Potency and spectrum of tigecycline tested against an international collection of bacterial pathogens associated with skin and soft tissue infections (2000–2004)

In vitro activity of tigecycline against multidrug-resistant Enterobacteriaceae isolates from skin and soft tissue infections

Background

Tigecycline, a new agent against multidrug-resistant (MDR) bacteria, is especially licensed for use in complicated skin and soft tissue and intra-abdominal infections. We aimed to study the recent in vitro activity of tigecycline against MDR Enterobacteriaceae skin and soft tissue isolates.

Methods

Consecutive isolates (56 Escherichia coli, 48 Klebsiella pneumoniae) were subjected to tigecycline susceptibility testing by Ezy MIC test and interpreted as per European Committee on Antimicrobial Susceptibility Testing.

Results

The minimum inhibitory concentrations (MICs) of tigecycline ranged from 0.016 to 48 μg/mL, with MIC₅₀ 0.19 μg/mL and MIC₉₀ 1.0 μg/mL respectively. Seven (6.7%) isolates were resistant to tigecycline, all K. pneumoniae.

Conclusion

Tigecycline remains a viable therapeutic option against MDR isolates, with excellent in vitro activity against E. coli and promising activity against K. pneumoniae. However, the limited availability of alternate therapeutic armamentarium necessitates its use with extreme judiciousness along with continuous monitoring for the emergence and spread of resistance.

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Tigecycline has excellent in vitro activity against MDR E. coli.

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Tigecycline has comparatively lower activity against MDR K. pneumoniae.

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Tigecycline remains a viable therapeutic option against MDR E. coli isolates.

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Limited availability of alternate therapy necessitates cautious use of tigecycline.

Tigecycline: a novel glycylcycline antibiotic

Tigecycline, the first-in-class glycylcycline, was developed to recapture the broad spectrum of activity of the tetracycline class and to treat patients with difficult-to-treat bacterial infections. Tigecycline's in vitro spectrum of activity encompasses aerobic, facultative and anaerobic Gram-positive and -negative bacteria, including antimicrobial-resistant bacteria such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis and Enterococcus faecium, and extended-spectrum beta-lactamase-producing Enterobacteriaceae. Clinical trials involving patients with complicated skin and skin-structure infections and complicated intra-abdominal infections, including patients infected with methicillin-resistant S. aureus, demonstrated that tigecycline was bacteriologically and clinically effective with mild-to-moderate gastrointestinal adverse events (i.e., nausea, vomiting and diarrhea) the most commonly reported. Tigecycline is a promising new broad-spectrum parenteral monotherapy for the treatment of patients with Gram-positive and -negative bacterial infections.

Antibiotic optimization in the difficult-to-treat patient with complicated intra-abdominal or complicated skin and skin structure infections: focus on tigecycline

Complicated intra-abdominal and skin and skin structure infections are widely varied in presentation. These infections very often lead to an increase in length of hospital stay, with a resulting increase in costs and mortality. In addition, these infections may be caused by a wide variety of bacteria and are often polymicrobial with the possibility of the presence of antimicrobial-resistant strains, such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, extended-spectrum β-lactamase strains (Escherichia coli, Klebsiella pneumoniae), and K. pneumoniae carbapenemase-producing strains. In combination with patients’ immunosuppression or comorbidities, the treatment and management options for initial therapy success are few. Tigecycline, a new glycylcyline antimicrobial from the tetracycline drug class, represents a viable option for the successful treatment of these infections. It has been shown to have activity against a wide variety of bacteria, including the antimicrobial-resistant strains. As with all tetracycline drugs, it is not recommended for pregnant or nursing women. The potential side effects are those typical of tetracycline drugs: nausea, vomiting, and headaches. Drug–drug interactions are not expected, and renal function monitoring is not necessary.

Efficacy of tigecycline vs. imipenem in the treatment of experimental Acinetobacter baumannii murine pneumonia

The in vivo activity of tigecycline was evaluated in an experimental pneumonia model (C57BL/6 mice) by Acinetobacter baumannii. Two clinical strains were used: minimum inhibitory concentrations (MICs) of imipenem and tigecycline 1 and 2 microg/mL (imipenem-susceptible, IPM-S), and 8 and 2 microg/mL (imipenem-intermediate, IPM-I), respectively. For imipenem (30 mg/Kg), T/CMI (h) were 1.04 and 0.51 for IPM-S and IPM-I, respectively. For tigecycline (5 mg/Kg), the area under the concentration-time curve (AUC)/MIC(0-24 h) (serum and lung) were 9.24 and 4.37 (for the two strains), respectively. In the efficacy experiments with the IPM-S, imipenem (log CFU/g 3.59 +/- 0.78, p = 0.006) and tigecycline (2.82 +/- 1.2, p = 0.054) decreased the bacterial counts in lungs with respect to its controls; with the IPM-I, both imipenem (1.21 +/- 0.52, p = 0.002) and tigecycline (3.21 +/- 0.28, p = 0.035) decreased the bacterial counts with respect to the controls. In the survival experiments, with the IPM-S, the mortality was the same in the control (67%) and in the tigecycline (77%) groups, and imipenem reduced it (21%, p = 0.025); with the IPM-I, the mortality was the same in the control (87%) and in the tigecycline (85%) groups, and imipenem (0%) reduced it (p < 0.001). In summary, the present study shows that tigecycline is less efficacious than imipenem in the treatment of experimental A. baumannii pneumonia caused by IPM-S and IPM-I strains.

