An Isocratic HPLC Method for the Determination of Cephalosporins in Plasma

Population pharmacokinetics of cefazolin before, during and after cardiopulmonary bypass in adult patients undergoing cardiac surgery

PURPOSE

The aims of the present study were to establish a population pharmacokinetic (PPK) model of cefazolin for adult patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) and to assess the probability of target attainment (PTA) for the prophylaxis of surgical site infection (SSI) using cefazolin.

METHODS

Adult patients who underwent cardiac surgery with CPB were enrolled in the prospective study. Blood samples for plasma cefazolin assay were collected, and total and unbound drug concentrations were measured and analysed using the nonlinear mixed-effects modelling (NONMEM) software considering saturable plasma protein binding. Using the PPK model, plasma unbound cefazolin concentration-time courses with current prophylaxis protocols were simulated, and the PTA for common SSI pathogens was estimated.

RESULTS

A total of 199 blood samples were obtained from 27 patients. A one-compartment model with first-order elimination plus an on/off CPB compartment best described the data. The population mean for systemic drug clearance (CL) was reduced and that for the volume of distribution (V) was increased during CPB compared with the pre-CPB values. CPB-induced hypoalbuminemia was associated with reduced maximum protein binding (B_max). The simulation studies suggested that the current dosing protocols are insufficient for attaining PTA > 0.9 throughout surgery against pathogens with minimum inhibitory concentrations (MICs) >8 mg/L. A new dosing protocol that achieves a PTA > 0.9 for pathogens with a MIC of 16 mg/L was proposed.

CONCLUSION

PPK modelling with simulation may be valuable for devising a cefazolin prophylaxis protocol for patients undergoing cardiac surgery with CPB.

Effects of cardiopulmonary bypass on the disposition of cefazolin in patients undergoing cardiothoracic surgery

The aim of the study was to evaluate the disposition of plasma unbound cefazolin in patients undergoing cardiothoracic surgery with cardiopulmonary bypass (CPB). Adult patients undergoing cardiothoracic surgery with CPB were enrolled in the study. Cefazolin sodium was given intravenously before skin incision (1 g) and at the beginning of CPB (2 g). Thereafter, an additional dose (1 g) was given every 4 hours. Seven to ten blood samples were collected before and during surgery. Plasma total and unbound (ultrafiltrated) cefazolin concentrations were analyzed using an HPLC-UV method. Plasma protein binding was analyzed with the Langmuir model. Twenty-seven patients (aged 70 ± 12 years, body weight 62 ± 12 kg, mean ± SD) with GFR >30 mL min-1 completed the study. There was a significant (P < 0.001) increase in median plasma unbound fraction of cefazolin from 21% before skin incision to 45% during CPB (P < 0.001), which was accompanied by a significant (P < 0.001) reduction in median plasma albumin concentration from 36 to 27 g L-1. Plasma concentrations of unbound cefazolin exceeded the assumed target thresholds of 2 μg mL-1 in all samples and of 8 μg mL-1 in all but one of 199 samples. The increased plasma unbound fraction of cefazolin would be attributable to dilutional reduction of serum albumin at the beginning of CPB and to saturable plasma protein binding of cefazolin. These data reveal CPB may alter the plasma protein binding and possibly distribution of cefazolin. Further studies are warranted to reappraise the protocol of antimicrobial prophylaxis with cefazolin in patients undergoing surgery with CPB.

Simple HPLC method for cefazolin determination in human serum - validation and stability testing

The paper presents an HPLC method for cefazolin determination in human serum. The preparation step was based on serum protein precipitation with acetonitrile followed by supernatant evaporation and sample reconstitution in water before injection. The separation of cefazolin and internal standard cefamandole was performed at ambient temperature under isocratic conditions on LiChrosorb RP8-5 column (250mm×4.6mm) using the mixture: CH(3)CN:H(2)O:0.5M KH(2)PO(4) (100:894:6, v/v) as a mobile phase with a flow rate of 1.5mL/min. UV detection was performed at 272nm with LLOQ of 0.2μg/mL. The precision was satisfactory in the whole range tested with RSD of 2.3-12.5% (accuracy: from -2.3% to +3.6%) and of 1.7-7.1% (accuracy: from -3.5% to +1.1%) for intra- and inter-assay, respectively. The method stability was confirmed in a series of experiments including: freeze-thaw and short- and long-term stability testing. Finally, the procedure described was found resistant to potential human errors.

