Evaluation of controlled-release mosquito repellent formulations.

Eight polymer and 9 microcapsule formulations of deet were tested on laboratory rabbits against Aedes aegypti and Anopheles albimanus. Several formulations were significantly more effective than simple (unformulated) deet at the same strength for periods up to 24 h. Best results were obtained with a polymer formulation containing a high molecular weight fatty acid and 3 microcapsule formulations containing lanolin, gum arabic, gelatin, tannic acid, stearic acid, polypropylene glycol, water, and a commercial lotion in the microcapsule and carrier fractions.

Evaluation of the laboratory rabbit model for screening topical mosquito repellents.

The laboratory rabbit was evaluated as a model for screening topical mosquito repellents, using data obtained in tests of deet (N,N-diethyl-3-methylbenzamide) against Aedes aegypti on humans and rabbits. Host-specific differences in the action of the test material were quantified by multiple regression analysis. The test material was less effective but more persistent in tests on rabbits, and responses of the mosquito test population were more variable.

A comparison of in vitro skin-penetration cells.

A new low-volume flow-through diffusion cell (LVFC) was designed to provide accurate determinations of penetrant flux across skin while minimizing the dilution of penetrant in receptor fluid and eliminating the need for magnetic stirring. The performance of the 0.3-mL LVFC was compared to a magnetically stirred, 4.3-mL high-volume flow cell (HVFC) and to a magnetically stirred, manually sampled 7.5-mL static cell (SC) with hydrophilic and lipophilic penetrants. The clearance of 14C-labeled benzoic acid from the LVFC and HVFC followed an exponential profile expected for complete mixing when the LVFC and HVFC were run at flow rates of 0.4-0.9 and 4.0-5.2 mL/h, respectively. The in vitro dispositions of 14C-labeled benzoic acid and estradiol were determined in the LVFC and HVFC by applying the compounds to split-thickness pig skin at a 4 micrograms/cm2 dose. Additionally, the effects of receptor fluid flow rate (1.2 vs 3.5 cell volumes/h) and method of skin attachment (O-ring vs compression) were determined on disposition in the HVFC. The percutaneous penetration of benzoic acid and the residue of estradiol within skin did not differ between the LVFC and HVFC. However, the percutaneous penetration of benzoic acid increased significantly (p < 0.05) using the O-ring attachment as compared to compression at a flow rate of 1.2 cell volumes/h. The in vitro permeation of benzoic acid-saturated water and 17 beta-estradiol-saturated propylene glycol monolaurate through human epidermis was compared between the LVFC, HVFC, and SC. The LVFC and HVFC had flow rates of 0.9-1.0 mL/h.(ABSTRACT TRUNCATED AT 250 WORDS)

Wound healing after laser injury to skin--the effect of occlusion and vitamin E.

The skin of Yorkshire pigs was irradiated with various doses of argon and copper-vapor laser and evaluated for effects on healing time of pretreatment with topical or intramuscular vitamin E or the Op-Site wound dressing. Incident irradiance for both lasers was between 3.5 and 4.5 W/cm2 for a 10-14-mm beam diameter with a nearly uniform intensity profile. Minimal erythemic dose for the copper-vapor laser was 35 +/- 2 J/cm2 (10 s exposure) and 22.4 +/- 0.1 J/cm2 (6-s exposure) for the argon laser. Three dose levels were administered: a low dose causing light erythema, an intermediate dose, and a high dose causing dermal stasis. The radiant exposures for low, intermediate, and high doses were 35, 70, and 138 J/cm2 for the copper-vapor laser and 22.4, 55, and 129 J/cm2 for the argon laser. Exposure to argon and copper-vapor lasers generally caused wounds with similar healing times. Healing time was significantly decreased for wounds caused by intermediate exposure of the copper-vapor laser and either pretreated with vitamin E or treated with the wound dressing. Healing times for corresponding argon-laser exposure were significantly decreased with pretreatment of intramuscular vitamin E only or after treatment with the wound dressing. These findings may be valuable in selecting treatment for accidental laser skin injuries in man.

Percutaneous penetration and skin retention of topically applied compounds: an in vitro-in vivo study.

