Selectivity of reversed-phase packing materials in high-performance liquid chromatography of cephalosporins

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.

Analysis of cefadroxil by micellar electrokinetic capillary chromatography: development and validation

A method is developed and validated for analysis of the antibiotic cefadroxil using micellar electrokinetic capillary chromatography. It permits cefadroxil to be completely separated from ten of its known related substances within 15 min (including the washing procedure). The separation is performed in an acetate buffer (50 mM, pH 5.25) containing sodium dodecyl sulfate (SDS; 110 mM). The fused-silica capillary was 44 cm long (36 cm effective length), 50 microm ID; the voltage, 18 kV; temperature, 15 degrees C; and the detection wavelength; 254 nm. The influence of the type of buffer, buffer pH and concentration, and of the SDS concentration was investigated. The robustness of the method was examined by means of a full-fraction factorial design. The parameters for validation such as linearity, precision, limit of detection and limit of quantitation are also reported.

Chromatography as an analytical tool for selected antibiotic classes: a reappraisal addressed to pharmacokinetic applications

The first antibiotic discovered, penicillin, appeared on the market just after the Second World War. Intensive research in subsequent years led to the discovery and development of cephalosporins, aminoglycosides, tetracyclines and rifamycin. The chemotherapeutic quinolones and the more recently discovered fluoroquinolones have added promising new therapeutic weapons to fight the microbial challenge. The major role pharmacokinetics has played in developing these compounds should be highlighted. Plasma concentration-time profiles and the therapeutic activity evoked by these compounds allow the therapeutic window, doses and dose turnovers to be appropriately defined as well as possible dose adjustment to be made in renal failure. The pharmacokinetics of antimicrobial agents were initially explored by using microbiological methods, but these lack specificity. The HPLC technique with UV, fluorometric, electrochemical and, in some cases, mass spectrometry detection has satisfactory solved the problem of antimicrobial agent assay for pharmacokinetic, bioavailability and bioequivalence purposes alike. Indeed, in these studies, plasma concentrations of the given analyte must be followed up for a period > or = 3 times the half-life, which calls for specific sensitive assays. In the review, the authors have described the analytical methods employed in the pharmacokinetics of antibiotics, including some chemotherapeutic agents which are used in medical practice as alternatives to antibiotics. The pharmacokinetic characteristics of each class of drugs are also briefly described, and some historical and chemical notes on the various classes are given.

A comparative study of LC methods for analysis of cefradine

A comparative study of two isocratic liquid chromatographic methods for the analysis of cefradine is described. The first method is prescribed by the European Pharmacopoeia for the assay of cefradine, using classical alkyl bonded phase (C18) as the stationary phase. Poor reproducibility of the selectivity towards cefradine and its related substances was observed when this method was used and none of the C18 columns examined was able to separate cefradine completely from its potential related substances under the prescribed LC conditions. On the other hand, the second method, which uses poly(styrene-divinylbenzene) as the stationary phase, shows good selectivity even when using columns from different manufacturers and of different age. Four bulk samples of cefradine were analysed following both methods and the results were compared.

Quantitative analysis of cefradine by liquid chromatography on poly(styrene-divinylbenzene)

A method is described for isocratic analysis of cefradine by liquid chromatography on a poly(styrene-divinylbenzene) column (PLRP-S, 250 x 4.6 mm i.d.) at 50 degrees C. Cefradine is separated from its related substances using a mobile phase of acetonitrile-0.02 M sodium 1-octanesulphonate-0.2 M phosphoric acid-water (14.5:10:5:up to 100, v/v/v/v). The flow rate was 1.0 ml min-1 and UV-detection was performed at 254 nm. The method was employed for the quantitative analysis of reference substances, bulk samples and pharmaceutical dosage forms.

Column liquid chromatography and microbiological assay compared for determination of cefadroxil preparations

A reversed-phase column liquid chromatographic method was developed for the assay of cefadroxil in bulk drugs and pharmaceutical preparations. An equation was derived showing a linear relationship between peak-area ratios of cefadroxil to dimethylphthalate (internal standard) and the cefadroxil concentration over a range of 0.02-0.8 mg/ml (r = 0.9999). Standard addition recoveries were generally greater than 97.7%. The coefficients of variation in the within-day assay were between 0.36 and 0.65, and in the between-day assay was 0.71%. The column liquid chromatographic assay results were compared with those obtained from a microbiological assay, which indicated that the proposed method is a suitable substitute for the microbiological method for potency assays and stability studies of cefadroxil preparations.

