Effect of saline iontophoresis on skin barrier function and cutaneous irritation in four ethnic groups.

The effect of saline iontophoresis on skin barrier function and irritation was investigated in four ethnic groups (Caucasians, Hispanics, Blacks and Asians). Forty healthy human volunteers were recruited according to specific entry criteria. Ten subjects, five males and five females, were assigned to each ethnic group. Skin barrier function was examined after 4 hours of saline iontophoresis at a current density of 0.2 mA/cm(2) on a 6.5 cm(2) area in terms of the measured responses: transepidermal water loss (TEWL), skin capacitance, skin temperature and visual scores. There were significant differences in TEWL among the ethnic groups prior to patch application. TEWL at baseline in ethnic groups was in the rank order: Caucasian>Asian>Hispanic>Black. Iontophoresis was generally well tolerated, and skin barrier function was not irreversibly affected by iontophoresis in any group. There was no significant skin temperature change, compared to baseline, in any ethnic groups at any observation point. Edema was not observed. At patch removal, the erythema score was elevated in comparison to baseline in all ethnic groups; erythema resolved within 24 hours. Thus, saline iontophoresis produced reversible changes in skin barrier function and irritation in healthy human subjects.     

An in vivo investigation of the rabbit skin responses to transdermal iontophoresis

To optimize the benefits of transdermal iontophoresis, it is necessary to develop a suitable animal model that would allow for extensive assessments of the biological effects associated with electro-transport. Rabbit skin responses to iontophoresis treatments were evaluated by visual scoring and by non-invasive bioengineering parameters and compared with available human data. In the current density range 0.1–1.0 mA/cm² applied for 1 h using 0.9% w/v NaCl and 0.5 mA/cm² for up to 4 h, no significant irritation was observed. 2 mA/cm² applied through an area of 1 cm² for 1 h resulted in slight erythema at both active electrode sites but without significant changes in transepidermal water loss (TEWL) and laser Doppler velocimetry (LDV). A value of 4 mA/cm² under similar conditions caused moderate erythema at the anode and cathode with TEWL and LDV being significantly elevated at both sites; 1 mA/cm² current applied for 4 h, caused moderate erythema at both anode and cathode; and 1 mA/cm² applied for 1 h caused no irritation when the area of exposure was increased from 1 to 4.5 cm². When significant irritation and barrier impairment occurred, the erythema was resolved within 24 h with barrier recovery complete 3–5 days post-treatment. Rabbit skin thus shows promise as an acceptable model for iontophoresis experiments.     

Dermal toxicity and microscopic alterations by JP-8 jet fuel components in vivo in rabbit

In this study, we investigated the skin irritation, macroscopic and microscopic barrier alteration in vivo in rabbits from aliphatic and aromatic components of jet propellant-8 (JP-8) jet fuel. Macroscopic barrier properties were evaluated by measuring transepidermal water loss (TEWL), skin capacitance, and skin temperature; microscopic changes were observed by light microscopy. Draize visual scoring system was used to measure skin irritation. We found significant (P<0.05) increase in temperature at the site of all chemically saturated patches immediately after patch removal in comparison to the control site. Tridecane (TRI) produced a greater increase in temperature and capacitance at all time points than all the other components of JP-8. Both the aliphatic and aromatic components increased the TEWL at all time points. Tridecane produced greater increase in TEWL followed by naphthalene (NAP), 1-methylnaphthalene (1-MN), 2-metylnaphthalene (2-MN), tetradecane (TET), and dodecane (DOD). All of the above components of JP-8 caused moderate to severe erythema and edema, which were not resolved to the baseline even after 24 h of patch removal. Light microscopy revealed an increase in epidermal thickness (ET), and decrease in length and thickness of collagen fibers’ bundle by the above components of JP-8. These results suggest potential dermatotoxicity from the JP-8 components.     

Pharmacokinetics of a rivastigmine transdermal patch formulation in healthy volunteers: relative effects of body site application

A patch formulation of rivastigmine, an inhibitor of acetylcholinesterase and butyrylcholinesterase, is under development. The current objective was to evaluate the pharmacokinetic profile and patch adhesiveness following application at the upper back, chest, abdomen, thigh, and upper arm. In a single-dose, open-label, crossover study with 40 (42.5% men) healthy subjects, a 10-cm(2) patch containing 18 mg rivastigmine was applied to each body site. Median t(max) was 16 hours for all sites except the thigh (22 hours). Exposure levels and C(max) were highest at the upper back, chest, and upper arm sites. Adhesiveness was greatest when applied to the thigh, followed by the abdomen, upper arm, chest, and upper back, although no statistically significant correlations with pharmacokinetic parameters were found, except at the chest (P=.02). Pharmacokinetic profiles and adhesiveness of the upper back, chest, and upper arm, coupled with low rates of erythema at these sites, suggest their suitability for clinical use.     

