Antibiotic monitoring in body fluids

Spectrophotometric Determination of Rifampicin through Chelate Formation and Charge Transfer Complexation in Pharmaceutical Preparation and Biological Fluids

Two simple and accurate spectrophotometric methods for determination of Rifampicin (RIF) are described. The first method is based on charge transfer (CT) complex formation of the drug with three pi-electron acceptors either 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 7,7,7,8-Tetracyanoquinodimethane (TCNQ) or 2,3,5,6-Tetrachloro-1,4-benzoquinone (p-chloranil) in acetonitrile. The method is followed spectrophotometrically by measuring the maximum absorbance at 584 nm, 761 nm (680 nm) or 560 nm for DDQ, TCNQ and p-chloranil, respectively. Under the optimized experimental conditions, the calibration curves showed a linear relationship over the concentration ranges of 5-140 microg/ml, 2-45 microg/ml (5-120 microg/ml) and 15-200 microg/ml, respectively. The second method is based on the reaction of RIF with iron(III) forming a water insoluble violet complex which is extracted into chloroform. The method determines RIF in concentration range of 10-240 microg/ml at 540 nm. The proposed methods applied to determination of RIF in capsule, human serum and urine samples with good accuracy and precision. The results were compared statistically with the official method and showed no significant different between the methods compared in terms of accuracy and precision.

Investigation of the interactions between beta-lactams and a metallo-beta-lactamase from bacillus cereus using a monoclonal antibody

A monoclonal antibody recognizing the active site of a beta-lactamase from Bacillus cereus was identified and characterized. The binding of the monoclonal antibody to the active site was quantitatively inhibited by a broad spectrum of beta-lactam antibiotics. The levels of inhibition were found to be associated with particular structural features of the antibiotics and their ability to form stable enzyme/substrate complexes. A novel, broad specificity assay for beta-lactams was developed based on the inhibition of antibody binding of all the beta-lactams studied. The assay is applicable to detection of beta-lactams at or close to the MRL level and would be complementary to existing receptor-based assays. The approach described is relevant to the study of kinetic aspects of beta-lactamases and could prove a useful tool in future drug development.

Determination of the cephalosporin antibiotic cephradine in human plasma by high-performance liquid chromatography with ultraviolet detection

A simple and sensitive high-performance liquid chromatographic method, for the determination of cephradine in human plasma samples has been developed and validated. Cephradine and cephaloridine (internal standard) were extracted from human plasma by perchloric acid protein precipitation followed by centrifugation. Aliquots of the extracts were analysed by reversed-phase high-performance liquid chromatography (HPLC) utilising a polymeric reversed-phase PLRP-S column, followed by ultraviolet detection at 260 nm. The method has a working dynamic range from 0.2 to 30.0 microg/ml from 200 microl human plasma. The precision of the method at 0.2 microg/ml was 4.9% (intra-assay) and negligible (inter-assay) as calculated by one-way analysis of variance and the accuracy of the method at 0.2 microg/ml was -4.1% in terms of percentage bias. This method has been successfully applied to clinical studies including an oral bioequivalence study comparing the pharmacokinetics of 500 mg tablets of Kefdrin with 500 mg tablets of Velosef in healthy human volunteers.

Rapid liquid chromatographic determination of oxytetracycline in milk

A simple method for the determination of residual oxytetracycline (OTC) in milk by high-performance liquid chromatography (HPLC) was developed. The sample preparation could be made without complex extraction and clean-up procedures. A LiChrospher 100 RP-8 end-capped column and a mobile phase of acetonitrile-acetic acid-water (28:4:68, v/v/v) with a photo-diode array detector was used. The average recoveries from spiked OTC (0.1, 0.5 and 1.0 microgram/ml) were in excess of 89.8% with coefficients of variation between 0.6 and 4.1%. The limit of detection was 0.05 microgram/ml. The total time required for the analysis of one sample was below 10 min.

