The aminoglycosides

Gut microbiota intervention attenuates thermogenesis in broilers exposed to high temperature through modulation of the hypothalamic 5-HT pathway

BACKGROUND

Broilers have a robust metabolism and high body temperature, which make them less tolerant to high-temperature (HT) environments and more susceptible to challenges from elevated temperatures. Gut microbes, functioning as symbionts within the host, possess the capacity to significantly regulate the physiological functions and environmental adaptability of the host. This study aims to investigate the effects of gut microbial intervention on the body temperature and thermogenesis of broilers at different ambient temperatures, as well as the underlying mechanism involving the "gut-brain" axis.

METHODS

Broilers were subjected to gut microbiota interference with or without antibiotics (control or ABX) starting at 1 day of age. At 21 day of age, they were divided into 4 groups and exposed to different environments for 7 d: The control and ABX groups at room temperature (RT, 24 ± 1 °C, 60% relative humidity (RH), 24 h/d) and the control-HT and ABX-HT groups at high temperature (HT, 32 ± 1 °C, 60% RH, 24 h/d). RESULTS : The results demonstrated that the antibiotic-induced gut microbiota intervention increased body weight and improved feed conversion in broiler chickens (P < 0.05). Under HT conditions, the microbiota intervention reduced the rectal temperature of broiler chickens (P < 0.05), inhibited the expression of avUCP and thermogenesis-related genes in breast muscle and liver (P < 0.05), and thus decreased thermogenesis capacity. Furthermore, the gut microbiota intervention blunted the hypothalamic‒pituitary‒adrenal axis and hypothalamic-pituitary-thyroid axis activation induced by HT conditions. By analyzing the cecal microbiota composition of control and ABX chickens maintained under HT conditions, we found that Alistipes was enriched in control chickens. In contrast, antibiotic-induced gut microbiota intervention resulted in a decrease in the relative abundance of Alistipes (P < 0.05). Moreover, this difference was accompanied by increased hypothalamic 5-hydroxytryptamine (5-HT) content and TPH2 expression (P < 0.05).

CONCLUSIONS

These findings underscore the critical role of the gut microbiota in regulating broiler thermogenesis via the gut-brain axis and suggest that the hypothalamic 5-HT pathway may be a potential mechanism by which the gut microbiota affects thermoregulation in broilers.

Identifying targets to prevent aminoglycoside ototoxicity

Aminoglycosides are potent antibiotics that are commonly prescribed worldwide. Their use carries significant risks of ototoxicity by directly causing inner ear hair cell degeneration. Despite their ototoxic side effects, there are currently no approved antidotes. Here we review recent advances in our understanding of aminoglycoside ototoxicity, mechanisms of drug transport, and promising sites for intervention to prevent ototoxicity.

Medicated Scaffolds Prepared with Hydroxyapatite/Streptomycin Nanoparticles Encapsulated into Polylactide Microfibers

The preparation, characterization, and controlled release of hydroxyapatite (HAp) nanoparticles loaded with streptomycin (STR) was studied. These nanoparticles are highly appropriate for the treatment of bacterial infections and are also promising for the treatment of cancer cells. The analyses involved scanning electron microscopy, dynamic light scattering (DLS) and Z-potential measurements, as well as infrared spectroscopy and X-ray diffraction. Both amorphous (ACP) and crystalline (cHAp) hydroxyapatite nanoparticles were considered since they differ in their release behavior (faster and slower for amorphous and crystalline particles, respectively). The encapsulated nanoparticles were finally incorporated into biodegradable and biocompatible polylactide (PLA) scaffolds. The STR load was carried out following different pathways during the synthesis/precipitation of the nanoparticles (i.e., nucleation steps) and also by simple adsorption once the nanoparticles were formed. The loaded nanoparticles were biocompatible according to the study of the cytotoxicity of extracts using different cell lines. FTIR microspectroscopy was also employed to evaluate the cytotoxic effect on cancer cell lines of nanoparticles internalized by endocytosis. The results were promising when amorphous nanoparticles were employed. The nanoparticles loaded with STR increased their size and changed their superficial negative charge to positive. The nanoparticles’ crystallinity decreased, with the consequence that their crystal sizes reduced, when STR was incorporated into their structure. STR maintained its antibacterial activity, although it was reduced during the adsorption into the nanoparticles formed. The STR release was faster from the amorphous ACP nanoparticles and slower from the crystalline cHAp nanoparticles. However, in both cases, the STR release was slower when incorporated in calcium and phosphate during the synthesis. The biocompatibility of these nanoparticles was assayed by two approximations. When extracts from the nanoparticles were evaluated in cultures of cell lines, no cytotoxic damage was observed at concentrations of less than 10 mg/mL. This demonstrated their biocompatibility. Another experiment using FTIR microspectroscopy evaluated the cytotoxic effect of nanoparticles internalized by endocytosis in cancer cells. The results demonstrated slight damage to the biomacromolecules when the cells were treated with ACP nanoparticles. Both ACP and cHAp nanoparticles were efficiently encapsulated in PLA electrospun matrices, providing functionality and bioactive properties.

