Aminoglycoside antibiotics in infectious diseases. An overview

Development of a drug discovery approach from microbes with a special focus on isolation sources and taxonomy

After the successful discoveries of numerous antibiotics from microorganisms, frequent reisolation of known compounds becomes an obstacle in further development of new drugs from natural products. Exploration of biological sources that can provide novel scaffolds is thus an urgent matter in drug lead screening. As an alternative source to the conventionally used soil microorganisms, we selected endophytic actinomycetes, marine actinomycetes, and actinomycetes in tropical areas for investigation and found an array of new bioactive compounds. Furthermore, based on the analysis of the distribution pattern of biosynthetic gene clusters in bacteria together with available genomic data, we speculated that biosynthetic gene clusters for secondary metabolites are specific to each genus. Based on this assumption, we investigated actinomycetal and marine bacterial genera from which no compounds have been reported, which led to the discovery of a variety of skeletally novel bioactive compounds. These findings suggest that consideration of environmental factor and taxonomic position is critically effective in the selection of potential strains producing structurally unique compounds.

Involvement of oxidative stress and toll-like receptor-4 signaling pathways in gentamicin-induced nephrotoxicity in male Sprague Dawley rats

Gentamicin (GM) is an antibiotic belonging to an aminoglycoside family that might induce nephrotoxicity in human and animal models via oxidative stress. Toll-like receptors (TLRs) are part of innate immune systems that participate in inflammatory responses. In this regard, we investigated the effect of GM on kidney functional and structural parameters, enzymatic antioxidant levels, and mRNA expression of TLR4 and IL6 in the rat kidney. Adult male Sprague Dawley rats were randomly divided into two groups (n = 10): Control and Gentamicin (100 mg/kg, i.p.). After ten days of GM administration, a blood sample was taken, and the kidneys were removed. The serum levels of creatinine (Cr) and blood urea nitrogen (BUN) were measured. Furthermore, the right kidney was preserved in formalin 10% for hematoxylin and eosin (H&E) staining, and the left kidney was kept at -80 °C for molecular and oxidative indexes analysis. Administration of GM caused tubular damages and functional disturbance. So that, Cr and BUN values in the GM group were higher than Control group. Furthermore, molecular findings showed upregulation of TLR4 and IL-6 mRNA expression in renal tissue of the GM-received group. In this study, superoxide dismutase (SOD) activity was slightly increased as a compensatory mechanism in response to elevated malondialdehyde (MDA) levels in the GM-treated group. On the other hand, the activity of catalase (CAT) and glutathione peroxidase (GPx) were significantly declined. Our results demonstrated that oxidative stress and subsequent TLR4 upregulation signaling pathways are involved in GM-induced nephrotoxicity.

Potential Antibiotics for the Treatment of Neonatal Sepsis Caused by Multidrug-Resistant Bacteria

Neonatal sepsis causes up to an estimated 680,000 deaths annually worldwide, predominantly in low- and middle-income countries (LMICs). A significant and growing proportion of bacteria causing neonatal sepsis are resistant to multiple antibiotics, including the World Health Organization-recommended empiric neonatal sepsis regimen of ampicillin/gentamicin. The Global Antibiotic Research and Development Partnership is aiming to develop alternative empiric antibiotic regimens that fulfil several criteria: (1) affordable in LMIC settings; (2) activity against neonatal bacterial pathogens, including extended-spectrum β-lactamase producers, gentamicin-resistant Gram-negative bacteria, and methicillin-resistant Staphylococcus aureus (MRSA); (3) a licence for neonatal use or extensive experience of use in neonates; and (4) minimal toxicities. In this review, we identify five antibiotics that fulfil these criteria: amikacin, tobramycin, fosfomycin, flomoxef, and cefepime. We describe the available characteristics of each in terms of mechanism of action, resistance mechanisms, clinical pharmacokinetics, pharmacodynamics, and toxicity profile. We also identify some knowledge gaps: (1) the neonatal pharmacokinetics of cefepime is reliant on relatively small and limited datasets, and the pharmacokinetics of flomoxef are also reliant on data from a limited demographic range and (2) for all reviewed agents, the pharmacodynamic index and target has not been definitively established for both bactericidal effect and emergence of resistance, with many assumed to have an identical index/target to similar class molecules. These five agents have the potential to be used in novel combination empiric regimens for neonatal sepsis. However, the data gaps need addressing by pharmacokinetic trials and pharmacodynamic characterisation.