The in vitro evaluation of tigecycline tested against pathogens isolated in eight countries in the Asia-Western Pacific region (2008)

OBJECTIVES

To determine the in vitro activity of tigecycline and comparator common use antimicrobial agents tested against contemporary bacterial pathogens from the Asia-Western Pacific region.

METHODS

As part of the SENTRY Antimicrobial Surveillance Program, a total of 5759 Gram-positive and Gram-negative isolates were collected from 28 medical centers in eight Asia-Western Pacific countries during 2008. Minimum inhibitory concentrations (MICs) were determined using Clinical and Laboratory Standards Institute (CLSI) broth microdilution method and interpreted using CLSI breakpoints. United States Food and Drug Administration (US-FDA) breakpoints were used to interpret tigecycline susceptibility.

RESULTS

Antimicrobial resistance was found to be widespread and prevalence varied considerably between the eight countries. Against pathogens for which breakpoints were available, >98% of all isolates were susceptible to tigecycline. Against all Gram-positive isolates, including methicillin (oxacillin)-resistant Staphylococcus aureus, penicillin- and multidrug-resistant pneumococci, and vancomycin-resistant enterococci, the highest tigecycline MIC found was 1 microg/ml. Against all Enterobacteriaceae, including extended-spectrum beta-lactamase phenotypes, tigecycline susceptibility was 97.5%. Tigecycline had good activity against Acinetobacter spp. but was much less active against Pseudomonas aeruginosa.

CONCLUSION

Tigecycline demonstrated excellent sustained in vitro activity against a wide spectrum of contemporary Gram-positive and -negative pathogens from Asia-Western Pacific countries.

Update on cutaneous manifestations of infectious diseases

Many emerging pathogens present in the skin and are of interest to dermatologists. Recent epidemics of measles, avian flu, and SARS demonstrated how an organism can rapidly spread worldwide because of airline travel. Travelers are often contagious before they are aware that they have the disease, contributing to the spread. This article reviews bacterial, mycobacterial, fungal, and viral pathogens important to dermatologists.

Antimicrobial susceptibility of tigecycline and comparators against bacterial isolates collected as part of the TEST study in Europe (2004-2007)

Tigecycline is a broad-spectrum antimicrobial agent that has been approved for the treatment of skin and soft-tissue infections as well as intra-abdominal infections. The Tigecycline Evaluation and Surveillance Trial (TEST) is a global, longitudinal surveillance study established in 2004 to monitor the in vitro activity of tigecycline and comparator agents against key Gram-negative and Gram-positive pathogens. This report examines data obtained for 24748 isolates collected across 24 European countries between 2004 and 2007. Tigecycline, meropenem and imipenem were the most active antimicrobial agents against most Gram-negative isolates including multidrug-resistant Acinetobacter baumannii (15.7% of the A. baumannii isolates in this study), extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli (8.5% of E. coli) and ESBL-producing Klebsiella pneumoniae (13.6% of K. pneumoniae). Only amikacin was active against >90% of Pseudomonas aeruginosa isolates (92.8% susceptible). Tigecycline, linezolid and vancomycin were the most active agents against Gram-positive agents across Europe between 2004 and 2007, with tigecycline displaying the lowest MIC(90) values (minimum inhibitory concentration for 90% of the organisms) against meticillin-resistant Staphylococcus aureus (26.5% of the collected S. aureus isolates), vancomycin-resistant Enterococcus faecium (15.7% of the E. faecium strains) and penicillin-resistant Streptococcus pneumoniae (9.3% of the S. pneumoniae strains). Longitudinal analysis showed no increase in tigecycline MIC values over the 4-year study period, whilst increased resistance was noted for several comparator agents.

Update on antimicrobial susceptibility rates among gram-negative and gram-positive organisms in the United States: results from the Tigecycline Evaluation and Surveillance Trial (TEST) 2005 to 2007

BACKGROUND

The Tigecycline Evaluation and Surveillance Trial (TTEST) is a global surveillance study initiated in 2004.Its goal is to assess the in vitro activity of the glycylcycline, tigecycline, and comparator antimicrobials.

OBJECTIVE

The aim of this study was to measure the in vitro activity of a panel of antimicrobial agents against gram-negative and gram-positive organisms collected in the United States in 2005, 2006, and 2007.

METHODS

Isolates were collected from 172 centers across the United States.In vitro activity was assessed using Clinical and Laboratory Standards Institute (CLSI) guidelines and CLSI or US Food and Drug Administration interpretive criteria.

