Pharmacokinetics, Pharmacodynamics, Safety and Tolerability of Tigecycline

Dose optimisation based on pharmacokinetic/pharmacodynamic target of tigecycline

Tigecycline, a new first-in-class glycylcycline antibiotic, has shown promising efficacy against a broad range of micro-organisms. It is widely prescribed for various infections, with most prescriptions being considered for off-label use. However, only a few years after its approval by the US Food and Drug Administration (FDA), tigecycline is suspected of increasing all-cause mortality. Some clinicians have suggested such unfavourable outcomes correlate with inadequate drug exposure at the infection site. The pharmacokinetic/pharmacodynamic (PK/PD) profile of a drug plays an important role in predicting its antibiotic effect, which for tigecycline is determined as the ratio of area under the concentration-time curve (AUC) to minimum inhibitory concentration (MIC). In this study, PK/PD targets based on infection sites, bacterial isolates and patient populations are discussed. Generally, a higher dosage of tigecycline for the treatment of serious infections has been recommended in previous reports. However, the latest finding of tigecycline's atypical protein binding property requires consideration when recommending further use. In addition, combination therapy with other antibiotics provides another option by potentially lowering the MICs of multidrug-resistant bacteria.

Tigecycline antibacterial activity, clinical effectiveness, and mechanisms and epidemiology of resistance: narrative review

Tigecycline is unique glycylcycline class of semisynthetic antimicrobial agents developed for the treatment of polymicrobial infections caused by multidrug-resistant Gram-positive and Gram-negative pathogens. Tigecycline evades the main tetracycline resistance genetic mechanisms, such as tetracycline-specific efflux pump acquisition and ribosomal protection, via the addition of a glycyclamide moiety to the 9-position of minocycline. The use of the parenteral form of tigecycline is approved for complicated skin and skin structure infections (excluding diabetes foot infection), complicated intra-abdominal infections, and community-acquired bacterial pneumonia in adults. New evidence also suggests the effectiveness of tigecycline for the treatment of severe Clostridioides difficile infections. Tigecycline showed in vitro susceptibility to Coxiella spp., Rickettsia spp., and multidrug-resistant Neisseria gonnorrhoeae strains which indicate the possible use of tigecycline in the treatment of infections caused by these pathogens. Except for intrinsic, or often reported resistance in some Gram-negatives, tigecycline is effective against a wide range of multidrug-resistant nosocomial pathogens. Herein, we summarize the currently available data on tigecycline pharmacokinetics and pharmacodynamics, its mechanism of action, the epidemiology of tigecycline resistance, and its clinical effectiveness.

Clostridioides difficile-Associated Antibiotics Alter Human Mucosal Barrier Functions by Microbiome-Independent Mechanisms

A clinically relevant risk factor for Clostridioides difficile-associated disease (CDAD) is recent antibiotic treatment. Although broad-spectrum antibiotics have been shown to disrupt the structure of the gut microbiota, some antibiotics appear to increase CDAD risk without being highly active against intestinal anaerobes, suggesting direct nonantimicrobial effects. We examined cell biological effects of antibiotic exposure that may be involved in bacterial pathogenesis using an in vitro germfree human colon epithelial culture model. We found a marked loss of mucosal barrier and immune function with exposure to the CDAD-associated antibiotics clindamycin and ciprofloxacin, distinct from the results of pretreatment with an antibiotic unassociated with CDAD, tigecycline, which did not reduce innate immune or mucosal barrier functions. Importantly, pretreatment with CDAD-associated antibiotics sensitized mucosal barriers to C. difficile toxin activity in primary cell-derived enteroid monolayers. These data implicate commensal-independent gut mucosal barrier changes in the increased risk of CDAD with specific antibiotics and warrant further studies in in vivo systems. We anticipate this work to suggest potential avenues of research for host-directed treatment and preventive therapies for CDAD.

In vitro synergy with fosfomycin plus doxycyclin against linezolid and vancomycin-resistant Enterococcus faecium

OBJECTIVE

Linezolid and vancomycin-resistant Enterococcus faecium (LRVREF) is globally emerging as a urinary nosocomial pathogen. A decrease in the amount of successful treatment options has created a necessity for the development of novel antimicrobial therapies. Combination therapy may provide an effective alternative for treatment. Fosfomycin and doxycyclin are currently used individually for the treatment of urinary tract infections. Fosfomycin has recently seen increased use because of its persistent activity against a large spectrum of multidrug-resistant organisms. The purpose of this study was to investigate the interaction of fosfomycin plus doxycyclin against LRVREF isolates.

