Source: FDA, National Drug Code (US) Revision Year: 2020
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, secreted by the adrenal cortex, to estrone by peripheral tissues. Thus, estrone and the sulfate conjugated form, estrone sulfate, are the most abundant circulating estrogens in postmenopausal women.
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 follicle stimulating hormone (FSH), through a negative feedback mechanism. Estrogens act to reduce the elevated levels of these hormones seen in postmenopausal women.
Estrogen drug products are absorbed through the skin, mucous membranes, and the gastrointestinal tract after release from the drug formulation.
The distribution of exogenous estrogens is similar to that of endogenous estrogens. Estrogens are widely distributed in the body and are generally found in higher concentrations in the sex hormone target organs. Estrogens circulate in the blood largely bound to sex hormone binding globulin (SHBG) and albumin.
Exogenous estrogens are metabolized in the same manner as endogenous estrogens. Circulating estrogens exist in a dynamic equilibrium of metabolic interconversions. These transformations take place mainly in the liver. Estradiol is converted reversibly to estrone, and both can be converted to estriol, which is the major urinary metabolite. Estrogens also undergo enterohepatic recirculation via sulfate and glucuronide conjugation in the liver, biliary secretion of conjugates into the intestine, and hydrolysis in the gut followed by reabsorption. In postmenopausal women, a significant proportion of the circulating estrogens exist as sulfate conjugates, especially estrone sulfate, which serves as a circulating reservoir for the formation of more active estrogens.
Estradiol, estrone, and estriol are excreted in the urine along with glucuronide and sulfate conjugates.
No pharmacokinetic studies were conducted in special populations, including patients with renal or hepatic impairment.
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 preparations (Hypericum perforatum), phenobarbital, carbamazepine, and rifampin may reduce plasma concentrations 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 plasma concentrations of estrogens and may result in side effects.
Long-term continuous administration of estrogen, with and without progestin, in women with and without a uterus, has shown an increased risk of endometrial cancer, breast cancer, and ovarian cancer. (See BOXED WARNINGS, WARNINGS and PRECAUTIONS.)
Long term continuous administration of natural and synthetic estrogens in certain animal species increases the frequency of carcinomas of the breast, uterus, cervix, vagina, testis, and liver.
The WHI enrolled approximately 27,000 predominantly healthy postmenopausal women in two substudies to assess the risks and benefits of daily oral CE (0.625 mg)-alone or in combination with MPA (2.5 mg) compared to placebo in the prevention of certain chronic diseases. The primary endpoint was the incidence of coronary heart disease (CHD) (defined as nonfatal MI, silent MI and CHD death), with invasive breast cancer as the primary adverse outcome. A “global index” included the earliest occurrence of CHD, invasive breast cancer, stroke, PE, endometrial cancer (only in the CE plus MPA substudy), colorectal cancer, hip fracture, or death due to other cause. These substudies did not evaluate the effects of CE or CE plus MPA on menopausal symptoms.
The WHI estrogen-alone substudy was stopped early because an increased risk of stroke was observed, and it was deemed that no further information would be obtained regarding the risks and benefits of estrogen-alone in predetermined primary endpoints.
Results of the estrogen-alone substudy, which included 10,739 women (average 63 years of age, range 50 to 79; 75.3 percent White, 15.1 percent Black, 6.1 percent Hispanic, 3.6 percent Other), after an average follow-up of 7.1 years are presented in Table 1.
Table 1. Relative and Absolute Risk Seen in the Estrogen-Alone Substudy of WHIa:
| Event | Relative Risk CE vs. Placebo (95% nCIb) | CE n=5,310 | Placebo n=5,429 |
|---|---|---|---|
| Absolute Risk per 10,000 Women-Years | |||
| CHD eventsc | 0.95 (0.78-1.16) | 54 | 57 |
| Non-fatal MIc | 0.91 (0.73-1.14) | 40 | 43 |
| CHD deathc | 1.01 (0.71-1.43) | 16 | 16 |
| All Strokec | 1.33 (1.15-1.68) | 45 | 33 |
| Ischemic strokec | 1.55 (1.19-2.01) | 38 | 25 |
| Deep vein thrombosisc,d | 1.47 (1.06-2.06) | 23 | 15 |
| Pulmonary embolismc | 1.37 (0.90-2.07) | 14 | 10 |
| Invasive breast cancerc | 0.80 (0.62-1.04) | 28 | 34 |
| Colorectal cancerc | 1.08 (0.75-1.55) | 17 | 16 |
| Hip fracturec | 0.65 (0.45-0.94) | 12 | 19 |
| Vertebral fracturesc,d | 0.64 (0.44-0.93) | 11 | 18 |
| Lower arm/wrist fracturesc,d | 0.58 (0.47-0.72) | 35 | 59 |
| Total fracturesc,d | 0.71 (0.64-0.80) | 144 | 197 |
| Death due to other causese,f | 1.08 (0.88-1.32) | 53 | 50 |
| Overall mortalityc,d | 1.04 (0.88-1.22) | 79 | 75 |
| Global Indexg | 1.02 (0.92-1.13) | 206 | 201 |
a Adapted from numerous WHI publications. WHI publications can be viewed at www.nhlbi.nih.gov/whi.
