Improved microdetermination of gentamicin and sisomicin in serum by high-performance liquid chromatography with ultraviolet detection

A new simple liquid chromatographic assay for gentamicin in presence of methylparaben and propylparaben

Gentamicin sulfate is a potent broad spectrum aminoglycoside antibiotic which is used against Gram-positive and Gram-negative bacteria. A simple, isocratic HPLC method for separation, identification and determination of gentamicin and parabens (methylparaben and propylparaben) was developed and validated. To our knowledge there is no report about simultaneous determination of those three analytes in pharmaceutical products. The optimum chromatographic conditions were achieved on CN column with a mobile phase consisting of 0.15% triethylamine in 10 mM KH2PO4 aqueous solution (final pH 3.0 adjusted with H3PO4) and methanol in the ratio 70:30 (v/v), providing selective quantification of analytes within 5 min. The method was successfully validated according to ICH guidelines acceptance criteria in terms of selectivity, linearity, accuracy, precision and robustness. The linearity of the method was proved in defined concentrations ranges for gentamicin (0.32–1.04 mg mL−1), methylparaben (0.0072–0.0234 mg mL−1) and propylparaben (0.0008–0.0026 mg mL−1). Relative standard deviations calculated for all analytes in precision testing were <2% (analysis repeatability) and <3% (intermediate precision). Recovery values were between 98.87% and 101.67%. Chromatographic parameters are not significantly influenced by small variations of column temperature, pH and molarity of KH2PO4. Finally, the method was successfully applied for quantitative determination of gentamicin and parabens in commercially available solution for injection. Proposed HPLC method is found to be promising in terms of simplicity, analysis times and non-use of derivatization and ion-pair agents.

Aminoglycoside antibiotics--two decades of their HPLC bioanalysis

Several reviews have been published on high-performance liquid chromatographic (HPLC) methods for the determination of aminoglycoside antibiotics (aminoglycosides) in biological fluids [e.g. Nilsson-Ehle, I. (1983). J. Liq. Chromat. 6: 251]. Of these, the paper by Maitra et al. [(1979a). Clin. Chem. 25: 1361.] briefly summarizes the early 2-3 years of experience on HPLC assaying of amikacin, gentamicin, netilmicin and tobramycin in body fluids. The reviews by Nilsson-Ehle, I. [(1983). J. Liq. Chromat. 6: 251] and by Miner, D. J. [(1985). Antibiotics. In Therapeutic Drug Monitoring and Toxicology by Liquid Chromatography, (Wong S. H. Y., ed.), ch. 10, p. 269. Marcel Dekker, New York and Basel.] devoted to the monitoring of antibiotics, also evaluated the first 6-8 years of the application of HPLC assays for the aminoglycosides amikacin, gentamicin, netilmicin, sisomicin and tobramycin. This report presents a great majority of the HPLC assay methods published during the last two decades for determining practically a dozen different aminoglycoside antibiotics in body fluids, particularly in the serum or plasma, and in urine.

Analysis of isepamicin in human plasma by radioimmunoassay, microbiologic assay, and high-performance liquid chromatography

Plasma concentrations of isepamicin, a new aminoglycoside antibiotic, were determined by radioimmunoassay (RIA), microbiological assay (MA), and high-performance liquid chromatography (HPLC) in healthy volunteers after administration of 7.5 mg/kg intramuscular dosages once daily for 10 days. Plasma samples were collected on days 1, 7, and 10. The limit of quantitation (LOQ) was 0.1 microg/ml for HPLC and RIA and 0.5 microg/ml for MA. The HPLC and RIA yielded superimposable plasma concentration-time curves, whereas the plasma concentrations obtained with MA appeared to be 20% to 30% lower. Regression analysis indicated good correlations among the three assays, with coefficients of correlation measuring 0.935 to 0.960 for RIA compared with HPLC, 0.925 to 0.945 for MA compared with HPLC, and 0.920 to 0.945 for RIA compared with MA.