METHODS

MICs for fosfomycin and doxycyclin were determined for 24 unique clinical LRVREF isolates (4%, fosfomycin-susceptible; 92%, doxycyclin-susceptible). In vitro synergy testing with the combination of fosfomycin and doxycyclin was performed using an Etest method and time-kill assay.

RESULTS

The combination of fosfomycin and doxycyclin demonstrated synergy with the Etest method in 11/24 (46%) isolates and in 10/24 (42%) isolates by the time-kill assay. Results from the Etest method and time-kill assay were in agreement for 7/24 (29.2%) of isolates. No antagonism was found.

CONCLUSIONS

The combination of fosfomycin and doxycyclin should be evaluated further with additional LRVREF isolates. In vivo studies should also be performed before use in clinical situations.

Spontaneous Knee Hemarthrosis Due to Hypofibrinogenemia Following Tigecycline Treatment for Periprosthetic Joint Infection

Tigecycline, a recently approved antibiotic, has a broad spectrum of antimicrobial activity. Its unique structure and properties make tigecycline a valuable option for the treatment of infections caused by many multidrug-resistant organisms. We present a case of an 82-year-old patient who developed a significant decrease of fibrinogen levels after the addition of tigecycline to his antibiotic regimen. The patient was treated for a periprosthetic knee joint infection caused by a multidrug-resistant extended-spectrum beta-lactamase-producing Escherichia coli. The reduction of fibrinogen levels, in this case, prompted severe spontaneous hemarthrosis. Tigecycline treatment was discontinued and coagulation disorders were normalized within the next few days. After several days, the joint had to be surgically debrided. Hypofibrinogenemia is a very scarcely reported side effect of tigecycline that can cause spontaneous hemarthrosis.

Efficacy and safety of high-dose tigecycline for the treatment of infectious diseases: A meta-analysis

BACKGROUND

High-dose (HD) tigecycline regimen is increasingly used in infectious diseases, however its efficacy and safety versus low-dose (LD) is still unclear.

METHODS

A systematic review and meta-analysis was performed; PubMed, Embase, Cochrane Library, ScienceDirect, Web of Science, clinicalTrials.gov, Wanfang, VIP, and China National Knowledge Infrastructure (CNKI), were searched using terms "tigecycline" AND "dose" up to October 31, 2018. Eligible studies were randomized trials or cohort studies comparing mortality, clinical response, microbiological eradication and safety of different tigecycline dose regimens for any bacterial infection. The primary outcome was mortality, and the secondary outcomes were clinical response rate, microbiological eradiation rate and adverse events (AEs). Meta-analysis was done with random-effects model, with risk ratios (RR) and 95% confidence intervals (CI) calculated for all outcomes.

RESULTS

Of 951 publications retrieved, 17 studies (n = 1041) were pooled in our meta-analysis. The primary outcome was available in 11 studies, and the RR for mortality was 0.67 (95% CI 0.53-0.84, P < .001). Clinical response (RR 1.46, 95% CI 1.30-1.65, P < .001) and microbiological eradication rate (RR 1.61, 95% CI 1.35-1.93, P < .001) were both higher in HD than in LD tigecycline regimen. However, non-Chinese study subgroup presented no statistical significance between HD and LD regimen, RR for mortality, clinical response and microbiological eradication were 0.79 (95% CI 0.56-1.14, P = .21), 1.35 (95% CI 0.96-1.92, P = .26), 1.00 (95% CI 0.22-4.43, P = 1.00), respectively. AEs did not differ between HD and LD tigecycline (RR 1.00, 95% CI 0.80-1.26, P = .97).

CONCLUSION

HD tigecycline regimen reduced mortality meanwhile improved clinical efficacy and should be considered in serious infections caused by multidrug-resistant and extensively drug-resistant (MDR/XDR) bacteria.

