Tigecycline: A Critical Analysis

Prosthetic joint infections: microbiology, diagnosis, management and prevention

Infections associated with prosthetic joints occur less frequently than aseptic failures but represent the most devastating complication, with high morbidity and substantial cost. The most important risk factors are co-morbidity and prior joint replacement (revision surgery). No single routinely used clinical or laboratory test has been shown to achieve ideal sensitivity, specificity and accuracy for the diagnosis of prosthetic joint infection (PJI). Therefore, only the sum of clinical signs and symptoms, blood tests, histopathology, radiography, bone scans and a microbiological work-up can provide an accurate diagnosis. Antimicrobial therapy must always be combined with the correct surgical treatment, which is chosen according to the duration of the infection and co-morbidities of the patient. This review will briefly discuss the microbiology, diagnosis, management and prevention of PJI.

In vitro activity of tigecycline against gram-positive and gram-negative pathogens as evaluated by broth microdilution and Etest

The current surveillance establishes the activity profile of tigecycline against recent clinical U.S. isolates of target pathogens. Findings from a distributed surveillance that utilized Etest yielded a tigecycline activity profile that varied from that observed in a separate centralized broth microdilution (BMD) surveillance (D. C. Draghi et al., Poster D-0701, 46th Intersci. Conf. Antimicrob. Agents Chemother., San Francisco, CA). Differences were noted among Acinetobacter spp. and Serratia marcescens and, to a lesser extent, with Streptococcus pyogenes. To address whether these differences were due to discordance in testing methodology or to variations among the analyzed populations, isolates from the current surveillance were concurrently tested by BMD and Etest. In all, 1,800 Staphylococcus aureus, 259 S. pyogenes, 226 Streptococcus pneumoniae, 93 Enterococcus faecalis, 1,356 Enterobacteriaceae, and 227 Acinetobacter baumannii strains were evaluated. Tigecycline had potent activity by BMD, with >99.6% susceptibility (%S) observed for all pathogens with interpretive criteria, excluding Enterobacter cloacae (98.3% S) and E. faecalis (86.0% S), and MIC(90)s ranged from 0.03 mug/ml (S. pyogenes/S. pneumoniae) to 1 mug/ml (Enterobacteriaceae/A. baumannii). Similar profiles were observed by Etest, with the exception of A. baumannii, although for most evaluated pathogens Etest MICs trended one doubling-dilution higher than BMD MICs. Major or very major errors were infrequent, and a high degree of essential agreement was observed, excluding A. baumannii, S. marcescens, and S. pneumoniae, for which >/=4-fold differences in MICs were observed for 29, 27.1, and 34% of the isolates, respectively. Further analysis regarding the suitability of the tigecycline Etest for testing S. marcescens, Acinetobacter spp., and S. pneumoniae is warranted.

Tigecycline in critical care

The emergence and spread of multidrug resistance in many pathogenic bacterial species is increasing at an alarming rate, especially with hospital-acquired infections in the critical care setting. Deaths associated with hospital-acquired infections have exceeded the number attributable to several of the top 10 leading causes of death reported in the United States. The emerging resistance limits the use of older antibiotics. Tigecycline is a new agent, and this article explores its role in the treatment of adults in the critical care setting.

In vitro activities of tigecycline against clinical isolates of Aeromonas, Vibrio, and Salmonella species in Taiwan

All 198 Salmonella isolates (58.6% of isolates were resistant to tetracycline), 92 Vibrio isolates (4.4% of isolates were resistant to tetracycline), and 200 of 201 Aeromonas isolates (39.3% of isolates were resistant to tetracycline; 1 A. caviae isolate had a tigecycline MIC of 4 mug/ml) in our study were susceptible to tigecycline, by U. S. Food and Drug Administration criteria for Enterobacteriaceae.

Natural products to drugs: natural product-derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or are in registration (as at 31st December 2007) have been reviewed, as well as natural product-derived compounds for which clinical trials have been halted or discontinued since 2005. Also discussed are natural product-derived drugs launched since 2005, new natural product templates and late-stage development candidates.

Activity of Tigecycline against Coryneform Bacteria of Clinical Interest and Listeria monocytogenes

The activities of tigecycline and eight other agents were evaluated against 220 coryneform bacteria and 42 Listeria monocytogenes isolates. All strains were inhibited by tigecycline at 0.5 mug/ml, except for 11 Corynebacterium striatum strains that were inhibited at 1 mug/ml. Tigecycline shows good in vitro activity against coryneform bacteria and L. monocytogenes.

Mother Nature's gifts to diseases of man: the impact of natural products on anti-infective, anticholestemics and anticancer drug discovery

This chapter is designed to demonstrate that compounds derived from nature are still in the forefront of drug discovery in diseases such as microbial and parasitic infections, carcinomas of many types and control of cholesterol/lipids in man. In each disease area we have provided short discussions of past, present and future agents, in general only considering compounds currently in clinical Phase II or later, that were/are derived from nature's chemical skeletons. Finishing with a discussion of the current and evolving role(s) of microbes (bacteria and fungi) in the production of old and new agents ostensibly produced by higher organisms.

