Identification of metabolites of ampicillin using liquid chromatography/thermospray mass spectrometry and fast atom bombardment tandem mass spectrometry

Neurosteroid pathway derangement in asphyctic infants treated with hypothermia: an untargeted metabolomic approach

BACKGROUND

The pathobiological mechanisms associated with perinatal asphyxia and hypoxic-ischemic encephalopathy are complex and poorly understood. The metabolic effects of therapeutic hypothermia have been partially explored.

METHODS

We conducted a single-center longitudinal study to investigate the metabolic effects of perinatal asphyxia and hypoxic-ischemic encephalopathy on the urinary metabolome of a group of 12 asphyctic infants over time compared to 22 matched healthy newborns, using untargeted metabolomics based on mass spectrometry.

FINDINGS

Over-representation pathway analysis identified the steroidogenesis pathway as being significantly disrupted, with reduced steroid levels in the first three days of life despite treatment with hypothermia. Comparison with matched healthy newborns showed that the urinary steroid content was lower in asphyctic infants before hypothermia. The lysine degradation and carnitine synthesis pathways were also significantly affected.

INTERPRETATION

Steroidogenesis is significantly disrupted in asphyctic infants compared to healthy newborns. Given how neurosteroids are involved in neuromodulation and neuroprotection, translational research is warranted on the potential role of neurosteroid-based intervention in asphyctic infants.

FUNDING

None.

Transformation products of amoxicillin and ampicillin after photolysis in aqueous matrices: Identification and kinetics

Antibiotics are widely used in human medicine and veterinary production. Residues of these compounds reach the water sources through waste or direct application (e.g. aquaculture). The constant input of the parent drugs and their transformation products into the environment leads these pharmaceuticals to be considered as emerging pollutants. For some molecules, the pathway of degradation and formation in products is less known. To assess the impact of these substances in the environment and in the human health, it is necessary to elucidate the transformation products and their kinetic of degradation to evaluate the possible risks. In the present report, the characterization and the degradation kinetic of two widely used β-lactams antibiotics - amoxicillin and ampicillin - was evaluated. Surface water samples containing these antibiotics were submitted to photolysis and analyzed by liquid chromatography coupled to mass spectrometry with Orbitrap detection in order to establish the profile of degradation and the formation of transformation products. Results showed that the degradation of amoxicillin and ampicillin is almost complete and reach their maximum at 48 h in river water. Moreover, a database containing >65 transformation products of amoxicillin and ampicillin was build and real samples of industrial wastewater were analyzed to investigate the occurrence of amoxicillin, ampicillin and their transformation products.

Identification of the related substances in ampicillin capsule by rapid resolution liquid chromatography coupled with electrospray ionization tandem mass spectrometry

Rapid Resolution Liquid Chromatography coupled with Electrospray Ionization Tandem Mass Spectrometry (RRLC-ESI-MS(n)) was used to separate and identify related substances in ampicillin capsule. The fragmentation behaviors of related substances were used to identify their chemical structures. Finally, a total of 13 related substances in ampicillin capsule were identified, including four identified components for the first time and three groups of isomers on the basis of the exact mass, fragmentation behaviors, retention time, and chemical structures in the literature. This study avoided time-consuming and complex chemosynthesis of related substances of ampicillin and the results could be useful for the quality control of ampicillin capsule to guarantee its safety in clinic. In the meantime, it provided a good example for the rapid identification of chemical structures of related substances of drugs.

Amoxicillin-degradation products formed under controlled environmental conditions: identification and determination in the aquatic environment

