Vancomycin quantitation by high-performance liquid chromatography in human serum

Development and validation of an HPLC method for vancomycin and its application to a pharmacokinetic study

A rapid and simple method of high performance liquid chromatography with UV detection for the quantification of vancomycin in artificial perfusion fluid and lung tissue samples has been developed and validated. Chromatographic separation was carried out in a Nucleosil 120 C(18) 5 microm column (length, 15 cm; inner diameter, 0.4 cm) using a mixture of 0.05 M NH(4)H(2)PO(4) (pH 4)-acetonitrile (92:8, v/v) as the mobile phase at a flow rate of 1 mL/min, with UV detection at 220 nm. The method used for the vancomycin quantification showed linearity for concentration ranges of 0.1-2, 2-15 and 15-250 microg/mL, with r(2)=0.9985, 0.9996 and 0.9985, respectively. The limit of quantification of the method was 0.1 microg/mL and the coefficients of variation of the between- and within-day precision showed values between 0.6% and 7.0%. The retention time of vancomycin was 8.5 min. The method was used successfully to study the pharmacokinetics of vancomycin in isolated rat lung after its administration through the systemic and inhalatory routes.

Study on pharmacokinetics and tissue distribution of norvancomycin in rats by CE with electrochemical detection

In this paper, we developed a sensitive and simple method to study the pharmacokinetics and tissue distribution of norvancomycin (NVCM) in experimental animals by using CE with electrochemical detection. Pharmacokinetics investigation was performed by the collection of blood samples at timed intervals following administration of NVCM. Pharmacokinetic parameters were calculated by the 3P87 pharmacokinetic program. The elimination half-life of NVCM was 42.4742 min with a clearance rate of 0.0233 mL x kg(-1) x min(-1). Additionally, drug distribution was studied by measuring the NVCM levels in kidney, lung, stomach, intestine, spleen, heart, liver, and cerebrum. Electrophoresis conditions such as buffer solution, working potential, separation voltage, and sampling time were also discussed. The linear range was from 0.8 to 540 microg/mL with a correlation coefficient of 0.9991. The detection limit was 0.3 microg/mL. This method was for the first time applied to study the pharmacokinetics and tissue distributions of NVCM in experimental animals.

Investigation of vancomycin and related substances by liquid chromatography/ion trap mass spectrometry

Liquid chromatography (LC) methods compatible with mass spectrometry (MS) that are suitable for impurity profiling of vancomycin mixtures have not been described in the literature. The mobile phases of the existing methods contain non-volatile additives and/or solvents that give problems in combination with MS. In this paper, a reversed-phase LC/tandem mass spectrometry method is described for the investigation of vancomycin and related substances. The LC method uses a Zorbax Extend C18 column (250 x 4.6 mm i.d.), 5 microm, and a mobile phase consisting of methanol, water and ammonium acetate solution (pH 9.0). This method allows us to separate vancomycin and its impurities. Mass spectral data are acquired on an LCQ ion trap mass spectrometer equipped with an electrospray interface operated in the positive and negative ion modes. The LCQ is ideally suited for identification of impurities and related substances because it provides on-line LC/MSn capability, which allows efficient identification without time-consuming isolation and purification procedures. Using this method, the fragmentation of vancomycin and known derivatives was studied and the structures of six substances occurring in commercial samples were elucidated.

Development and validation of an improved method for the analysis of vancomycin by liquid chromatography selectivity of reversed-phase columns towards vancomycin components

The current method prescribed in official monographs for the purity control of vancomycin is inappropriate in that several components are not separated from each other and other components are coeluted with the main component vancomycin B. The method uses an ODS column at pH 3.2. In this study, several changes were introduced in order to improve the separation. The optimization of the separation method at low pH indicated that pH 1.7 was optimum and that the use of dioxane as organic modifier drastically improved the separation. These conditions were used to test a set of more than 40 reversed-phase columns for their selectivity towards vancomycin components. The selection of the most suitable columns was performed by means of principal component analysis. Most of these columns did not allow the separation of didechlorovancomycin from monodechlorovancomycin 1. It was found that neutral to slightly alkaline mobile phases allowed better separation. Further optimization of the separation method and a robustness study were performed by means of experimental design. This optimization indicated that pH 7.7 was optimum and gradient elution was also used to effect complete analysis. The final method uses a Kromasil column and the mobile phase comprises dioxane, water and ammonium formate solution pH 7.7. The separation of monodechlorovancomycin 2 and of some unknown impurities from the main component vancomycin B is described for the first time. The method shows good repeatability, linearity and sensitivity.

