1-Octanol-water partition coefficients of the anionic and zwitterionic species of diprotic zwitterionic cephalosporin antibiotics

Effect of environmental factors on the oxidative transformation of cephalosporin antibiotics by manganese dioxides

This study aimed to explore the oxidation and transformation of the cephalosporins cefotaxime (CTX), cephalexin (CFX), cephradine (CFD), cephapirin (CFP) and cefazolin (CFZ) by δ-MnO2. The results showed that the MnO2 oxidation rate was promoted by environmental factors such as higher MnO2 loading, lower initial cephalosporin concentration and lower solution pH. The inhibitory effect occurred in the presence of dissolved organic matter and dissolved cations (inhibitory capacity: Mn2+ > Ca2+ > Mg2+ > Fe3+). Total organic carbon analysis indicated that the transformation byproducts of the cephalosporins are less reactive and persistent under MnO2 oxidation. Twelve transformation byproducts (9 CFP byproducts and 3 CTX byproducts) were identified, and two oxidative transformation pathways were proposed: one occurred in the cephem for CFP, and the other occurred at the substituent at the amine position for CTX. The effect of solar light on the oxidation of the five cephalosporin antibiotics by δ-MnO2 was also investigated, and the results indicated that the initial dissolution rate of δ-MnO2 under sunlight was approximately eight times faster than that in the dark in the presence of CFP.

Cephalosporin antibiotics in the aquatic environment: A critical review of occurrence, fate, ecotoxicity and removal technologies

Due to their widespread occurrence in the aquatic environment, human and veterinary cephalosporin antibiotics have been studied as water pollutants. In order to characterize environmental risks of this compound class, this review evaluates relevant data about physicochemical properties, occurrence, ecotoxicity and degradation of cephalosporins. Although application of cephalosporins is rather low compared to other antibiotics and their environmental life-time is believed to be short (i.e. days), the available data is insufficient to draw conclusions on their environmental relevance. Few studies concerning the fate of cephalosporins in soil are available, while hydrolysis and photo-degradation are suggested as the main attenuation processes in the aquatic environment. Cephalosporins have been detected in different aqueous matrices in concentrations ranging from 0.30 ng L^-1 to 0.03 mg L^-1, with sewage and wastewater being the main matrices with positive findings. For wastewater treatment purposes, several technologies have been tested for the abatement of cephalosporins, including photolysis and adsorption. In most cases, the technology employed led to complete or significant removal (>95%) of parental drugs but few authors reported on cephalosporins' metabolites and transformation products. Furthermore, the present ecotoxicological data are insufficient for comprehensive ecological risk quotient calculations. Considering the total of 53 cephalosporins, effective values (EC, LC, NOAEC, NOAEL, etc.) are only available for around 30% of parental drugs and are very scarce for cyanobacteria, which is considered to be the most sensitive group of organisms to antibiotics. Furthermore, it has been demonstrated that cephalosporins' transformation products can be more toxic and more persistent than the parental drugs. Few investigations considering this possibility are available. Consequently, more effort on ecotoxicological data generation and verification of biological inactivation of cephalosporins-related products is needed. Likewise, the lack of natural depletion rates and knowledge gaps on mixture effects for cephalosporins' degradation and toxicity have to be overcome.

Substructure Reactivity Affecting the Manganese Dioxide Oxidation of Cephalosporins

Cefotaxime (CTX), cephalexin (CFX), cephradine (CFD), cephapirin (CFP), and cefazolin (CFZ) were selected as target cephalosporin antibiotics to study their oxidative transformation by δ-MnO₂. Although they all have the same core structure (7-aminodesacetoxycephalosporanic acid), very different MnO₂ oxidation rates were observed at pH 4 (the initial reaction rate constant k_init ranged from 0.014 to 2.6 h^-1). An extensive investigation of the substructure compounds and byproduct analysis revealed that the oxidation mainly occurred at the following two sites on the core structure: (1) the sulfur atom in the cephem ring and (2) the carbon-carbon double bond (C═C) and its proximal carboxylic acid group. In the case of (2), when there is an acetyloxymethyl group at the C-3 position of the core structure, the formation of the keto-sulfone byproducts was inhibited. The overall results indicated that a substituent at the C-3 position could stabilize the core structure, which would result in a decrease in the oxidation rate; however, a substituent at the amine position of the core structure might affect the overall degradation rate of the cephalosporin, depending on its reactivity with MnO₂. Thus, the apparent reaction rates varied widely in the trend of CTX > CFP > CFD > core structure ≈ CFX > CFZ. The mechanistic elucidation can also help explain the degradation rates of cephalosporin antibiotics in other oxidation processes.

