Enhanced specificity due to method specific limits for relative ion intensities in a high-performance liquid chromatography - tandem mass spectrometry method for iohexol in human serum.

Background Accurate assessment of kidney function is needed for a variety of clinical indications and for research. The measurement of the serum clearance of iohexol has emerged as a feasible method to reach this objective. We report the analytical validation and clinical application of a new high-performance liquid chromatography (HPLC) - tandem mass spectrometry (MS/MS) assay to quantify iohexol in human serum. Specificity was enhanced due to the use of method specific acceptance limits for relative ion (RI) intensities. Methods The internal standard ioversol was added to 50 µL serum prior to protein precipitation with methanol. Linear gradient elution was performed on a Waters Oasis® HLB column. Three transitions for both iohexol and ioversol were monitored allowing calculation of RIs. Measurements acquired during method validation were used as a training set to establish stricter acceptance criteria for RIs which were then tested retrospectively on clinical routine measurements (86 measurements) and on mathematically simulated interferences. Results The method was linear between 5.0 µg/mL (lower limit of quantification [LLOQ]) and 100.3 µg/mL iohexol. Intraday and interday imprecision were ≤2.6% and ≤3.2%, respectively. Bias was -1.6% to 1.5%. All validation criteria were met, including selectivity, recovery, extraction efficiency and matrix effects. Retrospectively acceptance limits for RIs could be narrowed to ±4 relative standard deviations of the corresponding RIs in the training set. The new limits resulted in an enhanced sensitivity for the simulated interferences. Conclusions Criteria for validation were met and the assay is now used in our clinical routine diagnostics and in research.

Evaluation of a Meropenem and Piperacillin Monitoring Program in Intensive Care Unit Patients Calls for the Regular Assessment of Empirical Targets and Easy-to-Use Dosing Decision Tools.

The drug concentrations targeted in meropenem and piperacillin/tazobactam therapy also depend on the susceptibility of the pathogen. Yet, the pathogen is often unknown, and antibiotic therapy is guided by empirical targets. To reliably achieve the targeted concentrations, dosing needs to be adjusted for renal function. We aimed to evaluate a meropenem and piperacillin/tazobactam monitoring program in intensive care unit (ICU) patients by assessing (i) the adequacy of locally selected empirical targets, (ii) if dosing is adequately adjusted for renal function and individual target, and (iii) if dosing is adjusted in target attainment (TA) failure. In a prospective, observational clinical trial of drug concentrations, relevant patient characteristics and microbiological data (pathogen, minimum inhibitory concentration (MIC)) for patients receiving meropenem or piperacillin/tazobactam treatment were collected. If the MIC value was available, a target range of 1-5 × MIC was selected for minimum drug concentrations of both drugs. If the MIC value was not available, 8-40 mg/L and 16-80 mg/L were selected as empirical target ranges for meropenem and piperacillin, respectively. A total of 356 meropenem and 216 piperacillin samples were collected from 108 and 96 ICU patients, respectively. The vast majority of observed MIC values was lower than the empirical target (meropenem: 90.0%, piperacillin: 93.9%), suggesting empirical target value reductions. TA was found to be low (meropenem: 35.7%, piperacillin 50.5%) with the lowest TA for severely impaired renal function (meropenem: 13.9%, piperacillin: 29.2%), and observed drug concentrations did not significantly differ between patients with different targets, indicating dosing was not adequately adjusted for renal function or target. Dosing adjustments were rare for both drugs (meropenem: 6.13%, piperacillin: 4.78%) and for meropenem irrespective of TA, revealing that concentration monitoring alone was insufficient to guide dosing adjustment. Empirical targets should regularly be assessed and adjusted based on local susceptibility data. To improve TA, scientific knowledge should be translated into easy-to-use dosing strategies guiding antibiotic dosing.

Structural studies on the exopolysaccharide from Erwinia persicina.

The Gram-negative bacterial strain HKI 0380 was isolated from biofilms located on palaeolithic rock paintings in the Cave of Bats in Zuheros, southern Spain. It was identified as the phytopathogenic Erwinia persicina and attracted attention due to the production of considerable quantities of slime. The acidic exopolysaccharide produced by the E. persicina was studied after O-deacylation by sugar and methylation analyses, along with (1)H and (13)C NMR spectroscopy. The following structure of the branched pentasaccharide repeating unit of the O-deacylated exopolysaccharide was established: [carbohydrate structure: see text].

Development and validation of a high-performance liquid chromatography assay and a capillary electrophoresis assay for the analysis of adenosine and the degradation product adenine in infusions.

A high-performance liquid chromatography (HPLC) method and a capillary electrophoresis (CE) method for the analysis of adenosine and the degradation product adenine in infusion solutions have been developed and validated. The HPLC separation of the analytes was achieved on a RP-18 column, using a mobile phase, consisting of 20mM ammonium acetate, pH 6.0, containing 5% of acetonitrile at a flow rate of 1ml/min. Thymidine was used as internal standard. The CE separation was performed in a fused-silica capillary with a 100mM sodium phosphate buffer, pH 2.7, at an applied voltage of 25kV, using cytidine as internal standard. The assays were validated with regard to linearity, range, limit of detection (LOD), limit of quantitation (LOQ), specificity, and precision. Both methods were specific allowing reliable quantification of the analytes. Compared to the CE method, HPLC analysis yielded a two- to five-fold lower LOD. With respect to analysis time, CE was faster than HPLC. The applicability of both methods for the determination of the purity and stability of adenosine in the infusion solutions is demonstrated.