Effect of medium age and supplementation with the biocatalytic oxygen-reducing reagent oxyrase on in vitro activities of tigecycline against recent clinical isolates

Impact of erythrocytes on bacterial growth and antimicrobial activity of selected antibiotics

It has been shown that protein binding, temperature, and pH influence in vitro pharmacodynamic (PD) models. The fact that corpuscular blood compounds might also have an important impact is something which has, until now, often been neglected. We investigated if the addition of human erythrocytes to standard growth media (Mueller Hinton Broth, MHBII) has an influence on bacterial growth behavior and on antibiotic efficacy. We did this by using bacterial growth assays and time kill curves (TKC) of selected strains (Escherichia coli ATCC25922, Staphylococcus aureus ATCC29213, and Pseudomonas aeruginosa ATCC27853) over 24 h. The final concentration of erythrocytes was set to match the physiological concentrations in the blood of a healthy human, i.e., 3 × 10^6 cells/μl in MHBII. Meropenem, ciprofloxacin, and tigecycline were tested with concentrations several-fold above and below the minimal inhibitory concentration (MIC). Moreover, HPLC analysis of antibiotic stability and distribution in erythrocytes was performed. Meropenem, ciprofloxacin, and tigecycline showed the greatest decline in activity against E. coli when erythrocytes were present. A mean difference in log10 bacterial killing between pure MHBII and 50%-Ery of 3.83, 1.33, and 2.42 was found for ciprofloxacin, meropenem, and tigecycline, respectively. In the case of ciprofloxacin, HPLC analysis revealed that less extracellular antibiotic is available in the presence of erythrocytes. We have demonstrated that erythrocytes do influence antimicrobial activity and that this might have an impact on the extrapolation of in vitro activity testing to in vivo efficacy in patients.

Effect of Susceptibility Testing Conditions on the In Vitro Antibacterial Activity of ETX0914

The effect of various conditions including pH, inoculum, temperature, atmosphere, divalent cations, and several body fluids on the in vitro activity of the novel antibacterial spiropyrimidinetrione ETX0914 in standard susceptibility tests was investigated against several species. None of the parameters investigated affected the activity of ETX0914, with the exception of pH. Whereas the MIC values for ETX0914 with S. aureus, E. faecalis, and E. coli did not change when the pH of the growth medium was varied from 5 to 8, they did increase at least 8-fold at pH values above 8. This loss of activity can be attributed to the deprotonation of the molecule at elevated pH. The data suggest that routine susceptibility testing with ETX0914 should result in reproducible MIC values.

The common prophylactic therapy for bowel surgery is ineffective for clearing Bacteroidetes, the primary inducers of systemic inflammation, and causes faster death in response to intestinal barrier damage in mice

Introduction and objective

The role of secreted gut microbial components in the initiation of systemic inflammation and consequences of antibiotic therapies on this inflammatory process are poorly elucidated. We investigate whether peripheral innate cells mount an inflammatory response to gut microbial components, the immune cells that are the primary drivers of systemic inflammation, the bacterial populations that are predominantly responsible, and whether perioperative antibiotics affect these processes.

Method and experimental design

Conditioned supernatants from gut microbes were used to stimulate murine innate cell types in vitro and in vivo, and proinflammatory responses were characterised. Effects of antibiotic therapies on these responses were investigated using a model of experimental intestinal barrier damage induced by dextran sodium sulfate.

Results

Proinflammatory responses in the periphery are generated by components of anaerobes from the Bacteroidetes phylotype and these responses are primarily produced by myeloid dendritic cells. We found that the common prophylactic therapy for sepsis (oral neomycin and metronidazole administered to patients the day prior to surgery) is ineffective for clearing Bacteroidetes from the murine intestine. A point of critical consequence of this result is the increased systemic inflammation and premature death observed in treated mice, and these outcomes appear to be independent of gut bacterial spread in the initial phase of intestinal barrier damage. Importantly, spillage of gut microbial products, rather than dissemination of gut microbes, may underlay the initiation of systemic inflammation leading to death.

Conclusions

Our data further affirm the importance of a balanced gut microflora biodiversity in host immune homeostasis and reinforce the notion that inadequate antibiotic therapy can have detrimental effects on overall immune system.

