Time Course Of Urinary Excretion Research Articles

Diffusion modelling of percutaneous absorption kinetics. Predicting urinary excretion from in vitro skin permeation tests (IVPT) for an infinite dose

In this work, we developed a number of generalised skin diffusion based pharmacokinetic models to relate published in vivo urinary excretion data to matching experimentally generated in vitro human skin permeation test (IVPT) data for a series of topically applied salicylate esters. A simplified linear in vivo model was found to inadequately describe the time course of urinary excretion over the entire sampling period. We represented the skin barrier as both a one layer (stratum corneum) and a two-layer (stratum corneum with viable epidermis) diffusion model and convoluted their Laplace solutions with that for a single exponential disposition phase to describe the urinary excretion profiles in the Laplace domain. We also derived asymptotic approximations for the model and estimated the conditions under which they could be used. We then sought to develop in vitro - in vivo relationships (IVIVR) for topically applied methyl, ethyl and glycol salicylates using our experimental IVPT data and the literature urinary excretion data. Good linear IVIVRs for ethyl and glycol salicylates were obtained, but the IVIVR for methyl salicylate was poor, perhaps because of topical stimulation of local skin blood flow by methyl salicylate. The ratio of the hydrated to dehydrated skin permeation for all salicylate esters was the same in both the IVPT and in vivo studies. A diffusion based one compartment pharmacokinetic model was also developed to describe the urinary excretion of solutes after removal of topical products and to compare the methyl salicylate skin permeation for five different body sites. The work presented here is consistent with the development of skin IVIVRs, but suggests that different skin conditions, application sites and local skin effects may affect model predictions.

Toxicokinetics of a urinary metabolite of tebuconazole following controlled oral and dermal administration in human volunteers

Tebuconazole (TEB) is a widely used triazole fungicide, but the toxicokinetics of its human metabolites are not fully described. For proper interpretation of biological monitoring data, knowledge on the metabolism and elimination of the compound is required. A human volunteer study was performed with the aim to describe the time courses of urinary excretion after controlled oral and dermal administration of TEB. Six healthy volunteers (three males and three females) received on separate occasions a single oral dose of 1.5 mg of TEB and a single dermal dose of 2.5 mg during 1 h. In addition to a pre-exposure urine sample, complete urine voids were collected over 48 h post-administration. The main metabolite hydroxy-tebuconazole (TEB-OH) was quantified in each urine sample. Peak excretion rates after oral and dermal administration were reached after 1.4 and 21 h, mean elimination half-lives were 7.8 and 16 h, and recoveries within 48 h were 38% and 1%, respectively. The time courses of excretion were compared to simulations with an established physiologically based toxicokinetic model for TEB that was extended with a parallel model for TEB-OH. Overall, TEB-OH was rapidly excreted into urine after oral exposure, and renal elimination was considerably slower after dermal exposure. Urinary time courses between individuals were similar. The model predictions were in good agreement with the observed time courses of excretion.

Biological monitoring of o-toluidine in urine pretreated by an enzymatic deconjugation method.

ObjectivesTo establish an enzymatic deconjugation method to separately quantify urinary o‐toluidine (OT), its six metabolites, another six chemicals present in an OT‐processing plant, and one metabolite of p‐toluidine, and to propose optimal urinary biological monitoring items of OT exposure.MethodsThirty‐six urine samples of an OT‐processing plant's workers were obtained and pretreated by an enzymatic deconjugation method employing β‐glucuronidase/arylsulfatase for 3 hours at 37°C and measured by liquid chromatograph‐mass spectrometry (LC‐MS). An alkaline hydrolytic pretreatment and 1‐chlorobutane extraction procedure was also examined as a widely used urinary OT measurement method.ResultsThe 14 chemicals were separated by LC‐MS condition set by us and 13 chemicals other than 2‐chloroaniline showed satisfiable linearity and limits of determination. Standard substances of six OT metabolites decomposed after the alkaline heating. In the 36 urine samples, OT, N‐(4‐hydroxy‐2‐methylphenyl) acetamide (NHM), and 4‐amino‐m‐cresol (ACR) accounted for approx. 90% of the total OT and OT metabolites, but inter‐individual variation of the three substance excretion seemed to be wide. Time course of urinary excretion revealed that concentration of the three substances was higher 24 hours after the work shift's end rather than just after the work shift.ConclusionsOT and its six metabolites can each be determined with LC‐MS. The alkaline method is not so optimal for exact biological monitoring. Rather, the sum of urinary OT, NHM, and ACR measured by the enzymatic method is a better index, and "end of the workweek" is a good urine‐sampling time for the biological monitoring of OT exposure.