Protective effect of allicin against gentamicin-induced nephrotoxicity in rats

In this study, the modulator effect of allicin on the oxidative nephrotoxicity of gentamicin in the kidneys of rats was investigated by determining indices of lipid peroxidation and the activities of antioxidant enzymes, as well as by histological analyses. Furthermore, the effect of allicin on gentamicin induced hypersensitivity of urinary bladder rings to ACh was estimated. Twenty-four male Wistar albino rats were randomly divided into three groups, control, gentamicin (100mg/kg, i.p.) and gentamicin+allicin (50mg/kg, orally). At the end of the study, all rats were sacrificed and then urine, blood samples and kidneys were taken. Gentamicin administration caused a severe nephrotoxicity as evidenced by an elevated kidney/body weight ratio, serum creatinine, blood urea nitrogen (BUN), serum lactate dehydrogenase (LDH) and proteinuria with a reduction in serum albumin and creatinine clearance as compared with control group. In addition, a significant increase in renal contents of malondialdehyde (MDA), myeloperoxidase (MPO), nitric oxide (NOx) and tumor necrosis factor-alpha (TNF-α) concomitantly with a significant decrease in renal reduced glutathione (GSH) and superoxide dismutase (SOD) activities was detected upon gentamicin injection. Exposure to gentamicin increased the sensitivity of isolated urinary bladder rings to ACh and induced acute renal tubular epithelial cells necrosis. Administration of allicin significantly decreased kidney/body weight ratio, serum creatinine, LDH, renal MDA, MPO, NOx and TNF-α while it significantly increased creatinine clearance, renal GSH content and renal SOD activity when compared to gentamicin-treated group. Additionally, allicin significantly reduced the responses of isolated bladder rings to ACh and ameliorated tissue morphology as evidenced by histological evaluation. Our study indicates that allicin exerted protection against structural and functional damage induced by gentamicin possibly due to its antioxidant, anti-inflammatory and immunomodulatory properties in addition to its ability to retaining nitric oxide level.

Antibacterial drugs in the form of sprays for the topical treatment of pyodermas and dermatoses complicated with a secondary infection

The article covers issues related to the application of topical antibacterial drugs for the treatment of pyodermic skin diseases. The author describes mechanisms of action and advantages of the topical form of antibiotics and GCS for the topical treatment of pyodermas. The article substantiates indications for the administration of topical GCS drugs in a combination with antibacterial drugs. The efficacy and safety of antibacterial and combination topical drugs such as Neomycin, Oxycort and Polcortolon TC in the form sprays for the treatment of pyodermas and complicated forms of chronic dermatosis.

Salicylic acid attenuates gentamicin-induced nephrotoxicity in rats

Gentamicin (GM) is a widely used antibiotic against serious and life-threatening infections, but its usefulness is limited by the development of nephrotoxicity. The present study was designed to determine the protective effect of salicylic acid (SA) in gentamicin-induced nephrotoxicity in rats. Quantitative evaluation of gentamicin-induced structural alterations and degree of functional alterations in the kidneys were performed by histopathological and biochemical analyses in order to determine potential beneficial effects of SA coadministration with gentamicin. Gentamicin was observed to cause a severe nephrotoxicity which was evidenced by an elevation of serum urea and creatinine levels. The significant increases in malondialdehyde (MDA) levels and protein carbonyl groups indicated that GM-induced tissue injury was mediated through oxidative reactions. On the other hand, simultaneous SA administration protected kidney tissue against the oxidative damage and the nephrotoxic effect caused by GM treatment. Exposure to GM caused necrosis of tubular epithelial cells. Necrosis of tubules was found to be prevented by SA pretreatment. The results from our study indicate that SA supplement attenuates oxidative-stress associated renal injury by reducing oxygen free radicals and lipid peroxidation in gentamicin-treated rats.

Acquired antibiotic resistance genes: an overview

In this review an overview is given on antibiotic resistance (AR) mechanisms with special attentions to the AR genes described so far preceded by a short introduction on the discovery and mode of action of the different classes of antibiotics. As this review is only dealing with acquired resistance, attention is also paid to mobile genetic elements such as plasmids, transposons, and integrons, which are associated with AR genes, and involved in the dispersal of antimicrobial determinants between different bacteria.

Reno-protective role of flunarizine (mitochondrial permeability transition pore inactivator) against gentamicin induced nephrotoxicity in rats

This study was aimed to evaluate the role of flunarizine on gentamicin (GEM) induced nephrotoxicity in rat. Administration of GEM (40 mg/kg, s.c. for 10 consecutive days) significantly increased blood urea nitrogen (BUN), N-acetyl β-d-glucosaminidase (NAG), thiobarbituric acid reactive substances (TBARS) and total calcium whereas, decreased body weight, fractional excretion of sodium (FrNa), creatinine clearance (CrCl), reduced glutathione (GSH), mitochondrial cytochrome c oxidase (Cyt-C oxidase) and ATP levels resulting in nephrotoxicity. Further, flunarizine (100, 200 and 300 µmol/kg, p.o.) was administered to evaluate its renoprotective effect against GEM induced nephrotoxicity and the results were compared with cylcosporin A (CsA, 50 µmol/kg, p.o.). Flunarizine resulted in the attenuation of renal dysfunction and oxidative marker changes in rats subjected to GEM induced nephrotoxicity in a dose dependent manner. Medium and higher doses of flunarizine produced significant renal protective effect which was comparable to cyclosporin A. The results of this study clearly revealed that flunarizine protected the kidney against the nephrotoxic effect of GEM via mitochondrial permeability transition pore (MPTP) inactivation potential.

