Percutaneous absorption of hexachlorophene in rats, guinea pigs and pigs

Methodologies to Evaluate the Hair Follicle-Targeted Drug Delivery Provided by Nanoparticles

Nanotechnology has been investigated for treatments of hair follicle disorders mainly because of the natural accumulation of solid nanoparticles in the follicular openings following a topical application, which provides a drug "targeting effect". Despite the promising results regarding the therapeutic efficacy of topically applied nanoparticles, the literature has often presented controversial results regarding the targeting of hair follicle potential of nanoformulations. A closer look at the published works shows that study parameters such as the type of skin model, skin sections analyzed, employed controls, or even the extraction methodologies differ to a great extent among the studies, producing either unreliable results or precluding comparisons altogether. Hence, the present study proposes to review different skin models and methods for quantitative and qualitative analysis of follicular penetration of nano-entrapped drugs and their influence on the obtained results, as a way of providing more coherent study protocols for the intended application.

KMnO4-mediated reactions for hexachlorophene in aqueous solutions: Direct oxidation, self-coupling, and cross-coupling

Hexachlorophene (HCP) is used in a range of general cleaning and disinfecting products and has received increased attention due to its damaging effect to the central nervous system in animals and its toxicity in humans. The chemical oxidation of HCP by KMnO₄ was performed to systematically evaluate the effects of oxidant dose, pH, temperature, typical anions, humic acid (HA), and various matrices on HCP removal. The second-order rate constant for HCP was determined to be 4.83 × 10⁴ M^-1 s^-1 at pH 7.0 and 25 °C. The presence of HA can inhibit the removal of HCP by KMnO₄, while Cl^-, NO₃^-, SO₄^2-, PO₄^3-, and CO₃^2- have negligible effects. Degradation products analysis of the reaction, as well as theoretical calculations of HCP molecule and its phenoxy radical species, indicated that KMnO₄ oxidation for HCP included a C-C bridge bond cleavage, hydroxylation, direct oxidation and self-coupling, and cross-coupling reactions. This study revealed that KMnO₄ oxidation is an effective technique for eliminating HCP in real water and wastewater.

Porcine ear skin: an in vitro model for human skin

BACKGROUND/PURPOSE

Porcine ear skin is used in studies of percutaneous penetration as a substitute for human skin. The structure of this tissue, including hair follicles, was studied qualitatively and quantitatively in comparison with human skin.

METHODS

Sections of shock-frozen biopsies, biopsies embedded in paraffin and cyanoacrylate skin surface biopsies were investigated using microscopy. The thickness of the different skin layers and the follicular characteristics were determined.

RESULTS

The thickness of the stratum corneum was 17-28 microm, whereas the viable epidermis was 60-85 microm thick. On 1 cm(2), 11-25 hairs were detected, showing a diameter of 58-97 microm and a maximal extension depth of 0.96-1.38 mm into the skin. The orifices of the porcine infundibula showed a diameter of approximately 200 microm.

CONCLUSIONS

The results obtained are similar to those of human skin, indicating the suitability of this porcine tissue as a model for human skin.

Skin Permeation Rate as a Function of Chemical Structure

Multilinear and nonlinear QSAR models were built for the skin permeation rate (Log K(p)) of a set of 143 diverse compounds. Satisfactory models were obtained by three approaches applied: (i) CODESSA PRO, (ii) Neural Network modeling using large pools of theoretical molecular descriptors, and (iii) ISIDA modeling based on fragment descriptors. The predictive abilities of the models were assessed by internal and external validations. The descriptors involved in the equations are discussed from the physicochemical point of view to illuminate the factors that influence skin permeation.

