Utilization of a kinetic isotope effect to decrease decomposition of ceftriaxone in a mixture of D2O/H2O

The discovery of cephalosporin and demonstration of its improved stability in aqueous solution, as well as enhanced in vitro activity against penicillin-resistant organisms, were major breakthroughs in the development of β-lactam antibiotics. Although cephalosporins are more stable with respect to hydrolytic degradation than penicillins, they still experience a variety of chemical transformations. The present study offers an insight into the rates and mechanisms of ceftriaxone degradation at the therapeutic concentration in water, a mixture of water and deuterium oxide, and deuterium oxide itself at the neutral pH. Specific ceftriaxone degradation products were observed in aged samples (including a previously unreported dimer-type species), and by comparing the degradation rates in H₂O and D₂O, the observation of a kinetic isotope effect provided some valuable insight as to the nature of the initial ceftriaxone degradation. The effect of protium to deuterium isotope change on the degradation kinetics of ceftriaxone was evaluated using the method of initial rates based on HPLC analysis as well as by quantitative ¹H NMR spectroscopy. Moreover, computational analysis was utilized to get a molecular insight into chemical processes governing the ceftriaxone degradation and to rationalize the stabilizing effect of replacing H₂O with D₂O.

The prognostic impact of left ventricular thrombus resolution after acute coronary syndrome and risk modulation via antithrombotic treatment strategies

Background

Left ventricular thrombus (LVT) is a rare but dreaded complication during the acute phase of acute coronary syndrome (ACS). However, profound data on long‐term outcome and associated antithrombotic treatment strategies of this highly vulnerable patient population are scarce in current literature.

Methods

Patients presenting with ACS were screened for presence of LVT and subsequently included within a prospective clinical registry. All‐cause mortality and the composite of major adverse cardiac events (MACE) and thromboembolic events were defined as primary and secondary endpoint.

Results

Within 43 patients presenting with LVT, thrombus resolution during patient follow‐up was observed in 27 individuals (62.8%). Patients that reached a resolution of LVT experienced lower incidence rates of death (−23.9%; p = .022), MACE (−37.8%; p = .005), and thromboembolic events (−35.2%; p = .008). Even after adjustment for clinical variables, thrombus resolution showed an independent inverse association with all‐cause death with a hazard ratio (HR) of 0.14 (95% CI: 0.03–0.75; p = .021) and as well with MACE with a HR of 0.22 (95% CI: 0.07–0.68; p = .008) and thromboembolic events with a HR of 0.22 (95% CI: 0.06–0.75; p = .015). Triple antithrombotic therapy (TAT) with ticagrelor/prasugrel showed a strong and independent association with thrombus resolution with an adjusted HR of 3.25 (95% CI: 1.22–8.68; p = .019) compared to other strategies.

Conclusion

The presented data indicate a poor outcome of ACS patients experiencing LVT. In terms of a personalized risk stratification, thrombus resolution has a strong protective impact on both all‐cause death and MACE with the potential to tailor treatment decisions—including an intensified antithrombotic treatment approach—in this patient population.

Scale-up on basis of structured mixing models: A new concept

A new scale-up concept based upon mixing models for bioreactors equipped with Rushton turbines using the tanks-in-series concept is presented. The physical mixing model includes four adjustable parameters, i.e., radial and axial circulation time, number of ideally mixed elements in one cascade, and the volume of the ideally mixed turbine region. The values of the model parameters were adjusted with the application of a modified Monte-Carlo optimization method, which fitted the simulated response function to the experimental curve. The number of cascade elements turned out to be constant (N = 4). The model parameter radial circulation time is in good agreement with the one obtained by the pumping capacity. In case of remaining parameters a first or second order formal equation was developed, including four operational parameters (stirring and aeration intensity, scale, viscosity). This concept can be extended to several other types of bioreactors as well, and it seems to be a suitable tool to compare the bioprocess performance of different types of bioreactors. (c) 1994 John Wiley & Sons, Inc.

Bioprocess kinetics in a horizontal rotating tubular bioreactor

A horizontal rotating tubular bioreactor (HRTB) is a plug flow bioreactor whose interior is provided with O-ring-shaped partition walls that serve as carriers for microbial biomass. During this investigation, microbial biomass was grown in suspension and on the bioreactor inner surface as a microbial biofilm with average mass that was considerably higher than suspended biomass. The dynamics of bioprocess in HRTB was studied by different combinations of process parameters (bioreactor rotation speed and mean residence time) and it was monitored by withdrawing the samples from five positions along the bioreactor. During this investigation it was also observed that mean residence time had a more pronounced effect on the bioprocess dynamics than bioreactor rotation speed. For the description of bioprocess kinetics in HRTB an unstructured kinetic model was established that defines biomass growth, product formations and substrate consumption rate by using a modified Monod (Levenspiel) model. This kinetic model defines changes in suspension and in microbial biofilm, and it shows relatively good agreement with experimental data.

Role of nitrogen sources and metal ions in urease synthesis byMicrococcus varians

Urease (urea amidohydrolase E.C.3.5.1.5) synthesis inMicrococcus varians U-9 was not affected by nitrogen source (peptone or glutamic acid) or its concentration: but depended on the ratio of peptone and urea in culture medium. WhenM. varians grew in culture medium with peptone at or above 0.48g/l and NH4Cl as an additional nitrogen source, two maxima of urease synthesis occurred; one in the exponential growth phase and the second in the stationary growth phase. Though this bacterium could not utilize either urea or ammonia as the sole nitrogen source, urea caused only one maximum of urease synthesis to occur and shifted the maximum into late exponential phase, suggesting that urea acts as a regulatory factor in urease synthesis. Synthesis of urease was not induced either by urea or by nitrogen starvation and was not repressed by ammonia or by excess of complex nitrogen source. NI(2+) (up to 0.1 mM) stimulated urease synthesis but decreased bacterial growth, while Co(2+) only affected bacterial growth and at 0.1 mM Inhibited the growth.