Radiolabeled compounds with varying partition coefficients (paraoxon, benzoic acid, parathion, and DDT) were chosen to study the percutaneous penetration and extent of dermal retention in pig skin both in vitro and in vivo. Radiolabel distributions within the skin were determined from 1 min to 24 h after application in ethanol. The distribution of radioactivity in the skin during the first 4 h was comparable between in vitro and in vivo experiments. At 24 h, radioactive residues in the dermis were significantly higher in vitro than in vivo for DDT, the most lipophilic compound. Increasing air flow over the skin surface significantly increased evaporative loss for volatile compounds (benzoic acid, N,N-diethyl-m-toluamide, malathion, parathion, and DDT), significantly decreased the residues in the upper skin layer for N,N-diethyl-m-toluamide, malathion, parathion, and DDT, significantly decreased the dermal residue for malathion, and significantly decreased the penetration of N,N-diethyl-m-toluamide, malathion, and parathion. On a percentage basis, increasing the dose of parathion and paraoxon from 4 to 1000 micrograms/cm2 resulted in significantly lower residues in the dermis. When applied to the dermis, the more hydrophilic benzoic acid and paraoxon better penetrated the dermis than the more hydrophobic parathion and DDT. An ethanol vehicle facilitated the penetration of parathion into the dermis and receptor fluid. These results indicate that the dermis interacted with the penetrant during both in vitro and in vivo percutaneous absorption. Factors such as partition coefficient and dose of the penetrant, air flow over the skin, and vehicle changed the distribution of penetrants in the skin and percutaneous penetration.(ABSTRACT TRUNCATED AT 250 WORDS)

Methods for in vitro skin absorption studies of a lipophilic toxin produced by red tide.

The penetration and distribution of [3H]PbTx-3 into pig skin was determined using in vivo and in vitro methods. The dose used in each topical study was 0.3-0.4 micrograms/cm2 skin, with dimethylsulfoxide as the vehicle. In the in vivo study, mean cutaneous absorption after 48 h (expressed as percentage of the dose) was 11.5% (n = 3). In the in vitro study, mean cutaneous absorption after 48 h was 1.6% (n = 12), when based on accumulation of radioactivity in receptor fluid, or 9.9% when based on receptor fluid and dermis. [3H]PbTx-3 readily penetrated through the epidermis into the dermis, reaching maximal dermal accumulation at 4 h (9.1% in vivo and 18% in vitro). At 24 h, the amount in the dermis decreased to 2.3% and 15% in vivo and in vitro, respectively and at 48 h the amount in the dermis decreased to 8.2% in vitro. These results demonstrate the important role of the dermis as a reservoir for a lipophilic compound in both in vivo and in vitro percutaneous absorption studies.

Resistance of permethrin to weathering in fabrics treated for protection against mosquitoes (Diptera: Culicidae).

Two different methods of treating cotton and nylon-cotton fabrics with permethrin were evaluated for protection from mosquito bites after laboratory weathering. Cotton fabric treated by the individual dynamic absorption method provided consistently better protection than cotton fabric treated by the aerosol method. The nylon-cotton fabric provided similar protection regardless of the treatment method. After weathering, the toxic effects of both types of permethrin-treated fabrics treated by both methods diminished much more rapidly than did the repellent effect. Low residual amounts of permethrin in the fabrics provided 85% protection from bites against Aedes aegypti (L.) and 93% protection against Anopheles stephensi Liston. Permethrin-treated fabrics were effective in providing protection from mosquito bites for long periods, even after exposure to weathering, and appear to be an effective means of reducing nuisance effects and disease transmission by mosquitoes.

Effects of weathering on fabrics treated with permethrin for protection against mosquitoes.

Permethrin-impregnated and untreated fabrics were evaluated for their toxic and repellent effects against Anopheles stephensi and Aedes aegypti after both types of fabrics were subjected to accelerated weathering for 9 weeks, under a simulated wet/tropical environment. The toxic (knockdown) effect of permethrin-impregnated fabrics against both species of mosquitoes diminished rapidly after 1 week compared to the repellent effect. After 6 weeks of weathering, the remaining low amounts of permethrin provided fair protection from mosquito bites; however, no knockdown was observed at those levels. Permethrin-treated fabric was effective in providing protection from mosquito bites and appears to be a means of attenuating both the nuisance effects and, possibly, disease transmission by mosquitoes.

