Transdermal delivery of estradiol in postmenopausal women with a novel topical aerosol

Improvement of adult female acne with a novel weekly oestradiol-loaded peel-off mask: a split-face placebo-controlled study

BACKGROUND

Adult female acne (AFA) is characterized by a relapsing eruption of acne in women aged ≥ 25 years. It can be slower to respond to traditional adolescent acne treatments. Usually, androgens promote acne by stimulating sebum production, while oestrogens have the -opposite effect by reducing sebum output when present in adequate quantities. Oestradiol is a female sex hormone that has its highest absolute serum levels and highest oestrogenic activity during the reproductive years. Peel-off facial masks have been suggested to intensify the effect of added active ingredients by forming an occlusive film after drying.

OBJECTIVES

To study the safety and efficacy of weekly topical oestradiol 0.05% in the treatment of AFA.

METHODS

Twenty women with AFA were subjected to once-weekly application of an oestradiol 0.05% mask or placebo mask to either side of their face for 8 weeks. An acne lesion count was performed at baseline, at each visit and 8 weeks post-treatment.

RESULTS

At the end of the treatment period, the treated side showed significant improvement in comedones, papules and pustules. Although lesion counts increased 2 months post-treatment, they remained significantly less common on the oestradiol-treated side compared with the side of the face treated with placebo. No side-effects were reported. Limitations included the small number of patients studied and the short follow-up period. The oestradiol effect was not studied at the cellular or molecular levels.

CONCLUSIONS

Topical oestradiol peel-off masks may be a promising convenient, safe and effective treatment for AFA.

Enhanced in vitro and ex vivo transdermal permeation of microemulsion gel of tapentadol hydrochloride

Aim of the current study is to develop a microemulsion gel for transdermal delivery of tapentadol hydrochloride. Microemulsion was developed using phase diagram and subjected to assay, globule size, PDI, zeta potential, TEM and in vitro drug release studies. The optimized microemulsion was converted into gel using carbopol 934 NF and evaluated for viscosity, spreadability, in vitro, ex vivo, FTIR, DSC, stability and skin irritation studies. The mean globule size, PDI, zeta potential and in vitro drug release of microemulsion were found 247.3 nm, 0.298, -17.6 mV and 98.42% respectively. In vitro and ex vivo drug release of gel was found 92.2% and 88.6% in 24 h. Viscosity and spreadability results indicated ease of application and no incompatibility was observed from FTIR studies. The skin irritation studies showed absence of erythema. Key findings from the current research concluded that microemulsion gel was suitable for effective transdermal delivery.

Effects of solvent on percutaneous absorption of nonvolatile lipophilic solute

Understanding the effects of solvents upon percutaneous absorption can improve drug delivery across skin and allow better risk assessment of toxic compound exposure. The objective of the present study was to examine the effects of solvents upon the deposition of a moderately lipophilic solute at a low dose in the stratum corneum (SC) that could influence skin absorption of the solute after topical application. Skin permeation experiments were performed using Franz diffusion cells and human epidermal membrane (HEM). Radiolabeled corticosterone ((3)H-CS) was the model permeant. The solvents used had different evaporation and skin penetration properties that were expected to impact skin deposition of CS and its absorption across skin. The results show no correlation between the rate of absorption of the permeant and the rate of solvent evaporation/penetration with ethanol, hexane, isopropanol, and butanol as the solvent; all of these solvents have fast evaporation rates (complete evaporation in <30 min after application). This suggests no differences in solvent-induced deposition of CS in the SC for the fast-evaporating solvents. The results of these fast-evaporating solvents were different from those of water, propylene glycol, and polyethylene glycol 400, that a relationship between permeant absorption and the rate of solvent evaporation was observed.

Spray-on transdermal drug delivery systems

INTRODUCTION

Transdermal drug delivery possesses superior advantages over other routes of administration, particularly minimizing first-pass metabolism. Transdermal drug delivery is challenged by the barrier nature of skin. Numerous technologies have been developed to overcome the relatively low skin permeability, including spray-on transdermal systems.

