William R. Good

Pharmacokinetics and pharmacodynamics of transdermal dosage forms of 17β-estradiol: Comparison with conventional oral estrogens used for hormone replacement

This open-label, multiple-crossover study compared the pharmacokinetics and pharmacodynamics of transdermal 17 beta-estradiol and two oral forms of estrogen replacement therapy in postmenopausal women. The transdermal systems delivered either 0.025, 0.05, or 0.1 mg/day; oral dosages were 2 mg of micronized 17 beta-estradiol or 1.25 mg of conjugated equine estrogens. Transdermal estradiol provided serum and urinary levels of estradiol conjugates typical of the early follicular phase of the premenopausal woman and an estradiol/estrone ratio that approximated 1. The increments of both serum and urinary estradiol showed dose proportionality. Serum levels of estradiol obtained 24 hours after oral administration of estrogens were in a range similar to the steady-state levels obtained with transdermal estradiol delivery. Oral estrogens, however, induced an excessive rise in estrone to levels far beyond those observed in premenopausal women. Continuous application of transdermal estradiol over 3 weeks did not result in any accumulation of estradiol or estradiol conjugates. After only three doses of oral estrogens, there were signs of retention of estrogens. Suppression of gonadotropins by oral and transdermal administration of estrogens was in a similar range. This observation supports the conclusions that levels of circulating estradiol are relevant to efficacy, and that excessively high levels of estrone after oral administration of estrogens merely represents a nonphysiologic precursor or metabolite pattern.

A new transdermal delivery system for estradiol

Abstract The successful introduction of nitroglycerin transdermal delivery systems for the prophylactic treatment of angina pectoris has spawned an explosion of interest in this route of drug delivery in the field of pharmaceutics. Since that time, we have gained a great deal more knowledge concerning the design of membrane controlled delivery systems. This route of administration has been proposed and investigated in a number of disease states using several drugs. We would like to report our experience in investigating the transdermal route for long term treatment of postmenopausal symptoms using estradiol replacement therapy. The rationale for the development of a transdermal estradiol system is associated with the metabolic and pharmacological effects of orally administered estrogen replacement in post-menopausal women. Because estradiol is metabolized almost completely on first pass through the liver, orally administered estrogens result in nonphysiologic levels of the estrogenic metabolites of the natural ovarian hormone. Transdermal delivery of estradiol successfully by-passes the first pass effect and results in a more normal estrogen blood profile. The results of several biopharmaceutics studies demonstrate the characteristics of the membrane controlled delivery system which was designed around pharmacologic principles. In addition, a number of clinical trials have shown that total required doses of estradiol provided transdermally are only a fraction of those required by the oral route. We will also discuss problems associated with adequately defining total drug input from transdermal devices when working in these very small dosing ranges.

A double-blind comparative study of Estraderm and Premarin in the amelioration of postmenopausal symptoms

Patients whose postmenopausal symptoms were being satisfactorily controlled with conjugated equine estrogens, either 0.625 mg/day (n = 57) or 1.25 mg/day (n = 67), participated in a study that compared the efficacy of these oral regimens with that of 17 beta-estradiol, 0.1 mg/day, administered through intact skin. The study was a multicenter, double-blind, randomized, parallel-group trial during which two thirds of the patients who received each dosage of conjugated equine estrogens were changed to an estradiol transdermal system while the remainder continued with conjugated equine estrogens. A total of 124 patients was included in the analysis of efficacy. The analysis revealed no significant differences between the estradiol transdermal system and conjugated equine estrogens in control of hot flushes or other postmenopausal symptoms and no statistically significant differences between treatment groups in regard to estrogen-related side effects. Minor topical reactions to the transdermal systems were reported during only about 20% of study weeks. Thus, transdermal estradiol, 0.1 mg/day, appears to be equally effective as conjugated equine estrogens, 0.625 or 1.25 mg/day, for controlling postmenopausal symptoms and is well tolerated.

The effects of ethanol on the transport of lipophilic and polar permeants across hairless mouse skin: Methods/validation of a novel approach

