Search

The in vitro percutaneous absorption of carbon-14-labeled benzene ([(14)C]benzene) in dermatomed human skin was determined using 2 cleaning products containing benzene. This study utilized cleaning solutions commonly used in the workplace. As Environmental Protection Agency (EPA) guidelines cover dose occlusion for volatile chemicals, the treatments were both nonoccluded and occluded, with low (10 microL/cm(2)), high (30 microL/cm(2)), and multiple (10 microL/cm(2) x 3 at 0, 30, and 60 min) doses. In an open-to-air test, the benzene quickly evaporated, and only 0.5%-1.4% of the original dose remained after 30 minutes. In the diffusion studies, human skin absorption of benzene peaked in the first few hours without occlusion, but was sustained for 24 hours with occlusion. The absorption of a high single dose was 1.2 +/- 0.16 times (mean +/- standard deviation) greater than that of a multiple dose, whereas theory would predict 1.0. The low-dose to high- or multiple-dose ratio was 3.6 +/- 2.2, so there was a clear dose response. The effect of occlusion was significant. In this study occlusion increased absorption by 40.1 +/- 24.6 times. These data place into partial perspective the role of occlusion in benzene flux, but should not be generalized until other volatile substances are studied in the experimental system and further validated with in vivo systems.

Regulatory agencies have relied on dermal absorption data for soluble forms of arsenic as the technical basis for specific absorption values that are used to calculate exposure to arsenic in weathered soil. These evaluations indicate that percutaneous absorption of arsenic from soil ranges from 3.2 to 4.5% of the dermally applied dose, based on studies of arsenic freshly mixed with soil. When this value is incorporated into risk assessments and combined with other assumptions about dermal exposures to soil, the conclusion is often that dermal exposure to arsenic from soil may contribute significantly to overall exposure to arsenic in soil. Prior characterization research has indicated that the solubility of arsenic in soil varies, depending on the provenance of the soil, the source of the arsenic, and the chemical interaction of arsenic with other minerals present within the soil matrix. Weathering produces forms of arsenic that are more tightly bound within the soil and less available for absorption. Our research expands on prior in vivo studies to provide insights into the potential for dermal absorption of arsenic from the more environmentally relevant substrate of soil. Specifically, two soils with very high concentrations of arsenic were evaluated under two levels of skin hydration. One soil, containing 1400 mg/kg arsenic, was collected adjacent to a pesticide production facility in New York. The other soil, containing 1230 mg/kg arsenic, was collected from a residential area with a history of application of arsenical pesticides. Although the results of this research are constrained by the small study size dictated by the selection of an animal research model using monkeys, the statistical power was optimized by using a "crossover" study design, wherein each animal could serve as its own comparison control. No other models (animal or in vitro) were deemed adequate for studying the dermal absorption of soil arsenic. Our results show dermal absorption of soluble arsenic in solution to be 4.8 +/- 5.5%, which is similar to results reported earlier for arsenic in solution (and used by regulatory agencies in recommendations regarding dermal absorption of arsenic). Conversely, absorption following application of arsenic in the soil matrices resulted in mean estimated arsenic absorption of 0.5% or less for all soils, and all individual estimates were less than 1%. More specifically, following application of arsenic-bearing soils to the abdomens of monkeys, urinary arsenic excretion could not be readily distinguished from background. This was true across all five soil-dosing trials, including application of the two dry soils and three trials with wet soil. These findings are consistent with our understanding of the environmental chemistry of arsenic, wherein arsenic can be present in soils in complexed mineral forms. This research addresses an important component involved in estimating the true contribution of percutaneous exposures to arsenic in soil relative to exposures via ingestion. Our findings suggest that dermal absorption of arsenic from soil is truly negligible, and that EPA's current default assumption of 3% dermal absorption of arsenic from soils results in significant overestimates of exposure.

Onychomycosis is a challenging fungal infection to treat topically, likely due to the unique properties of the nail plate. This seemingly impenetrable barrier has high resistance to the passage of antifungal drugs in sufficient concentrations to kill the causative fungi deep in the nail bed. Recently, a new class of antifungal agent was described, termed oxaboroles, which have broad-spectrum activity. These oxaboroles were designed with properties believed to be required to allow for easier transit through the nail plate. Herein, we report (i) the nail penetration results of four oxaboroles that led to the selection of AN2690, (ii) the results of the nail penetration of AN2690 from four vehicles, and (iii) the nail penetration of AN2690 in its chosen vehicle compared to a commercial control, ciclopirox. AN2690 has superior penetration compared to ciclopirox, and achieves levels within and under the nail plate that suggest it has the potential to be an effective topical treatment for onychomycosis., ((c) 2007 Wiley-Liss, Inc.)

The in vitro absorption of panthenol into and through the human nail was examined in this study. Panthenol, the alcohol form of pantothenic acid (vitamin B5), is believed to act as a humectant and improve the flexibility and strength of nails. A liquid nail treatment formulated with panthenol (2%) was compared to a solution of panthenol (2%) in water. Fingernail specimens were dosed daily for 7 days with either the nail treatment (non-lacquer film forming) formulation or aqueous solution with sampling performed every 24 h. Panthenol concentrations were determined in the dorsal surface, interior (by drilling and removal) and in the supporting bed under the human nail. Panthenol levels in the dorsal nail (R(2) = 0.87; P < 0.001), nail interior (R(2) = 0.94; P < 0.001) and nail supporting bed (R(2) = 0.79; P < 0.003) showed a significant linear increase with each day of dosing. Significantly more panthenol was delivered into the interior nail and supporting bed by a nail treatment formulation than from an aqueous solution. The film acts not only as a reservoir of panthenol, but also acts to increase the hydration of the nail and the thermodynamic activity of panthenol as well, thereby enhancing diffusion.

This study determined the in vivo human bioavailability of topical estradiol, and the transfer of drug between dosed subject and naive recipient. In vivo bioavailability was determined in human volunteers by (14)C urinary excretion following topical [(14)C]-estradiol (0.06%) dose administration and were adjusted by intravenous human excretion amounts to give absolute bioavailability amounts. Drug transfer was determined by volunteer skin contact/rubbing for 15 minutes, 1 hour after topical dosing. [(14)C]-estradiol bioavailability as percent dose absorbed (n=6) was 7.5+/-4.1 from protected dose site, 8.2+/-6.3 from non-protected dose site, 6.6+/-7.6 from dosed volunteers subjected to skin contact/rub and 4.3+/-3.8 from non-dosed volunteers subjected to skin contact/rub. Between these small groups, the values were not statistically different. Under experimental conditions, a measurable dose of radioactive 17beta-estradiol dose was delivered to naive recipient volunteers through skin contact/rub with other volunteers previously topically dosed. Any residual topical bioactive chemical which resides on the open skin surface can transfer by skin contact to another individual. It is important for prescribing physicians and patients to understand that clinically significant transfer of topical bioactive drugs can occur. This may be particularly important for substances which may produce inadvertent effects.

Current knowledge of percutaneous absorption of arsenic is based on studies of rhesus monkeys using soluble arsenic in aqueous solution, and soluble arsenic mixed with soil (Wester et al., 1993). These studies produced mean dermal absorption rates in the range of 2.0-6.4% of the applied dose. Subsequently, questions arose as to whether these results represent arsenic absorption from environmental media. Factors such as chemical interactions, the presence of other metals, and the effects of weathering on environmental media all can affect the nature of arsenic and its potential for percutaneous absorption. Therefore, research specific to more relevant matrices is important. The focus of this effort is to outline study design considerations, including particle size, application rates, means of ensuring skin contact and appropriate statistical evaluation of the data. Appropriate reference groups are also important. The potential for background exposure to arsenic in the diet possibly obscuring a signal from a dermally applied dose of arsenic will also be addressed. We conclude that there are likely to be many site- or sample-specific factors that will control the absorption of arsenic, and matrix-specific analyses may be required to understand the degree of percutaneous absorption.