Isolation of doxycycline, 6-epidoxycycline and 2-acetyl-2- decarboxamidometacycline from commercial metacycline by preparative column liquid chromatography on silica gel

Isolation of doxycycline, 6-epidoxycycline and 2-acetyl-2-decaboxamidometacycline from commercial metacycline was achieved by preparative column liquid chromatography on silica gel, previously impregnated with edetate (EDTA). Careful control of the pH of EDTA allowed fine tuning of the separation. The mobile phases were composed of dichloromethane, methanol and .1 mM EDTA at pH 9.0 or 6.0. Structures were confirmed with nuclear magnetic resonance spectroscopy. The presence of doxycycline and its 6-epimer in commercial metacycline has not previously been described. The presence of the 2-acetyl derivative was not surprising since analogous 2-acetyl derivatives have been identified in other tetracyclines.

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.

Residue determination of two co-administered antibacterial agents--cephalexin and colistin--in calf tissues using high-performance liquid chromatography and microbiological methods

Residues of two antibacterial agents, cephalexin and colistin, co-administered by intramuscular injection to calves, were quantified in four different tissues (muscle, fat, liver and kidney) by column switching HPLC and by a microbiological method. For cephalexin assay, tissue samples with cephradin as internal standard were homogenized in a 5% trichloroacetic acid solution and filtrates were injected onto a concentration precolumn filled with LiChroprep RP-18 (25-40 microns). A clean-up step was incorporated by flowing a mobile phase (methanol-0.01 M phosphate buffer (pH 3.0); 15:85, v/v) through the enrichment column before elution on a LiChrospher RP-18e (5 microns) column with a methanol-phosphate buffer (30:70, v/v) at a flow rate of 1 ml min-1. Spectrometric detection was at 260 nm. An additional "off-line" washing step of extracts with methylene chloride was operated to achieve higher selectivity in the case of liver and kidney samples. The limit for quantitative assay was 0.045 micrograms g-1 with relative standard deviations in the range 5-8% and recoveries within 70%. For microbiological assay of colistin, samples were homogenized in 0.1 M hydrochloric acid-acetonitrile mixtures (3:1, v/v, for kidney and liver; 3:2, v/v, for fat and muscle). The supernatants were assayed by the cylinder plate method after evaporation to dryness under vacuum. Bordetella bronchiseptica ATCC 4617 was chosen as test organism. After a 3-h diffusion step at room temperature, the medium was incubated at 37 degrees C for 18 h and then the diameter of the growth inhibition zones was measured. Sensitivity reached 0.10-0.15 micrograms g-1. Results from the analysed samples over a 7-28 day period after drug administration show that no cephalexin was found at concentrations higher than the quantitation limit in the four test tissues and that colistin was found in muscle (injection site only) for 15 days and in kidney for 21 days.

Determination of the monocyclic beta-lactam antibiotic carumonam in plasma and urine by ion-pair and ion-suppression reversed-phase high-performance liquid chromatography

A sensitive and selective high-performance liquid chromatography method has been developed for the determination of the new monocyclic beta-lactam antibiotic carumonam in plasma and urine. The method for plasma involves protein precipitation with acetonitrile and removal of lipids with dichloromethane; urine is diluted with buffer. Separation and quantification are achieved using a mobile phase based on either ion-suppression or ion-pair chromatography on a reversed-phase column with UV detection. The limit of determination is 0.5 micrograms/ml plasma, using a 0.5-ml specimen, and 25 micrograms/ml urine, using a 50-microliter specimen. The inter-assay reproducibility is generally better than 4% when an internal standard is used. Since beta-lactam antibiotics may degrade on storage, close attention must be paid to the stability of these drugs in biological fluids; novel measures to prevent degradation on storage are described. The assay has been successfully applied to the analysis of several thousand samples from pharmacokinetic studies, including a study involving patients with impaired renal function.

Development of a reversed-phase ion-pairing liquid chromatographic assay of daunorubicin for pharmacopoeial use

A liquid chromatographic method is described for the determination of daunorubicin using octyldecylsilyl columns and sodium dodecyl sulphate as ion-pairing agent. The method based on previous publication [M. A. van Lancker et. al., J. Chromatogr., 254 (1983) 45] is specific for daunoribicin and separates it from likely impurities, e.g., the aglycone, duborimycin and related anthracyclines, doxorubicin and epirubicin. Several commercial batches have been examined in a number of laboratories employing various types of stationary phases. The intralaboratory reproducibilities varied from 1.0 to 1.6% and the interlaboratory reproducibility between 0.63 and 1.0% (based on the means of duplicate determinations), while with the preferred mobile phase the coefficient of variation was 0.3% (n = 4). The method is robust and is proposed for inclusion in a monograph on daunorubicin which is currently under consideration by the European Pharmacopoeia.