Design and characterization of 3D printed, neomycin-eluting poly-L-lactide mats for wound-healing applications

This study evaluates the suitability of 3D printed biodegradable mats to load and deliver the topical antibiotic, neomycin, for up to 3 weeks in vitro. A 3D printer equipped with a hot melt extruder was used to print bandage-like wound coverings with porous sizes appropriate for cellular attachment and viability. The semicrystalline polyester, poly-l-lactic acid (PLLA) was used as the base polymer, coated (post-printing) with polyethylene glycols (PEGs) of MWs 400 Da, 6 kDa, or 20 kDa to enable manipulation of physicochemical and biological properties to suit intended applications. The mats were further loaded with a topical antibiotic (neomycin sulfate), and cumulative drug-release monitored for 3 weeks in vitro. Microscopic imaging as well as Scanning Electron Microscopy (SEM) studies showed pore dimensions of 100 × 400 µm. These pore dimensions were achieved without compromising mechanical strength; because of the "tough" individual fibers constituting the mat (Young's Moduli of 50 ± 20 MPa and Elastic Elongation of 10 ± 5%). The in vitro dissolution study showed first-order release kinetics for neomycin during the first 20 h, followed by diffusion-controlled (Fickian) release for the remaining duration of the study. The release of neomycin suggested that the ability to load neomycin on to PLLA mats increases threefold, as the MW of the applied PEG coating is lowered from 20 kDa to 400 Da. Overall, this study demonstrates a successful approach to using a 3D printer to prepare porous degradable mats for antibiotic delivery with potential applications to dermal regeneration and tissue engineering. Illustration of the process used to create and characterize 3D printed PLLA mats.

Overcoming Aminoglycoside Enzymatic Resistance: Design of Novel Antibiotics and Inhibitors

Resistance to aminoglycoside antibiotics has had a profound impact on clinical practice. Despite their powerful bactericidal activity, aminoglycosides were one of the first groups of antibiotics to meet the challenge of resistance. The most prevalent source of clinically relevant resistance against these therapeutics is conferred by the enzymatic modification of the antibiotic. Therefore, a deeper knowledge of the aminoglycoside-modifying enzymes and their interactions with the antibiotics and solvent is of paramount importance in order to facilitate the design of more effective and potent inhibitors and/or novel semisynthetic aminoglycosides that are not susceptible to modifying enzymes.

Aminoglycoside resistance profile and structural architecture of the aminoglycoside acetyltransferase AAC(6')-Im

Aminoglycoside 6'-acetyltransferase-Im (AAC(6')-Im) is the closest monofunctional homolog of the AAC(6')-Ie acetyltransferase of the bifunctional enzyme AAC(6')-Ie/APH(2")-Ia. The AAC(6')-Im acetyltransferase confers 4- to 64-fold higher MICs to 4,6-disubstituted aminoglycosides and the 4,5-disubstituted aminoglycoside neomycin than AAC(6')-Ie, yet unlike AAC(6')-Ie, the AAC(6')-Im enzyme does not confer resistance to the atypical aminoglycoside fortimicin. The structure of the kanamycin A complex of AAC(6')-Im shows that the substrate binds in a shallow positively-charged pocket, with the N6' amino group positioned appropriately for an efficient nucleophilic attack on an acetyl-CoA cofactor. The AAC(6')-Ie enzyme binds kanamycin A in a sufficiently different manner to position the N6' group less efficiently, thereby reducing the activity of this enzyme towards the 4,6-disubstituted aminoglycosides. Conversely, docking studies with fortimicin in both acetyltransferases suggest that the atypical aminoglycoside might bind less productively in AAC(6')-Im, thus explaining the lack of resistance to this molecule.

Once-Daily Aminoglycosides: A Meta-Analysis of Nonneutropenic and Neutropenic Adults

Objective:

To compare the efficacy, nephrotoxicity, and ototoxicity of once-daily dosing of aminoglycosides versus conventional dosing.

Design:

Meta-analysis of 14 randomized trials identified through a MEDLINE search (January 1965-May 1996).

Patients:

Neutropenic and nonneutropenic adults.

Interventions:

Patients were randomly selected to receive an aminoglycoside once daily or in multiple daily doses.

Measurements and Main Outcomes:

The outcomes considered were clinical cure, bacteriologic cure, nephrotoxicity, auditory toxicity, and vestibular toxicity. The data were analyzed in the following subgroups: (1) all trials, (2) nonneutropenic patients, (3) neutropenic patients, and (4) patients with undefined neutrophil status. For all trials the pooled risk ratio was 1.268 (95% CI 0.828 to 1.939) for clinical cure, and was 1.390 (95% CI 1.350 to 1.392) for bacteriologic cure. Nephrotoxicity had a pooled risk ratio of 0.765 (95% CI 0.468 to 1.252), that for auditory toxicity was 1.117 (95% CI 0.151 to 5.636), and that for vestibular toxicity was 1.155 (95% CI 0.221 to 6.039). Analysis of the subgroups, including a separate analysis of neutropenic patients, demonstrated similar results.

Conclusions:

When all trials were considered, once-daily administration of aminoglycosides had similar efficacy and no increase in nephrotoxicity or ototoxicity compared with conventional aminoglycoside dosing.