Structural characterization of the tobramycin-piperacillin reaction product formed at pH 6.0

Tobramycin is an aminoglycoside antibiotic that loses a significant amount of activity in the presence of Zosyn at pH 6. As part of our investigation into ways to improve the compatibility of tobramycin with Zosyn (which contains piperacillin and tazobactam in an 8:1 ratio buffered at pH 6 by sodium citrate) by lowering the pH, we identified the reaction product of tobramycin and piperacillin at pH 6.0 and the order of the pK(a) values of tobramycin. The structure of the main reaction product of tobramycin and piperacillin at pH 6.0 was determined by 2D NMR to be the product of 3″-NH(2) reacting with the β-lactam of piperacillin. The order of the pK(a) values of the nitrogens of tobramycin was determined by (1)H and (15)N NMR titrations to be 6'-NH(2)>2'-NH(2)>1-NH(2)≈3″-NH(2)>3-NH(2). At pH 4.0, the reaction between tobramycin and Zosyn was almost negligible for a period of up to 2 h. The pH can be lowered by adding an acid such as HCl or citric acid to Zosyn to make a pH 4.0 buffer.

Metformin prevents experimental gentamicin-induced nephropathy by a mitochondria-dependent pathway

The antidiabetic drug metformin can diminish apoptosis induced by oxidative stress in endothelial cells and prevent vascular dysfunction even in nondiabetic patients. Here we tested whether it has a beneficial effect in a rat model of gentamicin toxicity. Mitochondrial analysis, respiration intensity, levels of reactive oxygen species, permeability transition, and cytochrome c release were assessed 3 and 6 days after gentamicin administration. Metformin treatment fully blocked gentamicin-mediated acute renal failure. This was accompanied by a lower activity of N-acetyl-beta-D-glucosaminidase, together with a decrease of lipid peroxidation and increase of antioxidant systems. Metformin also protected the kidney from histological damage 6 days after gentamicin administration. These in vivo markers of kidney dysfunction and their correction by metformin were complemented by in vitro studies of mitochondrial function. We found that gentamicin treatment depleted respiratory components (cytochrome c, NADH), probably due to the opening of mitochondrial transition pores. These injuries, partly mediated by a rise in reactive oxygen species from the electron transfer chain, were significantly decreased by metformin. Thus, our study suggests that pleiotropic effects of metformin can lessen gentamicin nephrotoxicity and improve mitochondrial homeostasis.

Effect of Cu(II) on the complex between kanamycin A and the bacterial ribosomal A site

The solution structure of kanamycin A interacting with a ribosomal A-site fragment was solved by transferred-NOE techniques and found to agree with the structure of the complex observed in the crystal. Despite the fast exchange conditions found for the interaction, the bound form was identified by NOESY spectroscopy. At 600 MHz, NOE effects are only observed for the RNA-associated antibiotic. Dissociation constants were measured by NMR spectroscopy for two sites of interaction (K(d1)=150+/-40 microM; K(d2)=360+/-50 microM). Furthermore, the effects of the Cu(II) ion on the antibiotic, on the RNA fragment that mimics the bacterial ribosomal A site, and on the complex formed between these two entities were analyzed. The study led to the proposal of a model that localizes the copper ion within the kanamycin-RNA complex.

Biosynthesis of unusual aminocyclitol-containing natural products

The aminocyclitol family of natural products is a class of sugar-derived microbial secondary metabolites that demonstrate significant biological activities. Within this class of natural products are the C7N-aminocyclitol-containing compounds, which were originally associated with potent sugar-hydrolase inhibition. However, recent discoveries indicate a broader array of chemical structures and biological activities of this class of compounds. Using both conventional feeding experiments and contemporary molecular genetic approaches, some progress has been made in understanding the biosynthesis of this class of natural products. Results of in silico investigation also suggest a wide distribution of this class of natural products or closely related compounds across different classes of microorganisms, including cyanobacteria and fungi. This review describes our recent progress in the biosynthetic studies of a number of C7N-aminocyclitol-containing compounds and the potential use of bioinformatic approaches to search for novel aminocyclitol-containing natural products.

Measurement of tobramycin by reversed-phase high-performance liquid chromatography with mass spectrometry detection

Analysis of tobramycin faces challenges owing to its significant basicity, hydrophilicity and lack of a UV absorbing chromophore. Chromatographic methods, coupled with derivatization to introduce chromophores for tobramycin analysis, were extensively studied. A direct reversed-phase HPLC method for tobramycin analysis has not been reported. Here, we would like to report a simple LC/MS method for quantitative analysis of tobramycin in pharmaceutical formulations. Reversed-phase HPLC analysis of tobramycin was achieved using a pH stable C18 column with basic (pH 11) aqueous mobile phase (ammonium hydroxide buffer), while direct detection was carried out employing a single quadruple mass detector in negative mode via electrospray ionization. This unique separation-detection combination provided simple and specific determination of tobramycin. This method was found to be linear at a tobramycin concentration range of 0.2-0.8 mg/mL with a correlation coefficient value of 0.999. The quantitation limit and detection limit were calculated as 0.210 and 0.063 microg/mL, respectively, with 99.994% confidence. This method was successfully applied to measure tobramycin content in matrices containing tobramycin and other pharmaceutical formulation ingredients. Recoveries of 101.8, 97.8 and 106.7% were obtained for tobramycin spiked in the pharmaceutical formulation at concentrations of 1.68, 1.0 and 0.35 mg/mL, respectively. The relative standard deviations for six injections of spiked samples ranged from 0.2 to 3.2%, indicating good method repeatability.