Evaporation and skin penetration characteristics of mosquito repellent formulations.

Formulations of the mosquito repellent N,N-diethyl-3-methylbenzamide (deet) in combination with a variety of additives were developed to control repellent evaporation and percutaneous penetration. Deet was also formulated with the repellent dimethyl phthalate to study the interaction of the two compounds on the skin. The evaporation and penetration processes were evaluated on whole and split-thickness pig skin using radiolabeled repellents with an in vitro apparatus. Under essentially still air and air flow conditions, one of the deet formulations resulted in significantly reduced total evaporation and percutaneous penetration of deet as compared to unformulated repellent. When deet and dimethyl phthalate were combined, neither repellent affected the total amount of evaporation and penetration of the other compound. However, initial percutaneous penetration and evaporation rates were slightly less and decayed less rapidly than when both chemicals were tested separately at the same dose. These results indicated a degree of competition of the two compounds for the same avenues of loss.

Distribution and fate of diethyl malonate and diisopropyl fluorophosphate on pig skin in vitro.

The in vitro distribution and fate of [14C]diethyl malonate and [14C]diisopropyl fluorophosphate were evaluated on normal and heat-treated pig skin. The extent of hydrolysis from the skin surface, skin, and receptor fluid was determined. A significant skin-mediated hydrolysis (15-35% of applied dose) was observed for diethyl malonate in normal skin, but not in heat-treated skin. These results indicated that a heat labile process (e.g., enzymatic hydrolysis) was in part responsible for the degradation of diethyl malonate after topical application to normal skin. Heat treatment tripled the skin penetration of diisopropyl fluorophosphate and reduced the amount of recovered hydrolysis product, diisopropyl phosphoric acid. Enzymatic and spontaneous hydrolysis, as well as impurity, accounted for the presence of degradation product.

Influence of skin source, penetration cell fluid, and partition coefficient on in vitro skin penetration.

Using split-thickness pig skin mounted on in vitro skin penetration-evaporation cells, standard conditions were developed to preserve the viability of the skin as judged by its ability to successfully graft to nude mice. The effects of variations from these conditions on the disposition of radioactivity of radiolabeled compounds were determined. No differences in percutaneous penetration were found for N,N-diethyl-m-toluamide, parathion, and progesterone when Tyrode's solution was used in place of tissue culture media. The percutaneous penetration of benzo(a)pyrene on human and pig skin was unaffected by the presence of sodium azide in the tissue culture media; however, with mouse skin, penetration was lower when sodium azide was present. The disposition of radioactivity following topical application of five radiolabeled compounds was similar on fresh skin compared with skin that had been frozen and exposed to ethylene oxide, although variability of the values was greater with the treated skin. The percutaneous penetration of several compounds was determined on skin with and without the epidermis. The penetration of compounds with a lower log P (log octanol-water partition coefficient) increased to a greater extent (e.g., benzoic acid, log P = 2, sixfold increase) than compounds with a higher log P (e.g., DDT, log P = 5, twofold increase). To further validate the use of pig skin, the percutaneous penetration of 11 compounds on pig skin were correlated (r = 0.79) with the values obtained for human skin under standardized in vitro conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution and metabolism of topically applied ethanolamine.