Transdermal Delivery of Interferon Alpha-2B using Microporation and Iontophoresis in Hairless Rats

Purpose To demonstrate transdermal delivery of interferon alpha-2b (IFNα2b) in hairless rats through aqueous microchannels (micropores) created in the skin and enhanced by iontophoresis. Materials and Methods The Altea Therapeutics PassPort™ System was configured to form an array of micropores (2.0 cm²; 72 micropores/cm²) on the rat abdomen. The transdermal patch (Iomed TransQ1-GS-hydrogel) was saturated with an IFNα2b solution (600 μg/ml) and applied for 4 h. Delivery was evaluated with and without cathodic iontophoresis (0.1 mA/cm²). Intravenous delivery (0.4 μg/100 g body weight) was performed to support pharmacokinetic calculations. Results IFNα2b was not delivered through intact skin by itself (passive delivery) or during iontophoresis. However, passive delivery through micropores was achieved in vivo in rats. A dose of 397 ± 67 ng was delivered over 6 h, with steady state serum concentrations reaching a plateau at 1 h post-patch application. These levels dropped rapidly after patch removal, and returned to baseline within 2 h of patch removal. Iontophoresis-enhanced delivery through micropores resulted in a two-fold increase in the dose delivered (722 ± 169 ng) in the hairless rat. Conclusions In vivo delivery of IFNα2b was demonstrated through micropores created in the outer layer of the skin. Iontophoresis enhanced delivery through microporated skin in hairless rats.     

Percutaneous absorption and skin irritation of JP-8 (jet fuel)

JP-8 is the major jet fuel used by US Army and Air Force. The purpose of the present study was to investigate the percutaneous absorption of JP-8 across pig ear skin and human skin in vitro and to study the effect of JP-8 exposure on the skin barrier function and irritation in Yucatan minipigs. JP-8 spiked with 5.0 microCi of radiolabeled (14C) tridecane, nonane, naphthalene or toluene (selected components of JP-8) was used for the in vitro percutaneous absorption studies with excised pig ear skin and human skin. For in vivo studies, 250 microl of JP-8 or two of its components (toluene or nonane) was placed in a Hill top chamber(R) and affixed over the marked treatment area for 24 h. Transepidermal water loss (TEWL), skin capacitance (moisture content) and skin irritation (erythema and edema) were evaluated before treatment and at 1,2 and 24 h after removal of the patches. The components of JP-8 such as tridecane, nonane, naphthalene and toluene permeated significantly through pig ear skin and human skin and the permeation rates were found to be proportional to their composition in JP-8. The steady state flux values of tridecane across pig ear skin and human skin did not differ significantly (P>0.05). Though the steady state flux values of nonane, naphthalene and toluene were statistically different between porcine and human skin (P<0.01), the values were close considering the large variations usually observed in the percutaneous absorption studies. Application of toluene, nonane or JP-8 increased the TEWL, JP-8 being the highest (3.5 times at 24 h compared to baseline level). The skin moisture content decreased after the application of JP-8, though it was not significantly different (P>0.05) from the baseline level. JP-8 caused a moderate erythema and a moderate to severe edema. Though the edema decreased after 24 h, the degree of erythema remained about the same until 24 h. The skin irritation caused by JP-8 was greater than neat toluene or nonane. The TEWL data of toluene, nonane and JP-8 correlated well with the skin irritation data (erythema and edema). Exposure of JP-8, which contains hundreds of aliphatic and aromatic hydrocarbons, caused significant changes in the barrier function of the skin as indicated by an increase in TEWL and produced a significant erythema and edema in minipigs. Furthermore, the disruption of barrier function of skin, as indicated by increased TEWL after exposure to JP-8 might result in increased permeation of its own components and/or other chemicals exposed to skin. The present study provides further evidence that pig ear skin may be used as a model for predicting the rates of permeation of chemicals through human skin.     