Immunomodulatory Effects of Tigecycline in Balb/C Mice

Tigecycline is a glycylcycline antibiotic approved by the FDA for the treatment of complicated infections. Despite its effectiveness, the FDA announced a warning of increasing mortality associated with its use. There is, however, no clear explanation for this side effect. Previous reports found a possible effect of tigecycline on leukocyte proliferation and proinflammatory cytokine release. We t herefore i nvestigated the effect of tigecycline on the immune components and response in Balb/c mice in vivo and in vitro. It was found that tigecycline enhanced lymphocyte proliferation and significantly increased cellular infiltration within the footpad, as based on DTH testing, but reduced the hemagglutination titer. In splenocyte cultures, tigecycline suppressed splenocyte proliferation with IC50 3-5 mmol L-1, significantly increased IL-2 secretion and reduced IL-17 secretion in a dose dependent mode. In conclusion, tigecycline is safe at therapeutic and sub-therapeutic doses, but it could still have an immunomodulatory effect at higher doses. Use of higher doses of tigecycline requires further investigation.

Once Daily High Dose Tigecycline Is Optimal: Tigecycline PK/PD Parameters Predict Clinical Effectiveness

OBJECTIVE

The clinical effectiveness of tigecycline depends on appropriate use, and PK/PD (pharmacokinetic/pharmacodynamic) parameters related to dose and dosing interval.

METHODS

In our 600-bed university-affiliated teaching hospital, we conducted a tigecycline efficacy review over a three-month period in 34 evaluable patients. Parameters assessed included clinical response, cure or treatment failure, once daily as q12h dosing, maintenance dosing, high dose vs. standard loading regimens, adverse effects, and the effect of infectious disease consultation on outcomes.

RESULTS

We found once daily high dose tigecycline (HDT) was highly effective in treating serious systemic infections due to MDR Gram-positive/negative pathogens as well as C. difficile colitis. Adverse effects were infrequent and limited to mild nausea/vomiting. Once daily HDT was highly effective, and the few treatment failures were related to suboptimal/split dosing regimens.

CONCLUSION

Once daily HDT was highly effective when used to treat susceptible pathogens and when optimally dosed, i.e., 200-400 mg (IV) loading dose ×1, followed by a once daily maintenance dose of 100-200 mg (IV) q24h.

Linezolid in liver failure: exploring the value of the maximal liver function capacity (LiMAx) test in a pharmacokinetic pilot study

Patients in the intensive care unit frequently require antibiotic treatment. Liver impairment poses substantial challenges for dose selection in these patients. The aim of the present pilot study was to assess the novel maximal liver function capacity (LiMAx test) in comparison with conventional liver function markers as covariates of drug clearance in liver failure using linezolid as a model drug. A total of 28 patients with different degrees of liver failure were recruited. LiMAx test as well as plasma, dialysate and urine sampling were performed under linezolid steady-state therapy (600 mg twice daily). NONMEM^® was used for a pharmacometric analysis in which the different clearance routes of linezolid were elucidated. Linezolid pharmacokinetics was highly variable in patients with liver failure. The LiMAx score displayed the strongest association with non-renal clearance (CL_non-renal) [ = 4.46∙(body weight/57.9) ^0.75∙(LiMAx/221.5)^0.388 L/h], which reduced interindividual variability in CL_non-renal from 46.6% to 33.6%, thereby being superior to other common markers of liver function (international normalised ratio, gamma-glutaryl transferase, bilirubin, thrombocytes, alanine aminotransferase, aspartate aminotransferase). For LiMAx < 100 µg/kg/h, 64% of linezolid trough concentrations were above the recommended trough concentration of 8 mg/L, indicating the necessity of therapeutic drug monitoring in these patients. This is the first pilot application of the LiMAx test in a pharmacokinetic (PK) study demonstrating its potential to explain PK variability in linezolid clearance. Further studies with a larger patient collective and further drugs are highly warranted to guide dosing in patients with severe liver impairment.

Use of tigecycline in pediatric clinical practice

INTRODUCTION

Tigecycline, a derivative of minocycline, is an extended-spectrum antimicrobial agent. It has a restricted approval field in children and the experience of its adoption in clinical practice is reserved for cases of challenging infections. The aim of this review was to summarize evidence regarding the use of tigecycline in infants and children, focusing on the drug's clinical efficacy data and tolerability profile. Areas covered: We have conducted a literature search of the Cochrane Library, EMBASE, and MEDLINE databases, from their inception through 5 January 2017, using the following terms: tigecycline, newborn, infant, child, pediatrics, adolescent, human, clinical trial, and case report. Articles were excluded if they were redundant or not pertinent. Bibliographies of all relevant articles were also evaluated. Seventeen publications were included: 1 pharmacokinetic study, 16 case reports. In the selected publications, the patients' mean age was 4.45 years, 38.7% of children was <3 years old and favorable clinical response was achieved in 74.2% of cases. Expert commentary: Tigecycline may be a considerable option in life-threatening infections in pediatric patients. Its administration is well tolerated and has demonstrated a good clinical response in nonbacteremic patients. However, the available clinical records are limited and more studies are needed.

