In vitro and in vivo studies have shown that estrogens are metabolized partially by cytochrome P450 3A4 (CYP3A4). Therefore, inducers or inhibitors of CYP3A4 may affect estrogen drug metabolism. Inducers of CYP3A4 such as St. John’s wort (Hypericum perforatum) preparations, phenobarbital, carbamazepine and rifampin may decrease the plasma concentration of estrogens, possibly resulting in a decrease in therapeutic effects and/or changes in the uterine bleeding profile. Inhibitors of CYP3A4 such as erythromycin, clarithromycin, ketoconazole, itraconazole, ritonavir and grapefruit juice may increase the plasma concentration of estrogens and may result in side effects. Co-administration of atorvastatin and certain hormonal products containing ethinyl estradiol increase AUC values for ethinyl estradiol approximately 20 percent. Ascorbic acid and acetaminophen may increase the plasma ethinyl estradiol concentration, possibly by inhibition of conjugation.
Combination hormonal products containing some synthetic estrogens (for example, ethinyl estradiol) may inhibit the metabolism of other compounds. Combination hormonal products have been shown to significantly decrease the plasma concentration of lamotrigine likely due to induction of lamotrigine glucuronidation. This may reduce seizure control; therefore, dosage adjustments of lamotrigine may be necessary.
Norethindrone acetate and ethinyl estradiol should not be used during pregnancy [see CONTRAINDICATIONS (4)]. There appears to be little or no increased risk of birth defects in children born to women who have used estrogens and progestins as an oral contraceptive inadvertently during early pregnancy.
Norethindrone acetate and ethinyl estradiol should not be used during lactation. Estrogen administration to nursing women has been shown to decrease the quantity and quality of the breast milk. Detectable amounts of estrogen and progestin have been identified in the breast milk of women receiving estrogen plus progestin therapy. Caution should be exercised when norethindrone acetate and ethinyl estradiol is administered to a nursing woman.
There have not been sufficient numbers of geriatric women involved in clinical studies utilizing norethindrone acetate and ethinyl estradiol to determine whether those over 65 years of age differ from younger subjects in their response to norethindrone acetate and ethinyl estradiol.
The Women’s Health Initiative Studies
In the WHI estrogen plus progestin substudy (daily CE [0.625 mg] plus MPA [2.5 mg] versus placebo), there was a higher relative risk of nonfatal stroke and invasive breast cancer in women greater than 65 years of age [see CLINICAL STUDIES (14.5)].
In the WHI estrogen-alone substudy (daily CE [0.625 mg]-alone versus placebo), there was a higher relative risk of stroke in women greater than 65 years of age [see CLINICAL STUDIES (14.5)].
The Women’s Health Initiative Memory Study
In the WHIMS ancillary studies of postmenopausal women 65 to 79 years of age, there was an increased risk of developing probable dementia in women receiving estrogen plus progestin or estrogen-alone when compared to placebo [see WARNINGS AND PRECAUTIONS (5.3), and CLINICAL STUDIES (14.6)].
Since both ancillary studies were conducted in women 65 to 79 years of age, it is unknown whether these findings apply to younger postmenopausal women8 [see WARNINGS AND PRECAUTIONS (5.3), and CLINICAL STUDIES (14.6)].
Overdosage of estrogen plus progestin may cause nausea, vomiting, breast tenderness, abdominal pain, drowsiness and fatigue, and withdrawal bleeding may occur in women. Treatment of overdose consists of discontinuation of Fyavolv with institution of appropriate symptomatic care.
The following two strengths of Fyavolv tablets are available:
Fyavolv (0.5 mg/0.0025 mg): Each white to off-white, round film-coated tablet, debossed with “F51” on one side and “LU” on the other side contains 0.5 mg norethindrone acetate and 0.0025 mg ethinyl estradiol.
Fyavolv (1 mg/0.005 mg): Each blue, round film-coated tablet, debossed with “F52” on one side and “LU” on the other side contains 1 mg norethindrone acetate and 0.005 mg ethinyl estradiol.
Each tablet contains the following inactive ingredients: calcium stearate, corn starch, hypromellose, lactose monohydrate, microcrystalline cellulose, polyethylene glycol 400, titanium dioxide and vitamin E. Each tablet of 1 mg/0.005 mg also contains FD&C Blue No. 2 Aluminum Lake.
The structural formulas are as follows.
Molecular Weight: 296.40
Molecular Formula: C20 H24 O2
Molecular Weight: 340.46
Molecular Formula: C22 H28 O3
Endogenous estrogens are largely responsible for the development and maintenance of the female reproductive system and secondary sexual characteristics. Although circulating estrogens exist in a dynamic equilibrium of metabolic interconversions, estradiol is the principal intracellular human estrogen and is substantially more potent than its metabolites, estrone and estriol, at the receptor level.
The primary source of estrogen in normally cycling adult women is the ovarian follicle, which secretes 70 to 500 mcg of estradiol daily, depending on the phase of the menstrual cycle. After menopause, most endogenous estrogen is produced by conversion of androstenedione, which is secreted by the adrenal cortex, to estrone in the peripheral tissues. Thus, estrone and the sulfate conjugated form, estrone sulfate, are the most abundant circulating estrogens in postmenopausal women. The pharmacologic effects of ethinyl estradiol are similar to those of endogenous estrogens.
Estrogens act through binding to nuclear receptors in estrogen-responsive tissues. To date, two estrogen receptors have been identified. These vary in proportion from tissue to tissue.
Circulating estrogens modulate the pituitary secretion of the gonadotropins, luteinizing hormone (LH) and FSH through a negative feedback mechanism. Estrogens act to reduce the elevated levels of these hormones seen in postmenopausal women.
Progestin compounds enhance cellular differentiation and generally oppose the actions of estrogens by decreasing estrogen receptor levels, increasing local metabolism of estrogens to less active metabolites, or inducing gene products that blunt cellular responses to estrogen. Progestins exert their effects in target cells by binding to specific progesterone receptors that interact with progesterone response elements in target genes. Progesterone receptors have been identified in the female reproductive tract, breast, pituitary, hypothalamus, bone, skeletal tissue and central nervous system. Progestins produce similar endometrial changes to those of the naturally occurring hormone progesterone.
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