RESULTS

Overall, data on 20,897 gram-negative and 8949 gram-positive isolates were collected. For the majority of organisms, percentage susceptibilities were unchanged over the 3 years of collection. One exception was Acinetobacter baumannii; rates of susceptibility to the majority of agents in the panel decreased by approximately 10% over the 3 years. Rates of resistant phenotypes were relatively unchanged with mean percentages over the 3 years of: 8.9% (337/3787) for extended beta-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae; 2.1% (17/801) for ESBL-producing Klebsiella oxytoca; 2.3% (111/4861) for ESBL-pproducing Escherichia coli; 56.2% (2564/4560) for methicillin-resistant Staphylococcus aureus; 5.1% (97/1903) for vancomycin-resistant Enterococcus faecalis; and 67.2% (487/725) for vancomycin-resistant Enterococcus faecium. The minimum inhibitory concentration required to inhibit the growth of 90% of organisms (MIC(90)) for tigecycline was stable over the 3 years and was < or = 22 mg/L against non-ESBL-producing K pneumoniae, K oxytoca, E coli, Enterobacter aerogenes, Enterobacter cloacae, Serratia marcescens, and A baumannii. Against methicillin susceptible and -resistant S aureus, E faecalis, E faecium, and Streptococcus agalactiae tigecycline MIC(90)s were < or = 0.25 mg/L.

CONCLUSIONS

This report of 3 years of data from the TEST study suggests stable susceptibility rates among gram-negative and gram-positive organisms, with the exception of decreased susceptibility rates for A baumannii. Tigecycline continued to have good activity against Enterobacteriaceae, A baumannii, S aureus, E faecalis, E faecium, and S agalactiae.

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.

Tigecycline for the treatment of multidrug-resistant (including carbapenem-resistant) Acinetobacter infections: a review of the scientific evidence

OBJECTIVES

New antibacterial agents are required for the treatment of infections caused by multidrug-resistant (MDR) Acinetobacter spp. Whether tigecycline constitutes an effective treatment option or not, is not well established. We sought to evaluate the available evidence regarding the microbiological activity and clinical effectiveness of tigecycline for MDR (including the subset of carbapenem-resistant) Acinetobacter spp.

METHODS

We searched PubMed for relevant articles and extracted/evaluated the available evidence.

RESULTS

We identified 22 microbiological studies reporting data for 2384 Acinetobacter spp. (1906 Acinetobacter baumannii). Susceptibility of at least 90% of the Acinetobacter isolates to tigecycline (with an MIC breakpoint of susceptibility < or =2 mg/L) was noted in 9/18 studies reporting data on MDR Acinetobacter and in 7/15 studies reporting specific data on carbapenem-resistant Acinetobacter. In an additional study reporting data for both resistance categories, adequate susceptibility of Acinetobacter spp. was observed by one (broth microdilution) of the methods employed. The effectiveness of tigecycline for MDR Acinetobacter infections was evaluated in eight identified clinical studies, reporting retrospective data regarding 42 severely ill patients, among whom 31 had respiratory tract infection (in 4 cases with secondary bacteraemia) and 4 had bacteraemia. Tigecycline therapy (in combination with other antibiotics in 28 patients) was effective in 32/42 cases. In three cases, resistance to tigecycline developed during treatment.

CONCLUSIONS

Tigecycline showed considerable, though not consistent, antimicrobial activity against MDR (including carbapenem-resistant) Acinetobacter spp. However, data to support its clinical use, particularly for ventilator-associated pneumonia or bacteraemia, caused by these pathogens, are still limited.

Evaluation of the in vitro activity of tigecycline against multiresistant Gram-positive cocci containing tetracycline resistance determinants

This study was undertaken to test the in vitro activity of tigecycline against 117 clinically relevant Gram-positive pathogens and to correlate this activity with their resistance gene content. Overall, tigecycline showed a minimal inhibitory concentration (MIC) range of 0.015-0.5mg/L, able to inhibit potently all multiresistant streptococci, enterococci and MR staphylococci. Tigecycline was active against methicillin-resistant Staphylococcus aureus (MRSA) and enterococci, with MICs for 90% of the organisms (MIC(90)) of 0.25 mg/L and 0.12 mg/L, respectively, being more active than linezolid (MIC(90)=2 mg/L) and quinupristin/dalfopristin (MIC(90)=0.5 and 2-4 mg/L, respectively). Molecular characterisation of resistance determinants demonstrated the concomitant presence of different classes of genes: in particular, tet(M), erm(B) and erm(C) in Streptococcus agalactiae; tet(O), variably associated with different erm genes, in Streptococcus pyogenes; vanA, tet(M) and erm(B) in Enterococcus faecalis, and vanA and erm(B) in Enterococcus faecium. All the MRSA strains harboured SCCmec and erm genes and 50% possessed tet(K) with tet(M) genes. Staphylococcus epidermidis strains were only resistant to erythromycin. These results clearly demonstrate that tigecycline has a MIC(90) range of 0.015-0.5 mg/L both against tetracycline-susceptible and -resistant isolates carrying other resistance determinants, suggesting that this drug could play an important role in the treatment of infections caused by these multiresistant Gram-positive pathogens.

