Separability of stereoisomers by electrokinetic chromatography in presence of a neutral selector - Fundamental aspects assessed by computer simulation.

The impact of the two essential parameters, the complexation constant and the mobility of the formed diastereomeric complex, on stereoisomer separation in presence of a neutral chiral selector was assessed by computer simulation for an electrokinetic chromatography configuration with a uniform background electrolyte and one with a cationic discontinues buffer system of isotachophoretic nature. With two enantiomers of norpseudoephedrine as model analytes, data for seven cases featuring complexation in free solution with various combinations of input values, complexation with an immobilized selector and no complexation were analyzed in a hitherto unexplored way. For the uniform buffer study, the determined differences of the effective mobilities and separation selectivities of the stereoisomers were found to be equal to those calculated with the well-known algebraic equations. For the isotachophoretic system with its Kohlrausch adjusted zones, separation is also based on differences in effective mobilities, but the mobility differences cannot be predicted with the same algebraic equation. In both techniques, chiral separations occur due to the presence of the selector and if there is inequality between the mobilities of the transient diastereomeric complexes and the mobility of the free, uncomplexed analyte. Separation of the stereoisomers is possible when complexation constants, complex mobilities or both of these parameters differ. In the isotachophoretic separation a migrating steady-state is formed in which analytes either establish consecutive zones with plateau concentrations or, if present in an insufficient amount, as a peak-like distribution that migrates within a moving steady-state boundary. Simulation data illustrate for the first time the use of a spacer compound that establishes an isotachophoretic zone between enantiomers and thereby provides complete separation of the enantiomers and the possibility of individual detection in peak-mode isotachophoresis. They demonstrate that such an approach could be employed to assess the enantiomeric purity of a chiral compound

Pharmacokinetic-pharmacodynamic modelling of the antinociceptive effect of a romifidine infusion in standing horses

OBJECTIVE To evaluate the effect of a romifidine infusion on antinociception and sedation, and to investigate its relationship with plasma concentration. STUDY DESIGN Prospective, experimental, nonrandomized trial. ANIMALS A total of 10 healthy adult warmblood horses. METHODS Romifidine (loading dose: 0.08 mg kg-1, infusion: 0.03 mg kg-1 hour-1) was administered intravenously over 120 minutes. Romifidine plasma concentrations were determined by capillary electrophoresis. Sedation quality and nociceptive thresholds were evaluated at regular time points before, during and after romifidine administration. The nociceptive withdrawal reflex was elicited by electrical stimulation at the thoracic limb using a dedicated threshold tracking algorithm and recorded by electromyography at the deltoid muscle. A pharmacokinetic-pharmacodynamic model was established and correlation between romifidine plasma concentration and main output variables tested. RESULTS A two compartmental model best described the romifidine pharmacokinetic profile. The nociceptive thresholds increased compared with baseline in all horses from 10 to 146 minutes after romifidine administration (p < 0.001). Peak effect reached 5.7 ± 2.3 times the baseline threshold (mean ± standard deviation). The effect/concentration relationship followed a counter-clockwise hysteresis loop. The mean plasma concentration was weakly correlated to nociceptive thresholds (p < 0.0071, r = 0.392). The sedative effects were significant until 160 minutes but variable, not correlated to plasma concentration (p = 0.067), and weakly correlated to nociceptive thresholds (p < 0.0001, r = 0.33). CONCLUSIONS AND CLINICAL RELEVANCE Romifidine elicited a marked antinociceptive effect. Romifidine-induced antinociception appeared with a delayed onset and lasted longer than sedation after discontinuing its administration

Ocular penetration of caspofungin in a rabbit uveitis model

Background: Little is known about the ocular penetration of echinocandin antifungals. We studied the ocular distribution of systemically administered caspofungin in a rabbit uveitis model. Methods: Caspofungin (1mg/kg per day) was given intravenously to rabbits as a single dose or as repeated daily doses on 7days starting 24h after induction of unilateral uveitis by intravitreal endotoxin injection. Caspofungin concentrations were determined by high-performance liquid chromatography in the cornea, aqueous humor, vitreous humor, and serum 4, 8, 16, and 24h after administration of a single dose and 24h after the last of seven doses. Results: The mean caspofungin concentration in the aqueous of the inflamed eye 4 and 8h after single-dose administration was 1.30 ± 0.39μg/ml and 1.12 ± 0.34μg/ml, respectively. Drug concentrations decreased to 0.24 ± 0.09μg/ml at 16h and 0.26 ± 0.14μg/ml at 24h. In the vitreous of inflamed eyes drug levels were undetectable at all time points. No drug was found in the aqueous of inflamed eyes 24h after the last of seven repeated doses, and the vitreous only contained trace amounts. In the corneas of inflamed eyes concentrations reached 1.64 ± 0.48μg/g at 4h, peaked at 2.16 ± 1.14μg/g at 8h, and declined to 1.87 ± 0.52μg/g and 1.49 ± 0.48μg/g at 16and 24h, respectively. After repeated dosing, corneal concentrations of caspofungin were 0.8 and 1.0μg/g and below the limit of detection in two of four animals. In non-inflamed eyes no drug was detectable in the aqueous and vitreous humor, and the corneas at any time point. Conclusions: In our model, caspofungin reached therapeutically relevant levels in the aqueous and cornea but not in the vitreous humor of inflamed eyes. Intraocular drug deposition was critically dependent on a disrupted blood-eye barrier. These findings suggest a limited role for caspofungin in the treatment of fungal endophthalmiti