AREAS COVERED

A transdermal spray-on system (TSS) usually consists of a solution containing the drug, a volatile solvent and in many cases a chemical penetration enhancer. TSS promotes drug delivery via the complex interplay between solvent evaporation and drug-solvent drag into skin. The volatile solvent carries the drug into the upper layers of the stratum corneum, and as the volatile solvent evaporates, an increase in the thermodynamic activity of the drug occurs resulting in an increased drug loading in skin.

EXPERT OPINION

TSS is easily applied, delivering flexible drug dosage and associated with lower incidence of skin irritation. TSS provides a fast-drying product where the volatile solvent enables uniform drug distribution with minimal vehicle deposition on skin. TSS ensures precise dose administration that is aesthetically appealing and eliminates concerns of residual drug associated with transdermal patches. Furthermore, it provides a better alternative to traditional transdermal products due to ease of product development and manufacturing.

Performance of transdermal therapeutic systems: Effects of biological factors

Transdermal drug delivery (TDD) is a technique that is used to deliver a drug into the systemic circulation across the skin. This mechanism of drug delivery route has many advantages, including steady drug plasma concentrations, improved patient compliance, elimination of hepatic first pass, and degradation in the gastrointestinal tract. Over the last 30 years, many transdermal products have been launched in the market. Despite the inherent advantages of TDD and the growing list of transdermal products, one of the major drawbacks to TDD is the occurrence of inter- and intraindividual variation in the absorption of the drug across the skin. A majority of these variations are caused by biological factors, such as gender, age, ethnicity, and skin hydration and metabolism. These factors affect the integrity and the barrier qualities of the skin, which subsequently result in the variation in the amount of drug absorbed. The main objective of this review article is to provide a concise commentary on the biological factors that contribute to the variation in transdermal permeation of drugs across human skin and the available transdermal therapeutic systems that may reduce the variations caused by biological factors.

Dermal delivery of desmopressin acetate using colloidal carrier systems

Recently, the transdermal route has received attention as a promising means to enhance the delivery of drug molecules, particularly peptides, across the skin. In this work, the skin penetration profiles of desmopressin acetate from a colloidal system (water-in-oil microemulsion) and an amphiphilic cream, a standard formulation, were determined using Franz diffusion cells and compared. In the case of the microemulsion, the total percentages of dose obtained from different skin layers (stratum corneum to subcutaneous tissue) were 3.30 ± 0.67, 7.37 ± 2.43 and 15.54 ± 2.72 at 30, 100 and 300 min, respectively. Similarly, 5.19 ± 0.96, 8.04 ± 0.97 and 14.4 ± 5.15% of the dose applied was extracted from the skin treated with the cream. About 6% of the applied dose reached the acceptor compartment from the microemulsion instead of 2% from the cream within 300 min. The concentration of drug that penetrated into the upper layers of the skin was higher from the cream than from the microemulsion at all time intervals. On the other hand, a higher amount of drug was found in the deeper skin layers and in the acceptor compartment from the microemulsion.

Effects of solvent deposited enhancers on transdermal permeation and their relationship with Emax

Many topical pharmaceuticals such as aerosols, topical sprays, and hydro-alcoholic and polymer based gels contain chemical enhancers. The objectives of the present study were to (a) determine the enhancement effects induced by enhancers deposited from a volatile solvent on human epidermal membrane (HEM) upon transdermal permeation enhancement, (b) compare these enhancement factors with Emax, and (c) examine the relationship between enhancer-induced permeation enhancement and stratum corneum equilibrium uptake enhancement. In this study, HEM was treated with enhancer/ethanol (enhancer dissolved in ethanol). After the evaporation of ethanol, passive transport experiments were conducted using corticosterone (CS) as the model permeant. The uptake of another model corticosteroid, estradiol (E2beta), into the intercellular lipid domain of stratum corneum after enhancer/ethanol treatment was also determined. The results show a correlation between Emax and the enhancement effect of most enhancers when the enhancers were deposited on the skin using the volatile solvent ethanol. The data suggest that the CS transport rate limiting domain was likely the same as the intercellular lipid domain probed by E2beta uptake. The correlation between steady-state permeation enhancement and uptake enhancement into the intercellular lipid domain suggests that the permeation enhancement mechanism is primarily due to enhancement of permeant partitioning into the transport rate limiting domain.

