High-performance liquid chromatographic analysis of aminoglycoside antibiotics

Case Studies on the use of Microsampling for Nonclinical Studies in Pharmaceutical Drug Discovery and Development

The implementation of microsampling approaches for use in nonclinical discovery and development pharmaceutical studies can have a major impact on improving animal ethics through the use of fewer animals and less invasive procedures for the collection of toxicokinetic and pharmacokinetic samples. In addition, the approach offers the opportunity for obtaining improved quality of data for these studies. This can include the determination of additional timepoints and endpoints, and the ability to obtain exposure data from the same animals utilized to measure other study endpoints. This manuscript presents a number of cases where a variety of microsampling approaches have been successfully implemented by a number of organizations and serves as a guide for those considering the use of microsampling approaches as part of their drug discovery and development programs, as the adoption of these approaches are not yet universal.

Simple spectrofluorimetric methods for determination of veterinary antibiotic drug (apramycin sulfate) in pharmaceutical preparations and milk samples

This work describes the development of highly sensitive as well as simple two spectrofluorimetric methods for the determination of apramycin sulfate. The first method depends on measuring the inherent native fluorescence of the aqueous neutral solution of the drug at 388 nm (λ_ex 335 nm). While the second method mainly based on enhancing the native fluorescence intensity of the drug using sodium dodecyl sulfate (SDS) micellar media by about 4 fold enhancement. The fluorescence intensity - concentration relationship for the two methods was found rectilinear over the concentration range 1.0-100.0 and 0.1-20.0 μg/mL for the first and second method respectively. The limit of detection for method I and II were 0.05 and 0.02 μg/mL respectively. The proposed methods can be effectively connected for the assurance of the medication without impedances from common normal excipients. Furthermore, the two methods were high sensitive enough for the assurance of the drug in spiked milk samples with high percentage recoveries.

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.

Uncertainty in Antibiotic Dosing in Critically Ill Neonate and Pediatric Patients: Can Microsampling Provide the Answers?

PURPOSE

With a decreasing supply of antibiotics that are effective against the pathogens that cause sepsis, it is critical that we learn to use currently available antibiotics optimally. Pharmacokinetic studies provide an evidence base from which we can optimize antibiotic dosing. However, these studies are challenging in critically ill neonate and pediatric patients due to the small blood volumes and associated risks and burden to the patient from taking blood. We investigate whether microsampling, that is, obtaining a biologic sample of low volume (<50 μL), can improve opportunities to conduct pharmacokinetic studies.

METHODS

We performed a literature search to find relevant articles using the following search terms: sepsis, critically ill, severe infection, intensive care AND antibiotic, pharmacokinetic, p(a)ediatric, neonate. For microsampling, we performed a search using antibiotics AND dried blood spots OR dried plasma spots OR volumetric absorptive microsampling OR solid-phase microextraction OR capillary microsampling OR microsampling. Databases searched include Web of Knowledge, PubMed, and EMbase.

FINDINGS

Of the 32 antibiotic pharmacokinetic studies performed on critically ill neonate or pediatric patients in this review, most of the authors identified changes to the pharmacokinetic properties in their patient group and recommended either further investigations into this patient population or therapeutic drug monitoring to ensure antibiotic doses are suitable. There remain considerable gaps in knowledge regarding the pharmacokinetic properties of antibiotics in critically ill pediatric patients. Implementing microsampling in an antibiotic pharmacokinetic study is contingent on the properties of the antibiotic, the pathophysiology of the patient (and how this can affect the microsample), and the location of the patient. A validation of the sampling technique is required before implementation.

IMPLICATIONS

Current antibiotic regimens for critically ill neonate and pediatric patients are frequently suboptimal due to a poor understanding of altered pharmacokinetic properties. An assessment of the suitability of microsampling for pharmacokinetic studies in neonate and pediatric patients is recommended before wider use. The method of sampling, as well as the method of bioanalysis, also requires validation to ensure the data obtained reflect the true result.