The influence of ethanol on the in vitro transport behavior of some lipophilic and polar/ionic permeants in hairless mouse skin has been investigated over a 0–100% ethanol/saline concentration range in a two-chamber diffusion cell. The lipophilic permeants were employed in probing the transport enhancing effects of ethanol upon the lipoidal pathway of the stratum corneum, and the polar/ionic permeants were used to quantify the influence of ethanol on thepore pathway of the stratum corneum over the entire range of ethanol concentrations. The following were the important interpretations of the data. The lipophilic permeants (estrone, s-estradiol, and hydrocortisone) were mainly transported via the lipoidal pathway up to around 50% ethanol. The permeation enhancement factor, E, for the lipoidal pathway was calcuklated from the transport data for the three lipophilic permeants. In order to calculate the E values, it was first necessary to establish the validity of Henrys law by comparing the ratios of permeant solubilities (in different ethanol/saline solutions) to ratios of permeant partition coefficients (in hexadecane/ethanol-saline systems). The calculated E values were found to be about the same for all three permeants: E = 7.0 ± 2.0 at 25% ethanol and E = 112 ± 19 at 50% ethanol. These large enhancing effects of ethanol upon the lipoidal pathway were somewhat surprising, and it is suggested that ethanol (< 50%) may work as an effective ‘fluidizing’ agent at some locus in the stratum corneum lipid bilayer at or near the polar head plane, but not in the bilayer hydrocarbon interiors. The polar/ionic permeants (tetraethylammonium bromide, mannitol, estrone ammonium sulfate, and vidarabine) all were transported via the pore pathway at all ethanol concentrations. Ethanol up to around 25% had little effect upon the pore pathway; however, at higher concentrations (∼ 50%), ethanol greatly enhanced pore transport and, at very high ethanol levels (t~ 75%), the pore pathway appeared to dominate the transport of all permeants including the lipophilic permeants.

COTRANSPORT OF ESTRADIOL AND ETHANOL THROUGH HUMAN SKIN IN VITRO : UNDERSTANDING THE PERMEANT/ENHANCER FLUX RELATIONSHIP

The thermodynamic and kinetic limits of ethanol-enhanced estradiol skin transport have been investigated by studying the relationship between estradiol and ethanol steady-state flux in the cotransport of permeant and enhancer in situations in which there exists an enhancer solvent gradient across the skin (“asymmetric” configuration). For aqueous ethanol solution saturated with estradiol, the flux of estradiol across the human epidermal membrane is empirically observed to be linear with the ethanol flux. A physical model approach has been used to determine the basis of this empirical linearity and to predict permeant/enhancer transport across the skin for the asymmetric configuration. Enhancement factors, determined with a balanced ethanol concentration across the skin (“symmetric” configurations), are used to predict fluxes in the asymmetric configurations. The model demonstrates that ethanol enhances the stratum corneum transport of estradiol and of itself by increasing the respective diffusion coefficients at lower concentrations (<50%) and by both increasing the diffusion coefficients and decreasing the membrane activity coefficients at moderate concentrations (50 to 75%). The model also demonstrates that the permeant flux, in general, is not linear with the cotransported enhancer flux.

A comparison of contact angle interpretations

Abstract Three methods of interpretation of contact angles in terms of surface tension of liquid and solid are correlated. It is shown that the critical surface tension for wetting γ c is dependant in a specific way on the nature of the liquid system used regardless of the nature of the solid. Equations are derived which express the limiting values γ c may assume for a liquid/solid system. γ c is also correlated with the Good-Girifalco treatment of contact angles and experimentally determined values of the parameter φ are compared with theoretical calculations from molar volumes of normal alcohol-paraffin wax interfaces. The Fowkes method of contact angle interpretation is used to derive values for the polar and dispersion force components of liquid surface tensions for three alcohol/water solution series and two organic acid/water solutions.

Transport of β-Estradiol in Freshly Excised Human Skin in Vitro: Diffusion and Metabolism in Each Skin Layer

This paper describes an experimental and theoretical evaluation of β-estradiol (E2) transport in post-surgery fresh human skin in vitro. Necessary auxiliary experimental methods were newly developed for these studies. The experimental fluxes of E2 and the metabolite, estrone (El), using the dermis, stripped skin, and split-thickness skin were consistent with a model considering the human skin as a three-layer (stratum corneum, viable epidermis, and dermis) membrane with the enzyme activity mainly residing in the basal layer of the viable epidermis. The diffusion and metabolism parameters for each skin layer were determined in the overall transdermal transport of E2. Compared to fresh hairless mouse skin, fresh human skin appears more resistant to the stratum corneum diffusion of E2 and is much less capable of metabolizing E2 to El. These in vitro results have been extrapolated to the possible in vivo human skin situation with blood vessels directly beneath the viable epidermis providing “sink” conditions a short distance from the dermo-epidermal junction. The model analysis has demonstrated that there would be less metabolism and that a much smaller amount of the transdermal metabolite (El) would be taken up by the blood capillary due to the shorter dermis path length for permeants in vivo than in the in vitro case using dermatomed split-thickness skin.

Effectiveness of Alora estradiol matrix transdermal delivery system in improving lumbar bone mineral density in healthy, postmenopausal women.

