Transdermal Drug Delivery Systems of a Beta Blocker: Design, In Vitro, and In Vivo Characterization

The matrix type transdermal drug delivery systems (TDDS) of metoprolol were prepared by film casting technique using a fabricated stainless steel film casting apparatus and characterized in vitro by drug release, skin permeation, skin irritation, and in vivo pharmacodynamic and stability studies. Four formulations were prepared that differed in the ratio of matrix forming polymers. Formulations M-1, M-2, M-3, and M-4 were composed of Eudragit RL-100 and polyvinyl acetate with the following ratios: 2:8, 4:6, 6:4, and 8:2, respectively. All the four formulations carried 10% (w/w) of metoprolol tartrate, 5% (w/w) of dibutylphthalate, and 5% (w/w) of (+/-) menthol in dichloromethane:isopropyl alcohol (80:20 v/v). Cumulative amount of drug released in 48 hr from the four formulations was 79.16%, 81.17%, 85.98%, and 95.04%. The corresponding values for cumulative amount of drug permeated for the said formulations were 59.72%, 66.52%, 77.36%, and 90.38%. On the basis of in vitro drug release and skin permeation performance, formulation M-4 was found to be better than the other three formulations and it was selected as the optimized formulation. The formulation appeared to be stable when stored at 40 degrees C and 75% RH with negligible degradation of the drug. The TDDS was found to be free of any skin irritation as suggested by skin irritation score of 1.16 (<2.00) under Draize score test. Statistically significant reduction in mean blood pressure (p < .01) was achieved in methyl prednisolone-induced hypertensive rats on treatment with the TDDS.

Poisoning with 1-propanol and 2-propanol

1-Propanol and 2-propanol are isomers of an alcohol with three carbons. They are colorless liquids with a sweet odor. 1-Propanol is metabolized by alcohol dehydrogenase to propionic acid and presents with metabolic acidosis and elevated anion gap, whereas 2-propanol is metabolized by alcohol dehydrogenase to acetone and presents with rapidly developing (within 3-4 h after exposure) ketosis and ketonuria but without metabolic acidosis. We report a patient who simultaneously ingested a lethal dose of 1-propanol and 2-propanol as a hand disinfectant in hospital. The patient lost consciousness and stopped breathing within half an hour after ingestion. He was intubated and artificially ventilated. Initial laboratory results showed mixed acidosis with elevated anion gap, but ketonuria appeared only 12 h after admission and 6 h following the regaining of consciousness. Therefore, laboratory results in simultaneous poisoning with two isomers of alcohol are not just a sum of laboratory results obtained in isolated poisoning with each isomer because they influence each other's metabolism: 1-propanol retards the metabolism of 2-propanol to acetone. In conclusion, 1-propanol and 2-propanol poisoning presents early with mixed acidosis and elevated anion gap and only later with ketonuria.

Can alcohol-based hand-rub solutions cause you to lose your driver's license? Comparative cutaneous absorption of various alcohols

We assessed cutaneous ethanol (ETOH) and isopropanol (ISOP) absorption after intensive (30 times per h) use of alcohol-based hand-rub solutions by healthcare workers (HCWs). ETOH was detectable in the breath of 6/20 HCWs (0.001 to 0.0025%) at 1 to 2 min postexposure and in the serum of 2/20 HCWs at 5 to 7 min postexposure. Serum ISOP levels were unrecordable at all time points.

A new technique to assess dermal absorption of volatile chemicals in vitro by thermal gravimetric analysis

Potential health hazards of dermal exposure, variability in reported dermal absorption rates and potential losses from the skin by evaporation indicate a need for a simple, inexpensive and standardized procedure to measure dermal absorption and desorption of chemical substances. The aim of this study was to explore the possibility to measure dermal absorption and desorption of volatile chemicals using a new gravimetric technique, namely thermal gravimetric analysis (TGA), and trypsinated stratum corneum from pig. Changes in skin weight were readily detected before, during and after exposure to vapours of water, 2-propanol, methanol and toluene. The shape and height of the weight curves differed between the four chemicals, reflecting differences in diffusivity and partial pressure and skin:air partitioning, respectively. As the skin weight is highly sensitive to the partial pressure of volatile chemicals, including water, this technique requires carefully controlled conditions with respect to air flow, temperature, chemical vapour generation and humidity. This new technique may help in the assessment of dermal uptake of volatile chemicals. Only a small piece of skin is needed and skin integrity is not necessary, facilitating the use of human samples. The high resolution weight-time curves obtained may also help to elucidate the characteristics of absorption, desorption and diffusion of chemicals in skin.