In vitro oxidative activity of cupric complexes of kanamycin A in comparison to in vivo bactericidal efficacy

The interactions of copper(II) complexes of kanamycin A with oxidation-susceptible biomolecules: 2'-deoxyguanosine, plasmid DNA and yeast tRNA(Phe) were studied in both the presence and absence of hydrogen peroxide. The mixture of complex with H(2)O(2) was found to be an efficient oxidant, converting dG to its 8-oxo derivative, generating strand breaks in plasmid DNA and multiple cleavages in tRNA(Phe). Some of these reactions may play a role in toxic effects of aminoglycoside antibiotics. These complexes were screened for their antibacterial activity. The microbiological studies undertaken to compare the bactericidal action of kanamycin A alone and complexed with copper(II) ions in both neutral and oxidative environment revealed that the enhancement of bactericidal action by Cu(II) was not statistically significant.

Beta-lactam resistance: clinical implications for pediatric patients

The emergence of resistance to established antibiotic agents such as beta-lactams has been reported worldwide and poses a serious challenge to the management of pediatric infections. The most common mechanism of resistance involves the production of an enzyme that inactivates the antibiotic before it can be effective. Streptococcus pneumoniae, the most common cause of pediatric respiratory tract infections, exhibits variable resistance to penicillins and aminopenicillin due to alterations in its penicillin-binding proteins (PBPs). Haemophilus influenzae and Moraxella catarrhalis show moderate and high beta-lactamase-mediated resistance to aminopenicillins, although they remain susceptible to beta-lactam/beta-lactamase inhibitor combinations. Methicillin-resistant Staphylococcus aureus, a frequent cause of skin and soft-tissue infections, has shown PBP-mediated beta-lactam resistance, prompting the wide-spread use of vancomycin to eradicate this pathogen. Finally, PBP-mediated resistance has been observed in a large proportion of isolates of coagulase-negative staphylococci, which account for a high proportion of nosocomial infections, particularly in neonatal intensive care units. The challenge is to control the emergence of beta-lactamase-mediated resistance by using beta-lactams judiciously. In this regard, the beta-lactam/beta-lactamase inhibitor combinations have an important role to play in extending the usefulness of established beta-lactam agents.

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.

The utility of aminoglycosides in an era of emerging drug resistance

As the problem of global antibiotic resistance continues to worsen, aminoglycosides have assumed increasing importance in clinical practice. Their broad antimicrobial spectrum, rapid bactericidal action, and ability to act synergistically with other drugs have made them especially useful in the treatment of serious nosocomial infections. However, as with other drugs, their overuse and misuse leads to the development of resistance in important microbial pathogens. The appropriate use of the aminoglycosides is essential to assure their continued efficacy. Therefore, physicians must familiarize themselves with both the clinical indications and the limitations of these drugs if they are to remain efficacious in the years to come.

Differential effects of immunosuppressants and antibiotics on human monoclonal antibody production in SCID mouse ascites by five heterohybridomas

SCID mice were inoculated with five human-mouse heterohybridomas derived by fusion of human lymph node lymphocytes from lung cancer patients with murine myeloma cells or human-mouse heteromyeloma cells, and the production of their human monoclonal antibodies (MAb) in the mouse ascites was investigated. In a comparison of the effects of pretreatment by i.p. (intraperitoneal) injection of pristane and anti-asialo GM1 serum on the antibody production of three of the hybridomas, pristane pretreatment resulted in substantial antibody production by all three, and pretreatment with anti-asialo GM1 serum resulted in similar or slightly lower levels of antibody production by two of the hybridomas but none by the third. In a second series of experiments using four of the hybridomas with pristane pretreatment, the co-injection of either penicillin G and streptomycin or kanamycin together with the hybridoma at the time of i.p. inoculation resulted in enhanced MAb production by the two heterohybridomas that had been propagated in medium containing hypoxanthine-aminopterin-thymidine (HAT) but not by the two that had been propagated in HAT-free medium.

Does vancomycine increase aminoglycoside nephrotoxicity?

Vancomycine and amikacin combined is an effective antibiotic combination used in the treatment of serious Gram-positive bacteremia in childhood. However, both drugs may have a potential nephrotoxic effect when used individually. The present study investigates whether the nephrotoxicity of these drugs that display a nephrotoxic effect when used separately increases when used in a combined manner. Ten 2-month-old rats were subjected to intraperitoneal injections of vancomycine (100 mg/kg) and amikacin (80 mg/kg) and ten other 2-month-old rats were administered amikacin (80 mg/kg) for a period of 15 days. The control group of animals consisting of five 2-month old rats were untreated. The renal tissues obtained by laparotomy were processed for both light and electron microscopy. Paraffin sections and ultrathin sections were evaluated in order to determine the renal structure of the control and the experimental groups. In addition, serum creatinine and blood, urea and nitrogen (BUN) levels were measured in blood samples obtained from the rats. In the amikacin and combined amikacin-vancomycine treatment groups, renal morphological changes were observed at the glomerular and tubular levels when compared to the control group, and the serum creatinine and BUN levels were also higher in these groups. Although both experimental groups were different from the control group, they had similar morphological and biochemical features. It was concluded that vancomycine did not influence the nephrotoxic effect of amikacin and both drugs could be used in a combined manner.

