Aminoglycoside antibiotics--two decades of their HPLC bioanalysis

A simple and rapid HPLC-MS/MS method for therapeutic drug monitoring of amikacin in dried matrix spots

Individualized treatment of amikacin under the guidance of therapeutic drug monitoring (TDM) is important to reduce the occurrence of toxicity and improve clinical efficacy. In the present study, we developed and validated a simple and high-throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to determine the concentration of amikacin in dried matrix spots (DMS) which the matrix is serum. DMS samples were obtained by spotting volumetric blood onto Whatman 903® cards. Samples were punched into 3 mm diameter discs and extracted with 0.2 % formic acid in water. The HILIC column (2.1 mm × 100 mm, 3.0 µm) under gradient elution was applied, and the analysis time was 3 min per injection. The mass spectrometry transitions were m/z 586.3 → 163.0 for amikacin and m/z 591.4 → 163.1 for D5-amikacin. Full validation was conducted for DMS method, and the method was applied for the amikacin TDM and compared with serum method. The linearity was ranged from 0.5 to 100 mg/L. Both within-run and between-run accuracy and precision of DMS ranged from 91.8 % to 109.6 % and 3.6 % to 14.2 %, respectively. The matrix effect was 100.5 %-106.5 % of DMS method. Amikacin remained stable in DMS for at least 6 days at room temperature, 16 days at 4 °C, 86 days at -20 °C and -70 °C. A good agreement between the DMS method and serum method has been shown in Bland-Altman plots and Passing-Bablok regression. All of the results demonstrated that the DMS methods can be a favorable replacement for amikacin TDM.

A Novel high throughput 96-well based Fluorimetric Method to Measure Amikacin in Pharmaceutical Formulations: Development using Response Surface Methodology

An aminoglycoside antibiotic, amikacin, is used to treat severe and recurring bacterial infections. Due to the absence of a chromophore, however, amikacin must be extensively derivatized before being quantified, both in analytical and bioanalytical samples. In this study, for the first time, we developed a simple and sensitive method for measuring amikacin sulfate by spectrofluorimetry using a 96-well plate reader, based on the design of the experiment's approach. To develop a robust and reproducible spectrofluorimetric method, the influence of essential attributes, namely pH of the buffer, heating temperature, and concentration of reagents, were evaluated by univariate analysis followed by multivariate analysis (central composite design). ICH guidelines were used to validate the optimized method. The developed technique is linear from 1.9 to 10 μg/mL with a regression coefficient of 0.9991. The detection and quantification limits were 0.649 μg/mL and 1.9 μg/mL, respectively. For the developed method, both intra- and inter-day precision (%RSD) were below 5%. Using the method, amikacin concentrations were quantified in prepared amikacin liposomes and commercial formulations of Amicin®. The developed method greatly reduces sample volume and is a rapid, high throughput microplate-based fluorescence approach for the convenient and cost-effective measurement of amikacin in pharmaceutical formulations. In comparison to previously published approaches, the suggested method allowed for quick analysis of a high number of samples in a short amount of time (96 samples in 125 seconds), resulting in an average duration of analysis of 1.3 seconds per sample.

Rapid determination of aminoglycosides in pharmaceutical preparations by electrospray ionization mass spectrometry

Aminoglycosides are broad-spectrum antibiotics often employed to combat Gram-negative bacterial infections. A technique based on electrospray-ionization mass spectrometry (ESI-MS) was developed for rapid determination of aminoglycosides. This method, which does not require prior chromatographic separation, or derivatization and extensive sample preparation steps, was deployed to estimate gentamicin, tobramycin, and amikacin in pharmaceutical formulations. Upon gas-phase collisional activation, protonated gentamicin, tobramycin, and amikacin undergo a facile loss of their respective “C” ring moiety to produce characteristic ions of m/z 322, 324, and 425, respectively. The mass spectral peak intensities for these specific product ions were monitored either by a flow-injection analysis selected-ion monitoring (FIA-SIM) time-intensity method or by a mass spectrometric internal-standard method. The linear dynamic ranges of detection for both methods were evaluated to be 10–1000 ng/mL for gentamicin, 25–2500 ng/mL for tobramycin, and 10–1000 ng/mL for amikacin. The internal-standard mass spectrometric method afforded lower intra-day and inter-day variations (2.3–3.0% RSD) compared to those from FIA-SIM method (4.5–5.0% RSD). This method was applied as a potential alternative procedure to determine gentamicin in commercial pharmaceutical samples and to monitor the release of gentamicin from “self-defensive” tannic acid-based layer-by-layer films into phosphate buffer solutions at different pHs.

