Classification of percutaneous penetration enhancers: a conceptional diagram

Effects and Mode of Action of Oleic Acid and Tween 80 on Skin Permeation of Disulfiram

Oral disulfiram (DSF) has been used clinically for alcohol dependence and recently has been found to have antitumor activity. A transdermal delivery system would be useful for maintaining drug concentration and reducing the frequency of administration of DSF for cancer treatment. Penetrating the stratum corneum (SC) barrier is a challenge to the transdermal delivery of DSF. Therefore, we investigated the promoting effects and mechanism of action of the combination of oleic acid (OA) and Tween 80 on the skin permeation of DSF. Hairless mouse skin was exposed to OA and Tween 80, combined in various ratios (1:0, 2:1, 1:1, 1:2, and 0:1). A permeation experiment was performed, and total internal reflection infrared spectroscopic measurements, differential scanning calorimetry, and synchrotron radiation X-ray diffraction measurements were taken of the SC with each applied formulation. The combination of OA and Tween 80 further enhanced the absorption-promoting effect of DSF, compared with individual application. The peak of the CH₂ inverse symmetric stretching vibration near the skin surface temperature was shifted by a high frequency due to the application of OA, and DSF solubility increased in response to Tween 80. We believe that the increased fluidity of the intercellular lipids due to OA and the increased solubility of DSF due to Tween 80 promoted the absorption of DSF. Our study clarifies the detailed mechanism of action of the skin permeation and promoting effect of DSF through the combined use of OA and Tween 80, contributing to the development of a transdermal preparation of DSF.

[Effects of Skin Environmental Changes by Steam Towel, Ethanol, l-Menthol and Carpronium on the Drug Behavior in the Minoxidil Nanoparticles-applied Mice]

We previously designed the formulation containing minoxidil (MXD) nanoparticles (MXD-NPs), and found that the MXD-NPs can mainly deliver MXD into hair bulbs via hair follicles pathway, and that the therapeutic efficiency for hair growth is higher in comparison with the formulation containing dissolved MXD. In this study, we investigated whether the skin environmental changes by the treatment of steam towel, ethanol, l-menthol and commercially available (CA) carpronium affect the drug behavior in the MXD-NPs-applied mice. The steam towel, ethanol, l-menthol and CA-carpronium were pre-treated 3 min before MXD-NPs application, and the MXD content in the hair bulge, bulb, skin tissue and blood of mice were measured 4 h after MXD-NPs application. No significant difference of MXD levels in the blood was observed by the pre-treatment of steam towel, ethanol, l-menthol and CA-carpronium. On the other hand, the pre-treatment of steam towel and l-menthol enhanced the MXD levels in hair bulge and/or bulb. Although, the MXD levels in hair bulge and bulb were not changed by the pre-treatment of ethanol, the MXD levels in skin tissue was higher than that of saline-pre-treated group (control). The MXD levels in hair bulge, bulb and skin tissue of mice pre-treated with CA-carpronium were remarkably higher in comparison with control. In conclusion, we showed that the changes in skin environment by the steam towel, ethanol, l-menthol and CA-carpronium affected the absorption of MXD-NPs, and these increased MXD levels in the hair bulb and blood by the combination may enhance the therapeutic efficiency without side effects.

Improvement of the skin penetration of hydrophobic drugs by polymeric micelles

Polymeric micelles, which form through the self-assembly of poly(ethylene glycol)-poly(amino acid) block copolymers, are systemic nanocarriers in targeted cancer therapy. These micelles can encapsulate therapeutic compounds, such as lipophilic substances, charged compounds, and metal complexes, that have characteristics of increased solubility, sustained release, and improved tissue distribution. However, few studies have been conducted on the local distribution of polymeric micelles. Thus, we evaluated the skin penetration pattern of hydrophobic drugs in polymeric micelles. We revealed that improved water solubility by the encapsulation of the hydrophobic drugs indomethacin and resveratrol in polymeric micelles significantly increased the amount of drugs penetrating into the skin. Moreover, polymeric micelles did not enhance the permeability of drugs. Furthermore, although the polymers remained on or in the stratum corneum, the encapsulated drugs gradually moved deeper into the skin. These results indicate that encapsulated hydrophobic drugs in polymeric micelles can penetrate the living cell layer of the skin without bringing about unexpected side effects associated with other ingredients in the formulation. Thus, polymeric micelles for encapsulating hydrophobic drugs can be used for skin applications.