In vitro susceptibility testing of eravacycline is unaffected by medium age and nonstandard assay parameters

Eravacycline is a fluorocycline antibiotic in phase 3 clinical development for complicated intra-abdominal and urinary tract infections. To support its clinical development, a study was conducted to evaluate the effects of various susceptibility test parameters on the MIC values for aerobic bacteria. The results showed that eravacycline appears to be largely unaffected by medium age, medium additives, and other nonstandard assay conditions.

A novel formulation of tigecycline has enhanced stability and sustained antibacterial and antileukemic activity

Tigecycline is a broad-spectrum, first-in-class glycylcycline antibiotic currently used to treat complicated skin and intra-abdominal infections, as well as community-acquired pneumonia. In addition, we have demonstrated that tigecycline also has in vitro and in vivo activity against acute myeloid leukemia (AML) due to its ability to inhibit mitochondrial translation. Tigecycline is relatively unstable after reconstitution, and this instability may limit the use of the drug in ambulatory infusions for the treatment of infection and may prevent the development of optimal dosing schedules for the treatment of AML. This study sought to identify a formulation that improved the stability of the drug after reconstitution and maintained its antimicrobial and antileukemic activity. A panel of chemical additives was tested to identify excipients that enhanced the stability of tigecycline in solution at room temperature for up to one week. We identified a novel formulation containing the oxygen-reducing agents ascorbic acid (3 mg/mL) and pyruvate (60 mg/mL), in saline solution, pH 7.0, in which tigecycline (1 mg/mL) remained intact when protected from light for at least 7 days. This formulation also preserved the drug's antibacterial and antileukemic activity in vitro. Moreover, the novel formulation retained tigecycline's antileukemic activity in vivo. Thus, we identified and characterized a novel formulation for tigecycline that preserves its stability and efficacy after reconstitution.

Optimal tigecycline dosage regimen is urgently needed: results from a pharmacokinetic/pharmacodynamic analysis of tigecycline by Monte Carlo simulation

BACKGROUND

The number of reported cases of resistance to tigecycline is increasing. The aim of this study was to evaluate the current standard tigecycline dosage regimen from a pharmacokinetic/pharmacodynamic (PK/PD) perspective.

METHODS

Pharmacokinetic parameters and microbiological data were analyzed by Monte Carlo simulation in an evaluation of effectiveness.

RESULTS

Tigecycline exhibits excellent in vitro antimicrobial activity, however the standard tigecycline dosing regimen fails to achieve the best outcome in vivo for the common drug-resistant strains, including Acinetobacter baumannii, Enterobacter spp, and Klebsiella pneumoniae. This may result in a lack of response to tigecycline therapy or to a further increase in the resistance rate.

CONCLUSIONS

In the absence of new drugs on the horizon, rather than using a single fixed dosing regimen, tigecycline dosing needs to be optimized in order to achieve the desired successful clinical response and to prevent an escalation in drug resistance.

Effect of manganese in test media on in vitro susceptibility of Enterobacteriaceae and Acinetobacter baumannii to tigecycline

We assessed the effect of increasing manganese concentrations in test media (0.001 to 1,024 mg/liter) on MICs of tigecycline. For both broth microdilution (BMD) and Etests, this effect was negligible for physiological concentrations, but MICs increased when concentrations exceeded 8 mg/liter. Susceptibility testing should be performed on media with standardized low manganese content.

Tigecycline pharmacokinetics in subjects with various degrees of renal function

The pharmacokinetic parameters of tigecycline were assessed in subjects with severe renal impairment (creatinine clearance <30 mL/min, n = 6), subjects receiving hemodialysis (4 received tigecycline before and 4 received tigecycline after hemodialysis), and subjects with age-adjusted, normal renal function (n = 6) after administration of single 100-mg doses. Serial serum and urine samples were collected and assayed using validated liquid chromatography with tandem mass spectrometer (LC/MS/MS) methods. Concentration-time data were then analyzed using noncompartmental pharmacokinetic methods. Tigecycline renal clearance in subjects with normal renal function represented approximately 20% of total systemic clearance. Tigecycline clearance was reduced by approximately 20%, and area under the tigecycline concentration-time curve increased by approximately 30% in subjects with severe renal impairment. Tigecycline was not efficiently removed by dialysis; thus, it can be administered without regard to timing of hemodialysis. Based on these pharmacokinetic data, tigecycline requires no dosage adjustment in patients with renal impairment.