High-performance liquid chromatographic analysis of aminoglycoside antibiotics

A simple precolumn derivatisation method for the determination of aminoglycoside antibiotics (AGs) is described. The stability of the o-phthalaldehyde (OPA) derivatives of the AGs obtain using beta-mercaptopropionic acid (beta-MP) was investigated by reversed-phase HPLC. One of the fluorescent derivatives of sisomicin was stable at least for 6 h in 50% methanol under the optimal conditions used (OPA concentration, pH and temperature). When plasma samples spiked with sisomicin were analysed the response was linear in the calibration range of 136-900 micrograms of sisomicin per injected volume (40 microliters). As little as 0.06 micrograms of sisomicin per 1 ml of plasma could be detected with a signal-to-noise ratio > or = 2. The method was also applied to whole blood samples from rabbit after a subcutaneous injection of 1 mg/kg of the AGs using dried blood spots (DBS) on the filter-paper punched discs. The detection of sisomicin and netilmicin in the DBSs on punched discs (10.1 micrograms of whole blood) were 0.053 and 0.50 micrograms per ml of whole blood, respectively (signal-to-noise ratio > or = 2). The method permits a simple collection of blood at the microlitre level and should prove particularly useful for monitoring the AGs in blood at therapeutic levels in geriatric and paediatric patients and could be also used for the preclinical study of the AGs blood levels of a number of mice or rats without killing. An RP-HPLC method using an on-line clean-up procedure for large sample-volume analysis of serum AGs is also described.

Analytical strategies for the screening of veterinary drugs and their residues in edible products

The development of analytical strategies for the regulatory control of drug residues in food-producing animals is discussed. Analytical methods for the determination of veterinary drugs in edible products are based on microbiological, immunochemical and physicochemical principles. Because of complexity of biological matrices such as egg, milk and meat, well designed, and often sophisticated, off-line or on-line sample treatment procedures are essential, especially when utilising physicochemical multi-residue screening procedures. Since large series of samples have often to be analysed, automation is increasingly becoming important. Confirmation of the identity of drug residues and validation of the analytical results implies the use of adequate analytical methods. In its turn, this requires well established criteria for those methods and/or equivalent reference methods.

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.

Determination of ampicillin in human plasma by high-performance liquid chromatography using ultraviolet detection

A high-performance liquid chromatographic method with isocratic elution has been developed for the determination of ampicillin in human plasma. The method comprises injection of the plasma after protein precipitation on to a reversed-phase C18 column, using phosphate buffer (pH3.5)-methanol as the mobile phase. The method involves UV detection at 225 nm. This method provides a simple technique for the rapid analysis of ampicillin within the concentration range 0.2-25 micrograms ml-1 with a high degree of accuracy and precision.

Development of a high performance liquid chromatographic assay measuring mezlocillin in serum or tissue

Objective: This study evaluated the blood and uterine tissue concentration of mezlocillin, a broadspectrum penicillin.

Methods: We adapted a liquid chromatographic method to measure mezlocillin in serum and tissue. Mezlocillin reference standard was diluted in water, chromatographed on a reversed phase C18 column eluted at 1.5 ml/min with acetonitrile and phosphate buffer (1:3 v:v), and detected spectrophotometrically at 210 nm. Mezlocillin was administered to 14 premenopausal women scheduled to undergo vaginal hysterectomy. Each patient received a 4 g IV infusion of the drug 30 to 60 min prior to surgery. During surgery, tissue was removed from the uterine cervix and blood was obtained for assay of mezlocillin content.

Results: Chromatography of the mezlocillin standard furnished a discrete peak with a retention time of 2.4 min. The sensitivity of the assay was 0.1 µg/ml with a linear response up to 100 µg/ml. The correlation coefficient for the standard curve was 0.9997. When reference standard was diluted in pooled human serum, the assay was complicated by interfering compounds. These were removed by ether extraction. The sensitivity of the assay performed in serum was 3 µg/ml. Serum samples contained from 81.2 to 358 µg of mezlocillin/ml with an average serum concentration of 207.5 µg/ml. When serum containing a known amount of mezlocillin was homogenized for a period of time similar to that required to homogenize tissue samples, a deteatable loss of drug was observed and was applied as a correction factor to the measured tisulevels. After correction, the average tissue level was 117.2 µg/ml and ranged from 27% to 98% of the serum levels.

Conclusions: The serum concentration of mezlocillin after IV infusion of 4 g was greater than that required to inhibit the majority of the most significant organisms responsible for post-hysterectomy sepsis. Although tissue levels appeared to be consistently lower than serum levels, they could be expected to provide an inhibitory effect against many of the bacterial strains that contaminate the surgical site.

Chromatographic methods for tetracycline analysis in foods

The tetracyclines have served for decades as an important class of antibiotics in food animal health and production. As such, they have also been a source of concern for residue monitoring authorities around the world. In response to this concern a number of microbial inhibition, immunoassay and bacterial receptor methods have evolved for the detection of this class of compounds in various foods of animal origin. However, these methods often lack specificity and are subject to false positive and false negative results. For these reasons a number of chromatographic methods for the separation and determination of the tetracyclines isolated from foods have been developed that are capable of identifying and quantifying individual tetracycline drugs. We present here an overview of tetracycline analytical methods, including microbial inhibition, immunoassay and receptor technologies for detection, techniques for isolation from food matrices, and thin-layer chromatographic, high-performance liquid chromatographic, gas chromatographic and mass spectrometric procedures for determination of this class of compounds. A discussion of the variables involved in such methodology and a review of method criteria are offered.

