Prediction of glycyrrhizin disposition in rat and man by a physiologically based pharmacokinetic model

Three physiologically based pharmacokinetic models A--C, incorporating enterohepatic recycling, were developed to predict glycyrrhizin (GLZ) disposition in rat plasma and tissues, and human serum. Model A, which included fourteen compartments (artery, vein, tissues except brain, and gut lumen) with the assumption of direct excretion of GLZ from the liver into the gut lumen gave fairly good agreement between the observed and predicted disposition profiles in rat, but was unsuitable in man, where elimination is very rapid. Models B and C for man were obtained by adding a gallbladder compartment (drug storage organ) for the excretion from the liver into the gut lumen and by assuming continuous transfer from the storage compartment or instantaneous emptying from it during meal ingestion as the excretion process from the gallbladder into the gut lumen, respectively. The agreement between the observed and predicted serum concentration time-course profiles was better with model C than model B, especially in the terminal elimination phase, where secondary peaks appeared. However, it was thought that the observed serum disposition can be sufficiently well predicted by model B. In conclusion, prediction in rat was successful in all compartments except the brain, which shows a negligible distribution. Scale-up of the disposition kinetics of GLZ from rat to man was also successful.     

In vivo determination of amino acid bioavailability in humans and model animals

Because the digestion of many dietary proteins is incomplete, and because there is a continuous (but variable) entry into the intestinal lumen of endogenous protein and amino acid nitrogen that is also subject to digestion, the fluxes of nitrogen, amino acids, and protein in the gut exhibit a rather complicated pattern. Methods to distinguish and quantitate the endogenous and dietary components of nitrogen and amino acids in ileal chyme or feces include the use of a protein-free diet, the enzyme-hydrolyzed protein method, different levels of protein intake, multiple regression methods, and stable-isotope labelling of endogenous or exogenous amino acids. Assessment of bioavailability can be made, with varying degrees of difficulty, in man directly but, for routine evaluation of foods, the use of model animals is attractive for several reasons, the main ones being cost and time. Various animals and birds have been proposed as models for man but, in determining their suitability as a model, their physiological, enzymological, and microbiological differences must be considered. Fecal or ileal digestibility measurements, as well as apparent and true nitrogen and amino acid digestibility measurements, have very different nutritional significance and can, thus, be used for different objectives. Measurements at the ileal level are critical for determining amino acid losses of both dietary and endogenous origin, whereas measurements at the fecal level are critical in assessing whole-body nitrogen losses. A complementary and still unresolved aspect is to take into account the recycling of intestinal nitrogen and bacterial amino acids to the body.     

A pharmacokinetic model for ocular drug delivery

A pharmacokinetic model of ocular drug delivery has been developed for describing the elimination and distribution of ocular drugs in the eye. The model, based on Fick's second law of diffusion, assumes a modified cylindrical eye with three pathways for drug transport across the surface of the eye: the anterior aqueous chamber, the posterior aqueous chamber and the retina/choroids/scleral membrane covering the vitreous body. The model parameters such as the diffusion coefficient and the partition coefficient in various eye tissues can be evaluated from the in vitro membrane penetration experiments using a side-by-side diffusion cell system. The diffusion coefficient for a drug is also predicted by taking account of the effect of the molecular weight of model compounds. The present ocular pharmacokinetic model, which can predict the local concentration distribution in the eye, has well described the in vivo concentration profile in the various eye tissues, the lens, the aqueous humor and the vitreous body, following not only topical eye drop instillation but systemic administration as well. The present model also simulates the effects of binding and metabolism in the eye as well as the individual difference in ocular functions and structure such as cataract surgery and vitreous fluidity on the distribution and elimination of drug molecules in the eye.     