Activities of tigecycline and comparators against Legionella pneumophila and Legionella micdadei extracellularly and in human monocyte-derived macrophages

The activity of tigecycline against Legionellae, which are intracellular pathogens, was evaluated intracellularly in human phagocytes and extracellularly, and compared to the activities of erythromycin and levofloxacin. Clinical isolates of L. pneumophila serogroups 1, 5, and 6 and L. micdadei were tested in time-kill experiments. Extracellular experiments were done using buffered yeast extract broth. For intracellular assays, monolayers of human monocyte-derived macrophages (MDM) were infected with L. pneumophila or L. micdadei. Antibiotics (0.05-2.5 × MIC) were then added. MDM were lysed at 0, 24, 48, and 72 h and viable bacteria in the lysates were enumerated. Based on multiples of the MICs, tigecycline was less active extracellularly than levofloxacin or erythromycin. However, intracellular killing of both L. pneumophila and L. micdadei by tigecycline at 72 h was greater than for erythromycin or levofloxacin. Currently, evidence does not support the use of tigecycline as a first-line drug for treatment of Legionella infections. However, since Legionellae are intracellular pathogens, these results suggest that tigecycline should be effective for treatment of infections caused by these bacteria.

Confronting multidrug-resistant Acinetobacter baumannii: a review

Multidrug-resistant Acinetobacter baumannii (MDR-AB) infections are difficult to treat owing to the extremely limited armamentarium. The present review reports all available treatment options against MDR-AB, including single molecules, combination schemes, and alternative modes of antimicrobial administration. Additionally, a group of recently reported peptides with anti-MDR-AB activity is described.

Influence of media and testing methodology on susceptibility to tigecycline of Enterobacteriaceae with reported high tigecycline MIC

The tigecycline susceptibility of six different Enterobacteriaceae strains with reported high tigecycline MICs was determined in quintuplicate by four methodologies using Mueller-Hinton agar and broth from six manufacturers. The MICs determined by Etest were a >or=1-fold dilution lower than those determined by broth microdilution and agar dilution, with the highest modal values given by agar dilution. The highest modal MICs were obtained using Oxoid medium, and the lowest inhibition zone values (disc diffusion) were obtained using Oxoid and bioMérieux media. The lowest MICs were obtained by Etest using Difco or Merck media.

A review of tigecycline

The first article in this supplement is an overall review of the first glycylcycline, tigecycline, which includes a brief overview of the problem of tetracycline resistance as well as tigecycline's mode of action, antibacterial activity, pharmacokinetics, pharmacodynamics, clinical efficacy, safety and tolerability. The remaining articles in the supplement report the European clinical experience from the pivotal clinical trials in complicated intra-abdominal infections, complicated skin and skin structure infections and community acquired pneumonia.

Comparison of tigecycline and vancomycin for treatment of experimental foreign-body infection due to methicillin-resistant Staphylococcus aureus

Twice-daily 7-day regimens of tigecycline (7 mg/kg) and vancomycin (50 mg/kg) were compared in a rat tissue cage model of chronic foreign-body infection due to methicillin (meticillin)-resistant Staphylococcus aureus strain MRGR3. Subcutaneously administered tigecycline reached levels in tissue cage fluid that were nearly equivalent or slightly superior to the antibiotic MIC (0.5 microg/ml) for strain MRGR3. After 7 days, equivalent, significant reductions in bacterial counts were recorded for tigecycline-treated and vancomycin-treated rats, compared with those for untreated animals.

