Simultaneous determination of phenoxyethanol and its major metabolite, phenoxyacetic acid, in rat biological matrices by LC–MS/MS with polarity switching: Application to ADME studies

Biotransformation and toxicokinetics of 2-phenoxyethanol after oral exposure in humans: a volunteer study

2-Phenoxyethanol (PhE) is an aromatic glycol ether and is used in a variety of functions and applications, e.g., as preservative in pharmaceuticals, cosmetic and personal care products, as biocide in disinfectants (e.g. human hygiene), or as a solvent in formulations (e.g. coatings, functional fluids). Despite its widespread use, little is yet known on its biotransformation and toxicokinetics in humans. Therefore, a pilot study was conducted with oral administration of PhE (5 mg/kg body weight) to five volunteers. Blood and urine samples were collected and analyzed for PhE and three of its presumed metabolites up to 48 h post-exposure. Additionally, one volunteer was dermally exposed to PhE and monitored until 72 h post-exposure. PhE was rapidly resorbed following both oral and dermal application with tmax-levels in blood of about 1 h and 3 h, respectively. Metabolism of PhE was observed to be rather extensive with phenoxyacetic acid (PhAA) and 4-hydroxyphenoxyacetic acid (4-OH-PhAA) as the main metabolites found in blood and urine following oral and dermal exposure. PhE was excreted rapidly and efficiently via urine mostly in metabolized form: following oral exposure, on average 77% and 12% of the applied dose was excreted within 48 h as PhAA and 4-OH-PhAA, respectively. A similar metabolism pattern was observed following the single dermal exposure experiment. The obtained data on biotransformation and toxicokinetics of PhE in humans provide valuable information on this important chemical and will be highly useful for pharmacokinetic modelling and evaluation of human PhE exposure.

Spectrophotometric determination of phenol impurity in phenoxyethanol and phenol index of drinking water and municipal wastewater effluent after salting-out assisted liquid phase microextraction (SA-LPME)

In this study, a novel and convenient analytical method based on salting-out-assisted liquid phase microextraction (SA-LPME) has been developed. A spectrophotometric technique was employed to quantify the concentration of phenol in drinking water and treated wastewater, as well as the phenol impurity in 2-phenoxyethanol (PE). To accomplish this, a solution containing dissolved PE was supplemented with 4-aminoantipyrine (4-AAP) and hexacyanoferrate. Subsequently, NaCl was added to induce the formation of a two-phase system, consisting of fine droplets of PE as an extractant phase in the aqueous phase. The resulting red derivative was then extracted into the extractant phase and separated through centrifugation. Finally, the absorbance of the extracted derivative was measured at 520 nm. The Response Surface Methodology (RSM) based on the Box-Behnken Design (BBD) was employed to optimize the influential factors, namely 4-Aminoantipyrine (4-AAP), buffer (pH = 10), hexacyanoferrate, and NaCl. By utilizing the optimal conditions (buffer: 50 μL, 4-AAP (1% w/v): 80 μL, hexacyanoferrate (10% w/v): 65 μL, and NaCl: 0.7 g per 10 mL of the sample), the limit of detection was determined to be 0.7 ng mL-1 and 0.22 μg g-1 for water and PE samples, respectively. The relative standard deviation (RSD) and correlation of determination (r2) obtained fell within the range of 2.4-6.8% and 0.9983-0.9994, respectively. Moreover, an enrichment factor of 65 was achieved for a sample volume of 10 mL. The phenol concentration in two PE samples (PE-1, PE-2), provided by a pharmaceutical company (Pars Sadra Fanavar, Iran), were determined to be 0.83 ± 0.05 μg g-1 and 2.70 ± 0.14 μg g-1, respectively. Additionally, the phenol index in drinking water and treated municipal wastewater was found to be 3.60 ± 1.06 ng mL-1 and 4.60 ± 1.17 ng mL-1, respectively. These mentioned samples were spiked in order to evaluate the potential influence of the matrix. The relative recoveries from PE-1, PE-2 samples, drinking water, and treated municipal wastewater samples were measured as 104.5%, 97.5%, 101.6%, and 107.8%, respectively, indicating no matrix effect.