Determination of cefcanel in plasma and urine by high-performance liquid chromatography using coupled columns, after administration of the new cephalosporin prodrug cefcanel daloxate hydrochloride

A rapid and sensitive high-performance liquid chromatographic method has been developed for the determination in plasma and urine of the new cephalosporin cefcanel. The method involves a simple deproteinizing step followed by separation on a coupled-column chromatographic system with ultraviolet detection. Limits of quantification were 0.2 microM for plasma samples and 2 microM for urine samples. The method has been used for the determination of cefcanel in various clinical studies.

Determination of ampicillin in biological fluids by coupled-column liquid chromatography and post-column derivatization

A rapid and sensitive high-performance liquid chromatographic method has been developed for the determination of ampicillin in plasma and urine. The method involves a simple deproteinization step and separation on a coupled-column chromatographic system followed by post-column derivatization and fluorescence detection. The method has been used for the determination of ampicillin in various clinical studies. The high sensitivity makes it especially useful for small sample volumes, e.g. samples from pediatric patients.

Reversed-phase high-performance liquid chromatography of amphoteric beta-lactam antibiotics: effects of columns, ion-pairing reagents and mobile phase pH on their retention times

The separation of five amino beta-lactam antibiotics by reversed-phase high-performance liquid chromatography was studied as an insight into their retention behaviour. These five amphoteric compounds are cephradine, cephalexine, cefaclor, ampicillin and amoxicillin. Both octadecylsilane-bonded silica (C18) columns and phenyl-bonded silica (phenyl) columns were used, with mobile phase pH values between 2.5 and 7.4. In the absence of ion-pairing reagents the retention times for all the five compounds were the shortest at pH 4-6. The phenyl column was found to improve the separation between cephradine and ampicillin at pH values lower than 3, when these two compounds appeared as fused peaks on the C18 on C18 columns, with mobile phases both with and without ion-pairing reagents, were compared. The addition of 0.005 or 0.02 M tetraethylammonium acetate to the mobile phase did not result in significant ion-pair formation, except at pH values higher than 5.5. A strong ion-pairing effect was obtained at pH values higher than 6 with 0.005 or 0.02 M tetrabutylammonium phosphate, and the retention was decreased at pH values lower than 4. On the other hand, 0.005 M heptanesulphonic acid exhibited an ion-pair retention effect at pH values lower than 5. The molecular structures and pK(a) values were used to account for the retention behaviour of these antibiotics in the various mobile phases.

Micro-method for the determination of piperacillin in plasma by high-performance liquid chromatography

A simple and sensitive high-performance liquid chromatographic method for the determination of piperacillin in plasma is described. A C8 reversed-phase column was used with a mobile phase consisting of methanol-water-triethylamine (550:450:4, v/v/v) adjusted to pH = 3 with orthophosphoric acid and UV detection at 270 nm. Cephalothin was used as internal standard. The method involves a plasma protein precipitation with acetonitrile followed by extraction of endogenous compound with chloroform and injection of the upper aqueous phase into the chromatograph. Within-day and between-day assays give relative standard deviations less than or equal to 5.7%. The detection limit is 0.2 microgram ml-1. Stability studies show that piperacillin degradation starts at -4 degrees C. Therefore, samples have to be processed promptly and stored at -20 degrees C. The method described is convenient for clinical monitoring and for pharmacokinetic studies.

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

Mass spectrometry is combined with liquid chromatography (LC/MS) and mass spectrometry (MS/MS) to identify ampicillin and two known metabolites--ampicillin penicilloic acid and ampicillin piperazine-2,5-dione--in human urine samples. Identifications were based on the fact that the metabolites or degradation products contain a substructure of ampicillin. In addition, two previously unidentified components in human urine samples were detected, corresponding to newly discovered metabolites or degradation products of ampicillin. Different chromatographic retention times in the LC mass spectra indicated two different compounds. However, the tandem mass spectra of these two components were similar, suggesting that they are stereoisomers. The use of LC/MS and MS/MS confirmed that the unknown components are the (3S,5R) and (3S,5S) epimers of ampicillin penilloic acid. Further study showed that only one of the components was eliminated from the body; the other arises from interconversion to the epimer in a urine sample. It is speculated that the component produced in vivo is the (3S,5R) epimer of ampicillin penilloic acid.