Nationwide surveillance in Taiwan of the in-vitro activity of tigecycline against clinical isolates of extended-spectrum beta-lactamase-producing Enterobacteriaceae

Tigecycline In-vitro Surveillance in Taiwan (TIST), initiated in 2006, is a nationwide surveillance programme designed to monitor longitudinally the in-vitro activity of tigecycline against commonly encountered resistant bacteria. This study compared the in-vitro activity of tigecycline against clinical isolates of resistant Gram-negative bacteria determined by the broth microdilution and Etest methods. A total of 622 isolates were collected from patients treated at 20 teaching hospitals. Tigecycline had excellent in-vitro activity against extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli (N = 275) with MIC(90) 0.5 microg/mL and a 99.6% susceptibility rate, and also against ESBL-producing Klebsiella pneumoniae (N = 324) with MIC(90) 2 microg/mL and a 98.5% susceptibility rate. For ESBL-producing Proteus mirabilis (N = 15) the MIC(90) was 4 microg/mL with a 73.3% susceptibility rate. For ESBL-producing Klebsiella oxytoca (N = 8) the MIC(50) and MIC(90) were 0.5 and 1 microg/mL, respectively, with a 100% susceptibility rate. Limited agreement (<80%) was found between the broth microdilution and the Etest methods when determining the in-vitro activity of tigecycline against ESBL- producing K. pneumoniae and K. oxytoca.

High concentrations of manganese in Mueller-Hinton agar increase MICs of tigecycline determined by Etest

MICs of tigecycline determined by Etest were 4 to 12 times (three ATCC strains) and 2 to 8 times (50 clinical isolates) higher in Mueller-Hinton agar from Merck than in Mueller-Hinton agar from either Oxoid or Difco. This was related to a much higher concentration of manganese in the medium from Merck.

In vitro activity of tigecycline and occurrence of tetracycline resistance determinants in isolates from patients enrolled in phase 3 clinical trials for community-acquired pneumonia

The in vitro activity of tigecycline was evaluated against baseline pathogens isolated from patients enrolled in phase 3 clinical trials for community-acquired pneumonia conducted in 29 countries worldwide. Tigecycline was active against the most prevalent pathogens, including Streptococcus pneumoniae (MIC(90) 0.06 mg/L), Staphylococcus aureus (MIC(90) 0.25 mg/L), Haemophilus influenzae (MIC(90) 0.5 mg/L) and Klebsiella pneumoniae (MIC(90) 1 mg/L). Twelve isolates of S. pneumoniae expressing tet(M) and two isolates of K. pneumoniae producing extended-spectrum beta-lactamases isolated during the study were susceptible to tigecycline. The excellent in vitro activity of tigecycline against these clinical isolates confirmed its potential utility against pathogens associated with community-acquired pneumonia.

Acinetobacter baumannii: emergence of a successful pathogen

Acinetobacter baumannii has emerged as a highly troublesome pathogen for many institutions globally. As a consequence of its immense ability to acquire or upregulate antibiotic drug resistance determinants, it has justifiably been propelled to the forefront of scientific attention. Apart from its predilection for the seriously ill within intensive care units, A. baumannii has more recently caused a range of infectious syndromes in military personnel injured in the Iraq and Afghanistan conflicts. This review details the significant advances that have been made in our understanding of this remarkable organism over the last 10 years, including current taxonomy and species identification, issues with susceptibility testing, mechanisms of antibiotic resistance, global epidemiology, clinical impact of infection, host-pathogen interactions, and infection control and therapeutic considerations.

Tigecycline for the treatment of multidrug-resistant Enterobacteriaceae: a systematic review of the evidence from microbiological and clinical studies

OBJECTIVES

Antimicrobial drug resistance is spreading among Enterobacteriaceae, limiting the utility of traditionally used agents. We sought to systematically review the microbiological activity and clinical effectiveness of tigecycline for multidrug-resistant (MDR) Enterobacteriaceae, including those resistant to broad-spectrum beta-lactams due to the expression of extended-spectrum beta-lactamases (ESBLs), AmpC enzymes and carbapenemases (including metallo-beta-lactamases).

METHODS

PubMed was searched for articles including relevant data.

