Mestranol

Mestranol, sold under the brand names Enovid, Norinyl, and Ortho-Novum among others, is an estrogen medication which has been used in birth control pills, menopausal hormone therapy, and the treatment of menstrual disorders.[1][7][8][9] It is formulated in combination with a progestin and is not available alone.[9] It is taken by mouth.[1]

Mestranol
Clinical data
Trade namesEnovid, Norinyl, Ortho-Novum, others
Other namesEthinylestradiol 3-methyl ether; EEME; EE3ME; CB-8027; L-33355; RS-1044; 17α-Ethynylestradiol 3-methyl ether; 17α-Ethynyl-3-methoxyestra-1,3,5(10)-trien-17β-ol; 3-Methoxy-19-norpregna-1,3,5(10)-trien-20-yn-17β-ol
AHFS/Drugs.comInternational Drug Names
MedlinePlusa601050
Routes of
administration		By mouth[1]
Drug classEstrogen; Estrogen ether
ATC code
  • None
Legal status
Legal status
  • In general: ℞ (Prescription only)
Pharmacokinetic data
MetabolitesEthinylestradiol
Elimination half-lifeMestranol: 50 min[2]
EE: 7–36 hours[3][4][5][6]
Identifiers
CAS Number
PubChem CID
IUPHAR/BPS
DrugBank
ChemSpider
UNII
KEGG
ChEBI
ChEMBL
CompTox Dashboard (EPA)
ECHA InfoCard100.000.707
Chemical and physical data
FormulaC21H26O2
Molar mass310.437 g·mol−1
3D model (JSmol)
  (verify)

Side effects of mestranol include nausea, breast tension, edema, and breakthrough bleeding among others.[10] It is an estrogen, or an agonist of the estrogen receptors, the biological target of estrogens like estradiol.[11] Mestranol is a prodrug of ethinylestradiol in the body.[11]

Mestranol was discovered in 1956 and was introduced for medical use in 1957.[12][13] It was the estrogen component in the first birth control pill.[12][13] In 1969, mestranol was replaced by ethinylestradiol in most birth control pills, although mestranol continues to be used in a few birth control pills even today.[14][9] Mestranol remains available only in a few countries, including the United States, United Kingdom, Japan, and Chile.[9]

Medical uses

Mestranol was employed as the estrogen component in many of the first oral contraceptives, such as mestranol/noretynodrel (brand name Enovid) and mestranol/norethisterone (brand names Ortho-Novum, Norinyl), and is still in use today.[7][8][9] In addition to its use as an oral contraceptive, mestranol has been used as a component of menopausal hormone therapy for the treatment of menopausal symptoms.[1]

Side effects
See also: Ethinylestradiol § Side effects, and Estrogen (medication) § Side effects

Pharmacology
Ethinylestradiol (EE), the active form of mestranol.

Mestranol is a biologically inactive prodrug of ethinylestradiol to which it is demethylated in the liver (via O-Dealkylation) with a conversion efficiency of 70% (50 μg of mestranol is pharmacokinetically bioequivalent to 35 μg of ethinylestradiol).[15][16][11] It has been found to possess 0.1 to 2.3% of the relative binding affinity of estradiol (100%) for the estrogen receptor, compared to 75 to 190% for ethinylestradiol.[17][18]

The elimination half-life of mestranol has been reported to be 50 minutes.[2] The elimination half-life of the active form of mestranol, ethinylestradiol, is 7 to 36 hours.[3][4][5][6]

The effective ovulation-inhibiting dosage of mestranol has been studied in women.[19][20][21] It has been reported to be about 98% effective at inhibiting ovulation at a dosage of 75 or 80 μg/day.[22][21][23] In another study, the ovulation rate was 15.4% at 50 μg/day, 5.7% at 80 μg/day, and 1.1% at 100 μg/day.[24]

