Progesterone Receptor

Norethisterone, also known as 19-nortestosterone derivative, is primarily progestational rather than androgenic, with some oestrogenic and anti-oestrogenic activity. It lacks a C19 methyl group and has C17 ethinyl substitution. (Source: ) Progesterone receptor binding and transactivation activities are two times stronger in NET compared to Org 2058 (100%) and five to eight times weaker in NET. 3.2 and 1.1%, respectively, are the binding and transactivation activities of NET for the androgen receptor (5α-dihydrotestosterone 100%), none for the estrogen receptor (estradiol 100%), and below 1% for the glucocorticoid receptor (dexamethasone 100%).[2] Serum-stimulated or oestradiol (0.1 nM)-induced MCF-7 proliferation is inhibited by norethisterone (1 nM) by 41% and 34%, respectively.[/3] Significant effects on rat osteoblast proliferation, differentiation, and mineralization processes are induced by norethisterone (50 nM), which is mediated by the estrogen receptor and mimics the effects of estradiol.[4]

Norethisterone displays hormonal properties in vivo. MNorethisterone s.c.'smeanactive dose (MAD) in the progestagenic test (McPhail), androgenic test (Hershberger), estrogenic test (Allen–Doisy), and in a progestagenic and estrogenic test (ovulation inhibition test) is, respectively, 0.63 mg/kg, 2.5 mg/kg, 4 mg/kg, and 0.235 mg/kg.When taken orally, the MAD is 0.25 mg/kg, 20 mg/kg, 8 mg/kg, and 12 mg/kg. **[2]** Both bone resorption and formation are influenced by norethisterone. In SO and OVX mice, norethisterone (80 μg/day) reduced bone resorption while promoting estradiol-stimulated endosteal bone formation. (5) In castrated mice, norethisterone at the dose used in hormonal therapy for osteoporosis prevention has a minor protective effect against bone mineral loss. (6)

In assay kit medium, 96-well plates are seeded with roughly 1000 MCF-7 cells per well. The cells are then incubated for three days in a medium containing serum that has been treated with dextran and charcoal. After that, the wells are filled solely with norethisterone, and they are incubated for seven days. The cells are treated with a combination of 0.1 nM oestradiol and 0.1 nM norethisterone for seven days in order to simulate continuous combined HRT. An ATP-chemosensitivity test is used to quantify cell proliferation following a seven-day incubation period. To put it briefly, the bioluminescence reaction of luciferine in the presence of ATP and luciferase is measured to determine the amount of light emitted during proliferation.

Rats: Individual caged Sprague-Dawley female rats (200-210 g), with six of them acting as controls, are housed in a brightly lit animal room from 9:00 a.m. to 9:00 p.m. For two weeks, each of the seven rats given norethindrone acetate is fed 35 μg per day. There is an abundance of water and the high-carb rat chow available.

Absorption, Distribution and Excretion
The Cmax of norethisterone following oral administration of a single dose ranges from 5.39 to 7.36 ng/mL with a Tmax of 1-2 hours. AUC0-24 values following single oral doses range from approximately 30 to 37 ng*hr/mL. The oral bioavailability of norethisterone is approximately 64%. When applied transdermally, norethisterone is well-absorbed through the skin, reaches steady-state concentrations within 24 hours, and has a Cmax ranging from 617 to 1060 pg/mL at steady state. Norethisterone is often formulated as norethisterone acetate, which is completely and rapidly deacetylated to norethisterone following oral administration - the disposition of norethisterone acetate is indistinguishable from that of orally administered norethisterone.
Following administration of radio-labeled norethisterone, slightly more than 50% of the administered dose was eliminated in the urine and 20-40% was eliminated in the feces.
The volume of distribution of norethisterone is approximately 4 L/kg. Sulfated metabolites of norethisterone, as well as small quantities of parent drug, have been shown to distribute into breast milk.
The plasma clearance of norethisterone has been estimated as 0.4 L/hr/kg, and the intrinsic clearance is approximately 73-81 L/h.
Norethindrone is 36% bound to sex hormone-binding globulin (SHBG) and 61% bound to albumin. Volume of distribution of norethindrone is about 4 L/kg.
Plasma clearance value for norethindrone is approximately 0.4 L/hr/kg.
In 25 BALB/c mice implanted subcutaneously with pellets containing 40% norethisterone and 60% cholesterol for 76-77 wk, absorption of norethisterone was estimated to be between 3.6 and 15.9 ug/day (mean, 7.7 ug/day).
Rabbits excrete norethisterone metabolites predominantly in the urine ... while rats excrete them to 80% in bile ... .
For more Absorption, Distribution and Excretion (Complete) data for NORETHINDRONE (8 total), please visit the HSDB record page.