In vitro kinetics of drug release and pulmonary retention of microencapsulated antibiotic in liposomal formulations in relation to the lipid composition

In previous in-vivo studies, we demonstrated that liposomal entrapment of tobramycin resulted in an increased availability of the antibiotic in the lungs without increasing bactericidal efficacy (Omri et al. 1994). With the aim of developing liposomal formulations allowing more efficient liposome-bacteria interactions, we studied the influence of lipid composition on both drug release and pulmonary retention of encapsulated tobramycin. The phase transition temperatures of nine liposome-tobramycin formulations consisting of two synthetic phospholipids (distearoyl phosphatidylcholine (DPSC) or dipalmitoyl phosphatidylcholine (DPPC) with dimyristoyl phosphatidyl-glycerol (DPMG) or dimyristoyl phosphatidylcholine (DMPC) were determined by differential scanning calorimetry. Liposomes, varying in terms of membrane fluidity and charge were submitted to in-vitro and in-vivo kinetic studies while retention and release of tobramycin were measured by high-performance liquid chromatography (HPLC). Five less fluid liposome formulations showed absence or very low tobramycin release in in-vitro tests and long term pulmonary retention of tobramycin. Four fluid liposome formulations showed in vitro tests modulated tobramycin release while pulmonary retention of tobramycin was dependent of the presence of charged phospholipids. Administration of charged fluid liposomes in mice showed a low level of tobramycin in the kidneys; non-charged fluid liposomes exhibited a relatively high level of tobramycin retention in the kidneys.

Determination of amikacin in human plasma by high-performance capillary electrophoresis with fluorescence detection

A selective and reproducible high-performance capillary electrophoretic (HPCE) method for the quantification of amikacin (AMK), an aminocyclitol antibiotic, in human plasma, has been developed for use in clinical laboratory tests. The method involves ultrafiltration (UF) of plasma before derivatization with the fluorescence derivatization reagent 1-methoxy-carbonylindolizine-3, 5-dicarbaldehyde at room temperature for 15 min in the dark. An aliquot of the derivatives is directly introduced into the fused-silica capillary [75 cm (effective length) x 50 microns I.D.] at the anode side by dynamic compression injection (50 hPa for 6 s). After electrophoresis with 40 mM SDS-20 mM phosphate-borate buffer (pH 7) in the micellar electrokinetic chromatography (MEKC) mode at 30 kV, the derivative had a retention time of 16.7 min and was detected by fluorescence intensity at 482 nm (with irradiation at 414 nm). The precision (n = 5) of the method is 4.08 and 1.59% (C.V.) at the 50 and 100 micrograms AMK/ml plasma levels, respectively. Linearity (r = 0.998) was established over the concentration range 5-100 mg of AMK/ml plasma and the detection limit (at a signal-to-noise ratio of 3) is 0.5 microgram AMK/ml plasma. This assay method could potentially have wider application in the determination of other aminocyclitol antibiotics, such as arbekacin, dibekacin, kanamycin, in human plasma as well as of AMK.

Eradication of mucoid Pseudomonas aeruginosa with fluid liposome-encapsulated tobramycin in an animal model of chronic pulmonary infection

Despite controversies associated with forms and value of antibiotic therapy for cystic fibrosis patients, antibiotherapy remains a cornerstone in the management of those patients. Locally administered liposome-encapsulated antibiotics may offer advantages over free antibiotics, including sustained concentration of the antibiotic, minimal systemic absorption, reduced toxicity, and increased efficacy. We evaluated the efficacy of free and encapsulated tobramycin in fluid and rigid liposomal formulations administered to rats chronically infected with Pseudomonas aeruginosa. Chronic infection in lungs was established by intratracheal administration of 10(5) CFU of a mucoid variant of P. aeruginosa PA 508 prepared in agar beads. Antibiotic treatments were given intratracheally at time intervals of 16 h. After the last treatment, lung bacterial counts were determined and tobramycin levels in the lungs and kidneys were evaluated by high-performance liquid chromatographic analysis and microbiological assay. Two independent experiments showed that animals treated with encapsulated tobramycin in fluid liposomes had a number of CFU less than the minimal CFU number required to be statistically acceptable compared with > or = 10(6) CFU per pair of lungs for animals treated with encapsulated tobramycin in rigid liposomes, free antibiotic, or liposomes without tobramycin. Tobramycin measured in the lungs at 16 h after the last treatment following the administration of encapsulated antibiotic was still active, and its concentration was > or = 27 micrograms/mg of tissue. Low levels of tobramycin were detected in the kidneys (0.59 to 0.87 micrograms/mg of tissue) after the administration of encapsulated antibiotic, while 5.31 micrograms/mg of tissue was detected in the kidneys following the administration of free antibiotic. These results suggest that the local administration of fluid liposomes with encapsulated tobramycin could greatly improve the management of chronic pulmonary infection in cystic fibrosis patients.