Transdermal delivery of gentamicin using dissolving microneedle arrays for potential treatment of neonatal sepsis

Neonatal infections are a leading cause of childhood mortality in low-resource settings. World Health Organization guidelines for outpatient treatment of possible serious bacterial infection (PSBI) in neonates and young infants when referral for hospital treatment is not feasible include intramuscular gentamicin (GEN) and oral amoxicillin. GEN is supplied as an aqueous solution of gentamicin sulphate in vials or ampoules and requires health care workers to be trained in dose calculation or selection of an appropriate dose based on the patient's weight band and to have access to safe injection supplies and appropriate sharps disposal. A simplified formulation, packaging, and delivery method to treat PSBI in low-resource settings could decrease user error and expand access to lifesaving outpatient antibiotic treatment for infants with severe infection during the neonatal period. We developed dissolving polymeric microneedles (MN) arrays to deliver GEN transdermally. MN arrays were produced from aqueous blends containing 30% (w/w) of GEN and two polymers approved by the US Food and Drug Administration: sodium hyaluronate and poly(vinylpyrrolidone). The arrays (19 × 19 needles and 500 μm height) were mechanically strong and were able to penetrate a skin simulant to a depth of 378 μm. The MN arrays were tested in vitro using a Franz Cell setup delivering approximately 4.45 mg of GEN over 6 h. Finally, three different doses (low, medium, and high) of GEN delivered by MN arrays were tested in an animal model. Maximum plasma levels of GEN were dose-dependent and ranged between 2 and 5 μg/mL. The time required to reach these levels post-MN array application ranged between 1 and 6 h. This work demonstrated the potential of dissolving MN arrays to deliver GEN transdermally at therapeutic levels in vivo.

Biomimetic Extracellular Environment Based on Natural Origin Polyelectrolyte Multilayers

Surface modification of biomaterials is a well-known approach to enable an adequate biointerface between the implant and the surrounding tissue, dictating the initial acceptance or rejection of the implantable device. Since its discovery in early 1990s layer-by-layer (LbL) approaches have become a popular and attractive technique to functionalize the biomaterials surface and also engineering various types of objects such as capsules, hollow tubes, and freestanding membranes in a controllable and versatile manner. Such versatility enables the incorporation of different nanostructured building blocks, including natural biopolymers, which appear as promising biomimetic multilayered systems due to their similarity to human tissues. In this review, the potential of natural origin polymer-based multilayers is highlighted in hopes of a better understanding of the mechanisms behind its use as building blocks of LbL assembly. A deep overview on the recent progresses achieved in the design, fabrication, and applications of natural origin multilayered films is provided. Such films may lead to novel biomimetic approaches for various biomedical applications, such as tissue engineering, regenerative medicine, implantable devices, cell-based biosensors, diagnostic systems, and basic cell biology.

Fit-for-purpose chromatographic method for the determination of amikacin in human plasma for the dosage control of patients

In this paper, a simple, rapid and sensitive method based on liquid chromatography with fluorimetric detection (HPLC-FLD) for the determination of amikacin (AMK) in human plasma is developed. Determination is performed by pre-column derivatization of AMK with ortho-phtalaldehyde (OPA) in presence of N-acetyl-L-cysteine (NAC) at pH 9.5 for 5 min at 80 °C. In our knowledge, this is the first time that NAC has been used in AMK derivatization. Derivatization conditions (pH, AMK/OPA/NAC molar ratios, temperature and reaction time) are optimized to obtain a single and stable, at room temperature, derivative. Separation of the derivative is achieved on a reversed phase LC column (Kromasil C18, 5 μm, 150 × 4.6 i.d. mm) with a mobile phase of 0.05 M phosphate buffer:acetonitrile (80:20, v/v) pumped at flow rate of 1.0 mL/min. Detection is performed using 337 and 439 nm for excitation and emission wavelengths, respectively. The method is fitted for the purpose of being a competitive alternative to the currently used method in many hospitals for AMK dosage control: fluorescence polarization immunoassay (FPIA). The method exhibits linearity in the 0.17-10 µg mL(-1) concentration range with a squared correlation coefficient higher than 0.995. Trueness and intermediate precision are estimated using spiked drug free plasma samples, which fulfill current UNE-EN ISO15189:2007 accreditation schemes. Finally, for the first time, statistical comparison against the FPIA method is demonstrated using plasma samples from 31 patients under treatment with AMK.

