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Estrasorb (Estradiol Hemihydrate Topical) - Description and Clinical Pharmacology

 
 



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Prescribing Information

Prescribing Information

DESCRIPTION

Estrasorb® (estradiol topical emulsion) is designed to deliver estradiol to the blood circulation following topical application of an emulsion. Each gram of Estrasorb® contains 2.5 mg of estradiol hemihydrate USP, EP, which is encapsulated using a micellar nanoparticle technology. Estrasorb® is packaged in foil pouches containing 1.74 grams of drug product. Daily topical application of the contents of two foil pouches provides systemic delivery of 0.05 mg of estradiol per day.

Estradiol hemihydrate USP, EP (estradiol) is a white, crystalline powder, chemically described as (17ß)-estra-1,3,5(10)-triene-3, 17-diol, hemihydrate. The molecular formula of estradiol hemihydrate is C18H24O2, 1/2 H2O, and the molecular weight is 281.4 g/mol.

The structural formula is:

The active ingredient in Estrasorb® is estradiol. The remaining components (soybean oil, water, polysorbate 80, and ethanol) are pharmacologically inactive.

CLINICAL PHARMACOLOGY

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 its 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.

Pharmacokinetics

Absorption

In a multiple-dose study, 125 patients were treated for 28 days once daily with placebo or 1.15 grams, 2.30 grams, or 3.45 grams of Estrasorb® containing 2.5 mg of estradiol per gram. The mean change from baseline in serum estradiol concentrations increased in a dose-dependent manner compared with placebo (Figure 1 below).

Serum estradiol concentrations were also assessed in a second study involving 200 postmenopausal women, who applied either a 3.45 gram daily dose of Estrasorb® (containing 2.5 mg of estradiol per gram; n = 100) or placebo (n = 100) for 12 weeks. Trough estradiol concentrations in the Estrasorb® treatment group increased from a mean of 8.9 pg/mL at baseline to 58.6 pg/mL and 70.2 pg/mL at Weeks 2 and 4, respectively (Figure 2). Trough levels of Estrasorb® remained at a plateau throughout the rest of the study: 67.3 pg/mL at Week 8 and 63.0 pg/mL at the end of the study.

Application of sunscreen 10 minutes prior to the application of Estrasorb® increased the exposure to estradiol by approximately 35%. When sunscreen is applied 25 minutes after the application of Estrasorb®, the increase in exposure to estradiol was approximately 15%. (See PRECAUTIONS.)

Distribution

No specific investigation of the tissue distribution of estradiol absorbed from Estrasorb® in humans has been conducted. 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.

Metabolism

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 intestines, and hydrolysis in the gut followed by reabsorption. In postmenopausal women a significant proportion of the circulating estrogens exists as sulfate conjugates, especially estrone sulfate, which serves as a circulating reservoir for the formation of more active estrogens.

Excretion

Estradiol, estrone, and estriol are excreted in the urine along with glucuronide and sulfate conjugates.

Special Populations

Estrasorb® was only investigated in postmenopausal women. Estrasorb® has not been studied in patients with hepatic or renal impairment.

Drug Interactions

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.

Clinical Studies

Effects on Vasomotor Symptoms

In a 12-week randomized, placebo-controlled clinical trial, a total of 200 postmenopausal women (average age 52 ± 6 years, 79% Caucasian in the Estrasorb® treatment group; average age 51.8 ± 6 years, 72% Caucasian in the placebo treatment group) were assigned to receive Estrasorb® (3.45 grams containing 2.5 mg of estradiol per gram) or placebo for a 12 weeks duration. Estrasorb® 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 (p-value <0.001 for Weeks 4 and 12). Frequency results are shown in Table 1. Severity results are shown in Table 2.