4-Aminobenzoic acid, 2-phenoxyethanol and iodine used as tracers in a short-term in vivo-kinetics study for tattoo ink ingredients: Mass spectrometry method development and validation

Tattoos have been gaining popularity in recent years, leading to a growing interest in researching tattoo inks and the tattooing process itself. Since the exposure to soluble tattoo ink ingredients has not yet been investigated, we here present the method validation for a short-term biokinetics study on soluble tattoo ink ingredients. The three tracers 4-aminobenzoic acid (PABA), 2-phenoxyethanol (PEtOH) and iodine will be added to commercially available tattoo inks, which will subsequently be used on healthy study participants. Following the tattooing process, blood and urine will be sampled at specific time points and analysed for these tracers. For this purpose, a method using liquid chromatography separation coupled to a quadrupole time-of-flight mass spectrometer (LC-QTOF-MS) in positive and negative ESI mode for the quantification of PABA, PEtOH and selected metabolites and an inductively-coupled plasma (ICP)-MS method for the determination of iodine were developed and validated. For LC-QTOF-MS analysis, the most applicable additives for LC eluents (0.01 % formic acid for positive and 0.005 % acetic acid for negative mode) were identified. Protein precipitation with acetonitrile was chosen for sample preparation. The methods were validated for selectivity, specificity, carryover, linearity, limit of detection (LOD) and quantification (LOQ), matrix effects, accuracy and precision, stability under different conditions and dilution integrity according to national and international guidelines with an allowed maximum variation of ±15 %. The LC-QTOF-MS method met the imposed guideline criteria for most parameters, however, some metabolites showed strong matrix effects. Validation of the ICP-MS method revealed that the KED-H2 collision mode is superior to the standard analysis mode due to enhanced method accuracy. The methods were validated for the relevant matrices plasma, urine, tattoo ink and tattoo consumables and proved to be applicable for the main target substances in the short-term biokinetics study. A proof-of-concept study showed successful quantification of iodine and PABA metabolites. The PEtOH metabolite was also quantified, but showed strong matrix effects in urine. Therefore standard addition was selected as an alternative quantification method.

Benzisothiazolinone: Pharmacokinetics, Tissue Distribution, and Mass Balance Studies in Rats

Humans are continuously exposed to benzisothiazolinone (BIT), which is used as a preservative, through multiple routes. BIT is known to be a sensitizer; in particular, dermal contact or aerosol inhalation could affect the local toxicity. In this study, we evaluated the pharmacokinetic properties of BIT in rats following various routes of administration. BIT levels were determined in rat plasma and tissues after oral inhalation and dermal application. Although the digestive system rapidly and completely absorbed orally administered BIT, it underwent severe first-pass effects that prevented high exposure. In an oral dose escalation study (5-50 mg/kg), nonlinear pharmacokinetic properties showed that C_max and the area under the curve (AUC) increased more than dose proportionality. In the inhalation study, the lungs of rats exposed to BIT aerosols had higher BIT concentrations than the plasma. Additionally, the pharmacokinetic profile of BIT after the dermal application was different; continuous skin absorption without the first-pass effect led to a 2.13-fold increase in bioavailability compared with oral exposure to BIT. The [¹⁴C]-BIT mass balance study revealed that BIT was extensively metabolized and excreted in the urine. These results can be used in risk assessments to investigate the relationship between BIT exposure and hazardous potential.

Development of an LC-MS/MS Assay and Toxicokinetic Characterization of Hexamethylenetetramine in Rats

Hexamethylenetetramine, an aldehyde-releasing agent, is used as a preservative in various food, cosmetics, and medical treatments, such as a treatment for urinary tract infections. It has been reported to be allergenic on contact with the skin, with the additional possibility of causing toxicity once absorbed systemically. Despite its potential toxicity, there are no reports on the in vivo bioavailability of hexamethylenetetramine following oral or dermal administration. In this study, we developed a new simple and sensitive LC-MS/MS method for the determination of hexamethylenetetramine in plasma and applied this method to characterize the toxicokinetics. The developed assay had a sufficient specificity and sensitivity for toxicokinetic characterization, and its accuracy and precision were verified. Following iv injection, the plasma concentration of hexamethylenetetramine showed mono exponential decay, with an elimination half-life of about 1.3 h. Following oral administration, the T_max reached an average of 0.47 h and bioavailability was estimated as 89.93%. After percutaneous administration, it reached C_max on average at 2.9-3.6 h. Although the absorption rate was relatively slow, its average bioavailability was calculated as 77.19-78.91%. Overall, most of the orally and percutaneously administered hexamethylenetetramine was absorbed into systemic circulation. The derived results in this study are expected to be utilized as the scientific evidence for further toxicokinetic study and risk assessment.