Changes in the distribution of type II transmembrane serine protease, TMPRSS2 and in paracellular permeability in IPEC-J2 cells exposed to oxidative stress

The effect of oxidative stress on barrier integrity and localization of transmembrane serine proteinase 2 (TMPRSS2) were studied using porcine epithelial IPEC-J2 cells on membrane inserts. Increased paracellular permeability of FITC-dextran 4 kDa (fluorescence intensity 43,508 ± 2,391 versus 3,550 ± 759) and that of gentamicin (3.41 ± 0.06 % increase to controls) were measured parallel with the reduced transepithelial electrical resistance (23.3 ± 4.06 % decrease) of cell layers 6 h after 1 h 1 mM H2O2 treatment. The immunohistochemical localization of adherens junctional β-catenin was not affected by reactive oxygen species (ROS) up to 4 mM H2O2. Peroxide-triggered enhanced paracellular permeability of IPEC-J2 cell layer was accompanied by predominantly cytoplasmic occurrence of TMPRSS2 embedded in cell membrane under physiological conditions. These results support that ROS can influence paracellular gate opening via multifaceted mode of action without involvement of β-catenin redistribution in adherens junction. Altered distribution pattern of TMPRSS2 and relocalized transmembrane serine protease activity may contribute to weakening of epithelial barrier integrity under acute oxidative stress.

Development of a liquid chromatographic method for the quantification of paromomycin. Application to in vitro release and ex vivo permeation studies

We have developed a reversed phase high performance liquid chromatography pulsed amperometric detection (RPHPLC-PAD) method for the determination of paromomycin. It is sensitive, repeatable, and selective without the pretreatment step. Trifluoroacetic acid-water was utilized as the eluent and detected by PAD under NaOH alkaline conditions. The paromomycin detection limit (S/N=3.3) was 2μgmL(-1) and the quantification limit (S/N=10) was 6μgmL(-1). Coefficients of linear regression were higher than 0.99 for concentrations between 6.25 and 200μgmL(-1). The intra and inter-day precision (RSD) was less than 6.5%. The average recoveries were 97.53-102.01%. The proposed HPLC-PAD method presented advantageous performance characteristics and it can be considered suitable for the evaluation of paromomycin loaded nanogel formulation in ex vivo permeation and in vitro release studies.

Reagent-free determination of amikacin content in amikacin sulfate injections by FTIR derivative spectroscopy in a continuous flow system

The quantitative estimation of amikacin (AMK) in AMK sulfate injection samples is reported using FTIR-derivative spectrometric method in a continuous flow system. Fourier transform of mid-IR spectra were recorded without any sample pretreatment. A good linear calibration (r>0.999, %RSD<2.0) in the range of 7.7–77.0 mg/mL was found. The results showed a good correlation with the manufacturer's and overall they all fell within acceptable limits of most pharmacopoeial monographs on AMK sulfate.

A simple and rapid high-performance liquid chromatographic method for determining tobramycin in pharmaceutical formulations by direct UV detection

Background:

Tobramycin, an aminoglycoside antibiotic, is a polar pharmaceutical compound which lacks a UV absorbing chromophore. Due to the absence of a UV absorbing chromophore and high polar nature of this antibiotic, the analysis of such compounds becomes a major challenge.

Objective:

To overcome these problems, a novel method for the determination aminoglycoside tobramycin was developed and validated based on reversed-phase high-performance liquid chromatography (RP-HPLC) with UV detector.

Materials and Methods:

An isocratic mobile phase consists of buffer 0.05 M diammonium hydrogen phosphate, pH adjusted to 10.0 using tetramethyl ammonium hydroxide. Chromatography was carried out at 25°C on a Purosphere RP-8e, 250 mm × 4.6 mm, 5mm. The detection was carried out using variable wavelength UV-Vis detector set at 210 nm. The compounds were eluted isocratically at a steady flow rate of 1.0 mL/min.

Result and Discussion:

Tobramycin retention time was about 9.0 min with an asymmetry factor of 1.4. A logarithmic calibration curve was obtained from 0.47 to 0.71 mg/mL (r > 0.9998). Within-day %RSD was 0.29 (n = 6, 0.60 mg/mL) and between-day %RSD was 0.54 Specificity/ selectivity experiments revealed the absence of interference from excipients, recovery from spiked samples was between 99.0–100.0 percent.

Conclusions:

A HPLC method based on UV detection has been developed and validated for determination of tobramycin from ophthalmic solution. The method is simple, rapid, specific, accurate (error 0.80%), precise (RSD <2.0%) and linear (r2=0.9998). The described method is suitable for routine analysis and quality control of ophthalmic solution containing tobramycin.