Framework for evaluation of physiologically-based pharmacokinetic models for use in safety or risk assessment

Proposed applications of increasingly sophisticated biologically-based computational models, such as physiologically-based pharmacokinetic models, raise the issue of how to evaluate whether the models are adequate for proposed uses, including safety or risk assessment. A six-step process for model evaluation is described. It relies on multidisciplinary expertise to address the biological, toxicological, mathematical, statistical, and risk assessment aspects of the modeling and its application. The first step is to have a clear definition of the purpose(s) of the model in the particular assessment; this provides critical perspectives on all subsequent steps. The second step is to evaluate the biological characterization described by the model structure based on the intended uses of the model and available information on the compound being modeled or related compounds. The next two steps review the mathematical equations used to describe the biology and their implementation in an appropriate computer program. At this point, the values selected for the model parameters (i.e., model calibration) must be evaluated. Thus, the fifth step is a combination of evaluating the model parameterization and calibration against data and evaluating the uncertainty in the model outputs. The final step is to evaluate specialized analyses that were done using the model, such as modeling of population distributions of parameters leading to population estimates for model outcomes or inclusion of early pharmacodynamic events. The process also helps to define the kinds of documentation that would be needed for a model to facilitate its evaluation and implementation.

Evaluation of the Potential Impact of Age- and Gender-Specific Pharmacokinetic Differences on Tissue Dosimetry 2Current address: Novartis Pharmaceuticals, East Hanover, NJ 07936

The physiological and biochemical processes that determine the tissue concentration time courses (pharmacokinetics) of xenobiotics vary, in some cases significantly, with age and gender. While it is known that age- and gender-specific differences have the potential to affect tissue concentrations and, hence, individual risk, the relative importance of the contributing processes and the quantitative impact of these differences for various life stages are not well characterized. The objective of this study was to identify age- and gender-specific differences in physiological and biochemical processes that affect tissue dosimetry and integrate them into a predictive physiologically based pharmacokinetic (PBPK) life-stage model. The life-stage model was exercised for several environmental chemicals with a variety of physicochemical, biochemical, and mode-of-action properties. In general, predictions of average pharmacokinetic dose metrics for a chemical across life stages were within a factor of two, although larger transient variations were predicted, particularly during the neonatal period. The most important age-dependent pharmacokinetic factor appears to be the potential for decreased clearance of a toxic chemical in the perinatal period due to the immaturity of many metabolic enzyme systems, although this same factor may also reduce the production of a reactive metabolite. Given the potential for age-dependent pharmacodynamic factors during early life, there may be chemicals and health outcomes for which decreased clearance over a relatively brief period could have a substantial impact on risk.

Dermal absorption of isopropyl alcohol from a commercial hand rub: implications for its use in hand decontamination

Isopropyl alcohol-containing hand rubs are widely used in healthcare for hand decontamination. Ten healthy adult volunteers applied a commercially available isopropyl alcohol-containing hand rub to their hands every 10 min over a 4 h period. Blood isopropyl alcohol levels were measured at the beginning and end of the study. At the end of the study, measurable blood isopropyl alcohol levels (range 0.5-1.8 mg/l) were recorded in nine subjects. We confirmed that isopropyl alcohol could be absorbed through the intact skin of adult humans. The social and medical implications are discussed.

Sex differences in the toxicokinetics of inhaled solvent vapors in humans 2. 2-propanol

The aim of this study was to evaluate possible sex differences in the inhalation toxicokinetics of 2-propanol vapor. Nine women and eight men were exposed on different occasions for 2 h during light physical exercise (50 W) to 2-propanol (350 mg/m3) and to clean air (control exposure). The level corresponds to the Swedish occupational exposure limit. 2-Propanol and its metabolite acetone were monitored up to 24 h after exposure in exhaled air, blood, saliva, and urine by headspace gas chromatography. Body fat and lean body mass were estimated from sex-specific equations using bioelectrical impedance, body weight, height, and age. Genotypes were determined by PCR-based assays for alcohol dehydrogenase and cytochrome P450 2E1 (CYP2E1). The CYP2E1 phenotype was assessed by the 2-h plasma 6-hydroxychlorzoxazone/chlorzoxazone metabolic ratio in vivo. The toxicokinetic profile in blood was analyzed using a one-compartment population model. The following sex differences were significant at the p = 0.05 level (Student's t test). The respiratory uptake was lower and the volume of distribution smaller in females. The women had a slightly shorter half-time of 2-propanol in blood and a higher apparent total clearance when corrected for body composition. However, women reached approximately four times higher 2-propanol levels in exhaled air at 10-min postexposure and onward. Acetone in blood was markedly higher in females than in males in the control experiment and slightly higher following exposure to 2-propanol. A marked sex difference was that of a 10-fold higher in vivo blood:breath ratio in men, suggesting sex differences in the lung metabolism of 2-propanol. The most marked sex difference was that of salivary acetone, for which an approximately 100-fold increase was seen in women, but no increase in men, after exposure to 2-propanol compared to clean air. The toxicokinetic analysis revealed no significant differences in toxicokinetics between subjects of different metabolic genotypes or phenotypes. In conclusion, the study indicates several sex differences in the inhalation toxicokinetics of 2-propanol. Most of these differences are consistent with anatomical differences between women and men. However, body build can not explain the sex differences in 2-propanol levels in expired air and acetone in saliva.