The distribution and metabolism of topical [14C]ethanolamine was studied in vivo, using athymic nude mice, human skin grafted onto athymic nude mice, and in vitro, using excised pig skin. Ethanolamine was the only radioactive phospholipid base detected in the human skin grafts, in the mouse skin, and in the pig skin. Ethanolamine that penetrated human skin grafts or mouse skin was extensively metabolized in the animal. The liver is a major site for metabolism of ethanolamine, containing over 24% of the applied radioactive dose. The kidneys, lungs, brain, and the heart contained 2.53, 0.55, 0.27, and 0.15% of the dose, respectively. The hepatic phospholipid bases, ethanolamine, choline, and serine, were all highly radioactive. Hepatic, human skin graft, and mouse skin proteins were also highly radioactive. Over 18% of the topical radioactive dose was oxidized to 14CO2 and 4.6% was excreted in the urine over 24 hr. Urea, glycine, serine, choline, and uric acid were the urinary metabolites of ethanolamine. In vitro data showed that a relatively small percentage of the applied dose was lost from the skin by evaporation and percutaneous penetration. The bulk of the dose remained in the epidermis. Radiometric and enzymatic assays suggest that ethanolamine enhances the hydrolysis of topically applied diisopropylfluorophosphate.

Topical glutaraldehyde-percutaneous penetration and skin irritation.

To investigate the safety of the topical application of glutaraldehyde to the ankle and heel of man, the in vitro penetration of glutaraldehyde in a 10% aqueous solution through isolated human thin stratum corneum (chest and abdomen), isolated human epidermis (abdominal), and human thick stratum corneum (blister tops from the sole) was determined 1 h after application. Under these conditions, glutaraldehyde did not penetrate thick stratum corneum, while 2.8%-4.4% of the applied dose penetrated the isolated epidermis, and 3.3%-13.8% of the applied dose penetrated thin stratum corneum. An 8-week irritancy test was conducted by applying a 10% aqueous solution of glutaraldehyde to the ankle and heel area of 12 volunteers. Irritation and one case of sensitization resulted from glutaraldehyde application to areas of thin stratum corneum (anterior ankle) but not from applications to thick stratum corneum (medial, posterior, and lateral heel and posterior ankle), which may be a privileged site with respect to glutaraldehyde sensitivity.

Evaluation of diethyl malonate as a simulant for 1,2,2-trimethylpropyl methylphosphonofluoridate (soman) in shower decontamination of the skin.

A shower decontamination bench model has been used to assess quantitatively the importance of several variables (water pressure and temperature, surfactant concentration in the decontamination fluid, nozzle type, and shower time) on decontamination of nontoxic chemical warfare-agent simulants diethyl malonate and thickened diethyl malonate from pig skin in vitro. Diethyl malonate was validated as a simulant for 1,2,2-trimethylpropyl methylphosphonofluoridate (soman) by comparison of the skin penetration and decontamination of radiolabeled diethyl malonate to the radiolabeled phosphonofluoridate in shower decontamination trials of pig skin in vitro. Percutaneous penetration of diethyl malonate was significantly greater than that of the phosphonofluoridate during the 15-min period after application. However, both were less than 0.1% of the applied dose. Showering or thickener had no significant effect on the percutaneous penetration of diethyl malonate or the phosphonofluoridate. Most of the phosphonofluoridate removed by showering or scrubbing the skin was inactivated. The quantity of intact 1,2,2-trimethylpropyl methylphosphonofluoridate that penetrated through the skin was below the detection limit of the enzymatic analysis. There was no statistically significant difference between the phosphonofluoridate and diethyl malonate in efficacy of shower decontamination. The presence of thickener did not have a significant effect on decontamination efficacy.

Percutaneous penetration in the hairless dog, weanling pig and grafted athymic nude mouse: evaluation of models for predicting skin penetration in man.

The human skin grafted congenitally athymic (nude) mouse, pig skin grafted nude mouse, hairless dog, and weanling Yorkshire pig were evaluated as models for predicting skin penetration in man. Nine radiolabelled compounds previously tested on man were applied topically (4 micrograms/cm2) to each model. These compounds included caffeine, benzoic acid, N, N-diethyl-m-toluamide, three steroids, and three insecticides. To correct for incomplete excretion of the label following topical absorption, per cent penetration was calculated by dividing the per cent of the topically applied radioactive dose recovered in the excreta by the corresponding percentage after parenteral administration and multiplication by 100. Calculated values of per cent penetration were confirmed in the case of the grafted nude mouse because significant correlations (r = 0.78 for human skin grafted athymic nude mouse and r = 0.97 for pig skin grafted athymic nude mouse) were found between the calculated values and the actual values obtained by summing the radioactivity recovered in the urine, faeces, tissues, and carcass. The results also revealed a significant correlation between human skin grafted athymic nude mouse values and human values (r = 0.74, P = 0.05) and between weanling Yorkshire pig values and human values (r = 0.83, P = 0.05). In contrast, no significant correlation existed between human values and those of the hairless dog and the pig skin grafted athymic nude mouse.

