A pharmacokinetic model of styrene inhalation with the fugacity approach

The physiologically based pharmacokinetic model of J. C. Ramsey and M. E. Andersen (1984, Toxicol. Appl. Pharmacol. 73, 159-175) of styrene inhalation in rats, with extrapolation to humans, was reformulated with the chemical equilibrium criterion of fugacity instead of concentration to describe compartment partitioning. Fugacity models have been used successfully to describe environmental partitioning processes which are similar in principle to pharmacokinetic processes. The fugacity and concentration models are mathematically equivalent and produce identical results. The use of fugacity provides direct insights into the relative chemical equilibrium partitioning status of compartments, thus facilitating interpretation of experimental and model data. It can help to elucidate dominant processes of transfer, reaction and accumulation, and the direction of diffusion. Certain model simplifications become apparent in which compartments which remain close to equilibrium may be grouped. Maximum steady-state tissue concentrations for a known exposure may be calculated readily. It is suggested that pharmacokinetic fugacity models can complement conventional concentration models and may facilitate linkage to fugacity models describing environmental sources, pathways, and exposure routes.     

Development of a physiologically based pharmacokinetic model for inhalation of jet fuels in the rat

The pharmacokinetic behavior of the majority of jet fuel constituents has not been previously described in the framework of a physiologically based pharmacokinetic (PBPK) model for inhalation exposure. Toxic effects have been reported in multiple organ systems, though exposure methods varied across studies, utilizing either vaporized or aerosolized fuels. The purpose of this work was to assess the pharmacokinetics of aerosolized and vaporized fuels, and develop a PBPK model capable of describing both types of exposures. To support model development, n-tetradecane and n-octane exposures were conducted at 89?mg/m(3) aerosol+vapor and 1000-5000?ppm vapor, respectively. Exposures to JP-8 and S-8 were conducted at ~900-1000?mg/m(3), and ~200?mg/m(3) to a 50:50 blend of both fuels. Sub-models were developed to assess the behavior of representative constituents and grouped unquantified constituents, termed "lumps", accounting for the remaining fuel mass. The sub-models were combined into the first PBPK model for petroleum and synthetic jet fuels. Inhalation of hydrocarbon vapors was described with simple gas-exchange assumptions for uptake and exhalation. For aerosol droplets systemic uptake occurred in the thoracic region. Visceral tissues were described using perfusion and diffusion-limited equations. The model described kinetics at multiple fuel concentrations, utilizing a chemical "lumping" strategy to estimate parameters for fractions of speciated and unspeciated hydrocarbons and gauge metabolic interactions. The model more accurately simulated aromatic and lower molecular weight (MW) n-alkanes than some higher MW chemicals. Metabolic interactions were more pronounced at high (~2700-1000?mg/m(3)) concentrations. This research represents the most detailed assessment of fuel pharmacokinetics to date.     

A closed inhalation system for pharmacokinetic and metabolism studies of volatile compounds with small laboratory animals.

In the inhalation system described an animal can be kept in the same atmosphere of a 2-liter desiccator for up to 24 h. The expired carbon dioxide is adsorbed with soda lime and the resulting reduced pressure is balanced by a supply of oxygen also used for the inflow of the chemical to be investigated. Urine and faeces can be collected separately and the system allows a periodical control of the concentration of the chemical by sampling the air with needle and syringe.     

Validation of subcutaneous microdialysis sampling for pharmacokinetic studies of flurbiprofen in the rat