Detailed Urinary Excretion Time Courses of Biomarkers of Exposure to Permethrin and Estimated Exposure in Workers of a Corn Production Farm in Quebec, Canada.

Permethrin is a synthetic pyrethroid insecticide widely used in agriculture. Farm workers are thus regularly exposed during spraying season. To help interpret routine biomonitoring results, a proper knowledge of the time courses of biomarkers of exposure is necessary. The kinetics of biomarkers of exposure to permethrin has recently been documented in volunteers exposed to permethrin under controlled conditions but there is a lack of detailed time profiles following real exposure conditions. This study aimed at obtaining data on the excretion time courses of permethrin metabolites in agricultural workers following typical exposure conditions in the field. Twelve workers exposed to permethrin were recruited from a corn production farm in the Montérégie, Quebec, Canada. They provided all their urine voided over a period of 3 days following the onset of a spraying episode of permethrin or work in a treated area. Three major metabolites of permethrin, trans- and cis- 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-l-carboxylic acid metabolites (trans-DCCA, cis-DCCA), and 3-phenoxybenzoic acid (3-PBA), were analyzed. For the applicator, a progressive rise in excretion values was observed with a single peak being reached 29h following the onset of the 3.5h exposure and ensuing elimination with a half-life of 6.4h for trans-DCCA and 8.7h for 3-PBA. In the other workers (supervisor and corn pickers), excretion profiles were generally more compatible with multiple entries in the treated area during the 3-day sampling period and rapid elimination between exposure episodes. In general, 3-PBA was found in slightly higher levels than trans-DCCA, except for the applicator and a harvester. For both trans-DCCA and 3-PBA in a given worker, excretion values expressed as creatinine-normalized concentrations were less variable than those expressed as excretion rates per kilogram body weight. Time-dependent variability in excretion values of workers confirms the need for serial urine sampling of at least two biomarkers of exposure, with minimally pre-exposure, end-of-shift sample the day of onset of exposure, and following morning void.

A Novel Toxicokinetic Modeling of Cypermethrin and Permethrin and Their Metabolites in Humans for Dose Reconstruction from Biomarker Data

To assess exposure to pyrethroids in the general population, one of most widely used method nowadays consists of measuring urinary metabolites. Unfortunately, interpretation of data is limited by the unspecified relation between dose and levels in biological tissues and excreta. The objective of this study was to develop a common multi-compartment toxicokinetic model to predict the time courses of two mainly used pyrethroid pesticides, permethrin and cypermethrin, and their metabolites (cis-DCCA, trans-DCCA and 3-PBA) in the human body and in accessible biological matrices following different exposure scenarios. Toxicokinetics was described mathematically by systems of differential equations to yield the time courses of these pyrethroids and their metabolites in the different compartments. Unknown transfer rate values between compartments were determined from best fits to available human data on the urinary excretion time courses of metabolites following an oral and dermal exposure to cypermethrin in volunteers. Since values for these coefficients have not yet been determined, a mathematical routine was programmed in MathCad to establish the possible range of values on the basis of physiological and mathematical considerations. The best combination of parameter values was then selected using a statistic measure (reliability factor) along with a statistically acceptable range of values for each parameter. With this approach, simulations provided a close approximation to published time course data. This model allows to predict urinary time courses of trans-DCCA, cis-DCCA and 3-PBA, whatever the exposure route. It can also serve to reconstruct absorbed doses of permethrin or cypermethrin in the population using measured biomarker data.

Renal response and acid-base balance alterations during furosemide administration

Furosemide is one of the most employed diuretics in the ICU for its ability to induce negative water balance. However, one common side effect is metabolic alkalosis [1]. We aimed to describe the time course of urinary excretion and changes in plasmatic acid-base balance in response to the administration of furosemide.

