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 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.
Pharmacokinetics
The skin metabolizes estradiol only to a small extent. In contrast, orally
administered estradiol is rapidly metabolized by the liver to estrone and its
conjugates, giving rise to higher circulating levels of estrone than estradiol.
Therefore, transdermal administration produces therapeutic plasma levels of
estradiol with lower circulating levels of estrone and estrone conjugates and
requires smaller total doses than does oral therapy.
Absorption
In a multiple-dose study consisting of three consecutive system applications
of the original formulation [Vivelle® (estradiol transdermal system)] which
was conducted in 17 healthy, postmenopausal women, blood levels of estradiol
and estrone were compared following application of these units to sites on the
abdomen and buttocks in a crossover fashion. Systems that deliver nominal estradiol
doses of approximately 0.0375 mg/day and 0.1 mg/day were applied to abdominal
application sites while the 0.1 mg/day doses were also applied to sites on the
buttocks. These systems increased estradiol levels above baseline within 4 hours
and maintained respective mean levels of 25 and 79 pg/mL above baseline following
application to the abdomen; slightly higher mean levels of 88 pg/mL above baseline
were observed following application to the buttocks. At the same time, increases
in estrone plasma concentrations averaged about 12 and 50 pg/mL, respectively,
following application to the abdomen and 61 pg/mL for the buttocks. While plasma
concentrations of estradiol and estrone remained slightly above baseline at
12 hours following removal of the systems in this study, results from another
study show these levels to return to baseline values within 24 hours following
removal of the systems.
Figure 1 illustrates the mean plasma concentrations of estradiol at steady-state
during application of these patches at four different dosages.
Figure 1: Steady-State Estradiol Plasma Concentrations for
Systems Applied to the Abdomen
Nonbaseline-corrected levels
The corresponding pharmacokinetic parameters are summarized in the table below.
Table 1: Steady-State Estradiol Pharmacokinetic Parameters
for Systems Applied to the Abdomen (mean ±standard deviation) Nonbaseline-corrected
data*
Dosage
(mg/day) |
Cmax†
(pg/mL) |
Cavg‡
(pg/mL) |
Cmin (84 hr)§
(pg/mL) |
0.0375 |
46 ±16 |
34 ±10 |
30 RMG10 |
0.05 |
83 ±41 |
57 ±23# |
41 ±11# |
0.075 |
99 ±35 |
72 ±24 |
60 ±24 |
0.1 |
133 ±51 |
89 ±38 |
90 ±44 |
0.1¶ |
145 ±71 |
104 ±52 |
85 ±47 |
*Mean baseline estradiol concentration =
11.7 pg/mL
† Peak plasma concentration
‡Average plasma concentration
§Minimum plasma concentration at 84 hr
#Measured over 80 hr
¶Applied to the buttocks |
Vivelle-Dot® (estradiol transdermal system), the revised formulation with
smaller system sizes, was shown to be bioequivalent to the original formulation,
Vivelle® (estradiol transdermal system), used in the clinical trials.
Distribution
No specific investigation of the tissue distribution of estradiol absorbed
from Vivelle-Dot (estradiol transdermal system) 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 intestine, and hydrolysis in the gut followed by reabsorption. In postmenopausal
women a significant portion of the circulating estrogens exist 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. The half-life values calculated after dosing with the
Vivelle-Dot (estradiol transdermal system) ranged from 5.9 to 7.7 hours. After removal of the transdermal systems,
serum concentrations of estradiol and estrone returned to baseline levels within
24 hours.
Special Populations
Vivelle-Dot (estradiol transdermal system) was only investigated in postmenopausal women.
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.
Adhesion
Based on combined data from three short-term clinical trials consisting of
471 observations, 85% of Vivelle-Dot (estradiol transdermal system) adhered completely to the skin over the
3.5-day wear period. Three (3%) of the systems detached and were reapplied or
replaced during the 3.5-day wear period. Approximately 80% of the transdermal
systems evaluated in these studies were Vivelle-Dot (estradiol transdermal system) 0.05 mg/day.
Clinical Studies
Effects on vasomotor symptoms
In a pharmacokinetic study, Vivelle-Dot (estradiol transdermal system) was shown to be bioequivalent to Vivelle.
In two controlled clinical trials with Vivelle, of 356 subjects, the 0.075 and
0.1 mg doses were superior to placebo in relieving vasomotor symptoms at Week
4, and maintained efficacy through Weeks 8 and 12 of treatment. In this original
study, the 0.0375 and 0.05 mg doses, however, did not differ from placebo until
approximately Week 6, therefore, an additional 12-week placebo-controlled study
in 255 patients was performed with Vivelle to establish the efficacy of the
lowest dose of 0.0375 mg. The baseline mean daily number of hot flushes in these
255 patients was 11.5. Results at Weeks 4, 8, and 12 of treatment are shown
in the figure below. (See Figure 2.)