Pharmacometric Approaches to Personalize Use of Primarily Renally Eliminated Antibiotics in Preterm and Term Neonates

Sepsis remains a major cause of mortality and morbidity in neonates, and, as a consequence, antibiotics are the most frequently prescribed drugs in this vulnerable patient population. Growth and dynamic maturation processes during the first weeks of life result in large inter- and intrasubject variability in the pharmacokinetics (PK) and pharmacodynamics (PD) of antibiotics. In this review we (1) summarize the available population PK data and models for primarily renally eliminated antibiotics, (2) discuss quantitative approaches to account for effects of growth and maturation processes on drug exposure and response, (3) evaluate current dose recommendations, and (4) identify opportunities to further optimize and personalize dosing strategies of these antibiotics in preterm and term neonates. Although population PK models have been developed for several of these drugs, exposure-response relationships of primarily renally eliminated antibiotics in these fragile infants are not well understood, monitoring strategies remain inconsistent, and consensus on optimal, personalized dosing of these drugs in these patients is absent. Tailored PK/PD studies and models are useful to better understand relationships between drug exposures and microbiological or clinical outcomes. Pharmacometric modeling and simulation approaches facilitate quantitative evaluation and optimization of treatment strategies. National and international collaborations and platforms are essential to standardize and harmonize not only studies and models but also monitoring and dosing strategies. Simple bedside decision tools assist clinical pharmacologists and neonatologists in their efforts to fine-tune and personalize the use of primarily renally eliminated antibiotics in term and preterm neonates.

Effect of Kidney Function on Drug Kinetics and Dosing in Neonates, Infants, and Children

Neonates, infants, and children differ from adults in many aspects, not just in age, weight, and body composition. Growth, maturation and environmental factors affect drug kinetics, response and dosing in pediatric patients. Almost 80% of drugs have not been studied in children, and dosing of these drugs is derived from adult doses by adjusting for body weight/size. As developmental and maturational changes are complex processes, such simplified methods may result in subtherapeutic effects or adverse events. Kidney function is impaired during the first 2 years of life as a result of normal growth and development. Reduced kidney function during childhood has an impact not only on renal clearance but also on absorption, distribution, metabolism and nonrenal clearance of drugs. 'Omics'-based technologies, such as proteomics and metabolomics, can be leveraged to uncover novel markers for kidney function during normal development, acute kidney injury, and chronic diseases. Pharmacometric modeling and simulation can be applied to simplify the design of pediatric investigations, characterize the effects of kidney function on drug exposure and response, and fine-tune dosing in pediatric patients, especially in those with impaired kidney function. One case study of amikacin dosing in neonates with reduced kidney function is presented. Collaborative efforts between clinicians and scientists in academia, industry, and regulatory agencies are required to evaluate new renal biomarkers, collect and share prospective pharmacokinetic, genetic and clinical data, build integrated pharmacometric models for key drugs, optimize and standardize dosing strategies, develop bedside decision tools, and enhance labels of drugs utilized in neonates, infants, and children.

Synthesis, characterization, controlled release, and antibacterial studies of a novel streptomycin chitosan magnetic nanoantibiotic

This study describes the preparation, characterization, and controlled release of a streptomycin-chitosan-magnetic nanoparticle-based antibiotic in an effort to improve the treatment of bacterial infections. Specifically, chitosan-magnetic nanoparticles were synthesized by an incorporation method and were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometry. Streptomycin was incorporated into the nanoparticles to form a streptomycin-coated chitosan-magnetic nanoparticle (Strep-CS-MNP) nanocomposite. The release profiles showed an initially fast release, which became slower as time progressed. The percentage of drug released after 350 minutes was around 100%, and the best fit mathematical model for drug release was the pseudo-second order model. The Strep-CS-MNP nanocomposite showed enhanced antibacterial activity against methicillin-resistant Staphylococcus aureus. This study forms a significant basis for further investigation of the Strep-CS-MNP nanocomposite in the treatment of various bacterial infections.

Aminoglycoside 2''-phosphotransferase IIIa (APH(2'')-IIIa) prefers GTP over ATP: structural templates for nucleotide recognition in the bacterial aminoglycoside-2'' kinases

Contrary to the accepted dogma that ATP is the canonical phosphate donor in aminoglycoside kinases and protein kinases, it was recently demonstrated that all members of the bacterial aminoglycoside 2''-phosphotransferase IIIa (APH(2'')) aminoglycoside kinase family are unique in their ability to utilize GTP as a cofactor for antibiotic modification. Here we describe the structural determinants for GTP recognition in these enzymes. The crystal structure of the GTP-dependent APH(2'')-IIIa shows that although this enzyme has templates for both ATP and GTP binding superimposed on a single nucleotide specificity motif, access to the ATP-binding template is blocked by a bulky tyrosine residue. Substitution of this tyrosine by a smaller amino acid opens access to the ATP template. Similar GTP binding templates are conserved in other bacterial aminoglycoside kinases, whereas in the structurally related eukaryotic protein kinases this template is less conserved. The aminoglycoside kinases are important antibiotic resistance enzymes in bacteria, whose wide dissemination severely limits available therapeutic options, and the GTP binding templates could be exploited as new, previously unexplored targets for inhibitors of these clinically important enzymes.

Aminoglycoside use in renal failure

Aminoglycosides are the mainstay in the treatment of serious gram negative infections including catheter-associated infections. They are not metabolized and are rapidly excreted as such by glomerular filtration resulting in a plasma t^½ of approximately two hours in those with normal renal function. The t^½, however, can extend to 30-60 hours in patients who are functionally anephric; therefore, dosage reduction or modification is necessary in renal failure patients. In patients on hemodialysis the clearance of aminoglycosides is significant and variable. The concept of conventional postdialysis dosing in patients on hemodialysis needs to be revised in favor of higher predialysis doses to maintain effective bactericidal activity. This article is a brief review of the use of aminoglycosides in renal failure patients.

