9,11,12,14,15,16,17-decahydrocyclopenta[a]phenanthren-3-yl] acetate

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)