A Detailed Urinary Excretion Time Course Study of Captan and Folpet Biomarkers in Workers for the Estimation of Dose, Main Route-of-Entry and Most Appropriate Sampling and Analysis Strategies

Captan and folpet are two fungicides largely used in agriculture, but biomonitoring data are mostly limited to measurements of captan metabolite concentrations in spot urine samples of workers, which complicate interpretation of results in terms of internal dose estimation, daily variations according to tasks performed, and most plausible routes of exposure. This study aimed at performing repeated biological measurements of exposure to captan and folpet in field workers (i) to better assess internal dose along with main routes-of-entry according to tasks and (ii) to establish most appropriate sampling and analysis strategies. The detailed urinary excretion time courses of specific and non-specific biomarkers of exposure to captan and folpet were established in tree farmers (n = 2) and grape growers (n = 3) over a typical workweek (seven consecutive days), including spraying and harvest activities. The impact of the expression of urinary measurements [excretion rate values adjusted or not for creatinine or cumulative amounts over given time periods (8, 12, and 24 h)] was evaluated. Absorbed doses and main routes-of-entry were then estimated from the 24-h cumulative urinary amounts through the use of a kinetic model. The time courses showed that exposure levels were higher during spraying than harvest activities. Model simulations also suggest a limited absorption in the studied workers and an exposure mostly through the dermal route. It further pointed out the advantage of expressing biomarker values in terms of body weight-adjusted amounts in repeated 24-h urine collections as compared to concentrations or excretion rates in spot samples, without the necessity for creatinine corrections.

Mathematical model insights into arsenic detoxification

BackgroundArsenic in drinking water, a major health hazard to millions of people in South and East Asia and in other parts of the world, is ingested primarily as trivalent inorganic arsenic (iAs), which then undergoes hepatic methylation to methylarsonic acid (MMAs) and a second methylation to dimethylarsinic acid (DMAs). Although MMAs and DMAs are also known to be toxic, DMAs is more easily excreted in the urine and therefore methylation has generally been considered a detoxification pathway. A collaborative modeling project between epidemiologists, biologists, and mathematicians has the purpose of explaining existing data on methylation in human studies in Bangladesh and also testing, by mathematical modeling, effects of nutritional supplements that could increase As methylation.MethodsWe develop a whole body mathematical model of arsenic metabolism including arsenic absorption, storage, methylation, and excretion. The parameters for arsenic methylation in the liver were taken from the biochemical literature. The transport parameters between compartments are largely unknown, so we adjust them so that the model accurately predicts the urine excretion rates of time for the iAs, MMAs, and DMAs in single dose experiments on human subjects.ResultsWe test the model by showing that, with no changes in parameters, it predicts accurately the time courses of urinary excretion in mutiple dose experiments conducted on human subjects. Our main purpose is to use the model to study and interpret the data on the effects of folate supplementation on arsenic methylation and excretion in clinical trials in Bangladesh. Folate supplementation of folate-deficient individuals resulted in a 14% decrease in arsenicals in the blood. This is confirmed by the model and the model predicts that arsenicals in the liver will decrease by 19% and arsenicals in other body stores by 26% in these same individuals. In addition, the model predicts that arsenic methyltransferase has been upregulated by a factor of two in this population. Finally, we also show that a modification of the model gives excellent fits to the data on arsenic metabolism in human cultured hepatocytes.ConclusionsThe analysis of the Bangladesh data using the model suggests that folate supplementation may be more effective at reducing whole body arsenic than previously expected. There is almost no data on the upregulation of arsenic methyltransferase in populations chronically exposed to arsenic. Our model predicts upregulation by a factor of two in the Bangladesh population studied. This prediction should be verified since it could have important public health consequences both for treatment strategies and for setting appropriate limits on arsenic in drinking water. Our model has compartments for the binding of arsenicals to proteins inside of cells and we show that these comparments are necessary to obtain good fits to data. Protein-binding of arsenicals should be explored in future biochemical studies.