Evaluation of the potential impact of age- and gender-specific lung morphology and ventilation rate on the dosimetry of vapors

In recent years, there have been growing concerns that due to differences, both pharmacokinetic and pharmacodynamic, between children and adults, children could be at greater risk of adverse effects following chemical exposure. The specific goal of this study was to demonstrate an approach for using physiologically based pharmacokinetic (PBPK) modeling to compare inhalation dosimetry in the adult and the child of both males and females. Three categories of gases were considered: rapidly and irreversibly reactive in the respiratory tract (ozone), relatively water-soluble and nonreactive (isopropanol), and relatively water-insoluble and nonreactive (styrene, vinyl chloride, and perchloroethylene). The nonreactive chemicals were also selected because they are metabolized in the respiratory tract. The age-related changes observed for the estimated dose metrics were a function of the physiochemical properties of the inhaled vapor and their interactions in the body. Blood concentrations estimated for all vapors, either poorly metabolized (e.g., PERC), moderately metabolized (e.g., ST), or highly metabolized vapors (e.g., IPA and VC), varied less than a factor of two between infants and adults. These changes, moreover, were confined to the first year after birth, a relatively short window compared to the total lifespan of the individual. In contrast, circulating metabolite concentrations estimated in the blood, as well as amounts metabolized in the liver and lung, appeared to be a strong function of age, due to their dependence on the maturity of the pertinent metabolic enzyme systems.

In vitro evaluation of the efficacy of skin barrier creams and protective gloves on percutaneous absorption of industrial solvents

OBJECTIVES

The aim of the experiments was to evaluate the efficacy of skin barrier creams (SBCs) and protective gloves and its potential for reduction of percutaneous absorption of industrial solvents.

METHODS

We assessed percutaneous absorption of ethylene glycol (EG), isopropyl alcohol (IA) and 1,2,4-trimethylbenzene (TMB), using static diffusion cells. These solvents were applied neat (EG, TMB) as well as in 10% and 50% aqueous solution (EG, IA) or in 10% and 50% ethanol-diluted solution (TMB). Furthermore, we tested the percutaneous absorption of IA mixed in one cleaning agent (CA), used in newspaper printing shops to clean the rollers of printing machines. Additionally, the penetration behaviour of 10% and 50% solutions of EG, IA and TMB was tested. The experiments were carried out on untreated and on SBC-treated excised human skin from one donor, and on protective gloves. Saline was used as receptor fluid for EG and IA, and neat ethanol for TMB.

RESULTS

The penetration of 50% EG, IA and TMB solutions through SBC-treated skin was higher than in untreated skin (factor 3.9 for EG, 0.32 for IA and 0.06 for TMB). The penetration of IA in the IA-CA mixture was five-times higher through untreated skin as for the single compound in 10% aqueous solution. In skin, treated with SBC, we found a 17-fold penetration enhancement of IA in the IA-CA mixture. No appreciable penetration of EG and IA was observed through nitrile rubber gloves.

CONCLUSIONS

Our in vitro experiments could not demonstrate an efficacy of SBC to protect skin penetration for the tested solvents. The percutaneous absorption of all solvents in 50% solution was increased through skin treated with SBCs. Furthermore, SBCs enhance the penetration rates of solvents from complex mixtures compared with the single solvents. The tested gloves showed sufficient protection for the hydrophilic solvents, but not for TMB.