Figure 2: Mean (SD) change from baseline in mean daily number
of flushes for Vivelle® 0.0375 mg versus Placebo in a 12-week trial.
The 0.0375 mg dose was superior to placebo in reducing both the frequency and
severity of vasomotor symptoms at Week 4 and maintained efficacy through Weeks
8 and 12 of treatment. All doses of Vivelle (0.0375 mg, 0.05 mg, 0.075 mg, and
0.1 mg) are effective for the control of vasomotor symptoms.
Effects on bone mineral density
Efficacy and safety of Vivelle in the prevention of postmenopausal osteoporosis
have been studied in a 2-year double-blind, randomized, placebo-controlled,
parallel group study. A total of 261 hysterectomized (161) and non-hysterectomized
(100), surgically or naturally menopausal women (within 5 years of menopause),
with no evidence of osteoporosis (lumbar spine bone mineral density within 2
standard deviations of average peak bone mass, i.e., ≥0.827 g/cm²) were
enrolled in this study; 194 patients were randomized to one of the four doses
of Vivelle (0.1, 0.05, 0.0375, or 0.025 mg/day) and 67 patients to placebo.
Over 2 years, study systems were applied to the buttock or the abdomen twice
a week. Non-hysterectomized women received oral medroxyprogesterone acetate
(2.5 mg/day) throughout the study.
The study population comprised naturally (82%) or surgically (18%) menopausal,
hysterectomized (61%) or non-hysterectomized (39%) women with a mean age of
52.0 years (range 27 to 62 years); the mean duration of menopause was 31.7 months
(range 2 to 72 months). Two hundred thirty-two (89%) of randomized subjects
(173 on active drug, 59 on placebo) contributed data to the analysis of percent
change from baseline in bone mineral density (BMD) of the AP lumbar spine, the
primary efficacy variable. Patients were given supplemental dietary calcium
(1000 mg elemental calcium/day) but no supplemental vitamin D. There was an
increase in BMD of the AP lumbar spine in all Vivelle dose groups; in contrast
to this, a decrease in AP lumbar spine BMD was observed in placebo patients.
All Vivelle doses were significantly superior to placebo (p<0.05) at all
time points with the exception of Vivelle 0.05 mg/day at 6 months. The highest
dose of Vivelle was superior to the three lower doses. There were no statistically
significant differences in pairwise comparisons among the three lower doses.
(See Figure 3.)
Figure 3: Bone mineral density - AP Lumbar spine Least squares
means of percentage change from baseline All randomized patients with at least
one post-baseline assessment available with last post-baseline observation carried
forward
Analysis of percent change from baseline in femoral neck BMD, a secondary efficacy
outcome variable, showed qualitatively similar results; all doses of Vivelle
were significantly superior to placebo (p<0.05) at 24 months. The highest
Vivelle dose was superior to placebo at all time points. A mixture of significant
and non-significant results were obtained for the lower dose groups at earlier
time points. The highest Vivelle dose was superior to the three lower doses,
and there were no significant differences among the three lower doses at this
skeletal site. (See Figure 4.)
Figure 4: Bone mineral density - Femoral neck Least squares
means of percentage change from baseline All randomized patients with at least
one post-baseline assessment available with last post-baseline observation carried
forward
The mean serum osteocalcin (a marker of bone formation) and urinary excretion
of cross-link N-telopeptides of Type 1 collagen (a marker of bone resorption)
decreased numerically in most of the active treatment groups relative to baseline.
However, the decreases in both markers were inconsistent across treatment groups
and the differences between active treatment groups and placebo were not statistically
significant.
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 the use of
oral 0.625 mg conjugated estrogens (CE) per day alone or the use of oral 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) (non-fatal 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 causes. 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 2 below.
Table 2: Relative and Absolute Risk Seen in the CE/MPA Substudy
of WHIa
EventC |
Relative
CE/MPA |
Risk vs. |
Placebo
n= 8102 |
CE/MPA
n= 8506 |
Placebo at 5.2 Years (95% CI*) 10,000 Women-Years |
Absolute Risk per |
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 |
Stroke |
1.41 (1.07-1.85) |
21 |
29 |
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 the events above |
0.92 (0.74-1.14) |
40 |
37 |
Global indexc |
1.15 (1.03-1.28) |
151 |
170 |
Deep vein thrombosisd |
2.07 (1.49-2.87) |
13 |
26 |
Vertebral fracturesd |
0.66 (0.44-0.98) |
15 |
9 |
Other osteoporotic fracturesd |
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
*Nominal confidence intervals unadjusted for multiple looks and multiple
comparisons |
For those outcomes included in the “global index”, 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 healthy 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.)