The objective of this study was to validate subcutaneous (sc) microdialysis sampling to study flurbiprofen pharmacokinetics and plasma protein binding in the awake freely moving rat. A linear microdialysis probe was manufactured using a Hemophane^® hollow fiber which was tested in vitro and in vivo for the recovery of flurbiprofen and naproxen used as retrodialysis marker. Flurbiprofen was administered intraperitoneally and intravenously at a dose of 20 mg/kg in rats. In both cases, conventional blood sampling and sc microdialysis sampling were simultaneously performed. The microdialysates were analyzed on-line by high-pressure liquid chromatography. Naproxen, which was shown to have a similar in vivo loss by retrodialysis as flurbiprofen (71.5 ± 0.9% and 71.0 ± 0.8% respectively, n = 3), was used to continuously monitor probe recovery. Concentration-dependent protein binding of flurbiprofen was demonstrated in vivo based on experiments with a simultaneous sc microdialysis and blood sampling. Values of unbound fraction were similar to those reported previously by intravenous microdialysis sampling, demonstrating that the sc unbound concentrations are very similar to those in the central compartment. There was no significant difference among pharmacokinetic parameters (AUC, CL, t_1/2z, Vd) for total or unbound flurbiprofen determined after intraperitoneal and intravenous administration. Subcutaneous microdialysis is a simple yet powerful tool to study the pharmacokinetics and the in vivo plasma protein binding of flurbiprofen in the awake unrestrained rat. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1897–1906, 2001     

Route-to-route extrapolation of 1,2-dichloroethane studies from the oral route to inhalation using physiologically based pharmacokinetic models

To help develop a comprehensive, quantitative understanding of the hazards of 1,2-dichloroethane (ethylene dichloride, EDC, CAS No. 107-06-2) exposure by the inhalation route, the results of existing subchronic studies and an extended one-generation reproductive toxicity (EOGRT) study recently conducted by the oral route in rats were extrapolated using a physiologically based pharmacokinetic (PBPK) model. The no observed adverse effects levels (NOAELs) for the endpoints of neurotoxicity and reproductive/developmental toxicity were the highest tested doses of 169 and 155 mg/kg-day, respectively. These NOAELs were equivalent to continuous exposure of rats to minimums of 76 ppm and 62 ppm EDC, respectively, using total metabolism of EDC as the dose metric that is equivalent in the oral and inhalation scenarios. In contrast, the subchronic study NOAEL of 37.5 mg/kg-day corresponded to continuous inhalation of 4.4 ppm EDC, based on equivalent extrahepatic metabolism. The selection of the internal metric which serves to establish route-to-route equivalency was found to profoundly influence the NOAEL-equivalent inhalation exposure concentration and thus will be a key determinant of inhalation toxicity reference criteria developed on the basis of EDC studies conducted by the oral route.     

HPLC-MS法测定大鼠血浆中双-O-甲基四氢呋喃愈创木素B的浓度及药代动力学参数

目的建立测定大鼠血浆中双-O-甲基四氢呋喃愈创木素B(DiB)含量的高效液相色谱-电喷雾离子化-质谱(HPLC-ESI-MS)联用的分析方法,并用于其在大鼠体内的药代动力学研究。方法 SD大鼠6只,单剂量静脉注射(10mg.kg-1)DiB,以三白草酮为内标,用HPLC-MS法测定给药后血浆中的药物浓度,并用DAS 2.0软件计算药动学参数。结果 DiB的血药浓度在0.025～5.0 mg.L-1范围内线性关系良好,最低定量限为0.025 mg.L-1,提取回收率≥91.1%,日间、日内RSD≤10.0%。大鼠单剂量尾静脉注射DiB 10 mg.kg-1后,主要动力学参数AUC(0-t)、T12β、CL、V1分别为:(11.44±2.44)mg.h.L-1、(3.73±1.30)h、(0.65±0.14)L.h-1.kg-1、(3.36±3.19)L.kg-1。结论该方法操作简便、灵敏、快速、专属性强,可用于DiB的血药浓度检测及药代动力学研究。     

Discrepancies in pharmacokinetic parameter estimation between bolus and infusion studies in the perfused rat hindlimb

Isolated, perfused rat hindlimb consists of skeletal muscle, skin, bone, and adipose. Hence, it is a heterogeneous preparation composed of slowly equilibrating tissues of different characteristics and fractional flow rates. This paper shows how caution should be exercised in interpreting the results following bolus administration and subsequent statistical moment analysis of intravascular markers (⁵¹Cr-erythrocytes and¹²⁵I-albumin) and lipophilic barbiturates. For the intravascular markers, the events in the hindlimb are overshadowed by events in the connecting tubing and cannulas, due to their comparable volumes. For the barbiturates, these estimates appear to apply to short-term effects as the volume estimates obtained following infusion to steady state are greater than after bolus administration. For the extravascular markers,¹⁴C-sucrose,¹⁴C-urea, and³H-water, no such time dependency was shown. However, it is only from the outflow profiles following bolus administration that events in the tissue beds can be elucidated.     