Formulation and evaluation of a folic acid receptor-targeted oral vancomycin liposomal dosage form

PURPOSE

To demonstrate utility of folic acid-coated liposomes for enhancing the delivery of a poorly absorbed glycopeptide, vancomycin. via the oral route.

METHODS

Liposomes prepared as dehydration-rehydration vesicles (DRVs) containing vancomycin were optimized for encapsulation efficiency and stability. A folic acid-poly(ethylene oxide)-cholesterol construct was synthesized for adsorption at DRV surfaces. Liposomes were characterized by differential scanning calorimetry (DSC) and assessed in vitro in the Caco-2 cell model and in vivo in male Sprague-Dawley rats. Non-compartmental pharmacokinetic analysis of vancomycin was conducted after intravenous and oral administration of solution or liposome-encapsulated vancomycin with or without 0.05 mole ratio FA-PEO-Chol adsorbed at liposome surfaces.

RESULTS

Optimal loading of vancomycin (32%) was achieved in DRVs of DSPC:Chol:DCP, 3:1:0.25 mole ratio (m.r.) after liposome extrusion. Liposomes released less than 40% of the entrapped drug after 2 hours incubation in simulated gastrointestinal (GI) fluid and simulated intestinal fluid containing a 10 mM bile salt cocktail. Incorporation of FA-PEO-Chol in liposomes increased drug leakage by 20% but resulted in a 5.7-fold increase in Caco-2 cell uptake of vancomycin. Liposomal delivery significantly increased the area under the curve of oral vancomycin resulting in a mean 3.9-fold and 12.5-fold increase in relative bioavailability for uncoated and FA-PEO-Chol-coated liposomes, respectively, compared with an oral solution.

CONCLUSIONS

The design of FA-PEO-Chol-coated liposomes resulted in a dramatic increase in the oral delivery of a moderate-size glycopeptide in the rat compared with uncoated liposomes or oral solution. It is speculated that the cause of the observed effect was due to binding of liposome-surface folic acid to receptors in the GI tract with subsequent receptor-mediated endocytosis of entrapped vancomycin by enterocytes.

A modified HPLC method for the determination of vancomycin in plasma and tissues and comparison to FPIA (TDX)

A modified high performance liquid chromatography (HPLC) method for the quantification of vancomycin levels in plasma and tissues is described. The method uses solid phase extraction (SPE) of vancomycin from the samples and reversed phase HPLC with UV detection. The method was fully validated in terms of recovery, linearity, selectivity and various stability conditions. Vancomycin was determined in plasma samples obtained from 15 patients undergoing cardiopulmonary bypass, before and repeatedly during 12 h after drug administration. The vancomycin levels in plasma were measured by HPLC and by fluorescence polarization immunoassay (FPIA) (TDX). The following correlation was found: TDX = 0.84 HPLC + 1.04. The mean vancomycin levels in skin, fat, atrium, pericardium and sternum, before and after bypass, are reported.

Quantitation of vancomycin and its crystalline degradation product (CDP-1) in human serum by high performance liquid chromatography

The delayed clearance of vancomycin results in accumulation of vancomycin crystalline degradation product, CDP-1, in the bodies of renally impaired patients. The 2 isomers, CDP-1-M (major) and CDP-1-m (minor), of CDP-1 are antibiotically inactive but cross-react with some immunoassays that use polyclonal antibodies resulting in falsely elevated results. A high performance liquid chromatographic (HPLC) method was developed to quantitate vancomycin and CDP-1 in the serum of renal patients. After solid phase extraction of 200 microliters serum, the separation of vancomycin, the 2 isomers of CDP-1 and the internal standard (cefazolin) was accomplished by gradient HPLC on a reversed phase C18 column with detection at 210 nm. Linearity was established from 1 to 25 and 25 to 100 micrograms ml-1 vancomycin and 1 to 25 micrograms ml-1 CDP-1. Coefficients of variation for vancomycin and CDP-1 were 3.3-8.6% (n = 10) and 2.8-5.2% (n = 8).