The human nail penetration of the antifungal ciclopirox was determined for marketed gel containing 0.77% of ciclopirox, an experimental gel containing 2% of ciclopirox, and a marketed lacquer containing 8% of ciclopirox. After 14 days dosing, unabsorbed drug remaining on the surface, drug within the infection-prone area, and the amount that had penetrated through the nail were determined. Ciclopirox delivery into and through the nail was significantly greater from the marketed gel, than from either the experimental gel or the nail lacquer (p < 0.05). In addition, the surface nail contained more unabsorbed drug from the lacquer. Further, the drug penetrating into and through the nail was also greater from the marketed gel, leading to a higher Calculated Efficacy Coefficient for the marketed gel, than from the marketed lacquer or the experimental gel. The formulation plays an important role in the enhancement of ciclopirox permeation into and through the human nail plate, and the concentration of ciclopirox in the formulation was not a factor in determining penetration., (Copyright 2004 Wiley-Liss, Inc. and the American Pharmacists Association)

This study was conducted to evaluate the dermal absorption of arsenic from residues present on the surface of wood preserved with chromated copper arsenate (CCA). The research reported herein used methods parallel to those of earlier research on the dermal absorption of radiolabeled arsenic (R. C. Wester et al., 1993, Fund. Appl. Toxicol. 20, 336-340), with modifications to allow use of environmental matrices that are not radiolabeled. These modifications include the surface area of application and dietary intake of arsenic, thus maximizing the potential for detection of dermally absorbed arsenic in exposed animals above diet-associated background levels of exposure. Two forms of arsenic were administered in this work. The first, arsenic in solution, was applied to the skin of monkeys to calibrate the model against prior absorption research and to serve as the basis of comparison for absorption of arsenic from CCA-treated wood residues. The second substrate was residue that resides on the surface of CCA-treated wood. Results from this research indicate that this study methodology can be used to evaluate dermally absorbed arsenic without the use of a radiolabel. Urinary excretion of arsenic above background levels can be measured following application of soluble arsenic, and absorption rates (0.6-4.4% absorption) are consistent with prior research using the more sensitive, radiolabeled technique. Additionally, the results show that arsenic is poorly absorbed from CCA-treated wood residues (i.e., does not result in urinary arsenic excretion above background levels).

This study determines the enhancing effects of 2-n-nonyl-1,3-dioxolane on the penetration of econazole, an antifungal drug, into the deeper layers of the human nail where fungal infection resides. Aliquots (10 microL) of Econail lacquer formulation containing 0.45 mg of [(14)C]-econazole with 18% 2-n-nonyl-1,3-dioxolane (test group) or without 2-n-nonyl-1,3-dioxolane (control group) were applied twice daily for 14 days to human nails that had been washed with ethanol before each morning's application. The hydration of the nail sample was well controlled to simulate normal physiological conditions. After 14 days of dosing, the inner ventral section of the nail plate was assayed for absorbed drug content, using a micrometer-controlled drilling and nail powder removal system. The mass balance values of [(14)C]-econazole in this study were 90.8 and 96.4% for the test and control groups, respectively. The weight-normalized econazole content in the ventral/intermediate nail plate center in the test group was 6-fold greater than that in the control (p = 0.008). The total econazole absorbed into the supporting bed cotton ball in the test group was nearly 200-fold greater than that in the control group (p = 0.008) over the 14-day period. The amount of econazole after dosing in the inner part of the human nail (potential diseased area) was 11.1 +/- 2.6 (SD) microg/mg of nail powder with 2-n-nonyl-1,3-dioxolane in the lacquer and 1.78 +/- 0.32 microg/mg without 2-n-nonyl-1,3-dioxolane (p = 0.008). The surface nail contained more econazole (p = 0.004), that is, nonabsorbed drug, where 2-n-nonyl-1,3-dioxolane was not part of the dosing solution. Econazole in the support bed under the nail (the total absorbed dose) was 47.5 +/- 22.0 mg in the lacquer with 2-n-nonyl-1,3-dioxolane and 0.2 +/- 0.1 mg in the lacquer without 2-n-nonyl-1,3-dioxolane (p = 0.008). Moreover the concentration in the deep nail layer in the test group is 14,000 times higher than minimum inhibitory concentration (MIC) believed necessary to inhibit the growth of infecting fungi (Dermatophytes species). In a subsequent study, [(14)C]-dioxolane did not penetrate the nail well. Therefore, the mechanism of enhancement of econazole penetration is at the formulation/nail interface., (Copyright 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association)

Macromolecules have gained interest as drug entities unto themselves and as transport facilitators to alter initial phases of percutaneous absorption. Two macromolecular polymers (MW 2081 and 2565) were designed to hold cosmetics and drugs to the skin surface by altering initial chemical and skin partitioning. The effect of these polymers on the partition coefficient (PC) of estradiol with powdered human stratum corneum (PHSC) and water was determined. There was no statistically significant effect on the PC when the concentration of estradiol was increased 100-fold (0.028-2.8 microg/mL), when the incubation time was increased from 0 to 24 h, or when PHSC was delipidized. The addition of a liphophilic polymer had no effect on the PC; however, the hydrophilic polymer showed a significant polymer concentration-dependent increase (p < 0.01) in log PC for estradiol concentrations. Thus, a macromolecular chemical has the potential to alter the partitioning of chemical into the outer layers of skin, the first step in percutaneous absorption., (Copyright 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:2642-2645, 2002)

The contribution of benzene to body burden after skin absorption compared with that due to inhalation absorption is of potential interest in the setting and interpretation of benzene (inhalation) exposure standards. However, an understanding of the quantitative relationship between skin and inhalation absorption, under different exposure conditions, is required. Such knowledge may be gained through physiological based pharmacokinetic (PBPK) modeling. The intake of benzene to the body via inhalation has been studied extensively. Physiological parameters enabling the calculation of amounts of benzene entering the blood stream per unit time are readily available for use in a PBPK model. Unfortunately, some data (i.e., partition coefficients) that would enable biologically plausible calculation of amounts of benzene entering the blood stream via skin absorption in a PBPK model are not available. Hence, the aim of this research was to determine partition coefficients across the epidermal and dermal layers of human skin so that these could be used within a PBPK model to determine quantitatively the flow rate of benzene per unit time through intact skin into the blood stream. The partition coefficients found for blood substitute: viable epidermis and blood substitute: dermis were, respectively, 2.4 and 11.2. Partition coefficients for benzene : stratum corneum (4.2), whole skin : blood substitute (2.2), benzene : water (109/126), and benzene : blood substitute (55/59) also were determined for the purposes of validating the blood substitute: viable epidermis and blood substitute : dermis partition coefficients.

Perchloroethylene (PCE) is a widely used volatile organic chemical. Exposures to PCE are primarily through inhalation and dermal contact. The dermal absorption of PCE from a soil matrix was compared in rats and humans using real-time MS/MS exhaled breath technology and physiologically based pharmacokinetic (PBPK) modeling. Studies with rats were performed to compare the effects of loading volume, concentration, and occlusion. In rats, the percutaneous permeability coefficient (K(P)) for PCE was 0.102 +/- 0.017, and was independent of loading volume, concentration, or occlusion. Exhaled breath concentrations peaked within 1 h in nonoccluded exposures, but were maintained over the 5 h exposure period when the system was occluded. Three human volunteers submerged a hand in a container of PCE-laden soil for 2 h and their exhaled breath was continually monitored during and for 2.5 h following exposure. The absorption and elimination kinetics of PCE were slower in these subjects than initially predicted based upon the PBPK model developed from rat dermal kinetic data. The resulting K(P) for humans was over 100-fold lower than for the rat utilizing a single, well-stirred dermal compartment. Therefore, two additional PBPK skin compartment models were evaluated: a parallel model to simulate follicular uptake and a layered model to portray a stratum corneum barrier. The parallel dual dermal compartment model was not capable of describing the exhaled breath kinetics, whereas the layered model substantially improved the fit of the model to the complex kinetics of dermal absorption through the hand. In real-world situations, percutaneous absorption of PCE is likely to be minimal.

The purpose of this study was to develop an assay method of the human inner nail plate and to compare nail drug penetration by a penetrating enhancing formulation (the test carrier formulation). The test carrier and saline formulations were tested using radiolabeled urea, ketoconazole, and salicylic acid. After twice dosing daily for 7 days on human nail plates, the under inner section of the nail plate was assayed for absorbed drug content using a unique drilling/removal system. Results show that the weight-normalized radioactivity contents of three chemicals in the inner intermediate nail plate center in the carrier formulation were two fold higher than those from saline (p < 0.05). Total radioactivity recovery of dosed [(14)C]-salicylic acid was 89 +/- 2% in the carrier formulation and 88 +/- 5% in saline. In saline formulation, salicylic acid showed greater binding to the outer nail, making it less bioavailable for the inner nail area. This didn't occur with carrier formulation. In conclusion, topical treatment of nail diseases such as onychomycosis is not yet sufficiently effective, likely because of minimal drug penetration into the inner nail plate where the disease perpetuates. The assay system has the unique characteristic of being able to assay the inner part of the nail where the disease resides., (Copyright 2002 Wiley-Liss, Inc.)