Risk of gentamicin toxicity in neonates treated for possible severe bacterial infection in low- and middle-income countries: Systematic Review

OBJECTIVES

To assess the risk of gentamicin toxicity and potential number of neonates exposed annually to this risk, through treatment with WHO-recommended first-line antibiotics (gentamicin with penicillin) for the 6.9 million neonates with possible serious bacterial infection (PSBI).

METHODS

Systematic literature review and assessment of the evidence using Cochrane and GRADE criteria. Meta-analysis was undertaken for pooled estimates where appropriate.

RESULTS

Eleven studies (946 neonates) were included (nine randomised controlled trials and two prospective cohort studies). Six trials reported consistently measured ototoxicity outcomes in neonates treated with gentamicin, and the pooled estimate for hearing loss was 3% (95% CI 0-7%). Nephrotoxicity could not be assessed due to variation in case definitions used. Estimates of the number of neonates potentially affected by gentamicin toxicity were not undertaken due to insufficient data.

CONCLUSION

Given wider scale-up of outpatient-based and lower-level treatment of PSBI, improved data are essential to better assess the risks from neonatal gentamicin treatment without assessment of blood levels, to maximise benefit and reduce harm.

Can finger-prick sampling replace venous sampling to determine the pharmacokinetic profile of oral paracetamol?

WHAT IS ALREADY KNOWN ABOUT THE SUBJECT: Finger-prick blood samples are increasingly used for the clinical and biomedical measurement of drugs and endogenous substance concentration. The use of different sampling sites can give rise to different drug concentration measurements.

WHAT THIS STUDY ADDS

During the absorption phase, the paracetamol concentration in finger-prick blood samples is significantly greater than that in venous blood samples, following oral administration. Finger-prick and venous blood samples will result in equivalent pharmacokinetic parameters of oral paracetamol only after distribution equilibrium is attained. The drive to increase the availability of paediatric pharmacokinetic data with minimum blood loss has led to the development of micro-sampling techniques. However studies have suggested that pharmacokinetic data from venous or capillary blood samples may not be directly comparable.

AIM

The aim of this study was to determine whether paracetamol demonstrates concentration differences between finger-prick and venous blood samples.

METHODS

Paired finger-prick and venous blood samples were taken at 0, 15, 30 and 60 min following 1 g oral paracetamol, from 12 male adult subjects. Paracetamol concentration was determined using HPLC and UV detection with a LLOQ of 2200 pg on column. Intra-assay coefficient of variation for paracetamol at the LLOQ was 3%.

RESULTS

At 15, 30, and 60 min post dose the median finger-prick paracetamol concentration was 349%, 72%, and 9.3% greater than the equivalent venous concentrations, respectively. Regression analysis confirmed a significant relationship between finger-prick and venous paracetamol concentrations at 15 min (r(2) = 0.81, P = 0.006), at 30 min (r(2) = 0.82, P < 0.0001) and at 60 min (r(2) = 0.87, P < 0.0001) post dose. The regression equation for venous and finger-prick blood concentrations at 15, 30 and 60 min post dose were Venous(15) = Finger(15) - 3.4, Venous(30) = Finger(30) - 3.4 and Venous(60) = 0.68 Finger(60) + 3.06, respectively.

CONCLUSIONS

Paracetamol demonstrates an arteriovenous difference in concentration, and the use of finger-prick samples may give rise to results which differ from those obtained with traditional venous sampling especially during the first 1 h following drug ingestion.