The loss of the chemical tanker Ievoli Sun in the English Channel, October 2000

A chemical product tanker, The Ievoli Sun, was abandoned and later sank approximately 11 miles NW of Alderney in the English Channel in October 2000. The vessel carried a mixed cargo comprising 4000 tonnes of styrene, and 1000 tonnes each of methyl ethyl ketone and isopropyl alcohol. These chemicals are of low to moderate toxicity to aquatic life, are not persistent and have a low potential for bio-accumulation. Both of the solvents are miscible in water, whilst styrene is practically insoluble and, following release, it will rise to the sea surface and rapidly evaporate. More than 1000 tonnes of styrene are believed to have been lost to sea during the incident, resulting in an aerial plume of vapour which crossed Alderney and episodic contamination of air and water in the immediate vicinity of the wreck site. Analysis of edible tissues using coupled gas chromatography/mass spectrometry demonstrated low-level styrene contamination of crabs recovered from pots laid very close to the wreck site prior to the incident. These concentrations posed no risks to human consumers, and no fishery controls were implemented. The remainder of the styrene and the ship's main bunker fuel were recovered from the wreck on the seabed, whilst the two chemical solvents were released to the water column in a slow, controlled manner.

Isopropyl alcohol intoxication: a diagnostic challenge

Isopropyl alcohol (IPA) is an ingredient of commonly used household solutions. Accidental and suicidal ingestion of IPA sometimes can be fatal if it goes unrecognized and untreated. There are few published reports on IPA intoxication. We describe a case of repeated IPA ingestion in a single individual, followed by a review of the literature on the subject. The differential diagnosis, diagnostic pitfalls, and therapeutic interventions in patients with IPA intoxications are discussed.

Application of a physiologically based pharmacokinetic model for isopropanol in the derivation of a reference dose and reference concentration

An interspecies physiologically based pharmacokinetic (PBPK) model describing isopropanol (IPA) and its major metabolite, acetone, was applied to perform route-to-route and cross-species dosimetry to derive reference dose (RfD) and reference concentration (RfC) values for IPA. Adult PBPK models for rats and humans were extended to simulate exposure to IPA during pregnancy and used to estimate internal dose metrics in the mother and fetus during development. Endpoints from chronic, developmental, and reproductive toxicity studies were considered for the derivation of RfDs and RfCs. Due to uncertainties in the mode of action of toxicity for IPA and acetone, the dose metric used for most responses was the total area under the blood concentration curve (AUC) for the combination of IPA and acetone. This combined dose metric provided a more conservative estimate than those based on AUCs for IPA or acetone. Peak blood concentration of IPA was the dose metric for neurobehavioral effects. The recommended RfD and RfC for IPA are 10 mg/kg/day and 40 ppm, respectively, based on decreased fetal body weights. All of the PBPK-derived RfD or RfC values for various endpoints were similar (within a factor of 3), regardless of route of exposure in the animal study.

Development of a physiologically based pharmacokinetic model of isopropanol and its metabolite acetone

A physiologically based pharmacokinetic (PBPK) model for isopropanol (IPA) and its major metabolite, acetone, is described. The structure of the parent chemical model, which can be used for either IPA or acetone by choosing the appropriate chemical-specific parameters, is similar to previously published models of volatile organic chemicals such as styrene. However, in order to properly simulate data on the exhalation of IPA and acetone during inhalation exposures, it was necessary to expand the description of the lung compartment to include a subcompartment for the upper respiratory tract mucus layer. This elaboration is consistent with published PBPK models of other water-soluble vapors in which the mucus layer serves to absorb the chemical during inhalation and then release it during exhalation. In the case of IPA exposure, a similar PBPK structure is used to describe the kinetics of the acetone produced from the metabolism of IPA. The resulting model is able to provide a coherent description of IPA and acetone kinetics in the rat and human for exposures to IPA by several routes: intravenous, intraperitoneal, oral, inhalation, and dermal. It is also able to consistently reproduce kinetic data for exposures of rats or humans to acetone. Thus, the model provides a validated framework for performing chemical-specific route-to-route extrapolation and cross-species dosimetry, which can be used in place of generic default calculations in support of risk assessments for IPA and acetone.

Treatment of methanol and isopropanol poisoning with intravenous fomepizole

CASE REPORT

We report a case of mixed methanol and isopropanol poisoning in a patient who refused dialysis but agreed to treatment with intravenous fomepizole. The patient was asymptomatic on arrival, with initial blood methanol and isopropanol concentrations of 146 mg/dL and 39 mg/dL, respectively. Blood ethanol was undetectable. The patient was treated with fomepizole twice daily intravenously until blood methanol was undetectable. No side effects of therapy, other than transient eosinophilia, were observed. The evolution was uneventful and no metabolites of either alcohol were detected at any time during the hospitalization. The decay of plasma methanol and isopropanol under fomepizole treatment were well described by first-order kinetics. The plasma elimination half-lives of methanol and isopropanol were 47.6 hours and 27.7 hours, respectively. Fomepizole appears to have been effective in blocking the toxic metabolism of both methanol and isopropanol and was associated with a favorable outcome.