Chemical warfare agents (CWA) are easily and inexpensively produced and are a significant threat to military forces and the public. Most well-known CWAs are organophosphorus compounds, a number or which are used as pesticides, including parathion. This study determined the in vitro percutaneous absorption of parathion as a CWA simulant through naked human skin and uniformed skin (dry and sweated). Parathion percentage dose absorbed through naked skin (1.78 +/- 0. 41) was greater than dry uniformed skin (0.29 +/- 0.17; p = 0.000) and sweated uniformed skin (0.65 +/- 0.16; p = 0.000). Sweated and dry uniformed skin absorption were also different (p = 0.007). These relative dry and sweated uniformed skin absorptions were then applied to VX skin permeability for naked skin (head, neck, arms, and hands) and the remaining uniformed skin over the various regions of the human body. Risk assessment shows VX 50% lethality within the first hour for a soldier wearing a sweated uniform. By 8 h postexposure to naked skin plus trunk area predicted lethality for both dry and sweated uniform, and, at 96 h postexposure, all body regions individually exposed would produce lethality. Military uniform and public clothing provide some immediate protection but absorption through cloth and skin does occur. Immediate safety response to skin and clothing is required., (Copyright 2000 Academic Press.)

The development and validation of noninvasive techniques for estimating the dermal bioavailability of solvents in contaminated soil and water can facilitate the overall understanding of human health risk. To assess the dermal bioavailability of trichloroethylene (TCE), exhaled breath was monitored in real time using an ion trap mass spectrometer (MS/MS) to track the uptake and elimination of TCE from dermal exposures in rats and humans. A physiologically based pharmacokinetic (PBPK) model was used to estimate total bioavailability. Male F344 rats were exposed to TCE in water or soil under occluded or nonoccluded conditions by applying a patch to a clipper-shaved area of the back. Rats were placed in off-gassing chambers and chamber air TCE concentration was quantified for 3-5 h postdosing using the MS/MS. Human volunteers were exposed either by whole-hand immersion or by attaching patches containing TCE in soil or water on each forearm. Volunteers were provided breathing air via a face mask to eliminate inhalation exposure, and exhaled breath was analyzed using the MS/MS. The total TCE absorbed and the dermal permeability coefficient (K(P)) were estimated for each individual by optimization of the PBPK model to the exhaled breath data and the changing media and/or dermal patch concentrations. Rat skin was significantly more permeable than human skin. Estimates for K(P) in a water matrix were 0.31 +/- 0.01 cm/h and 0.015 +/- 0.003 cm/h in rats and humans, respectively. K(P) estimates were more than three times higher from water than soil matrices in both species. K(P) values calculated using the standard Fick's Law equation were strongly affected by exposure length and volatilization of TCE. In comparison, K(P) values estimated using noninvasive real-time breath analysis coupled with the PBPK model were consistent, regardless of volatilization, exposure concentration, or duration.

Local and systemic toxicity from percutaneous absorption depends on a chemical's penetrating the skin, which is both a barrier to absorption and a primary route to the systemic circulation. The skin's barrier properties are such that fluids and precious chemicals are reasonably retained within the body, while foreign chemicals are restricted from entering the systemic circulation. The skin is a primary body contact with the environment and the route by which many chemicals enter the body. In most instances, the toxicity of the chemical is slight and/or its bioavailability is too low to cause an immediate response. However, some chemicals are toxic when applied to the skin, and more chemicals that come in contact with the skin are being found to be potentially toxic. This article describes percutaneous absorption, methods to determine it, and factors that can affect it.

Realistic estimates of percutaneous absorption following exposures to solvents in the workplace, or through contaminated soil and water, are critical to understanding human health risks. A method was developed to determine dermal uptake of solvents under non-steady-state conditions using real-time breath analysis in rats, monkeys, and humans. The exhaled breath was analyzed using an ion-trap mass spectrometer, which can quantitate chemicals in the exhaled breath stream in the 1-5 ppb range. The resulting data were evaluated using physiologically-based pharmacokinetic (PBPK) models to estimate dermal permeability constants (Kp) under various exposure conditions. The effects of exposure matrix (soil versus water), occlusion versus non-occlusion, and species differences on the absorption of methyl chloroform, trichloroethylene, and benzene were compared. Exposure concentrations were analyzed before and at 0.5-hour intervals throughout the exposures. The percentage of each chemical absorbed and the corresponding Kp were estimated by optimization of the PBPK model to the medium concentration and the exhaled-breath data. The method was found to be sufficiently sensitive for animal and human dermal studies at low exposure concentrations over small body surface areas, for short periods, using non-steady-state exposure conditions.

Skin is one of several exposure routes whereby benzene, a widely distributed environmental contaminant that causes leukemia, enters the body, so accurate predictions of its percutaneous absorption are important for risk assessment. Determining benzene's skin-exposure dose and subsequent absorption is difficult because it has a low boiling point and exists as both liquid and vapor. Industrial and environmental benzene is present as a contaminant in other vehicles/solvents, and its percutaneous absorption is in part dependent upon co-solvent volatility. Co-solvents such as benzene in toluene rapidly evaporate from skin, whereas benzene contaminant in water is retained on skin longer due to water's lower volatility. Co-solvents can also affect benzene-skin partition coefficients; thus, permeability coefficients and percentage doses absorbed can vary many-fold. The exposure situation will determine percutaneous absorption, which, if low, can be overwhelmed by benzene intake from the food we eat and the air we breathe.

Due to the large surface area of the skin, percutaneous absorption has the potential to contribute significantly to the total bioavailability of some compounds. Breath elimination data, acquired in real-time using a novel MS/MS system, was assessed using a PBPK model with a dermal compartment to determine the percutaneous absorption of methyl chloroform (MC) in rats and humans from exposures to MC in non-occluded soil or occluded water matrices. Rats were exposed to MC using a dermal exposure cell attached to a clipper-shaved area on their back. The soil exposure cell was covered with a charcoal patch to capture volatilized MC and prevent contamination of exhaled breath. This technique allowed the determination of MC dermal absorption kinetics under realistic, non-occluded conditions. Human exposures were conducted by immersing one hand in 0.1% MC in water, or 0.75% MC in soil. The dermal PBPK model was used to estimate skin permeability (Kp) based on the fit of the exhaled breath data. Rat skin K(p)s were estimated to be 0.25 and 0.15 cm/h for MC in water and soil matrices, respectively. In comparison, human permeability coefficients for water matrix exposures were 40-fold lower at 0.006 cm/h. Due to evaporation and differences in apparent Kp, nearly twice as much MC was absorbed from the occluded water (61.3%) compared to the non-occluded soil (32.5%) system in the rat. The PBPK model was used to simulate dermal exposures to MC-contaminated water and soil in children and adults using worst-case EPA default assumptions. The simulations indicate that neither children nor adults will absorb significant amounts of MC from non-occluded exposures, independent of the length of exposure. The results from these simulations reiterate the importance of conducting dermal exposures under realistic conditions.

The extent of metabolism of diclofenac sodium in excised viable human skin was investigated using combination HPLC and radioactivity assay. In an earlier diffusion experiment using an in vitro flow-through diffusion system, radiolabelled diclofenac sodium in either lotion (Pennsaid) or aqueous solution was applied to viable human skin, either as single dose or multiple dose (8 times over 2 days). In this study, the receptor fluid samples from the diffusion experiment were subjected to extraction and the aliquot was analysed using HPLC to separate diclofenac and authentic metabolites. Based on the radioactivity of each HPLC fraction, the collection time of the fractions was compared with the retention time of diclofenac and metabolites in standard solutions. The samples from a single or multiple dose application of lotion showed radioactivity in mainly one fraction, whose retention time corresponded with diclofenac. Other HPLC fractions showed none or only small amounts of radioactivity within the error range of the assay. The same results were obtained with the pooled samples from the application of the lotion or of aqueous solution. The results suggest that diclofenac sodium does not undergo metabolism in viable human epidermis during percutaneous absorption in vitro. Hence, with topical application to human skin in vivo, diclofenac will be delivered with minimal, if any, metabolism.