Characterization of impurities in sisomicin and netilmicin by liquid chromatography/mass spectrometry

The characterization of unknown impurities present in netilmicin and sisomicin by liquid chromatography (LC) coupled with mass spectrometry (MS) is described. The volatile ion-pairing agent trifluoroacetic acid (TFA) was used for the retention of the main compounds and their impurities on a reversed-phase (RP) C18 column, because they are highly hydrophilic and basic compounds. The method showed good separation between netilmicin and its four potential related substances prescribed in the European Pharmacopoeia, which were identified by comparison of their retention times with those of the reference substances. Furthermore, in total 16 unknown impurities in a netilmicin sample and six in a sisomicin sample with unknown identity were detected. The structures of the unknown compounds were deduced based on comparison of fragmentation patterns with those of the reference substances investigated in LC/MSn experiments by the use of electrospray ion trap mass spectrometry.

Trace analysis of aminoglycoside antibiotics in bovine milk by MEKC with LIF detection

This work describes a straightforward and sensitive method for the multi-residue analysis of aminoglycoside antibiotics (kanamycin B, amikacin, neomycin B and paromomycin I) in bovine milk samples. The method involves the pre-capillary derivatization of antibiotics with sulfoindocyanine succinimidyl ester (Cy5) and their separation and determination by MEKC with LIF detection. The optimum procedure includes a derivatization step of the antibiotics at 25 degrees C for 30 min and direct injection for MEKC analysis, which is performed in about 20 min by using borate buffer (35 mM; pH 9.2) with 55 mM SDS as an anionic surfactant and 20% ACN as the organic modifier. Under these conditions, dynamic ranges of 10-500 microg/L and RSDs (within-day precision) from 3.8 to 5.3% were obtained. These results indicate that the proposed MEKC-LIF method is useful as a selective and sensitive tool for the determination of these antibiotics and surpasses other reported electrophoretic alternatives. Finally, the method was successfully applied to bovine milk samples after a simple solid-phase extraction clean-up and preconcentration procedure. The aminoglycosides were readily detected at 0.5-1.5 microg/kg levels with average recoveries ranging from 89.4 to 93.3%.

A simply and sensitive fluorometric method for determination of gentamicin in liposomal suspensions

A new method for measuring gentamicin in liposomes fluorometrically is described. The assay is based on the reaction between the amino groups in the gentamicin molecule and o-phthaldialdehyde (OPA), under basic pH conditions; the product's fluorescence can be read directly on a simple fluorimeter. The effects of several factors (time of reaction, volume of the OPA reagent, and product stability) were investigated. The standard curve was linear in the concentration range of 0.5-4.0microg, showing an excellent determination coefficient of r(2)=0.99. Additionally, the influence of different liposomal lipids on gentamicin determination was tested. Liposomal lipids containing no free amino groups (PC, Chol, DOTAP) have no influence on the reaction when present in the reaction mixture. In contrast, amino groups containing lipid (SA) showed intense method interference. Therefore, a method of lipid extraction was adapted to remove undesired lipids. The described method was successfully utilised during 2 years of liposomal gentamicin experiments.

Assay of amikacin in the skin by high-performance liquid chromatography

Amikacin is used in the systemic treatment of serious infections, but also locally for the treatment of skin infections. The aim of this work was to develop and validate a simple procedure for amikacin determination inside the epidermal tissue: this implies a simple method for an efficient drug extraction from the skin and a clean and easy HPLC analysis. Amikacin was extracted from epidermis samples with 500 microl of a mixture methanol-water-0.05 M NaOH (5:5:2 v/v/v) at 60 degrees C for 1 h. After filtration, the obtained solution was derivatized (1-fluoro-2,4-dinitrobenzene at 90 degrees C for 10 min) and analyzed by HPLC, on a C18 microBondapack 300 mmx4.6 mm column thermostatted at 45 degrees C. The mobile phase was a mixture of acetonitrile-water-acetic acid (47:53:0.1 v/v/v) at a flow rate of 1.5 ml/min and the UV detector was set at 365 nm. The derivatization and HPLC analysis were validated in the concentration interval 1.64-49.21 microg/ml. The linearity resulted very good (R=0.9995); the R.S.D.% varied between 0.20% and 3.89% depending on the concentration and the ER% was included between 5.4 and 0.9. The extraction method used demonstrated to be specific and the recovery resulted about 93%. The extraction, derivatization and HPLC assay has good reproducibility, sensitivity and specificity resulting in a reliable method for biopharmaceutical studies of AK distribution in the epidermis.

