The estradiol transdermal therapeutic system is a cutaneous delivery device which delivers estradiol into the systemic circulation via the stratum corneum at a constant rate for up to 4 days. Physiological levels of estradiol (the major estrogen secreted by the ovaries in premenopausal women) can therefore be maintained in postmenopausal women with low daily doses because first-pass hepatic metabolism is avoided.
In short term clinical studies, the beneficial effects of transdermal estradiol on plasma gonadotrophins, maturation of the vaginal epithelium, metabolic parameters of bone resorption and menopausal symptoms (hot flushes, sleep disturbance, genitourinary discomfort and mood alteration) appear to be comparable to those of oral and subcutaneous estrogens, while the undesirable effects of oral estrogens on hepatic metabolism are avoided. As with oral or injectable estrogen replacement therapy, concomitant sequential progestagen is recommended for patients with an intact uterus during transdermal estradiol administration, in order to reduce endometrial stimulation. Transdermal estradiol has been well tolerated in clinical trials, with local irritation at the site of application being the most common adverse effect. The incidence of systemic estrogenic effects appears to be comparable to that observed with oral therapy.
Thus, transdermal estradiol offers near-physiological estrogen replacement in postmenopausal women in a convenient low-dose form which may avoid some of the complications of higher dose oral therapy. Long term epidemiological studies are warranted to determine whether transdermal estradiol therapy provides protection against osteoporosis and fractures and cardiovascular disease equivalent to that offered by oral and injectable estrogens. However, despite the importance of such data, it seems reasonable to conclude at this stage of its development that transdermal estradiol represents an important advance in hormone replacement therapy.
17β-Estradiol is the predominant estrogen produced by the ovaries in premenopausal women. Administration of transdermal estradiol to postmenopausal women (in dosages of 0.05 to 0.2 mg/day) elevates plasma estradiol concentrations into the range observed in premenopausal women at the early to mid follicular stage. Plasma estrone concentrations are increased to a much lesser degree and a physiological plasma ratio of estradiol to estrone (approximately 1: 1) is thus produced. As a result of the increased plasma estradiol concentrations, plasma concentrations of follicle-stimulating hormone (FSH) and luteinising hormone (LH) are decreased and vaginal cytology is converted to a pattern resembling that found in premenopausal women, with improvement of the maturation and karyopyknotic indices. Bone resorption is inhibited, as evidenced by a reduction in the urinary ratios of calcium and hydroxyproline to creatinine, and an increase in bone mineral density has been achieved in patients receiving long term treatment. Transdermal estradiol has a less marked effect than oral estrogens on lipid and lipoprotein metabolism; the plasma lipid profile does not appear to be significantly altered by short term treatment, but some studies of ⩾ 6 months’ duration have reported potentially beneficial changes in various lipid and lipoprotein fractions.
The estradiol transdermal therapeutic system is designed to deliver estradiol at a constant rate for up to 4 days. Currently, 3 sizes of delivery system are available, with nominal delivery rates of 0.025, 0.05 and 0.1 mg/24 hours. Following application of transdermal estradiol to intact skin, maximum plasma estradiol concentrations are attained in postmenopausal women within 2 to 8 hours. Steady-state plasma concentrations of estradiol are linearly proportional to the dose administered; mean levels of around 23, 40, 75 and 100 ng/L occur in women with pretreatment estradiol levels ⩽ 10 ng/L from administration of 0.025, 0.05, 0.1 and 0.2 mg/day, respectively. Plasma levels of estradiol during transdermal therapy and reduction in menopausal symptoms, plasma FSH concentrations and urinary excretion of calcium are closely related.
Estradiol is mainly metabolised in the liver, the major metabolites being estrone and estriol and their conjugates, which are considerably less potent than estradiol. The bulk of the metabolites are excreted in the urine as glucuronides and sulphates, although some enterohepatic recirculation may occur. Within 24 hours of removal of transdermal delivery systems, plasma concentrations of estradiol and estrone, and urinary excretion of estradiol and estrone conjugates, return to pretreatment levels. The plasma elimination half-life of estradiol is approximately 1 hour irrespective of the route of administration and the metabolic plasma clearance rate is between 650 and 900 L/day/m2.
