Comparison of the electrospray ionization (ESI) responses of penicillins with ESI responses of their methanolysis products

The electrospray ionization (ESI) responses, defined as the area of chromatographic peak of ion [M+H]⁺ obtained upon HPLC/ESI-MS analysis, of three β-lactam antibiotics, namely penicillin G, ampicillin and carbenicillin have been compared with the ESI responses of their methanolysis products. It has been found that methanolyzed penicillin G has much higher ESI response than the penicillin G. Methanolyzed ampicillin also has higher ESI response than ampicillin; however, the effect is less pronounced than for penicillin. Methanolyzed carbenicillin does not have pronouncedly higher ESI response than carbenicillin.

Pharmacodynamic modelling of β-lactam/β-lactamase inhibitor checkerboard data: illustration with aztreonam-avibactam

OBJECTIVES

Checkerboard experiments followed by fractional inhibitory concentration (FIC) index determinations are commonly used to assess in vitro pharmacodynamic interactions between combined antibiotics, but FIC index cannot be determined in case of antibiotic/non-active compound combinations. The aim of this study was to use a simple modelling approach to quantify the in vitro activity of aztreonam-avibactam, a new β-lactam-β-lactamase inhibitor combination.

METHODS

MIC checkerboard experiments were performed with 12 Enterobacteriaceae with diverse β-lactamases profiles. Aztreonam MICs in the absence and presence of avibactam at different concentrations (ranging from 0.0625 to 4 mg/L) were determined. Aztreonam MIC versus avibactam concentrations were fitted by an inhibitory E_max model with a baseline effect parameter.

RESULTS

A concentration-dependent relationship was observed with a steep initial reduction of aztreonam MIC at low avibactam concentrations and reaching a maximum at higher avibactam concentrations that was adequately fitted by the model. Maximum avibactam effect was characterized by the ratio of aztreonam MICs in the absence of avibactam (MIC₀) and when avibactam concentration tends toward infinity (MIC_∞), and this ratio ranged between 90 and 10 068 depending on the strain. Avibactam potency was characterized by avibactam concentrations corresponding to 50% of the maximum effect (IC₅₀ values between 0.00022 and 0.053 mg/L).

CONCLUSIONS

An inhibitory E_max model with a baseline effect could quantify maximum avibactam effect and potency among various strains. This simple modelling approach can be used to compare the activity of other combinations of antibiotics with non-antibiotic drugs when FIC index is inappropriate.

Influence of the T to S mutation at the STMK motif on antibiotic resistance of penicillin binding protein 1A: A comprehensive computational study

The emergence of antibiotic resistance has attracted the attention of scientists and scientific circles over the decades. β-Lactam antibiotics resistance is a worldwide therapeutic challenge in bacterial infections, mediated through several mechanisms of which mutations in Penicillin Binding Proteins (PBPs) are an important issue, making critical therapeutic problems in the human population. Accordingly, investigating the dynamic structures of mutant variants could result in a profound understanding of such a specific resistance. Therefore, this work investigated structural properties sampled by all-atom molecular dynamics (MD) simulations, umbrella sampling, and binding free energy calculations for both a wild-type and a cefotaxime-resistant T to S mutant of PBP1A. The T to S mutation significantly reduces the binding affinity of cefotaxime (a frequently clinically-administrated β-lactam antibiotic) as the PBP1A inhibitor. In the conventional MD simulations presented here, more fluctuations of the mutant's active site cleft margins were detected. The cleft of the mutant protein also opened remarkably more than the wild-type's cleft and displayed more flexibility. Thus, our findings have shown that flexibility of cleft margins of the active site in the mutant PBP1A immediately results in the catalytic cleft opening. In addition, binding free energy calculation suggests that reducing hydrophobic contacts and increasing the polar contribution in the binding energy may play an important role in cefotaxime resistance.

