In vitro percutaneous absorption of benzene in human skin.

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.

In Vitro penetration of a novel oxaborole antifungal (AN2690) into the human nail plate.

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.

In vivo percutaneous absorption of arsenic from water and CCA-treated wood residue.

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).

Enhanced econazole penetration into human nail by 2-n-nonyl-1,3-dioxolane.

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.

Ciclopirox delivery into the human nail plate.

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.

Recovery from mercury-induced burning mouth syndrome due to mercury allergy.

We report a case in which burning mouth syndrome (BMS) was associated with a strong allergy to mercury. The aim of this case history is to strengthen knowledge of the relationship among allergy to mercury, systemic allergic contact dermatitis, and hypersensitivity of the oral mucosa. We performed series of standard and dental patch tests for screening for contact allergy to dental materials, in accordance with International Contact Dermatitis Research Group guidelines. Positive extreme allergic reactions to mercury (+++) and amalgam (++) were seen at the patch site and caused a flare-up of the systemic erythematous reaction. Full recovery from BMS and complete remission of systemic dermatitis were achieved after the mercury tooth filling was removed. Mercury is thought to be an allergen implicated in BMS as well as in the systemic reactivation of allergic contact dermatitis. Patch testing with dental series seems to have greater sensitivity and relevance in BMS patients.

Percutaneous absorption of arsenic from environmental media.

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.