High-performance liquid chromatographic determination of vancomycin in rabbit serum, vitreous and aqueous humour after intravitreal injection of the drug

A high-performance liquid chromatographic method for the determination of vancomycin in rabbit serum, vitreous and aqueous humour has been developed. No clean-up step was necessary for vitreous and aqueous humour samples. For serum samples liquid-liquid and solid-phase extraction were tested and the best results were achieved using C18 cartridges. The extracts were analyzed on a C18 reversed-phase column, using a mixture of 0.05 M phosphate buffer (pH 4) with 10% of acetonitrile as mobile phase. The detection was carried out at 198 nm, which allows higher sensitivity. The average quantitation limit obtained was 0.03 micrograms/ml. The method has been applied to the study of the residual quantities of vancomycin in serum and rabbit eyes after intravitreal administration of the drug in endophthalmitis treatment.

Comparison of high-performance liquid chromatography with fluorescence polarization immunoassay for the analysis of vancomycin in patients with chronic renal failure

Eighty-two plasma samples from patients with chronic renal failure undergoing vancomycin treatment and hemodialysis (HD) were analyzed with fluorescence polarization immunoassay (FPIA) and high-performance liquid chromatography (HPLC). Vancomycin was infused once and the samples were collected during three subsequent HD sessions at 2 h, 3 days and 5 days post-infusion. The HPLC method, modified from an earlier assay, was simple. There was a wide variation in the estimated concentration between the two assay methods. The results obtained by HPLC were 69% lower than those obtained by FPIA. This difference in vancomycin concentration was independent of the sampling time after vancomycin infusion. HPLC analysis commenced approximately 1.5 year after that of FPIA. To study the effect of in vitro degradation, the vancomycin concentration in ten of the samples was redetermined with FPIA during HPLC analysis. The concentrations of those samples decreased to 78-98% (average 92%) of the original concentration. Because FPIA appears to lack specificity, there is a need of other methods such as HPLC for vancomycin measurements, particularly in samples from patients with end-stage renal failure.

Serum protein-binding characteristics of vancomycin

A synthesis of studies of serum protein binding of vancomycin and its reported abnormal binding in serum with very high concentrations of immunoglobulin A (IgA) suggests that this antibiotic may be bound to more than one serum protein. Using an ultrafiltration method for separating free from bound drug and high-performance liquid chromatography to measure drug concentration, we studied the binding characteristics of vancomycin for alpha-1 acid glycoprotein, IgG, IgM, IgA, and albumin. The results showed that vancomycin does not bind to alpha-1 acid glycoprotein, IgG, or IgM. Major binding to albumin and IgA occurs, and total drug binding to serum proteins can be fully explained by binding to these two proteins. We calculated an N (number of binding sites per molecule) of 1.3 +/- 0.4 and a K (association constant) of 3.3 x 10(5) +/- 6.3 x 10(4) M-1 (NK = 4.3 x 10(5) M-1) for binding to IgA, whereas the corresponding NK value for albumin was only 527.5 M-1, indicating that vancomycin preferentially binds to IgA. Very high concentrations of IgA in serum (i.e., grams per deciliter), such as in patients with IgA myeloma, may result in the paradox of high (total) concentrations of vancomycin in serum that may be clinically ineffective.

Arterial and venous blood samplings in pharmacokinetic studies: vancomycin in rabbits