RESULTS

Twenty-six microbiological and 10 clinical studies were identified. Tigecycline was active against more than 99% of 1936 Escherichia coli isolates characterized by any of the above resistance patterns (including 1636 ESBL-producing isolates) using the US Food and Drug Administration (FDA) breakpoint of susceptibility (MIC < or = 2 mg/L). Findings were not different using the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoint (< or = 1 mg/L). Susceptibility rates for Klebsiella spp. with any of the above resistance patterns were 91.2% for 2627 isolates by the FDA criteria and 72.3% for 1504 isolates by the EUCAST criteria (92.3% for 2030 and 72.3% for 1284 ESBL-producing isolates, by the FDA and EUCAST criteria, respectively). The degree of microbiological activity of tigecycline against 576 MDR Enterobacter spp. isolates was moderate. In clinical studies, 69.7% of the 33 reported patients treated with tigecycline achieved resolution of an infection caused by a carbapenem-resistant or ESBL-producing or MDR Enterobacteriaceae.

CONCLUSIONS

Tigecycline is microbiologically active against almost all of the ESBL or MDR E. coli isolates and the great majority of ESBL or MDR Klebsiella spp. isolates. Further evaluation of its clinical utility against such resistant Enterobacteriaceae, particularly regarding non-labelled indications, is warranted.

In vitro antibacterial activities of tigecycline and comparative agents by time-kill kinetic studies in fresh Mueller-Hinton broth

Time-kill kinetics performed with tigecycline, in fresh MHB, demonstrated a consistent 1 to 2 log(10) CFU/ml reduction in bacterial counts against the majority of clinically relevant pathogens tested. Although classified as a bacteriostatic agent, tigecycline shows bactericidal activity against select isolates associated with serious infection. In general, vancomycin and imipenem demonstrated bactericidal activity.

Validation and reproducibility assessment of tigecycline MIC determinations by Etest

A multicenter study was conducted to validate Etest tigecycline compared to the Clinical Laboratory Standards Institute reference broth microdilution and agar dilution methodologies. A large collection of gram-negative (n = 266) and gram-positive (n = 162) aerobic bacteria, a collection of anaerobes (n = 385), and selected collections of nonpneumococcal streptococci (n = 369), Streptococcus pneumoniae (n = 372), and Haemophilus influenzae (n = 372) were tested. Strains with reduced susceptibility to tigecycline were used with all test methods. The Etest showed excellent inter- and intralaboratory reproducibility for all organism groups tested regardless of the test methodology. The essential agreement values with the reference method (+/-1 dilution) were >99% for the collection of gram-negative and gram-positive aerobes; >98% for the S. pneumoniae, H. influenzae, and anaerobe collections; and 100% for the group of nonpneumococcal streptococci. These results validate the performance accuracy and utility of Etest tigecycline and verify the reproducibility of this convenient predefined gradient methodology for tigecycline susceptibility determination.

Comparative in vitro antimicrobial activity of tigecycline, a new glycylcycline compound, in freshly prepared medium and quality control

The in vitro spectra of activity of tigecycline and tetracycline were determined for 2,490 bacterial isolates representing 50 different species or phenotypic groups. All isolates were tested simultaneously by broth microdilution using freshly prepared Mueller-Hinton broth and by disk diffusion. Portions of these data were submitted to the Food and Drug Administration (FDA) in support of the sponsor's application for new drug approval. In a separate study, MIC and disk diffusion quality control ranges were determined. The tigecycline MICs at which 50%/90% of bacteria were inhibited were (in microg/ml) as follows: for Streptococcus spp., 0.06/0.12; for Moraxella catarrhalis, 0.06/0.12; for Staphylococcus spp., 0.12/0.25; for Enterococcus spp., 0.12/0.25; for Listeria monocytogenes, 0.12/0.12; for Neisseria meningitidis, 0.12/0.25; for Haemophilus spp., 0.25/0.5; for Enterobacteriaceae, 0.05/2.0; for non-Enterobacteriaceae, 0.5/8.0. Tigecycline was consistently more potent than tetracycline against all species studied. The data from this study confirm the FDA-approved MIC and disk diffusion breakpoints for tigecycline for Streptococcus spp. other than Streptococcus pneumoniae, enterococci, and Enterobacteriaceae. Provisional breakpoints for Haemophilus spp. and S. pneumoniae are proposed based on the data from this study. The following MIC and/or disk diffusion quality control ranges are proposed: Staphylococcus aureus ATCC 29213, 0.03 to 0.25 microg/ml; S. aureus ATCC 25923, 20 to 25 mm; Escherichia coli ATCC 25922, 0.03 to 0.25 microg/ml and 20 to 27 mm; Pseudomonas aeruginosa ATCC 27853, 9 to 13 mm, Enterococcus faecalis ATCC 29212, 0.03 to 0.12 microg/ml; S. pneumoniae ATCC 49619, 0.015 to 0.12 microg/ml and 23 to 29 mm; Haemophilus influenzae ATCC 49247, 0.06 to 0.5 microg/ml and 23 to 31 mm; and Neisseria gonorrhoeae ATCC 49226, 30 to 40 mm.