Antimicrobial activity of mupirocin, daptomycin, linezolid, quinupristin/dalfopristin and tigecycline against vancomycin-resistant enterococci (VRE) from clinical isolates in Korea (1998 and 2005)

It is a hot clinical issue whether newly approved antimicrobial agents such as daptomycin, linezolid, quinupristin/dalfopristin (synercid) and tigecycline are active enough to be used for infections caused by vancomycin resistant bacteria. We performed susceptibility tests for mupirocin, which is in widespread clinical use in Korea, and four new antimicrobials, daptomycin, linezolid, quinupristin/dalfopristin and tigecycline, against vancomycin-resistant Enterococcus faecalis and Enterococcus faecium isolated from Korean patients in 1998 and 2005 to evaluate and compare the in vitro activity of these antimicrobials. Among these agents, quinupristin/dalfopristin, which is rarely used in hospitals in Korea, showed relatively high resistance to several vancomycin-resistant enterococci (VRE) isolated in 2005. Likewise, daptomycin, linezolid and tigecycline have not yet been in clinical use in Korea. However, our results showed that most of the 2005 VRE isolates were already resistant to linezolid and daptomycin (highest minimum inhibitory concentration (MIC) value >100 microg/ml). Compared with the other four antimicrobial agents tested in this study, tigecycline generally showed the greatest activity against VRE. However, four strains of 2005 isolates exhibited resistance against tigecycline (MIC >12.5 microg/ml). Almost all VRE were resistant to mupirocin, whereas all E. faecium isolated in 1998 were inhibited at concentrations between 0.8 to approximately 1.6 microg/ml. In conclusion, resistances to these new antimicrobial agents were exhibited in most of VRE strains even though these new antibiotics have been rarely used in Korean hospitals.

Daptomycin and tigecycline: a review of clinical efficacy in the antimicrobial era

There is a clinical need for new treatment options as a result of continued increase in the expression of resistance among bacterial pathogens. A number of compounds currently in development show promise. However, in some cases, there is concern that resistance may develop quickly to new compounds that are based on existing antimicrobial agents. Therefore, daptomycin, a novel lipopeptide with a unique mode of action, is of particular interest. It has rapid bactericidal activity against growing and stationary-phase bacteria, once-daily dosing regimen, and has a low potential for the development of resistance. It has been approved for the treatment of complicated skin and soft tissue infections caused by Gram-positive bacteria, and registration for treatment of infective endocarditis and bacteraemia is anticipated. Daptomycin is a welcome addition to the antimicrobial armamentarium for the treatment of bacterial infections. Tigecycline is a new glycyclcycline antimicrobial recently approved for use in the USA, Europe and elsewhere. While related to the tetracyclines, tigecycline overcomes many of the mechanisms responsible for resistance to this class. It 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. It is efficacious in complicated skin and soft tissue infections and in intra-abdominal infections. This review aims to summarise the key clinical data of daptomycin and tigecycline which hold promise for widespread clinical use in the next decade.

Prevalence and regional variation in meticillin-resistant Staphylococcus aureus (MRSA) in the USA and comparative in vitro activity of tigecycline, a glycylcycline antimicrobial

The Tigecycline Evaluation and Surveillance Trial (T.E.S.T.) is a surveillance study established in 2004 to monitor the activity of tigecycline, the first glycylcycline, and comparator agents [β-lactams (including penicillins, cephalosporins and carbapenems), glycopeptides, tetracyclines, fluoroquinolones and oxazolidinones] against Gram-positive and Gram-negative pathogens worldwide. This report examines 1692 isolates of Staphylococcus aureus collected in the continental United States between January 2004 and September 2005. Meticillin-resistant S. aureus (MRSA) accounted for 52.0 % of isolates. Prevalence of MRSA by state ranged from 12.5 % in New Hampshire to 100 % in Kentucky. All isolates were susceptible to tigecycline, linezolid and vancomycin. In vitro, tigecycline was potent against both meticillin-susceptible S. aureus (MSSA) (MIC50 and MIC90=0.12 μg ml−1) and MRSA (MIC50=0.12 μg ml−1; MIC90=0.25 μg ml−1). Only a single isolate was resistant to three or more antimicrobial classes. Ninety-six isolates (5.7 %) were susceptible to the complete antimicrobial panel.

Staphylococci

Staphylococci are among the leading causes of nosocomial infections. Increasing insusceptibility to beta-lactams and the glycopeptides complicates treatment of these infections. This review examines the current status and future perspectives for the therapy of infections caused by Staphylococcus aureus and coagulase-negative staphylococci.

Non-fermentative Gram-negative bacteria

Over the past decade, non-fermenting Gram-negative bacteria have emerged as important opportunistic pathogens in the increasing population of patients who are immunocompromised by their disease or medical treatment. These bacteria are assisted by their ubiquitous distribution in the environment and have a propensity for multiple, intrinsic or acquired drug resistance. The infections that they cause now pose significant problems in terms of treatment and infection control, whilst the commonly observed rapid emergence of bacterial resistance to new antimicrobial compounds raises concerns regarding the clinical lifespan of these agents. Studies are urgently required to assess whether combination therapy can improve the long-term utility of new drugs in the treatment of patients infected with non-fermenters.