The efficacy of transdermal estradiol as estrogen replacement therapy in peri- or postmenopausal women has been evaluated in noncomparative, placebo-controlled and comparative clinical trials. Dosages ranging from 0.025 to 0.2mg daily have been used. In studies of ⩾ 2 months duration, treatment has generally been cyclical (3 weeks on, 1 week off) and sequential progestagen therapy has usually been administered for 5 to 12 days per cycle to patients with an intact uterus, in order to minimise endometrial proliferation. Climacteric symptoms — hot flushes, sweating, sleep disturbance, vaginal discomfort, poor concentration and irritability — have been eliminated or significantly improved during transdermal estradiol replacement therapy. In comparative studies transdermal estradiol has demonstrated efficacy in the control of climacteric symptoms at least equivalent to those of oral estradiol preparations, ethinylestradiol and conjugated estrogens, and subcutaneous estradiol implants or estradiol/prasterone depot injections. Data from preliminary studies suggest that transdermal estradiol, usually with sequential progestagen, is also effective in other indications for which estrogen therapy is prescribed, such as contraception and as hormone replacement therapy in patients with premature ovarian failure or bilateral oophorectomy participating in fertility programmes. Although transdermal estradiol inhibits bone resorption, few data are currently available regarding its effect on the incidence of osteoporosis and fractures in treated menopausal women.
Analysis of patient acceptability of the transdermal route for estrogen replacement in several studies indicated that > 70% of patients preferred transdermal estradiol over oral or injectable therapies.
A significant proportion of patients experience dermatological reactions to the transdermal delivery device. Although these mostly consist of transient erythema/itching at the site of application, which can be minimised by rotation of patch application sites, severe irritation leading to discontinuation of therapy occurs in about 2.5 to 7% of patients overall.
Otherwise, transdermal estradiol therapy is generally well tolerated, the most common systemic adverse symptoms being typical estrogenic effects, such as breast tenderness and spotting/bleeding and general effects such as fatigue, abdominal bloating and nausea, which result in discontinuation of treatment in < 4% of patients. Estrogenic stimulation of the endometrium occurs with transdermal estradiol therapy and coadministration of a sequential progestagen (which may also produce a more acceptable bleeding pattern) is therefore recommended for patients with an intact uterus in order to minimise endometrial proliferation.
Unlike oral estrogens, transdermal estradiol does not stimulate hepatic metabolism and consequently plasma concentrations of renin substrate, sex hormone-, thyroxine- and cortisol-binding globulins and clotting factors are not elevated.
It has been suggested that transdermal estradiol might be associated with a lower incidence of adverse effects than oral estrogen replacement therapies because of the lower circulating estrogen concentrations involved and the lack of untoward effects on liver metabolism. However, this has not been confirmed in comparative studies to date; generally, adverse effects have been comparable in patients receiving transdermal estradiol and those receiving oral or injectable estrogens.
Dosage and Administration
The recommended initial dosage of transdermal estradiol for the treatment of menopausal symptoms is 0.05mg daily, which may be increased in cases of inadequate response after 2 to 3 weeks’ treatment, or decreased if breast discomfort or breakthrough bleeding occur. For maintenance therapy the lowest effective dose should be used. Treatment may be continuous or may be given in 4-week cycles (3 weeks on/1 off). Sequential progestagen treatment should be administered for 10 to 12 days per month to patients with an intact uterus.
The transdermal estradiol delivery system should be changed twice weekly. Contraindications to the use of estradiol include carcinoma of the breast or endometrium, leiomyoma of the uterus, endometriosis, vaginal bleeding of unknown origin, severe renal, hepatic, or cardiac disease and active or previous thromboembolic disease.