Micro-scale analysis of aminoglycoside antibiotics in human plasma by capillary liquid chromatography and nanospray tandem mass spectrometry with column switching

A simple liquid chromatographic method combined with tandem mass spectrometry (LC-MS-MS) is described for the analysis of aminoglycoside antibiotics. Clinically these antibiotics may cause both ototoxicity and nephrotoxicity; therefore, the monitoring of aminoglycoside levels in patient plasma is required for protecting human health. In this study separation of the method is based on ion-pair chromatographic technology on a short capillary reversed-phase C18 column. The method was successfully applied to analyze amikacin in human plasma. In human plasma after deproteinisation with HFBA, an aliquot of 1 microL supernatant was injected into the chromatographic system. Only a small amount of plasma sample, 10 microL, is sufficient for the monitoring of amikacin levels in clinically therapeutic range. The relative standard deviations (RSD) of the method for intra- and inter-day analyses (n=5) are less than 5.8%. Application of this method for the trace analysis of amikacin in human plasma proved simple and workable.

Quantitative determination of dihydrostreptomycin in bovine tissues and milk by liquid chromatography-electrospray ionization-tandem mass spectrometry

Dihydrostreptomycin (DHS) is an aminoglycoside antibiotic used in veterinary medicine in combination with benzylpenicillin for the treatment of bacterial infections in cattle, pigs and sheep. A method to determine its residues in edible tissues of cattle, as well as in milk, was developed and validated. Extraction of DHS from the tissues was performed using a liquid extraction with a 10 mM phosphate buffer containing 2% (w/v) trichloroacetic acid, while milk samples were treated with a 50% (w/v) trichloroacetic acid solution, followed by a solid-phase clean-up procedure on a carboxypropyl (CBA) weak cation exchange column. Ion-pair chromatography, using a mixture of 20 mM pentafluoropropionic acid in water and acetonitrile as the mobile phase, was used to retain DHS and the internal standard streptomycin (STR) on a Nucleosil (5 microm) reversed-phase C18 column. The components were detected and quantified by electrospray ionization (ESI) tandem mass spectrometry. The method could be validated according to EC (European Community) requirements with respect to linearity, trueness and precision, the latter evaluated at the maximum residue limit (MRL) - 1000 ng g(-1) for kidney, 500 ng g(-1) for muscle, liver and fat, and 200 ng g(-1) for milk -, at one-half of the MRL and at one and a half times the MRL. A limit of quantification of 10 ng g(-1) and 1 ng ml(-1) was obtained for all tissues and for milk, respectively, which is far below one-half of the MRL as requested, while the limit of detection was in the low ppb range, varying between 1.9 and 4.2 ng g(-1) for the different tissues tested, and being 0.6 ng ml(-1) for milk. The method was used for the monitoring of DHS residues in incurred tissue and milk samples coming from cattle medicated with DHS in combination with benzylpenicillin by intramuscular injection, in order to evaluate withdrawal times.

On-line concentration of neomycin and screening aminoglycosides in milk by short capillary column and tandem mass spectrometry

An MS-MS method was established for the trace analysis of neomycin and screening aminoglycoside antibiotics (such as amikacin, gentamicin, kanamycin, and tobramycin) in a milk sample. The extraction and purification are based on ion-pair SPE technology on a short fused-silica capillary RP C18 column. The capillary SPE column provided the stationary phase to retain aminoglycoside antibiotics and MS-MS compatible organic acid heptafluorobutyric acid (HFBA) was used as protein precipitation and ion-pair reagent. Aminoglycosides were extracted in this short column and directly eluted to MS-MS without evaporating to dryness and reconstituted with MS-MS compatible solvent after SPE. The LOQ was 0.1 microg/mL and the calibration curve was linear up to 6.4 microg/mL. A small amount of milk product, 10 microL, is sufficient for the analysis and application of this method as the trace analysis of neomycin in the biological matrix proved simple and workable.

Determination of amikacin in body fluid by high-performance liquid-chromatography with chemiluminescence detection

A simple and sensitive method was developed for the quantification of amikacin in human plasma and urine samples. The method involves centrifugation of body fluid plasma after dilution with an ethanol/sodium carbonate mixture, and then an aliquot of the supernatant is directly injected into the chromatograph. After separation on a reversed-phase C18 column (runtime 20 min), aminoglycoside is detected on the basis of its complex formation reaction with Cu(II), the catalyst of the luminol/hydrogen peroxide chemiluminescence system. Using a volume of 500 microl biological sample, linearity is established over the concentration range 0.15-2.0 microg/ml and the limit of detection (LOD) is ca. 50 microg/l in plasma or urine. The intra-day and inter-day precision (measured by relative standard deviation, R.S.D.%) are always less than 9%, and relative recoveries are found to be over 92%.