Amoxicillin (AMX) is a widely used penicillin-type antibiotic whose presence in the environment has been widely investigated, despite its rapid hydrolysis to various degradation products (DPs). In this work, the formation of AMX DPs was studied in various aqueous solutions containing 100μgmL(-1) AMX. Three phosphate buffer solutions, at pH 5, pH 7 and pH 8, and a fourth buffer solution at pH 7 with the addition of the bivalent ions Mg(2+)and Ca(2) as chelating agents, were examined under controlled environmental conditions. In addition, two solutions from natural sources were examined secondary effluents and tap water. The obtained DPs were identified by their MS/MS, UV and NMR spectra (obtained from pure compounds isolated by preparative HPLC) as: AMX penicilloic acid (ADP1/2), AMX penilloic acid (ADP4/5) and phenol hydroxypyrazine (ADP6). Two additional detected DPs AMX 2',5'-diketopiperazine (ADP8/9), and AMX-S-oxide (ADP3) were reported and discussed in our previous publications. These DPs were then detected in secondary effluent and groundwater from a well located beneath agricultural fields continuously irrigated with secondary effluent. Concentrations in the secondary effluent were: ADP1/2, several micrograms per liter; ADP4/5, 0.15μgL(-1), and ADP8/9, 0.5μgL(-1). ADP6 were detected but not quantified. In the groundwater, only ADP8/9 was detected, at a concentration of 0.03μgL(-1). The detection and quantification of DPs of other investigated drugs is recommended as an integral part of any study, method or technique dealing with pharmaceutical residues in aquatic environments.

Residues of beta-lactam antibiotics in bovine milk: confirmatory analysis by liquid chromatography tandem mass spectrometry after microbial assay screening

A procedure for the simultaneous determination of the residues of seven beta-lactam antibiotics (penicillin G, ampicillin, oxacillin, amoxicillin, dicloxacillin, cephalexin, cephapirin) in bovine raw milk using tandem liquid chromatography mass spectrometry (LC-MS/MS) is described. The antibiotics were extracted by an acetic acid solution after centrifugation and filtration. The beta-lactams were separated using reversed-phase liquid chromatography. A triple quadrupole mass spectrometer was used in positive-ion mode as a detector via a Turbo Ionspray interface for electrospray ionization (ESI). The limits of detection and quantitation of the method were below the legal tolerances, except for ampicillin. The method was used to confirm 53 samples found positive by a microbial method (Delvotest SP) at the Istituto Zooprofilattico Sperimentale per la Lombardia e l'Emilia Romagna of Brescia during 2001. Penicillin G was found in 26 samples at concentrations ranging from less than 4 to 6240+/-550 microg x l(-1). Amoxicillin was found in three samples at concentrations ranging from 8.5+/-0.1 to 53.7+/-2.3 microg x l(-1). Cephapirin was found in two samples at 5.7+/-0.1 and 6.4+/-0.3 microg x l(-1).

Monitoring of ampicillin and its related substances by NMR

A 1H NMR procedure for the monitoring of ampicillin (Amp) and its main related substance in different media, has been developed. The characteristics peak of Amp, 6-aminopenicillanic acid (6-APA), phenylglycine (PhG), and penicilloic acid in the range of 0.5-0.9 and 3.0-4.5 ppm were used for their identification in drugs and serum samples. The quantitative works were performed based on the intensity of protons of the methyl group link to the beta-lactam cyclic of Amp and 6-APA and the aromatic protons of PhG relative to the protons of methylene group of maleic acid, as internal standard, at constant temperature. The resulting data are compared with those obtained with an HPLC method proposed by British Pharmacopoeia. Statistical studies show that, at a confidence limit of %95, there is no significant difference between the two methods. In comparison with the HPLC method, the proposed NMR method does not require any sample pretreatment, standard solution preparation, long analysis time and use of any carcinogenic solvent. The method was applied to the determination of Amp and its related substances in synthetic mixtures, drug powders and serum samples.

Radiosterilization of cefotaxime: investigation of potential degradation compounds by liquid chromatography-electrospray mass spectrometry

The nonvolatile radiolytic compounds produced by irradiation of cefotaxime were studied by a liquid chromatography-electrospray mass spectrometry method. Full scan LC-MS was first performed in order to obtain the m/z value of the protonated molecules of all detected peaks. LC-MS-MS was then carried out on the compounds of interest. A comparison between the MS-MS spectrum of cefotaxime and those of the radiolytic compounds showed that their fragmentation patterns were very similar suggesting that they were structural analogues of the main drug. The examination of the two main fragmentation pathways also permitted the location of the modified substructures. Moreover, it was shown that some stereoisomers appeared with the irradiation process. The complete fragmentation pattern of cefotaxime was studied by MSn and used to obtain information about the structure of the radiolytic compounds. A complete structure was proposed for four of these.