Bioanalytical technique for determination of tasimelteon in human plasma by LC–MS/MS and its application to pharmacokinetic study in humans

A highly sensitive, specific and rapid liquid chromatography–tandem mass spectrometry technique for the quantification of tasimelteon in human plasma has been developed and validated using tasimelteon‐d₅ as internal standard. Liquid–liquid extraction technique with ethyl acetate was used for extraction of tasimelteon from the plasma. The chromatographic separation was achieved on an Agilent Zorbax, Eclipse, C₁₈ (4.6 × 50 mm, 5 μm) column using a mobile phase of acetonitrile and 0.02% formic acid buffer (85:15, v/v) with a flow rate of 0.5 mL/min. A detailed method validation was performed as per the United States Food and Drug Administration guidelines. The linear calibration curve was obtained over the concentration range 0.30–299 ng/mL. The API‐4000 liquid chromatography–tandem mass spectrometry was operated under multiple reaction monitoring mode during analysis. The validated method was successfully applied to estimate plasma concentration of tasimelteon after oral administration of a single dose of a 20 mg capsule in healthy volunteers under fasting conditions. The maximum concentration of the drug achieved in the plasma was 314 ± 147 ng/mL and the time at which this concentration was attained was 0.54 ± 0.22 h.     

A sensitive column-switching HPLC method for aripiprazole and dehydroaripiprazole and its application to human pharmacokinetic studies

A simple and sensitive column‐switching HPLC‐UV method was developed for the simultaneous determination of aripiprazole, a novel atypical antipsychotic drug, and its active metabolite, dehydroaripiprazole in human plasma. Aripiprazole, its active metabolite and 7‐[5‐[4‐(3‐chloro‐2‐methylphenyl)‐1‐piperazinyl]pentyloxy]‐3,4‐dihydro‐2(1H)‐quinolinone (OPC‐14558) as an internal standard were extracted from 1 mL of plasma using a mixture of chloroform/n‐heptane (3:7, v/v), and the extract was injected into a column I (TSK BSA‐ODS/S precolumn, 5 μm) for cleanup and column II (C₁₈ STR ODS‐II analytical column, 5 μm) for separation. Peaks were detected with an UV detector set at a wavelength of 254 nm, and the total time for chromatographic separation was ～20 min. Mean absolute recoveries were 74.0 and 74.7% for aripiprazole and dehydroaripiprazole, respectively. Intra‐ and inter‐day CVs were less than 7.5 and 7.1% for aripiprazole concentrations ranging from 2 to 600 ng/mL, and 9.2 and 4.5% for dehydroaripiprazole concentrations ranging from 2 to 160 ng/mL. The validated concentration ranges for this method were 1–500 ng/mL and the limits of detection were 0.5 ng/mL for both aripiprazole and dehydroaripiprazole. This method was applied to pharmacokinetic study in human volunteers and patients taking aripiprazole.     

A substructure-based SAR model for odor perception in humans relevant to health risk assessments

The ability of human to perceive odors is a very complex phenomenon involving the selective binding of molecules to approximately 1000 olfactory receptors. Accordingly, the derivation of a substructure-based SAR model can be expected to be problematic. Yet, based upon published data on odor thresholds of volatile organic chemicals, we were able to derive such an SAR model. An examination of the structural determinants and related modulators indicates that lipophilicity is a major contributor to olfactory perception. The availability of a substructure-based SAR model permits an examination of the relationship between the presence in the environment of odorous chemicals and public health risks.     

A substructure-based SAR model for odor perception in humans relevant to health risk assessments

The ability of humans to perceive odors is a very complex phenomenon involving the selective binding of molecules to approximately 1000 olfactory receptors. Accordingly, the derivation of a substructure-based SAR model can be expected to be problematic. Yet, based upon published data on odor thresholds of volatile organic chemicals, we were able to derive such an SAR model. An examination of the structural determinants and related modulators indicates that lipophilicity is a major contributor to olfactory perception. The availability of a substructure-based SAR model permits an examination of the relationship between the presence in the environment of odorous chemicals and public health risks.     

HPLC assay method for ceftibuten in plasma and its application to pharmacokinetic study

The purpose of this study was to validate a reliable analytical method for pharmacokinetic study of ceftibuten in human plasma by high performance liquid chromatography (HPLC) system with UV detection. Ceftizoxime was used as the internal standard. After plasma sample was precipitated with acetonitrile and dichloromethane, the supernatant was directly injected into the HPLC system. Separation was performed on a Capcell Pak C₁₈ UG120 column (4.6 mm × 250 mm, 5 μm particles) with a mobile phase of acetonitrile/50 mM ammonium acetate (5: 95, v/v) and UV detection at a wavelength of 262 nm. The intra- and inter-day precision expressed as the relative standard deviation was less than 15%. The lower limit of quantification was 0.5 hg/mL of ceftibuten using 0.5 mL of plasma. The calibration curve was linear in concentration range of 0.5–30 μg/mL (r ² = 0.9998). The mean accuracy was 96–102%. The coefficient of variation (precision) in the intra- and inter-day validation was 0.9–3.9 and 0.9–2.4%, respectively. The pharmacokinetics of ceftibuten was evaluated after a single oral administration of 400 mg to healthy volunteers. The AUC_{0–9 h}, c _max, T _max, and T _1/2 were 86.6 ± 12.7 μg h/mL, 18.4 ± 1.5 μg/mL, 2.63 ± 0.83 and 2.65 ± 0.41 h, respectively. The method was demonstrated to be highly reproducible and feasible for pharmacokinetic studies of ceftibuten in eight volunteers after oral administration (400 mg as ceftibuten).     