Rapid and sensitive determination of aminoglycoside antibiotics in water samples using a strong cation-exchange chromatography non-derivatisation method with chemiluminescence detection

A simple and sensitive chemiluminescence (CL) detection approach was developed for the direct analysis of aminoglycoside antibiotics in water samples following strong cation-exchange chromatographic (SCX-HPLC) separation. This detection system, which eliminates the need for sample derivatisation, is based on the inhibitory effect of aminoglycosides on the CL reaction between luminol and hydrogen peroxide catalysed by copper(II). As the operational and chemical variables that affect the CL signal were optimised, ionic strength and the Triton X-100 micelles turned out to be the keys to obtain maximum CL efficiency. Aminoglycosides were successfully separated in 10 min on a SCX column using a mobile phase consisting of an aqueous solution containing 5.0 x 10(-3)mol/l sodium acetate and 0.65 mol/l sodium chloride at pH 6.1. Sample volumes of 50 ml were preconcentrated by passage through a weakly acidic IRC-50 exchange column. Limits of detection from 0.7 to 10 microg/l and relative standard deviations from 2.7 to 5.4% were thus obtained. The proposed method surpasses other chromatographic alternatives in terms of the limit of detection, sample requirements for analysis and cost.

Use of in vitro critical inhibitory concentration, a novel approach to predict in vivo synergistic bactericidal effect of combined amikacin and piperacillin against Pseudomonas aeruginosa in a systemic rat infection model

PURPOSE

This study was undertaken to explore the use of in vitro critical inhibitory concentration (CIC) as a surrogate marker relating the pharmacokinetic (PK) parameters to in vivo bactericidal synergistic effect [pharmacodynamic (PD)] of amikacin + piperacillin combination against Pseudomonas aeruginosa in a systemic rat infection model.

METHODS

The in vitro antibacterial activities of amikacin and piperacillin, alone and in combinations at various ratios of the concentrations, were tested against a standard [5 x 10(5) colony-forming units (CFU)/ml] and a large (1.5 x 10(8) CFU/ml) inoculum of P. aeruginosa ATCC 9027 using a modified survival-time method. The CIC of each individual antibiotic for the different combinations was determined using a cup-plate method. In vivo studies were performed on Sprague-Dawley rats using a systemic model of infection with P. aeruginosa ATCC 9027. PK profiles and in vivo killing effects of the combination at different dosing ratios were studied.

RESULTS

An inoculum effect was observed with the antibiotics studied. Synergy was seen against both the inocula at the following concentration ratios: 70% C(ami) + 30% C(pip) and 75% C(ami) + 25% C(pip), where C(ami) and C(pip) are the concentrations of amikacin and piperacillin to produce a 1000-fold decrease in bacterial population over 5 h, respectively. The CIC values determined corroborated with the order of in vitro bacterial killing observed for the antibiotic combinations. The dosing ratio of 12.6 mg/kg amikacin + 36 mg/kg piperacillin (a 70:30 ratio of the individual doses) exhibited the greatest killing in vivo when compared to the other ratios. The PK-PD relationships were described by simple, linear regression equations using the area under the in vivo killing curve as a PD marker and the AUCIC(ami)/CIC(ami) + AUCIC(pip)/CIC(pip), AUC(ami)/CIC(ami) + AUC(pip)/CIC(pip), C(max,ami)/CIC(ami) + C(max,pip)/CIC(pip), and AUCIC(ami)/MIC(ami) + AUCIC(pip)/MIC(pip) as PK markers for the amikacin + piperacillin combination.

CONCLUSION

The combination of amikacin and piperacillin exhibited synergistic killing effect on P. aeruginosa that could be modeled using CIC as a surrogate marker relating the PK parameters to in vivo bactericidal effect.

Determination of Streptomycin in a Pharmaceutical Sample Based on Its Degradation by Hydrogen Peroxide in the Presence of Copper(II)

The kinetics of streptomycin degradation by hydrogen peroxide at pH 7.4 was investigated. The reaction was catalyzed by traces of Cu(II) ions, and it was followed spectrophotometrically at 322 nm by applying the initial-rate method. The kinetic parameters of the reaction are reported, and a rate equation is suggested. From the dependence of the relative rate constants on the temperature, the activation energy was calculated to be 57.5 kJ/mol. Based on this reaction, a kinetic method for streptomycin determination is proposed. The calibration graph is linear in the ranges 1.94 - 15.48 microg/cm(3) and 0.15 - 1.94 microg/cm(3). The influence of foreign ions and molecules on the accuracy of the determinations was investigated. The proposed kinetic method has high selectivity and good sensitivity, and enabled to determine streptomycin in pharmaceutical samples.