Simultaneous determination of five beta-lactam antibiotics in bovine milk using liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A multiresidue method for the detection of five important beta-lactam antibiotics (amoxicillin, ampicillin, cloxacillin, oxacillin, penicillin G) in fresh milk is presented that allows quantitation of the analytes well below established legislative limits. The method avoids the use of acid during the extraction procedure and entails a cleanup step over a C18 cartridge. The analytes are separated and detected by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) using a stable isotope-labeled internal standard. Mass spectral acquisition is done in the positive ion mode by applying selected reaction monitoring of two or more fragmentation transitions per analyte to provide a high degree of sensitivity and specificity. The typical recoveries for all five beta-lactams in fresh milk ranged from 76 to 94% at a fortification level of 4 microg/kg. This study also addresses common problems encountered in the stability of penicillins during sample preparation as well as the employment of postcolumn infusion of a standard compound to verify potential matrix-induced signal suppression in ESI-MS.

Identification of cephapirin metabolites and degradants in bovine milk by electrospray ionization--ion trap tandem mass spectrometry

Liquid chromatography-ion trap tandem mass spectrometry (LC-MS/MS) with electrospray ionization was used to identify cephapirin metabolites and degradants in milk from cows dosed with cephapirin. The milk was extracted according to a previously published procedure. Structures for various components were tentatively identified by their molecular weight, product ion mass spectra, and/or correspondence to standard mass spectra. These components may have occurred as metabolites or as degradants that occurred on storage or during extraction. Compounds identified in the milk included cephapirin, desacetylcephapirin, cephapirin lactone, hydrolyzed cephapirin, and a reduced cephapirin lactone that has not previously been reported. Methylcephapirin was also identified, possibly as a trace contaminant in the formulation. Analysis of incurred milk extracts showed that cephapirin and desacetylcephapirin are the major residues in milk. Desacetylcephapirin residues persisted about as long as the parent drug. The detection limit for both residues by LC-MS/MS was approximately 1 ng/mL in milk. These results have implications for microbiological methods or rapid test kits, if such methods or kits respond to cephapirin metabolites and degradants present in the milk.

Electrospray mass spectrometry in the structural characterization of cephalosporins

Six cephalosporins of pharmacological interest, cephalexin, cephuroxime, cephazolin, cephoperazone sodium salt, cephatrizin free acid and cephonicid disodium salt, were analysed by electrospray mass spectrometry. [M - Na]- anions were produced in high yield in the case of cephalexin, cephuroxime, cephazolin and cephoperazone, leading to signals at least two orders of magnitude more intense than those related to [M + Na]+ cations observed in the positive ion mode. In cephatrizin, [M - H]- represented the most abundant species, whereas in cephonicid the [M - 2Na + H]- anions were easily produced. No fragment ions were detectable in the electrospray spectra of any of the compounds, and MSn turned out to be essential to draw the fragmentation patterns. Most of these patterns were related to the substituent of the 7-aminocephalosporin nucleus, suggesting that the nucleus itself is highly stable.

Analysis of antibiotics by liquid chromatography-mass spectrometry

The current status of the application of LC-MS in the analysis of antibiotic and antibacterial compounds is reviewed. The main application area of LC-MS in this field is the confirmation of identity in animal food products for human consumption at maximum residue levels, set by the regulatory authorities. LC-MS is found to play an important role in the determination and confirmation of sulphonamides, beta-lactam antibiotics, (fluoro) quinolone antibiotics, as well as various other groups including aminoglycosides, chloramphenicol, ionophore antibiotics, 5-nitrofuran derived compounds and macrolide antibiotics. Currently available data on these compound classes are reviewed, with special emphasis on important aspects especially relevant to LC-MS and on the mass spectral information obtained.