Enhancement of skin permeation of flurbiprofen via its transdermal patches using isopulegol decanoate (ISO-C10) as an absorption enhancer: pharmacokinetic and pharmacodynamic evaluation

Objectives

The study aimed to prepare a transdermal patch for flurbiprofen using isopulegol decanoate (ISO-C10) as a permeation enhancer, and to evaluate the in-vitro and in-vivo percutaneous permeation of the drug, as well as the pharmacodynamic efficacy of the formulation.

Methods

The permeation experiments were conducted on rabbit skin, and the pharmacokinetic profiles and synovial fluid drug concentration were measured after in-vivo transdermal administration. A deconvolution approach was employed to analyse the correlation between the in-vitro and in-vivo drug permeation. The anti-inflammatory and analgesic effects were, respectively, assessed using the adjuvant arthritis model and the acetic acid induced pain model.

Key findings

ISO-C10 could increase the in-vitro permeation of flurbiprofen from 46.22 ± 5.65 μg/cm2 to 101.07 ± 10.85 μg/cm2. The in-vivo absorption of the drug was also improved by the enhancer, and a good linear correlation was observed between the in-vitro and in-vivo drug permeation. Meanwhile, the ISO-C10 contained patches increased the drug disposition in synovial fluid and enhanced the pharmacodynamic efficacy of the formulation.

Conclusions

ISO-C10 would be a promising permeation enhancer for improving the in-vitro and in-vivo delivery of flurbiprofen from its transdermal patches.

Percutaneous Penetration Enhancers: An Overview

Transdermal drug delivery is the controlled release of drugs through the skin to obtain therapeutic levels systematically. Several technological advances have been made in the recent decades to enhance percutaneous drug penetration. This overview focuses on the physical, biochemical, and chemical means of penetration enhancement, as well as the classification and mechanisms of chemical penetration enhancers, their application in transdermal drug delivery, and trends and development in penetration enhancement.

Release characteristics of anionic drug compounds from liquid crystalline gels

This is the second in a series of papers that report on the release and transport of a range of anionic drugs (diclofenac, salicylic acid) from liquid crystalline gels and ultimately on their use in transdermal delivery. The previous paper [Fitzpatrick, D., Corish, J., 2005. Release characteristics of anionic drug compounds from liquid crystalline gels for transdermal delivery. Part I. Passive release across non-rate limiting membranes. Int. J. Pharm. 301, 226-236] investigated passive release profiles across a non-rate-limiting membrane: here we report on the search for a suitable model enhancer (benzyl dimethyldodecyl ammonium bromide) for the transdermal delivery of anionic compounds. The results presented reveal a significant role for ion pairing and for buffering, analogous to those found in the investigations of cationic species (salbutamol) by Nolan, L.M.A., Corish, J., Corrigan, O.I., Fitzpatrick, D., 2003. Iontophoretic and chemical enhancement of drug delivery. Part I. Across artificial membranes. Int. J. Pharm. 12, 41-55. The method of vehicle preparation is also investigated. It is shown that ion pairing of the drug with the enhancer decreases the amount of drug available for transport from the liquid crystalline gels into aqueous receptor media. This decrease is directly related to the ratio of the concentration of drug to that of the enhancer. Buffering the vehicle inhibits the ion-pair formation to some extent. Vehicle preparation was also found to influence the degree of ion-pair association. The inclusion of a similarly charged enhancer (oleic acid) to the drug was found not to impede the diffusion of the drug from the gels.

Novel mechanisms and devices to enable successful transdermal drug delivery

Optimisation of drug delivery through human skin is important in modern therapy. This review considers drug-vehicle interactions (drug or prodrug selection, chemical potential control, ion pairs, coacervates and eutectic systems) and the role of vesicles and particles (liposomes, transfersomes, ethosomes, niosomes). We can modify the stratum corneum by hydration and chemical enhancers, or bypass or remove this tissue via microneedles, ablation and follicular delivery. Electrically assisted methods (ultrasound, iontophoresis, electroporation, magnetophoresis, photomechanical waves) show considerable promise. Of particular interest is the synergy between chemical enhancers, ultrasound, iontophoresis and electroporation.

Percutaneous penetration enhancement and its quantification

True penetration enhancing effects resulting from structural alterations of the barrier stratum corneum manifest themselves in an increase of the drug diffusion coefficient DB and/or of the drug solubility in the barrier csB. The quantification of enhancing effects on drug penetration is possible either by the direct determination of the drug fluxes or by an indirect determination through the measurement of the pharmacodynamic response. In both cases the thermodynamic drug activity has to be considered. In the case of pharmacodynamic measurements, enhancing effects may be determined from the horizontal distance of activity-response lines obtained without and with enhancer, respectively, i.e. the quotient of the drug concentrations that induce the same effect. The activity-standardized bioavailability factors fa obtained from the horizontal distances correspond to the enhancer-induced relative changes in the permeabilities PB, or more exactly in the product DB X csB. On the other hand, the vertical distance between the activity-response lines, i.e. the differences in the drug response after application of preparations with equal (even maximum) thermodynamic drug activities may be used to quantify penetration enhancing effects.