A new method for the analysis of amikacin using 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) derivatization and high-performance liquid chromatography with UV-detection

A simple and sensitive reversed-phase liquid chromatographic method has been developed for the determination of amikacin (AMK) by derivatization. The method is based on the pre-column derivatization of AMK with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC). The derivatization reaction proceeds in aqueous solution at room temperature with a borate buffer of pH 8.0. The formation of the corresponding derivative of AMK is instantaneous and it is stable for more than 36 h. Detection was performed by UV-absorption instead of fluorescence. Several factors influencing the derivatization reaction yields were studied and optimized. The system offered the following analytical parameters: limit of detection (LOD) of 0.068 micro g ml(-1) (3sigma), linear correlation coefficient of 0.9998 and linear range response from 2 to 50 microg ml(-1). The precision of the method was <1%. As a preliminary application, the method has been successfully applied to the amikacin determination in parenteral pharmaceutical formulations.

Antibiotic Elution from Hydroxyapatite Cement Cranioplasty Materials

Hydroxyapatite cements (HAC) are a contemporary material used for multiple cranioplasty applications. In an effort to decrease the risk of postoperative infection, mixing antibiotics into the material during intraoperative application is frequently done. It has been assumed, but never substantiated, that significant antibiotic release from the material occurs after implantation. Using standardized morphologies, a mixture of a specific HAC (Mimix bone void filler) and tobramycin antibiotic was prepared, hydrated in phosphate-buffered saline, and tested in vitro for as long as 22 days after preparation. The results show that the majority of the antibiotic (91%) was released within the first 24 hours, with the balance being eluted during the next 8 days. Overall, the release of tobramycin from Mimix bone void filler appears to fit the pattern of antibiotic release demonstrated to occur from other bioabsorbable ceramic-type carriers.

Development and validation of a novel HPLC/ELSD method for the direct determination of tobramycin in pharmaceuticals, plasma, and urine

A novel method for the direct determination of the aminoglycoside tobramycin was developed and validated based on reversed-phase high-performance liquid chromatography (RP-HPLC) with evaporative light scattering detector (ELSD). Using a Waters ODS-2 C18 Spherisorb column with an evaporation temperature of 45 degrees C and nitrogen pressure of 3.5 bar, the selected mobile phase consisted of water/acetonitrile 55:45 containing 1.5 mL L(-1) HFBA (11.6 mM) in an isocratic mode at a rate of 1.0 mL min(-1). Tobramycin's retention time was 4.3 min with an asymmetry factor of 1.7. A logarithmic calibration curve was obtained from 1 to 38 microg mL(-1) (r > 0.9998). LOD was 0.3 microg mL(-1); within-day %RSD was 1.0 (n = 3, 4.7 microg mL(-1)) and between-day %RSD was 1.1 (3 days within a week). The developed method was applied to the determination of tobramycin in a pharmaceutical crude substance and formulations (eye drops and ointments). Dilution experiments revealed the absence of interference from excipients (no constant and proportional errors); recovery from spiked samples was 99-103% with %RSD < 2.2 (n = 3x3). The developed HPLC/ELSD method was also found to be applicable in the determination of tobramycin in human plasma (0.6-12.5 microg mL(-1)) and urine (1.5-12.5 microg mL(-1)) after solid-phase extraction using carboxylate cartridges followed by solvent evaporation (x2 preconcentration). A mean recovery of 86% for plasma and 91% for urine was obtained.

Rapid and selective micellar electrokinetic chromatography for simultaneous determination of amikacin, kanamycin A, and tobramycin with UV detection and application in drug formulations

A simple and selective micellar electrokinetic chromatography (MEKC) with UV detection is described for simultaneous determination of amikacin, tobramycin, and kanamycin A, performed in Tris buffer (180 mM; pH 9.1) with 300 mM sodium pentanesulfonate (SPS) as an anionic surfactant. Under this condition, good separation with high efficiency and the required short analysis time is achieved. The linear ranges of the method for the determination of amikacin, tobramycin, and kanamycin A were 0.1-0.5 mg / mL, 0.4-2.0 mg / mL, and 0.4-2.0 mg / mL, respectively; the detection limits (signal-to-noise ratio = 3; injection, 0.5 psi 5 s) were 0.08, 0.2, and 0.2 mg / mL, respectively. The small amount of sample required and the expeditiousness of the procedure allow content uniformity to be determined in individual commercial products.

Enzyme immunoassays for the analysis of streptomycin in milk, serum and water: development and assessment of a polyclonal antiserum and assay procedures using novel streptomycin derivatives

A polyclonal antiserum to streptomycin was generated in sheep using a streptomycin-bovine serum albumin conjugate as immunogen. Streptomycin was linked to the carrier protein with cyanuric chloride using a new two-step conjugation method. Plate coating antigen conjugates of streptomycin and gelatine were prepared using either cyanuric chloride (homologous bridge) or 1,4-butanediol diglycidyl ether to provide an heterologous complex. The reagents enabled the generation of a specific antiserum with a titre of 1/40,000 and the development of a sensitive ELISA method suitable for the measurement of streptomycin sulfate in milk, serum and water samples. A minimum detection value of 1 ng mL(-1) and a dynamic range of 1 to 200 ng mL(-1) were demonstrated in the three matrices. No detectable cross reactivity with any of the common aminoglycosides was found except the related dihydrostreptomycin which gave a 75% cross reaction value. The details of the preparation of the hapten-protein conjugates, characterisation of the antiserum and assay construction and assessment methods are presented. The introduction of new coupling methods and antibody assessment provide improved basic methodologies necessary for the advancement of immuno-analysis of streptomycin, one of the most widely used antimicrobial substances.