Metabolites of atrazine were measured in human urine after dermal exposure using HPLC to separate and identify metabolites and accelerator mass spectrometry (AMS) to quantify them. Ring-labeled [14C]atrazine was applied for 24 h with a dermal patch to human volunteers at low (0.167 mg, 6.45 muCi) and high (1.98 mg, 24.7 muCi) doses. Urine was collected for 7 days. The urine was centrifuged to remove solids, and the supernatant was measured by liquid scintillation counting prior to injection on the HPLC to ensure that < 0.17 Bq (4.5 pCi) was injected on the column. A reversed-phase gradient of 0.1% acetic acid in water and 0.1% acetic acid in acetonitrile became less polar with increasing time and separated the parent compound and major atrazine metabolites over 31 min on an octadecylsilane column. Peaks were identified by coelution with known standards. Elution fractions were collected in 1-min increments; half of each fraction was analyzed by AMS to obtain limits of quantitation of 14 amol. Mercapturate metabolites of atrazine and dealkylated atrazine dominated the early metabolic time points, accounting for approximately 90% of the 14C in the urine. No parent compound was detected. The excreted atrazine metabolites became more polar with increasing time, and an unidentified polar metabolite that was present in all samples became as prevalent as any of the known ring metabolites several days after the dose was delivered. Knowledge of metabolite dynamics is crucial to developing useful assays for monitoring atrazine exposure in agricultural workers.

In the home and workplace, decontamination of a chemical from skin is traditionally done with a soap-and-water wash, although some workplaces may have emergency showers. It has been assumed that these procedures are effective, yet workplace illness and even death occur from chemical contamination. Water, or soap and water, may not be the most effective means of skin decontamination, particularly for fat-soluble materials. This study was undertaken to help determine whether there are more effective means of removing methylene bisphenyl isocyanate (MDI), a potent contact sensitizer, from the skin. MDI is an industrial chemical for which skin decontamination, using traditional soap and water and nontraditional polypropylene glycol, a polyglycol-based cleanser (PG-C), and corn oil were all tried in vivo on the rhesus monkey, over 8 h. Water, alone and with soap (5% and 50% soap), were partially effective in the first h after exposure, removing 51-69% of the applied dose. However, decontamination fell to 40-52% at 4 h and 29-46% by 8 h. Thus, the majority of MDI was not removed by the traditional soap-and-water wash; skin tape stripping after washing confirmed that MDI was still on the skin. In contrast, polypropylene glycol, PG-C, and corn oil all removed 68-86% of the MDI in the first h, 74-79% at 4 h, and 72-86% at 8 h. Statistically, polypropylene glycol, PG-C, and corn oil were all better (p < 0.05) than soap and water at 4 and 8 h after dose application. These results indicate that a traditional soap-and-water wash and the emergency water shower are relatively ineffective at removing MDI from the skin. More effective decontamination procedures, as shown here, are available. These procedures are consistent with the partial miscibility of MDI in corn oil and polyglycols.

Literature from the first half of this century reports concern for toxicity from topical use of boric acid, but assessment of percutaneous absorption has been impaired by lack of analytical sensitivity. Analytical methods in this study included inductively coupled plasma-mass spectrometry which now allows quantitation of percutaneous absorption of 10B in 10B-enriched boric acid, borax and disodium octaborate tetrahydrate (DOT) in biological matrices. In vitro human skin percent doses of boric acid absorbed were 1.2 for a 0.05% solution, 0.28 for a 0.5% solution, and 0.70 for a 5.0% solution. These absorption amounts translated into flux values of, respectively, 0.25, 0.58, and 14.58 microg/cm2/h, and permeability constants (Kp) of 5.0 x 10(-4), 1.2 x 10(-4), and 2.9 x 10(-4) cm/h for the 0.05%, 0.5%, and 5.0% solutions. The above in vitro doses were at infinite, 1000 microL/cm2 volume. At 2 microL/cm2 (the in vivo dosing volume), flux decreased some 200-fold to 0.07 microg/cm2/h and Kp of 1.4 x 10(-6) cm/h, while percent dose absorbed was 1.75%. Borax dosed at 5.0%/1000 microL/cm2 had 0.41 percent dose absorbed, flux at 8.5 microg/cm2/h, and Kp was 1.7 x 10(-4) cm/h. Disodium octaborate tetrahydrate (DOT) dosed at 10%/1000 microL/cm2 was 0.19 percent dose absorbed, flux at 7.9 microg/cm2/h, and Kp was 0.8 x 10(-4) cm/h. These in vitro results from infinite doses (1000 microL/cm2) were a 1000-fold greater than those obtained in the companion in vivo study. The results from the finite (2 microL/cm2) dosing were closer (10-fold difference) to the in vivo results. General application of infinite dose percutaneous absorption values for risk assessment is questioned by these results.

Literature from the first half of this century reports concern for toxicity from topical use of boric acid, but assessment of percutaneous absorption has been impaired by lack of analytical sensitivity. Analytical methods in this study included inductively coupled plasma-mass spectrometry, which now allows quantitation of percutaneous absorption of 10B in 10B-enriched boric acid, borax, and disodium octaborate tetrahydrate (DOT) in biological matrices. This made it possible, in the presence of comparatively large natural dietary boron intakes for the in vivo segment of this study, to quantify the boron passing through skin. Human volunteers were dosed with 10B-enriched boric acid, 5.0%, borax, 5.0%, or disodium octaborate tetrahydrate, 10% in aqueous solutions. Urinalysis, for boron and changes in boron isotope ratios, was used to measure absorption. Boric acid in vivo percutaneous absorption was 0.226 (SD = 0.125) mean percent dose, with flux and permeability constant (Kp) calculated at 0.009 microg/cm2/h and 1.9 x 10(-7) cm/h, respectively. Borax absorption was 0.210 (SD = 0.194) mean percent dose, with flux and Kp calculated at 0.009 microg/cm2/h and 1.8 x 10(-7) cm/h, respectively. DOT absorption was 0.122 (SD = 0.108) mean percent, with flux and Kp calculated at 0.01 microg/cm2/h and 1.0 x 10(-7) cm/h, respectively. Pretreatment with the potential skin irritant 2% sodium lauryl sulfate had no effect on boron skin absorption. These in vivo results show that percutaneous absorption of boron, as boric acid, borax, and disodium octaborate tetrahydrate, through intact human skin is low and is significantly less than the average daily dietary intake. This very low boron skin absorption makes it apparent that, for the borates tested, the use of gloves to prevent systemic uptake is unnecessary. These findings do not apply to abraded or otherwise damaged skin.

Purpose: The primary objective of this study was to determine the rate and extent of transdermal absorption for systemic delivery of diclofenac from Pennsaid (Dimethaid Research, Inc.) topical lotion into the systemic circulation after the lotion was applied to human volunteers, in an open treatment, non-blinded, non-vehicle controlled study. In addition, the in vivo metabolism of this topical diclofenac lotion has also been studied., Methods: Human volunteers were dosed with topical [14C]-diclofenac sodium 1.5% lotion on the knee for 24 h. Sequential time blood and urine samples were taken to determine pharmacokinetics, bioavailability and metabolism., Results: Topical absorption was 6.6% of applied dose. Peak plasma 14C occurred at 30 h after dosing, and peak urinary 14C excretion was at 24-48 h. The urinary 14C excretion pattern exhibits more elimination towards 24 h and beyond, as opposed to early urinary 14C excretion. This suggests a continuous delivery of [14C]-diclofenac sodium from the lotion into and through skin which only ceased when the dosing site was washed. Skin surface residue at 24 h was 26 +/- 9.5% dose (remainder assumed lost to clothing and bedding). Extraction of metabolites from urine amounted to 7.4-22.7% in untreated urine, suggesting substantial diclofenac metabolism to more water soluble metabolites, probably conjugates, which could not be extracted by the method employed. Two Dimensional TLC analysis of untreated urine showed minimal or no diclofenac, again emphasizing the extensive in vivo metabolism of this drug. Treatment of the same urine samples with the enzymes sulfatase and beta-glucuronidase showed a substantial increase in the extractable material. Three spots were consistently present in each sample run, namely diclofenac, 3'hydroxy diclofenac and an intermediate polar metabolite (probably a hydroxylated metabolite). Therefore, there was significant sulfation and glucuronidation of both diclofenac and numerous hydroxy metabolites of diclofenac, but many of the metabolites/conjugates remain unidentified. CONCLUSIONS; There was a continuous delivery of diclofenac sodium from the lotion into and through the skin, which ceased after the dosing site was washed. The majority of the material excreted in the urine were conjugates of hydroxylated metabolites, and not the parent chemical, although further identification is required.