Drug delivery systems for hormone therapy

Various types of formulations and delivery devices have been developed for hormone therapy (HT) and their modes of hormone action and patient responses have been evaluated. Although the Women's Health Initiative (WHI) reported the controversial results on estrogen/progestin combination therapy, HT still remains a primary therapeutic option for the treatment of menopausal symptoms and osteoporosis. As a novel alternative to HT may not be probable in clinical use for the next decade, the currently available formulations containing estrogen and progestogen should be properly optimized for HT. The extensive reviews and comparisons on the characteristics of various types of HT could lead to the development of an efficient delivery formulation which maximizes patient compliance and minimizes adverse effects for individual users.

Buccal penetration enhancers--how do they really work?

Certain agents that increase drug delivery through the skin, including surfactants, bile salts, and fatty acids, have been shown to exert a similar effect on the buccal mucosa. These agents enhance skin permeability by interacting with and disrupting the ordered intercellular lipid lamellae within the keratinized stratum corneum, and it has been assumed that a similar mechanism of action occurs in the nonkeratinized buccal mucosa. However, the chemical and structural nature of the lipids present within the intercellular regions of the buccal mucosa is quite different to that found within the stratum corneum, and so extrapolation of results between these two tissues may be misleading. To assume that the mechanism of action of buccal penetration enhancers is based on the disruption of intercellular lipids may be erroneous, and may result in the inappropriate prediction that certain skin penetration enhancers will similarly enhance drug delivery through the buccal mucosa. The data available in the literature suggest that agents that enhance buccal penetration exert their effect by a mechanism other than by disruption of intercellular lipids. Rather, buccal penetration enhancement appears to result from agents being able to (a) increase the partitioning of drugs into the buccal epithelium, (b) extract (and not disrupt) intercellular lipids, (c) interact with epithelial protein domains, and/or (d) increase the retention of drugs at the buccal mucosal surface. The purpose of this review is to identify the major differences in the structural and chemical nature of the permeability barriers between the buccal mucosa and skin, to clarify the mechanisms of action of buccal penetration enhancers, and to identify the limitations of certain models that are used to assess the effect of buccal penetration enhancers.

Mechanisms of action of novel skin penetration enhancers: Phospholipid versus skin lipid liposomes

Employing thermal analysis, we investigated the mechanism of action of novel enhancers and probed phospholipid (PL) versus stratum corneum lipid (SCL) liposomes as model membranes. The enhancers included octyl salicylate (OS), padimate O (PADO) and 2-(1-nonyl)-1,3-dioxolane (ND). The negative controls were the empty liposomes. Positive controls employed dimethylsulfoxide (DMSO) and Azone (AZ). For PL liposomes, DMSO sharpened the transitions. AZ abolished the pre-transition, broadened the main transition and linearly reduced its transition temperature (T(m)). OS or PADO reduced T(m) and size of pre-transition, broadened the main transition and decreased its T(m) (non-linearly). ND abolished the pre-transition but increased T(m) of the main endotherm, suggesting retardation rather than enhancement. The results of SCL correlated with PL liposomes except for ND. In SCL liposomes, ND reduced T(m) and broadened the peaks indicating lipid disruption, which indicated its enhancing effects. In conclusion, OS, PADO and ND can enhance drugs by disrupting intercellular lipid domain but they differ from AZ in terms of the relationship between efficacy and concentration. Although PL liposomes are simple model membranes with sharp transitions which give detailed information about the effects of enhancers, they can provide misleading results. Simultaneous use of other models like SCL liposomes is recommended.