Pulmonary retention of free and liposome-encapsulated tobramycin after intratracheal administration in uninfected rats and rats infected with Pseudomonas aeruginosa

The pulmonary residence time of free and liposome-encapsulated tobramycin was studied with uninfected rats and rats infected with Pseudomonas aeruginosa. Chronic infection in lungs was established by intratracheal administration of 10(8) CFU of P. aeruginosa PA 508 prepared in agar beads. After 3 days, a single dose (300 micrograms) of free or liposome-encapsulated tobramycin was given intratracheally to both infected and uninfected rats. At various time intervals (0.25 to 16 h) after drug instillations, the remaining tobramycin was evaluated in blood, lungs, and kidneys by a microbiological assay. Intratracheal instillation of liposome-encapsulated tobramycin resulted in high and sustained levels of tobramycin in lungs of uninfected and infected rats over the 16-h period studied; however, the tobramycin levels were two times higher in uninfected rats. There was no tobramycin detected in the blood or kidneys from these animals. In contrast, the intratracheally instilled free tobramycin was cleared within 3 and 1 h from the lungs of uninfected and infected animals, respectively. These data suggest that the encapsulation of tobramycin in liposomes can result in a significant increase of its residence time within lungs. This study also shows that pulmonary infection was associated with a lowering of tobramycin levels in lungs.

Chromatographic analysis of antibiotic materials in food

The monitoring of food materials for antibiotic residues is an area of increasing concern and importance due to the potential impact on human health. Large-scale screening applications require methods that are rapid, accurate, provide low detection limits and are free from interference. The problem is further complicated by the wide range of chemical functionalities and modes of operation exhibited by the antibiotic materials of physiological significance in use today. As demonstrated, chromatographic methods provide many of the advantages necessary for screening applications. Judicious choice of sample preparation method, separation mode and detection strategy can provide significant immunity from problems associated with the food matrix. Gas chromatography can provide extremely high separation efficiencies, however, only a limited number of antibiotic compounds are inherently volatile enough for direct analysis by gas chromatography. Derivatization to enhance the volatility of the antibiotic is one approach to overcome this limitation. Among the methods available, reversed-phase high-performance liquid chromatography is used extensively for the analysis of many antibiotic systems as it does not require derivatization and it combines relatively high separation efficiencies with low detection limits. The diverse group of properties exhibited by the antibiotic materials in use today suggests that the choice of detection strategy is a key component in the successful development of an analysis technique. Derivatization of the antibiotic material is frequently used to add either a fluorogenic of chromogenic moiety to the antibiotic compound to enhance detection. Derivatization procedures suffer from several limitations which are problematic when making measurements in complicated food matrices. Among the different detection modes utilized for antibiotic analysis, polarimetric detection has the potential to provide extremely selective detection of most antibiotic materials, and this selective response can minimize many of the constraints placed upon the separation system by the sample matrix. Although many of the separation modes used for antibiotic analysis are well developed, separations based on capillary electrophoretic methods have much potential in the field of antibiotic analysis. Future investigations are needed to extend the generality of these techniques and expand their use into the field of food analysis.

High-performance liquid chromatographic assays for the quantification of amikacin in human plasma and urine

Amikacin, an aminoglycoside antibiotic, is frequently coadministered with penicillins and broad-spectrum cephalosporins to synergize the activity of these agents. Sensitive, selective and reproducible high-performance liquid chromatographic assays have been developed for the quantification of amikacin in plasma and urine collected from human subjects. The plasma method involves the ultrafiltration of plasma prior to derivatization. An aliquot of plasma ultrafiltrate or urine is mixed with dimethyl sulfoxide and tris(hydroxymethyl)aminoethane followed by derivatization of amikacin with 1-fluoro-2,4-dinitrobenzene at 58 degrees C for 30 min. The reaction mixture is then injected directly onto a reversed-phase C18 column preceded by a guard column. The column is eluted with a mobile phase containing acetonitrile and 2-methoxyethanol in 1% Tris buffer. Amikacin derivative is detected at 340 nm. The methods were applied for the analysis of amikacin in plasma and urine samples from volunteers receiving amikacin and cefepime, a fourth-generation cephalosporin, in a clinical pharmacokinetic drug interaction study.

High-performance liquid chromatographic determination of netilmicin in guinea-pig and human serum by fluorodinitrobenzene derivatization with spectrophotometric detection

A high-performance liquid chromatographic procedure for netilmicin determination in guinea-pig and human serum using pre-column derivatization with 1-fluoro-2,4-dinitrobenzene and UV detection is described. Linearity was established over the range 0.5-40 micrograms/ml using only 50 microliters of serum. Accuracy and precision were good, with a mean coefficient of variation less than 5% and a mean relative error less than 4%. This procedure correlates well with an enzyme multiplied immunoassay technique and has a sensitivity similar to those of published fluorescence derivatization methods.