A comparative study of the in vitro permeation of 2-phenoxyethanol in the skin PAMPA model and mammalian skin

For permeation studies that use excised skin, experimental data may show variability associated with the use of biological tissues. As a consequence, achieving reproducible results and data interpretation may be challenging. The skin parallel artificial membrane permeability assay (skin PAMPA) model has been proposed as a high-throughput tool for predicting skin permeation of chemicals. A number of skin cleansing wipe formulations for the diaper area of infants contain 2-phenoxyethanol (PE) as a preservative and cetylpyridinium chloride (CPC) as a surfactant with antimicrobial activity. However, information regarding cutaneous absorption of PE and CPC in the scientific literatures is remarkably limited. The main aim of the present study was to assess the suitability of the skin PAMPA model for prediction of skin permeation of PE. A secondary aim was to investigate the influence of CPC on the dermal absorption of PE. PE (1 % w/w) was prepared in two vehicles, namely propylene glycol (PG) and water-PG (WP). Permeability of PE was investigated in vitro using the skin PAMPA membrane, porcine skin and human skin under finite dose conditions. The highest permeation of PE was observed for the water-PG preparation with 0.2 % w/w of CPC. This finding was consistently observed in the skin PAMPA model and in Franz cell studies using porcine skin and human skin. Permeation of CPC was not detected in the three permeation models. However, permeation of PE increased significantly (p < 0.05) in the presence of CPC compared with formulations without CPC. When comparing the skin PAMPA data and the mammalian skin data for the cumulative amount of PE permeated, the r² values for PAMPA-porcine skin and PAMPA-human skin were 0.84 and 0.89, respectively. The findings in this study demonstrate the capability of the skin PAMPA model to differentiate between various doses and formulations and are encouraging for further applications of this model as a high throughput screening tool in topical formulation development.

Analytical Method Development of Benzisothiazolinone, a Biocide, Using LC-MS/MS and a Pharmacokinetic Application in Rat Biological Matrices

Benzisothiazolinone (BIT), a biocide widely used as a preservative in household cleaning and personal care products, is cytotoxic to lung cells and a known skin allergen in humans, which highlights the importance of assessing its toxicity and pharmacokinetics. In this study, a simple, sensitive, and accurate LC−MS/MS method for the quantification of BIT in rat plasma, urine, or tissue homogenates (50 μL) using phenacetin as an internal standard was developed and validated. Samples were extracted with ethyl acetate and separated using a Kinetex phenyl−hexyl column (100 × 2.1 mm, 2.6 μm) with isocratic 0.1% formic acid in methanol and distilled water over a run time of 6 min. Positive electrospray ionization with multiple reaction monitoring transitions of m/z 152.2 > 134.1 for BIT and 180.2 > 110.1 for phenacetin was used for quantification. This assay achieved good linearity in the calibration ranges of 2−2000 ng/mL (plasma and urine) and 10−1000 ng/mL (tissue homogenates), with r ≥ 0.9929. All validation parameters met the acceptance criteria. BIT pharmacokinetics was evaluated via an intravenous and dermal application. This is the first study that evaluated BIT pharmacokinetics in rats, providing insights into the relationship between BIT exposure and toxicity and a basis for future risk assessment studies in humans.