Determination of thalidomide by high performance liquid chromatography: plasma pharmacokinetic studies in the rat

A sensitive and simple high performance liquid chromatography (HPLC) method was developed and validated for the determination of thalidomide in rat plasma. Chromatography was accomplished with a reversed-phase Hypersil C18 column. Mobile phase consisted of acetonitrile-10 mM ammonium acetate buffer (pH 5.50) (28:72, v/v), at a flow rate of 0.8 ml/min. Thalidomide was monitored by ultraviolet detector at 220 nm and it gave a linear response as a function of concentration over 0.02-50 microM. The limit of quantitation in rat plasma was 0.50 ng (0.02 microM plasma concentration) with an aliquot of 20 microl. Results from a 3-day validation study indicated that this method allows for simple and rapid quantitation of thalidomide with excellent accuracy and reliability. Using this validated assay, the effect of coadministered irinotecan (CPT-11) on the plasma pharmacokinetics of thalidomide in rats was determined. Coadministration of CPT-11 (intravenously, 60 mg/kg) increased the maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC(0-10h)) of thalidomide by 32.29 and 11.66%, respectively, as compared to the control, but none of the effect of CPT-11 was of statistical significance (P > 0.05). Concomitant CPT-11 also caused a 10.04% decrease in plasma clearance (CL) and 14.51% decrease in volume of distribution (V(d)) (P > 0.05). These results suggest that coadministered CPT-11 did not significantly alter the plasma pharmacokinetics of thalidomide in rats. Further studies are warranted to explore the pharmacokinetic and pharmacodynamic interactions between CPT-11 and thalidomide.     

HPLC determination of polydatin in rat biological matrices: application to pharmacokinetic studies

A reversed-phase high-performance liquid chromatographic (RPHPLC) method has been developed for the determination of polydatin (PD) in rat plasma, bile, urine, feces and tissue homogenates using 2,3,5,4'-tetrahydroxychrysophenine-beta-d-glucoside as an internal standard. The sample pretreatment included deproteinization for plasma samples and a liquid-liquid extraction for bile, urine, feces and tissue homogenates. Separation was obtained on a C18 reversed-phase column with the mobile phase consisting of methanol and water (35:65 v/v). The flow rate was 1 ml/min and the effluent was monitored at 310 nm. The method showed good linearity over the concentration ranges employed for various matrices (r > 0.998). The quantification limits of PD in rat plasma, bile, urine, feces and tissue homogenates were 0.0251, 0.126, 0.025 microg/ml, 0.189 and 0.0378 microg/g, respectively. The accuracy and precision of the method were less than 12.0% for the various matrices. No interferences from endogenous substances were found. The method was successfully applied to study the pharmacokinetics of PD in rats after intravenous administration.     

Tizanidine — Initial pharmacokinetic studies in patients with spasticity

The time-course of plasma concentrations of the antispasticity agent tizanidine were measured by a specific radioimmune-assay in six adults who had severe spasticity due to multiple sclerosis. The drug was given as a single oral 4 mg dose to each subject. The drug had a mean absorption half-life of 0.30 +/- 0.155 h following a mean lagtime of 0.361 +/- 0.118 h, and a mean terminal elimination half-life of 4.16 +/- 2.06 h. Only 2.65 +/- 0.82% of the dose was excreted unchanged in urine in 2 h. Calculated values of clearance and apparent volume of distribution were almost certainly overestimates as it seems probable that the orally-administered drug undergoes significant presystemic elimination (its bioavailability was not determined in the investigation here reported). Relief of spasticity, from the dosage used, was relatively slight and appeared greatest at the time of peak plasma levels of the drug.     