b Nominal confidence intervals unadjusted for multiple looks and multiple comparisons.
c Results are based on centrally adjudicated data for an average follow-up of 7.1 years.
d Not included in “global index”.
e Results are base on an average follow-up of 6.8 years.
f All deaths, except from beast or colorectal cancer, definite or probable CHD, PE, or cerebrovascular disease.
g A subset of the events was combined in a “global index” defined as the earliest occurrence of CHD events, invasive breast cancer, stroke, pulmonary embolism, endometrial cancer, colorectal cancer, hip fracture, or death due to other causes.
For those outcomes included in the WHI “global index” that reached statistical significance, the absolute excess risk per 10,000 women-years in the group treated with CE-alone was 12 more strokes, while the absolute risk reduction per 10,000 women-years was 7 fewer hip fractures1. The absolute excess risk of events included in the “global index” was a non-significant 5 events per 10,000 women-years. There was no difference between the groups in terms of all-cause mortality.
No overall difference for primary CHD events (nonfatal MI, silent MI and CHD death) and invasive breast cancer incidence in women receiving CE-alone compared with placebo was reported in final centrally adjudicated results from the estrogen-alone substudy, after an average follow-up of 7.1 years.
Centrally adjudicated results for stroke events from the estrogen-alone substudy, after an average follow-up of 7.1 years, reported no significant differences in distribution of stroke subtypes or severity, including fatal strokes, in women receiving CE-alone compared to placebo. Estrogen-alone increased the risk for ischemic stroke, and this excess risk was present in all subgroups of women examined2.
Timing of the initiation of estrogen-alone therapy relative to the start of menopause may affect the overall risk benefit profile. The WHI estrogen-alone substudy stratified by age showed in women 50 to 59 years of age a non-significant trend toward reduced risk for CHD [hazard ratio (HR) 0.63 (95 percent CI, 0.36-1.09)] and overall mortality [HR 0.71 (95 percent CI, 0.46-1.11)].
The WHI estrogen plus progestin substudy was also stopped early. According to the predefined stopping rule, after an average follow-up of 5.6 years of treatment, the increased risk of breast cancer and cardiovascular events exceeded the specified benefits included in the “global index.” The absolute excess risk of events included in the “global index” was 19 per 10,000 women-years.
For those outcomes included in the WHI “global index” that reached statistical significance after 5.6 years of follow-up, the absolute excess risks per 10,000 women-years in the group treated with CE plus MPA were 7 more CHD events, 8 more strokes, 10 more PEs, and 8 more invasive breast cancers, while the absolute risk reductions per 10,000 women-years were 6 fewer colorectal cancers and 5 fewer hip fractures.
Results of the CE plus MPA substudy, which included 16,608 women (average 63 years of age, range 50 to 79; 83.9 percent White, 6.8 percent Black, 5.4 percent Hispanic, 3.9 percent Other), are presented in Table 2. These results reflect centrally adjudicated data after an average follow-up of 5.6 years.
Table 2. Relative and Absolute Risk Seen in the Estrogen Plus Progestin Substudy of WHI at an Average of 5.6 Yearsa,b:
| Event | Relative Risk CE/MPA vs. Placebo (95% nCIc) | CE/MPA n=8,506 | Placebo n=8,102 |
|---|---|---|---|
| Absolute Risk per 10,000 Women-Years | |||
| CHD events | 1.23 (0.99-1.53) | 41 | 34 |
| Non-fatal MI | 1.28 (1.00-1.63) | 31 | 25 |
| CHD death | 1.10 (0.70-1.75) | 8 | 8 |
| All Strokes | 1.31 (1.03-1.68) | 33 | 25 |
| Ischemic stroke | 1.44 (1.09-1.90) | 26 | 18 |
| Deep vein thrombosisd | 1.95 (1.43-2.67) | 26 | 13 |
| Pulmonary embolism | 2.13 (1.45-3.11) | 18 | 8 |
| Invasive breast cancerg | 1.24 (1.01-1.54) | 41 | 33 |
| Colorectal cancer | 0.61 (0.42-0.87) | 10 | 16 |
| Endometrial cancerd | 0.81 (0.48-1.36) | 6 | 7 |
| Cervical cancerd | 1.44 (0.47-4.42) | 2 | 1 |
| Hip fracture | 0.67 (0.47-4.42) | 11 | 16 |
| Vertebral fracturesd | 0.65 (0.46-0.92) | 11 | 17 |
| Lower arm/wrist fracturesd | 0.71 (0.59-0.85) | 44 | 62 |
| Total fracturesd | 0.76 (0.69-0.83) | 152 | 199 |
| Overall mortalityf | 1.00 (0.83-1.19) | 52 | 52 |
| Global Indexg | 1.13 (1.02-1.25) | 184 | 165 |
a Adapted from numerous WHI publications. WHI publications can be viewed at www.nhlbi.nih.gov/whi.