Synergistic enhancement of testosterone transdermal delivery

In this study, the effects of occlusion, octisalate (OS), and propylene glycol (PG) on the in vitro skin permeability of testosterone (TES) have been investigated. TES (either alone or with OS 5% w/v) was applied as a finite dose to full-thickness neonatal porcine skin mounted in flow-through diffusion cells and the amount of TES appearing in the receptor solution (20% v/v ethanol) was determined over 24 h. The skin was occluded with a microscope glass cover slip and to determine the effect of PG, 400 microl of PG/water mixtures (of varying PG concentration) was applied. In addition, the effect of Solugel (a proprietary hydrogel containing PG 25% w/w) and Tegaderm (a semipermeable film dressing) on the permeation of TES was assessed. Occlusion had no effect on the permeation of TES, however, OS increased the flux of TES 2.9-fold. The concentration of PG which produced optimal TES flux was 20% v/v, and this concentration resulted in a 1.9-fold increase in TES permeation. By combining OS, PG, and occlusion, TES permeation was increased 8.7-fold, which was a synergistic enhancement. In addition, Solugel and Tegaderm, when applied to the skin, produced a similar enhancement in TES permeation to that produced by PG 25% w/w and occlusion.

Enhanced Buccal Mucosal Retention and Reduced Buccal Permeability of Estradiol in the Presence of Padimate O and Azone®: A Mechanistic Study

In previous experiments, it was suggested that the reduction in estradiol (E2) buccal permeability after pretreatment with some skin penetration enhancers was attributed to enhanced membrane storage. To verify this, further in vitro permeability experiments were performed and the kinetics of E2 buccal mucosal uptake and permeability was assessed. Porcine buccal mucosa was pretreated with the skin penetration enhancers octisalate, padimate O (PO), or Azone (AZ) and placed in modified Ussing chambers. The disappearance of E2 from the donor chamber and appearance of E2 in the receptor chamber was then monitored over 4 h. The final concentration of E2 associated with the buccal mucosa and donor chamber walls in the presence of each enhancer was also determined. The rate of E2 disappearance from the donor chamber was 3.1-fold greater than the rate of E2 appearance in the receptor chamber, indicating significant membrane storage of E2. Pretreatment with PO and AZ significantly increased the rate of E2 disappearance and reduced the rate of E2 appearance in the receptor chamber. The corresponding enhancement in E2 tissue concentration after PO and AZ pretreatment was 1.7- and 3-fold, respectively. However, PO and AZ also increased the amount of E2 adsorbed to the walls of the donor chamber, which contributed to the reduction in E2 flux through the buccal mucosa.

Optical spectroscopy of hydrophobic sunscreen molecules adsorbed to dielectric nanospheres

Fluorescence and absorption spectra of hydrophobic sunscreens, weakly fluorescent octyl methoxycinnamate, moderately fluorescent octyl salicylate and highly fluorescent 2-ethylhexyl-4-(dimethylamino)benzoate (padimate O) adsorbed to dielectric microspheres in aqueous suspension, have been compared with spectra in organic solution. The fluorescence of adsorbed salicylate and padimate is enhanced compared with fluorescence in methanol: about a factor of 6 and 30 in terms of fluorescence yield per molecule of salicylate and padimate, respectively. Cinnamate, which has a low fluorescence yield, does not show a comparable fluorescence enhancement. The fluorescence amplification is independent of sphere diameter from 30 to 1500 nm, at least for salicylate. The enhancement, as well as the location of absorption spectral peaks, is consistent with a low-dielectric constant environment of the molecules, in spite of the presumed location near the interface between polystyrene (epsilon = 2.4-3.8) and water (epsilon = 78). The adsorbed state of these sunscreens represents a proposed improved in vitro model for the environment of sunscreens in vivo, as well as a general model for chromophores in heterogeneous environments.

Skin deep

Over the past 30 or so years there has been a considerable advance in our knowledge of the mechanisms of skin permeation. This has largely been brought about by the development of sophisticated biophysical techniques and increased computing powers. The advanced technology has clearly provided indications, at a molecular level, about routes of permeation and how the barrier function can be modulated by excipients with which actives are formulated. This publication reviews some of the advances that have been made and mathematical models that have been constructed to predict percutaneous penetration and transdermal delivery. The models also indicate the various enhancement strategies that can be used in dermal penetration. In the past, it has been difficult to identify precise mechanisms of action of the different classes of enhancer but a combination of appropriate biophysical techniques, mathematical modelling and chemometric analysis can help identify the contributing processes. The models can also be used to indicate rate control in transdermal delivery, whether it is in the applied delivery device or in the skin.