Ethanol, isopropanol, methanol, and ethylene glycol poisoning

Alcohol intoxication, commonly encountered in emergency department and clinic settings, is by no means a benign condition. Ethanol ingested alone or in combination with other CNS depressants (eg, isopropanol, methanol, ethylene glycol, sedatives, opioids) can be fatal. Obtaining the patient's history and careful observation for clinical signs and symptoms, along with appropriate analysis of results of laboratory tests, are the key to determining and differentiating the agent ingested. It is critical that poisoning due to ethanol and/or other related alcohols should be recognized early in order to initiate appropriate treatments and prevent fatalities. Emergency department nurses may be the first persons to collect the essential data, and it is incumbent upon them to plan and initiate appropriate care. In continuing management for these patients, critical care nurses must understand the factors contributing to the observed signs and symptoms in order to initiate and monitor ongoing care and prevent serious complications.

Tests of potential functional barriers for laminated multilayer food packages. Part I: Low molecular weight permeants

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 microns-thick oriented PP) into the food stimulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.

Topical absorption of isopropyl alcohol induced cardiac and neurologic deficits in an adult female with intact skin

Topical exposure to isopropyl alcohol has been reported in the literature to be toxic if sufficient isopropyl alcohol is absorbed (1-5). A clinical case is reported where a 48-y-old female presented with multiple unexplained cardiac and neurological deficits. The woman had developed the deficits over a 6-mo period in which she had been soaking towels with isopropyl alcohol and applying then to her skin overnight to ease arm pain she was experiencing. Cessation of the isopropyl alcohol exposure resolved her deficits within 3 d. A controlled repeat dermal exposure to isopropyl alcohol under clinical observation reproduced the deficits noted with corresponding serum and urine concentrations of isopropyl alcohol and acetone. Cessation of topical isopropyl alcohol exposure lead to subsequent resolution of all toxicities.

Dermal absorption and pharmacokinetics of isopropanol in the male and female F-344 rat

Isopropanol (IPA), as a 70% aqueous solution, was applied under occluded conditions to the shaved backs of male and female Fischer F-344 rats for a period of 4 hr. Maximum analyzed blood concentrations of IPA were attained at 4 hr and decreased steadily following removal of the test material. Blood concentrations were below the limit of quantification at 8 hr. Acetone (ACE) blood levels rose steadily during the 4-hr exposures and continued to rise following removal of the test material, reaching peak analyzed levels at 4.5 hr (male) and 5 hr (females). ACE blood concentrations were below the limit of quantification at 24 hr. Basic pharmacokinetic parameters were similar for male and female rats with mean, first-order elimination half-lives for IPA and ACE of 0.8 to 0.9 hr and 2.1 to 2.2 hr, respectively. Following iv administration of [14C]IPA, 50-55% of the dose was eliminated as 14CO2 with lesser amounts recovered as expired volatiles or in urine. Total recoveries following iv administration were 83% for both males and females. Following a 4-hr dermal exposure to [14C]IPA (70% aqueous solution), 84-86% of the dose was recovered from the application site. Dermal absorption rates were calculated by two independent methods. The values obtained were 0.78 +/- 0.03 and 0.85 +/- 0.04 mg/cm2/hr for males and 0.77 +/- 0.13 and 0.78 +/- 0.16 mg/cm2/hr for females. Calculated permeability coefficients of 1.37 to 1.50 x 10(-3) cm/hr for males and 1.35 to 1.37 x 10(-3) cm/hr for females indicate that in the rat, IPA is rapidly absorbed dermally when applied under occluded conditions.

Molecular factors influencing drug transfer across the blood-brain barrier

A recently reported approach to the prediction of blood-brain drug distribution uses the general linear free energy equation to correlate equilibrium blood-brain solute distributions (logBB) with five solute descriptors: R2 an excess molar refraction term; pi2H, solute dipolarity or polarizability; alpha2H and beta2H, the hydrogen bond acidity or basicity, and Vx, the solute McGowan volume. In this study we examine whether the model can be used to analyse kinetic transfer rates across the blood-brain barrier in the rat. The permeability (logPS) of the blood-brain barrier to a chemically diverse series of compounds was measured using a short duration vascular perfusion method. LogPS data were correlated with calculated solute descriptors, and octanol-water partition coefficients (logP(oct)) for comparison. It is shown that a general linear free energy equation can be constructed to predict and interpret logPS values. The utility of this model over other physicochemical descriptors for interpreting logPS and logBB values is discussed.