Sub-acute toxicity study of a new aminoglycoside etimicin sulphate in swiss albino mice

Etimicin sulfate, an ethylization derivative of gentamicin, is a new soluble wide-spectrum synthetic aminoglycoside drug. It has wide antibacterial spectrum with high effect and less cross resistance as compared to other aminoglycosides. In order to further explore its safety and tolerance, we have conducted a subactute toxicity study on swiss albino mice. Results from the present study have elucidated that treatment of etimicin sulfate exerts no significant signs of toxicity at any dose level used in the study. Physiological as well as hematological parameters were unaltered throughout the study. Biochemical examination and histopathology of all organs confirmed no significant alteration at any dose levels. The result of this study has suggested there was no obvious toxicity observed with the treatment of etimicin sulphate. It was found to be a safe alternative for various severe infections.

Crystal structure and kinetic mechanism of aminoglycoside phosphotransferase-2''-IVa

Acquired resistance to aminoglycoside antibiotics primarily results from deactivation by three families of aminoglycoside-modifying enzymes. Here, we report the kinetic mechanism and structure of the aminoglycoside phosphotransferase 2''-IVa (APH(2'')-IVa), an enzyme responsible for resistance to aminoglycoside antibiotics in clinical enterococcal and staphylococcal isolates. The enzyme operates via a Bi-Bi sequential mechanism in which the two substrates (ATP or GTP and an aminoglycoside) bind in a random manner. The APH(2'')-IVa enzyme phosphorylates various 4,6-disubstituted aminoglycoside antibiotics with catalytic efficiencies (k(cat)/K(m)) of 1.5 x 10(3) to 1.2 x 10(6) (M(-1) s(-1)). The enzyme uses both ATP and GTP as the phosphate source, an extremely rare occurrence in the phosphotransferase and protein kinase enzymes. Based on an analysis of the APH(2'')-IVa structure, two overlapping binding templates specifically tuned for hydrogen bonding to either ATP or GTP have been identified and described. A detailed understanding of the structure and mechanism of the GTP-utilizing phosphotransferases is crucial for the development of either novel aminoglycosides or, more importantly, GTP-based enzyme inhibitors which would not be expected to interfere with crucial ATP-dependent enzymes.

Mitochondrial 12S rRNA mutations associated with aminoglycoside ototoxicity

The mitochondrial 12S rRNA is a hot spot for mutations associated with both aminoglycoside-induced and nonsyndromic hearing loss. Of those, the homoplasmic 1555A>G and 1494C>T mutations at the highly conserved decoding region of the 12S rRNA have been associated with hearing loss worldwide. In particular, these two mutations account for a significant number of cases of aminoglycoside ototoxicity. The 1555A>G or 1494C>T mutation is expected to form a novel 1494C-G1555 or 1494U-A1555 base-pair at the highly conserved A-site of 12S rRNA. These transitions make the human mitochondrial ribosomes more bacteria-like and alter binding sites for aminoglycosides. As a result, the exposure to aminoglycosides can induce or worsen hearing loss in individuals carrying one of these mutations. Biochemical characterization demonstrated an impairment of mitochondrial protein synthesis and subsequent defects in respiration in cells carrying the A1555G or 1494C>T mutation. Furthermore, a wide range of severity, age-at-onset and penetrance of hearing loss was observed within and among families carrying these mutations. Nuclear modifier genes, mitochondrial haplotypes and aminoglycosides should modulate the phenotypic manifestation of the 12S rRNA 1555A>G and 1494C>T mutations. Therefore, these data provide valuable information and technology: (1) to predict which individuals are at risk for ototoxicity; (2) to improve the safety of aminoglycoside antibiotic therapy; and (3) eventually to decrease the incidence of hearing loss.

Class-dependent relevance of tissue distribution in the interpretation of anti-infective pharmacokinetic/pharmacodynamic indices

The pharmacokinetic/pharmacodynamic (PK/PD) indices useful for predicting antimicrobial clinical efficacy are well established. The most common indices include the time free drug concentration in plasma is above the minimum inhibitory concentration (MIC) (fT(>MIC)) expressed as a percent of the dosing interval, the ratio of maximum concentration to MIC (C(max)/MIC), and the ratio of the area under the 24-h concentration-time curve to MIC (AUC(0-24)/MIC). A single PK/PD index may correlate well with an entire antimicrobial class. For example, the beta-lactams correlate well with the fT(>MIC). However, other classes may be more complex and a single index cannot be generalised to the class, e.g. the macrolides. The rationale behind which PK/PD index best correlates with efficacy depends on several factors, including the mechanism of action, the microbial kill kinetics, the degree of protein binding and the degree of tissue distribution. Studies have traditionally emphasised the first two factors, whilst the significance of protein binding and tissue distribution is increasingly appreciated. In fact, the latter two factors may partially elucidate why the magnitude of reported target indices are not always as expected. For example, tigecycline and telithromycin are clinically efficacious with average serum concentrations below their MICs over a 24-h period. Therefore, to understand more fully the PK/PD relationship of antibiotics and to better predict the clinical efficacy of antibiotic dosing regimens, assessment of free drug concentrations at the site of action is warranted.

Effect of once-daily dosing vs. multiple daily dosing of tobramycin on enzyme markers of nephrotoxicity

OBJECTIVE

To determine the incidence of nephrotoxicity of once-daily dosing (ODD) and multiple daily dosing (MDD) regimens of tobramycin in critically ill patients.