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.

Dried blood spot liquid chromatography assay for therapeutic drug monitoring of metformin

The use of blood spot collection cards is a simple way to obtain specimens for analysis of drugs for the purpose of therapeutic drug monitoring, assessing adherence to medications and preventing toxicity in routine clinical setting. We describe the development and validation of a microanalytical technique for the determination of metformin from dried blood spots. The method is based on reversed phase high-performance liquid chromatography with ultraviolet detection. Drug recovery in the developed method was found to be more than 84%. The limits of detection and quantification were calculated to be to be 90 and 150 ng/ml, respectively. The intraday and interday precision (measured by CV%) was always less than 9%. The accuracy (measured by relative error, %) was always less than 12%. Stability analysis showed that metformin is stable for at least 2 months when stored at -70 degrees C. The small volume of blood required (10 microL), combined with the simplicity of the analytical technique makes this a useful procedure for monitoring metformin concentrations in routine clinical settings. The method is currently being applied to the analysis of blood spots taken from diabetic patients to assess adherence to medications and relationship between metformin level and metabolic control of diabetes.

Oral solid gentamicin preparation using emulsifier and adsorbent

Oral gentamicin (GM) therapy has been challenged by formulating GM in oral solid preparation. GM was dispersed with a surfactant used for the self-microemulsifying drug delivery system (SMEDDS), PEG-8 caprylic/capric glycerides (Labrasol), and the mixture was solidified with several kinds of adsorbents. The used adsorbents were microporous calcium silicate (Florite RE), magnesium alminometa silicate (Neusilin US2), and silicon dioxide (Sylysia 320). In vitro release study showed that the percentage released of GM from each preparation per 2 h was 99.8+/-0.06% for Florite RE 10 mg, 96.7+/-1.16% for Florite RE 20 mg, 98.3+/-0.32% for Neusilin US2, and 94.4+/-0.23% for Sylysia 320. The T50% values were 0.35+/-0.05 h for Florite RE 10 mg, 0.34+/-0.03 h for Florite RE 20 mg, 0.26+/-0.03 h for Neusilin US2, and 0.15+/-0.01 h for Sylysia 320. The in vivo rat absorption study showed that Florite RE 10 mg preparation had the highest C(max) (2.14+/-0.67 microg/ml) and AUC (4.74+/-1.21 microg h/ml). Other preparations had C(max) and AUC of 0.69+/-0.10 microg/ml and 1.56+/-0.43 microg h/ml for Florite RE 20 mg, 1.07+/-0.31 microg/ml and 1.80+/-0.33 microg h/ml for Neusilin US2, and 0.99+/-0.21 microg/ml and 1.77+/-0.50 micorg h/ml for Sylysia 320, respectively. The bioavailability (BA) of GM from the microporous calcium silicate preparation, Florite RE 10 mg, was 14.1% in rats, derived by comparing the AUC obtained after intravenous injection of GM, 1.0 mg/kg, to another group of rats. The microporous calcium silicate preparation using Florite RE 10 mg was evaluated in dogs after oral administration in an enteric capsule, Eudragit S100 (50 mg/dog). High plasma GM levels were obtained (i.e., the C(max) was 1.26+/-0.20 microg/ml and the AUC was 2.59+/-0.33 microg h/ml). These results suggest that an adsorbent system is useful as an oral solid delivery system of poorly absorbable drugs such as GM.

Stability indicating reversed-phase ion-pairing liquid chromatographic determination of vertilmicin sulfate as bulk drug and in injections

A simple reversed-phase high performance liquid chromatographic method was developed for the analysis of vertilmicin sulfate, a novel aminoglycoside (AG). UV detection was used to determine vertilmicin sulfate and its related compounds in drug substance and products without sample derivatization. The method was used to determine the content of vertilmicin and its related compounds and test the stability of vertilmicin sulfate as drug substance and in injections, which was required for registration of new drug.