Monographs on drugs which are frequently analyzed in therapeutic drug monitoring/Arzneimittel-Monographien für Medikamente, die regelmäßig im Rahmen des Therapeutic Drug Monitorings analysiert werden

In addition to the monographs which have been published in the last 6 years by the working group "Drug Monitoring” of the Swiss Society of Clinical Chemistry (SSCC) [Rentsch, Fathi, Grignaschi, Magnin, Printzen, Thormann, J Lab Med 29: 287-97, 2005 - Rentsch, Buhl, Eap, Fathi, Jöchle, Magnin, J Lab Med 34: 129-39, 2010], new monographs have been written. The data presented in these monographs provide an overview of the information which is important for the request and interpretation of the results. Therefore, laboratory health professionals and the receivers of the reports are the targeted readers. With the exception of digoxin, the drugs presented in this series are not administered frequently and are only analyzed in special situations. First, information about pharmacology and pharmacokinetics of these drugs (protein binding, metabolic pathways and enzymes involved, elimination half-life time and elimination route(s) of the parent drug and therapeutic as well as toxic concentrations) is given. Secondly, the indications for therapeutic drug monitoring are listed. Last but not least, important preanalytical information is provided, including time points of blood sampling and time interval after which steady-state concentrations are reached after changing the dose. Furthermore, the stability of the drug and its metabolite(s) after blood sampling are described. For readers with a specific interest, references to important publications are given. The number of the monographs will be further enlarged. The updated files are presented on the homepage of the SSCC (www.sscc.ch). We hope that these monographs are helpful for the better handling of therapeutic drug monitoring and we are looking forward to receiving comments from the readers.

Monitoring of cefepime in human serum and plasma by micellar electrokinetic capillary chromatography: Improvement of sample preparation and validation by liquid chromatography coupled to mass spectrometry.

Cefepime monitoring in deproteinized human serum and plasma by micellar electrokinetic capillary chromatography and liquid chromatography coupled to mass spectrometry in presence of other drugs is reported. For micellar electrokinetic capillary chromatography, sample preparation comprised dodecylsulfate protein precipitation at pH 4.5 using an increased buffer concentration compared to that of a previous assay and removal of hydrophobic compounds with dichloromethane. This provided robust conditions for cefepime analysis in the presence of sulfamethoxazole and thus enabled its determination in samples of patients that receive co-trimoxazole. The liquid chromatography assay is based upon use of a column with a pentafluorophenyl-propyl modified and multi-endcapped stationary phase and the coupling to electrospray ionization with a single quadrupole detector. The performances of both assays with multi-level internal calibration were assessed with calibration and control samples and both assays were determined to be robust. Cefepime levels monitored by micellar electrokinetic capillary chromatography in samples from patients that were treated with cefepime only and with cefepime and co-trimoxazole were found to compare well with those obtained by liquid chromatography coupled to mass spectrometry. Cefepime drug levels determined by micellar electrokinetic capillary chromatography could thereby be validated. This article is protected by copyright. All rights reserved

Monographs on drugs which are frequently analyzed in therapeutic drug monitoring

In addition to the monographs which have been published in the past 4 years by the working group "Drug Monitoring” of the Swiss Society of Clinical Chemistry (SSCC) [1-4], new monographs have been written. The data presented in these monographs provide an overview of important information for the request and interpretation of results. Therefore, laboratory health professionals and the receivers of the reports are the targeted readers. In this series, several antiepileptic drugs are presented. Monographs on carbamazepine [1], lamotrigine [2], phenobarbital [2], and valproic acid [2] have been published previously. First, information about pharmacology and pharmacokinetics of these drugs (protein binding, metabolic pathways and enzymes involved, elimination half-life time and elimination route(s) of the parent drug and therapeutic as well as toxic concentrations) is given. Second, the indications for therapeutic drug monitoring are listed. Last but not least, important pre-analytical information is provided, including time points of blood sampling and time interval after which steady-state concentrations are reached after changing the dose. Furthermore, the stability of the drug and its metabolite(s) after blood sampling is described. For readers with a specific interest, references to important publications are given. The number of the monographs will be further enlarged. The updated files are presented on the homepage of the SSCC (www.sscc.ch). We hope that these monographs are helpful for the better handling of therapeutic drug monitoring and we are looking forward to comments from the reader