DESIGN

Randomized, prospective clinical trial.

SETTING

: Adult intensive care units at two university hospitals.

PATIENTS

Fifty-eight critically ill patients with a suspected or documented aerobic Gram-negative infection.

INTERVENTIONS

Patients were randomized to receive tobramycin by ODD (7 mg/kg) or MDD. Baseline urine aliquots and 24-hr urine collections were collected on days 3, 7, and 11 during therapy and on days 3, 7, and 11 following discontinuation of therapy for measurement of alanine aminopeptidase (AAP), N-acetyl-beta-d-glucosaminidase (NAG), and creatinine.

MEASUREMENTS AND MAIN RESULTS

Fifty-four patients were evaluable (ODD n = 25; MDD n = 29). The groups were similar with regard to demographic and clinical variables. The tobramycin dose was higher in the ODD group compared with the MDD group (425 +/- 122.5 mg vs. 312.8 +/- 116.6 mg, p <.001). Patients in the MDD group received a mean of 3.89 +/- 1.14 mg.kg(-1)day(-1) at intervals of 11.92 +/- 3.12 hrs. In the ODD group, patients had a higher measured creatinine clearance at the end of therapy compared with MDD group (70 +/- 18.6 vs. 64.8 +/- 17.5 mL/min, p =.047). Fewer patients in the ODD group developed nephrotoxicity than the MDD group (5 vs. 12, p =.142). Although there were increases in urinary enzymes in both treatment groups (AAP, 8.7 +/- 2.9 vs. 5.2 +/- 2.1 units/24 hrs, p <.01 MDD vs. ODD; NAG, 14.7 +/- 4.9 vs. 6.8 +/- 3.1, p <.01 MDD vs. ODD), the increases in the ODD group were significantly lower than in the MDD group.

CONCLUSIONS

: The ODD tobramycin regimen appeared to be less nephrotoxic than the MDD regimen despite significantly higher doses. Tobramycin administered by ODD may be the preferred dosing method in selected critically ill medical patients to reduce the incidence and extent of renal damage.

Synthesis of linked carbohydrates and evaluation of Their binding for 16S RNA by mass spectrometry

A library of linked molecules were synthesized from the common sugar moieties existing in the natural amino glycosides. These linked molecules were screened against bacterial 16S RNA for their binding affinity using a mass spectrometry-based technology. Some of these compounds exhibited low micromolar affinity and could serve as leads for further development as antibacterial agents.

In vitro activity of beta-lactams in combination with other antimicrobial agents against resistant strains of Pseudomonas aeruginosa

Using the chequerboard titration method, the activity in combination of beta-lactams, fluoroquinolones and aminoglycosides was investigated against 24 Pseudomonas aeruginosa isolates resistant to these antibiotics. Synergy was detected with one or more antimicrobial combinations against 15 of 24 (63%) isolates and partial synergy was detected with one or more combinations against all 24 isolates. No antagonism was seen with any combination. Ceftazidime and cefepime with aztreonam, amikacin and isepamicin showed synergy or partial synergy against 12-20 (50-80%) isolates. Imipenem and meropenem with amikacin and isepamicin showed synergy or partial synergy against eight to 12 (33-50%) isolates. The results of this study indicate that against P. aeruginosa, synergy may occur between beta-lactams, fluoroquinolones and aminoglycosides although the strains are resistant to the individual antibiotics.

Renal transport of antibiotics and nephrotoxicity: a review

The renal excretion of a drug can essentially be divided schematically into three functional processes: glomerular filtration, tubular reabsorption and tubular secretion. When assessing nephrotoxicity, the tubular secretion system, which allows transport of the drug from the blood to the urine via the tubular cells, is particularly important. Historically, two distinct tubular secretion mechanisms have been described for drugs: one via organic cations and the other via organic anions. More recently, a third tubular secretion mechanism has been identified, mediated by P-glycoprotein. In the present review, a number of examples will be given relating to antibiotic-induced kidney damage determined via the tubular reabsorption mechanism (aminoglycosides, amphotericin B) and via the tubular secretion mechanism (cephalosporins, vancomycin), respectively. Drug transport within the tubular cells is the first fundamental stage in the onset of the nephrotoxic process. Knowledge of these concepts is important for the prevention of iatrogenic kidney damage, particularly in patients with underlying disease receiving concomitant treatment with several potentially nephrotoxic molecules.

Evaluating the efficacy of amikacin in low-clearance unilamellar liposomes in a s. Aureus local infection model

Traditional therapies for Staphylococcal infections such as osteomyelitis or localized abscesses have a difficult time penetrating into tissue sites. To effectively ameliorate these infections, prolonged therapy and/or high doses of antibiotics are frequently required. Aminoglycosides, such as amikacin, are not routinely utilized for treating local infections due to poor efficacy associated with ineffective tissue penetration, toxicity, and poor penetration in an acid millieu. We postulated that a formulation of amikacin in small unilamellar liposomes might readily be engulfed by inflammatory macrophages facilitating drug delivery to the site of infection. This increased drug load to the site of bacterial infection may result in enhanced bactericidal action compared to conventional aminoglycosides. Tissue drug concentrations were determined for liposomal amikacin (L-AN) and conventional amikacin (AN). Plasma amikacin levels were determined for L-AN. The L-AN was very effective at concentrating at the site of infection compared to AN. Following confirmation of adequate tissue drug levels, a rodent subcutaneous abscess infection using S. aureus as the bacterial challenge agent was evaluated. Sprague-Dawley rats were intravenously administered L-AN every other day due to its prolonged half-life, while the comparator agent, AN, was administered daily. Abscess size, weights, severity, histology, and tissue colony counts were examined. In efficacy studies, L-AN was superior to AN in reducing colony counts.