A comparison of the activity of tigecycline against multiresistant clinical isolates of Staphylococcus aureus and Streptococcus agalactiae

We evaluated the activity of several antibiotics against 225 clinical isolates of Staphylococcus aureus and 252 isolates of Streptococcus agalactiae. Only tigecycline, glycopeptides, and linezolid were active against all the isolates of S. aureus, whereas the beta-lactams were also active against S. agalactiae. Tigecycline could be a good alternative to ampicillin in the treatment of group B Streptococcus infections in patients allergic to beta-lactam.

Occurrence of tetracycline resistance genes among Escherichia coli isolates from the phase 3 clinical trials for tigecycline

Tigecycline, a member of the glycylcycline class of antibiotics, was designed to maintain the antibacterial spectrum of the tetracyclines while overcoming the classic mechanisms of tetracycline resistance. The current study was designed to monitor the prevalence of the tet(A), tet(B), tet(C), tet(D), tet(E), and tet(M) resistance determinants in Escherichia coli isolates collected during the worldwide tigecycline phase 3 clinical trials. A subset of strains were also screened for the tet(G), tet(K), tet(L), and tet(Y) genes. Of the 1,680 E. coli clinical isolates screened for resistance to classical tetracyclines, 405 (24%) were minocycline resistant (MIC > or = 8 microg/ml) and 248 (15%) were tetracycline resistant (MIC > or = 8 microg/ml) but susceptible to minocycline (MIC < or = 4 microg/ml). A total of 452 tetracycline-resistant, nonduplicate isolates were positive by PCR for at least one of the six tetracycline resistance determinants examined. Over half of the isolates encoding a single determinant were positive for tet(A) (26%) or tet(B) (32%) with tet(C), tet(D), tet(E), and tet(M), collectively, found in 4% of isolates. Approximately 33% of the isolates were positive for more than one resistance determinant, with the tet(B) plus tet(E) combination the most highly represented, found in 11% of isolates. The susceptibilities of the tetracycline-resistant strains to tigecycline (MIC(90), 0.5 microg/ml), regardless of the encoded tet determinant(s), were comparable to the tigecycline susceptibility of tetracycline-susceptible strains (MIC(90), 0.5 microg/ml). The results provide a current (2002 to 2006) picture of the distribution of common tetracycline resistance determinants encoded in a globally sourced collection of clinical E. coli strains.

Antimicrobial susceptibility among Acinetobacter calcoaceticus-baumannii complex and Enterobacteriaceae collected as part of the Tigecycline Evaluation and Surveillance Trial

OBJECTIVE

To measure the in vitro activity of a panel of antimicrobial agents against gram-negative pathogens collected from the nine census regions of the USA.

METHODS

Isolates were collected from 76 centers between January 2004 and September 2005. In vitro activity was assessed using CLSI guidelines and CLSI or FDA interpretive criteria.

RESULTS

The lowest overall antimicrobial susceptibilities for Acinetobacter calcoaceticus-baumannii complex isolates (n=851) were detected in the Middle Atlantic and East South Central regions. Overall, 29.3% of A. calcoaceticus-baumannii complex isolates were multidrug-resistant (resistant to > or =3 antimicrobial classes). Tigecycline (2 microg/mL) had the lowest MIC90 against this organism. Imipenem, tigecycline, and levofloxacin had low MIC90s (0.25-4 microg/mL) against Enterobacter spp. (n=1557), although the MIC90 for levofloxacin was elevated for East South Central region isolates (> or = 16 microg/mL). Susceptibility to levofloxacin among the E. coli isolates (n=1785) ranged from 71.7% (Pacific) to 88.5% (New England). The prevalence of ESBL-producing K. pneumoniae (126/1460) varied from 1.7% of isolates (Pacific) to 21.2% (Middle Atlantic). ESBL-producing K. pneumoniae MICs were lowest for imipenem and tigecycline.

CONCLUSIONS

Antimicrobial susceptibility varies among the census regions of the USA. The broad-spectrum in vitro activity of tigecycline may make it a suitable candidate for use in the empiric treatment of serious infections.

Clinical management of diabetic foot infection: diagnostics, therapeutics and the future

Diabetic foot infection accounts for a substantial global burden of morbidity, psychosocial disruption and economic cost. Recommendations for best practice are continuously evolving in parallel with improvements in imaging modalities, development and clinical use of new antimicrobial agents and data surrounding novel adjunctive strategies. We discuss this complex group of infections with a particular emphasis on medical management of osteomyelitis, while also highlighting the importance of a broad multidisciplinary approach to eradicating infection.