Assessment of absorbed doses of carbaryl and associated health risks in a group of horticultural greenhouse workers

This study was undertaken to estimate the absorbed doses of carbaryl and the associated health risks in a group of horticultural greenhouse workers in the Province of Quebec, Canada, using a toxicokinetic modeling approach. A mathematical model was developed to relate the absorbed dose of carbaryl, the evolution of its body burden and that of its metabolites and the urinary excretion rate of biomarkers. The free parameters of this model were determined using published time course data in volunteers exposed to carbaryl under controlled conditions. The model was used to determine cumulative urinary amounts of 1-naphthol that would be excreted by a typical worker exposed to a pre-established no-observed-adverse-effect level (NOAEL) dose; this biomarker amount was then taken as a biological reference value below which the risks of health effects were considered negligible. As a measure of the applicability of this approach to practical situations, the model was used to estimate the dose of carbaryl absorbed by each greenhouse worker, starting from his/her cumulative urinary excretion time courses of 1-naphthol over a 24-h period following the onset of a work exposure. Their cumulative 1-naphthol levels were then compared to the biological reference value obtained from the model and the NOAEL dose. Following the onset of a work exposure to carbaryl, a clear increase in the urinary excretion rate of 1-naphthol was observed in most workers. The reconstructed absorbed doses were found to vary between 3.3 and 143 nmol/kg of body weight (bw) depending on the working conditions. Simulations of the observed cumulative urinary excretion time course of each worker also showed that exposure appeared to occur mainly (a) through inhalation for the applicators and individuals without direct contact with treated plants and (b) through the dermal route for individuals manipulating treated plants. Although the workers under study clearly appeared to have been exposed to carbaryl in the greenhouses, 24-h cumulative 1-naphthol levels ranged from 4.8 to 65.1% of the proposed biological reference value of 32 nmol/kg bw in 24-h urine collections following the onset of a work exposure. This suggests that the workers under study probably did not incur a serious health risk under the normal exposure conditions prevailing during the study period.

Biological Monitoring of Exposure to Organophosphorus Insecticides in a Group of Horticultural Greenhouse Workers

Exposure to selected organophosphorus insecticides (OPs), malathion, diazinon and acephate, was evaluated in a group of horticultural greenhouse workers. This was achieved through measurements of the cumulative urinary excretion time courses of specific and non-specific biomarkers over a 24 h period following the onset of work exposure. For malathion, the absorbed daily doses were estimated from the 24 h cumulative urinary amounts of the specific mono- and di-carboxylic acid metabolites (the sum of MCA and DCA) through the use of a kinetic model. The observed 24 h urinary levels were also compared with a biological reference value (BRV) of 57 nmol kg(-1) of body weight established in a previous work on the basis of a human no-observed-effect level exposure dose. Excretion values were found to be 2.5% or less of the BRV, suggesting a negligible health risk. Both median and 95th percentile concentrations of DCA (n = 57 samples) were, however, slightly higher than the baseline values determined by the Centers for Disease Control and Prevention (CDC) in the US civilian population (MCA was not analyzed by the CDC). The cumulative urinary excretion time course of the methyl phosphoric (MP) derivatives, which are metabolites of malathion but also of several other OPs, was also determined. Though relatively low, the MP levels were from 3 to 31 times higher than would be expected on the basis of the malathion specific MCA and DCA excretions, indicating that MP excretions stem from sources other than malathion exposure. Accordingly, only the time courses of MCA and DCA excretion rate (nmol h(-1)) were compatible with the time of work exposure. Urinary biomarkers of exposure to diazinon and acephate were also measured. Urinary concentrations were essentially below or equal to the analytical limit of detection of 1 microg l(-1) for 2-isopropyl-4-methyl-6-hydroxypyrimidine (n = 54) and of 0.8 microg l(-1) for acephate and methamidophos (n = 59): values within the baseline range of the US civilian population, like the observed phosphoric metabolite concentrations. The workers under study thus appeared to be only slightly more exposed to malathion than the general population. However, their overall exposure to OPs, as measured by non-specific phosphoric metabolites, was similar to that of the general population, whose exposure occurs mainly through the ingestion of contaminated food. These results question the relevance of measuring non-specific phosphoric metabolites when attempting to assess low-dose occupational exposure to a specific OP.