---

Metabolism / Metabolites
Norethisterone is extensively metabolized, primarily in the liver, to a number of metabolites via partial and total reduction of its A-ring. The enzymes predominantly involved are 3α- and 3β-hydroxysteroid dehydrogenase (HSD) as well as 5α- and 5β-reductase. The 5α-reduced metabolites, including 5α-dihydronorethisterone and its derivatives, appear to carry biological activity while the 5β-reduced metabolites appear inactive. Norethisterone and its metabolites are also extensively conjugated - most of the plasmatic metabolites are sulfate conjugates, while most of the urinary metabolites are glucuronide conjugates. The major metabolites in plasma are a disulfate conjugate of 3α,5α-tetrahydronorethisterone and a monosulfate conjugate of 3α,5β-tetrahydronorethisterone, while the major metabolite(s) in the urine are comprised of glucuronide and/or sulfate conjugates of 3α,5β-tetrahydronorethisterone. Norethisterone has also been observed to undergo some degree of metabolism via the cytochrome P450 enzyme system, predominantly by CYP3A4 and, to a much lesser extent, by CYP2C19, CYP1A2, and CYP2A6. The metabolites generated by these reactions have not been fully characterized.
Norethindrone undergoes extensive biotransformation, primarily via reduction, followed by sulfate and glucuronide conjugation. The majority of metabolites in the circulation are sulfates, with glucuronides accounting for most of the urinary metabolites.
Norethisterone undergoes extensive ring A reduction to form dihydro- and tetrahydronorethisterone metabolites that undergo conjugation; it can also be aromatized. Low serum levels of ethinylestradiol have been measured in postmenopausal women following oral administration of relatively large doses of norethisterone acetate or norethisterone. On the basis of the area-under-the-curve (AUC) values that were determined for ethinylestradiol and norethisterone, it was shown that the mean conversion ratio of norethisterone to ethinylestradiol was 0.7 and 1.0% at doses of 5 and 10 mg, respectively. The authors calculated that this corresponds to an oral dose equivalent of about 6 ug ethinylestradiol/ mg of norethisterone acetate. Similarly, it was shown that a dose of 5 mg norethisterone administered orally was equivalent to about 4 ug ethinylestradiol/mg norethisterone.
After incubation of norethisterone with dog liver microsomes the 4beta,5beta-epoxide of norethisterone and a 6-oxygenated norethisterone derivative were obtained as minor metabolites ... .
Rabbit liver homogenates ... catalyze the deethinylation of norethisterone, giving rise to the metabolite oestr-4-ene-3,17-dione.
For more Metabolism/Metabolites (Complete) data for NORETHINDRONE (7 total), please visit the HSDB record page.
Norethindrone has known human metabolites that include Norethindrone-O-glucuronide.
Hepatic. Norethindrone is extensively metabolized, primarily via reduction. It also undergoes sulfate and glucuronide conjugation. The majority of metabolites in the circulation are sulfates, with glucuronides accounting for most of the urinary metabolites.
Route of Elimination: Norethindrone is excreted in both urine and feces, primarily as metabolites.
Half Life: 8.51±2.19 (when a single dose is given to healthy women)

---

Biological Half-Life
The half-life of norethisterone has been variably estimated as 8-10 hours.
The mean terminal elimination half-life of norethindrone following a single dose administration of AYGESTIN is approximately 9 hours.
The plasma half-life, MCR and plasma metabolite levels at various time intervals have been studied in six women after an intravenous injection of 3H-norethindrone acetate. The disappearance curve due to norethindrone acetate showed an initial rapid disappearance of 3H with an average half-life of 7.5 minutes and a subsequent slow disapperance with a half-life of 51.5 hours. Norethindrone acetate was cleared from the plasma with an average MCR of 495 L/day. Norethindrone acetate is rapidly metabolised after an intravenous injection. Norethindrone, the main metabolite, disappears from the plasma with an average half-life of 34.8 hours. Norethindrone maintains a high level compared with norethindrone acetate at all time intervals up to 24 hours and an equilibrium is reached between the two at 24 to 48 hours.
The half-life (of the beta phase of a two-component model) of elimination ranged from 4.8 to 12.8 hr (mean, 7.6 hr) with no significant differences between oral and intravenous administration.

Toxicity Summary
Progestins diffuse freely into target cells and bind to the progesterone receptor. Target cells include the female reproductive tract, the mammary gland, the hypothalamus, and the pituitary. Once bound to the receptor, progestins slow the frequency of release of gonadotropin releasing hormone (GnRH) from the hypothalamus and blunt the pre-ovulatory LH surge.