Antibiotic use in the emergency department. II The aminoglycosides, macrolides, tetracyclines, sulfa drugs, and urinary antiseptics

The aminoglycoside, macrolide, tetracycline, and sulfa classes of antibiotics provide antimicrobial coverage pertinent to many infectious diseases diagnosed in the emergency department (ED). The aminoglycosides are parenteral agents that are useful in Gram-negative infections and as synergistic drugs in the management of some Gram-positive infections. The macrolides, of which erythromycin is the prototype, are used for a number of Gram-positive and atypical bacterial infections, while the tetracyclines are appropriate for ED treatment of a diverse group of infections such as chlamydiae, spirochetes, and rickettsiae. The sulfa agents are appropriate for many urinary and respiratory tract infections, and also have particular utility in some infections encountered primarily in patients with AIDS. The urinary antiseptics are a group of antimicrobials that may be effective for cystitis but have no systemic efficacy. This article, which is the second in a four-part series on antibiotic use in the ED, reviews the pharmacology and clinical utility of these diverse agents for the emergency physician.

Gentamicin nephrotoxicity in humans and animals: some recent research

It would appear from the literature cited in this article, that interest in gentamicin nephrotoxicity is still thriving. Despite extensive studies, the mechanism(s) of the nephrotoxicity is uncertain. Several clinical and experimental strategies have been employed in order to ameliorate or abolish the signs of gentamicin nephrotoxicity. Most of these were unsuccessful, impractical or unsafe. Therefore there is still a need for further studies to elucidate the mechanism(s) of action of the drugs nephrotoxicity, and to discover safe, practical and effective agents to ameliorate the nephrotoxicity in patients at risk.

Toxicodynamics and toxicokinetics of amikacin in the guinea pig cochlea

An extensive overview of the relationship between cochlear toxicity and amikacin blood concentrations in the guinea pig is provided which should assist in the clinical application of this class of antibiotic. A data set previously used to relate the incidence of amikacin ototoxicity to dosing rates and blood concentrations was re-examined to assess the toxicodynamics of amikacin in terms of decibels of hearing loss across dosing rate, hearing frequency and time following drug exposure. Animals in this data set had received continuously i.v. infused amikacin over an 8-fold range of dosing rates. Preliminary analysis indicated that the data were consistent with a sigmoid relationship between hearing loss (decibels) and area under the amikacin plasma concentration vs time curve cumulated over the entire course of drug administration (cAUC). The sigmoid model was therefore used as the backbone of a far more comprehensive toxicodynamic model which described all the data with a single equation. Testing with this model showed that the cAUC required to produce half-maximum hearing loss (cAUC-1/2) was related to dosing rate (P < 0.01), to hearing frequency (P < 0.00001), and to post-drug interval (P < 0.00001). Maximum hearing loss (difference between upper and lower sigmoid asymptotes) was less than total and was significantly related to frequency (P < 0.00001). No effects could be detected on the sigmoid slope. Further modelling of the significant effects detected by the comprehensive toxicodynamic model was done to determine if they could be described by simple relationships or by biologically relevant sub-models. Modelling of maximum hearing loss (postulated to represent loss of mainly outer hair cell function) indicated that this parameter was constant at about 61 decibels for 2-12 kHz and linearly decreased with log frequency for frequencies > 12 kHz. Modelling of cAUC-1/2 on frequency indicated that there was a strong inverse linear relationship to log frequency. Modelling of cAUC-1/2 on post-drug interval indicated that delayed ototoxicity continued at progressively slower rates for at least 56 days after drug administration had ceased. Modelling of cAUC-1/2 on dosing rate showed an increased requirement for drug as the dosing rate decreased. However, cAUC-1/2 changed no more than 20% across the range of dosing rates compared to the 8-fold difference in mean steady-state plasma concentrations, suggesting that plasma concentration is not a primary determinant of ototoxicity. A toxicokinetic model was developed which explained the dosing rate effect on cAUC-1/2 very successfully.(ABSTRACT TRUNCATED AT 400 WORDS)

Antibiotics for pneumonia therapy

When treating any infectious disease, a physician selects an antimicrobial based on the following considerations: the in vitro activity of the drug, its pharmacokinetic properties, the efficacy data based on properly designed and conducted clinical trials, and finally the adverse effects. In this article, all of these factors, with the exception of adverse effects, were discussed. It was neither my intent nor my purpose to deal with side effects or adverse drug reactions because these are well covered in standard texts or physician references such as the Physicians' Desk Reference and the American Hospital Formulary Service (United States) and the Compendium of Pharmaceuticals and Specialties (Canada).

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.