Impact of β-lactam antibiotic therapeutic drug monitoring on dose adjustments in critically ill patients undergoing continuous renal replacement therapy

The objective of this study was to describe the effect of therapeutic drug monitoring (TDM) and dose adjustments of β-lactam antibiotics administered to critically ill patients undergoing continuous renal replacement therapy (CRRT) in a 30-bed tertiary intensive care unit (ICU). β-Lactam TDM data in our tertiary referral ICU were retrospectively reviewed. Clinical, demographic and dosing data were collected for patients administered β-lactam antibiotics while undergoing CRRT. The target trough concentration range was 1-10× the minimum inhibitory concentration (MIC). A total of 111 TDM samples from 76 patients (46 male) with a mean ± standard deviation age of 56.6 ± 15.9 years and weight of 89.1 ± 25.8 kg were identified. The duration of antibiotic therapy was between 2 days and 42 days. TDM identified a need for dose modification of β-lactam antibiotics in 39 (35%) instances; in 27 (24%) samples, TDM values resulted in decreasing the prescribed dose of β-lactam antibiotic whereas an increase in the prescribed dose occurred in 12 (11%) cases. In patients treated for hospital-acquired pneumonia and primary or secondary bacteraemia, the dose was required to be decreased in 10/25 (40%) and 7/46 (15%) cases, respectively, to attain target concentrations. β-Lactam TDM is a useful tool for guiding drug dosing in complex patients such as those receiving CRRT. Although over one-third of patients manifested concentrations outside the therapeutic range, most of these CRRT patients had excessive β-lactam concentrations.

Removal of antibiotic cloxacillin by means of electrochemical oxidation, TiO2 photocatalysis, and photo-Fenton processes: analysis of degradation pathways and effect of the water matrix on the elimination of antimicrobial activity

This study evaluates the treatment of the antibiotic cloxacillin (CLX) in water by means of electrochemical oxidation, TiO₂ photocatalysis, and the photo-Fenton system. The three treatments completely removed cloxacillin and eliminated the residual antimicrobial activity from synthetic pharmaceutical wastewater containing the antibiotic, commercial excipients, and inorganic ions. However, significant differences in the degradation routes were found. In the photo-Fenton process, the hydroxyl radical was involved in the antibiotic removal, while in the TiO₂ photocatalysis process, the action of both the holes and the adsorbed hydroxyl radicals degraded the pollutant. In the electrochemical treatment (using a Ti/IrO₂ anode in sodium chloride as supporting electrolyte), oxidation via HClO played the main role in the removal of CLX. The analysis of initial by-products showed five different mechanistic pathways: oxidation of the thioether group, opening of the central β-lactam ring, breakdown of the secondary amide, hydroxylation of the aromatic ring, and decarboxylation. All the oxidation processes exhibited the three first pathways. Moreover, the aromatic ring hydroxylation was found in both photochemical treatments, while the decarboxylation of the pollutant was only observed in the TiO₂ photocatalysis process. As a consequence of the degradation routes and mechanistic pathways, the elimination of organic carbon was different. After 480 and 240 min, the TiO₂ photocatalysis and photo-Fenton processes achieved ∼45 and ∼15 % of mineralization, respectively. During the electrochemical treatment, 100 % of the organic carbon remained even after the antibiotic was treated four times the time needed to degrade it. In contrast, in all processes, a natural matrix (mineral water) did not considerably inhibit pollutant elimination. However, the presence of glucose in the water significantly affected the degradation of CLX by means of TiO₂ photocatalysis.

Enhancement of antibiotic-activity through complexation with metal ions - Combined ITC, NMR, enzymatic and biological studies

Alternative solutions need to be developed to overcome the growing problem of multi-drug resistant bacteria. This study explored the possibility of creating complexes of antibiotics with metal ions, thereby increasing their activity. Analytical techniques such as isothermal titration calorimetry and nuclear magnetic resonance were used to examine the structure and interactions between Cu(II), Ag(I) or Zn(II) and β-lactam antibiotics. The metal-β-lactam complexes were also tested for antimicrobial activity, by micro-broth dilution and disk diffusion methods, showing a synergistic increase in the activity of the drugs, and enzymatic inhibition assays confirming inhibition of β-lactamases responsible for resistance. The metal-antibiotic complex concept was proven to be successful with the activity of the drugs enhanced against β-lactamase-producing bacteria. The highest synergistic effects were observed for complexes formed with Ag(I).