Development of an in vitro model for determining the fate of chemicals applied to skin.

An in vitro apparatus was developed to determine the evaporation and percutaneous penetration of radiolabeled chemicals applied to pig skin. The dermal side of the skin was mounted on a penetration cell. Appearance of radioactivity in the fluid flowing past the dermal side of the skin indicated percutaneous penetration. An evaporation manifold, with replaceable vapor traps, was mounted on the stratum corneum side of the skin. Using the model, the influence of a number of factors (storage conditions, flow rate and composition of fluid in the penetration cell, and temperature and humidity of air flowing through the evaporation manifold) on the disposition of chemicals on the skin was determined. The percutaneous penetration and evaporation of N,N-diethyl-m-toluamide were determined on skin samples immediately after excision and after a freezing period of 1 to 6 weeks at -80 degrees C. Progressively greater percutaneous penetration values were associated with samples which had the greater storage times. Thereafter, only fresh skin was used. When the penetration cell flow was increased from 5 to 10 ml/hr of Tyrodes solution, or when porcine serum was substituted for Tyrodes solution as the fluid flowing through the penetration cell, no significant difference was found in total percutaneous penetration of several control compounds. However, total percutaneous penetration of N,N-diethyl-m-toluamide more than doubled when the air temperature was increased from 20 to 32 degrees C, whereas total evaporation decreased. Increasing the humidity of air flowing through the evaporation manifold enhanced the percutaneous penetration of polar organic compounds but had little effect of the percutaneous penetration of highly lipid soluble organic compounds. Using the model under standardized conditions, the percutaneous penetration of 10 control compounds (N,N-diethyl-m-toluamide, benzoic acid, caffeine, three steroids, and four insecticides) were found to correlate with the corresponding published values for man (r = 0.77, p = 0.05). The skin disposition of the nerve agent analog (diisopropylfluorophosphate, DFP) and simulant (diethyl malonate) was determined using the model. When applied to the skin at a dose of 0.1 mg/cm2, DFP and diethyl malonate were lost from the skin surface mainly by evaporation. Skin penetration was limited due to loss by evaporation.

Evaluation of animal models for predicting skin penetration in man.

The human skin grafted athymic nude mouse, pig skin grafted athymic nude mouse, hairless dog, and weanling Yorkshire pig were evaluated as models for predicting skin penetration in man. Nine radiolabeled compounds previously tested on man were applied topically (4 micrograms/cm2) to each animal. These compounds included caffeine, benzoic acid, N,N-diethyl-m-toluamide, three steroids, and three insecticides. To correct for incomplete excretion of the label following topical absorption, percentage penetration was calculated by dividing the percentage of the topically applied radioactive dose recovered in the excreta by the corresponding percentage after parenteral administration and multiplication by 100. In the case of the grafted athymic nude mouse, calculated values of percentage penetration were confirmed because significant correlations (r = 0.78 for the human skin grafted athymic nude mouse and r = 0.97 for the pig skin grafted athymic nude mouse) were found between the calculated values and percentage penetration determined by summing radioactivity recovered in the urine, feces, tissues, and carcass. The results revealed a significant correlation between human skin grafted athymic nude mouse values and human values (r = 0.74, p = 0.05), and between weanling Yorkshire pig values and human values (r = 0.83, p = 0.05). In contrast, no significant correlation existed between human values and those of the hairless dog and pig skin grafted athymic nude mouse. The disposition of radioactivity following topical application of the radiolabeled nerve agent analog ( diisopropylfluorophosphonate ) and simulant (diethyl malonate) was determined in the weanling pig and the human skin grafted athymic nude mouse.(ABSTRACT TRUNCATED AT 250 WORDS)