Comparative modulating effects of captopril, diltiazem, dietary calcium and pyridoxal-5'-phosphate on gentamicin-induced nephrotoxicity in the rat

1. Nephrotoxicity was induced in rats by injecting gentamicin intramuscularly (i.m.) at a dose of 80 mg/kg/day for 6 days. Treated animals demonstrated a typical pattern of aminoglycoside nephrotoxicity characterized histopathologically by necrosis of proximal tubular epithelium, and biochemically by increased serum creatinine and urea concentrations. Reduced glutathione (GSH) concentration in renal cortex was significantly decreased by gentamicin. 2. Simultaneous treatment of rats with gentamicin and either captopril or diltiazem significantly potentiated the gentamicin-induced increases in serum creatinine and urea and did not significantly affect the gentamicin-induced decrease in cortical GSH concentration. 3. Concomitant treatment with gentamicin and either Ca2+ or pyridoxal-5'-phosphate decreased serum urea level, did not significantly affect serum creatinine concentration, and significantly increased cortical GSH concentration in comparison to the values of these parameters following gentamicin treatment. 4. Histopathologically, the severity of gentamicin-induced renal damage was exacerbated by captopril, and even more so by diltiazem. Simultaneous treatment with gentamicin and either Ca2+ or pyridoxal-5'-phosphate produced only mild focal atrophy of renal tubular epithelium. Control rats had apparently normal histology. 5. In conclusion, captopril and diltiazem, at the doses used, significantly potentiated gentamicin-induced nephrotoxicity to a broadly similar extent. Although Ca2+ and pyridoxal-5'-phosphate, at the doses used, reduced significantly the severity of some of the manifestations of nephrotoxicity, they were equally ineffective in completely preventing the development of nephrotoxicity.

Disposition of liposomal gentamicin following intrabronchial administration in rabbits

Use of liposomes as carriers of gentamicin for intrabronchial pulmonary delivery was investigated in rabbits. Gentamicin, in isotonic glutamic acid buffer, pH 4.5, was encapsulated in multilamellar vesicles (MLVs) and administered intrabronchially. Higher drug concentrations were found at the pulmonary site of liposome instillation for 1 day as compared with free unencapsulated antibiotic. When time-course distributions of gentamicin given in the liposomal or free form were measured in bronchoalveolar lavages (BAL), similar accumulations were observed up to 4 h, but the drug remained longer (24 h) after administration of the liposomal formulation. Higher amounts of antibiotic were detected in BAL supernatant 1 h after instillation of plain gentamicin; this difference stopped being significant after 4 h. A microbiological assay outlined the bacteriostatic activity of gentamicin released from MLVs and recovered in BAL supernatant. Liposomal gentamicin accumulated in the BAL cell pellet 1 h after intrabronchial instillation; it decreased progressively but minute amounts were still detected after 1 day. On the contrary, no gentamicin was found in the pellet at any time after free drug administration. Comparison of aminoglycoside concentrations in plasma and kidneys indicated lower and constant levels when the liposomal form was instilled. Liposome encapsulation altered the disposition of gentamicin in a way suggesting improved pulmonary concentration and lower systemic toxicity.

Biosafety of kanamycin-resistant transgenic plants

Kanamycin resistance is one of the most frequently used selection markers for obtaining transgenic plants. The introduction of these transgenic plants into agricultural practice will cause the kanamycin resistance gene and the gene product to be present on a large scale. The desirability of this situation is analysed. The nature, properties and applications of the antibiotic kanamycin are briefly reviewed, as are the mechanisms of kanamycin resistance. It is argued that the gene used for resistance is an excellent choice because of the high substrate specificity of the enzyme encoded. Human or veterinary antibiotic therapies will not be compromised. Also, the physico-chemical characteristics of the antibiotic exclude the existence of selective conditions in the environment. Therefore, a transgenic plant or any other organism that might have acquired the gene will not get any selective advantage because of this gene. Evidence further suggests there is no toxicity or predictable harm of both gene or gene product for human or animal consumption. Full legislative clearance of this transgenic trait is therefore acceptable.

Penetration of netilmicin in the lower respiratory tract after once-daily dosing

A major criticism of the use of aminoglycosides for the treatment of pneumonia is the poor penetration in infected airways. Once-daily dosing of aminoglycosides results in higher peak plasma concentrations without increasing toxic reactions and with optimization of pharmacodynamic properties. To predict intrapulmonary antimicrobial activity after once-daily dosing of aminoglycosides, it is necessary to determine the respective bronchial and alveolar disposition. We prospectively conducted a pharmacokinetic study of netilmicin following the first intravenous administration of a once-daily dosing schedule in 20 ventilated patients with pneumonia. A bronchoscopic sampling of bronchial secretions and a subsegmental bronchoalveolar lavage (BAL) were performed 60, 90, 120, and 180 min (five patients at each time point) on the first treatment day after intravenous administration over 30 min of 450 mg of netilmicin. The netilmicin concentrations in the alveolar lining fluid (ALF) were calculated using urea as an endogenous marker of dilution. In bronchial secretions, a peak concentration of 2.00 (SEM: 0.26) mg/L or 6 percent of the 30-min plasma concentration was reached at 120 min. In ALF, much higher levels were found. At 120 min, a peak ALF concentration of 14.7 (SEM: 2.22) mg/L or 41 percent of the 30-min plasma concentration was reached. Spearman's rank correlation testing failed to show a correlation between bronchial and ALF concentrations. Higher plasma concentrations of netilmicin after once-daily dosing give rise to ALF concentrations exceeding the minimum inhibitory concentration of susceptible respiratory pathogens involved in nosocomial pneumonia, while bronchial concentrations remain low. Aminoglycoside concentrations in bronchial secretions cannot be used to predict alveolar concentrations. Low diffusibility can no longer be considered as a disadvantage of aminoglycosides for treating pneumonias.