Modification of buccal drug delivery following pretreatment with skin penetration enhancers

The effect of the lipophilic skin penetration enhancers octisalate (OS), padimate O (PO), and Azone (AZ) on in vitro buccal permeability was assessed using caffeine (CAF), estradiol (E2), and triamcinolone acetonide (TAC) as model permeants. Buccal permeability was assessed in modified Ussing chambers, through both untreated porcine buccal mucosa and mucosa pretreated with an enhancer (5% w/v in 95% v/v ethanol) or ethanol alone. To ensure sink conditions were present, E2 permeability experiments were also performed with bovine serum albumin (BSA) 4% in the receptor solution. Mucosa-buffer partition studies were performed to determine the effect of enhancer pretreatment on the log mucosa-buffer partition coefficient (logK) of E2 and TAC. CAF permeability was only increased following pretreatment with ethanol 95%. E2 buccal transport was not altered following OS pretreatment, but was reduced by 26.3% with PO pretreatment and 67.6% with AZ pretreatment. Similar results were obtained with BSA 4% in the receptor solution. The logK of E2 was increased 1.4-fold and 2.2-fold in PO- and AZ-pretreated tissues, respectively, suggesting that the reduction in flux caused by PO and AZ may have been due to enhanced E2 tissue retention. The effect of OS and PO on TAC permeability was no different to that of ethanol. However, AZ enhanced TAC permeability 4.1-fold and this was accompanied by a 2.4-fold increase in the logK of TAC.

Active ingredients in sunscreens act as topical penetration enhancers for the herbicide 2,4-dichlorophenoxyacetic acid

Agricultural workers are encouraged to use sunscreen to decrease the risk of UV-related skin cancer. Our previous studies have shown certain commercial sunscreens to be penetration enhancers. The focus of this project is to determine whether active ingredients in sunscreen formulations (i.e., the UV absorbing components and insect repellants for the sunscreen/bug repellant combinations) also act as dermal penetration enhancers for herbicides in vitro. The total percentages of 2,4-dichlorophenoxyacetic acid (2,4-D) penetrating through hairless mouse skin in 24 h ranged from 54.9 +/- 4.7 for the no sunscreen control to 86.9 +/- 2.5 for padimate-o. Of the active ingredients tested (7.5% octyl methoxycinnamate, 7% octocrylene, 0.6% oxybenzone, 5% homosalate, 5% octyl salicylate, 8% padimate-o, 10% sulisobenzone, and 9.5% and 19% N,N-diethyl-m-toluamide [DEET]), all but octocrylene led to a significant increase in total 2,4-D penetration as compared to the control (P < 0.05), and only octocrylene and oxybenzone did not significantly decrease the corresponding lag time. Octyl salicylate (P < 0.01) and octyl methoxycinnimate (P < 0.05) significantly increased the 3H2O penetration across mouse skin, indicating physical damage to the stratum corneum. Additional studies demonstrated that the penetration enhancement seen across hairless mouse skin also occurred with human skin. Thus, the active ingredients of sunscreen formulations enhance dermal penetration of the moderately lipophilic herbicide 2,4-D.

Transdermal delivery of drugs for the treatment of bone diseases

The current status of transdermal drug delivery for the treatment of bone diseases is described in this review. The structure, physiology and function of skin and their importance in determining delivery into and across skin are discussed. Special emphasis has been devoted to a description of the major pathways of transport across the skin and the quite continuing controversy over the importance of the transfollicular route. An overview of anatomic site-dependent drug absorption is also provided and is particularly relevant to determination of transdermal patch location. Brief descriptions of the criteria for selection of transdermal drug candidate, transdermal patch designs and currently marketed transdermal products are also included. Transdermal estradiol delivery systems are examined in more detail for their clinical and biological effects. Finally, the feasibility of delivering drugs such as bisphosphonates across skin is discussed.