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.

Evaluation of oral formulations of gentamicin containing labrasol in beagle dogs

Gentamicin (GM) is a polarized water-soluble compound having very poor intestinal membrane permeability resulting in low oral bioavailability. Labrasol was found to improve the intestinal absorption of GM in rats. In the present study, GM formulations containing labrasol were evaluated in beagle dogs after filling into hydroxypropylmethyl cellulose (HPMC) capsules wrapped with Eudragit L100 (Eud L) and Eudragit S100 (Eud S) films. The results of the in vitro drug release studies could not differentiate between two kinds of enteric capsules and among the three kinds of GM formulations. Oral administration of GM solution at a dose of 50.0 mg per dog of GM and 0.60 ml per dog of labrasol has resulted in Cmax values of 2.38 +/- 0.50 microg/ml and 2.30 +/- 0.42 microg/ml with Eud L and Eud S capsules, respectively. The AUC values obtained were also higher at 4.35 +/- 1.31 microg h/ml and 5.34 +/- 0.95 microg h/ml with Eud L and Eud S capsules, respectively. Formulation of GM as a suspension in labrasol has resulted in the decrease of Cmax values by two to four times and AUC values by > 2.5 times compared to the solution formulation. The above results indicate that solution formulation was better over the suspension. An absorbent, synthetic sponge was used to absorb GM solution formulation and encapsulated with Eud L and Eud S capsules. The Cmax and AUC values obtained with sponge formulation were higher than those of suspension formulations but were lower than solution formulations. There was no significant difference in the extent of GM absorption between Eud L and Eud S capsules used for encapsulating GM formulations.

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.

Liquid chromatography analysis of enrofloxacin and ciprofloxacin in chicken blood spotted on filter-paper disks

A simple, low-cost, sensitive and selective LC method was developed for the determination of enrofloxacin and ciprofloxacin in chicken blood. The method was applied to whole blood from a chicken using dried blood spots on filter paper disks. The detection limits of enrofloxacin and ciprofloxacin (100 microl of whole blood on a disk) were 0.005 and 0.01 microg/ml, respectively. The whole procedure was verified in intra-laboratory studies (recoveries of both compounds were above 90%), and its applicability was tested with blood from the chicken receiving enrofloxacin in a single oral dose at a level of 10 mg/kg body mass. The method permits the use of a small volume of blood from a chicken and should be useful for pharmacokinetic studies.

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.

Diethyl ether fraction of Labrasol having a stronger absorption enhancing effect on gentamicin than Labrasol itself

In our previous study, we had reported that Labrasol has a good gastrointestinal (GI) absorption enhancing effect on poorly absorbable drugs. In order to improve further absorption enhancing effect of Labrasol on gentamicin (GM), which is a representative water-soluble, poorly absorbable drug, Labrasol was fractionated with hexane, diethyl ether, ethyl acetate and water. The absorption enhancing effect of each fraction of Labrasol and Labrasol alone were evaluated in vivo using rats. Each test formulation of GM was administered into the rat colon at a dose of 5.0 mg/kg and plasma GM concentrations were measured by a HPLC method. Among the four fractions of Labrasol and Labrasol, diethyl ether fraction showed the strongest absorption enhancing effect on GM. When the doses of diethyl ether fraction were 1.0, 0.5 and 0.1 ml/kg, the Cmax values were 8.95 +/- 1.46, 8.02 +/- 2.14 and 7.41 +/- 1.25 microg/ml, respectively. Moreover, AUC(0-6) values were also maintained at high level, i.e. 27.28 +/- 5.90, 20.32 +/- 3.79 and 19.61 +/- 2.09 microg h/ml. Based on the AUC(0-6) values obtained with each fraction, the rank order of absorption enhancing effect on GM was diethyl ether > ethyl acetate=hexane > aqueous fraction.

