20 LC-MS/MS 21 Vancomycin 22Tandem mass spectrometry 23Therapeutic drug monitoring 24 Background: Accurate quantification of vancomycin in plasma is important for adequate dose-adjustment.25 As literature suggests between-method differences, our first objective was to develop a novel liquid 26 chromatography-tandem mass spectrometry (LC-MS/MS) method for total vancomycin in human plasma and to 27 compare frequently used immunoassays with this method. Secondly, we investigated the clinical impact of 28 between-method quantification differences.29 Methods: For LC-MS/MS, lithium heparin plasma was extracted by adding a precipitation reagent containing the in-30 ternal standard (vancomycin-des-leucine). Analysis was performed on an Acquity TQD mass spectrometer 31 equipped with an Acquity UPLC 2795 separations module. Our method was analytically validated and compared 32 with four frequently used immunoassays from four different manufacturers. Vancomycin concentrations were 33 clinically classified as toxic, therapeutic and sub-therapeutic. Clinical discordance was calculated using LC-MS/MS 34 as a reference.35 Results: A novel LC-MS/MS method using protein precipitation as sole pretreatment and an analysis time of 5.0 min 36 was developed. The assay had a total imprecision of 2.6-8.5%, a limit of quantification of 0.3 mg/L and an accuracy 37 ranging from 101.4 to 111.2%. Using LC-MS/MS as reference, three immunoassays showed a mean proportional 38 difference within 10% and one showed a substantial mean proportional difference of N 20%. Clinical discordant 39 interpretation of the obtained concentrations ranged from 6.1 to 22.2%. 40 Conclusions: We developed a novel LC-MS/MS method for rapid analysis of total vancomycin concentrations in 41 human plasma. Correlation of the method with immunoassays showed a mean proportional difference N20% for 42 one of the assays, causing discordant clinical interpretation in more than 1 out of 5 samples.Q4 43

Background: Deranged energy metabolism contributes to the pathophysiology of heart failure (HF). Recent studies showed diminished free fatty acid (FFA) oxidation in experimental HF models with a shift towards oxidation of ketone bodies. However, conflicting clinical data on FFA metabolism and limited knowledge on ketone body metabolism in human HF mandate additional metabolic profiling studies. We, therefore, investigated cardiac uptake of FFAs and ketone bodies (β-hydroxybutyrate and acetoacetate) in patients with HF with reduced ejection fraction (HFrEF) or with aortic stenosis (AS)–induced left ventricular hypertrophy. We hypothesized that FFA oxidation is impaired in HFrEF and in AS and results in decreased concentrations of free carnitine, the necessary carrier for mitochondrial entry of activated FFAs, and in accumulation of metabolic intermediates. Methods and Results: We collected arterial and coronary sinus blood samples in patients with HFrEF (n=15), in AS patients with preserved systolic function (n=15), and in control patients (n=15). Plasma concentration gradients across the heart show significantly greater uptake of ketone bodies in patients with HFrEF than in controls. Patients with AS show significantly increased uptake of β-hydroxybutyrate and FFAs. Free carnitine concentration and concentration gradients of intermediates of FFA oxidation were comparable between groups. Conclusions: In conclusion, our results show significantly increased cardiac uptake of ketone bodies in patients with stable HFrEF and AS and increased uptake of FFAs in AS compared with control patients. The lack of myocardial release of acyl-carnitine species or change in free carnitine uptake suggests no impairment of FFA oxidation.

Posaconazole is a promising antifungal agent to be used prophylactically in hematologic patients aged 13 years or younger. Administering posaconazole oral suspension in a dosage of 120 mg/m tid results in adequate posaconazole plasma exposure, without significant adverse events.

These data suggest that elevated glucagon availability during critical illness increases hepatic amino acid catabolism, explaining the illness-induced hypoaminoacidemia, without affecting muscle wasting and without a sustained impact on blood glucose. Furthermore, amino acid infusion likely results in a further breakdown of amino acids in the liver, mediated by increased glucagon, without preventing muscle wasting. Clinical trial registered with www.clinicaltrials.gov (NCT 00512122).

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