Reliable determination of the main metabolites of 2-phenoxyethanol in human blood and urine using LC-MS/MS analysis

2-Phenoxyethanol (PhE) is used as a broad-spectrum preservative in several consumer products like cosmetics and cleaning agents. To enable the analysis and assessment of human exposure to PhE, a fast and sensitive LC-MS/MS method for the quantification of two PhE metabolites, namely phenoxyacetic acid (PhAA) and 4-hydroxyphenoxyacetic acid (4-OH-PhAA) in human urine and blood was developed and validated. The method is based on liquid chromatography combined with tandem mass spectrometry (LC-MS/MS). Sample preparation was different for both matrices: either a simple "dilute&shoot"-approach for urine samples or a liquid-liquid-extraction (LLE) for blood samples was used. The limit of quantification (LOQ) is 10 μg L^-1 and 6 μg L^-1 for PhAA and 20 μg L^-1 and 10 μg L^-1 for 4-OH-PhAA in urine and blood, respectively. The method was applied to urine samples of 153 persons without occupational exposure to PhE and to blood samples of 7 additional volunteers. In blood, PhAA was detected in 57% of all samples (range: <LOQ - 0.017 mg L^-1), while 4-OH-PhAA was not detectable. In contrast to that, PhAA was found in 99% and 4-OH-PhAA in 95% of all urine samples. The median concentrations in urine were 0.99 mg L^-1 (range: <LOQ - 53.83 mg L^-1) for PhAA and 0.11 mg L^-1 (<LOQ - 4.98 mg L^-1) for 4-OH-PhAA, respectively. Analyses after acid hydrolysis showed that both urinary metabolites are excreted unconjugated.

Prediction of tissue and urine concentrations of 2-phenoxyethanol and its metabolite 2-phenoxyacetic acid in rat and human after oral and dermal exposures via GastroPlusTM physiologically based pharmacokinetic modelling

A physiologically based pharmacokinetic (PBPK) model for the important chemical phenoxyethanol (PhE) and its metabolite phenoxyacetic acid (PhAA) was built via GastroPlus^TM software (version 9.0) using currently available analytically measured plasma and urinary time-courses of both PhE and its metabolite PhAA. This model was validated and used to predict tissue and urine concentrations of PhE and its metabolite PhAA in rats and humans after oral and dermal exposures. The prediction results showed that most predicted tissue concentrations of PhE or PhAA were lower than the experimental tissue concentrations based on total radioactivity. The predicted cumulative excretion of PhAA in both rats and humans fits very well with most experimental data. With this GastroPlus^TM-based model, the margins of exposure (MOE) of PhE and PhAA were also calculated as 194 and 73.7, respectively. The predicted MOE of PhE is two-fold higher than the previous PBPK model built using total radioactivity-based tissue time courses, and the predicted MOE of PhAA was comparable to the previous PBPK model. These data indicate that for chemicals like PhE, GastroPlus^TM can integrate multiple data sets into PBPK models to predict PK parameters for parent and metabolites in both rats and humans following intravenous, dermal, or oral exposures.

Differential effects of aquatic anaesthetics on the pharmacokinetics of antibiotics: Examples using florfenicol in Nile tilapia (Oreochromis niloticus)

Anaesthetics are commonly applied in pharmacokinetic (PK) studies to assure smooth handling of experimental procedures or to promote animal welfare. However, the influence of anaesthetics on the PK of co-administered drug is generally unknown but assumes ignorable. The goal of the study was to investigate the effect of tricaine methanesulfonate (MS-222), 2-phenoxyethanol (2-PE) and eugenol (EUG) on the PK of florfenicol (FF) in Nile tilapia. Twenty-eight fish were repeatedly exposed to 90 ppm EUG, 300 ppm MS-222 or 900 ppm 2-PE before FF oral administration (15 mg/kg) and each successive blood sampling. The serum concentration-time profiles were analysed by a 2-compartmental model, and the generated parameters in the control (without anaesthetic) and anaesthetic groups were statistically compared. The results demonstrated that the serum concentrations of each anaesthetic were similar at every FF sampling times (70 μg/ml for MS-222; 277 μg/ml for 2-PE; and 61 μg/ml for EUG). In comparison with the control group, the repeated use of MS-222 did not result in a statistical difference in most of the PK parameters. In contrast, the elimination half-lives of the 2-PE and EUG groups were significantly longer whereas the absorption and distribution half-lives of the 2-PE group were significantly shorter than the control, resulting in altered optimal dosages in the simulation modelling. Whether or not the numbers and extent of PK parameters change mitigate subsequent estimations of other PK-derived secondary values such as dosing regimen and withdrawal time remains to be elucidated, but the auxiliary use of anaesthetics in PK studies should not assume uninfluential.