Prophylaxis of implant-related staphylococcal infections using tobramycin-containing bone cement

In a rabbit model, premixed tobramycin-containing bone cement was studied for its efficacy to prevent infections with two frequently encountered staphylococcal species in arthroplasty surgery. After intramedullary inoculation with staphylococci, either standard or premixed tobramycin-containing Simplex-P bone cement was injected in the right femur of 120 rabbits. Development of infection was examined by culture of femoral bone after 7 or 28 days. Loss of body weight and elevated erythrocyte sedimentation rate in the control rabbits inoculated with Staphylococcus aureus were seen in the first postoperative week, returning to normal in 28 days. Inoculation with Staphylococcus epidermidis resulted only in a low-grade infection. All rabbits receiving premixed tobramycin-containing bone cement were free of signs of infection, and all their cultures were negative. Culture yield from Staphylococcus aureus controls increased with time and inoculum dose. Staphylococcus epidermidis controls needed higher inoculum doses to establish an infection, while culture yield decreased in time. These differences in mode of prosthesis-related infection are explained by differences in virulence factors.

Gentamicin for the practicing urologist: review of efficacy, single daily dosing and "switch" therapy

PURPOSE

We review the literature on gentamicin, including single daily dosing and "switch" therapy.

MATERIALS AND METHODS

We used MEDLINE to search the literature from 1966 to June 1997, and then manually searched bibliographies to identify studies that our initial search might have missed.

RESULTS

Gentamicin has attractive characteristics, including wide spectrum, infrequent resistance, economy and familiarity. Although limited by well known toxicities, gentamicin remains a drug of choice for serious Gram-negative infections. Dosing strategies, such as single daily dosing and switch therapy, have renewed enthusiasm for this time-honored drug.

CONCLUSIONS

Gentamicin remains a valuable drug in urology. Once daily dosing and switch therapy offer the potential to increase effectiveness and convenience while decreasing toxicity and costs.

Iron chelators protect from aminoglycoside-induced cochleo- and vestibulo-toxicity

The attenuation of gentamicin-induced hearing loss by iron chelators and radical scavengers has recently been demonstrated in guinea pig in vivo. The present study investigated whether this protective treatment is effective against hearing loss and vestibular damage caused by other aminoglycosides. In a direct comparison, dihydroxybenzoate was chosen over deferoxamine because of its more effective action against gentamicin-induced hearing loss. Guinea pigs received daily injections of kanamycin (250 mg/kg/d) or streptomycin (300 mg/kg/d) for 23 d to induce severe cochlear or vestibular toxicity, respectively. Kanamycin injections resulted in a progressive threshold shift of 60 to 80 dB at 18 kHz, while streptomycin injections induced only a small threshold shift. In contrast, streptomycin abolished almost all vestibular responses. Coinjection of aminoglycosides with a mixture of dihydroxybenzoate (100 mg/kg/d) and mannitol (30 mg/kg/d) significantly attenuated kanamycin-induced hearing loss and protected against streptomycin-induced vestibulotoxicity. DHB/mannitol did not affect serum levels or the antibacterial efficacy of either aminoglycoside. This study supports the idea that iron and free radicals play a critical role in the toxic side effects of aminoglycoside antibiotics. Furthermore, the previously proposed therapeutic protection is not limited to gentamicin but applicable to other aminoglycosides as well.

Determination of activities of levofloxacin, alone and combined with gentamicin, ceftazidime, cefpirome, and meropenem, against 124 strains of Pseudomonas aeruginosa by checkerboard and time-kill methodology

A total of 124 Pseudomonas aeruginosa strains were tested for synergy between levofloxacin and cefpirome, ceftazidime, gentamicin, and meropenem. Checkerboards yielded synergistic fractional inhibitory concentration (FIC) indices (< or =0.5) with 25 of 496 possible combinations. All other FIC indices were >0.5 to 2 (additive or indifferent), with no antagonism. Time-kill studies with 12 strains showed that levofloxacin (0.06 to 0.5 microg/ml) was synergistic with cefpirome, ceftazidime, gentamicin, and meropenem in 10, 9, 4, and 11 strains, respectively.

Inhibition of aminoglycoside antibiotic resistance enzymes by protein kinase inhibitors

Bacterial resistance to the aminoglycoside antibiotics is manifested primarily through the expression of enzymes which covalently modify these drugs. One important mechanism of aminoglycoside modification is through ATP-dependent O-phosphorylation, catalyzed by a family of aminoglycoside kinases. The structure of one of these kinases, APH(3')-IIIa has recently been determined by x-ray crystallography, and the general fold is strikingly similar to eukaryotic protein kinases (Hon, W. C., McKay, G. A., Thompson, P. R., Sweet, R. M., Yang, D. S. C., Wright, G. D., and Berghuis, A. M. (1997) Cell 89, 887-895). Based on this similarity, we have examined the effect of known inhibitors of eukaryotic protein kinases on two aminoglycoside kinases, APH(3')-IIIa and the enzyme AAC(6')-APH(2") which also exhibits acetyl-CoA-dependent aminoglycoside modification activity. We report that several known protein kinase inhibitors are also good inhibitors of aminoglycoside kinases. Compounds belonging to the isoquinolinesulfonamide group are especially effective in this regard, giving competitive inhibition in the micromolar range with respect to ATP and noncompetitive inhibition versus the aminoglycoside substrate. This study provides the basis for future aminoglycoside kinase inhibitor design and for the development of compounds which could reverse antibiotic resistance in the clinic.