Biocompatible implantable antimicrobial release for necrotizing external otitis

The efficacy of a biocompatible, surgically implantable, antimicrobial release system (IARS) as the exclusive antimicrobial therapy of necrotizing external otitis (NEO) was evaluated in six NEO patients. Gentamicin incorporated polymethyl-methacrylate beads were implanted, following surgical debridement and were removed two months later. Post-implantation alleviation of clinical symptoms: pain, periauricular tissue swelling, otorrhoea, eradication of pseudomonal infection (100 per cent) and substantially shortened hospitalization (4-15 days) were the salient results of this therapeutic modality. Three patients recovered. Two patients who died, one of sudden cardiac arrest and the other of paralytic ileus, 15 and 60 days post-operatively while the beads were still implanted, were symptomless. Recurrence was seen in one patient with early bead extrusion. Ipsilateral sensorineural hearing loss (one patient) and external meatal stenosis were the main complications. IARS appears to offer an effective alternative to long-term systemic antibiotic administration for the eradication of NEO-pseudomonal infection in patients who are sensitive, develop resistance, or when quinolone medical treatment has failed or is contra-indicated.

Aminoglycoside therapy. Current use and future prospects

The microbiological, pharmacokinetic, toxicological and clinical aspects of aminoglycosides are reviewed. Aminoglycosides still have an important place in serious infections in neutropenic patients, endocarditis and Pseudomonas aeruginosa infections, all in combination with beta-lactams. Monotherapy (with streptomycin) is indicated in less common diseases like tularemia and bubonic plague. Several experimental studies support a once-daily dosing regimen for aminoglycosides (comparable or better efficacy with less ototoxicity and nephrotoxicity). Only a very limited number of prospective comparative studies have been performed, and much more data on efficacy, development of resistance and toxicity is needed before once-daily administration can be recommended. The choice of an aminoglycoside should be based primarily on the local sensitivity patterns and cost. Differences in ototoxicity and nephrotoxicity are usually minor. If the acquisition costs of amikacin decline, it is to be expected that amikacin will be the aminoglycoside of choice.

Shifts in auditory brainstem response latencies following plasma-level-controlled aminoglycoside therapy

The ototoxic effect of plasma-level-controlled netilmicin and tobramycin was monitored in 20 intensive care patients, using auditory brainstem responses (ABRs). ABRs were recorded at the onset and after 6 days of treatment. Significant shifts in the ABR wave V latency were observed independent of the type of medication received or whether the patients were intubated or not. Shifts were also observed in wave I latencies. These latter changes were only significant for the complete population, probably because this potential is more difficult to elicit and measure than is wave V. The I-V interlatency time was greater for netilmicin than for tobramycin. These results indicate that the cumulative effects of aminoglycoside ototoxicity may be different for the central and peripheral nervous systems, and therefore ABR measurements may be the most accurate way of controlling ototoxicity in intensive care patients.

Prospective randomized study of once-daily versus thrice-daily netilmicin regimens in patients with intraabdominal infections

One hundred and ninety-seven patients with intraabdominal infections were enrolled in a prospective randomized multicenter study of netilmicin administered once daily (n = 98) versus thrice daily (n = 99) in combination with tinidazole administered once daily. Randomization was achieved for the infection site, clinical severity score, daily and total netilmicin dose, and duration of treatment. The mean maximum peak and trough levels of netilmicin in serum were 21.1 and 1.3 mg/l respectively for once daily treated patients, and 10.0 and 2.3 mg/l for thrice daily treated patients (p less than 0.05 for both parameters). The clinical response did not differ between patients treated once daily and those treated thrice daily. Overall rates for clinical cure, improvement and failure of therapy were 77%, 17% and 6% respectively. No significant differences were found between once daily and thrice daily regimens in the occurrence of auditory, vestibular and renal toxicity, overall rates being 5%, 1% and 10% respectively. Impairment of renal function was significantly related to higher maximum netilmicin serum trough levels during therapy, a higher clinical severity score and advanced age. It is concluded that netilmicin given once daily is as effective and safe as the multiple dose regimen. However, monitoring of aminoglycoside serum through levels is still advisable, especially in the old and severely ill patient.

