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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.
Transdermal administration of Climara produces mean serum concentrations of estradiol comparable to those produced by premenopausal women in the early follicular phase of the ovulatory cycle. The pharmacokinetics of estradiol following application of the Climara (estradiol transdermal) system were investigated in 197 healthy postmenopausal women in six studies. In five of the studies Climara (estradiol transdermal) system was applied to the abdomen and in a sixth study application to the buttocks and abdomen were compared.
Absorption: The Climara transdermal delivery system continuously releases estradiol which is transported across intact skin leading to sustained circulating levels of estradiol during a 7-day treatment period. The systemic availability of estradiol after transdermal administration is about 20 times higher than that after oral administration. This difference is due to the absence of first pass metabolism when estradiol is given by the transdermal route.
In a bioavailability study, the Climara (estradiol transdermal) 6.5 cm² was studied with the Climara 12.5 cm² as reference. The mean estradiol levels in serum from the two sizes are shown in Figure 1.
Figure 1: Mean Serum 17β-Estradiol Concentrations vs.
Time Profile following Application of a 6.5 cm² Transdermal Patch and Application
of a 12.5 cm² Climara (estradiol transdermal) patch
Dose proportionality was demonstrated for the Climara (estradiol transdermal) 6.5 cm² transdermal system as compared to the Climara (estradiol transdermal) 12.5 cm² transdermal system in a 2-week crossover study with a 1-week washout period between the two-transdermal systems in 24 postmenopausal women.
Dose proportionality was also demonstrated for the Climara (estradiol transdermal) system (12.5 cm² and 25 cm²) in a 1-week study conducted in 54 postmenopausal women. The mean steady state levels (Cavg) of the estradiol during the application of Climara (estradiol transdermal) 25 cm² and 12.5 cm² on the abdomen were about 80 and 40 pg/mL, respectively. In a 3 week multiple application study in 24 postmenopausal women, the 25 cm² Climara system produced average peak estradiol concentrations (Cmax) of approximately 100 pg/mL. Trough values at the end of each wear interval (Cmin) were approximately 35 pg/mL. Nearly identical serum curves were seen each week, indicating little or no accumulation of estradiol in the body. Serum estrone peak and trough levels were 60 and 40 pg/mL, respectively.
In a single dose, randomized, crossover study conducted to compare the effect of site of application, 38 postmenopausal women wore a single Climara (estradiol transdermal) 25 cm² system for 1 week on the abdomen and buttocks. The estradiol serum concentration profiles are shown in Figure 2. Cmax and Cavg values were, respectively, 25% and 17% higher with the buttock application than with the abdomen application.
Figure 2: Observed Mean ( ± S.E.) Estradiol Serum
Concentrations for a One Week Application of the Climara (estradiol transdermal) system (25 cm²)
to the abdomen and buttocks of 38 postmenopausal women
Table 1 provides a summary of estradiol pharmacokinetic parameters determined during evaluation of Climara (estradiol transdermal) .
Table 1 - Pharmacokinetic Summary (Mean Estradiol Values)
|Climara (estradiol transdermal)
The relative standard deviation of each pharmacokinetic parameter after application to the abdomen averaged 50%, which is indicative of the considerable intersubject variability associated with transdermal drug delivery. The relative standard deviation of each pharmacokinetic parameter after application to the buttock was lower than that after application to the abdomen (e.g., for Cmax 39% vs 62%, and for Cavg 35% vs 48%).
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.
Geriatric: There have not been sufficient numbers of geriatric patients involved in clinical studies utilizing Climara (estradiol transdermal) to determine whether those over 65 years of age differ from younger subjects in their response to Climara (estradiol transdermal) .
Pediatric: No pharmacokinetic study for Climara (estradiol transdermal) has been conducted in a pediatric population.
Gender: Climara (estradiol transdermal) is indicated for use in women only.
Race: No studies were done to determine the effect of race on the pharmacokinetics of Climara.
Patients with Renal Impairment: Total estradiol serum levels are higher in postmenopausal women with end stage renal disease (ESRD) receiving maintenance hemodialysis than in normal subjects at baseline and following oral doses of estradiol. Therefore, conventional transdermal estradiol doses used in individuals with normal renal function may be excessive for postmenopausal women with ESRD receiving maintenance hemodialysis.
Patients with Hepatic Impairment: Estrogens may be poorly metabolized in patients with impaired liver function and should be administered with caution.
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.
An open-label study of adhesion potentials of placebo transdermal systems that correspond to the 6.5 cm² and 12.5 cm² sizes of Climara (estradiol transdermal) was conducted in 112 healthy women of 45-75 years of age. Each woman applied both transdermal systems weekly, on the upper outer abdomen, for 3 consecutive weeks. It should be noted that lower abdomen and upper quadrant of the buttock are the approved sites of application for Climara (estradiol transdermal) .