b Results are based on centrally adjudicated data
c Nominal confidence intervals unadjusted for multiple looks and multiple comparisons.
d Not included in “global index”.
e Includes metastatic and non-metastatic breast cancer, with the exception of in situ cancer.
f All deaths, except from beast or colorectal cancer, definite or probable CHD, PE, or cerebrovascular disease.
g A subset of the events was combined in a “global index” defined as the earliest occurrence of CHD events, invasive breast cancer, stroke, pulmonary embolism, colorectal cancer, hip fracture, or death due to other causes.
Timing of the initiation of estrogen plus progestin therapy relative to the start of menopause may affect the overall risk benefit profile. The WHI estrogen plus progestin substudy stratified by age showed in women 50 to 59 years of age, a non-significant trend toward reduced risk for overall mortality [HR 0.69 (95 percent CI, 0.44-1.07)].
The WHIMS estrogen-alone ancillary study of WHI enrolled 2,947 predominantly healthy hysterectomized postmenopausal women 65 to 79 years of age and older (45 percent were 65 to 69 years of age; 36 percent were 70 to 74 years of age; 19 percent were 75 years of age and older) to evaluate the effects of daily CE (0.625 mg)-alone on the incidence of probable dementia (primary outcome) compared to placebo.
After an average follow-up of 5.2 years, the relative risk of probable dementia for CE-alone versus placebo was 1.49 (95 percent CI, 0.83-2.66). The absolute risk of probable dementia for CE-alone versus placebo was 37 versus 25 cases per 10,000 women-years. Probable dementia as defined in this study included Alzheimer’s disease (AD), vascular dementia (VaD) and mixed types (having features of both AD and VaD). The most common classification of probable dementia in the treatment group and the placebo group was AD. Since the ancillary study was conducted in women 65 to 79 years of age, it is unknown whether these findings apply to younger postmenopausal women [see BOXED WARNINGS, WARNINGS, Probable Dementia and PRECAUTIONS, Geriatric Use].
The WHIMS estrogen plus progestin ancillary study of WHI enrolled 4,532 predominantly healthy postmenopausal women 65 years of age and older (47 percent were 65 to 69 years of age; 35 percent were 70 to 74 years; 18 percent were 75 years of age and older) to evaluate the effects of daily CE (0.625 mg) plus MPA (2.5 mg) on the incidence of probable dementia (primary outcome) compared to placebo.
After an average follow-up of 4 years, the relative risk of probable dementia for CE plus MPA versus placebo was 2.05 (95 percent CI, 1.21-3.48). The absolute risk of probable dementia for CE plus MPA versus placebo was 45 versus 22 per 10,000 women-years. Probable dementia as defined in this study included AD, VaD and mixed types (having features of both AD and VaD). The most common classification of probable dementia in the treatment group and the placebo group was AD. Since the ancillary study was conducted in women 65 to 79 years of age, it is unknown whether these findings apply to younger postmenopausal women [see WARNINGS, Probable Dementia and PRECAUTIONS, Geriatric Use].
When data from the two populations were pooled as planned in the WHIMS protocol, the reported overall relative risk for probable dementia was 1.76 (95 percent CI, 1.19-2.60). Differences between groups became apparent in the first year of treatment. It is unknown whether these findings apply to younger postmenopausal women [see WARNINGS, Probable Dementia and PRECAUTIONS, Geriatric Use].
© All content on this website, including data entry, data processing, decision support tools, "RxReasoner" logo and graphics, is the intellectual property of RxReasoner and is protected by copyright laws. Unauthorized reproduction or distribution of any part of this content without explicit written permission from RxReasoner is strictly prohibited. Any third-party content used on this site is acknowledged and utilized under fair use principles.