Pharmacokinetics of 2-phenoxyethanol and its major metabolite, phenoxyacetic acid, after dermal and inhaled routes of exposure: application to development PBPK model in rats

2-Phenoxyethanol (PE), ethylene glycol monophenyl ether, is widely used as a preservative in cosmetic products as well as in non-cosmetics. Since PE has been used in many types of products, it can be absorbed via dermal or inhaled route for systemic exposures. In this study, the pharmacokinetic (PK) studies of PE and its major metabolite, phenoxyacetic acid (PAA), after dermal (30 mg and 100 mg) and inhaled administration (77 mg) of PE in rats were performed. PE was administered daily for 4 days and blood samples were collected at day 1 and day 4 for PK analysis. PE was rapidly absorbed and extensively metabolized to form PAA. After multiple dosing, the exposures of PE and PAA were decreased presumably due to the induction of metabolizing enzymes of PE and PAA. In dermal mass balance study using [¹⁴C]-phenoxyethanol ([¹⁴C]PE) as a microtracer, most of the PE and its derivatives were excreted in urine (73.03%) and rarely found in feces (0.66%). Based on these PK results, a whole-body physiologically-based pharmacokinetic (PBPK) model of PE and PAA after dermal application and inhalation in rats was successfully developed. Most of parameters were obtained from the literatures and experiments, and intrinsic clearance at steady-state (CL_int,ss) were optimized based on the observed multiple PK data. With the developed model, systemic exposures of PE and PAA after dermal application and inhalation were simulated following no-observed-adverse-effect level (NOAEL) of 500 mg/kg/day for dermal application and that of 12.7 mg/kg/day for inhalation provided by the Environmental Protection Agency. The area under the concentration-time curve at steady state (AUC_ss) in kidney and liver (and lung for inhalations), which are known target organs of exhibiting toxicity of PE, as well as AUC_ss in plasma of PE and PAA were obtained from the model.

Safety review of phenoxyethanol when used as a preservative in cosmetics

Phenoxyethanol, or 2-phenoxyethanol, has a large spectrum of antimicrobial activity and has been widely used as a preservative in cosmetic products for decades. It is effective against various Gram-negative and Gram-positive bacteria, as well as against yeasts, and has only a weak inhibitory effect on resident skin flora. According to the European Scientific Committee on Consumer Safety, phenoxyethanol is safe for all consumers - including children of all ages - when used as a preservative in cosmetic products at a maximum concentration of 1%. Adverse systemic effects have been observed in toxicological studies on animals but only when the levels of exposure were many magnitudes higher (around 200-fold higher) than those to which consumers are exposed when using phenoxyethanol-containing cosmetic products. Despite its widespread use in cosmetic products, phenoxyethanol is a rare sensitizer. It can be considered as one of the most well-tolerated preservatives used in cosmetic products.

Simultaneous Determination of Twenty-Five Compounds in Rat Plasma Using Ultra-High Performance Liquid Chromatography-Polarity Switching Tandem Mass Spectrometry and Its Application to a Pharmacokinetic Study

An attempt was made to characterize the pharmacokinetic profiles of Qishen Keli (QSKL) that has been widely proved to be effective in clinical practice. A method using ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) for the simultaneous determination of 25 analytes in rat plasma was developed and validated. Satisfactory chromatographic separation was achieved on an ACQUITY UPLC HSS T3 column with gradient elution using mobile phase consisting of 0.02% aqueous formic acid (A) and acetonitrile fortified with 0.02% formic acid (B), and analyte detection was carried out using polarity-switching multiple reaction monitoring mode. Method validation assays in terms of selectivity, linearity, inter- and intra-day variations, matrix effect, and recovery demonstrated the newly developed method to be specific, sensitive, accurate, and precise. Following the oral administration of QSKL at a single dose, the qualified method was successfully applied for pharmacokinetic investigations in sham and model rats. Mild differences occurred for the pharmacokinetic patterns of most components between those two groups, whereas significant differences were observed for glycyrrhizic acid and glycyrrhetic acid. The obtained findings could provide meaningful information for the clarification of the effective material basis of QSKL.