Comparison of the urinary excretion time courses of pyrene-1,6-dione, pyrene-1,8-dione and 1-hydroxypyrene in rats intravenously exposed to pyrene

The urinary excretion time courses of pyrene-1,6-dione (P16D), pyrene-1,8-dione (P18D) and 1-hydroxypyrene (1-OHP) were compared in Sprague–Dawley and Wistar rats. Groups of five male rats, of about 200 g of body weight, were injected intravenously with 0.05, 0.5, 5 and 50 µmol pyrene kg−1 of body weight. Urine was collected at 2, 4, 6, 8, 10, 12, 18, 24, 30, 42 and 48 h post-dosing. Pyrene metabolites were measured by high-performance liquid chromatography (HPLC)/fluorescence after enzymatic hydrolysis of the glucurono- and sulfo-conjugates, extraction on Sep-Pak C18 cartridges and, for the analysis of dione metabolites, derivatization to stable diacetoxypyrene molecules. Over the 48-h sampling period, on average 17.4–25.6% of the injected pyrene was excreted overall as P16D, 6.4–8.8% as P18D and 0.6–0.8% as 1-OHP in the urine of Sprague–Dawley rats. By comparison, on average 10.3–14.7% of the intravenous pyrene dose was recovered as P16D, 4.8–6.4% as P18D and 0.3–0.4% as 1-OHP in the urine of Wistar rats. In both strains of rats there was no clear effect of the dose on the 0–48-h cumulative urinary excretion of P18D and 1-OHP over the entire dose range, while the percentage of dose recovered overall as P16D in urine at the highest dose (50 µmol kg−1) was statistically lower than at the other doses. The 0–48-h cumulative percentage of pyrene dose excreted as metabolites in the urine of Sprague–Dawley rats was also significantly higher than in Wistar rats (p<0.01) exposed under identical conditions. As for the urinary excretion-time courses of the different metabolites, for a given dose and strain of rats, excretion curves of P16D, P18D and 1-OHP generally evolved in parallel. There was also no clear effect of the dose on the excretion rate, thus half-life, of pyrene metabolites, except for P16D in Sprague–Dawley rats at the highest dose where elimination tended to be slower compared with the other doses (p<0.01). The average first-order elimination half-life of P16D, P18D and 1-OHP was 4.0, 5.7 and 4.1 h, respectively, in Sprague–Dawley rats, and 5.1, 6.1 and 5.1 h, respectively, in Wistar rats (all doses combined but excluding the highest dose for P16D). This study showed the relative importance of metabolic pathways leading to diones compared with 1-OHP. These dioxygenated metabolites appear to be interesting biomarkers of pyrene exposure at environmentally and occupationally relevant doses. Their adequacy as biomarkers of human exposure has yet to be confirmed.

Blunted renal dopaminergic system activity in HgCl 2-induced membranous nephropathy

The present study evaluated the possible role of the renal dopaminergic system in the sodium retention of HgCl 2-induced nephrotic syndrome. The time courses of urinary excretion of sodium, protein, dopamine and the precursor l-3,4-dihydroxyphenylalanine ( l-Dopa) were evaluated in HgCl 2-treated and control rats up to day 21. The renal aromatic l-amino acid decarboxylase (AADC) activity, the enzyme responsible for the synthesis of renal dopamine, was evaluated during negligible proteinuria accompanied with enhanced sodium retention (day 7), increased proteinuria accompanied with greatest sodium retention (day 14) as well as during increased proteinuria accompanied with negative sodium balance (day 21). Also, the influence of volume expansion (VE, 5% bw) and the effects of the D 1-like agonist fenoldopam (10 μg kg bw − 1 min − 1 ) on natriuresis and on proximal tubular Na +,K +-ATPase activity were examined on day 14. The daily urinary dopamine output and urinary dopamine / l-Dopa ratios were reduced in HgCl 2-treated rats from day 2 and beyond. This was accompanied by a marked decrease in renal AADC throughout the study. During VE, the fenoldopam-induced inhibition of proximal tubular Na +,K +-ATPase activity was similar between HgCl 2-treated and control rats. However, the urinary sodium excretion during fenoldopam infusion was markedly increased by 60% to 120% in control rats but was not altered in HgCl 2-treated rats. It is concluded that HgCl 2 nephrosis is associated with a blunted renal dopaminergic system activity. However, the lack of renal dopamine in HgCl 2 nephrosis does not appear to be related with the overall renal sodium retention in a state of proteinuria.