The vulva is relatively insensitive to menses-induced irritation

Skin patch testing of menses and venous blood on the vulva (labia majora) and the upper arm was performed to assess the potential contribution of these biological fluids to vulvar irritation during menstruation. After 24 and 48 hours of occlusive exposure, the skin of the labia majora was relatively unaffected by these fluids compared to the skin of the upper arm: no significant irritation was observed on the labia at either exposure time, but discernible irritation was elicited on the upper arm after 48 hours of exposure. Pre-treatment of the upper arm with a petrolatum-based emollient attenuated the upper arm response. Semi-occlusive conditions also reduced the degree of upper-arm irritation elicited test materials and an irritant control, sodium lauryl sulfate. The relative insensitivity of the vulva to irritation by menses or blood was not predictable a priori because some irritants elicit heightened responses on the vulva relative to the arm (3). These results suggest that the vulva (labia majora) may be adapted to be less sensitive to menses-induced skin irritation than other anatomical sites.     

Sodium lauryl sulfate-induced irritation in the human face: regional and age-related differences

The particular sensitivity of the human face to care products prompted us to study irritation induced by sodium lauryl sulfate (SLS) in its various regions. We examined regional and age-related differences, correlating basal transepidermal water loss (TEWL) and capacitance to SLS irritation. SLS (2% aq.) was applied under occlusion for 1 h to the forehead, cheek, nose, nasolabial and perioral areas, chin, neck and forearm to two groups of subjects--one with 10 subjects with an average age of 25.2 +/- 4.7 years and another with 10 subjects with an average age of 73.7 +/- 3.9 years. TEWL was measured before and 1 h and 23 h after patch removal. Baseline stratum corneum hydration was also measured. Irritation was assessed by the changes in TEWL (deltaTEWL = TEWL after patch removal - basal TEWL) after corrections to the control. In the younger group, all areas of the face and the neck reacted to SLS, whereas the forearm did not. In the older group, the nose, perioral area and forearm did not react. In both age groups, some significant differences between the regions of the face were detected. The younger group showed higher changes in TEWL than the older group in all the areas studied, but only in the chin and nasolabial area were the differences statistically significant. Significant correlations were found between basal TEWL and deltaTEWL in 5 of the 7 areas which reacted to SLS. Baseline TEWL is one parameter that correlates with the susceptibility of the face to this irritant.     

The Effect of Saline Iontophoresis on Skin Integrity in Human Volunteers: I. Methodology and Reproducibility

This study, conducted in 36 human volunteers, was an evaluationof the effects of saline iontophoresis on skin temperature,irritation, and barrier function. The major objectives wereto assess the effects of low-level ionic currents, to validatethe proposed methodology of assessment, and to establish reproducibilityin repeated saline iontophoresis applications. This was thefirst of a multistage study designed to assess the safety of24-hr saline iontophoresis episodes at selected currents andcurrent densities. Since an iontophoresis patch challenges theskin harrier both by occluding the skin surface and by passingionic current through the skin, the experimental protocol wasdesigned to permit measurement of the contribution of each ofthese processes to the overall response. In this first stagewe investigated the effect of 10 min of current delivery, at0.1 mA/cm² on a 1-cm² area patch and 0.2 mA/cm² on a 6.5-cm²area patch compared to unpowered control patches. Twelve subjectswere tested under each condition on two separate occasions toexamine reproducibility of the response variable measurements.A further 12 subjects were tested once under the 0.2 mA/cm 6.5-cm2condition. Skin irritation was evaluated via repeated measurementsof transepidermal water loss, capacitance, skin temperature,skin color, and a visual scoring system, before the iontophoresisepisode and after patch removal. No damage to skin harrier functionin terms of skin-water loss or skin-water content was detected.Slight, subclinical, short-lasting erythema was observed forboth conditions. Assessment of correlation coefficients showedhighly statistically significant indications of reproducibilityfor all five response variables measured. The experimental design,in combination with a repeated measures analysis, provided clearseparation of the occlusion and ionic current components ofthe iontophoretic patch challenge. Further, the repeated measuresanalysis gave a highly sensitive assessment of skin irritationand resolution after patch removal. We conclude that the experimentalmethodology is appropriate for assessing possible changes inskin integrity resulting from saline iontophoresis under similaroperating conditions for longer durations and for other skinchallenges from which a subclinical response is expected.     