Quantitative determination and separation of analogues of aminoglycoside antibiotics by high-performance liquid chromatography

Commercial bulk products and pharmaceutical drug formulations of aminoglycoside antibiotics obtained by fermentation (kanamycin, gentamicin, sisomicin and tobramycin) or by synthesis (amikacin) were analysed with high-performance liquid chromatography on a C8 reversed-phase column. The method is based on a pre-column derivatization of the aminoglycosides with a 2,4,6-trinitrobenzenesulphonic acid reagent and UV detection (350 nm). The quantitative determination was carried out vs. an external standard; both peak heights and areas were used. A gentamicin mixture was separated into five or four components, depending on the column used. Amikacin was separated from its possible regioisomers and kanamycin A was easily separated from its minor components B and C.

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.

Determination of the component ratio of commercial gentamicins by high-performance liquid chromatography using pre-column derivatization

Commercial samples of gentamicin from different origins were analyzed by paired-ion high-performance liquid chromatography (HPLC) on a C18 bonded phase. The procedure uses pre-column derivatization with a omicron-phthalaldehyde-mercaptoacetic acid reagent and UV detection (350 nm). The ratios of the four gentamicin components (C1, C1a, C2a and C2) were determined and compared with the compositions obtained by an independent method based on 13C NMR spectrometry. Quantitation by HPLC, based on peak heights and peak areas, was performed with the aid of an external standard, which was an artificial mixture of the four components. The latter were prepared by separation of the gentamicins C1, C2 + C2a and C1a by chromatography on silica gel, followed by chromatography of the C2 + C2a fraction on a cellulose phosphate column.

Determination of amikacin in serum by high-performance liquid chromatography with ultraviolet detection

A procedure for the determination of amikacin in serum is described. The aminoglycoside is extracted from serum by using a disposable cation-exchange column. The eluate of this column is derivatized with 1-fluoro-2,4-dinitrobenzene and subsequently analysed by reversed-phase high-performance liquid chromatography with ultraviolet detection at 365 nm. The absolute recovery of amikacin by this procedure is 72%. Kanamycin is used as the internal standard. The sensitivity is 1 mg/l for amikacin with samples of 200 microliters. Precision, expressed as the coefficient of variation, is about 3% in the therapeutic concentration range. The 2,4-dinitrophenyl derivative of amikacin is synthesized on a preparative scale by a new method and its structure is demonstrated to be the fully derivatized amikacin. The analysis of serum samples obtained in an in vivo experiment correlates well with the results from a microbiological assay.

The determination of aminoglycoside antibiotics in serum: a comparison of a high performance liquid chromatographic method with a microbiological assay

A high performance liquid chromatographic (HPLC) method for the determination of gentamicin and tobramycin in serum is compared with a microbiological method. The determination of gentamicin by chromatographic methods is complicated by the fact that gentamicin is a mixture of related compounds, giving rise to several chromatographic peaks. Good results were obtained when the sum of the peak heights of the chromatographic peaks corresponding with the gentamicin components are taken as a measure for the gentamicin concentration. Accuracy, precision and selectivity of the methods are discussed.

Determination of amikacin in microlitre quantities of biological fluids by high-performance liquid chromatography using 1-fluoro-2,4-dinitrobenzene derivatization

Pre-column derivatization of amikacin with 1-fluoro-2,4-dinitrobenzene in 25 microliter of guinea pig plasma or human serum produced a stable chromophore which was measured by UV detection after rapid separation on normal-phase or reversed-phase high-performance liquid chromatography systems. The reversed-phase system, selected for routine analysis due to instability of the normal-phase column, consisted of an Ultrasphere-ODS C18 column preceded by a guard column, and used acetonitrile--water (68:32) as the mobile phase. A high degree of linearity was found in the range of 2-64 microgram/ml with a coefficient of variation averaging less than 5%.

Micro-determination of tobramycin in serum by high-performance liquid chromatography with ultraviolet detection

A procedure for the high-performance liquid chromatographic determination of tobramycin in serum is described using pre-column derivatisation with 1-fluoro-2,4-dinitrobenzene and subsequent chromatographic analysis on a reversed-phase column with ultraviolet detection. Gentamicin is used as the internal standard. The sensitivity is 0.5 mg/l with 50-microliters samples. Precision, expressed as the coefficient of variation, is 3% or better in the concentration range 0.5-16 mg/l. The absolute recovery of tobramycin is 41%. The analyses of serum samples obtained in an in vivo experiment correlated well with the results from a microbiological assay. The influence of variation of derivatisation conditions and the implications for the reliability of the internal standardisation were studied. The 2,4-dinitrophenyl tobramycin derivative was synthesized and its structure was proved to be the fully derivatized tobramycin. Side-products of the derivatisation reaction were isolated.