Literature from the first half of this century report concern for toxicity from topical use of boric acid, but assessment of percutaneous absorption has been impaired by lack of analytical sensitivity. Analytical methods in this study included inductively coupled plasma-mass spectrometry which now allows quantitation of percutaneous absorption of 10B in 10B-enriched boric acid, borax, and disodium octaborate tetrahydrate (DOT) in biological matrices. This made it possible, in the presence of comparatively large natural dietary boron intakes for the in vivo segment of this study, to quantify the boron passing through skin. Human volunteers were dosed with 10B-enriched boric acid, 5.0%, borax, 5.0%, or disodium octaborate tetrahydrate, 10%, in aqueous solutions. Urinalysis, for boron and changes in boron isotope ratios, was used to measure absorption. Boric acid in vivo percutaneous absorption was 0.226 (SD = 0.125) mean percentage dose, with flux and permeability constant (Kp) calculated at 0.009 microgram/cm2/h and 1.9 x 10(-7) cm/h, respectively. Borax absorption was 0.210 (SD = 0.194) mean percentage of dose, with flux and Kp calculated at 0.009 microgram/cm2/h and 1.8 x 10(-7) cm/h, respectively. DOT absorption was 0.122 (SD = 0.108) mean percentage, with flux and Kp calculated at 0.01 microgram/cm2/h and 1.0 x 10(-7) cm/h, respectively. Pretreatment with the potential skin irritant 2% sodium lauryl sulfate had no effect on boron skin absorption. In vitro human skin percentage of doses of boric acid absorbed were 1.2 for a 0.05% solution, 0.28 for a 0.5% solution, and 0.70 for a 5.0% solution. These absorption amounts translated into flux values of, respectively, 0.25, 0.58, and 14.58 micrograms/cm2/h and permeability constants (Kp) of 5.0 x 10(-4), 1.2 x 10(-4), and 2.9 x 10(-4) cm/h for the 0.05, 0.5, and 5.0% solutions. The above in vitro doses were at infinite, 1000 microliters/cm2 volume. At 2 microliters/cm2 (the in vivo dosing volume), flux decreased some 200-fold to 0.07 microgram/cm2/h and Kp of 1.4 x 10(-6) cm/h, while percentage of dose absorbed was 1.75%. Borax dosed at 5.0%/1000 microliters/cm2 had 0.41% dose absorbed, flux at 8.5 micrograms/cm2/h, and Kp was 1.7 x 10(-4) cm/h. Disodium octaborate tetrahydrate (DOT) dosed at 10%/1000 microliters/cm2 was 0.19% dose absorbed, flux at 7.9 micrograms/cm2/h, and Kp was 0.8 x 10(-4) cm/h. These in vitro results from infinite doses (1000 microliters/cm2) were 1000-fold greater than those obtained in the companion in vivo study. The results from the finite (2 microliters/cm2) dosing were closer (10-fold difference) to the in vivo results. General application of infinite dose percutaneous absorption values for risk assessment is questioned by these results. These in vivo results show that percutaneous absorption of boron, as boric acid, borax, and disodium octaborate tetrahydrate, through intact human skin, is low and is significantly less than the average daily dietary intake. This very low boron skin absorption makes it apparent that, for the borates tested, the use of gloves to prevent systemic uptake is unnecessary. These findings do not apply to abraded or otherwise damaged skin.

Accelerator mass spectrometry (AMS) has been applied to the detection of 14C-labeled urinary metabolites of the triazine herbicide, atrazine, and the analytical performance of AMS has been directly compared to that of liquid scintillation counting (LSC). Ten human subjects were given a dermal dose of 14C-labeled atrazine over 24 h, and urine from the subjects was collected over a 7-day period. Concentrations of 14C in the samples have been determined by AMS and LSC and range from 1.8 fmol/mL to 4.3 pmol/mL. Data from these two methods have a correlation coefficient of 0.998 for a linear plot of the entire sample set. Accelerator mass spectrometry provides superior concentration (2.2 vs 27 fmol/mL) and mass (5.5 vs 54,000 amol) detection limits relative to those of LSC for these samples. The precision of the data provided by AMS for low-level samples is 1.7%, and the day-to-day reproducibility of the AMS measurements is 3.9%. Factors limiting AMS detection limits for these samples and ways in which these can be improved are examined.

Human risk assessment for topical exposure requires percutaneous absorption data to link environmental contamination to potential systemic dose. Human absorption data are not readily available, so absorption models are used. In vitro diffusion systems are easy to use but have proved to be somewhat unreliable and are not validated to man. This study compares percutaneous absorption in the isolated perfused porcine skin flap (IPPSF) system with that in man in vivo. The study design utilized the same compounds and the same dose concentration and vehicle in both systems. Methodology for each system was that which is routinely used ineach system. The skin surface was not protected during the absorption dosing period. Percutaneous absorption values were, for man and the IPPSF system, respectively: salicylic acid (6.5 +/- 5.0%; 7.5 +/- 2.6%), theophylline (16.9 +/- 11.3%; 11.8 +/- 3.8%), 2,4-dimethylamine (1.1 +/- 0.3%; 3.8 +/- 0.6%), diethyl hexyl phthalic acid (1.8 +/- 0.5%; 3.9 +/- 2.4%), and p-aminobenzoic acid (11.5 +/- 6.3%; 5.9 +/- 3.7%) (correlation coefficient was 0.78; p < 0.04). The skin surface wash recovery postapplication was similar for salicylic acid in man (53.4 +/- 6.3%) and the IPPSF system (48.2 +/- 4.9%). With the other compounds the majority of surface chemical was recovered in the surface wash and skin tape strip in the IPPSF system. With man, other than salicylic acid, only a few percent applied dose was recovered with surface washing and tape stripping. Since the wash procedure was effective with pig skin, we can assume that these chemicals in man were lost to adsorption to any clothing or bedding with the volunteers. The absorption in man was not less than that in the IPPSF. Assuming the dose was lost in man, it seems plausible that whatever compound was to penetrate human skin in solvent vehicle did so in the period of time before the chemical was removed. The IPPSF system appears to be a good model for predicting percutaneous absorption relative to man. This study design should be used to validate other systems to humans in vivo., (Copyright 1998 Academic Press.)

Purpose: This study determines comparative bioavailability of diclofenac sodium lotion compared to an aqueous solution after topical application to viable human skin in vitro. In addition, the difference between a single dose and multiple doses (8 times) was also determined., Methods: An in vitro flow-through diffusion cell system was employed, using radiolabelled diclofenac sodium., Results: Multiple doses of lotion (2 microl/cm2 and 5 microl/cm2) delivered a total of 40.1 +/- 17.6 microg and 85.6 micro 41.4 microg diclofenac, respectively, at 48 h, compared to only 9.4 +/- 2.9 microg and 35.7 +/- 19.0 microg absorbed after topical application of diclofenac as an aqueous solution (P < 0.05). A single dose study showed no statistical difference between diclofenac delivered in lotion or an aqueous solution. Over 48 h the total absorption from lotion was 10.2 +/- 6.7 microg and 26.2 +/- 17.6 microg (2 microl/cm2 and 5 microl/cm2, respectively), compared to 8.3 +/- 1.5 microg and 12.5 +/- 5.7 microg from an aqueous solution. Both single doses of lotion and aqueous diclofenac showed decreased diclofenac absorption into the receptor fluid between 12 and 24 h. However, when applied multiple times, absorption from lotion was continually increasing up to 48 h. The total dose accountability ranged from 76.8 +/- 8.2% to 110.6 +/- 15. 1% of the applied dose., Conclusions: Diclofenac lotion exhibited enhanced diclofenac percutaneous absorption rate through human skin (mass, flux and partition coefficient) when applied a multiple number of times and this enhanced absorption was maintained over 48 h. This suggests that a constituent of the lotion (DMSO) will enhance human skin absorption of diclofenac when used in a multi-dose regimen, but not after a single dose.