Potency and spectrum of garenoxacin tested against an international collection of skin and soft tissue infection pathogens: report from the SENTRY antimicrobial surveillance program (1999-2004)

The spectrum and potency of garenoxacin, a novel des-F(6)-quinolone, against a large international collection (11723 strains) of Gram-positive and Gram-negative bacterial pathogens that cause skin and soft tissue infections (SSTIs) were evaluated for the years 1999 to 2004. Consecutive nonduplicate bacterial isolates were collected from patients with documented community-acquired or nosocomial SSTI in >70 medical centers participating in the SENTRY Antimicrobial Surveillance Program in North America (37.4%), Europe (26.7%), Latin America (16.7%), and the Asia-Pacific region (19.2%). All isolates were tested using the reference broth microdilution methods against garenoxacin, ciprofloxacin, levofloxacin, gatifloxacin, moxifloxacin, and representative comparator agents used for the empiric or directed therapy for SSTI. Ranking pathogens producing SSTI during these years included Staphylococcus aureus (42.8%), Pseudomonas aeruginosa (11.1%), Escherichia coli (9.0%), Enterococcus spp. (7.3%), Klebsiella spp. (4.8%), Enterobacter spp. (4.7%), beta-hemolytic streptococci (4.3%), coagulase-negative staphylococci (4.0%), Proteus mirabilis (2.5%), and Acinetobacter spp. (2.1%). Garenoxacin was the most potent agent tested against S. aureus and was at least 2-fold more active than gatifloxacin (MIC(50), 0.06 mg/L) and 8-fold more active than levofloxacin (MIC(50), 0.25 mg/L). Furthermore, garenoxacin was 2- to 8-fold more potent than the fluoroquinolones against beta-hemolytic and viridans group streptococci, as well as up to 4-fold more active against enterococci. Garenoxacin was largely comparable with the comparator fluoroquinolones against E. coli, Klebsiella spp., and Acinetobacter spp., but it is less active than these agents against P. aeruginosa. In summary, garenoxacin was documented to be the most potent quinolone when tested against key Gram-positive pathogens (S. aureus, beta-hemolytic streptococci, viridans group streptococci, and enterococci) and was similar in activity to these agents against other species (Enterobacteriaceae and Acinetobacter spp.). These in vitro data suggest that garenoxacin warrants further clinical studies in SSTI, especially against staphylococci and streptococcal pathogens.

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.

Emerging Options for Treatment of Invasive, Multidrug-ResistantStaphylococcus aureusInfections

Limited established treatment options exist for the treatment of serious, invasive infections caused by multidrug-resistant Staphylococcus aureus, most notably nosocomially acquired methicillin-resistant S. aureus (MRSA). Although vancomycin represents the gold standard for therapy of such invasive infections, reports of increasing in vitro resistance to vancomycin, combined with reports of clinical failures (with this and other antistaphylococcal agents), underscore the need for alternative therapies. Older agents with favorable in vitro activity available in both oral and intravenous dose forms include trimethoprim-sulfamethoxazole and clindamycin. Limited clinical data exist to support their routine use as initial therapy in the treatment of invasive disease. However, these and other options (e.g., tetracyclines) are being reexplored in the setting of increasing concern over MRSA acquired in the community setting. Newer treatment options for MRSA include linezolid, quinupristin-dalfopristin, daptomycin, and tigecycline. With the exception of linezolid, these newer agents require intravenous administration. Combination therapy may be considered in select invasive diseases refractory to standard monotherapies. These diseases include infections such as endocarditis, meningitis, and prosthetic device infections. Additional alternatives to vancomycin are under clinical investigation. Those in later stages of development include oritavancin, dalbavancin, telavancin, and ceftobiprole.

Contemporary causes of skin and soft tissue infections in North America, Latin America, and Europe: Report from the SENTRY Antimicrobial Surveillance Program (1998–2004)

The morbidity and cost for cure associated with skin and soft tissue infections (SSTIs) have recently become more complicated because of the increasing prevalence of multidrug-resistant pathogens associated with this healthcare problem. The SENTRY Antimicrobial Surveillance Program has been monitoring SSTI since 1997, and now presents data from 3 continents over a 7-year period (1998-2004). Isolates were tested by reference broth microdilution methods at a central laboratory using the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) methods and interpretative criteria. The predominant pathogens included Staphylococcus aureus (ranked 1st in all geographic regions), Pseudomonas aeruginosa, Escherichia coli, and Enterococcus spp. A considerable variation in the methicillin (oxacillin)-resistant S. aureus rate was noted between countries and continents, with the overall rate highest in North America (35.9%) compared with Latin America (29.4%) and Europe (22.8%). Vancomycin-resistant Enterococcus spp. increased in Europe (4.1%) and North America (6.2%) during the period, but remained low and relatively unchanged in Latin America. Among the P. aeruginosa isolates tested, susceptibility to imipenem was much lower in Latin America (65.3%) compared with the other regions (80.7-88.7%), and resistance being associated with an increase in metallo-beta-lactamase-producing strains in Latin America and in some European countries. Multidrug-resistant strains of P. aeruginosa were also more of a concern in Latin America (24.7%) compared with Europe (10.8%) or North America (3.2%). Latin America also had the highest occurrence of extended-spectrum beta-lactamase-producing isolates among E. coli (15.1%) and Klebsiella spp. (48.0%) when compared with other regions. Continued surveillance of pathogen prevalence and antimicrobial resistance patterns should provide information that is important to improve empiric care particularly in the hospital environment.