The effect of damaged skin barrier induced by subclinical irritation on the sequential irritant contact dermatitis

Skin damage caused by a single specific stimulus has been extensively studied. However, many additional mild skin irritants are experienced every day before obvious irritant contact dermatitis (ICD) appears. The effect that these previously experienced mild irritations have on the incidence and severity of sequential ICD remains undefined. The purpose of this work was to explore whether the effects of skin barrier damage induced by either the open patch test with 1% sodium lauryl sulfate (SLS), tape stripping test (TAP) (10×), or irradiation with 0.75 median erythemal dose UVB (MED) will affect the severity of sequential irritant dermatitis induced by a 0.5% SLS occlusive patch test (PT). Nine treatments were applied to nine different locations of the ventral forearm of each subject at random. The nine treatment types were as follows: open patch test with 1% SLS; 10× TAP; UVB irradiation with 0.75 MED; open patch test with 1% SLS + PT with 0.5% SLS (SLSPT); 10× TAP + PT with 0.5% SLS (TAPPT); UVB irradiation with 0.75 MED + PT with 0.5% SLS (UVPT); PT with distilled water (DISPT); PT with 0.5% SLS (PT); and the CONTROL (no treatment). After 5 days of subclinical irritation, the PT was applied on day 6. Transepidermal water loss (TEWL), capacitance (CAP), and skin color (a*) were measured at baseline and on days 6, 7, and 8. After the PT, indices of irritancy of PT, UVPT, SLSPT, and TAPPT were 60, 80, 87 and 100%, respectively. The index of irritancy of TAPPT and SLSPT were significantly higher than that of PT (p < 0.05). Clinical scores of SLSPT and TAPPT were also significantly higher than PT (p < 0.05). After 5 days of irritation, TEWL of SLS, TAP, SLSPT, and TAPPT were increased significantly compared to that of baseline. After the PT, D-value of TEWL between day 8 and day 6 ((≥6-8)TEWL) of SLSPT and TAPPT were greater than that of PT, and D-value of TEWL between day 8 and day 7 ((≥7-8)TEWL) of SLSPT and TAPPT were less than that of PT values. After the PT, a* values of SLSPT, TAPPT and PT all increased. The D-value of a* between day 8 and day 6 ((≥6-8)a*) of SLSPT and TAPPT were significantly greater than that of PT. After the PT, D-value of CAP between day 8 and day 6 ((≥6-8)CAP) of SLSPT was significantly different as compared to PT. The open patch test with 1% SLS and 10× TAP destroys the skin barrier and is able to significantly increase the irritancy and severity of sequential ICD by 0.5% SLS PT, and therefore influences the recovery speed of inflammation. The open patch test with 1% SLS, 10× TAP, and UVB irradiation with 0.75 MED affects the skin barrier to different degrees. TEWL is a sensitive biophysical parameter that can reflect mild damage to the skin barrier induced by subclinical irritation.     

Unexpected skin barrier influence from nonionic emulsifiers

Skin disorders are often treated with creams containing various active substances. The creams also contain emulsifiers, which are surface-active ingredients used to stabilize the emulsion. Emulsifiers are potential irritants and in the present study the influence of stearic acid, glyceryl stearate, PEG-2, -9, -40, and -100 stearate, steareth-2, -10 and -21 on normal as well as on irritated skin have been evaluated with non-invasive measurements. Test emulsions were created by incorporating 5% emulsifiers in a water/mineral oil mixture (50:50). The emulsions and their vehicle were then applied to normal skin for 48 h and to sodium lauryl sulfate (SLS) damaged skin for 17 h in aluminum chambers. Twenty-four hours after removal of the chambers the test sites were evaluated for degree of irritation. In normal skin, the emulsifiers induced significant differences in TEWL but not in skin blood flow. Five of the emulsifiers increased TEWL. In SLS-damaged skin an aggravation of the irritation was expected. However, no differences regarding skin blood flow was noted from the emulsifiers. Furthermore, three emulsifiers unexpectedly decreased TEWL. These results highlight the possibility of absorption of these emulsifiers into the lipid bilayer, which increase TEWL in normal skin and decrease TEWL in damaged skin.     