Short-term inhalation toxicity studies with peroxyacetyl nitrate in rats

The inhalation toxicity of peroxyacetyl nitrate (PAN) was examined in acute (single exposure), sub-acute (4-week repeated exposure) and subchronic (13-week repeated exposure) studies in rats. The 4-h LC₅₀ was found to be 95 ppm.In the 4-week study rats were exposed to 0, 0.9, 4.1 or 11.8 ppm PAN vapour for 6 h/day, 5 days/week. Exposure to 11.8 ppm caused abnormal behaviour, growth retardation, mortality, elevated haemoglobin contents, haematocrit values and erythrocyte counts, increased lung weights and severe inflammatory changes and epithelial hyper- and metaplasia in the respiratory tract. At 4.1 ppm minimal behavioral disturbance, transient growth depression, slightly increased lung weights and mild histopathological changes in the respiratory tract were found. At 0.9 ppm no treatment-related alterations were detected.In the 13-week study rats were exposed to 0, 0.2, 1.0 or 4.6 ppm PAN vapour for 6.5 h/day, 5 days.week. Exposure to 4.6 ppm resulted in changes similar to those found at 11.8 ppm in the 4-week experiment, but no mortality occurred. At 1.0 ppm minimal irritation of the mucous membranes in the nasal cavity was the only PAN-related effect observed. No treatment- related changes were seen at 0.2 ppm. It was concluded that the no-toxic- effect level is between 0.2 and 1.0 ppm, and very probably close to the upper value.     

Errors in time in pharmacokinetic studies

Pharmacokinetic models with errors in the time variable were developed and explored by simulation in NONMEM. The precision of estimated parameters decreased with increasing error magnitude. The usual asymptotic standard error estimates were biased low by 10-50% Accuracy and precision were not greatly diminished by ignoring errors in time when fitting models.     

High-throughput analysis of standardized pharmacokinetic studies in the rat using sample pooling and UPLC-MS/MS

As a consequence of a continuous demand for increased throughput of pharmacokinetic (PK) studies, industries have introduced strategies to reduce the number of samples such as cassette analysis (pooling of samples after the in-life phase). Here, we have investigated whether relevant PK parameters change as a consequence of cassette analysis, and whether there are circumstances that disqualify this technique from being used. 22 compounds were intravenously and orally administered to parallel groups of 3 rats. Each compound was administered discretely. Equal volumes of three plasma samples corresponding to each time point of three discretely dosed rats with different compounds were pooled (cassette analysis). Samples were prepared by protein precipitation followed by UPLC-MS/MS analysis using pos/neg switching when required. With cassette analysis, 4 compounds, morphine, phenytoin, rofecoxib and diclofenac, showed high limit of quantification (LOQ) values after pooling, which led to less reliable PK analyses. Of all samples with contents above LOQ, about 5% could not be detected in pool samples compared to single samples. However, an excellent correlation was seen for all PK parameters when comparing the parameters obtained from discrete analysis versus those obtained from cassette analysis, although half life showed somewhat more scatter than the others. When PK parameters were grouped as low-medium-high, clearance, volume of distribution, half life and bioavailability were similar between discrete and cassette analysis for 90%, 86%, 95% and 90% of the total number of compounds tested, respectively. Some additional improvement was achieved if compounds with a low MS response were excluded. In summary, cassette analysis is an effective strategy to reduce samples without affecting the estimated PK parameters that are important for decision-making.     