Chemical synthesis of the first lignans to be found in humans and animals

$\text{Trans}$-2,3-$\text{bis}$-(3′-hydroxybenzyl)-butyrolactone (1) and 2,3-$\text{bis}$-(3′-hydroxybenzyl)-butane-1,4-diol (2), recently identified in urine, have been synthesised in racemic form.     

Simultaneous stereoselective analysis of tramadol and its primary phase I metabolites in plasma by liquid chromatography. Application to a pharmacokinetic study in humans

This paper describes a bioanalytical method involving a simple liquid-liquid extraction for the simultaneous HPLC determination of the enantiomers of tramadol, the active metabolite O-desmethyltramadol (M1), and the other main metabolite N-desmethyltramadol (M2) in biological samples. Chromatography was performed at 5 degrees C on a Chiracel OD-R column containing cellulose tris(3,5-dimethylphenylcarbamate) as chiral selector, preceded by a achiral end-capped C8 column (LiChrospher 60-RP-selected B 5 microm, 250 mm x 4 mm). The mobile phase was a mixture of phosphate buffer containing sodium perchlorate (1 M) adjusted to pH 2.5-acetonitrile-N,N-dimethyloctylamine (74.8:25:0.2). The flow rate was 0.5 ml/min. Fluorescence detection (lambda(ex) 200 nm/lambda(em) 301 nm) was used. Fluconazol was selected as internal standard. The limit of quantitation of each enantiomer of tramadol and their metabolites was 0.5 ng/ml (sample size = 0.5 ml). The chiral conditions and the LC optimisation were investigated in order to select the most appropriate operating conditions. The method developed has also been validated. Mean recoveries above of 95% for each enantiomer were obtained. Calibration curves for tramadol enantiomers (range 1-500 ng/ml), M1 enantiomers (range 0.5-100 ng/ml), and M2 enantiomers (range 0.5-250 ng/ml) were linear with coefficients of correlation better than 0.996. Within-day variation determined on four different concentrations showed acceptable values. The relative standard deviation (R.S.D.) was determined to be less than 10%. This method was successfully used to investigate plasma concentration of enantiomers of tramadol, O-desmethyltramadol and N-desmethyltramadol in a pharmacokinetic study.     

A validated LC-MS/MS method for the determination of vinflunine in plasma and its application to pharmacokinetic studies

A rapid, simple and sensitive LC‐MS/MS method for the quantification of vinflunine in plasma was developed and validated. The analysis involved a simple liquid–liquid extraction. After making alkaline with NaOH, plasma was extracted with methyl tert‐butyl ether and the organic extract was then evaporated and the residue was reconstituted in mobile phase. The reconstituted solution was injected into an HPLC system and was subjected to reverse‐phase HPLC on a 5 µm ODS‐3 column at a flow‐rate of 0.2 mL/min. The mobile phase consisted of ammonium acetate (0.02 mol/L, pH = 3.0) and acetonitrile (20:80). Vinflunine was detected in the single ion monitoring mode using target ions at m/z 817.4/160.1/142.3 for vinflunine and m/z 447.2/128.3/112.1 for gefitinib (internal standard). Standard curves were linear over the concentration range of 5–1000 ng/mL. The mean predicted concentrations of the quality control samples deviated by less than 2% from the corresponding nominal values; the intra‐assay and inter‐assay precisions of the assay were within 7% relative standard deviation. The extraction recovery of vinflunine was more than 80%. The validated assay was applied to a pharmacokinetic study of vinflunine in plasma following the administration of a single vinflunine injection (2 mg/kg). Copyright © 2011 John Wiley & Sons, Ltd.     