Tigecycline (GAR-936) activity against Streptococcus gallolyticus (bovis) and viridans group streptococci

Viridans group streptococci including Streptococcus gallolyticus (formerly S. bovis) represent serious invasive pathogens often associated with endocarditis or sepsis among immunocompromised or cancer patients. Tigecycline (GAR-936), the first clinically studied glycylcycline, has a potent gram-positive activity with a potential treatment option for these streptococcal infections. The studied collection (848 strains) included 100 isolates each of Streptococcus anginosus, Streptococcus constellatus, Streptococcus intermedius, Streptococcus mitis, Streptococcus oralis, Streptococcus salivarius, Streptococcus sanguis, and fewer strains of S. gallolyticus (98 strains) and Streptococcus mutans (50 strains). These strains were isolated from patients on 3 continents in the SENTRY Antimicrobial Surveillance Program and tested for susceptibility and interpreted by Clinical and Laboratory Standards Institute broth microdilution methods and criteria (< or = 0.25 microg/mL for tigecycline per US Food and Drug Administration). Penicillin susceptibility rates for the entire collection varied from 61% (S. sanguis) to 98% (S. constellatus), and macrolide susceptibility was also compromised (49-88%; average, 69%). Tigecycline was active against all isolates tested, in contrast to tetracycline resistance rates of 8-66%, and highest for S. gallolyticus. In conclusion tigecycline was quite active against bacteremic isolates of viridans group streptococci species and S. gallolyticus with an overall MIC90 at < or = 0.06 microg/mL; the highest MIC was only 0.25 microg/mL.

Multicenter studies of tigecycline disk diffusion susceptibility results for Acinetobacter spp

Acinetobacter sp. isolates having multidrug resistance (MDR) patterns have become common in many medical centers worldwide, limiting therapeutic options. A five-center study tested 103 contemporary clinical Acinetobacter spp., including MDR strains, by reference broth microdilution and disk diffusion (15-mug disk content) methods against tigecycline. Applying U.S. Food and Drug Administration tigecycline breakpoint criteria for Enterobacteriaceae (susceptibility at < or =2 microg/ml [< or =1 microg/ml by the European Committee on Antimicrobial Susceptibility Testing]; disk diffusion breakpoints at > or =19 mm and < or =14 mm) to Acinetobacter spp. led to an unacceptable error rate (23.3%). However, an adjustment of tigecycline disk diffusion breakpoints (susceptible/resistant) to > or =16/ < or =12 mm reduced intermethod errors to an acceptable level (only 9.7%, all minor).

Antimicrobial activity of tigecycline against clinical isolates from Spanish medical centers. Second multicenter study

The antimicrobial activity of tigecycline, a novel glycylcycline, was evaluated against 1102 bacterial isolates from 20 centers in Spain. The MIC of tigecycline at which 90% (MIC(90)) of the pneumococci tested were inhibited was the lowest (0.06 microg/mL) of all the antibiotics tested. The MICs of tigecycline against enterococci ranged from 0.03 to 0.125 microg/mL. All staphylococci were inhibited by < or =0.25 microg/mL of tigecycline, and 99.6% of Enterobacteriaceae isolates were inhibited by < or =2 microg/mL of tigecycline. Tigecycline demonstrated good activity against Bacteroides fragilis group organisms with an MIC(90) of 4 microg/mL. The results of this study confirm the excellent activity of tigecycline against multiresistant Gram-positive and Gram-negative pathogens.