Table 1. Mean Number and Mean Change From Baseline in the Number of Moderate to Severe Vasomotor Symptoms Per Day (Intent-To-Treat Population)
Time point Treatment Group

Placebo


Estrasorb®


Baseline (observed values)(N = 100)(N = 100)
Mean Number of Hot Flushes (SD)13.63 (5.48)13.05 (5.78)
Week 4 (N = 97)(N =96)
Mean Number of Hot Flashes (SD)7.46 (6.42)4.42 (5.60)
Mean Change from Baseline (SD)-5.97 (4.76)-8.56 (6.19)
P-value vs. PlaceboNA<0.001
Week 12 (N =90)(N =90)
Mean Number of Hot Flushes (SD)5.88 (6.17)2.00 (3.64)
Mean Change from Baseline-7.20 (5.39)-11.11 6.84)
P-value vs. PlaceboNA<0.001

SD = Standard Deviation; NA = Not applicable

The severity score per day is determined by calculating the sum of recorded daily severity and dividing this number by the total number of hot flushes on that day.

a

Table 2: Mean Change from Baseline in the Severity Scorea of Hot Flushes Per Day, Intent-to-Treat Population, Most Recent Value Carried Forward

Time point

Treatment Group



Placebo


Estrasorb®


Baseline (observed value)

(N=100)(N=100)

Mean Severity Score per Day (SD)

2.44 (0.37)2.36 (0.36)

Week 4

(N=97)(N=96)

Mean Severity Score per Day (SD)

1.99 (0.81)1.47 (1.03)

Mean Change from Baseline (SD)

-0.45 (0.75)-0.89 (1.04)

P-value versus Placebo

NA<0.001

Week 12

(N=90)(N=90)

Mean Severity Score per Day (SD)

1.88 (0.98)0.92 (1.00)

Mean Change from Baseline (SD)

-0.55 (0.91)-1.44 (1.04)

P-value versus Placebo

NA<0.001

SD = Standard deviation; NA = Not applicable

Potential for estradiol transfer

Estradiol was detected on the skin at 2 and 8 hours post-application. Washing the application area with soap and water 8 hours post-application removed detectable estradiol from the application site. Upon physical contact of Estrasorb® application sites by adult males at 2 and 8 hours postapplication over a two-day period in a second study, a mean increase of approximately 25% in serum estradiol concentration was identified. (See DOSAGE AND ADMINISTRATION.)

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 0.625 mg conjugated equine estrogens (CE) per day alone or the use of 0.625 mg conjugated equine 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 (PE), endometrial cancer, colorectal cancer, hip fracture, or death due to other cause. The study did not evaluate the effects of CE or CE/MPA on menopausal symptoms.

The CE-only substudy is continuing and results have not been reported. 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.

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

* nominal confidence intervals unadjusted for multiple looks and multiple comparisons

Table 3. RELATIVE AND ABSOLUTE RISK SEEN IN THE CE/MPA SUBSTUDY OF WHIa

Eventc

Relative Risk

Prempro vs Placebo

at 5.2 Years

(95% CI*)

Placebo

n = 8102

CE/MPA

n = 8506

Absolute Risk per 10, 000 Person-years
CHD events1.29 (1.02-1.63)3037
Non-fatal MI 1.32 (1.02-1.72)2330

CHD death

1.18 (0.70-1.97)67

Invasive breast cancerb

1.26 (1.00-1.59)3038

Stroke

1.41 (1.07-1.85)2129

Pulmonary embolism

2.13 (1.39-3.25)816

Colorectal cancer

0.63 (0.43-0.92)1610

Endometrial cancer

0.83 (0.47-1.47)65

Hip fracture

0.66 (0.45-0.98)1510

Death due to causes other than the events above

0.92 (0.74-1.14)4037
Global Indexc1.15 (1.03-1.28)151170

Deep vein thrombosisd

2.07 (1.49-2.87)1326

Verterbral fracturesd

0.66 (0.44-0.98)159
Other osteoporotic fracturesd0.77 (0.69-0.86)170131

For those outcomes included in the "global index," absolute excess risks per 10,000 person-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 person-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 person-years. There was difference between the groups in terms of all-cause mortality. (See BOXED WARNINGS, WARNINGS, and PRECAUTIONS.)

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