Community-acquired methicillin-resistant Staphylococcus aureus

Published data confirm that community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections are increasing in incidence in both urban and rural settings. The statistical risk is higher for athletes, military personnel, prison inmates, intravenous drug abusers, the homeless, children in daycare, and certain Native American groups, but the infections are by no means restricted to these populations. Roughly 85% of the infections involve the skin and subcutaneous tissue, with the most common presentations being an abscess or folliculitis. The typical associated gene cassette is quite small and codes only for methicillin resistance. Abscesses generally respond to drainage.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should recognize groups at high risk for community-acquired MSRA infections and manage these infections appropriately.

Tigecycline: a glycylcycline antimicrobial agent

BACKGROUND

Tigecycline, the first glycylcycline to be approved by the US Food and Drug Administration, is a structural analogue of minocycline that was designed to avoid tetracycline resistance mediated by ribosomal protection and drug efflux. It is indicated for the treatment of complicated skin and skin-structure infections and complicated intra-abdominal infections and is available for intravenous administration only.

OBJECTIVE

This article summarizes the in vitro and in vivo activities and pharmacologic and pharmacokinetic properties of tigecycline, and reviews its clinical efficacy and tolerability profile.

METHODS

Relevant information was identified through a search of MEDLINE (1966-April 2006), Iowa Drug Information Service (1966-April 2006), and International Pharmaceutical Abstracts (1970-April 2006) using the terms tigecycline, GAR-936, and glycylcycline. Also consulted were abstracts and posters from meetings of the Infectious Diseases Society of America and the Interscience Conference on Antimicrobial Agents and Chemotherapy (1999-2006) and documents provided for formulary consideration by the US manufacturer of tigecycline.

RESULTS

Like the tetracyclines, tigecycline binds to the 30S subunit of bacterial ribosomes and inhibits protein synthesis by preventing the incorporation of amino acid residues into elongating peptide chains. In vitro, tigecycline exhibits activity against a wide range of clinically significant gram-positive and gram-negative bacteria, including multidrug-resistant strains (eg, oxacillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, extended-spectrum beta-lactamase-producing Enterobacteriaceae), and anaerobes (eg, Bacteroides spp). In pharmacokinetic studies in human adults, tigecycline had a large Vd (7-9 L/kg), was moderately bound to plasma protein (71%-89%), had an elimination t(1/2) of 42.4 hours, and was eliminated primarily by biliary/fecal (59%) and renal (33%) excretion. Dose adjustment did not appear to be necessary based on age, sex, renal function, or mild to moderate hepatic impairment (Child-Pugh class A-B). In patients with severe hepatic impairment (Child-Pugh class C), the maintenance dose should be reduced by 50%. In 4 Phase III clinical trials in patients with complicated skin and skin-structure infections and complicated intra-abdominal infections, tigecycline was reported to be noninferior to its comparators (vancomycin + aztreonam in 2 studies and imipenem/cilastatin in 2 studies), with clinical cure rates among clinically evaluable patients of >80% (P < 0.001 for noninferiority). The most frequently reported (> or =5 %) adverse events with tigecycline were nausea (28.5%), vomiting (19.4%), diarrhea (11.6%), local IV-site reaction (8.2%), infection (6.7%), fever (6.3%), abdominal pain (6.0%), and headache (5.6%). The recommended dosage of tigecycline is 100 mg IV given as a loading dose, followed by 50 mg IV g12h for 5 to 14 days.

CONCLUSIONS

In clinical trials, tigecycline was effective for the treatment of complicated skin and skin-structure infections and complicated intra-abdominal infections. With the exception of gastrointestinal adverse events, tigecycline was generally well tolerated. With a broad spectrum of activity that includes multidrug-resistant gram-positive and gram-negative pathogens, tigecycline may be useful in the treatment of conditions caused by these pathogens.

Tigecycline: first of a new class of antimicrobial agents

Tigecycline is the first commercially available member of the glycylcyclines, a new class of antimicrobial agents. The glycylcyclines are derivatives of the tetracycline antibiotics, with structural modifications that allow for potent gram-positive, gram-negative, and anaerobic activity, including certain multidrug-resistant strains. The enhanced activity can be attributed to stronger binding affinity and enhanced protection against several mechanisms of resistance that affect other antibiotic classes such as tetracyclines. Tigecycline exhibits generally bacteriostatic action by reversibly binding to the 30S ribosomal subunit and inhibiting protein translation. In vitro activity has been demonstrated against multidrug-resistant gram-positive pathogens including methicillin-resistant and glycopeptide-intermediate and -resistant Staphylococcus aureus, as well as vancomycin-resistant enterococci. Multidrug-resistant gram-negative pathogens, such as Acinetobacter baumannii and extended-spectrum beta-lactamase-producing Klebsiella pneumoniae and Escherichia coli, are typically highly susceptible to tigecycline. The drug also has displayed significant activity against many clinically important anaerobic organisms. This agent demonstrates a predictable pharmacokinetic profile and minimal drug interactions, and is generally well tolerated, with nausea being the most common adverse event. It was approved in June 2005 for the treatment of complicated skin and skin structure infections (SSSIs) and complicated intraabdominal infections. Currently, a limited number of broad-spectrum antimicrobials are available to combat multidrug-resistant organisms. The addition of new agents is essential to limiting the spread of these pathogens and improving outcomes in patients with these types of infections. Tigecycline has demonstrated promising results in initial in vitro and clinical studies for SSSIs and complicated intraabdominal infections; however, further clinical experience will clarify its role as a broad-spectrum agent.