---

Interactions
The concomitant use of antibiotics and oral contraceptives should be included in the assessment of contraceptive failure. A case of unwanted adolescent pregnancy in an 18-year-old female who had a severe staphylococcal skin infection and an underlying chronic granulomatous disease is presented and discussed. She had been receiving semisynthetic penicillin (500 mg. of oxacillin sodium every 6 hours) for 6 weeks and reported not having a menstrual period for 40 days. She was also on an oral contraceptive (1 mg. norethindrone/0.035 mg. estradiol). Results of a beta subunit human chorionic gonadotropin in serum test confirmed that she was pregnant. Careful review of her contraceptive package and antibiotic prescription suggests that indeed she had faithfully followed directions with both medicines. She and her boyfriend and the family received counseling; a therapeutic abortion was done. Advising a different contraceptive method or an additional contraceptive modality may be indicated in adolescents taking longterm antibiotic medication.
... In a randomized, 2-way crossover study, 20 healthy female subjects received Treatments A and B. Treatment A consisted of a single dose of OrthoNovum containing 1 mg norethisterone (norethindrone) and 35 microg ethinyl estradiol. Treatment B consisted of bosentan, 125 mg b.i.d. for 7 days plus concomitant norethisterone and ethinyl estradiol on Day 7. Plasma concentrations of norethisterone and ethinyl estradiol were measured on days of oral contraceptive administration. In the absence of bosentan, the pharmacokinetics of norethisterone and ethinyl estradiol were characterized by Cmax and AUC0-infinity values (95% CI) of 9.8 (8.1, 11.9) ng/mL and 72.9 (57.0, 93.1) ng x hr/mL, and 53.0 (47.0, 59.9) pg/mL and 758 (655, 878) pg x hr/mL, respectively. Concomitant bosentan did not affect the Cmax but significantly decreased the AUC of norethisterone and ethinyl estradiol by 13.7% (-23.5, -2.6) and 31.0% (-40.5,-20.2), respectively. The maximum decrease in AUC of norethisterone and ethinyl estradiol in an individual subject was 56% and 66%, respectively. Bosentan decreases the AUC of norethisterone and ethinyl estradiol in healthy female subjects. In patients treated with bosentan, reduced efficacy of hormonal contraceptives should be considered.
The effects of phenytoin treatment on plasma concentrations of norethisterone (NET) was studied in 7 healthy female rhesus monkeys. Before phenytoin treatment was started each monkey received an oral dose of 0.5 mg NET and 2 weeks later the same dose was given intravenously. On both occasions, plasma concentrations of NET were measured at frequent intervals during 24 hours. The monkeys were given phenytoin daily orally for more than 4 weeks. The absorption of phenytoin was confirmed by plasma determinations of phenytoin. While still on phenytoin treatment, the monkeys were again given 0.5 mg NET orally and 2 weeks later i.v. and blood sampling was repeated. During phenytoin treatment, plasma NET concentrations were always below those found before treatment. Both at iv and oral administration, the areas under the plasma concentration vs time curve (AUC) were reduced to 55% of the pretreatment AUCs. No difference in plasma half-life was found during phenytoin treatment. The results of this study may suggest that women on antiepileptic treatment with phenytoin should be given an oral contraceptive with a comparatively high dose of the steroids to provide contraceptive efficacy.
The pharmacokinetics of norethisterone have been studied in 8 women during and one month after treatment with rifampicin (450--600 mg/day). Rifampicin caused a significant reduction in the AUC of a single dose of 1 mg norethisterone from 37.8 +/- 13.1 to 21.9 +/- 5.9 ng/mL X hr (p less than 0.01). The plasma norethisterone half life (beta-phase) was also reduced from 6.2 +/- 1.7 to 3.2 +/- 1.0 hr (p less than 0.0025). In one additional woman on long term oral contraceptive therapy the 12 hour plasma norethisterone concentration was reduced by rifampicin from 12.3 ng/mL to 2.3 ng/mL. Rifampicin caused a significant increase in antipyrine clearance, 6 beta-hydroxycortisol excretion and plasma gamma-glutamyltranspeptidase activity but there was no significant correlations between changes in these indices of liver microsomal enzyme induction. There was a significant correlation between the percentage increase in antipyrine clearance and the percentage decrease in norethisterone AUC during rifampicin. The changes in norethisterone pharmacokinetics during rifampicin therapy are compatible with the known enzyme inducing effect of rifampicin.
For more Interactions (Complete) data for NORETHINDRONE (8 total), please visit the HSDB record page.

---

Non-Human Toxicity Values
LD50 Mouse oral 6 g/kg

[1]. Maturitas . 2003 Dec 10:46 Suppl 1:S7-S16.

[2]. J Steroid Biochem Mol Biol . 2000 Nov 15;74(4):213-22.

[3]. J Br Menopause Soc. 2003 Mar;9(1):36-8.

[4]. J Endocrinol . 2007 Jun;193(3):493-504.