Urinary excretion of selegiline N -oxide, a new indicator for selegiline administration in man

1. The metabolism of selegiline (SG) has been studied by investigating the timecourse of urinary excretion of SG and its metabolites using high-performance liquid chromatography-electrospray ionization mass spectrometry (LC-ESI MS) in combination with solid-phase extraction. 2. The excretion profiles of SG and its four major metabolites, selegiline- N -oxide (SGO), N -desmethylselegiline (DM-SG), methamphetamine (MA) and amphetamine (AP), were investigated in six healthy volunteers after oral administrations of SG hydrochloride in a single dose of 2.5 or 7.5mg, and a repeat twice-daily dose of 5.0 mg day -1 (for 3 days). 3. The cumulative amount of SGO excreted within approximately the first 8-12h was comparable with MA, and the amount in the first 72 h was 2.0-7.8 times larger (2.8-13.2% of the dose) than that of DM-SG. 4. These results demonstrate that SGO can be used in place of DM-SG, which is known to be a main specific metabolite of SG, as a new indicator for the discrimination of SG use compared with MA abuse.

Collecting duct (Na+/K+)-ATPase activity is correlated with urinary sodium excretion in rat nephrotic syndromes.

In puromycin aminonucleoside (PAN)-treated nephrotic rats, sodium retention is associated with increased (Na+/K+)-ATPase activity in the cortical collecting ducts (CCD). This study was undertaken to determine whether stimulation of (Na+/K+)-ATPase in the CCD is a feature of other experimental nephrotic syndromes, whether it might be responsible for renal sodium retention, and whether it is mediated by increased plasma vasopressin levels or activation of calcineurin. For this purpose, the time courses of urinary excretion of sodium and protein, sodium balance, ascites, and (Na+/K+)-ATPase activities in microdissected CCD were studied in rats with PAN or adriamycin nephrosis or HgCl2 nephropathy. The roles of vasopressin and calcineurin in PAN nephrosis were evaluated by measuring these parameters in Brattleboro rats and in rats treated with cyclosporin or tacrolimus. Despite different patterns of changes in urinary sodium and protein excretion in the three nephrotic syndrome models, there was a linear relationship between CCD (Na+/K+)-ATPase activities and sodium excretion in all three cases. The results also indicated that there was no correlation between proteinuria and sodium retention, but ascites was present only when proteinuria was associated with marked reduction of sodium excretion. Finally, the lack of vasopressin in Brattleboro rats or the inhibition of calcineurin by administration of either cyclosporin or tacrolimus did not prevent development of the nephrotic syndrome in PAN-treated rats or stimulation of CCD (Na+/K+)-ATPase. It is concluded that stimulation of Na(+/K+)-ATPase in the CCD of nephrotic rats might be responsible for sodium retention and that this phenomenon is independent of proteinuria and vasopressin and calcineurin activities.

Evaluation of the metabolism and hepatotoxicity of styrene in F344 rats, B6C3F1 mice, and CD-1 mice following single and repeated inhalation exposures