Skin tests of a novel nicotine patch, PHK-301p, in healthy male volunteers: phase I, placebo-controlled study

Major local adverse reactions in the nicotine patches are skin reactions. To assess the skin reaction of PHK-301p, a newly developed nicotine patch, we conducted a phase I study that consisted of 2 parts: a skin irritation test (48-h closed patch test) and a photosensitivity test (24-h closed patch test + Ultraviolet A irradiation). Twenty healthy men were treated with PHK-301p and placebo. Both preparations were punched out to a circle of 6-mm diameter and were applied simultaneously to each participant. Skin irritation and photosensitivity were assessed by a physician who was kept unaware of the treatment. In the skin irritation test, moderate and mild erythemas were observed in each participant 72 h after application (24 h after removal) for PHK-301p. Mild erythema was observed in one participant 49 h after application (1 h after removal) for placebo. The skin irritation index, which was calculated based on the skin reactions of participants, was 7.5 for PHK-301p and 2.5 for placebo. In the photosensitivity test, one participant had mild erythema (+/-) approximately 25 and 72 h after application of PHK-301p. No solar urticaria was observed. From these results, we concluded that PHK-301p is an acceptable product as a nicotine patch.     

Novel transdermal delivery of Timolol maleate using sugar esters: Preclinical and clinical studies

The feasibility of matrix controlled transdermal patch based on sugar fatty acid ester (SE) as penetration and absorption enhancer containing Timolol maleate (TM) was investigated. The influence of fatty acid type, chain length and hydrophile-lipophile balance (HLB) on the in vitro drug release as well as its permeation across hairless rat skin were studied and compared aiming to select a patch formula for clinical performance. Skin irritation induced by SE patch was evaluated by visual scoring, color reflectance measurements and non-invasive transepidermal water loss (TEWL) technique. The results indicated that among different SEs tried, laurate SE with shorter fatty acid chain length and higher HLB value significantly increased the amount of TM liberated from the patch (99 ± 2.1%) and its permeation across rat skin (86 ± 4.3%). The total drug permeation and flux values were approximately 5-fold greater compared to SE free patch. The extent of absorption of TM-SE patch expressed by AUC was 64% larger as compared to the oral solution with steady plasma concentration over 18 h and relative bioavailability (F_rel) of 163%. The developed patch was well tolerated by all the subjects with only moderate skin irritation, which was recovered in 24 h after patch removal. The results are very encouraging and offer an alternative approach to maintain higher, prolonged and controlled blood level profile of the drug over 18-24 h.     

Effect of iontophoresis and switching iontophoresis on skin accumulation of ketoprofen

The effect of iontophoresis and switching iontophoresis on the skin accumulation of drugs was investigated. An acrylic diffusion cell mounted with electrode cells (bore: 2.2 cm) with circular platinum electrodes (diameter: 2.0 cm) was used for the skin accumulation study. The skin accumulation of fluorescein after non-switching and switching iontophoresis was macroscopically compared with that achieved by passive diffusion (control). Intense fluorescence was observed after the application of non-switching and switching iontophoresis. Furthermore, fluorescence was observed just under the electrode cell and hardly spread in the skin beyond the area of the electrode cell. The skin accumulation of ketoprofen after non-switching and switching iontophoresis was also compared with control data. Although non-switching iontophoresis showed the highest amount of ketoprofen accumulated in skin, skin irritation was observed. Among the various switching intervals, switching iontophoresis using 10-min intervals achieved the highest value, and there was no skin irritation. Furthermore, the amount of ketoprofen accumulated was maintained after switching iontophoresis at 10-min intervals up to 180 min. Since the amount of ketoprofen in skin after switching iontophoresis was greater than that after intermittent iontophoresis, switching iontophoresis should increase the amount of ketoprofen due to enhancement of skin penetration by skin hydration. These findings suggest that switching iontophoresis using an optimal switching interval can prevent skin irritation and enhance drug accumulation in the skin.     