Affinities and estrogenic potencies of estrogen esters and ethers at the estrogen receptors
Estrogen Other names RBA (%)a REP (%)b
ER ERα ERβ
Estradiol E2 100 100 100
Estradiol 3-sulfate E2S; E2-3S ? 0.02 0.04
Estradiol 3-glucuronide E2-3G ? 0.02 0.09
Estradiol 17β-glucuronide E2-17G ? 0.002 0.0002
Estradiol benzoate EB; Estradiol 3-benzoate 10 1.1 0.52
Estradiol 17β-acetate E2-17A 31–45 24 ?
Estradiol diacetate EDA; Estradiol 3,17β-diacetate ? 0.79 ?
Estradiol propionate EP; Estradiol 17β-propionate 19–26 2.6 ?
Estradiol valerate EV; Estradiol 17β-valerate 2–11 0.04–21 ?
Estradiol cypionate EC; Estradiol 17β-cypionate ?c 4.0 ?
Estradiol palmitate Estradiol 17β-palmitate 0 ? ?
Estradiol stearate Estradiol 17β-stearate 0 ? ?
Estrone E1; 17-Ketoestradiol 11 5.3–38 14
Estrone sulfate E1S; Estrone 3-sulfate 2 0.004 0.002
Estrone glucuronide E1G; Estrone 3-glucuronide ? <0.001 0.0006
Ethinylestradiol EE; 17α-Ethynylestradiol 100 17–150 129
Mestranol EE 3-methyl ether 1 1.3–8.2 0.16
Quinestrol EE 3-cyclopentyl ether ? 0.37 ?
Footnotes: a = Relative binding affinities (RBAs) were determined via in-vitro displacement of labeled estradiol from estrogen receptors (ERs) generally of rodent uterine cytosol. Estrogen esters are variably hydrolyzed into estrogens in these systems (shorter ester chain length -> greater rate of hydrolysis) and the ER RBAs of the esters decrease strongly when hydrolysis is prevented. b = Relative estrogenic potencies (REPs) were calculated from half-maximal effective concentrations (EC50) that were determined via in-vitro β‐galactosidase (β-gal) and green fluorescent protein (GFP) production assays in yeast expressing human ERα and human ERβ. Both mammalian cells and yeast have the capacity to hydrolyze estrogen esters. c = The affinities of estradiol cypionate for the ERs are similar to those of estradiol valerate and estradiol benzoate (figure). Sources: See template page.
Potencies of oral estrogens[data sources 1]
Compound Dosage for specific uses (mg usually)[lower-alpha 1]
ETD[lower-alpha 2] EPD[lower-alpha 2] MSD[lower-alpha 2] MSD[lower-alpha 3] OID[lower-alpha 3] TSD[lower-alpha 3]
Estradiol (non-micron.) 30≥120–3001206--
Estradiol (micronized) 6–1260–8014–421–2>5>8
Estradiol valerate 6–1260–8014–421–2->8
Estradiol benzoate -60–140----
Estriol ≥20120–150[lower-alpha 4]28–1261–6>5-
Estriol succinate -140–150[lower-alpha 4]28–1262–6--
Estrone sulfate 1260422--
Conjugated estrogens 5–1260–808.4–250.625–1.25>3.757.5
Ethinylestradiol 200 μg1–2280 μg20–40 μg100 μg100 μg
Mestranol 300 μg1.5–3.0300–600 μg25–30 μg>80 μg-
Quinestrol 300 μg2–4500 μg25–50 μg--
Methylestradiol -2----
Diethylstilbestrol 2.520–30110.5–2.0>53
DES dipropionate -15–30----
Dienestrol 530–40420.5–4.0--
Dienestrol diacetate 3–530–60----
Hexestrol -70–110----
Chlorotrianisene ->100-->48-
Methallenestril -400----
Sources and footnotes:
  1. [25][26][27][28][29][30] [31][32][33][34] [35][36][37][38][39][40][21][23][41]
  1. Dosages are given in milligrams unless otherwise noted.
  2. Dosed every 2 to 3 weeks
  3. Dosed daily
  4. In divided doses, 3x/day; irregular and atypical proliferation.

Chemistry
See also: List of estrogens and List of estrogen esters § Ethers of steroidal estrogens

Mestranol, also known as ethinylestradiol 3-methyl ether (EEME) or as 17α-ethynyl-3-methoxyestra-1,3,5(10)-trien-17β-ol, is a synthetic estrane steroid and a derivative of estradiol.[42][43][44] It is specifically a derivative of ethinylestradiol (17α-ethynylestradiol) with a methyl ether at the C3 position.[42][43]

History

In April 1956, noretynodrel was investigated, in Puerto Rico, in the first large-scale clinical trial of a progestogen as an oral contraceptive.[12][13] The trial was conducted in Puerto Rico due to the high birth rate in the country and concerns of moral censure in the United States.[45] It was discovered early into the study that the initial chemical syntheses of noretynodrel had been contaminated with small amounts (1–2%) of the 3-methyl ether of ethinylestradiol (noretynodrel having been synthesized from ethinylestradiol).[12][13] When this impurity was removed, higher rates of breakthrough bleeding occurred.[12][13] As a result, mestranol, that same year (1956),[46] was developed and serendipitously identified as a very potent synthetic estrogen (and eventually as a prodrug of ethinylestradiol), given its name, and added back to the formulation.[12][13] This resulted in Enovid by G. D. Searle & Company, the first oral contraceptive and a combination of 9.85 mg noretynodrel and 150 μg mestranol per pill.[12][13]

Around 1969, mestranol was replaced by ethinylestradiol in most combined oral contraceptives due to widespread panic about the recently uncovered increased risk of venous thromboembolism with estrogen-containing oral contraceptives.[14] The rationale was that ethinylestradiol was approximately twice as potent by weight as mestranol and hence that the dose could be halved, which it was thought might result in a lower incidence of venous thromboembolism.[14] Whether this actually did result in a lower incidence of venous thromboembolism has never been assessed.[14]

Society and culture

Generic names

Mestranol is the generic name of the drug and its INN, USAN, USP, BAN, DCF, and JAN, while mestranolo is its DCIT.[42][43][1][9]

Brand names

Mestranol has been marketed under a variety of brand names, mostly or exclusively in combination with progestins, including Devocin, Enavid, Enovid, Femigen, Mestranol, Norbiogest, Ortho-Novin, Ortho-Novum, Ovastol, and Tranel among others.[7][42][47][43] Today, it continues to be sold in combination with progestins under brand names including Lutedion, Necon, Norinyl, Ortho-Novum, and Sophia.[9]

Availability

Mestranol remains available only in the United States, the United Kingdom, Japan, and Chile.[9] It is only marketed in combination with progestins, such as norethisterone.[9]

Research

Mestranol has been studied as a male contraceptive and was found to be highly effective.[48][49][50][51] At a dosage of 0.45 mg/day, it suppressed gonadotropin levels, reduced sperm count to zero within 4 to 6 weeks, and decreased libido, erectile function, and testicular size.[48][49][51][50] Gynecomastia occurred in all of the men.[48][49][51][50] These findings contributed to the conclusion that estrogens would be unacceptable as contraceptives for men.[49]

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