In vitro analysis of the elution of tobramycin from a calcium sulfate bone void filler

The use of synthetic calcium-based bone replacements has a recent history in craniofacial surgery as a non- to minimally load-bearing graft substitute. Given its avascular nature at the time of placement, infection is an ever present risk. Antibiotics are often added to the material during surgery based on an empirical impression. Whether effective antibiotic release actually occurs and over what time are not known for many of the available calcium-based preparations. The purpose of this study was to investigate the release kinetics of tobramycin from molded cylinders of Calcigen S bone void filler (Biomet, Warsaw, IN) and to compare this with the release kinetics of tobramycin from plaster of Paris-based systems as reported in the literature. Calcigen S bone void filler is a form of calcium sulfate that is closely related to plaster of Paris yet remains distinct. In vitro studies as well as clinical series have demonstrated that plaster of Paris is an effective vehicle to deliver tobramycin in which therapeutic doses of the antibiotic are released after implantation. In vitro analysis of the elution of tobramycin from Calcigen S bone void filler substrate is similar to that of plaster of Paris.

Shelf lives of aseptically prepared medicines—stability of netilmicin injection in polypropylene syringes

There is no published information on the stability of netilmicin solutions in prefilled syringes. The purpose of this study was to evaluate the stability of netilmicin in polypropylene syringes and to determine the optimum validated shelf life so that they may be prepared in bulk in appropriately licensed facilities. The syringes containing netilmicin 10 or 100mg/ml were stored at 7 degrees C, room temperature in the light (RTL) and 25 degrees C/60% relative humidity for up to 300 days. Netilmicin concentration was determined by reversed phase high performance liquid chromatography (RP-HPLC) of the isoindole derivative formed with o-phthalaldehyde (OPA). The shelf lives were calculated using the maximum rate method applied to the netilmicin analytical data. At 7 degrees C 10 and 100mg/ml solutions were stable for 90 days falling to 30 days at 25 degrees C and 60% RH. At RTL the 10mg/ml solution was stable for 9 days.

Determination of tobramycin in serum using liquid chromatography-tandem mass spectrometry and comparison with a fluorescence polarisation assay

We have developed a tandem mass spectrometry (LC-MS-MS) method for measuring tobramycin concentrations in serum samples and have compared it with a fluorescence polarisation immunoassay. After protein precipitation with acetonitrile supernatant was injected into the LC-MS-MS system. A C(18) cartridge (4x2 mm) was eluted with a step gradient of 20-100% methanol containing HFBA. The retention times were, tobramycin 1.05 min and sisomycin 1.05 min. The MRM transitions were: m/z 467.8>163 (tobramycin) and m/z 447.8>160 (sisomycin). The limit of quantification was 0.15 mg/l and the assay was linear up to 50 mg/l. Assay precision was <6% within and between batch.

Analytical method for the determination of the aminoglycoside gentamicin in hospital wastewater via liquid chromatography-electrospray-tandem mass spectrometry

A method for the determination of gentamicin residues in hospital wastewater has been developed using kanamycin as a surrogate standard. The method consists of solid-phase extraction (SPE) and detection by ion-pair chromatography with electrospray tandem mass spectrometry (LC-ES-tandem MS). The SPE was performed on a weak cation exchanger. Filtration should be avoided in the sample preparation, otherwise a significant loss of gentamicin occurs. Chromatographic separation on a C18-column was achieved using a ternary eluent containing methanol, water and 1(-1) heptafluorobutyric acid solution. Mean relative recoveries of the analytes in hospital wastewater varied between 107 and 111%. The limit of quantification (LOQ) was 0.20 microg l(-1) in hospital wastewater. Gentamicin was found in native hospital wastewater in a concentration range between 0.4 and 7.6 microg l(-1).