Evaluation of capillary zone electrophoresis and micellar electrokinetic capillary chromatography with direct injection of plasma for the determination of cefotaxime and its metabolite

Quantitative aspects of capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MECC) were investigated for the determination of cefotaxime (C) and its deacetyl metabolite (DA) in human plasma in a concentration range of therapeutic interest. For CZE, plasma samples spiked with C and DA were injected after deproteinization with acetonitrile, and analytes were separated in a fused silica capillary using a borate buffer at pH 9.2 as electrolyte; no suitable internal standard was found. For MECC, plasma samples spiked with C, DA, and theobromine as internal standard were directly injected after dilution with water and analyzed using a phosphate buffer, pH 8.00, containing 165 mM SDS as separation electrolyte and a fused silica capillary. Both methods gave satisfactory interday precision with respect to migration times (RSD < 1%) and gave linear responses over the concentration ranges investigated (5-100 mg L-1 C and 5-20 mg L-1 DA). For CZE, intraday RSD (n = 4 graphs) between the slopes of the calibration graphs was acceptable (5.7%) for C. The corresponding figures for interday precision (n = 4 days) were fair (16.1%) in comparison to those obtained with MECC, for which the RSD was 1.49% when theobromine was used as internal standard. A satisfactory interday precision between slopes was also obtained with MECC even without the use of an internal standard (RSD = 4.38%), which demonstrated the ruggedness of this method. Detection limits (S/N = 3) were about 2 mg L-1 (CZE) and 1 mg L-1 in plasma (MECC) for C and DA. MECC was shown to be superior with regard to simplicity, rapidity, precision, and sensitivity.

Application of capillary zone electrophoresis in cephalosporin analysis

Cephalosporins have structures and antibiotic activity similar to those of penicillins which represent a class of compounds with closely related structures. Most of the cephalosporins contain aromatic groups and show distinctive UV spectra. Separating the different types of cephalosporins is a challenging task for HPLC. but the resolving power of capillary zone electrophoresis (CZE) makes this separation fast and simple. The present study reports the application of CZE for cephalosporin analysis and the separation of cephalosporins from plasma. Both field strength and temperature were shown to influence the plate number. The influence of injection time on the peak height was studied. Furthermore, the influence of pH value on the separation of cephalosporins by CZE was investigated. The low sample amount required and the relatively short analysis time are the main advantages of this method.

High-performance liquid chromatographic assay of cefazolin in rat tissues

A rapid, sensitive and reproducible high-performance liquid chromatographic (HPLC) assay for cefazolin in rat tissues was developed. Tissue samples were homogenized in distilled water, acidified with 8.5% phosphoric acid, and centrifuged. Cefazolin was isolated from the supernatant by solid-phase extraction on C18 cartridges. The eluate containing cefazolin and internal standard, cephalexin, was injected onto a reversed-phase C18 column and eluted with a mobile phase of 23% methanol in 0.02 M sodium phosphate monobasic (pH 5.0) and detected with UV absorbance at 270 nm. Recoveries of cefazolin were 33.7 +/- 2.5%, 45.4 +/- 2.1%, and 42.9 +/- 1.0% from liver, spleen and lung, respectively. The calibration curves for cefazolin were established at 0.5-1500 micrograms/g in spleen, 0.1-250 micrograms/g in liver and 0.1-75 micrograms/g in lung. The assay was reproducible with within-day and between-day variations of 1-2 and 1-4%, respectively. Application of the assay for tissue distribution of cefazolin in liposomal targeting study was demonstrated.

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.

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.

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.

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.