Epidemiologic background of hand hygiene and evaluation of the most important agents for scrubs and rubs

The etiology of nosocomial infections, the frequency of contaminated hands with the different nosocomial pathogens, and the role of health care workers' hands during outbreaks suggest that a hand hygiene preparation should at least have activity against bacteria, yeasts, and coated viruses. The importance of efficacy in choosing the right hand hygiene product is reflected in the new Centers for Disease Control and Prevention guideline on hand hygiene (J. M. Boyce and D. Pittet, Morb. Mortal. Wkly. Rep. 51:1-45, 2002). The best antimicrobial efficacy can be achieved with ethanol (60 to 85%), isopropanol (60 to 80%), and n-propanol (60 to 80%). The activity is broad and immediate. Ethanol at high concentrations (e.g., 95%) is the most effective treatment against naked viruses, whereas n-propanol seems to be more effective against the resident bacterial flora. The combination of alcohols may have a synergistic effect. The antimicrobial efficacy of chlorhexidine (2 to 4%) and triclosan (1 to 2%) is both lower and slower. Additionally, both agents have a risk of bacterial resistance, which is higher for chlorhexidine than triclosan. Their activity is often supported by the mechanical removal of pathogens during hand washing. Taking the antimicrobial efficacy and the mechanical removal together, they are still less effective than the alcohols. Plain soap and water has the lowest efficacy of all. In the new Centers for Disease Control and Prevention guideline, promotion of alcohol-based hand rubs containing various emollients instead of irritating soaps and detergents is one strategy to reduce skin damage, dryness, and irritation. Irritant contact dermatitis is highest with preparations containing 4% chlorhexidine gluconate, less frequent with nonantimicrobial soaps and preparations containing lower concentrations of chlorhexidine gluconate, and lowest with well-formulated alcohol-based hand rubs containing emollients and other skin conditioners. Too few published data from comparative trials are available to reliably rank triclosan. Personnel should be reminded that it is neither necessary nor recommended to routinely wash hands after each application of an alcohol-based hand rub. Long-lasting improvement of compliance with hand hygiene protocols can be successful if an effective and accessible alcohol-based hand rub with a proven dermal tolerance and an excellent user acceptability is supplied, accompanied by education of health care workers and promotion of the use of the product.

Quantitative structure-permeability relationships (QSPRs) for percutaneous absorption

Quantitative structure-permeability relationships (QSPRs) have been derived by many researchers to model the passive, diffusion-controlled, percutaneous penetration of exogenous chemicals. Most of these relationships are based on experimental data from the published literature. They indicate that molecular size (as molecular weight) and hydrophobicity (as the logarithm of the octanol-water partition coefficient; log k(ow)) are the main determinants of transdermal penetration. This article reviews the current state of the art in QSPRs for absorption of chemicals through the skin, and where this technology can be exploited in future research. The main shortfalls in QSPR models result from inconsistency and error of the experimental values used to derive them. This is probably caused by the manner in which they employ data from a variety of sources and, in some cases, slightly different experimental protocols. Further, most current models are based on data generated from either aqueous or ethanolic solution, where each penetrant is present at its saturated solubility or a fraction of its saturated solubility. No models currently account for the influences of formulation upon percutaneous penetration. Current QSPR models provide a significant tool for assessing the percutaneous penetration of chemicals. They may be important in determining the bioavailability of a range of topically applied exogenous chemicals, and in issues of dermal toxicology and risk assessment. However, their current use may be limited by their lack of applicability across different formulation types. As a consequence, their true value may be to make predictions within specific formulation types, as opposed to a general model based on a range of formulation types. In addition, the endpoint of models may be inappropriate for specific applications other than the systemic delivery of topically applied chemicals.

The pig as an experimental animal model of percutaneous permeation in man: qualitative and quantitative observations--an overview

The pig has been a well-recognized experimental animal in biomedical research for many centuries. Physiological and anatomical similarities between man and pig made this animal a good model for man in many research areas. Pharmacological and toxicological research on the skin is often based on knowledge of skin absorption and percutaneous permeation. Anatomical, physiological and biochemical similarities are cited and various uses of the pig as a model for man in the investigation of skin permeation are reviewed. Further, several isolated organ models are reviewed. The importance of full details of the experimental animal, namely its age, sex, breed, size (weight) and body region, is emphasized.