A Phase 1 study of intravenous infusions of tigecycline in patients with acute myeloid leukemia

Acute myeloid leukemia (AML) cells meet the higher energy, metabolic, and signaling demands of the cell by increasing mitochondrial biogenesis and mitochondrial protein translation. Blocking mitochondrial protein synthesis through genetic and chemical approaches kills human AML cells at all stages of development in vitro and in vivo. Tigecycline is an antimicrobial that we found inhibits mitochondrial protein synthesis in AML cells. Therefore, we conducted a phase 1 dose‐escalation study of tigecycline administered intravenously daily 5 of 7 days for 2 weeks to patients with AML. A total of 27 adult patients with relapsed and refractory AML were enrolled in this study with 42 cycles being administered over seven dose levels (50–350 mg/day). Two patients experienced DLTs related to tigecycline at the 350 mg/day level resulting in a maximal tolerated dose of tigecycline of 300 mg as a once daily infusion. Pharmacokinetic experiments showed that tigecycline had a markedly shorter half‐life in these patients than reported for noncancer patients. No significant pharmacodynamic changes or clinical responses were observed. Thus, we have defined the safety of once daily tigecycline in patients with refractory AML. Future studies should focus on schedules of the drug that permit more sustained target inhibition.

Tigecycline : a critical safety review

INTRODUCTION

The emergence of multidrug-resistant (MDR) infections has been extensively observed worldwide and has become a priority issue over past decade. Tigecycline , a broad spectrum antibiotic covering against many MDR organisms, has been widely used. However, recent meta-analysis studies have raised a concern for its efficacy and safety. Reviewing tigecycline safety data would enhance the appropriate use of this medication.

AREAS COVERED

This article reviews the safety profile of tigecycline, including its side effects and drug interactions.

EXPERT OPINION

The increased mortality associated with tigecycline is not yet well understood. Based on current evidence, alternative options must be prioritized over tigecycline if available. When tigecycline use is warranted, vigilant observation to identify any breakthrough infections and careful monitoring of progression of the original infection are highly recommended. Considering a second agent (either for synergism or enhancing coverage) may be required.

Clostridium difficile with Moxifloxacin/Clindamycin Resistance in Vegetables in Ohio, USA, and Prevalence Meta-Analysis

We (i) determined the prevalence of Clostridium difficile and their antimicrobial resistance to six antimicrobial classes, in a variety of fresh vegetables sold in retail in Ohio, USA, and (ii) conducted cumulative meta-analysis of reported prevalence in vegetables since the 1990s. Six antimicrobial classes were tested for their relevance as risk factors for C. difficile infections (CDIs) (clindamycin, moxifloxacin) or their clinical priority as exhaustive therapeutic options (metronidazole, vancomycin, linezolid, and tigecycline). By using an enrichment protocol we isolated C. difficile from three of 125 vegetable products (2.4%). All isolates were toxigenic, and originated from 4.6% of 65 vegetables cultivated above the ground (n = 3; outer leaves of iceberg lettuce, green pepper, and eggplant). Root vegetables yielded no C. difficile. The C. difficile isolates belonged to two PCR ribotypes, one with an unusual antimicrobial resistance for moxifloxacin and clindamycin (lettuce and pepper; 027-like, A⁺B⁺CDT⁺; tcdC 18 bp deletion); the other PCR ribotype (eggplant, A⁺B⁺ CDT⁻; classic tcdC) was susceptible to all antimicrobials. Results of the cumulative weighted meta-analysis (6 studies) indicate that the prevalence of C. difficile in vegetables is 2.1% and homogeneous (P < 0.001) since the first report in 1996 (2.4%). The present study is the first report of the isolation of C. difficile from retail vegetables in the USA. Of public health relevance, antimicrobial resistance to moxifloxacin/clindamycin (a bacterial-associated risk factor for severe CDIs) was identified on the surface of vegetables that are consumed raw.