Recognition of aminoglycoside antibiotics by enterococcal-staphylococcal aminoglycoside 3'-phosphotransferase type IIIa: role of substrate amino groups

The interactions of the aminoglycoside 3'-phosphotransferase IIIa with aminoglycoside antibiotics lacking specific amino groups were examined by steady-state kinetic analyses. The results demonstrate that an amino group on C-1 and either an amino or a hydroxyl group at the 2' and 6' positions are important for detoxification of aminoglycosides by this enzyme.

Lipid-based slow-release formulation of amikacin sulfate reduces foreign body-associated infections in mice

Treatment and prophylaxis of uncomplicated infections with standard systemic antibiotics are usually successful. However, standard systemic antibiotic therapy alone is frequently unsatisfactory in certain circumstances, such as the presence of a foreign body (FB), necrotic tissue, overwhelming bacterial inoculum, or poor vascular supply to the involved tissues. We have developed a lipid-based sustained release formulation of amikacin sulfate (DepoFoam encapsulated amikacin sulfate [DEAS]) as a biodegradable, locally injectable antibiotic for such circumstances. The encapsulated drug is released over 7 to 10 days. We tested the efficacy of this formulation in an FB infection model in which Teflon tubes (length, 1 cm; outside diameter, 1.6 mm) were implanted into the subcutaneous tissue in mice and the local site was inoculated with 0.87 x 10(7) CFU of Staphylococcus aureus 3 days later. Inoculation was followed by either no treatment or a local injection of DEAS, free amikacin sulfate, non-drug-containing DepoFoam, or systemic free amikacin sulfate. All drug applications contained 1 mg of amikacin. One group was implanted with the FB and left unchallenged with bacteria and untreated as a sterile control group. All animals were sacrificed 10 days following FB implantation. FBs were retrieved from tissues by an aseptic technique and incubated in liquid culture media for 7 days. Local wound tissue was excised and processed to determine the number of CFU per gram of tissue. Treatment with local or systemic free amikacin had no effect on the number of infected FBs or on the log CFU in wound tissue compared with the untreated or non-drug-containing DepoFoam group. Compared with local free amikacin therapy, the number of infected FBs was reduced from 86 to 25% (P=0.02) following treatment with DEAS, and log CFU per gram of tissue was significantly decreased from 4.8 +/- 0.9 to 1.3 +/- 0.6 (P<0.0005). DEAS may have clinical utility as locally injected antibiotic in certain infections.

Aminoglycoside-associated nephrotoxicity in extrahepatic obstructive jaundice

Experimental data demonstrate that biliary obstruction increases renal sensitivity to gentamicin. In the present study the incidence of and risk factors for aminoglycoside nephrotoxicity were prospectively studied in patients with extrahepatic obstructive jaundice. Two hundred and thirty-seven hospitalized adult patients were classified into three groups. Group I consisted of 84 patients with extrahepatic obstructive jaundice, who received aminoglycoside (gentamicin or tobramycin). Group II consisted of 81 patients with extrahepatic obstructive jaundice, who received either antibiotics other than aminoglycoside or no antimicrobial therapy. Group III consisted of 72 noncholestatic patients receiving aminoglycosides for different disorders. Nephrotoxicity developed in 27 patients (32%) in group I vs 9 patients (11%) in group II and 4 patients (5.6%) in group III (p < 0.00001). In group I, a comparison of patients with and without nephrotoxicity revealed significantly higher values in the former for mean serum bilirubin concentration, initial steady-state trough aminoglycoside concentration and estimated half-life. Stepwise multivariate analysis with nephrotoxicity status as the dependent variable determined that the most significant variable for predicting nephrotoxicity was serum total bilirubin level. In extrahepatic cholestasis a high serum bilirubin level is a distinct factor predisposing to aminoglycoside nephrotoxicity.

Effect of route of administration and age on the pharmacokinetics of amikacin administered by the intravenous and intraosseous routes to 3 and 5-day-old foals

The suitability of the intraosseous (i.o.) route for drug administration to equine neonates was evaluated in a study comparing the pharmacokinetics of amikacin administered by the i.o. and intravenous (i.v.) routes. Using a cross-over study design amikacin sulphate (7 mg/kg bwt) was administered i.o. or i.v. to 6 healthy foals at 3 and 5 days of age. Amikacin was instantaneously and completely absorbed after i.o. administration, achieving a mean +/- sd peak concentration (34.17 +/- 3.54 micrograms/ml) in the first sample collected 3 min after administration which was not significantly different from the mean +/- sd peak concentration (32.92 +/- 2.63 micrograms/ml) achieved after i.v. administration. The plasma amikacin concentration-time profiles for the i.o. and i.v. routes were not different and both were appropriately described by a 2-compartment open pharmacokinetic model. No significant differences attributable to route of administration were found in values for the major pharmacokinetic variables. The degree of inter-individual variation in values for indices of clearance was considerably greater than the degree of variation attributable to age. Despite this, values for body clearance (ClB) were significantly higher (P < 0.05) and values for area under the plasma amikacin concentration-time curve (AUC) and concentration of amikacin in plasma at 8 h [Cp(8h)] were significantly lower in 5- than in 3-day-old foals, indicating that amikacin was more rapidly cleared by the older foals. Technical difficulties were not encountered during i.o. needle placement in the medial aspect of the proximal tibia. Mild diffuse soft tissue swelling which developed at the i.o. site resolved completely within 1-2 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Broad spectrum aminoglycoside phosphotransferase type III from Enterococcus: overexpression, purification, and substrate specificity