Styrene is used for the manufacture of plastics and polymers. The metabolism and hepatotoxicity (mice only) of styrene was compared in male B6C3F1 mice, CD-1 mice, and F344 rats to evaluate biochemical mechanisms of toxicity. Rats and mice were exposed to 250 ppm styrene for 6 h/day for 1 to 5 days, and liver (mice only) and blood were collected following each day of exposure. Mortality and increased serum alanine aminotransferase (ALT) activity were observed in mice but not in rats. Hepatotoxicity in B6C3F1 mice was characterized by severe centrilobular congestion after one exposure followed by acute centrilobular necrosis. Hepatotoxicity was delayed by 1 day in CD-1 mice, and the increase in ALT and degree of necrosis was less than observed for B6C3F1 mice. Following exposure to unlabeled styrene for 0, 2, or 4 days, rats and mice were exposed to [7- 14C]-styrene (60 μCi/mmol) for 6 h. Urine, feces, and expired air were collected for up to 48 h. Most styrene-derived radioactivity was excreted in urine. The time-course of urinary excretion indicates that rats and CD-1 mice eliminated radioactivity at a faster rate than B6C3F1 mice following a single 250 ppm exposure, consistent with a greater extent of liver injury for B6C3F1 mice. The elimination rate following 3 or 5 days of exposure was similar for rats and both mouse strains. Following three exposures, the total radioactivity eliminated in excreta was elevated over that measured for one exposure for both mouse strains. An increased excretion of metabolites on multiple exposure is consistent with the absence of ongoing acute necrosis following 4 to 5 daily exposures. These data indicate that an induction in styrene metabolism occurs after multiple exposures, resulting in an increased uptake and/or clearance for styrene.

Age-dependent enzymuria, proteinuria and changes in renal blood flow and glomerular filtration rate in rats

The time course of urinary excretion of two enzymatic indicators of renal damage, N-acetyl-β-D-glucosaminidase (NAG) and alanine aminopeptidase (AAP) was measured in female Wistar rats at different ages. NAG and AAP are localized at different sites of the nephron and are released into the urine when kidney damage occurs. Total protein flow, urinary volume and creatinine flow were also determined. In a parallel experiment, the effect of aging on renal blood flow (RBF) and glomerular filtration rate (GFR) was examined in young (1.5-month) adult (3-month) and elderly (20-month) female rats. Clearance following a single injection of [ 131I] o-iodohippurate (hippuran, OIH) was used for the measurement of effective RBF and as an index of tubular cell function. [ 125I]Iothalamate (IOT) clearance was used to measure GFR. With advancing age, an increase in NAG and AAP urinary flow appeared. The increases in protein excretion were greater than and previous to those of enzyme excretion. It is shown that absolute RBF and GFR (ml/min) in old rats are greater than in young or adult animals. When absolute RBF or GFR was divided by kidney weight (ml/min/g) no clearance changes appeared in any age group studied; only when clearance was expressed in relation to body weight (ml/min/100 g), a decrease in RBF and GFR was evidenced. This indicates that the rate of increase of both RBF and GFR with age is similar to that of kidney weight and lower than that of body weight. The present findings indicate that urinary markers of renal injury increase with age, whereas GFR and RBF only decrease when expressed as clearance related to body weight.

Simultaneous High-Performance Liquid Chromatography-Electrochemical Detection Determination of Imipramine, Desipramine, Their 2-Hydroxylated Metabolites, and Imipramine N-Oxide in Human Plasma and Urine

This assay method allows a simultaneous determination of imipramine, desipramine, their 2-hydroxylated metabolites, and imipramine-N-oxide in 0.5 ml of plasma or 0.1 ml of urine within 35 min by an ion-paired, reversed phase (C18) high-performance liquid chromatography (HPLC) with electrochemical detection. The analytes are extracted from alkalinized plasma or urine with 5 ml of a 90/10 mixture (by vol) of diethyl either/2-propanol, back-extracted into 0.5 ml of 0.1 mol/L phosphoric acid. Urine samples are enzymatically treated with beta-glucuronidase/arylsulfatase before extraction. The electrochemical detection is performed with a glassy carbon electrode set at +0.85 V against the Ag/AgCl reference electrode. Recoveries for the analytes and the internal standard (propericiazine) from plasma or urine ranged from 66.4 to 105.7% with coefficients of variation (CVs) of < 6.8%. The intra- and interassay CVs for the analytes were < 17.4% in plasma and < 14.2% in urine. The limits of determination (a signal-to-noise ratio of 3) for imipramine, desipramine, 2-hydroxyimipramine, 2-hydroxydesipramine, and imipramine-N-oxide were 0.5, 0.3, 0.02, 0.02, and 1.0 microgram/L, respectively. Only four of the 23 psychotropic drugs, which might be coadministered with imipramine or desipramine, were considered to be the possible sources to interfere with the assay. We evaluated clinical applicability of this method by determining plasma concentration- and urinary excretion-time courses of the respective analytes in an extensive and a poor metabolizer of the debrisoquine/sparteine-type oxidation after a single oral dose of imipramine HCl (25 mg). The present method appears to be suitable not only for the therapeutic drug monitoring of imipramine and its active metabolites but also for studying the pharmacogenetically related metabolism of imipramine or desipramine.