Tigecycline: a new glycylcycline antimicrobial

Tigecycline is a new glycyclcycline antimicrobial recently approved for use in the USA, Europe and elsewhere. While related to the tetracyclines, tigecycline overcomes many of the mechanisms responsible for resistance to this class. It demonstrates favourable in vitro potency against a variety of aerobic and anaerobic Gram-positive and Gram-negative pathogens, including those frequently demonstrating resistance to multiple classes of antimicrobials. This includes methicillin-resistant Staphylococcus aureus, penicillin-resistant S. pneumoniae, vancomycin-resistant enterococci, Acinetobacter baumannii, beta-lactamase producing strains of Haemophilis influenzae and Moraxella catarrhalis, and extended-spectrum beta-lactamase producing strains of Escherichia coli and Klebsiella pneumoniae. In contrast, minimum inhibitory concentrations for Pseudomonas and Proteus spp. are markedly elevated. Tigecycline is administered parenterally twice daily. Randomised, controlled trials have demonstrated that tigecycline is non-inferior to the comparators for the treatment of complicated skin and skin structure infections, as well as complicated intra-abdominal infections. The most frequent and problematic side effect associated with its administration to date has been nausea and/or vomiting.

Activity of tigecycline against clinical isolates of Staphylococcus aureus and extended-spectrum β-lactamase-producing Escherichia coli in Granada, Spain

We evaluated the in vitro activity of tigecycline using the Etest and disk diffusion method according to Clinical and Laboratory Standards Institute guidelines against clinical isolates of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) as well as for CTX-M-9 extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and SHV ESBL-producing E. coli. All isolates were susceptible to tigecycline according to US Food and Drug Administration cut-off points. There were no differences in the activity of tigecycline between MSSA and MRSA isolates or between the presence of either type of ESBL. For each type of microorganism studied, we established the equation relating the minimum inhibitory concentration to the diameter of the zone of inhibition.

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).

Activity of retapamulin (SB-275833), a novel pleuromutilin, against selected resistant gram-positive cocci

Retapamulin (SB-275833), the first pleuromutilin to be developed for human topical use, was tested against a selected population of staphylococci and beta-hemolytic streptococci. The MIC90 results for retapamulin were 0.12 microg/ml for Staphylococcus aureus and < or = 0.03 microg/ml for Streptococcus pyogenes; no cross-resistance was observed for organism subsets resistant to oxacillin, erythromycin, or mupirocin.

Case studies in current drug development: 'glycylcyclines'

Glycylcyclines represent a new class of tetracycline antibiotics with potent antibacterial activities against resistant pathogens. One of the glycylcyclines, Tygacil, was selected for further development and has been approved by the FDA. It has an expanded broad-spectrum of antibacterial activity both in vitro and in vivo. It is active against a wide range of clinically relevant pathogens including Gram-positive, Gram-negative, atypical, and anaerobic bacteria and bacterial strains carrying either or both of the two major forms of tetracycline resistance (efflux and ribosomal protection). Most importantly, it is active against the multiply antibiotic resistant Gram-positive pathogenic bacteria, including methicillin-resistant Staphylococcus aureus (MRSA).

Tigecycline

Tigecycline is the first member of a new class of broad-spectrum antibacterials, the glycylcyclines, that has been specifically developed to overcome the two major mechanisms of tetracycline resistance (ribosomal protection and efflux). In vitro, tigecycline was active against a wide range of Gram-positive and -negative aerobic and anaerobic bacteria implicated in complicated skin and skin structure infections (cSSSIs) and complicated intra-abdominal infections (cIAIs). Intravenously administered tigecycline (recommended dosage regimen 100 mg initially, followed by 50 mg every 12 hours for 5-14 days) has been approved by the US FDA for the treatment of cSSSIs and cIAIs. In well designed, pivotal phase III studies, tigecycline monotherapy was noninferior to combination therapy with vancomycin 1 g plus aztreonam 2 g every 12 hours in hospitalised adult patients with cSSSIs (two trials; pooled clinical cure rates, 86.5% vs 88.6%) or broad-spectrum therapy with imipenem/cilastatin 200-500 mg/200-500 mg every 6 hours in hospitalised adult patients with cIAIs (two trials; pooled clinical cure rates, 86.1% vs 86.2%). Tigecycline was generally well tolerated in phase III studies; nausea, vomiting and diarrhoea were the most frequent adverse events in patients treated with tigecycline or an active comparator (vancomycin plus aztreonam or imipenem/cilastatin).