Use of liquid chromatography-mass spectrometry in the analysis of residues of antibiotics in meat and milk

The advent of affordable LC-MS systems has led to a massive increase in a number of publications describing quantitative methods for the analysis and confirmation of veterinary drug residues. The lack of volatility and thermal instability of many antibiotics makes LC-MS the method of choice for their analysis. In the review, analytical methods for the determination of residues of each of the major classes of antibiotics are presented.

Degradation pathways of ampicillin in alkaline solutions

Ampicillin trihydrate, sodium salt, in aqueous solution has a pH of about 8. No complete degradation pathway has been proposed to explain the degradation of ampicillin under alkaline conditions and the information available explains the formation of only certain products. The present work was carried out with the aim of providing this information. The formation of degradation products of ampicillin trihydrate, sodium salt, produced in aqueous solutions (pH 12 and 37 degrees C) have been studied as an accelerated form of the possible degradation that may occur in aqueous solutions at pH 8. Some of the degradation products formed under these conditions were then obtained either by synthesis or by degradation of ampicillin sodium followed by isolation using semi-preparative HPLC. These compounds were characterized by 1H NMR spectroscopy. The information obtained from the experiments by HPLC and NMR spectroscopy made it possible to propose a degradation pathway for ampicillin under the conditions described above. 5R-penicilloic acid is the first degradation product of ampicillin and subsequently undergoes epimerization at C-5 to form the 5S isomer via the imine tautomer. Mechanisms for the formation of compounds previously believed to form only under acidic conditions are proposed, i.e. ampicillin penilloic acid and 2-hydroxy-3-phenylpyrazine. The formation of ampicillin polymers was detected in dilute solutions (1% w/v) within a few hours of dissolution. The presence of ampicillin penicillenic acid and ampicillin penamaldic acid was detected by 1H NMR and their main spectroscopic features determined.

High resolution 1H NMR spectroscopic studies of the metabolism and excretion of ampicillin in rats and amoxycillin in rats and man

High resolution proton nuclear magnetic resonance (1H NMR) spectroscopy has been used to investigate the metabolism and urinary excretion of the aminopenicillins, ampicillin and amoxycillin, in rats and of amoxycillin in man. 1H NMR resonances of the aminopenicillins, together with those for their 5R, 6R and 5S, 6R penicilloic acids and diketopiperazine metabolites were detected, assigned and quantified in urine samples with the aid of spin-echo NMR techniques. The dimer of amoxycillin was detected in rat urine for the first time together with novel drug-related resonances assigned to amoxycillin carbamate. Quantitative 1H NMR spectroscopic results were consistent with HPLC and microbiological data considering that only single measurements were recorded. Due to the short analysis time and simple sample preparation, NMR was particularly useful for studying the metabolism of the aminopenicillins for which sample degradation poses analytical problems. The non-invasive character of 1H NMR spectroscopic analysis of urine also provided unique information on a reversible reaction between amoxycillin and bicarbonate, an endogenous urinary metabolite.

Determination of penicillin G, ampicillin, amoxicillin, cloxacillin and cephapirin by high-performance liquid chromatography-electrospray mass spectrometry

This report contributes to a preliminary investigation of high-performance liquid chromatographic (HPLC)-mass spectrometric (MS) methods for confirming beta-lactam antibiotic residues in bovine milk. Initial work for each antibiotic evaluated the collisional activated dissociation (CAD) spectra that could be generated between the capillary and skimmer in the electrospray (ESP) interface. The drugs show various characteristic fragmentation, mostly within the beta-lactam ring and the amide group. Response for a particular compound in a given solvent can vary drastically. Usually, the more organic component in the solvent, the higher the ESP response. In many cases use of acetonitrile also results in slightly better ion currents than for methanol when comparing equal percentages of either organic solvent in water. The ESP response of most of the tested antibiotics can be enhanced by the addition of formic acid or acetic acid to the mobile phase methanol-water (1:1). In general, the negative ion spectra are lower in intensity, exhibiting an [M-H]- ion and producing less fragmentation at higher CAD voltages as compared to positive ion spectra. An isocratic reversed-phase HPLC method for the separation of a mixture of five common beta-lactam antibiotics was developed using acetic acid as a mobile phase additive and optimized for detection with a new ESP HPLC-MS interface. A post-column split ratio of 70:1 for the eluent from a 150 x 2 mm I.D. column was chosen to provide the required lower flow-rate (approximately 4 microliters/min). The limit of detection for the simultaneous determination of these antibiotics was estimated to be 100 ppb. Electrospray HPLC-MS could be used to confirm these antibiotics for quantities down to about 100 pg entering the mass spectrometer. Multiresidue analysis with microbore HPLC-ESP-MS has the advantage that no post-column splitting of the eluent is required and all of the analyte (on-column injected) will be transferred into the ESP interface. Preliminary work showed good mass spectrometric sensitivity down to the level of regulatory interest, but chromatographic separation efficiency must be improved.