Dermal penetration of 14C-labeled diisopropyl methylphosphonate in swine

Diisopropyl methylphosphonate (DIMP) has been identified as a groundwater contaminant on or near sites of former chemical warfare production facilities. The material is a by-product of GB (or Sarin) manufacture and does not occur naturally in the environment. The present study measured the dermal absorption of 14C-labeled DIMP in swine to establish the basis for estimating health risk from this portal of entry. Yorkshire cross swine were treated by sc injection of labeled DIMP to measure the efficiency of bioelimination. Additional pigs each received a single percutaneous (pc) exposure of 400, 40, or 4 micrograms/cm2 of labeled DIMP. Absorption through 7 d was measured by the appearance of 14C label in the urine and feces. Tissue specimens, collected at necropsy, were assessed for residual radioactivity. The results showed that between 3 and 7% of cutaneous DIMP was absorbed through 7 d. Urinary elimination accounted for about 95% of the absorbed dose in the first 24 h. No significant tissue deposition was observed. Pigs treated by the sc route excreted nearly 100% of the injected material demonstrating an extremely efficient metabolic process. It was concluded that humans may be expected to absorb less than 10% of an unoccluded single dermal exposure to DIMP. Absorbed dose would likely be metabolized to isopropyl methylphosphonic acid and excreted primarily in the urine within 24 h. Significant evaporation of the material from the open skin surface would be expected to occur.

Penetration of trolamine salicylate into the skeletal muscle of the pig

Studies to determine the extent of local tissue penetration of topically applied trolamine [14C]salicylate were conducted in domestic pigs. The preparation was applied onto a 100-cm2 shaved area of skin overlying the biceps femoris at a concentration of 0.7 mg of salicylate/cm2 to closely approximate the actual use in humans. At least 82% of the topically applied trolamine salicylate was absorbed over a 2-h period. Based on blood and muscle salicylate levels, a localization of the absorbed drug occurred in muscle underlying the treated area within 120 min. Muscle from the treated area had a concentration of salicylate that was 13 times that of blood and 49 times that of muscle taken from untreated areas. Blood samples taken from the treated area at 10, 20, and 30 min showed that salicylate levels ranged from 15.8 to 5.3 micrograms/g. Less than 0.5% of the applied drug was excreted in the urine during the 2-h period.

Gastrointestinal and dermal absorption: interspecies differences

It has been repeatedly demonstrated that there are considerable interspecies differences with respect to the dermal absorptions of a chemically diverse set of substances, ranging from ionic substances to complex organic molecules, some of which are of great relevance to environmental/occupational health (e.g., the organophosphate insecticides). In general, human skin was found to be much less permeable to the substances evaluated when compared to rabbit and rodent skin; however, the pig and monkey appear to most closely simulate the absorption capabilities of human skin for a variety of substances. Unfortunately, no truly systematic evaluations of numerous classes of compounds have been made via interspecies comparisons. Thus, even though the data derived until now are very consistent, one could argue that strong general conclusions with respect to interspecies differences in dermal absorption cannot yet be made because the substances evaluated thus far may not be sufficiently representative. Clearly, further research along these lines is required.

Vaginal absorption of hexachlorophene in the rat

The pharmacokinetics of hexachlorophene (HCP) was studied in sexually mature virgin Wistar rats. [14C] HCP was injected either via the femoral vein, (ivn, 0.87 or 3.87 mg/kg in saline) or into the vaginal orifice (ivg, 0.87 mg/kg in corn oil). The disappearance of 14C from the blood after ivn administration followed the kinetics of a 2 compartment open model. The blood 14C profiles were superimposable, suggesting that the distribution and elimination rate constants for both doses were similar. After ivg application of [14C] HCP, 14C was detected in tail blood at 0.5 h, peaked between 2 and 4 h and disappeared slowly to 12 h but more rapidly thereafter. Less than 10% of the ivg dose of [14C] HCP remained in the vagina after 4 h. The cumulative recoveries of 14C in the faeces and urine 5 days after ivn administration were 85% and 4.6% of the dose, respectively. Comparable recoveries following ivg administration were 72% and 3.7%. The results suggest that HCP readily penetrates through the vaginal mucosa of the rat.