ObjectiveTo determine the lowest effective dose of an estradiol (E2) matrix-type transdermal delivery system (EMTDS; Alora) for preventing bone loss in postmenopausal women. DesignThis double-blind, double-dummy, randomized, placebo-controlled, multicenter study enrolled 355 nonosteoporotic postmenopausal women who had been hysterectomized with or without oophorectomy at least 12 months earlier. Participants were randomly assigned to one of three doses of the EMTDS (0.025, 0.05, or 0.075 mg/day) or placebo administered twice weekly. Lumbar bone mineral density (LBMD) was measured by dual-energy x-ray absorptiometry at screening and after 1 and 2 years of treatment. Safety was assessed at regularly scheduled visits. ResultsEMTDS provided statistically significant and clinically meaningful changes in LBMD relative to placebo. At 2 years, LBMD declined from baseline by 0.59% in the placebo group, but it increased from baseline by 1.65% (p = 0.0065), 4.08% (p = 0.0001), and 4.82% (p = 0.0001) in the EMTDS 0.025, 0.05, and 0.075 mg/day groups, respectively. The corresponding responder rates (defined as no change or increase in LBMD at endpoint) were 39.7% for placebo, 59.6%, 79.3%, and 83.9% in the EMTDS 0.025, 0.05, and 0.075 mg/day groups, respectively. Mean serum E2 concentrations were proportional to the dose of the E2 transdermal system and did not accumulate over the course of the study. Adverse events were generally comparable across treatment groups, with the majority being mild or moderate in severity and unrelated to study medication. Mammogram findings and other safety assessments were also comparable across groups and did not reveal any safety concerns with 2-y transdermal E2 treatment. ConclusionsThe EMTDS (Alora) administered twice weekly improves lumbar bone mineral density in healthy postmenopausal women, with the benefit of treatment evident by 1 year. The lowest effective dose is 0.025 mg/day.

Quantitation of simultaneous diffusion and metabolism of β-estradiol in hairless mouse skin: Enzyme distribution and intrinsic diffusion/metabolism parameters

Abstract This paper describes a systematic experimental and theoretical study of the simultaneous diffusion and metabolism of β-estradiol (E 2β ) in hairless mouse skin (in vitro). The strategy involved (a) considering a general three-layer skin model (stratum corneum, epidermis, and dermis), (b) considering three possible enzyme distributions (Model A: homogeneous enzyme distribution across both epidermis and dermis; Model B: homogeneous enzyme distribution in the epidermis; and Model C: homogeneous enzyme distribution in the ‘basal cell layer’ only of the epidermis), and (c) carrying out a wide range of independent diffusion experiments so that a ‘best’ model may be deduced in which all of the experimental data are consistent with the model and a single set of transport and metabolism parameters. The various diffusion/metabolism experiments included using three skin membranes (dermis, stripped skin, and full-thickness skin), two membrane configurations (transport of permeants in the direction: stratum corneum → epidermis → dermis, and in the reverse direction), two permeants (E 2β and estrone, E 1 , the principal metabolite), and measuring three fluxes (forward fluxes of E 2β and E 1 and the back flux of E 1 ). Analysis of all of the experimental data demonstrated that Model C was superior to Models B and A; within the uncertainties of the experiments and model fitting, Model C agreed well with the data in all instances while the predictions of Models B and A exhibited significant deviations from the experimental data.

In vivo percutaneous penetration/absorption: Sponsored by the American Association of Pharmaceutical Scientist, U.S. Food and Drug Administration, American Academy of Dermatology, Skin Pharmacology Society and the U.S. Army Environmental Hygiene Agency May 1–3, 1989, Washington, DC

Abstract This workshop, ‘In Vivo Percutaneous Penetration/Absorption’ was held in Washington, DC, on May 1–3, 1989. The first workshop in this series, ‘In Vitro Percutaneous Penetration’, took place in November 1986 (the report of this earlier meeting was published in Pharmaceutical Research , 4 (1987) 265–267). The objectives of the workshop were to review the relevant literature and to address in detail: (1) In vivo percutaneous penetration/absorption methodology; (2) The characteristics of dosage forms designed for application to the skin; (3) Critical factors controlling in vivo drug transport into and across the skin; (4) The use of models in the assessment and evaluation of in vivo percutaneous penetration/absorption; and (5) Bioavailability/bioequivalence considerations for topical drug products. Scientific knowledge and technology are rapidly evolving in the topical and transdermal drug products area. This report focuses on the methodologies available for the measurement of percutaneous penetration in vivo; each scientific approach is discussed briefly followed by advantages and disadvantages of the methodology.