Determination of tobramycin in human serum by capillary electrophoresis with contactless conductivity detection

A study on the determination of the antibiotic tobramycin by CE with capacitively coupled contactless conductivity detection is presented. This method enabled the direct quantification of the non-UV-absorbing species without incurring the disadvantages of the indirect approaches which would be needed for optical detection. The separation of tobramycin from inorganic cations present in serum samples was achieved by optimizing the composition of the acetic acid buffer. Field-amplified sample stacking was employed to enhance the sensitivity of the method and a detection limit of 50 microg/L (S/N = 3) was reached. The RSDs obtained for migration time and peak area using kanamycin B as internal standard were typically 0.12 and 4%, respectively. The newly developed method was validated by measuring the concentration of tobramycin in serum standards containing typical therapeutic concentrations of 2 and 10 mg/L. The recoveries were 96 and 97% for the two concentrations, respectively.

Selective kinetic determination of amikacin in serum using long-wavelength fluorimetry

A simple and rapid method for the determination of the antibiotic amikacin, involving the use of a long-wavelength fluorophor, namely indocyanine green, (ICG) is presented. The dye is oxidised by cerium(IV) in acidic medium, resulting in a sharp decrease of the fluorescence, but this fluorescence quenching is inhibited in the presence of amikacin, which can be ascribed to the formation of an ion pair between the fluorophor and the analyte. The initial rate of the system is monitored at lambda(ex): 765 nm and lambda(em): 812 nm as excitation and emission wavelengths, respectively, using the stopped-flow mixing technique, which makes the method applicable to automatic routine analysis. Each measurement is obtained in only 2-3s. The method presents a detection limit of 0.02 microg m1(-1) in standard solutions, which corresponds to 2.5 microg ml(-1) in serum samples. The precision is in the range 4.8-6%. The good selectivity of the method allows amikacin to be determined in the presence of other antibiotics, including other aminoglycoside antibiotics, in serum. The recoveries obtained from the analysis of different samples were in the range 89.4-104.7%.

Trace analysis of tobramycin in human plasma by derivatization and high-performance liquid chromatography with ultraviolet detection

A simple and sensitive high-performance liquid chromatographic (HPLC) method is established for the trace determination of tobramycin in human plasma by derivatization. The method is based on the chemical derivatization of aminoglycoside antibiotic, tobramycin in human plasma, with 1-naphthyl isothiocyanate (NITC) in pyridine at 70 degrees C. After derivatization reaction, a methylamine/acetonitrile solution was added to the reaction mixture to eliminate the excess derivatizing agent and shorten the analysis time. The resulting derivative was separated using a Purospher STAR RP-18e column and a water-acetonitrile (50:50, v/v) mobile phase (detection at 230 nm). Optimization conditions for the derivatization of tobramycin were investigated by HPLC. The linear range for the quantitation of tobramycin in spiked plasma was over 0.93-9.34 mg/l; the detection limit (signal-to-noise ratio=3; injection volume, 10 microl) was about 0.23 mg/l. The relative standard deviation was less than 2.1% for intra-day assay (n=6) and 5.2% for inter-day assay (n=6) and relative recoveries were found greater than 99%.

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.

High-performance liquid chromatographic analysis of aminoglycoside antibiotics

A simple precolumn derivatisation method for the determination of aminoglycoside antibiotics (AGs) is described. The stability of the o-phthalaldehyde (OPA) derivatives of the AGs obtain using beta-mercaptopropionic acid (beta-MP) was investigated by reversed-phase HPLC. One of the fluorescent derivatives of sisomicin was stable at least for 6 h in 50% methanol under the optimal conditions used (OPA concentration, pH and temperature). When plasma samples spiked with sisomicin were analysed the response was linear in the calibration range of 136-900 micrograms of sisomicin per injected volume (40 microliters). As little as 0.06 micrograms of sisomicin per 1 ml of plasma could be detected with a signal-to-noise ratio > or = 2. The method was also applied to whole blood samples from rabbit after a subcutaneous injection of 1 mg/kg of the AGs using dried blood spots (DBS) on the filter-paper punched discs. The detection of sisomicin and netilmicin in the DBSs on punched discs (10.1 micrograms of whole blood) were 0.053 and 0.50 micrograms per ml of whole blood, respectively (signal-to-noise ratio > or = 2). The method permits a simple collection of blood at the microlitre level and should prove particularly useful for monitoring the AGs in blood at therapeutic levels in geriatric and paediatric patients and could be also used for the preclinical study of the AGs blood levels of a number of mice or rats without killing. An RP-HPLC method using an on-line clean-up procedure for large sample-volume analysis of serum AGs is also described.