Probability assessment approach to therapeutic drug monitoring: tobramycin

Pharmacokinetic monitoring is an important therapeutic goal of aminoglycoside therapy. The overall goal of this study was to identify specific patient groups that would derive the maximum benefit from therapeutic drug monitoring services. These groups are patient populations with high probabilities of achieving toxic or subtherapeutic concentrations. Out of a total population of 86 stable, noncritically ill patients, 27 toxic concentrations (trough greater than 2.0 micrograms/mL) occurred in 15 patients. In comparison to patients (n = 46) with therapeutic concentrations (trough less than 2.0 micrograms/mL, peak greater than 4.0 micrograms/mL), these patients were older (64 +/- 11 vs. 54 +/- 18 years; p less than 0.02) and had a higher percentage of females (66.7 vs. 37 percent; p less than 0.05). Those patients with subtherapeutic concentrations (43 concentrations in 25 patients) had higher estimated creatinine clearance values than those with therapeutic concentrations (94 +/- 45 vs. 74 +/- 27 mL/min; p less than 0.005). Probability assessment analysis of the data showed a sevenfold increase in toxic concentrations in patients above 50 years. Females over age 50 had 2.3 times the risk of developing toxic concentrations as males over age 50. In contrast, the development of low concentrations was not predicted by age or sex. Underdosage by greater than or equal to 30 percent was a reasonable predictor (75 percent) of low peak concentrations. Furthermore, toxic concentrations did not occur in patients who were underdosed, justifying dosage increases prior to obtaining serum concentrations in these patients. The group with the highest probability of attaining therapeutic concentrations was males receiving therapeutic doses who were under age 50 (85.5 percent).(ABSTRACT TRUNCATED AT 250 WORDS)

Diltiazem enhances gentamicin nephrotoxicity in rats

The effect of the calcium antagonist, diltiazem, was examined in gentamicin-induced nephrotoxicity states in rats. Animals were injected for 5 days with diltiazem intraperitoneally (40 mg/kg/day), or gentamicin subcutaneously (100 mg/kg/day) or simultaneously with both preparations using the same doses. At the time of sacrifice, the urea and creatinine clearances, as well as urine osmolality were determined and the renal tissues were processed for examination by light microscopy. Gentamicin-injected rats demonstrated the typical pattern of aminoglycoside nephrotoxicity characterized by poliuric renal failure and necrosis of the proximal tubular epithelium. Rats injected with diltiazem revealed only mild depression of urine osmolality. There was no elevation of blood urea nitrogen and serum creatinine or depression of urea and creatinine clearances, and no focal tubular cell necrosis was detected. However, concomitant administration of both compounds considerably increased nephrotoxicity by according both histological indications and renal function measurements. Thus, we conclude that the combination of diltiazem and gentamicin must be used carefully in human clinical practice.

Aminoglycosides: current role in antimicrobial therapy

Aminoglycosides remain the cornerstone of antibiotic therapy for nosocomial, gram-negative bacillary infections despite the recent introduction of broad-spectrum beta-lactam antibiotics and quinolones with antipseudomonal activity. Initially, aminoglycosides were used as antiaerobic gram-negative antimicrobial therapy. Currently, they have a key role in many types of infections, such as gram-negative urosepsis and in febrile granulocytopenic patients, because of their established antipseudomonal activity. Empiric treatment of febrile episodes in granulocytopenic cancer patients with an aminoglycoside, in combination with an anti-pseudomonal beta-lactam, accounts for much of the aminoglycoside use. Amikacin is emerging as one of the most effective aminoglycosides on the basis of resistance rates, pharmacokinetic factors likely to affect clinical efficacy, safety, and overall cost of therapy.

Aminoglycoside antibiotics in clinical use

Aminoglycosides are among the most used antibiotics despite competitive pressure from newer beta-lactam agents. The activity profile, pharmacology, toxicity potential, and methods of toxicity prevention of aminoglycosides are well appreciated after three decades. Nephrotoxicity, ototoxicity, and the added costs of drug level monitoring limit wider usage, but great activity against highly antibiotic resistant gram negative bacteria often outweigh these disadvantages and will likely keep aminoglycosides available for the foreseeable future.

Univariate and multivariate analyses of risk factors predisposing to auditory toxicity in patients receiving aminoglycosides

Risk factors predisposing to auditory toxicity of aminoglycosides were analyzed from records of 187 patients enrolled in three prospective randomized trials comparing the toxicity of netilmicin, tobramycin, and amikacin. Patients were eligible if they received three or more days of therapy and at least two serial audiograms were available. The overall auditory toxicity rate was 9.6% (18 of 187). Auditory toxicity was detected in 4.4, 10.8, and 23.5% of patients given netilmicin, tobramycin, and amikacin, respectively (P = 0.05). In the univariate analysis, patients who developed auditory toxicity were significantly older (P = 0.01) and had a significantly higher (P = 0.04) percentage of trough levels of netilmicin or tobramycin above 2 mg/liter or amikacin above 5 mg/liter. In the final logistic regression model, only age was retained as independently influencing the development of auditory toxicity (P less than 0.00001). Conversely, factors that did not add significantly to the prediction of auditory toxicity were aminoglycoside serum levels, total aminoglycoside dose, duration of therapy, sex, peak temperature, presence of bacteremia, shock, liver cirrhosis, dehydration, previous otic pathology or renal failure, and development of renal toxicity. At least in certain populations, age is the most important predisposing factor for the development of auditory toxicity in patients receiving aminoglycosides.