The biomechanics and histopathology of chemically processed patellar tendon allografts for anterior cruciate ligament replacement

A study was initiated to examine chemically processed patellar tendon allografts in sheep anterior cruciate ligament repairs, both mechanically and histologically. One group of animals received frozen, untreated allografts, one group received frozen grafts that were processed with a chloroform-methanol solvent extraction technique, and one group received frozen tendons treated with a permeation-enhanced extraction technique. All animals were operated on unilaterally, with the contralateral knee acting as a normal, intact control. Histologic analysis after 2 months of implantation revealed similar enhanced cellular repopulation in both chemically treated ligament allografts compared with the more hypocellular, untreated grafts. At 6 months the chloroform-methanol group demonstrated a more aggressive chronic cellular response with numerous thick-walled vessels relative to the untreated and permeation-enhanced grafts. Mechanical testing after 6 months of implantation showed statistically similar anterior drawer resistance in all grafted knees, yet the two chemically extracted grafts had significantly less stiffness than untreated anterior cruciate ligament grafts. Both treatment groups also tended to be weaker than the untreated allografts. All anterior cruciate ligament reconstructions showed excessive anterior drawer laxity and, regardless of treatment, had lower strength and less stiffness than normal anterior cruciate ligament tissue at the 6-month period.

Analysis of the combined effect of 1-menthol and ethanol as skin permeation enhancers based on a two-layer skin model

The combined effects of 1-menthol and ethanol as a skin permeation enhancer were evaluated with two equations describing the permeability coefficient through full-thickness skin (PFT) and the full-thickness skin/vehicle concentration ratio (CFT/CV) of drugs as a function of their octanol/vehicle partition coefficient (KOV). A two-layer model was applied for skin, which consists of a stratum corneum (SC) with lipid and porous pathways and a viable epidermis and dermis (ED). The two equations contain one variable (KOV) and nine coefficients, six of which (three diffusion coefficients, the porosity of the SC, and two terms of the linear free energy relationship) were considered different, dependent on the drug vehicle. In vitro permeation of four drugs (morphine hydrochloride, atenolol, nifedipine, and vinpocetine) was determined using excised hairless rat skin and four aqueous vehicles (water, 5% 1-menthol, 40% ethanol, and 5% 1-menthol-40% ethanol) to measure each PFT. Drug concentrations in full-thickness skin were also measured to obtain CFT/CV. A nonlinear least-squares method was employed to determine six coefficients using the two equations and experimentally obtained PFT and CFT/CV. The addition of 1-menthol to water and 40% ethanol increased the diffusion coefficient of drugs in lipid and pore pathways of SC, whereas the addition of ethanol to water and 5% 1-menthol increased the drug solubility in the vehicle, decreased the skin polarity, and increased the contribution of the pore pathway to whole-skin permeation.

Role of the appendageal pathway in the percutaneous absorption of pyridostigmine bromide in various vehicles

We studied the percutaneous absorption of [14C]-labelled pyridostigmine bromide mixed into various vehicles through normal and appendage-free scar rat skin, in vitro during 72 h. At the end of the experiment, the percentages of the drug absorbed were higher for nerol 8% in ethanol (respectively 78.4 +/- 3.6% and 72.8 +/- 4.5% on normal and scar skin) and azone 5% in ethanol-propylene glycol (90:10) (respectively 76.4 +/- 4.4% and 57.2 +/- 7.1% on normal and scar skin). Propylene glycol 10% in ethanol inhibits pyridostigmine absorption: 9.9 +/- 2.6% and 2.2 +/- 1.2% vs 14.7 +/- 3.8% and 5.5 +/- 5.1% with ethanol on control and scar skin. The transappendageal pathway seems to be less important for nerol (55% to 82% of the absorption routes between 4 h and 32 h) and azone (60% to 79% of the absorption routes until 32 h) than for propylene glycol (63% to 96% of the absorption pathways during the whole experiment), dimethylsulfoxide (about 78% during the first 32 h) and ethanol (more than 50% during most of the time). These results show that it is possible to increase or decrease the percutaneous absorption, as well as to modulate the relative importance of the transepidermal route and the transfollicular pathway.