The adhesion assessment was done visually on Days 2, 4, 5, 6, 7 of each week of transdermal system wear. A total of 1654 adhesion observations were conducted for 333 transdermal systems of each size.
Of these observations, approximately 90% showed essentially no lift for both the 6.5 cm² and 12.5 cm² transdermal systems. Of the total number of transdermal systems applied, approximately 5% showed complete detachment for each size. Adhesion potentials of the 18.75 cm² and 25cm² sizes of transdermal systems (0.075 mg/day and 0.1 mg/day) have not been studied.
Effects on vasomotor symptoms
A study of 214 women 25 to 74 years old met the qualification criteria and were randomly assigned to one of the three treatment groups: 72 to the 0.05 mg estradiol patch, 70 to the 0.1 mg estradiol patch, and 72 to placebo. Potential subjects were postmenopausal women in good general health who experienced vasomotor symptoms. Natural menopause patients had not menstruated for at least 12 months and surgical menopause patients had undergone bilateral oophorectomy at least 4 weeks before evaluation for study entry. In order to enter the 11-week treatment phase of the study, potential subjects must have experienced a minimum of five moderate to severe hot flushes per week, or a minimum of 15 hot flushes of any severity per week, for 2 consecutive weeks. Women wore the patches in a cyclical fashion (three weeks on and one week off).
During treatment, all subjects used diaries to record the number and severity of hot flushes. Subjects were monitored by clinic visits at the end of weeks 1, 3, 7, and 11 and by telephone at the end of weeks 4, 5, 8, and 9.
Adequate data for the analysis of efficacy was available from 191 subjects. The results are presented as the mean ± SD number of flushes in each of the 3 treatment weeks of each 4-week cycle. In the 0.05 mg estradiol group, the mean weekly hot flush rate across all treatment cycles decreased from 46 ± 6.5 at baseline to 20 ± 3 (-67.0%). The 0.1 mg estradiol group had a decline in the mean weekly hot flush rate from 52 ± 4.4 at baseline to 16 ± 2.4 (-72%). In the placebo group, the mean weekly hot flush rate declined from 53 ± 4.5 at baseline to 46 ± 6.5 (-18.1%). Compared with placebo, the 0.05 mg and 0.1 mg estradiol groups showed a statistically significantly larger mean decrease in hot flushes across all treatment cycles (P<0.05). When the response to treatment was analyzed for each of the three cycles of therapy, similar statistically significant differences were observed between both estradiol treatment groups and the placebo group during all treatment cycles.
In a double-blind, placebo-controlled, randomized study of 187 women receiving Climara (estradiol transdermal) 0.025 mg/day or placebo continuously for up to three 28-day cycles, the Climara (estradiol transdermal) 0.025 mg/day dosage was shown to be statistically better than placebo at weeks 4 and 12 for relief of both the frequency and severity of moderate-to-severe vasomotor symptoms.
Table 2 - Mean Change from Baseline in the Number of Moderate-to-Severe
Vasomotor Symptoms (ITT)
|Treatment Group||Statistics||Week 4||Week 8||Week 12|
A second active-control trial of 193 randomized subjects was supportive of the placebo-controlled trial.
Effects on bone mineral density
A two-year clinical trial enrolled a total of 175 healthy, hysterectomized, postmenopausal, non-osteoporotic (i.e., lumbar spine bone mineral density >0.9 gm/cm²) women at 10 study centers in the United States. 129 subjects were allocated to receive active treatment with 4 different doses of estradiol patches (6.5, 12.5, 15, 25 cm²) and 46 subjects were allocated to receive placebo patches. 77% of the randomized subjects (100 on active drug and 34 on placebo) contributed data to the analysis of percent change of A-P spine bone mineral density (BMD), the primary efficacy variable (see Figure 3). A statistically significant overall treatment effect at each timepoint was noted, implying bone preservation for all active treatment groups at all timepoints, as opposed to bone loss for placebo at all timepoints.
Figure 3: Mean Percent Change from Baseline in Lumbar Spine
(A-P View) Bone Mineral Density By Treatment and Time last observation carried
Percent change in BMD of the total hip (see Figure 4) was also statistically significantly different from placebo for all active treatment groups. The results of the measurements of biochemical markers supported the finding of efficacy for all doses of transdermal estradiol. Serum osteocalcin levels decreased, indicative of a decrease in bone formation, at all timepoints for all active treatment doses, statistically significantly different from placebo (which generally rose). Urinary deoxypyridinoline and pyridinoline changes also suggested a decrease in bone turnover for all active treatment groups.