Estimation of a concentration profile of acyclovir in the skin after topical administration

The Laplace transformed equations for the time courses of drug concentration in the skin and net absorption were derived from Fick's diffusion law assuming a two-layer skin model. Based on these equations, a new method for estimating drug concentration in the skin directly from the absorption profile was developed by the use of a fast inverse Laplace transform (FILT) algorithm. The absorption profiles of topically administered acyclovir in rats obtained through deconvolution of urinary excretion time courses against i.v. injection data were analyzed according to this method. The amount of acyclovir excreted into urine was only 0.42% of the applied dose at 8 h after topical application with polyethylene glycol ointment, suggesting low skin permeability, while most of acyclovir injected intravenously was excreted within 4 h. However, the analysis revealed that a considerable level (57 jug/cm3) higher than the minimum inhibitory concentration (MIC) was maintained in the viable tissue under the steady-state conditions.

Simultaneous determination of omeprazole and its metabolites in plasma and urine by reversed-phase high-performance liquid chromatography with an alkaline-resistant polymer-coated C 18 column

Omeprazole (OPZ) is a proton pump inhibitor in gastric parietal cells. A reversed-phase high-performance liquid chromatographic method was developed that enables concentrations of OPZ and its major metabolites, omeprazole sulphone (OPZ-SFN) and hydroxyomeprazole (H-OPZ), to be determined simultaneously in plasma and that of H-OPZ in urine. To prevent decomposition of OPZ, all the processes (extraction, injection and elution) were carried out under alkaline conditions. Recoveries of the analytes and internal standard were >93.1%. The intra- and inter-assay coefficients of variation were <9.1 and 6.4% for plasma samples and <2.9 and 3.9% for urine samples, respectively. The minimum determinable concentration (relative standard deviation 10–15%) was 10 ng/ml for all analytes in plasma and H-OPZ in urine samples. The clinical applicability of this assay method was evaluated by determining plasma concentration— and urinary excretion—time courses of the respective analyte(s) in four healthy volunteers after an oral dose of 20 mg of OPZ. The present assay is considered to be simple, precise and accurate and suitable for the study of the kinetic disposition and metabolism of OPZ, which is an extensively metabolized drug in the human liver.

Dosage forms with controlled gastrointestinal passage — studies on the absorption of nitrofurantoin

The aim of the present investigation was to describe theoretically the influence of the rate of gastrointestinal passage on the absorption of drugs after peroral administration and to use this description in the practical development of new types of dosage forms. The intention in these studies was to devise peroral dosage forms that display a delayed gastrointestinal passage through the release of a passage-influencing excipient. The saturated fatty acid myristic acid was used as a substance for controlling gastrointestinal passage, since this acid, as a constituent of fat-rich food, delays transit through the alimentary tract. The ammonium salt was used to optimise the properties of myristic acid for use in oral dosage forms. In a comparative in vivo study with 5 healthy subjects, the effects of 107.5 mg ammonium myristate on the absorption of nitrofurantoin after the administration of sustained release preparations (dose: 100 mg) was determined indirectly on the basis of the renal excretion of the drug. A commercially available sustained release preparation in capsule form was used, that was given with and without ammonium myristate in a larger hard gelatine capsule. The addition of ammonium myristate led to an average increase of 23.8% of the total amount of nitrofurantoin excreted in the urine compared to the values obtained from the reference dosage form without the additional substance. The increase in renal excretion was statistically significant ( P < 0.01). On evaluating the time course of urinary excretion of the drug, the amounts of nitrofurantoin excreted after administration of the dosage form with myristic acid were significantly higher ( P < 0.05) in the 5th, 6th, 7th and 9th hours after dosage.