Nanoscale packed capillary liquid chromatography-electrospray ionization mass spectrometry: analysis of penicillins and cephems

A series of seventeen penicillins and cephems (cephalosporins and cephamycins) was examined by electrospray ionization. Separations by nanoscale packed-capillary liquid chromatography, with sub-microliter flow-rates, were performed using methanol-water and acetonitrile-water both containing trifluoroacetic acid gradients. In the on-column analyses, the protonated species usually predominate, and the fragment ions are often present which can be used for confirmation of compound identity. With combined nanoscale packed-capillary liquid chromatography-electrospray ionization mass spectrometry, separations and full-scan mass spectra can be obtained on *q12-15 ng of analyte, allowing the analysis of therapeutic levels of these antibiotics from only a few microliters of serum.

Structural analysis of non-volatile compounds by liquid chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry: thermal isomerization of benzylpenicillin in a Plasmaspray interface

Isomerization and degradation of benzylpenicillin ((2S,5R,6R)-3,3-dimethyl-7-oxo-6-(2-phenylacetamido)-4-thia-1- azabicyclo[3.2.0]heptane-2-carboxylic acid) were studied using a combination of Plasmaspray (PSP) liquid chromatography/tandem mass spectrometry (LC/MS/MS) and liquid secondary ion tandem mass spectrometry (LSI MS/MS). Benzylpenicillin was isomerized to benzylpenicillenic acid (3-mercapto-N-[[5-oxo-2-(phenylmethyl)-4(5H)- oxazolylidene]methyl]valine) in the PSP interface/ion source. The isomerization was inferred from the probe temperature dependence of PSP LC tandem mass spectra and discrepancies in the daughter ions between PSP LC and LSI tandem mass spectra. High temperature at the PSP interface was responsible for the isomerization, since the difference between PSP LC and LSI tandem mass spectra became smaller as the probe temperature was lowered. It was also found that benzylpenicillin was decomposed to benzylpenilloic acid (5,5-dimethyl-2-[(phenylacetamido)methyl]thiazolidine-4-carboxylic acid), N-(phenylacetyl)glycine, N-(phenylacetyl)glycinal and 3-mercaptovaline in the PSP interface/ion source. The degradation products formed in the interface/ion source were identical to those formed in acidic solution. The results show that degradation of penicillins can be investigated by PSP LC/MS and PSP LC/MS/MS.

Development of analytical methods for some penicillins in bovine milk by ion-paired chromatography and confirmation by thermospray mass spectrometry

Analytical methods for the determination of cloxacillin, ampicillin/hetacillin, and amoxicillin in bovine milk were developed. The methods involved ultrafiltration of milk diluted with methanol, acetonitrile, and water on a 10,000-dalton cut-off filter. Separation of penicillins from other milk components was accomplished by ion-paired chromatography using a microbore column. The penicillins were detected using ultraviolet photodiode array (UV-PDA) detection and confirmed by thermospray liquid chromatography-mass spectrometry (LC-MS). The thermospray spectra of these compounds exhibited [M + H]+ and [M + Na]+ ions along with several fragment ions. The limits of detection for these antibiotics were estimated to be 50 to 100 ppb for LC with UV-PDA detection and 100-200 ppb for thermospray LC-MS detection.