A high-performance liquid chromatographic method for determination of mitragynine in serum and its application to a pharmacokinetic study in rats

A simple HPLC technique for determining mitragynine levels in serum was developed. The separation system consisted of a C18 column heated to 35 degrees C, a methanol-water (80:20, v/v) mobile phase, a flow rate of 0.8 mL/min and detection in the ultraviolet at 225 nm. Mitragynine, with a retention time of 10.09 min, was well resolved from any interferences in human serum and the internal standard peak. The calibration curve was linear from 0.1 to 10 microg/mL (r = 0.9995). Extraction of mitragy-nine from alkalinized serum using diethyl ether gave a high recovery (>or=85%). The intra- and inter-day precisions of the method were 4.29-5.88%RSD and 7.06-8.45%RSD, respectively. The accuracy ranged from -9.54 to +0.67%DEV. The limit of detection was 0.03 microg/mL and the lower limit of quantification was 0.1 microg/mL. Mitragynine in the stock solution was stable during 30 days of storage at 4 degrees C. This method was successfully applied to determine the pharmacokinetic characteristics of mitragynine levels in the serum of rats after it was administered orally.     

A simple RP‐HPLC method for quantification of columbianadin in rat plasma and its application to pharmacokinetic study

A rapid and sensitive reversed‐phase high‐performance liquid chromatographic (RP‐HPLC) method was developed to investigate pharmacokinetics of columbianadin, one of the main bioactive constituents in the roots of Angelica pubescens f. biserrata, in rat plasma after intravenous administration to rats at two doses of 10 and 20 mg/kg. The method involves a plasma clean‐up step using liquid–liquid extraction by diethyl ether, followed by RP‐HPLC separation and detection. Separation of columbianadin was performed on an analytical Diamonsil? ODS C₁₈ column, with a mobile phase of MeOH–H₂O (85 : 15, v/v) at a flow‐rate of 1.0 mL/min, and UV detection was set at 325 nm. The retention time of columbianadin and scoparone (internal standard) was 6.7 and 3.5 min, respectively. The calibration curve was linear over the range of 0.2–20.0 μg/mL (r² = 0.9986) in rat plasma. The lower limits of detection and quantification were 0.05 and 0.1 μg/mL, respectively. The extraction recovery from plasma was in the range of 81.61–89.93%. The intra‐ and inter‐day precisions (relative standard deviation) were between 1.01 and 9.33%, with accuracies ranging from 89.76 to 109.22%. The results indicated that the method established was suitable for the determination and pharmacokinetic study of columbianadin in rat plasma. Copyright © 2009 John Wiley & Sons, Ltd.     

HPLC-based measurement of the chelator 1,2-dimethyl-3-hydroxy-pyrid-4-one (L1) and its iron complex for pharmacokinetic studies in humans

An improved HPLC based method to assay the oral active iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one (L1, CP20) in serum and urine is described. The L1 peak has been well separated from other endogenous compounds, allowing the exact determination of the drug in both biological fluids. Moreover urinary iron excretion due to L1 therapy has been monitored by measuring urine Fe-(L1)₃ complex concentrations using reverse phase HPLC and subsequent detection at 450 nm. In patients and normal volunteers receiving this drug there is a good correlation between urine iron excretion measured by AAS and by the HPLC based method.     

Assay of underivatized intrazepam and clonazepam in plasma by capillary gas chromatography applied to pharmacokinetic and bioavailability studies in humans

The assay procedure of underivatized, intact nitrazepam and clonazepam in human plasma is described, using gas chromatography with a support-coated open tubular column (OV-17), a solid injection system and electron-capture detection. Clonazepam is used as a internal standard in the assay of nitrazepam and vice versa. Linear calibration curves after a single extraction step were obtained in the concentration range 10--100 ng/ml plasma, with standard deviations less than 4.9%. The sensitivity limit of the method is about 1 ng/ml plasma for both drugs. The method was applied to pharmacokinetic and bioavailability studies of nitrazepam in humans. Seven healthy volunteers received two nitrazepam-containing tablet preparations (5 mg) and plasma concentrations were determined regularly from 15 min to 80 h following drug administration. The mean elimination half-life of nitrazepam was 27 h (range 13-34 h). Considerable intra-individual differences in peak level times between the two preparations were observed, whereas the extent of bioavailability was rather similar.