High-performance liquid chromatographic determination of cephalexin in human plasma, urine and saliva

High-performance liquid chromatographic determination of cephalosporin antibiotics using 0.3 mm I.D. columns

Four cephalosporins, cefazolin, ceftizoxime, cefaloridine and cefaclor, were determined using a novel microbore high-performance liquid chromatographic system designed to be entirely compatible with direct liquid interfacing (DLI) for mass spectrometric analysis. The chromatographic support was a 5-micron C18 column of 0.3 mm I.D., compared with the usual microbore column diameters of 1-2 mm. The mobile phase contained no buffers or salts which may have caused column blocking or mobile phase crystallization, and the use of a concentration column allowed the injection of large volumes of analyte (up to 500 microliters). The assay was reproducible, the relative standard deviations being less than 20% within-day and between-day for all the drugs. The detection limit for cefaloridine and cefazolin was 1 ng and for cefaclor and ceftizoxime 5 ng.

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.

High performance liquid chromatographic analysis of cephalexin in serum and urine

A rapid, highly sensitive high performance liquid chromatographic method has been developed for the determination of cephalexin in serum and urine. Serum protein was precipitated with 1% zinc sulphate solution containing cephradine as the internal standard. The drugs were eluted from a 5 micron, C-18 reversed-phase column at ambient temperature with a mobile phase consisting of acetonitrile-methanol-acetate buffer of pH 4.2 (10:10:80%), at a flow rate of 1.4 ml/min with ultraviolet detection at 254 nm. Each analysis lasted 9 min. Quantification was achieved by the measurement of the peak-height ratio and the relative and absolute recoveries varied from 98 to 103%. Detection limits for cephalexin were 1 microgram/ml in serum and 5 micrograms/ml in urine. Within-run coefficient of variation ranged from 0.73 to 5.63% at three different concentrations for the serum and urine assay.

Recent analytical methods for cephalosporins in biological fluids

Since 1980, RP chromatography has been the principal analytical technique used for cephalosporins. This technology offers selectivity, accuracy, and ease of use. Most of the methods rely on protein precipitation and, to a lesser extent, solid-phase isolation or extraction procedures. The proper selection of a method depends on the analytical constraints imposed by the overall objective of the study. For example, pharmacokinetic datum interpretation mandates that the method be validated and provide specific and accurate results. LC is the preferred technique, since it not only meets these specifications but may also distinguish between the drug and metabolites. Those chromatographic methods which quantify several different cephalosporins are not desirable for pharmacokinetic datum interpretation, since accuracy and precision are usually compromised in order that many different drugs may be quantified in a single analysis. The proper selection of sample preparation method is dependent on the presence of potential interferences and the acceptable lower limit of quantitation. Protein precipitation methods offer ease of sample preparation but may suffer from nonselectivity. Solid-phase isolation and extraction procedures may increase selectivity and improve the limit of quantitation. Although LC provides specific and accurate results, clinical laboratories may prefer to use the less specific methods for therapeutic drug monitoring. In this case, microbiological, enzymatic, and fluorimetric methods offer improved sample throughput but less specificity. However, these methods should not be used for drugs that may have a low margin of safety or if the patient is on multiple-antibiotic therapy. Future methods may involve incorporating solid-phase isolation columns to enhance the specificity of chromatographic, microbiological, enzymatic, and fluorescence methods. Advancements in microbore column technology may allow improvements in the selectivity and sensitivity of LC methods. Many investigators prefer to use simple protein precipitation procedures for sample preparation because of sample throughput constraints. However, advances in robotic sample preparation may allow the more cumbersome solid-phase isolation or extraction techniques to be used to improved sample throughput and specificity.

Antibiotic monitoring in body fluids

Analytical procedures recently described for the quantitative determination of antibiotics in body fluids are reviewed. High-performance liquid chromatography (HPLC) and immunoassays appear as an alternative to current microbiological assays. HPLC has been applied to most antibiotics in clinical use and a major part of the review deals with this technique. Attention is given to sample pretreatment, characteristics of chromatography and detection, and limit of sensitivity. Non-isotopic immunoassays have been essentially applied to aminoglycosides and vancomycin and are also reviewed. Advantages and drawbacks of HPLC and immunoassays are presented.

Systematic approach to the determination of cephalosporins in biological fluids by reversed-phase liquid chromatography

The chromatographic behaviour of some cephalosporins as a function of pH and ionic strength of the mobile phase was studied on 10-microns LiChrosorb RP-18. Acidic cephalosporins were retained longest in their neutral form with an acidic eluent. Amphoteric cephalosporins were retained longest in their protonated form with an acidic eluent of low ionic strength. Cefotiam was retained longer with an alkaline mobile phase. LiChrosorb RP-18, Nucleosil C18 and muBondapak C18 gave rise to different selectivities when an acidic eluent, methanol-water (25:75) containing 0.2% of 1.8 M H2SO4 was used. This may be related to interactions with residual silanol groups. The studied cephalosporins (with the exception of cefotiam and cefsulodin) were separated from compounds present in biological fluids on 5-microns LiChrosorb RP-18 using the mobile phase 0.2% of 1.8 M H2SO4 in a mixture of methanol and water with various methanol contents. The determination of cefotiam in biological fluids was performed with an alkaline mobile phase. The preparation of the sample was simple and rapid: precipitation of plasma proteins or dilution of urine. The method was applied to the determination of ceftizoxime in human plasma and urine. Concentrations down to 0.2 micrograms/ml of plasma and 25 micrograms/ml of urine could be determined with good reproducibility and accuracy.