Antimicrobial resistance prevention initiative--an update: proceedings of an expert panel on resistance

Antimicrobial resistance is a growing problem that complicates the treatment of important nosocomial and community-acquired infections. It is a worldwide problem that spans the range of human pathogens, including bacteria, fungi, and viruses. This update from the Antimicrobial Resistance Prevention Initiative (ARPI) provides a review of some important trends in antibiotic, antifungal, and antiviral resistance. Areas of focus include multidrug-resistant bacteria in the hospital setting; the growing problem of community-acquired methicillin-resistant Staphylococcus aureus; triazole and polyene resistance in nosocomial infections caused by non-Candida albicans or Aspergillus species, and the utility of in vitro susceptibility testing for these fungal infections; antiviral resistance in alpha- or beta-herpesviruses causing genital herpes or cytomegalovirus infection in immunocompromised hosts; and concerns about a possible pandemic involving avian influenza A and the importance of minimizing emergence of resistant strains of this highly pathogenic virus. The challenges in each area are different, but the general keys to addressing the growing problem of antimicrobial resistance continue to be responsible antimicrobial stewardship and the development of newer antimicrobial agents.

Phase 2 study of ceftaroline versus standard therapy in treatment of complicated skin and skin structure infections

Ceftaroline, the bioactive metabolite of ceftaroline fosamil (previously PPI-0903, TAK-599), is a broad-spectrum cephalosporin with potent in vitro activity against multidrug-resistant gram-positive aerobic pathogens, including methicillin-resistant Staphylococcus aureus. A randomized, observer-blinded study to evaluate the safety and efficacy of ceftaroline versus standard therapy in treating complicated skin and skin structure infections (cSSSI) was performed. Adults with cSSSI, including at least one systemic marker of inflammation, were randomized (2:1) to receive intravenous (i.v.) ceftaroline (600 mg every 12 h) or i.v. vancomycin (1 g every 12 h) with or without adjunctive i.v. aztreonam (1 g every 8 h) for 7 to 14 days. The primary outcome measure was the clinical cure rate at a test-of-cure (TOC) visit 8 to 14 days after treatment. Secondary outcomes included the microbiological success rate (eradication or presumed eradication) at TOC and the clinical relapse rate 21 to 28 days following treatment. Of 100 subjects enrolled, 88 were clinically evaluable; the clinical cure rate was 96.7% (59/61) for ceftaroline versus 88.9% (24/27) for standard therapy. Among the microbiologically evaluable subjects (i.e., clinically evaluable and having had at least one susceptible pathogen isolated at baseline), the microbiological success rate was 95.2% (40/42) for ceftaroline versus 85.7% (18/21) for standard therapy. Relapse occurred in one subject in each group (ceftaroline, 1.8%; standard therapy, 4.3%). Ceftaroline exhibited a very favorable safety and tolerability profile, consistent with that of marketed cephalosporins. Most adverse events from ceftaroline were mild and not related to treatment. Ceftaroline holds promise as a new therapy for treatment of cSSSI and other serious polymicrobial infections.

New drugs to treat skin and soft tissue infections

Due to increasing antimicrobial resistance, a pressing need exists for new antibiotics to treat skin and soft tissue infections. Several newer agents such as tigecycline, daptomycin, and linezolid have been important additions for the treatment of multidrug-resistant pathogens. New drugs in development such as dalbavancin and ceftobiprole will further enhance our ability to treat mixed infections and improve patient compliance. These promising new antimicrobials will likely grow in importance as resistant bacterial strains increase in community-acquired infections.

Community-associated methicillin-resistant Staphylococcus aureus: Incidence, clinical presentation, and treatment decisions

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections have been reported with increasing frequency from many parts of the world. Most infections involve the skin and soft tissue structures, and CA-MRSA is now the most commonly identifiable cause of purulent skin and soft tissue infections. The spectrum of disease can range from simple cutaneous abscesses to fulminant necrotizing infection. CA-MRSA strains, in contrast to healthcare-associated strains, are generally extra virulent and produce more toxins. Unlike the healthcare-associated strains, they demonstrate variable susceptibility patterns to various classes of antibiotics. Empiric antibiotic therapy for patients with purulent skin and soft tissue infection and for those presenting with severe, life-threatening infections should include an agent active against CA-MRSA.

Will longer antimicrobial patents improve global public health?

The problem of antimicrobial resistance has led some infectious disease experts and their professional societies to propose the use of transferable intellectual property rights (wildcard patents) and patent term extensions as methods to encourage antimicrobial research and development. We evaluate recent approvals of new antimicrobial classes and find that the number of new introductions is higher than previously suggested. More importantly, creating new patent rights is shown to be an inefficient and possibly counterproductive response to antimicrobial resistance. Wildcard patents would operate as a more than US$40 billion annual tax on heart disease, hypertension, chronic obstructive pulmonary disease, asthma, and depression to inefficiently cross-subsidise antimicrobial research and development. Patent term extensions would likewise cost more than $5 billion per year, hinder access, and allocate resources inefficiently. Alternative uses for these funds are proposed, with greater potential positive effects on global public health. Additional public funding of antimicrobial research could be a more effective use of these funds. Conservation efforts to encourage the prudent use of antimicrobial drugs should be directly reimbursed. Patent owners should be compensated for both conservation efforts and valuable innovation.