Non-derivatization approach to high-performance liquid chromatography-fluorescence detection for aminoglycoside antibiotics based on a ligand displacement reaction

An indirect fluorescence detection method has been developed for detecting the aminoglycoside antibiotics following chromatographic separation. This approach to detection is based on a displacement reaction between the aminoglycosides and a copper(II)-L-tryptophan (L-Trp) complex, Cu(L-Trp)2. The aminoglycosides, which contain multiple amino groups, have strong affinities for the Cu(II) ion and displace L-Trp from the Cu(L-Trp)2 complex. The resulting increase in L-Trp fluorescence, which is quenched when coordinated to Cu(II), is indicative of the presence of the aminoglycoside. Fluorescence titration data indicate that there is a stoichiometric ratio of 1:1 between the reaction of the aminoglycosides with Cu(L-Trp)2. This HPLC detection scheme is implemented postcolumn by mixing a buffered Cu(L-Trp)2 solution with the column eluent prior to detection. The aminoglycosides were separated with the use of a column packed with a polymeric strong cation-exchanger. Separation and detection variables were optimized and are discussed. The detection limits for the aminoglycosides tested ranged from 4.2 to 14.5 ng injected (S/N=3). A linear working curve was achieved for amikacin in the range of 29-586 ng for a six point linearity test. The developed separation and detection scheme was further tested by analyzing commercial pharmaceutical formulations of these antibiotics.

[Determination of streptomycin and dihydrostreptomycin in meat by liquid chromatography/mass spectrometry]

A sensitive and selective method using liquid chromatography-electrospray mass spectrometry (LC-ESI-MS) for the determination of aminoglycoside antibiotics, streptomycin and dihydrostreptomycin, in meat has been developed. The LC separation was performed on a TSK-gel Super ODS column (10 cm x 2 mm i.d.) using 5 mmol/L heptafluoro-n-butyric acid (HFBA)-acetonitrile (88:12) as the mobile phase at a flow rate of 0.18 mL/min. The positive ionization produced typical [M + H]+ molecular ions of both drugs (streptomycin m/z 582; dihydrostreptomycin m/z 584). The calibration graphs for streptomycin and dihydrostreptomycin were rectilinear from 0.25 to 25 ng with selected ion monitoring (SIM). The drugs were extracted with 1% metaphosphoric acid, and the extracts were added to 2 mL of 0.1 mol/L heptanesulfonic acid. The solution was cleaned up on a Bond Elut C18 (500 mg) cartridge. The recoveries of streptomycin and dihydrostreptomycin from swine and bovine muscle fortified at 0.2 microgram/g were 73.2-82.6%, and the detection limits were 0.01 microgram/g for both drugs.

Applications of a copper microparticle-modified carbon fiber microdisk array electrode for the simultaneous determination of aminoglycoside antibiotics by capillary electrophoresis

A copper microparticle-modified carbon fiber microdisk array electrode was fabricated and employed in capillary electrophoresis for the simultaneous determination of the five aminoglycoside antibiotics (AGs) including netilmicin, tobramycin, lincomycin, kanamycin and amikacin. The array electrode exhibited high catalytic activity for AGs, good reproducibility and stability. Under the optimum separation conditions (separation voltage of 6.2 kV, electrophoretic medium of 125 mM NaOH), the five AGs above were baseline separated within 20 min. At a working electrode potential of 0.7 V (versus saturated calomel electrode), the calibration curves were linear over two orders of magnitude of concentration, and the detection limits (SIN=3) were below 2 microM except for lincomycin (6.7 microM). The developed method was successfully employed for the simultaneous determination of the five AGs studied in pharmaceutical injections. The feasibility of this method for the simultaneous determination of lincomycin, kanamycin and amikacin in urine sample was also demonstrated.

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.