Penicillins and cephalosporins. Physicochemical properties and analysis in pharmaceutical and biological matrices

Penicillins and cephalosporins belong to the most prescribed antibiotics. Despite the relatively extended knowledge of these drugs, the qualitative and quantitative analysis of the compounds still gives rise to many problems. These difficulties are due to the chemical instability of the common beta-lactam nucleus, the minor differences in chemical structures between the analogues, and the complex and relatively fast degradation of the compounds in aqueous solutions. In this review a compilation of the physicochemical properties, the degradation routes and methods for analysis of these substances in biological and other matrices is presented.

Quantitative determination by high-performance liquid chromatography of acetylsalicylic acid and related substances in tablets

High-performance liquid chromatography on a Zorbax C8 7-micron column (25 cm X 0.46 cm I.D.) with methanol-water-1 M phosphoric acid (59:36:5) as the mobile phase has been used for the analysis of several naturally aged batches of fourteen brands of acetylsalicyclic acid tablets. The extraction solvent is methanol, containing 2% v/v of formic acid. Salicylic acid is the main impurity. Acetylsalicylsalicylic acid is the second most important impurity, and the corresponding salicylsalicylic acid is rarely present. Buffered or dispersible tablets contain relatively more of the latter two impurities and eventually also the corresponding higher oligomers. Acetylsalicylic anhydride is always a minor impurity. Comparison is made with classical spectrophotometric methods, which are observed to be selective for salicylic acid.

Separation of corticosteroids by high-performance liquid chromatography on dynamically modified silica

High-performance liquid chromatographic methods have been elaborated for the separation of 12 different corticosteroids by reversed-phase chromatography on bare silica, dynamically modified by cetyltrimethylammonium bromide added to the eluent. The selectivity of the systems towards a mixture of the 12 corticosteroids and towards a mixture of hydrocortisone and its related impurities were investigated using different brands of silica. The variations in selectivity were found to be substantially smaller than those of chromatographic systems based on chemically bonded ODS-silicas from the same sources.

Stability-indicating liquid chromatographic determination of cephapirin, desacetyl cephapirin and cephapirin lactone in sodium cephapirin bulk and injectable formulations

A specific, stability-indicating, high-performance liquid chromatographic assay was developed for the determination of cephapirin, desacetyl cephapirin and cephapirin lactone in sodium cephapirin (cefadyl) bulk and injectables. The procedure uses a muBondapak C18 column and a mobile phase of dimethylformamide-acetic acid-potassium hydroxide in water. UV detection at 254 nm is used for quantitation with acetanilide used as the internal standard. The assay is precise, accurate and linear over the range of 100-300 micrograms/ml for cephapirin and over the range of 2-6 micrograms/ml for desacetyl cephapirin and cephapirin lactone. The assay is also stability-indicating for the described thermal, acid, base, aqueous and accelerated light degradations.

Analysis of a complex analgesic formulation by high-performance liquid chromatography with column-switching

An isocratic method is described which allows the complete separation of acetylsalicylic acid, paracetamol, caffeine, carbromal, bromisoval and codeine as well as the potential impurities salicylic acid, diacetyl-p-aminophenol and acetylcodeine. A column-switching technique was developed employing two columns (10 cm and 25 cm) containing 7-microm Zorbax C(8) material. The separation is better and faster than that obtained with a gradient elution method.

Dynamically-modified silica — an alternative to reversed-phase high-performance liquid chromatography on chemically bonded phases

An alternative to the well known reversed-phase separations on chemically-bonded phases has been developed. The approach is based on a dynamic modification of bare silica with long chain quaternary ammonium ions. The influence of the concentration and type of the quaternary ammonium ion, the pH value and the ionic strength of the eluent on the selectivity towards test solutes has been investigated. The large number of parameters that can be varied in the system offers numerous possibilities by which the desired selectivity can be attained. Once established, a high degree of reproducibility of the selectivity between solutes is obtained even when using different brands of silica; this is in contrast to the situation when using chemically-bonded phases, such as, for example, different brands of octadecylsilyl-bonded silica materials.