Figure 4: Mean Percent Change from Baseline in Total Hip
by Treatment and Time* last observation carried forward**
Footnote: This figure is based on 74% of the randomized subjects (95 on active drug and 34 on placebo).
Women's Health Initiative Studies
The Women's Health Initiative (WHI) enrolled a total of 27,000 predominantly healthy postmenopausal women to assess the risks and benefits of either the use of oral 0.625 mg conjugated estrogens (CE) per day alone or the use of 0.625 mg conjugated estrogens plus 2.5 mg medroxyprogesterone acetate (MPA) per day compared to placebo in the prevention of certain chronic diseases. The primary endpoint was the incidence of coronary heart disease (CHD) (nonfatal myocardial infarction and CHD death), with invasive breast cancer as the primary adverse outcome studied. A “global index” included the earliest occurrence of CHD, invasive breast cancer, stroke, pulmonary embolism (PB), endometrial cancer, colorectal cancer, hip fixture, or death due to other cause. The study did not evaluate the effects of CE or CE/MPA on menopausal symptoms.
The CE/MPA substudy was stopped early because, according to the predefined stopping rule, the increased risk of breast cancer and cardiovascular events exceeded the specified benefits included in the “global index.” Results of the CE/MPA substudy, which included 16,608 women (average age of 63 years, range 50 to 79; 83.9% White, 6.5% Black, 5.5% Hispanic), after an average follow-up of 5.2 years are presented in Table 3 below:
Table 3 - Relative and Absolute Risk Seen in the CE/MPA Substudy
CE/MPA vs placebo
at 5.2 Years
n = 8102
n = 8506
|Absolute Risk per 10,000 Person-years|
|CHD events||1.29 (1.02-1.63)||30||37|
|Non-fatal MI||1.32 (1.02-1.72)||23||30|
|CHD death||1.18 (0.70-1.97)||6||7|
|Invasive breast cancerb||1.26 (1.00-1.59)||30||38|
|Pulmonary embolism||2.13 (1.39-3.25)||8||16|
|Colorectal cancer||0.63 (0.43-0.92)||16||10|
|Endometrial cancer||0.83 (0.47-1.47)||6||5|
|Hip fracture||0.66 (0.45-0.98)||15||10|
|Death due to causes other than||0.92 (0.74-1.14)||40||37|
|the events above|
|Global Index c||1.15 (1.03-1.28)||151||170|
|Deep vein thrombosisd||2.07 (1.49-2.87)||13||26|
|Vertebral fractures d||0.66 (0.44-0.98)||15||9|
|Other osteoporotic fractures d||0.77 (0.69-0.86)||170||131|
| a) adapted from JAMA, 2002; 288:321-333
b) includes metastatic and non-metastatic breast cancer with the exception of in situ breast cancer
c) 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
d) not included in Global Index
e) * nominal confidence intervals unadjusted for multiple looks and multiple comparisons
For those outcomes included in the “global index,” the absolute excess risks per 10,000 women-years in the group treated with CE/MPA were 7 more CHD events, 8 more strokes, 8 more PEs, and 8 more invasive breast cancers, while absolute risk reductions per 10,000 women-years were 6 fewer colorectal cancers and 5 fewer hip fractures. The absolute excess risk of events included in the “global index” was 19 per 10,000 women-years. There was no difference between the groups in terms of all-cause mortality. (See BOXED WARNINGS, WARNINGS, and PRECAUTIONS.)
Women's Health Initiative Memory Study
The Women's Health Initiative Memory Study (WHIMS), a substudy of WHI, enrolled 4,532 predominantly postmenopausal women 65 years of age and older (47% were age 65 to 69 years, 35% were 70 to 74 years, and 18% were 75 years of age and older) to evaluate the effects of CE/MPA (0.625 mg conjugated estrogens plus 2.5 mg medroxyprogesterone acetate) on the incidence of probable dementia (primary outcome) compared with placebo. After an average follow-up of 4 years, 40 women in the estrogen/progestin group (45 per 10,000 women-years) and 21 in the placebo group (22 per 10,000 women-years) were diagnosed with probable dementia. The relative risk of probable dementia in the hormone therapy group was 2.05 (95% CI, 1.21 to 3.48) compared to placebo. Differences between groups became apparent in the first year of treatment. It is unknown whether these findings apply to younger postmenopausal women. (See BOXED WARNINGS and WARNINGS, Dementia and PRECAUTIONS, Geriatric Use.)
Last reviewed on RxList: 10/2/2008
This monograph has been modified to include the generic and brand name in many instances.
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