Tandem mass spectrometric studies of the fragmentation of penicillins and their metabolites

The fragmentation of two penicillins, ampicillin and amoxicillin, and their principal metabolites has been studied by a combination of liquid chromatography/thermospray mass spectrometry and tandem mass spectrometry. A high-resolution tandem mass spectrometer was used to obtain chemical ionization, fast-atom bombardment, and collision-induced dissociation mass spectra. Structural information and fragmentation mechanisms have been deduced from ions in the mass and collision spectra. This knowledge is useful in the analysis and identification of metabolites of ampicillin and related drugs in human body fluids.

Analysis of cephalexin from canine skin biopsy by liquid chromatography with ultraviolet-visible photodiode-array detection

A sensitive and selective ion-paired liquid chromatographic method with UV-VIS photodiode-array detection was developed to measure cephalexin in skin biopsy samples. The method involved a sonication of minced canine skin with ethanol-acetonitrile-water (30:20:50, v/v/v) and ultrafiltration of received extract through 10,000 daltons. Separation of cephalexin from other components was by liquid chromatography using a reversed-phase column which was eluted with an ion-paired acetonitrile-water solution. Detection was achieved with a UV-VIS photodiode-array detector scanning from 230 to 320 nm. Cephalexin in the eluate was quantitated at its wavelength maximum of 260 nm. The evaluation of chromatographic peak homogeneity was performed by absorbance ratios, contour maps, first-derivative spectra and a three-dimensional spectrochromatogram. Additionally, the cephalexin peak identity was confirmed by liquid chromatography-mass spectrometry.

Pre-column derivatization of sisomicin with o-phthalaldehyde-beta-mercaptopropionic acid and its application to sensitive high-performance liquid chromatographic determination with fluorimetric detection

The stability of the o-phthalaldehyde (OPA) derivatives of sisomicin obtained using beta-mercaptopropionic acid was investigated by reversed-phase high-performance liquid chromatography. One of the fluorescent derivatives of sisomicin was stable at least for 6 h in 50% methanol under the optimal conditions used (OPA concentration, pH and temperature). When plasma samples spiked with sisomicin were analysed, the response was linear in the calibration range 136-900 pg of sisomicin per injected volume (40 microliters). As little as 0.06 micrograms of sisomicin per 1 ml of plasma could be detected with signal-to-noise ratio greater than or equal to 2. For plasma samples spiked with 0.2 micrograms/ml sisomicin, the recovery was 97.1 +/- 6.6% (mean +/- S.D., n = 5) with a within-run coefficient of variation of 6.8% and a day-to-day coefficient of variation of 7.2%. The method was also applied to plasma samples from rabbit after a subcutaneous injection of 1 mg/kg sisomicin.

High-performance liquid chromatographic determination of chloramphenicol and four analogues using reductive and oxidative electrochemical and ultraviolet detection

A high-performance liquid chromatographic procedure is described for the separation, quantitation and identification of chloramphenicol, dehydrochloramphenicol, nitrophenylaminopropanedione, nitrosochloramphenicol and aminochloramphenicol. An isocratic reversed-phase system with ultraviolet and electrochemical detectors in tandem was assembled and used. The system was constructed with special accommodation to enable us to use the electrochemical detector in both reductive and oxidative modes. Retention characteristics, hydrodynamic voltammograms under reductive and oxidative conditions and ultraviolet absorbance are reported. Applicability of the procedure to biological fluids was demonstrated by separation and detection of chloramphenicol after incubation with human blood.

Hospital routine analysis of penicillins, third-generation cephalosporins and aztreonam by conventional and high-speed high-performance liquid chromatography

A high-performance liquid chromatographic procedure for the measurement of fifteen beta-lactam antibiotics in body fluids is described, with special reference to high-speed techniques. The procedure involves a unique sample preparation before analysis for all the following fifteen compounds: benzylpenicillin, ampicillin, cloxacillin, ticarcillin, mezlocillin, azlocillin, piperacillin, cefotaxime and its desacetyl metabolite, cefsulodin, cefoperazone, cefmenoxime, ceftazidime, ceftriaxone and the monobactam aztreonam; thus all biological samples arriving at the laboratory can be treated in batch. Of these fifteen antibiotics, eleven can be chromatographed with the same type of mobile phase, which consists of a mixture of ammonium acetate and acetonitrile in various ratios. Three others need ionpairing chromatography because of their polarity, and ticarcillin requires citric acid. High-speed high-performance liquid chromatography seems to be particularly suitable for the routine analysis of beta-lactam antibiotics because columns equilibrate more rapidly, retention times are much shorter, detection limits are lower and the longer lifetime of columns reduces analysis costs.