Carbapenem-resistant Klebsiella pneumoniae infections in kidney transplant recipients: a case-control study

INTRODUCTION

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections have emerged as a significant challenge in solid organ transplantation. CRKP infections in other patient populations have been associated with higher mortality, when compared to infections caused by carbapenem-sensitive K. pneumoniae (CSKP).

AIMS

The aim of this study was to evaluate possible risk factors, clinical characteristics, and outcomes of CRKP infections compared with CSKP infections in kidney transplant recipients (KTR).

METHODS

We retrospectively investigated 13 CRKP infections and 39 CSKP infections in KTR (2006-2010).

RESULTS

CRKP was not significantly associated with age, gender, or comorbidities. CRKP infections were significantly associated with recent exposure to broad-spectrum antibiotics and were more likely to have been managed on an inpatient basis and to have required source control. CRKP was significantly associated with earlier mortality. Six of 13 (46%) patients with CRKP infection, and none of the patients with CSKP infection, died within 6.5 months of infection onset. Although cases and controls did not differ significantly with respect to diabetes, all patients (100%, n = 9) who died during the study had diabetes, while 58% of the 43 survivors had diabetes (P = 0.02).

CONCLUSION

In conclusion, CRKP compared with CSKP is associated with greater risk of mortality. Investigations on ways to better prevent CRKP are urgently needed.

Major variation in MICs of tigecycline in Gram-negative bacilli as a function of testing method

Tigecycline is one of the few remaining therapeutic options for extensively drug-resistant (XDR) Gram-negative bacilli (GNB). MICs of tigecycline to Acinetobacter baumannii have been reported to be elevated when determined by the Etest compared to determinations by the broth microdilution (BMD) method. The study aim was to compare the susceptibility of GNB to tigecycline by four different testing methods. GNB were collected from six health care systems (25 hospitals) in southeast Michigan from January 2010 to September 2011. Tigecycline MICs among A. baumannii, carbapenem-resistant Enterobacteriaceae (CRE), extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae, and susceptible Enterobacteriaceae isolates were determined by Etest, BMD, Vitek-2, and MicroScan. Nonsusceptibility was categorized as a tigecycline MIC of ≥4 μg/ml for both A. baumannii and Enterobacteriaceae. The study included 4,427 isolates: 2,065 ESBL-producing Enterobacteriaceae, 1,105 A. baumannii, 888 susceptible Enterobacteriaceae, and 369 CRE isolates. Tigecycline nonsusceptibility among A. baumannii isolates was significantly more common as determined by Etest compared to that determined by BMD (odds ratio [OR], 10.3; P<0.001), MicroScan (OR, 12.4; P<0.001), or Vitek-2 (OR, 9.4; P<0.001). These differences were not evident with the other pathogens. Tigecycline MICs varied greatly according to the in vitro testing methods among A. baumannii isolates. Etest should probably not be used by laboratories for tigecycline MIC testing of A. baumannii isolates, since MICs are significantly elevated with Etest compared to those determined by the three other methods.

Worldwide challenges of multidrug-resistant bacteria in patients with hematologic malignancies

SUMMARY The emergence of infections due to multidrug-resistant (MDR) bacteria poses a major public health threat to all patients, but patients with hematologic malignancies are especially at risk. A common thread across all classes of bacteria is that increased reliance on and usage of broad-spectrum antibacterial agents, combined with the intrinsic ability of bacteria to develop and transmit resistance-conferring mutations, has led to the widespread dissemination of MDR organisms. In this article, we summarize the most worrisome MDR bacteria, assess their clinical impact on patients with hematologic malignancies and outline measures that are required to mitigate this impact.

Recent advances in antibacterial drugs

The incidence of antimicrobial resistance is on continued rise with a threat to return to the “pre-antibiotic” era. This has led to emergence of such bacterial infections which are essentially untreatable by the current armamentarium of available treatment options. Various efforts have been made to develop the newer antimicrobials with novel modes of action which can act against these multi-drug resistant strains. This review aims to focus on these newly available and investigational antibacterials approved after year 2000, their mechanism of actions/resistance, and spectrum of activity and their phases of clinical trials. Newer unexploited targets and strategies for the next generation of antimicrobial drugs for combating the drug resistance and emerging pathogens in the 21^st century have also been reviewed in the present article.