Stereoselective pharmacokinetics of ketamine and norketamine after racemic ketamine or S-ketamine administration during isoflurane anaesthesia in Shetland ponies

Background. The arterial pharmacokinetics of ketamine and norketamine enantiomers after racemic ketamine or S-ketamine i.v. administration were evaluated in seven gelding ponies in a crossover study (2-month interval). Methods. Anaesthesia was induced with isoflurane in oxygen via a face-mask and then maintained at each pony's individual MAC. Racemic ketamine (2.2 mg kg-1) or S-ketamine (1.1 mg kg-1) was injected in the right jugular vein. Blood samples were collected from the right carotid artery before and at 1, 2, 4, 8, 16, 32, 64, and 128 min after ketamine administration. Ketamine and norketamine enantiomer plasma concentrations were determined by capillary electrophoresis. Individual R-ketamine and S-ketamine concentration vs time curves were analysed by non-linear least square regression two-compartment model analysis using PCNonlin. Plasma disposition curves for R-norketamine and S-norketamine were described by estimating AUC, Cmax, and Tmax. Pulse rate (PR), respiratory rate (Rf), tidal volume (VT), minute volume ventilation (VE), end-tidal partial pressure of carbon dioxide (Pe′CO2), and mean arterial blood pressure (MAP) were also evaluated. Results. The pharmacokinetic parameters of S- and R-ketamine administered in the racemic mixture or S-ketamine administered separately did not differ significantly. Statistically significant higher AUC and Cmax were found for S-norketamine compared with R-norketamine in the racemic group. Overall, Rf, VE, Pe′CO2, and MAP were significantly higher in the racemic group, whereas PR was higher in the S-ketamine group. Conclusions. Norketamine enantiomers showed different pharmacokinetic profiles after single i.v. administration of racemic ketamine in ponies anaesthetised with isoflurane in oxygen (1 MAC). Cardiopulmonary variables require further investigation.Facultad de Ciencias Veterinaria

Drug monographs on drugs which are frequently analysed in the context of Therapeutic Drug Monitoring

In addition to the monographs which were published last year by the working group "Drug Monitoring” of the Swiss Society of Clinical Chemistry (SSCC) [1], new monographs have been written. The aim of these monographs is to give an overview of the most important information necessary for ordering a drug analysis or interpreting the results. Therefore, the targeted readers comprise laboratory health professionals and all receivers of laboratory reports. There is information provided on the indication for therapeutic drug monitoring, protein binding, metabolic pathways and enzymes involved, elimination half-life and elimination routes, and on therapeutic or toxic concentrations. Preanalytical considerations are of particular importance for therapeutic drug monitoring. Therefore, information is provided regarding a reasonable timing for the determination of drug concentrations as well as steady-state concentrations after changing the dose. Furthermore, the stability of the drug and its metabolite(s) after blood sampling is described. For readers with a specific interest in drug analysis, references to important publications are given. The number of monographs will be continuously enlarged. The updated files are presented on the homepage of the SSCC (www.sscc.ch). We hope that these monographs are helpful and look forward to receiving comments from the audienc

Significance of serum adiponectin levels in patients with chronic liver disease

Adiponectin, which plays a pivotal role in metabolic liver diseases, is reduced in concentration in patients with NASH (non-alcoholic steatohepatitis). The aim of the present study was to determine adiponectin concentrations in patients with different forms and stages of chronic liver diseases. Serum adiponectin concentrations were measured in 232 fasting patients with chronic liver disease: 64 with NAFLD (non-alcoholic fatty liver disease), 123 with other chronic liver disease (e.g. viral hepatitis, n=71; autoimmune disease, n=18; alcohol-induced liver disease, n=3; or elevated liver enzymes of unknown origin, n=31) and 45 with cirrhosis. Circulating adiponectin levels were significantly lower in patients with NAFLD in comparison with patients with other chronic liver disease (4.8±3.5 compared with 10.4±6.3 μg/ml respectively; P<0.0001). Circulating adiponectin levels were significantly higher in patients with cirrhosis in comparison with patients without cirrhosis (18.6±14.5 compared with 8.4±6.1 μg/ml respectively; P<0.0001). Adiponectin concentrations correlated negatively with body weight (P<0.001), serum triacylglycerols (triglycerides) (P<0.001) and, in women, with BMI (body mass index) (P<0.001). Adiponectin concentrations correlated positively with serum bile acids (P<0.001), serum hyaluronic acid (P<0.001) and elastography values (P<0.001). Adiponectin levels were decreased in patients with NAFLD. In conclusion, adiponectin levels correlate positively with surrogate markers of hepatic fibrosis (transient elastography, fasting serum bile acids and hyaluronate) and are significantly elevated in cases of cirrhosis