Functional, biophysical, and structural bases for antibacterial activity of tigecycline

Tigecycline is a novel glycylcycline antibiotic that possesses broad-spectrum activity against many clinically relevant species of bacterial pathogens. The mechanism of action of tigecycline was delineated using functional, biophysical, and molecular modeling experiments in this study. Functional assays showed that tigecycline specifically inhibits bacterial protein synthesis with potency 3- and 20-fold greater than that of minocycline and tetracycline, respectively. Biophysical analyses demonstrated that isolated ribosomes bind tigecycline, minocycline, and tetracycline with dissociation constant values of 10(-8), 10(-7), and >10(-6) M, respectively. A molecular model of tigecycline bound to the ribosome was generated with the aid of a 3.40-angstrom resolution X-ray diffraction structure of the 30S ribosomal subunit from Thermus thermophilus. This model places tigecycline in the A site of the 30S subunit and involves substantial interactions with residues of H34 of the ribosomal subunit. These interactions were not observed in a model of tetracycline binding. Modeling data were consistent with the biochemical and biophysical data generated in this and other recent studies and suggested that tigecycline binds to bacterial ribosomes in a novel way that allows it to overcome tetracycline resistance due to ribosomal protection.

Diagnostic PCR analysis of the occurrence of methicillin and tetracycline resistance genes among Staphylococcus aureus isolates from phase 3 clinical trials of tigecycline for complicated skin and skin structure infections

Diagnostic PCR assays were developed to track common genetic determinants of oxacillin resistance as well as resistance to classical tetracyclines in Staphylococcus aureus isolates from the recently completed worldwide phase 3 clinical trials of tigecycline. A total of 503 unique S. aureus strains isolated from complicated skin and skin structure infections were analyzed. The mecA gene was amplified from 120 strains (23.9%) determined to be resistant to oxacillin (MICs > or = 4 microg/ml). The prevalence of the mecA gene was found to vary regionally from 6.5% to 50.9% among isolates originating in Eastern Europe and North America, respectively. The presence of a tetracycline resistance determinant, tet(M) or tet(K), among methicillin-resistant S. aureus (MRSA) isolates also varied regionally, with a range of 11.9% to 46.2% among isolates tested from North America and Eastern Europe, respectively. The occurrence of a tetracycline resistance marker in methicillin-susceptible S. aureus (MSSA) strains varied from 2.5 to 16.1% among the isolates tested across the regions of study. The presence of tet(M) or tet(K) had no discernible effect on the tigecycline MICs for either MRSA or MSSA strains, which is consistent with the ability of the glycylcyclines to retain activity in the presence of both the ribosomal protection and efflux mechanisms of resistance to the tetracyclines.

Tigecycline: an evidence-based review of its antibacterial activity and effectiveness in complicated skin and soft tissue and intraabdominal infections

INTRODUCTION

There is an urgent need for novel agents to manage serious bacterial infections, particularly those contracted in healthcare facilities. Tigecycline is a novel broad-spectrum glycylcycline with good activity against Gram-positive, many Gram-negative, anaerobic, and some atypical pathogens that has been developed to address this need.

AIMS

To review the evidence for the use of tigecycline in serious and complicated skin and soft tissue and intraabdominal infections.

EVIDENCE REVIEW

There is substantial evidence that tigecycline is as effective as vancomycin plus aztreonam in complicated skin and skin structure infections (SSSIs) and as effective as imipenem plus cilastatin in intraabdominal infections. Limited evidence shows effectiveness in patients with resistant Acinetobacter infection in an intensive care unit, and the possibility that the use of tigecycline may reduce length of hospital stay. The drug is well tolerated, with nausea and vomiting as the major adverse effects.

OUTCOMES SUMMARY

The introduction of tigecycline should be beneficial at a time of increasing problems with bacterial resistance, and evidence to date has been sufficient for regulatory approval for complicated SSSIs and intraabdominal infections. Research into tigecycline's efficacy in other infectious diseases (notably pneumonia and bacteremia) is ongoing. Further good quality studies and ongoing surveillance for any emerging bacterial resistance will be needed to determine outcomes with tigecycline relative to other novel antibacterial agents, and to explore the economic implications of its adoption.