Enhanced transdermal delivery of low molecular weight heparin by barrier perturbation

The purpose of this work was to investigate the in vitro transdermal delivery of low molecular weight heparin (LMWH). Hairless rat skin was mounted on Franz diffusion cells and treated with various enhancement strategies. Passive flux was essentially zero and remained low even after iontophoresis (0.065 U cm(-2) h(-1)) or application of ultrasound (0.058 U cm(-2) h(-1)). A significant increase in flux across tape stripped skin (4.0 U cm(-2) h(-1)) suggests the interaction of stratum corneum (SC) with LMWH which was confirmed using Differential Scanning Calorimetry and Fourier Transform-Infrared spectrophotometry. Maltose microneedles were then employed as a means to locally disrupt and bypass the SC. Transepidermal water loss (TEWL) and transcutaneous electrical resistance (TER) were measured to confirm the barrier disruption. Microneedles breached the SC resulting in increased TEWL, decreased TER and enhanced LMWH permeability (0.175 U cm(-2) h(-1)). Microneedles when used in conjunction with iontophoresis had a synergistic effect on LMWH delivery resulting in enhancement of flux by 14.7-fold as compared to iontophoresis used alone. Confocal laser scanning microscopy substantiated the evidence about LMWH interaction with SC. In conclusion, LMWH was shown to interact with SC and therefore tape stripping or microneedles dramatically increased its delivery due to disruption of the SC skin barrier.     

Effect of application sites and multiple doses on nicotine pharmacokinetics in healthy male Japanese smokers following application of the transdermal nicotine patch

The transdermal nicotine patch, which contains 25 mg nicotine per 30 cm(2), is designed to deliver approximately 15 mg nicotine to the blood circulation in 16 hours of application for the treatment of smoking cessation. It was applied to 3 different skin sites (upper arm, abdomen, and back) to examine regional variations in percutaneous nicotine absorption in a single-dose, 3-period, crossover study involving 9 healthy male Japanese smokers. Nicotine pharmacokinetics during once-daily application of the transdermal nicotine patch for 5 days was also investigated in 10 healthy smokers. There were statistically significant effects of application sites on percutaneous nicotine absorption. The ratios (90% confidence intervals) of AUC and C(max) for comparison to the upper arm were 102% (88, 117%) and 106% (95, 119%) for the back and 75% (65, 87%) and 75% (66, 84%) for the abdomen, respectively. These suggest that systemic exposure after application to the upper arm was greater compared with the abdomen but equivalent to the back. Following multiple doses, linear pharmacokinetics and no significant accumulation of nicotine concentrations were observed, and steady state was reached by day 2. Only mild itching and erythema were observed at the application sites. The transdermal nicotine patch was well tolerated in both studies.     

Transdermal delivery using a novel electrochemical device, part 1: device design and in vitro release/permeation of fentanyl

A new type of electrochemical transdermal patch has been investigated using release/permeation experiments with excised nude mouse skin. The patch comprises a drug-containing hydrogel sandwiched between two electrodes that are arranged parallel to the skin surface. The objective was to determine the mechanism of working of enhanced flux for the drug fentanyl when low voltages are applied. The results indicate that a voltage-induced hydrolysis of the water present in the patch's hydrogel occurs. This causes a pH shift that results in deprotonization of the fentanyl and hence enhanced release/permeation. The enhanced flux is up to approximately 30 μg/(cm(2) h) over 20 h and requires only a low-voltage application over a duration of just 60 s. Because the enhancement mechanism occurs in the patch and not in the skin, the potential for substantially reduced skin irritation compared with iontophoresis is given.     

Effect of jet fuels on the skin morphology and irritation in hairless rats

Jet A and JP-8 are the major jet fuels used in civilian and military (US Air Force) flights, respectively. JP-8+100 is a new jet fuel recently introduced by US Air Force in some of its locations. The purpose of this study was to investigate the effects of dermal exposure of jet fuels (Jet A, JP-8, and JP-8+100) on the skin morphology, barrier function, moisture content, blood flow, and skin irritation (erythema and edema) in hairless rats. Jet fuels were applied by both occlusive and unocclusive methods. The skin of treated and control (untreated) sites were excised and analyzed by magnetic resonance imaging (MRI) (500 MHz, 11.7 Tesla). Unocclusive application of JP-8, Jet A, and JP-8+100 increased the transepidermal water loss (TEWL) gradually and the values at 120 h were significantly greater than the baseline value (P<0.05). Both occlusive and unocclusive application of jet fuels decreased the skin moisture content significantly (P<0.05). Unocclusive application of JP-8, Jet A, and JP-8+100 increased the skin blood flow, though the values returned to the baseline levels within 24 h. Occlusive application of jet fuels (8 h/day for 2 days) caused a substantial increase in the skin blood flow and the values at 48 h were about 6-fold greater than the baseline value. Occlusive application of jet fuels caused a moderate to severe erythema and a moderate edema. MRI was used to obtain proton images and water self-diffusion maps of hairless rat skin exposed to jet fuel. Exposure to JP-8 showed the largest difference from the control with regards to visual observations of the stratum corneum and hair follicles, while JP-8+100 appeared to affect the hair follicle region. The results of the present study demonstrate that exposure to jet fuels can disrupt the skin barrier function, cause skin irritation, and alter the skin structure (stratum corneum and viable epidermis) and MRI can be used as a tool to investigate the alterations in the skin morphology after exposure to toxic chemicals.     