The pharmacokinetics of vancomycin were evaluated simultaneously using both arterial and venous plasma data in five rabbits after a rapid bolus intravenous (i.v.) dosing. Initial arterial to venous concentration ratios at 5 s after i.v. injection were the highest, with values of 27.1, 36.2, 36.6, 43.7 and 29.7 for rabbits 1-5, respectively. This could be the result of diffusion of vancomycin from the arterial plasma into the extravascular tissues. Both curves decayed in parallel at the terminal phase with the venous levels higher than the arterial levels by 23, 37, 34, 13 and 14% for rabbits 1-5, respectively. This difference could be the result of continuous release of vancomycin from the extravascular tissues to the venous blood. Detailed analysis showed differences in various pharmacokinetic parameters based on arterial and venous data. For example, values for venous Vc were 9.2, 11, 1.9, 7.2 and 8.8 times greater than the arterial values for rabbits 1-5, respectively. The values for both venous Vss and MRT were higher than those of the arterial values in all five rabbits studied. This could be due to more extensive distribution of vancomycin in the extravascular tissues. A plot of 1/Q (urine flow rate) versus 1/ClR of vancomycin yielded a straight line in rabbits 6-10, indicating that the renal clearance of vancomycin in rabbits is dependent upon urine flow.

Rapid and specific method for the determination of vancomycin in plasma by high-performance liquid chromatography on an aminopropyl column

A high-performance liquid chromatographic method has been developed for the quantitative analysis of vancomycin in plasma. The method involves protein precipitation with acetonitrile, followed by normal-phase chromatography on an aminopropyl column. The clear supernatant was injected after centrifugation, and the eluent was monitored at 240 nm. No interference was found either with endogenous substances or with many currently used drugs, indicating a good selectivity for the procedure. The standard curve was linear between 0.1 and 100 micrograms/ml, and the detection limit was 0.01 microgram/ml of plasma. The mean intra- and inter-assay coefficients of variation were 2.4 and 4.0%, respectively, in the 10-50 micrograms/ml range. Application of the method to the study of vancomycin pharmacokinetics in a rabbit after a single intravenous dose is also reported.

Pharmacokinetics and serum bactericidal activity of vancomycin alone and in combination with ceftazidime in healthy volunteers

The pharmacokinetics and serum bactericidal activity of vancomycin alone and in combination with ceftazidime were investigated in 10 healthy volunteers. The pharmacokinetic parameters showed no significant differences (P less than 0.05) between single and combined administration. No antagonistic effects were observed in serum bactericidal activity with the combination against 20 gram-positive and 20 gram-negative locally isolated bacteria. A titer of greater than or equal to 1:8 was generated by the combination against all test strains except enterococci. Seven of ten volunteers developed a typical "red man's syndrome" during the administration of 1.0 g of vancomycin.

Determination of vancomycin related substances by gradient high-performance liquid chromatography

A gradient high-performance liquid chromatographic method for the determination of vancomycin related substances is described. This method was developed to profile vancomycin, co-fermentation products, and degradation products. The resultant chromatograms confirm the multifactored nature of vancomycin, separating a number of peaks from the main component. The development of acceptable chromatographic performance is described, with the final method intended for use as a control assay. Quantitation of total related substances is made by comparing the relative area of the main peak to total peak area in a pair of chromatograms from a stock solution and a twenty-five fold dilution. A rapid-scan UV detector was used to demonstrate the similar spectral characteristics of the vancomycin related substances, confirming the validity of the relative area approach. Statistical method validation data are included, evaluating the use of this method for quantitative applications. Example applications demonstrate the effectiveness of this method.

Once weekly intraperitoneal therapy for gram-positive peritonitis

The pharmacokinetics and clinical outcome following a 30 mg/kg/2 L intraperitoneal (IP) dose of vancomycin, which was administered once a week for 3 weeks, was studied in ten continuous ambulatory peritoneal dialysis patients with peritonitis. Vancomycin was 91% absorbed following the first dose and rapidly achieved therapeutic serum concentrations, 19 +/- 8 mcg/mL at 1 hour and a peak of 37 +/- 8 mcg/mL at 6 hours. Vancomycin was eliminated slowly with a mean total clearance of 7 +/- 3 mL/min/70 kg and a distribution volume of 1.2 +/- 0.3 L/kg. The resultant mean serum t1/2 over the first week was 184 hours and the mean serum concentration at 168 hours was 10 +/- 4 mcg/mL. Based on the positive clinical outcome (100% cure) among patients with uncomplicated gram-positive peritonitis, the potential use of this alternative vancomycin dosing regimen is proposed.