Phototransformation of cephalosporin antibiotics in an aqueous environment results in higher toxicity

Photodegradation may be the most important elimination process for cephalosporin antibiotics in surface water. Cefazolin (CFZ) and cephapirin (CFP) underwent mainly direct photolysis (t(1/2) = 0.7, 3.9 h), while cephalexin (CFX) and cephradine (CFD) were mainly transformed by indirect photolysis, which during the process a bicarbonate-enhanced nitrate system contributed most to the loss rate of CFX, CFD, and cefotaxime (CTX) (t(1/2) = 4.5, 5.3, and 1.3 h, respectively). Laboratory data suggested that bicarbonate enhanced the phototransformation of CFD and CFX in natural water environments. When used together, NO(3)(-), HCO(3)(-), and DOM closely simulated the photolysis behavior in the Jingmei River and were the strongest determinants in the fate of cephalosporins. TOC and byproducts were investigated and identified. Direct photolysis led to decarboxylation of CFD, CFX, and CFP. Transformation only (no mineralization) of all cephalosporins was observed through direct photolysis; byproducts were found to be even less photolabile and more toxic (via the Microtox test). CFZ exhibited the strongest acute toxicity after just a few hours, which may be largely attributed to its 5-methyl-1,3,4-thiadiazole-2-thiol moiety. Many pharmaceuticals were previously known to undergo direct sunlight photolysis and transformation in surface waters; however, the synergistic increase in toxicity caused by this cocktail (via pharmaceutical photobyproducts) cannot be ignored and warrants future research attention.

Determination of lipophilicity of two quinolone antibacterials, ciprofloxacin and grepafloxacin, in the protonation equilibrium

The objective of this study was to compare protonation equilibrium and lipophilicity of two quinolone antibacterials, grepafloxacin (GPFX) and ciprofloxacin (CPFX), in order to give an insight into effects on the physicochemical properties by slight structural motifs. The protonation equilibrium was investigated by a spectrophotometry. Macro- and micro-dissociation constants were simultaneously determined, based on nonlinear regression analysis using the MULTI program, and then microspecies distribution could be described accordingly. Zwitterionic microspecies predominated at isoelectrical point (pI) for both drugs, and the concentration ratio of neutral to zwitterionic forms was near 4-fold greater for GPFX than that for CPFX. The apparent partition coefficient (D(O/B,pH)) versus pH profiles had the shape of a parabolic curve in an n-octanol/buffer system, and reached the maximum around pI for both, respectively. Moreover, two introduced methyl groups in GPFX increased not only intrinsic lipophilicity but also neutral microspecies fraction relative to CPFX, and D(O/B,pH) of GPFX was consequently far higher than that of CPFX. The results emphasized that there were significant differences in protonation equilibrium and lipophilicity between GPFX and CPFX, which conduced to explaining their different behavior in terms of antibacterial activities and pharmacokinetics.

Hydrophobicity of beta-lactam antibiotics. Explanation and prediction of their behaviour in various partitioning solvent systems and reversed-phase chromatography

beta-Lactam antibiotics tend to undergo self-association in hydrophilic organic solvents, which leads to a strong dependence of their experimentally observable log P values on the partitioning conditions. As a result, most of the earlier obtained log P values for beta-lactam antibiotics cannot be applied as a common hydrophobicity measure, but they proved to be linearly related to each other and to a large body of reversed-phase chromatographic data. The retention of cephalosporins on reversed-phase liquid chromatographic columns is complicated by silanophilic interactions. However, under elution conditions that eliminate these silanophilic interactions, good correlations with log P data are observed, and a unified hydrophobicity scale for 90 penicillin and cephalosporin compounds could be evaluated. The Hansch and Leo additive scheme was shown to be valid for the calculation of hydrophobicities for penicillin and cephalosporin C-6(7) substituents, but it failed when applied to the prediction of cephalosporin C-3-substituent hydrophobicities. The hydrophobic increments for the sixteen most common cephalosporin C-3-substituents were empirically evaluated from literature data, and a simple equation was derived for an overall beta-lactam antibiotic hydrophobicity calculation. The proposed scale is valid for predicting the partitioning of most beta-lactam antibiotics in both hydrophilic and lipophilic organic-water systems, although it should be used with caution when applied to antibiotics containing additionally charged side-chains.