Removal of antibiotic cloxacillin by means of electrochemical oxidation, TiO2 photocatalysis, and photo-Fenton processes: analysis of degradation pathways and effect of the water matrix on the elimination of antimicrobial activity

This study evaluates the treatment of the antibiotic cloxacillin (CLX) in water by means of electrochemical oxidation, TiO₂ photocatalysis, and the photo-Fenton system. The three treatments completely removed cloxacillin and eliminated the residual antimicrobial activity from synthetic pharmaceutical wastewater containing the antibiotic, commercial excipients, and inorganic ions. However, significant differences in the degradation routes were found. In the photo-Fenton process, the hydroxyl radical was involved in the antibiotic removal, while in the TiO₂ photocatalysis process, the action of both the holes and the adsorbed hydroxyl radicals degraded the pollutant. In the electrochemical treatment (using a Ti/IrO₂ anode in sodium chloride as supporting electrolyte), oxidation via HClO played the main role in the removal of CLX. The analysis of initial by-products showed five different mechanistic pathways: oxidation of the thioether group, opening of the central β-lactam ring, breakdown of the secondary amide, hydroxylation of the aromatic ring, and decarboxylation. All the oxidation processes exhibited the three first pathways. Moreover, the aromatic ring hydroxylation was found in both photochemical treatments, while the decarboxylation of the pollutant was only observed in the TiO₂ photocatalysis process. As a consequence of the degradation routes and mechanistic pathways, the elimination of organic carbon was different. After 480 and 240 min, the TiO₂ photocatalysis and photo-Fenton processes achieved ∼45 and ∼15 % of mineralization, respectively. During the electrochemical treatment, 100 % of the organic carbon remained even after the antibiotic was treated four times the time needed to degrade it. In contrast, in all processes, a natural matrix (mineral water) did not considerably inhibit pollutant elimination. However, the presence of glucose in the water significantly affected the degradation of CLX by means of TiO₂ photocatalysis.

Clavulanic acid reduces rewarding, hyperthermic and locomotor-sensitizing effects of morphine in rats: a new indication for an old drug?

BACKGROUND

Despite the efficacy of ceftriaxone (CTX) in animal models of CNS diseases, including drug addiction, its utility as a CNS-active therapeutic may be limited by poor brain penetrability and cumbersome parenteral administration. An alternative is the β-lactamase inhibitor clavulanic acid (CA), a constituent of Augmentin that prevents antibiotic degradation. CA possesses the β-lactam core necessary for CNS activity but, relative to CTX, possesses: (1) oral activity; (2) 2.5-fold greater brain penetrability; and (3) negligible antibiotic activity.

METHODS

To compare the effectiveness of CA (10mg/kg) and CTX (200mg/kg) against centrally-mediated endpoints, we investigated their effects against morphine's rewarding, hyperthermic, and locomotor-sensitizing actions. Endpoints were based on prior evidence that CTX attenuates morphine-induced physical dependence, tolerance, and hyperthermia.

RESULTS

As expected, rats treated with morphine (4 mg/kg) displayed hyperthermia and conditioned place preference (CPP). Co-treatment with CTX or CA inhibited development of morphine-induced CPP by approximately 70%. Morphine's hyperthermic effect was also suppressed, with CTX and CA producing 57% and 47% inhibition, respectively. Locomotor sensitization induced by repeated morphine exposures was inhibited by CA but not CTX.

CONCLUSIONS

The present findings are the first to suggest that CA disrupts the in vivo actions of morphine and point toward further studying CA as a potential therapy for drug addiction. Further, its ability to disrupt morphine's rewarding effects at 20-fold lower doses than CTX identifies CA as an existing, orally-active alternative to direct CTX therapy for CNS diseases.

Ceftriaxone attenuates locomotor activity induced by acute and repeated cocaine exposure in mice

Ceftriaxone (CTX) decreases locomotor activation produced by initial cocaine exposure and attenuates development of behavioral sensitization produced by repeated cocaine exposure. An important question that has not yet been answered is whether or not CTX reduces behavioral sensitization to cocaine in cases in which the antibiotic is administered only during the period of cocaine absence that follows repeated cocaine exposure and precedes reintroduction to cocaine. We investigated this question using C57BL/6 mice. Mice pretreated with cocaine (15mg/kg×14 days) and then challenged with cocaine (15mg/kg) after 30 days of cocaine absence displayed sensitization of locomotor activity. For combination experiments, CTX injected during the 30 days of cocaine absence attenuated behavioral sensitization produced by cocaine challenge. In the case in which CTX was injected together with cocaine for 14 days, development of behavioral sensitization to cocaine challenge was also reduced. CTX attenuated the increase in locomotor activity produced by acute cocaine exposure; however, its efficacy was dependent on the dose of cocaine as inhibition was detected against 30mg/kg, but not 15mg/kg, of cocaine. These results from mice indicate that CTX attenuates locomotor activity produced by acute and repeated cocaine exposure and counters cocaine's locomotor activating properties in a paradigm in which the antibiotic is injected during the period of forced cocaine absence that follows repeated cocaine exposure.