The disposition of five therapeutically important antimicrobial agents in llamas

The disposition of five therapeutic antimicrobial agents was studied in llamas (Lama glama) following intravenous bolus administration. Six llamas were each given ampicillin, tobramycin, trimethoprim, sulfamethoxazole, enrofloxacin and ceftiofur at a dose of 12 mg/kg, 1 mg/kg, 3 mg/kg, 15 mg/kg, 5 mg/kg, and 2.2 mg/kg of body weight, respectively, with a wash out period of at least 3 days between treatments. Plasma concentrations of these antimicrobial agents over 12 h following i.v. bolus dosing were determined by reverse phase HPLC. Disposition of the five antimicrobial agents was described by a two compartment open model with elimination from the central compartment, and also by non-compartmental methods. From compartmental analysis, the elimination rate constant, half-life, and apparent volume of distribution in the central compartment were determined. Statistical moment theory was used to determine noncompartmental pharmacokinetic parameters of mean residence time, clearance, and volume of distribution at steady state. Based on the disposition parameters determined, and stated assumptions of likely effective minimum inhibitory concentrations (MIC) a dose and dosing interval for each of five antimicrobial agents were suggested as 6 mg/kg every 12 h for ampicillin; 4 mg/kg once a day or 0.75 mg/kg every 8 h for tobramycin; 3.0 mg/kg/15 mg/kg every 12 h for trimethoprim/sulfamethoxazole; 5 mg/kg every 12 h for enrofloxacin; and 2.2 mg/kg every 12 h for ceftiofur sodium for llamas. Steady-state peak and trough plasma concentrations were also predicted for the drugs in this study for llamas.

A liquid-chromatographic method for the determination of tobramycin

A rapid and sensitive liquid-chromatographic method was developed to quantify the release of tobramycin from polymeric drug delivery systems in vitro. Pre-column derivatization of tobramycin and kanamycin B sulphate (internal standard) was carried out with 2,4,6-trinitrobenzenesulphonic acid. The sample volume required was only 50 microliters. The chromatographic separation was achieved on an octyl reversed-phase column with UV detection at 340 nm. This isocratic method was performed at ambient temperature and required only 8 min of chromatography time. The standard curves were linear over the concentration range 0.50-50.0 mg l-1. Inter-day and intra-day relative standard deviations ranged from 3.6 to 9.3% and from 1.6 to 6.8%, respectively. The assay method was used to determine the tobramycin content in different pharmaceutical formulations and to study the stability of the drug both in the solid-state and in solution.

Comparison of new and existing spectrophotometric methods for the analysis of tobramycin and other aminoglycosides

New indirect spectrophotometric methods of analysis of tobramycin using the derivatizing agents o-phthaldialdehyde, fluorescamine, and dansyl chloride were developed and compared with existing methods. Optimum reaction conditions were established for the complex formation between tobramycin and each reagent. The sensitivity and reproducibility of these new procedures were compared with results obtained using published methods. Of the new methods, the o-phthaldialdehyde and fluorescamine procedures were more sensitive and reproducible than the dansyl chloride procedure. Further, these procedures were subsequently applied to the analysis of aqueous solutions of other aminoglycosides including amikacin, neomycin, gentamicin, and kanamycin.

Pre-column derivatization of sisomicin with o-phthalaldehyde-beta-mercaptopropionic acid and its application to sensitive high-performance liquid chromatographic determination with fluorimetric detection

The stability of the o-phthalaldehyde (OPA) derivatives of sisomicin obtained using beta-mercaptopropionic acid was investigated by reversed-phase high-performance liquid chromatography. One of the fluorescent derivatives of sisomicin was stable at least for 6 h in 50% methanol under the optimal conditions used (OPA concentration, pH and temperature). When plasma samples spiked with sisomicin were analysed, the response was linear in the calibration range 136-900 pg of sisomicin per injected volume (40 microliters). As little as 0.06 micrograms of sisomicin per 1 ml of plasma could be detected with signal-to-noise ratio greater than or equal to 2. For plasma samples spiked with 0.2 micrograms/ml sisomicin, the recovery was 97.1 +/- 6.6% (mean +/- S.D., n = 5) with a within-run coefficient of variation of 6.8% and a day-to-day coefficient of variation of 7.2%. The method was also applied to plasma samples from rabbit after a subcutaneous injection of 1 mg/kg sisomicin.

Comparison of venous and capillary blood sampling for the clinical determination of tobramycin serum concentrations

Tobramycin concentrations have been determined in serum from capillary, venous and arterial blood samples taken from 16 patients during and after surgery. In 73 paired samples the concentrations in capillary samples were not significantly different from those measured in venous samples. The small concentration differences were neither dependent upon sampling time nor core-peripheral temperature differences. In 26 paired samples, concentrations in capillary samples were not significantly different from those determined in arterial samples. We conclude that concentrations in capillary samples are precise and unbiased estimators of venous concentrations and may be used in the adjustment of tobramycin dosage regimens.