Relugolix + Estradiol + Norethindrone

Uses

Relugolix + Estradiol + Norethindrone is also used to associated treatment for these conditions: Atrophic Vaginitis, Breast Cancer, Breast engorgement caused by Postpartum state, Hypogonadism female, Kraurosis Vulvae, Metastatic Breast Cancer, Osteoporosis, Postmenopausal Osteoporosis, Premature Ovarian Failure (POF), Prostate Cancer, Urogenital atrophy, Vasomotor Symptoms Associated With Menopause, Vulvovaginal Atrophy, Advanced androgen dependent Prostate cancer, Female castration, Hypoestrogenism, Contraception, Hormone Replacement Therapy, PalliationAdvanced Prostate Cancer, Heavy Menstrual Bleeding

How Relugolix + Estradiol + Norethindrone works

Estrogen is found in the the breast, uterine, ovarian, skin, prostate, bone, fat, and brain tissues. The main source of estrogen in adult women during the reproductive period of life is the ovarian follicle, which secretes 70 to 500 mcg of estradiol each day. After menopause, however, the majority of endogenous estrogen is produced by transformation of androstenedione (which is secreted by the adrenal cortex) to estrone in the peripheral tissues. Both estrone and its sulphate conjugated form, estrone sulphate, represent the most abundant estrogens found in postmenopausal women.

Estradiol, however, is considerably more potent than estrone and estriol at the estrogen receptor (ER). As a result, the higher estrone concentration in postmenopausal population, can cause various undesirable effects. These effects may include hot flashes, chills, vaginal dryness, mood swings, irregular menstruation, and chills, in addition to sleep problems.

Estradiol workings by binding to subtypes of the estrogen receptor: estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ). It also exerts potent agonism of G Protein-coupled estrogen receptor (GPER), which is recognized an important regulator of this drug's rapid effects. Once the estrogen receptor has bound to its ligand, it enters the nucleus of the target cell, regulating gene transcription and formation of of messenger RNA. This mRNA makes contact with ribosomes producing specific proteins that express the effect of estradiol upon the target cell. Agonism of estrogen receptors increases pro-estrogenic effects, leading to the relief of vasomotor and urogenital symptoms of a postmenopausal or low estradiol state.

The pathogenesis and progression of prostate cancer appear driven, at least in part, by the effects of testosterone. Androgen deprivation has been demonstrated to result in cell death and tumor regression in many well-differentiated prostate cancer cell lines - for this reason, androgen deprivation therapy (ADT) has become a standard in the treatment of prostate cancer, particularly in advanced disease.

Testosterone production in males is carried out in the Leydig cells of testes and is stimulated by luteinizing hormone (LH), which itself is produced in the pituitary gland following the binding of gonadotropin-releasing hormone (GnRH) to corresponding GnRH receptors. Relugolix is a competitive antagonist of these GnRH receptors, thereby decreasing the release of LH and, ultimately, testosterone.

Dosage

Relugolix + Estradiol + Norethindrone dosage

Side Effects

Toxicity

The NOAEL (no-observed-adverse-effect-level) oral toxicity of estradiol after 90 day in rats was 0.003 mg/kg/day for blood, female reproductive, and male reproductive, endocrine, and liver toxicity. Oral TDLO of ethinyl estradiol is 21 mg/kg/21D intermittent, woman) with an oral LD50 of 960 mg/kg in the rat.

There is limited information in the literature regarding estrogen overdose. Estradiol overdose likely leads to the occurrence of estrogen-associated adverse effects, including nausea, vomiting, abdominal pain, breast tenderness, venous thrombosis, and vaginal bleeding. It is generally recommend to discontinue estradiol treatment and offer supportive care in the case of an overdose.

Data regarding overdose of relugolix are unavailable.

Precaution

Interaction

Volume of Distribution

Estrogens administered exogenously distribute in a similar fashion to endogenous estrogens. They can be found throughout the body, especially in the sex hormone target organs, such as the breast, ovaries and uterus.

Elimination Route

The absorption of several formulations of estradiol is described below:

Oral tablets and injections

First-pass metabolism in the gastrointestinal tract rapidly breaks down estradiol tablets before entering the systemic circulation. The bioavailability of oral estrogens is said to be 2-10% due to significant first-pass effects. The esterification of estradiol improves the administration (such as with estradiol valerate) or to sustain release from intramuscular depot injections (including estradiol cypionate) via higher lipophilicity. After absorption, the esters are cleaved, which leads to the release of endogenous estradiol, or 17β-estradiol.

Transdermal preparations

The transdermal preparations slowly release estradiol through intact skin, which sustains circulating levels of estradiol during a 1 week period of time. Notably, the bioavailability of estradiol after transdermal administration is about 20 times higher than after oral administration. Transdermal estradiol avoids first pass metabolism effects that reduce bioavailability. Administration via the buttock leads to a Cmax of about 174 pg/mL compared to 147 pg/mL via the abdomen.

Spray preparations

After daily administration, the spray formulations of estradiol reach steady state within 7-8 days. After 3 sprays daily, Cmax is about 54 pg/mL with a Tmax of 20 hours. AUC is about 471 pg•hr/mL.

Vaginal ring and cream preparations

Estradiol is efficiently absorbed through the mucous membranes of the vagina. The vaginal administration of estrogens evades first-pass metabolism. Tmax after vaginal ring delivery ranges from 0.5 to 1 hour. Cmax is about 63 pg/mL. The vaginal cream preparation has a Cmax of estradiol (a component of Premarin vaginal estrogen conjugate cream) was a Cmax of 12.8 ± 16.6 pg/mL, Tmax of 8.5 ± 6.2 hours, with an AUC of 231 ± 285 pg•hr/mL.

The C_max and AUC of orally-administered relugolix increase proportionally following single doses - in contrast, with repeat dosing the AUC remains proportional to the dose while the C_max increases greater than proportionally to the dose. Following the administration of 120mg once daily, the steady-state AUC and C_max of relugolix were 407 (± 168) ng.hr/mL and 70 (± 65) ng/mL, respectively.

The absolute oral bioavailability of relugolix is approximately 12% and the median T_max following oral administration is 2.25 hours.

Half Life

The terminal half-lives for various estrogen products post oral or intravenous administration has been reported to range from 1-12 hours. One pharmacokinetic study of oral estradiol valerate administration in postmenopausal women revealed a terminal elimination half-life of 16.9 ± 6.0 h. A pharmacokinetic study of intravenous estradiol administration in postmenopausal women showed an elimination half-life of 27.45 ± 5.65 minutes. The half-life of estradiol appears to vary by route of administration.

The average effective half-life of relugolix is 25 hours, while the average terminal elimination half-life is 60.8 hours.

Clearance

In one pharmacokinetic study, the clearance of orally administered micronized estradiol in postmenopausal women was 29.9±15.5 mL/min/kg. Another study revealed a clearance of intravenously administered estradiol was 1.3 mL/min/kg.

The average renal clearance of relugolix is 8 L/h with a total clearance of 26.4 L/h.

Elimination Route

Estradiol is excreted in the urine with both glucuronide and sulfate conjugates.

Approximately 81% of an orally administered dose was recovered in the feces, of which 4.2% was unchanged parent drug, while 4.1% of the dose was recovered in the urine, of which 2.2% remained unchanged.

Pregnancy & Breastfeeding use

Contraindication

Acute Overdose

Storage Condition

Innovators Monograph

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