The aminoglycoside phosphotransferases (APHs) are responsible for the bacterial inactivation of many clinically useful aminoglycoside antibiotics. We report the characterization of an enterococcal enzyme, APH(3')-IIIa, which inactivates a broad spectrum of aminoglycosides by ATP-dependent O-phosphorylation. Overproduction of APH(3')-IIIa has permitted the isolation of 30-40 mg of pure protein/(L of cell culture). Purified APH(3')-IIIa is a mixture of monomer and dimer which is slowly converted to dimer only over time. Dimer could be dissociated into monomer by incubation with 2-mercaptoethanol, suggesting that dimerization is mediated by formation of disulfide bond(s). Both monomer and dimer show Km values in the low micromolar range for good substrates such as kanamycin and neomycin, and kcat values of 1-4 s-1. All aminoglycosides show substrate inhibition except amikacin and kanamycin B. Determination of minimum inhibitory concentrations indicates a positive correlation between antibiotic activity and kcat/Km, but not with Km or kcat. NMR analysis of phosphorylated kanamycin A has directly demonstrated regiospecific phosphoryl transfer to the 3'-hydroxyl of the 6-aminohexose ring of the antibiotic. Analysis of structure-activity relationships with a variety of aminoglycosides has revealed that the deoxystreptamine aminocyclitol ring plays a critical role in substrate binding. This information will form the basis for future design of inhibitors of APH(3')-IIIa.

Physiological changes due to age. Implications for respiratory drug therapy

The pulmonary system is modified in various ways over time and it is particularly vulnerable to environmental insults. Of particular interest are the implications of aging for therapy of respiratory illnesses. The changes in pulmonary structure and function due simply to aging, and changes due to diseases, should be distinguished from each other. The great reserve function of the lung permits reasonable physical capacity in healthy individuals despite aging changes. In principle, loss of function equivalent to more than one lung is necessary to impair aerobic capacity at any age. Elderly people are subject to the same respiratory diseases as younger adults but may manifest them differently. They may present in atypical ways such as in bacterial pneumonia, tuberculosis, and asthma, all modified by anatomical alterations or deterioration of immunological defence mechanisms. Accumulation of toxic substances over time such as cigarette smoke or environmental pollutants may give rise to chronic bronchitis, emphysema, bronchogenic carcinoma and interstitial lung disease. Changes in the number or function of airway receptors modulate responses to bronchodilator drugs. Chronic inflammation of the bronchial wall has blurred the distinction between traditional asthma and chronic bronchitis and emphysema, and similar drug therapy can be useful for all. Adverse reactions to respiratory drugs such as theophylline, oral corticosteroids, and isoniazid increase with age. As more data accumulate, drug therapy of respiratory diseases in older patients will become more effective and safer.

Combination antibiotic supplementation of corneal storage medium

Gram-positive cocci frequently contaminate donor corneal tissue and represent the most common cause of postkeratoplasty endophthalmitis. Although gentamicin is currently added to corneal storage medium in an effort to decrease bacterial contamination of donor tissue, it has poor or variable in vitro activity against many strains of streptococci and staphylococci. To investigate whether the antibiotic supplementation of corneal storage media could be improved, we surveyed 11 antibiotics for antimicrobial efficacy under simulated storage conditions against gentamicin-resistant strains of Staphylococcus aureus, S. epidermidis, Streptococcus pneumoniae, and St. viridans. All antibiotics showed markedly reduced activity at 4 C as compared to their predicted activity at 37 C. Bactericidal activity of streptomycin and tobramycin was enhanced by preceding 4 C storage with a three-hour period at room temperature (23 C). Under these conditions, streptomycin showed the best antimicrobial activity of the 11 antibiotics tested. Addition of gentamicin to streptomycin resulted in further improvement of activity against S. aureus and S. epidermidis, whereas the addition of penicillin G to streptomycin enhanced the activity against St. viridans. Optimal antibiotic activity (99% or more killing) against all four isolates of gentamicin-resistant gram-positive cocci was best achieved with the combination of gentamicin, streptomycin, and penicillin G, coupled with a three-hour period at room temperature before 4 C storage.

Antituberculous agents

Antituberculous agents have radically improved the prognosis of patients with active tuberculosis. Generally, 6-month and 9-month antituberculous regimens have been successful, and surgical therapy is rarely needed. Extrapulmonary tuberculosis should be managed with the same drug regimens as pulmonary tuberculosis. The major cause of therapeutic failure is poor compliance of the patient in taking the prescribed medication regularly. A second cause of failure of treatment is resistance of tubercule bacilli to antimicrobial agents used. When failure of treatment is apparent, careful reassessment by physicians experienced in the treatment of tuberculosis is indicated. A single drug should never be added to a failing regimen. Isoniazid administered prophylactically for 6 to 12 months is effective in most cases.