Transdermal delivery of naloxone: skin permeation, pharmacokinetic, irritancy and stability studies

The current investigation aims to evaluate ex vivo, in vivo performance, stability and irritancy potential of a transdermal formulation of naloxone (NLX) developed at our laboratory at different concentrations (10, 20 and 30mg/g of gel) in a transdermal reservoir patch. Ex vivo permeation studies were performed by employing porcine and rat skins. In vivo performance was assessed in Sprague-Dawley rats by single and multiple application of the patch. Further stability of the formulation was established for 3 months at accelerated stability conditions as per ICH guidelines. Amongst the barriers used the rat skin was found to be more permeable than the porcine epidermis and the flux across each barrier increased with increasing thermodynamic activity of drug in the gel. Based on ex vivo data, the surface area (SA) of the patch was predicted to be 39.6 cm(2) in order to achieve therapeutic blood levels. Upon single dose administration, the steady-state levels were maintained from 4-48 h, which proves the clear advantage of transdermal delivery system over the current mode of administration, i.e., intravenous (i.v.) bolus which is effective upto a maximum of 1.5h. Upon multiple dose administration, the sustained steady state for 12h, even after patch removal proves the formation of drug depot in the skin. The formulations were found to be stable with respect to NLX assay and penetration enhancer efficacy upto 3 months under accelerated stability conditions. The alteration of penetration barrier function, as evidenced by increased trans epidermal water loss (TEWL) was not accompanied by any significant amount of skin irritation measured using laser doppler velocimetry (LDV). The developed transdermal delivery system of NLX is efficacious, stable and safe upon single and multiple dose applications each lasting for 48 h.     

Assessment of skin irritation and molecular responses in rat skin exposed to nonane, dodecane and tetradecane

Aliphatic hydrocarbons constitute a major portion of jet fuels, kerosene and other solvents. This study investigated the effects of dermal exposures of selected aliphatic hydrocarbons (nonane, dodecane and tetradecane) on the skin irritation (erythema), transepidermal waterloss (TEWL) and expression of interleukin-1alpha (IL-1alpha), tumor necrosis factor (TNF-alpha) and monocyte chemoattractant protein-1 (MCP-1) in the skin and blood of hairless rats. Dermal exposures were carried out by occlusive application of chemicals (230 microl for 1 h, using Hill Top Chambers) for 1 h. The expression of IL-1alpha, TNF-alpha and MCP-1 was measured by enzyme immunoassay (EIA), and the regulatory proteins NFkappaB and IkappaBalpha were measured by Western blot analysis. The skin irritation and TEWL data indicate that the irritation was in the following decreasing order: nonane > dodecane > tetradecane. Likewise, nonane significantly increased the expression of IL-1alpha, TNF-alpha and MCP-1 in skin and blood as compared to control at different time points. Dodecane and tetradecane did not show any increase in the expression of IL-1alpha and MCP-1 as compared to control (P > 0.05), but the expression of TNF-alpha by dodecane and tetradecane was significantly higher than control at all time points. The release of cytokines by nonane exposure was further supported by activation of NFkappaB p65 and corresponding degradation of IkappaBalpha in the skin. In conclusion, this study demonstrates that the biophysical parameters (TEWL and erythema scores) were correlated to the biomarker expressions after dermal exposures with nonane but not with dodecane and tetradecane. Dodecane produced only mild irritation in response to experimental conditions of the present study and further did not show significant differences in IL-1alpha and MCP-1 levels in skin and blood. However, TNF-alpha was well expressed in response to all the chemicals. Tetradecane did not show any visible signs of skin irritation and also did not produce any significant difference in IL-1alpha and MCP-1 release profiles as compared with control. The expression of TNF-alpha in skin due to tetradecane support the fact that visually indistinguishable skin irritation reactions can induce significant changes in the biological marker profile.