Hydroquinone is a ubiquitous chemical readily available as monographed in cosmetic and nonprescription forms for skin lightening, and is an important industrial chemical. The in vivo bioavailability for 24-h application in humans was 45.3+/-11.2% of dose from a 2% cream formulation containing [14C]hydroquinone, with the majority of radioactivity excreted in the first 24 h. Timed skin wash and skin tape-stripping sequences showed a rapid and continuous movement of hydroquinone into the stratum corneum of human volunteers. Plasma levels taken both ipsilateral and contralateral to the topical dosing site contained radioactivity at the first 0.5-h sampling time. Peak plasma radioactivity was at 4 h in the 8-h blood sampling period. In vitro percutaneous absorption with fresh viable human skin gave a bioavailability of 43.3% of dose, and flux was calculated at 2.85 microg/cm2/h. In vitro, some of the skin samples were pretreated with the metabolic inhibitor sodium azide, which had no effect on percutaneous absorption. Receptor fluid accumulations and 24-h skin samples were extracted and the extracts subjected to thin-layer chromatography (TLC). Control [14C]hydroquinone extraction and TLC had one radioactivity peak, hydroquinone. Receptor fluid and skin extraction had a second peak with the same Rf as benzoquinone, which was decreased with azide treatment. No other peaks were found. Ethyl acetate extraction of urine from the in vivo study showed all radioactivity to be only water-soluble, free hydroquinone released following glucuronidase treatment. Risk assessment should not only involve the bioavailability of intact topical hydroquinone, but also consider phase I and phase II metabolism in both humans and any animal for which toxicity potential was assessed.

Purpose: For decades, human cadaver skin has been banked and utilized by hospitals for burn wounds and to study percutaneous absorption and transdermal delivery. Skin storage maintenance and confirmation of skin viability is important for both uses, especially for the absorption process where the in vivo situation is simulated., Methods: Our system uses dermatomed human cadaver skin immediately placed in Eagles MEM-BSS, and refrigerated after donor death, then transferred to the laboratory and placed in Eagles MEM-BSS with 50 micrograms/ml gentamicin at 4 degrees C for storage., Results: Skin viability, determined by anaerobic metabolism where glucose is converted to lactose, was highest (p < 0.000) during the 18 hours of the first day after donor death, decreased some 3-fold by day 2 (p < 0.000), but then maintained steady-state viability through day 8. Viability then decreased by approximately one-half by day 13. Thus, using the above criteria, human skin will sustain viability for 8 days following donor death in this system. Heat-treated (60 degrees C water for one minute) and heat-separated epidermis and dermis lose viability., Conclusions: Human skin viability can be maintained for absorption studies. It is recommended that this system be used, and that heat-separation and skin freezing not be used, in absorption studies where skin viability and metabolism might be contributing factors to the study.

Ethylene oxide, a colourless gas at ordinary room temperature and pressure, is widely used as a fumigant, coming in contact with clothing and human skin. It is genotoxic in somatic and germ cells. [1,2-14C]Ethylene oxide and fabric discs were sealed in a glass container; the fabric discs were then removed and placed on human skin mounted in glass diffusion cells. Percutaneous absorption was 1.3% of the dose when the fabric/skin surface was open to surrounding air, and increased to 46.0% when the surface was occluded with latex glove material. The absorption was rapid, occurring within the first 0-4 hr assay period. Absorbed chemical was confirmed to be unchanged ethylene oxide in the receptor fluid. This study also serves as a model for exposure of fabric/skin to any potentially hazardous gas.

Percutaneous absorption of three topical dose levels of [14C]acetochlor in the rhesus monkey were determined for exposure risk assessment. The topical doses were 30.7, 0.43 and 0.03 mg acetochlor in 40 microliters commercial formulation and aqueous dilutions thereof, spread over 10 cm3 skin surface area (lower abdominal). The dosing area was not covered. The skin application time was 24 hr. The dosed skin surface area was washed with 50% soap (Ivory Liquid) and water at the end of the 24-hr dosing period. An intravenous dose of 0.43 mg was also administered to determine the excretory kinetics of acetochlor in the rhesus monkey. The same four monkeys were used for all dose administrations. Bioavailability was determined by radioactivity disposition in blood, urine and faeces. Percutaneous absorption was 23.1 +/- 8.7, 17.3 +/- 5.9 and 4.9 +/- 1.4% for 0.03, 0.43 and 30.7 mg doses, respectively. Assuming a constant state of absorption, the hourly exposure flux (microgram/cm2/hr) was 0.03 +/- 0.01 for the 0.03 mg dose (3 micrograms/cm2). Increasing the dose approximately 15-fold to 0.43 mg (43 micrograms/cm2) resulted in a 10-fold increase in flux to 0.3 microgram/cm2/hr. Increasing the dose a further 70-fold to 30.7 mg (3070 micrograms/cm2) resulted in only another 21-fold increase in flux (6.3 +/- 1.8 micrograms/cm2/hr). Thus, the efficiency of absorption (%) decreased with increased topical dose, but the amount (mass/flux) of acetochlor absorbed always increased with increased dose. Plasma levels of topical acetochlor at the high dose were detectable at 1 hr and continued at a relatively steady level through the 24-hr dosing period. After the skin surface wash (24 hr) plasma levels decreased but were still detectable at the last 168-hr sampling period. Acetochlor, recently EPA approved as an herbicide for corn crops, is carcinogenic; however, farmers will use half as much acetochlor/acre as other herbicides. The percutaneous absorption of acetochlor is equal to that of alachlor. Therefore, human exposure based on one-half usage suggests that human risk assessment should be one-half all other factors being equal.

Chemicals are introduced to fabric at many steps during manufacture and use. Fabrics containing chemicals can cause medical problems such as dermatitis and death. Insecticides impregnated into uniforms worn by "Desert Storm" personnel are implicated in "Gulf War Syndrome'. These chemicals must get from fabric into and through skin to cause toxic effects. The objective of the present study was to determine in vitro percutaneous absorption of model chemicals glyphosate (water soluble) and malathion (relative water insoluble) from cotton fabric into and through human skin. The percutaneous absorption of glyphosate from water solution was 1.42 +/- 0.25% dose. This decreased to 0.74 +/- 0.26% for glyphosate added to cotton sheets and immediately put onto skin. If the cotton sheets were dried for 1 or 2 days, then applied to skin, absorption was 0.08 +/- 0.02% and 0.08 +/- 0.01% respectively. However, wetting the 2-day dried cotton sheet with water to simulate sweating or wet conditions increased absorption to 0.36 +/- 0.07%. Similar results were found for malathion. Absorption of malathion from aqueous ethanol solution was 8.77 +/- 1.43%. This decreased to 3.92 +/- 0.49%, 0.62 +/- 0.11% and 0.60 +/- 0.14% for 0, 1- and 2-day-treated cotton sheets. However, malathion absorption from 2-day treated/dried cotton sheets increased to 7.34 +/- 0.61% when wetted with aqueous ethanol. These results show that chemicals in fabric (clothing, rug, upholstery, etc.) can transfer from fabric into and through human skin to cause toxic effects.

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), used for control of weeds in agriculture, forestry, and rights of way, can accumulate as a residual chemical in soil. The objective was to determine percutaneous absorption of 2,4-D from soil, with emphasis on soil load and skin contact time. With control acetone vehicle, in vivo absorption of 2,4-D in the rhesus monkey was 8.6 +/- 2.1% of the dose, which compared closely to published human absorption of 6.0 +/- 2.4%. Percutaneous absorption from soil loads of 1 and 40 mg/cm2 were 9.8 +/- 4.0 and 15.9 +/- 4.7%, respectively, values similar to acetone vehicle. In vitro absorption in human skin calculated from skin contact accumulation over 24 h was 1.8 +/- 1.7, 1.7 +/- 1.3, and 1.4 +/- 1.2% for soil loads of 5, 10, and 40 mg/cm2, respectively. Thus, soil load did not affect 24-h percutaneous absorption. Current Environmental Protection Agency (EPA) recommended calculated reductions due to soil load are not supported by these results with 2,4-D. Percutaneous absorption of 2,4-D from acetone vehicle for 8 h dosing period was 3.2 +/- 1.0%, one-third the value of 8.6 +/- 2.1% over 24 h. With soil vehicle, absorption for 8 h was only 0.03 +/- 0.02% for 40 mg/cm2 soil load and 0.05 +/- 0/.004% for 1 mg/cm2 soil load. Absorption for 16 h was 2.2 +/- 1.2%. Absorption over time was linear for acetone vehicle, where total dose is deposited on skin, but not linear for soil vehicle, which had an 8-h delay (lag time). This equates with a normal 8-h work day where most of the contaminated soil can be washed off the skin. The apparent partition coefficient of 2,4-D between soil and water changed over time. This suggests there is a "mobility" phase for 2,4-D in soil that will change with time. For soil vehicle, percutaneous absorption of 2,4-D was not linear in respect to soil load or to skin contact time. Calculation based on assumed linearity can falsely estimate potential human health hazard. Clearly, the dermatokinetics with soil and skin represent complex interactive forces that require detailed evaluation before overgeneralizing rules for interpretation in terms of risk assessment.