Development of generic continuous-flow enzyme immunoassay system for analysis of aminoglycosides in serum

A simple generic continuous-flow enzyme immunoassay (CFEIA) for analysis of aminoglycosides in serum has been successfully developed. The developed assay employed a specific monoclonal antibody and beta-galactosidase (beta-GAL) enzyme as label. The assay involves an off-line competitive binding reaction between the analyte and free labelled analyte for the binding sites of the antibody. After equilibrium is reached, the sample was injected into the flow system. The bound antibody complexes with the analyte and the labelled analyte were trapped in a protein G column, while the unbound free labelled analyte was eluted and detected colorimetrically down-stream, after reaction with chlorophenolic red-beta-D-galactopyranoside as a substrate for the beta-GAL enzyme. The concentration of the analyte in a sample was quantified by its ability to inhibit the binding of the analyte-enzyme conjugate to the antibody, and the signal was directly proportional to the concentration of the analyte in the original sample. The optimum conditions for the developed CFEIA were investigated and applied to the analysis of tobramycin, as a representative example of the aminoglycosides, in serum samples. The detection limit of the assay was 0.06 microgml(-1). The assay showed good precision; the coefficients of variation were 2.49-4.33 and 3.30-6.82% for intra- and inter-assay precision, respectively. Serum matrix constituents and the endogenous compounds did not interfere with the assay. Analytical recovery of spiked tobramycin, in the concentration range between 0.5 and 8.0 microgml(-1), was 101.55+/-3.14. The assay results correlated well with those obtained by high-performance liquid chromatography (r=0.991). All the obtained results strongly demonstrate that the developed CFEIA is a suitable method for a rapid and reliable analysis of aminoglycosides in serum.

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%.

HPLC separation of antibiotics present in formulated and unformulated samples

Analysis of antibiotics in formulated and unformulated samples demand a highly specific and rapid method as many antibiotics (e.g. beta-lactams) have serious stability problems. HPLC techniques can provide a valuable tool for generating highly pure preparations for characterizing the antimicrobial activities. In the present review article, column and mobile phase conditions for the various classes of antibiotics viz. penicillins, cephalosporins, macrolides, tetracyclines, aminoglycosides, quinolones, rifamycins etc. have been presented from April 1998 to November 2000. A brief discussion on chemical structure, spectrum of activity and action mechanism of each class has also been given.

Spectrofluorimetric determination of streptomycin in dosage forms and in spiked plasma using 9,10-phenanthraquinone

A simple and highly sensitive method is proposed for the fluorimetric determination of streptomycin in dosage forms and in biological fluids. The method involves the reaction of streptomycin with 9,10-phenanthraquinone in alkaline medium to give a highly fluorescent derivative. The experimental parameters were carefully studied and incorporated into the procedures. The results obtained compared favourably with those obtained by the official methods. The concentration-fluorescence plots were rectilinear over the range 0.025-0.4 microg/ml, with minimum detectability (S/N=2) 0.006 microg/ml (4.19x10(-9) M). The proposed method was applied for the determination of streptomycin in dosage forms. The results obtained were in good agreement with those obtained by the official method. The proposed method was further applied to the determination of streptomycin in human plasma. The percentage recovery was 101.82. A proposal of the reaction pathway was presented.

Chromatography of guanidino compounds

Guanidino compounds involved in the urea and guanidine cycles have been found in serum of nephritic patients, and some guanidino compounds have been suspected to be uremic toxins. The simultaneous analysis of naturally occurring metabolites is important for diagnosis of diseases. In this review, liquid chromatographic analysis of natural metabolites of guanidino compounds are described. the information about arginine as a precursor of nitric oxide are included. The reports of pharmaceutical compounds having a guanidino group, peptides containing arginine and aminoglycosides are summarized in Table 1.

Current methodologies for the analysis of aminoglycosides

The aminoglycosides are a large and diverse class of antibiotics that characteristically contain two or more aminosugars linked by glycosidic bonds to an aminocyclitol component. Structures are presented for over 30 of the most important members of this family of compounds. The use of aminoglycosides in clinical and veterinary medicine and in agriculture is described. Qualitative methods for aminoglycoside analysis include X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). The major part of this article comprises a comprehensive review of quantitative methods for the determination of aminoglycosides. These are microbiological assay, radiochemical assay, radioimmunoassay, enzyme immunoassay, fluoroimmunoassay and other immunoassays, spectrophotometric and other non-separative methods, gas chromatography (GC), thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and capillary electrophoresis (CE). Simple spectrophotometric methods may be adequate for the assay of bulk pharmaceuticals and their formulations. Microbiological assays make useful semi-quantitative screening tests for the analysis of veterinary drug residues in food, but rapid enzyme immunoassays are more suitable for accurate measurements of aminoglycosides in complex matrices. Automated immunoassays are the most appropriate methods for serum aminoglycoside determinations during therapeutic drug monitoring. HPLC techniques provide the specificity and sensitivity required for pharmacokinetic and other research studies, while HPLC-MS is employed for the confirmation of veterinary drug residues. The potential for further development of chromatographic and CE methods for the analysis of biological samples is outlined.