卡铂对肿瘤患者的药物动力学与药效学

目的:研究国产卡铂(CBP)的临床药物动力学与药效学,方法:12例肿瘤病人iv gtt CBP 400mg,用反相HPLC法测定血清CBP浓度,并按残数法拟合药物动力学模型和参数.结果:12例肿瘤病人iv gtt CBP结束时的平均血药浓度(?).为55.10±13.00)mg/L,消除半衰期(T._(2?))为(143.09±49.36)min,清除率(CL)为(45.17±16.68)ml min.有效组和无效组的(?)分别为(61.03±9.28)和(52.14±12.77)mg/L,T_(?)分别为(191.27±26.92)和(119.00±35.31)min(P<0.01),CL分别为(31.42±6.79)和(52.04±15.97)ml/min(P<0.05).在2～10h内.有效组血清CBP浓度高于无效组(P<0.05).结论:肿瘤病人iv gtt CBP的血药浓度存在明显个体差异,且疗效与血药浓度和清除快慢有关.     

Sampling methods for pharmacokinetic studies in the mouse

Pharmacokinetics data on 2,4,5-T are used to illustrate design considerations, agent administration and sampling techniques required for single-animal studies in mice. Detailed methods for intravenous and intragastric delivery of chemicals are described, as are small volume (3 μl) blood sampling techniques from tail vein and orbital plexus. A mouse metabolism cage is described that prohibits feed contamination of urine and feces, and also effectively segregates these elimination products. Techniques for blood, urine, and feces sample preparation and quality control assessments are also presented. Multi-sample blood concentration-time curves obtained from a single mouse are compared to data obtained using a single-sample design using many mice. While a single-animal, multiple-sample design requires the availability of microanalytical methods, it has many economic and practical advantages and results in a more accurate pharmacokinetic profile of the chemical in mice.     

Metabolic and pharmacokinetic studies of scutellarin in rat plasma, urine, and feces

Aim:

To study the metabolic and pharmacokinetic profile of scutellarin, an active component from the medical plant Erigeron breviscapus (Vant) Hand-Mazz, and to investigate the mechanisms underlying the low bioavailability of scutellarin though oral or intravenous administration in rats.

Methods:

HPLC method was developed for simultaneous detection of scutellarin and scutellarein (the aglycone of scutellarin) in rat plasma, urine and feces. The in vitro metabolic stability study was carried out in rat liver microsomes from different genders.

Results:

After a single oral dose of scutellarin (400 mg/kg), the plasma concentrations of scutellarin and scutellarein in female rats were significantly higher than in male ones. Between the female and male rats, significant differences in AUC, t_max2 and C_max2 for scutellarin were found. The pharmacokinetic parameters of scutellarin in the urine also showed significant gender differences. After a single oral dose of scutellarin (400 mg/kg), the total percentage excretion of scutellarein in male and female rats was 16.5% and 8.61%, respectively. The total percentage excretion of scutellarin and scutellarein in the feces was higher with oral administration than with intravenous administration. The in vitro t_1/2 and CL_int value for scutellarin in male rats was significantly higher than that in female rats.

Conclusion:

The results suggest that a large amount of ingested scutellarin was metabolized into scutellarein in the gastrointestinal tract and then excreted with the feces, leading to the extremely low oral bioavailability of scutellarin. The gender differences of pharmacokinetic parameters of scutellarin and scutellarein are due to the higher CL_int and lower absorption in male rats.     

Instantaneous input hypothesis in pharmacokinetic studies

Observed venous plasma concentrations of furosemide, propranolol, griseofulvin, and theophylline at 0.33 and 0.66 min after intravenous bolus injections to unanesthetized dogs were compared with those extrapolated using the instantaneous input hypothesis. At 0.33 min, extrapolated/observed plasma level ratios as high as 20.5, 65.5, 226, and 1.17 were found for these four drugs, respectively. Venous plasma levels peaked at 1 min postinjection in all studies. Total plasma areas (AUC0-->infinity) estimated using the instantaneous input principle were higher by as much as 6.0, 6.8, and 19.6% for propranolol, griseofulvin, and furosemide, respectively, when compared with experimental data. The effect on theophylline was negligible. These results suggest the need for cautious interpretation of some venous pharmacokinetic data. More studies in animals and humans are required to assess the magnitude of deviation from the instantaneous input hypothesis for drugs in general.