[5]. J Bone Miner Res . 1993 Feb;8(2):219-30.

[6]. Prague Med Rep . 2006;107(4):401-8.

Therapeutic Uses
Contraceptives, Oral, Synthetic; Progestational Hormones, Synthetic
AYGESTIN is indicated for the treatment of secondary amenorrhea, endometriosis, and abnormal uterine bleeding due to hormonal imbalance in the absence of organic pathology, such as submucous fibroids or uterine cancer. AYGESTIN is not intended, recommended or approved to be used with concomitant estrogen therapy in postmenopausal women for endometrial protection. /Included in US product label/
Oral contraceptives are indicated for the prevention of pregnancy in women who elect to use this product as a method of contraception. /Included in US product label/
Progestin-only oral contraceptives are indicated for the prevention of pregnancy. /Included in US product label/
For more Therapeutic Uses (Complete) data for NORETHINDRONE (6 total), please visit the HSDB record page.

---

Drug Warnings
VET: MARKED RAT, MONKEY, & DOG FETAL MASCULINIZATION HAS BEEN OBSERVED AS IN HUMAN. EXCESSIVE DOSAGE DURING PREGNANCY MAY ALSO CAUSE FETAL DEATH, TERATOGENICITY, & DELAYED PARTURITION.
Cigarette smoking increases the risk of serious cardiovascular side effects from oral contraceptive use. This risk increases with age and with heavy smoking (15 or more cigarettes per day) and is quite marked in women over 35 years of age. Women who use oral contraceptives should be strongly advised not to smoke.
Norethindrone, like other progestins, may cause breakthrough bleeding, spotting, changes in menstrual flow, amenorrhea, changes in cervical erosion and secretions, edema, weight gain or loss, cholestatic jaundice, allergic rash with or without pruritus, melasma or chloasma, and mental depression.
When breakthrough bleeding or irregular vaginal bleeding occurs during norethindrone therapy, nonfunctional causes should be considered. Adequate diagnostic procedures should be performed in patients with undiagnosed vaginal bleeding.
For more Drug Warnings (Complete) data for NORETHINDRONE (44 total), please visit the HSDB record page.

---

Pharmacodynamics
Norethisterone is a synthetic oral progestin used for contraception or to treat other hormone-related conditions such as menopausal symptoms and endometriosis. As a synthetic progestin, norethisterone acts similarly to endogenous progesterone but with a much higher potency - it acts at the pelvic level to alter cervical and endometrial function, as well as via the inhibition of pituitary hormones that play a role in follicular maturation and ovulation. A small increase in the risk of developing breast cancer has been observed in patients using combined oral contraceptives, with some evidence also implicating progestin-only pills - patients starting hormonal contraception should be advised of this risk and should employ routine breast self-examinations to check for evidence of any developing masses.

C20H26O2

298.4192

298.193

C, 80.50; H, 8.78; O, 10.72

68-22-4

Norethindrone (Standard);68-22-4;Norethindrone-d6;2376036-05-2

6230

White to off-white solid powder

1.2±0.1 g/cm3

447.0±45.0 °C at 760 mmHg

205-206 °C(lit.)

190.5±21.3 °C

0.0±2.5 mmHg at 25°C

1.577

3.38

1

2

1

22

594

6

O([H])[C@@]1(C#C[H])C([H])([H])C([H])([H])[C@@]2([H])[C@]3([H])C([H])([H])C([H])([H])C4=C([H])C(C([H])([H])C([H])([H])[C@]4([H])[C@@]3([H])C([H])([H])C([H])([H])[C@@]21C([H])([H])[H])=O

VIKNJXKGJWUCNN-XGXHKTLJSA-N

InChI=1S/C20H26O2/c1-3-20(22)11-9-18-17-6-4-13-12-14(21)5-7-15(13)16(17)8-10-19(18,20)2/h1,12,15-18,22H,4-11H2,2H3/t15-,16+,17+,18-,19-,20-/m0/s1

(8R,9S,10R,13S,14S,17R)-17-ethynyl-17-hydroxy-13-methyl-1,2,6,7,8,9,10,11,12,14,15,16-dodecahydrocyclopenta[a]phenanthren-3-one

Utovlan; Norethindrone; 19-nor-17α-ethynyltestosterone; Norethisterone

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)

DMSO: 25~60 mg/mL (83.8~201.1 mM)
Ethanol: ~5 mg/mL (~16.8 mM)

Solubility in Formulation 1: 2.5 mg/mL (8.38 mM) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), suspension solution; with sonication.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

---

Solubility in Formulation 2: ≥ 2.5 mg/mL (8.38 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
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.

---

View More

Solubility in Formulation 3: ≥ 2.5 mg/mL (8.38 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

---

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