Environmental exposure in field studies is generally monitored by the cloth patch technique. Many investigators question the accuracy of the technique, in part due to lack of validation. The objective was to examine extraction of chemicals from cloth patches for potential technique validation. Chemicals studied were glyphosate, atrazine, malathion, alachlor and 2,4-dichlorophenoxy acetic acid (2,4-D), a selection of hydrophilic (glyphosate) and varying lipophilic compounds. The 14C-radiolabeled chemical was applied to a cotton patch (two types used) and solvent extracted over a 48-h time period. The chemical was soluble in the application solvent and in the extraction solvent. Extraction was near 100% at time 0 h, but statistically (P < 0.05 or greater) decreased to levels of 20-50% by 48 h. The missing chemical was detected in cloth residue and accountability was always excellent. The chemicals exhibited a time-response by incorporating into the cotton patch and not being available for extraction. Thus, validation of the cloth patch technique must include the time-period from the start of a field trial until laboratory analysis, a process which can take several days. This may account in part for differences noted between cloth patch technique and biological monitoring. It was subsequently shown that sonication loosens chemicals incorporated in the cloth patch, making the chemicals available for extraction. That sonication dislodged the chemicals suggests that the chemicals were not chemically bonded within the fabric but were probably sequestered within the fabric away from the solvent.

Azone (1-dodecylazacycloheptan-2-one) is an agent that has been shown to enhance percutaneous absorption of drugs. Azone is thought to act by partitioning into skin lipid bilayers and thereby disrupting the structure. An open-label study was done with nine volunteers (two males, seven females; aged 51-76 years) in which Azone cream (1.6%; 100 mg) was topically dosed on a 5 x 10-cm area of the ventral forearm for 21 consecutive days. On days 1, 8, and 15, the Azone cream contained 47 microCi of [14C]Azone. The skin application site was washed with soap and water after each 24-h dosing. Percutaneous absorption was determined by urinary radioactivity excretion. The [14C]Azone was ring labeled [14C-2-cyclo-heptan]. Radiochemical purity was > 98.6% and cold Azone purity was 99%. Percutaneous absorption of the first dose (day 1) was 1.84 +/- 1.56% (SD) of applied dose for 24-h skin application time. Day 8 percutaneous absorption, after repeated application, increased significantly (p < 0.002) to 2.76 +/- 1.91%. Day 15 percutaneous absorption, after continued repeated application, stayed the same at 2.72 +/- 1.21%. In humans, repeated application of Azone results in an initial self-absorption enhancement, probably due to its mechanism of action. However, steady-state percutaneous absorption of Azone is established after this initial change. Thus, Azone can enhance its own absorption as well as that of other compounds. This should be considered relevant for any pharmacological or toxicological evaluation. Washing the skin site of application with soap and water only recovered 1-2% of applied radioactivity. Previous published studies recovered the Azone dose with ethanol washes. Thus, there could potentially be an accumulation of Azone in skin.

In order to determine the human in vivo percutaneous absorption of pyrethrin and piperonyl butoxide, a commercial formulation containing either [14C]pyrethrin (3.8 mCi/mmol) or [14C]piperonyl butoxide (3.4 mCi/mmol) was applied to the ventral forearm of six human volunteers. The formulation contained 0.3% pyrethrin and 3.0% piperonyl butoxide. Spreadability studies showed that concentrations of 5.5 micrograms pyrethrin/cm2 and 75.8 micrograms piperonyl butoxide/cm2 (used in this study) would be consistent with levels found in actual use. The forearms were thoroughly cleansed with soap and water 30 min after application (as recommended for actual use). Percutaneous absorption was determined by urinary cumulative excretion following dose application. With a 7-day urinary accumulation, 1.9 +/- 1.2% (SD) of the dose of pyrethrin and 2.1 +/- 0.6% of the dose of piperonyl butoxide applied was absorbed through the forearm skin. 1 hr after application blood samples contained no detectable radioactivity. The percutaneous absorption of pyrethrin and piperonyl butoxide from the scalp was calculated to be 7.5% of the applied dose for pyrethrin and 8.3% for piperonyl butoxide. The calculated half-life of 14C excretion was 50 hr for pyrethrin and 32 hr for piperonyl butoxide. The data should be of relevance to appropriate risk assessment in extrapolating animal data to humans.

Diazinon is an organophosphorus insecticide which, through general use, comes into contact with human skin. To investigate its percutaneous absorption, human volunteers were exposed for 24 hr to 14C-labelled diazinon applied in acetone solution (2 micrograms/cm2) to the forearm or abdomen, or in lanolin wool grease (1.47 micrograms/cm2) to the abdomen. Complete void urine samples were collected daily for 7 days. Percutaneous absorption ranged from 2.87 +/- 1.16% (mean +/- SD, n = 6) to 3.85 +/- 2.16% of the applied dose, and there were no statistically significant differences with regard to site or vehicle of application. In rhesus monkeys, over the 7 days after iv dosing (2.1 microCi [14C]diazinon, 31.8 micrograms) a total of 55.8 +/- 6.8% (n = 4) of the dose was excreted in the urine, and 22.6 +/- 5.2% was eliminated in the faeces (78.4% total accountability). In in vitro percutaneous absorption studies with human abdominal skin, 14.1 +/- 9.2% of the applied dose accumulated in the receptor fluid over 24 hr of exposure to 0.25 microgram/cm2 (acetone vehicle). The calculated mass absorbed was the same (0.035 microgram/cm2) for both in vitro and in vivo absorption through human skin.

This in vitro study evaluated the extent of the absorption and metabolism of propranolol in human skin from four sources. Between 10.4 +/- 3.1 and 36.6 +/- 2.6% of the applied dose was absorbed; however, only a small portion (between 4.1 +/- 0.9 and 16.1 +/- 1.3%) of the dose permeated through the skin. Naphthoxyacetic acid formed during percutaneous absorption was located in the skin supernate. 4'-Hydroxypropranol was formed during percutaneous absorption and by skin microsomes. In addition, the microsomes biotransformed propranolol to norpropranolol. The retention of some of the absorbed drug and metabolites in the skin could explain the low plasma concentration and irritation observed following topical application of propranolol.

The objective of this study was to determine the percutaneous absorption of ethylene glycol through human skin in vitro. The in vitro diffusion cells were of the flow-through design with 1 cm2 surface area. Three separate donor skin samples, taken from the thighs of white males, 16, 37, and 57 years old, were used and three replicates were performed for each experiment. Phosphate buffered saline, at a flow rate of three ml per hour, served as the receptor fluid. The human cadaver skin samples were dermatomed to 500 microns. [14C]-labeled ethylene glycol was applied to the skin surface in acetone vehicle at a dose of 8 micrograms/cm2. After 24-hr dermal exposure, 18.28 +/- 11.66% of the applied dose was recovered in the receptor fluid, 8.29 +/- 5.02% in the skin and 12.53 +/- 6.77% in the skin surface wash (total accountability was 39.11 +/- 7.23%). Individual difference existed (P < 0.05) for the three human skin sources. The combined skin and receptor fluid partitioning resulted in a potential absorbed dose of 26.57% relative to the 8 micrograms/cm2 applied dose for a 24-hr exposure duration. This represents a flux of approximately 2 micrograms/cm2/24 hr or 0.09 micrograms/cm2/hr for ethylene glycol. The maximum flux observed was 2.82%/hr/cm2 or 0.25 micrograms/cm2/hr.