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.

Antimicrobial resistance prevention initiative--an update: proceedings of an expert panel on resistance

Antimicrobial resistance is a growing problem that complicates the treatment of important nosocomial and community-acquired infections. It is a worldwide problem that spans the range of human pathogens, including bacteria, fungi, and viruses. This update from the Antimicrobial Resistance Prevention Initiative (ARPI) provides a review of some important trends in antibiotic, antifungal, and antiviral resistance. Areas of focus include multidrug-resistant bacteria in the hospital setting; the growing problem of community-acquired methicillin-resistant Staphylococcus aureus; triazole and polyene resistance in nosocomial infections caused by non-Candida albicans or Aspergillus species, and the utility of in vitro susceptibility testing for these fungal infections; antiviral resistance in alpha- or beta-herpesviruses causing genital herpes or cytomegalovirus infection in immunocompromised hosts; and concerns about a possible pandemic involving avian influenza A and the importance of minimizing emergence of resistant strains of this highly pathogenic virus. The challenges in each area are different, but the general keys to addressing the growing problem of antimicrobial resistance continue to be responsible antimicrobial stewardship and the development of newer antimicrobial agents.

New aspects of natural products in drug discovery

During the past 15 years, most large pharmaceutical companies have decreased the screening of natural products for drug discovery in favor of synthetic compound libraries. Main reasons for this include the incompatibility of natural product libraries with high-throughput screening and the marginal improvement in core technologies for natural product screening in the late 1980s and early 1990 s. Recently, the development of new technologies has revolutionized the screening of natural products. Applying these technologies compensates for the inherent limitations of natural products and offers a unique opportunity to re-establish natural products as a major source for drug discovery. Examples of these new advances and technologies are described in this review.

Tigecycline: a novel broad-spectrum antimicrobial

OBJECTIVE

To review the literature on tigecycline, a novel antibiotic.

DATA SOURCES

References were identified through MEDLINE (1966-February 2007) and International Pharmaceutical Abstracts (1970-February 2007) databases, using the key words tigecycline, glycylcycline, complicated skin and skin structure infections (cSSSI), complicated intraabdominal infections (cIAI), and in vitro. Additional articles for this review were identified by reviewing the bibliographies of articles cited. The package insert was also used as a reference.

STUDY SELECTION AND DATA EXTRACTION

In vitro, clinical, and pharmacokinetic studies evaluating tigecycline's safety and efficacy were selected.

DATA SYNTHESIS

A tigecycline 100 mg intravenous loading dose followed by an intravenous infusion of 50 mg every 12 hours was shown in clinical trials to be as effective as comparator antibiotics in treating cSSSI and cIAI. Tigecycline has a broad spectrum of activity that includes many resistant bacteria with few treatment options, such as methicillin-resistant Staphylococcus aureus and extended-spectrum beta-lactamase-producing bacteria such as Escherichia coli and Klebsiella pneumoniae. In cSSSI studies, tigecycline was found to be noninferior to vancomycin plus aztreonam with test-of-cure rates of 86.5% and 88.6%, respectively. Tigecycline was also found to be noninferior to imipenem/cilastatin in cIAI studies; clinical cure rates were 86.1% and 86.2%, respectively. In vitro activity has been demonstrated against other multidrug-resistant microorganisms of concern, such as Acinetobacter spp. Although it has a broad spectrum of activity, tigecycline has inadequate activity against Pseudomonas spp. Nausea and vomiting were the most frequently reported adverse effects.

CONCLUSIONS

Tigecycline is approved for the treatment of cSSSI and cIAI infections. To date, little resistance to tigecycline has been reported; however, with widespread use of the drug, resistance will likely occur. Since published studies have not dealt with seriously ill patients, it is recommended that, until further studies have been completed, other agents be used in the treatment of these patients unless no option other than tigecycline exists.

Molecular Mechanisms of Antibacterial Multidrug Resistance

Treatment of infections is compromised worldwide by the emergence of bacteria that are resistant to multiple antibiotics. Although classically attributed to chromosomal mutations, resistance is most commonly associated with extrachromosomal elements acquired from other bacteria in the environment. These include different types of mobile DNA segments, such as plasmids, transposons, and integrons. However, intrinsic mechanisms not commonly specified by mobile elements-such as efflux pumps that expel multiple kinds of antibiotics-are now recognized as major contributors to multidrug resistance in bacteria. Once established, multidrug-resistant organisms persist and spread worldwide, causing clinical failures in the treatment of infections and public health crises.

Multi-targeting by monotherapeutic antibacterials

Antibacterial discovery research has been driven, medically, commercially and intellectually, by the need for new therapeutics that are not subject to the resistance mechanisms that have evolved to combat previous generations of antibacterial agents. This need has often been equated with the identification and exploitation of novel targets. But efforts towards discovery and development of inhibitors of novel targets have proved frustrating. It might be that the 'good old targets' are qualitatively different from the crop of all possible novel targets. What has been learned from existing targets that can be applied to the quest for new antibacterials?