High-performance liquid chromatographic analysis of vancomycin in plasma, bone, atrial appendage tissue and pericardial fluid

Solid-phase extraction coupled with reversed-phase high-performance liquid chromatography and UV detection was employed for the analysis of the antibiotic vancomycin in patient plasma, bone, atrial appendage, and pericardial fluid. Vancomycin was quantitated in samples from patients undergoing cardiac surgery. Calibrations were linear in the range 3-100 micrograms/ml vancomycin; the lower limit of detection was approximately 3 micrograms/ml in fluids with an absolute limit of detection in bone samples of 0.75 microgram per injection.

Comparative study of intraperitoneal and intravenous vancomycin pharmacokinetics during continuous ambulatory peritoneal dialysis

The pharmacokinetic characteristics of vancomycin were investigated in eight patients undergoing continuous ambulatory peritoneal dialysis. A crossover design was used. Four noninfected patients received both a 15-mg/kg (body weight) intravenous dose and a 30-mg/kg intraperitoneal (i.p.) dose. Bioavailability ranged from 0.35 to 0.65 after i.p. administration. i.p. absorption was rapid, with concentrations in serum of 8.8 +/- 6 micrograms/ml noted at 1 h peak values of 30.4 +/- 7 micrograms/ml at 6 h. A slow distribution phase was apparent, with a terminal elimination phase emerging after 12 to 24 h. Vancomycin was eliminated slowly, with a mean total clearance of 5.0 +/- 1.3 ml/min, and concentrations in serum were 7.0 +/- 1.2 micrograms/ml at 168 h. The mean serum half-life was 91.7 +/- 28.1 h, and similar pharmacokinetics were noted after intravenous administration. Subsequently, four patients with catheter-related exit site or tunnel infections received a 30-mg/kg i.p. dose of vancomycin and displayed a similar kinetic pattern. This method of administering vancomycin achieved therapeutic serum and end-dwell dialysate concentrations over a 1-week period, represents a simple, cost-effective therapy which avoids the possibility of infusion-related toxicity, and deserves further investigation in patients with continuous ambulatory peritoneal dialysis-related peritonitis.

Determination of vancomycin in human serum by high-pressure liquid chromatography

A rapid, accurate, reverse-phase high-pressure liquid chromatographic procedure for vancomycin quantitation in human serum, cerebrospinal fluid, and peritoneal fluid was developed. This procedure involves a simple chemical extraction of the antibiotic and is suitable for each of these body fluids. The column and mobile phase used provided a good resolution of the vancomycin peak with a retention time of 6.1 min. The precision of the assay was within the requirement for a daily routine clinical application. Coefficients of variation for within-day reproducibility were 5.80 and 6.28%, respectively, for samples at 50 and 25 micrograms/ml, and for between-day reproducibility they were 11.4 and 11.1%, respectively. No interference was found with respect to beta-lactam and aminoglycoside antibiotics and many other currently used drugs, indicating a good specificity for the procedure. The detection limit of 100 ng/ml has proven to be sufficient for monitoring drug levels in serum obtained after usual dosages. Drug levels in 112 clinical serum specimens assayed by high-pressure liquid chromatography were regressed against the levels obtained for the same samples by radioimmunoassay and fluorescent polarization immunoassay. Correlation coefficients were 0.945 and 0.967, respectively, and were highly significant (alpha less than 0.001).

Comparison of fluorescence polarization immunoassay and bioassay of vancomycin

Human serum samples were analyzed for vancomycin concentrations by two different methods: the fluorescence polarization immunoassay and the disk plate bioassay. Each assay method offered acceptable precision. The correlation between both assay methods was excellent (correlation coefficient = 0.985). Excluding technical time, the bioassay was the least expensive method to perform but was more labor intensive than the fluorescence polarization immunoassay.

Comparison of radioimmunoassay and fluorescent polarization immunoassay for quantitative determination of vancomycin concentrations in serum

A new fluorescent polarization immunoassay (Abbott Laboratories, Diagnostics Division, North Chicago, Ill.) was compared with a standard radioimmunoassay (American Diagnostics Corp., Newport Beach, Calif.) in 34 patients being treated with vancomycin. A total of 123 serum samples were divided and quantitatively analyzed for vancomycin by both assay methods. The results obtained indicated that the two assay methods are comparable (y = 1.01x - 0.81; r = 0.99).