Studies have demonstrated that several chemicals are absorbed and metabolized during skin permeation. We investigated the absorption and metabolism of the pesticide butachlor. Radiolabeled butachlor was measured in human (n = 5) skin and the unchanged compound and metabolites were quantified by high-pressure liquid chromatography (HPLC) and thin-layer chromatography (TLC). Following a 24-hr exposure, an average butachlor quantity of approximately 5.00% of the applied dose (1.01 micrograms) was absorbed by the skin. The mean peak penetration rate was 0.7% of the applied dose per hour. The skin retained 1.40 to 8.10% of the applied butachlor. The retention of 1.4 to 8.1% of the pesticide by the skin suggests the importance of monitoring human skin following topical exposure. Of the dose recovered in the skin, 0.9% was metabolized to 4-hydroxybutachlor, while 1.8% of the dose in the receptor fluid was recovered as polar conjugates (cysteine, 0.29% dose; glutathione, 0.1% dose; unidentified metabolites, 1.4% dose); 2.8 and 6.8% of the dose absorbed by the skin (approximately 5.0%) were recovered as metabolites in the receptor fluids and skin homogenates, respectively. Similar to metabolism during percutaneous absorption, butachlor was metabolized to its conjugated and hydroxyl derivatives by skin fractions. The rate of butachlor glutathione and butachlor cysteine formation using skin cytosolic fractions were 12.0 +/- 1.5 and 48.0 +/- 3.6 pmol/min/mg protein +/- SD, respectively. When human skin microsomes were incubated with butachlor, 4-hydroxybutachlor was formed at the rate of 55.0 +/- 15.0 pmol/min/mg protein +/- SD. 4-Hydroxybutachlor formation was totally dependent on the presence of NADPH. The biotransformation of butachlor using skin fractions indicates the metabolic capacity of the tissue. The biological significance of these metabolites in the disposition of butachlor requires further investigation.

Polychlorinated biphenyls (PCBs) are ubiquitous and persistent environmental pollutants. The major resident site for these PCBs is the soil, and human skin is frequently in contact with soil. Our objective was to determine the percutaneous absorption of the PCBs Aroclor 1242 and Aroclor 1254 from soil. PCB-contaminated soil was prepared at levels of 44 ppm Aroclor 1242 and 23 ppm Aroclor 1254. PCB concentrations on skin were 1.75 micrograms/cm2 for Aroclor 1242 and 0.91 microgram/cm2 for Aroclor 1254. In vivo percutaneous absorption in the rhesus monkey was determined by urinary and fecal [14C]-PCB excretion for a 5-wk period following topical dosing. Absorption of Aroclor 1242 was determined in vitro with human skin for comparative purposes. In vivo in the rhesus monkey the percutaneous absorption of Aroclor 1242 was 13.8 +/- 2.7 (SD)% of the dose and the absorption of Aroclor 1254 was 14.1 +/- 1.0%. These absorption amounts are similar to the absorption of Aroclor 1242 and 1254 from other vehicles (mineral oil, trichlorobenzene, acetone). With in vitro percutaneous absorption through human skin, most of the Aroclor 1242 and Aroclor 1254 resided in the skin and the amounts were dependent upon dosing vehicle (water > mineral oil > soil). Both PCBs readily partitioned from water into soil and human powdered stratum corneum. By difference the partitioning favored both PCBs going from soil into stratum corneum. These data emphasize the role of soil in percutaneous absorption and provide information for appropriate risk assessment.

The objective was to determine the percutaneous absorption of arsenic-73 as H3ASO4 from water and soil. Soil (Yolo County 65-California-57-8) was passed through 10-, 20-, and 48-mesh sieves. Soil retained by 80 mesh was mixed with radioactive arsenic-73 at a low (trace) level of 0.0004 microgram/cm2 (micrograms arsenic per square centimeter skin surface area) and a higher dose of 0.6 micrograms/cm2. Water solutions of arsenic-73 at a low (trace) level of 0.000024 micrograms/cm2 and a higher dose of 2.1 micrograms/cm2 were prepared for comparative analysis. In vivo in Rhesus monkey a total of 80.1 +/- 6.7% (SD) intravenous arsenic-73 dose was recovered in urine over 7 days; the majority of the dose was excreted in the first day. With topical administration for 24 hr, absorption of the low dose from water was 6.4 +/- 3.9% and 2.0 +/- 1.2% from the high dose. In vitro percutaneous absorption of the low dose from water with human skin resulted in 24-hr receptor fluid (phosphate-buffered saline) accumulation of 0.93 +/- 1.1% dose and skin concentration (after washing) of 0.98 +/- 0.96%. Combining receptor fluid accumulation and skin concentration gave a combined amount of 1.9%, a value less than that in vivo (6.4%) in the Rhesus monkey. From soil, receptor fluid accumulation was 0.43 +/- 0.54% and skin concentration was 0.33 +/- 0.25%. Combining receptor fluid plus skin concentrations gave an absorption value of 0.8%, an amount less than that with in vivo absorption (4.5%) in the Rhesus. These absorption values did not match current EPA default assumptions.(ABSTRACT TRUNCATED AT 250 WORDS)

This study assessed the in vitro percutaneous absorption and metabolism of 3-indolylacetic acid after topical dosing to human skin from four sources. The metabolism of the compound during percutaneous absorption was assessed. The absorbed and metabolized chemicals were analyzed by radioactive scintillation counting and thin-layer chromatography: 1.2% +/- 0.04%, 1.4% +/- 0.07%, 3.0% +/- 1.0%, and 0.1% +/- 0.02% of the applied doses permeated through human skin samples from sources A to D, respectively, whereas 3.4% +/- 0.5% to 20.0% +/- 0.2% of the applied doses were retained by the skin. Of the absorbed dose, 2.1% +/- 1.0% to 12.1% +/- 3.5% was present as metabolites in the receptor fluid, and 2.2% +/- 0.5% to 5.2% +/- 0.1% was present as metabolites retained in the skin. Microsomal fractions were prepared from the skin samples, and the actions of these preparations on 3-indolylacetic acid were estimated. 5'-Hydroxyl-3-indolylacetic acid, 5',6'-dihydroxy-3-indolylacetic acid, and 5,6-dihydroxyindole were formed both during percutaneous absorption and by skin microsomal preparations. In addition, the skin samples biotransformed the acid to metabolic indican (3-indoxylsulfuric acid) and to the glucuronide conjugate of indole. The possible functional significance of the metabolism is discussed.

Pentachlorophenol (PCP) is one of the most heavily used pesticides. About 80% of PCP is used for wood preservation, whereas the remainder is used as an herbicide, fungicide, and disinfectant. PCP is a probable human carcinogen, based on animal studies. Illness and death have been reported where PCP is in direct contact with skin. PCP is the most ubiquitous compound found when the general population is screened for pesticide residue. PCP is found in soil as well as other environmental sources. Our objective was to determine the skin bioavailability of PCP from soil and from the control vehicle acetone. In vivo in the Rhesus monkey, percutaneous absorption of PCP was 24.4 +/- 6.4% of applied dose from soil and 29.2 +/- 5.8% of applied dose from acetone vehicle for a 24-hr exposure period. This amount of absorption makes PCP one of the more extensively absorbed compounds to date. Additionally, the 14C half-life was 4.5 days following both intravenous and skin administration of [14C]PCP. These data suggest high bioavailability and an extended biological interaction period with the long half-life. In vitro percutaneous absorption with human cadaver skin and human plasma receptor fluid underestimated the in vivo absorption. Receptor fluid accumulation was 0.6 +/- 0.09% and 1.5 +/- 0.2% for two skin sources for PCP in acetone vehicle and 0.01 +/- 0.00% and 0.00 +/- 0.08% for two skin sources with soil vehicle. Skin content after skin surface wash ranged from 2.6 to 3.7% for acetone vehicle and 0.07-0.11% for soil vehicle. Overall accountability for in vitro dose ranged from 81 to 96%.

Individual differences exist between patients, and, for topical therapy, differences in skin due to race may be a consideration. Pharmacological response depends upon the percutaneous absorption and the inherent activity of the chemical once absorbed into the biological system. Our objective was to determine the in vivo percutaneous absorption of three test chemicals in human subjects with Asian (A), black (B) and Caucasian (C) ethnic skin. Following a 30 min topical application on the upper outer arm of 1 mumol/cm2 14C-labeled chemical, percutaneous absorption was determined by both urinary excretion and the stripping technique. Amounts absorbed were: for benzoic acid 1.43 +/- 0.27% (SD) (A), 1.07 +/- 0.18% (B), 1.2 +/- 0.19% (C); for caffeine 1.06 +/- 0.17% (A), 1.01 +/- 0.19% (B) and 0.96 +/- 0.12% (C); for acetylsalicylic acid 1.8 +/- 0.31% (A), 1.59 +/- 0.31% (B) and 2.12 +/- 0.36% (C). No statistical difference (P > 0.05) was found in percutaneous absorption of benzoic acid, caffeine or acetylsalicylic acid between Asian, black and Caucasian subjects.