Population Pharmacokinetics of Tigecycline in Healthy Volunteers

Tigecycline, a novel glycylcycline, possesses broad-spectrum antimicrobial activity. A structural population pharmacokinetic model for tigecycline was developed based on data pooled from 5 phase I studies. Intravenous tigecycline was administered as single (12.5-300 mg) or multiple (25-100 mg) doses every 12 hours for up to 10 days. Three-compartment models with zero-order input and first-order elimination separately described the single- or multiple-dose full-profile data. Additional models were evaluated using a subset of the phase I data mimicking the phase II/III trial sparse-sampling scheme and dosage. A 2-compartment model best described the reduced phase I data following single or multiple doses and provided reliably accurate estimates of tigecycline AUC(0-12). This modeling supported phase II/III population pharmacokinetic model development to further determine individual patient tigecycline exposures for safety and efficacy analyses.

Emergence of carbapenem-resistant Enterobacteriaceae as causes of bloodstream infections in patients with hematologic malignancies

Carbapenem-resistant Enterobacteriaceae (CRE) are increasingly prevalent pathogens. However, little is known about their emergence in patients with hematologic malignancies. We identified 18 patients with hematologic malignancies over 3.5 years who developed bloodstream infections (BSIs) caused by CRE. Fourteen BSIs were caused by Klebsiella pneumoniae, three by Enterobacter cloacae, and one was polymicrobial. Initial empirical antimicrobial therapy was active in two patients (11%), and a median of 55 h elapsed between culture collection and receipt of an active agent. Ten patients (56%) died, including nine (69%) of 13 neutropenic patients, with a median of 4 days from culture collection until death. CRE isolates were analyzed for carbapenemase production, β-lactamase genes and outer membrane porin deletions and characterized by multilocus sequence typing and pulsed-field gel electrophoresis (PFGE). Carbapenem resistance mechanisms included Klebsiella pneumoniae carbapenemase production and CTX-M-15 production with an absent outer membrane porin protein. No isolate had ≥95% homology on PFGE, indicating a heterogeneous, non-outbreak population of isolates. CRE BSIs are emerging in patients with hematologic malignancies and are associated with ineffective initial empirical therapy, long delays in administration of active antimicrobials and high mortality rates. New diagnostic, therapeutic and preventive strategies for CRE infections in this vulnerable population are needed.

Comparative effectiveness of aminoglycosides, polymyxin B, and tigecycline for clearance of carbapenem-resistant Klebsiella pneumoniae from urine

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is an increasingly common cause of health care-associated urinary tract infections. Antimicrobials with in vitro activity against CRKP are typically limited to polymyxins, tigecycline, and often, aminoglycosides. We conducted a retrospective cohort study of cases of CRKP bacteriuria at New York-Presbyterian Hospital from January 2005 through June 2010 to compare microbiologic clearance rates based on the use of polymyxin B, tigecycline, or an aminoglycoside. We constructed three active antimicrobial cohorts based on the active agent used and an untreated cohort of cases that did not receive antimicrobial therapy with Gram-negative activity. Microbiologic clearance was defined as having a follow-up urine culture that did not yield CRKP. Cases without an appropriate follow-up culture or that received multiple active agents or less than 3 days of the active agent were excluded. Eighty-seven cases were included in the active antimicrobial cohorts, and 69 were included in the untreated cohort. The microbiologic clearance rate was 88% in the aminoglycoside cohort (n = 41), compared to 64% in the polymyxin B (P = 0.02; n = 25), 43% in the tigecycline (P < 0.001; n = 21), and 36% in the untreated (P < 0.001; n = 69) cohorts. Using multivariate analysis, the odds of clearance were lower for the polymyxin B (odds ratio [OR], 0.10; P = 0.003), tigecycline (OR, 0.08; P = 0.001), and untreated (OR, 0.14; P = 0.003) cohorts than for the aminoglycoside cohort. Treatment with an aminoglycoside, when active in vitro, was associated with a significantly higher rate of microbiologic clearance of CRKP bacteriuria than treatment with either polymyxin B or tigecycline.

Prevalence, enumeration, and antimicrobial agent resistance of Clostridium difficile in cattle at harvest in the United States

To assess the potential for food contamination with Clostridium difficile from food animals, we conducted a cross-sectional fecal prevalence study in 944 randomly selected cattle harvested at seven commercial meat processing plants, representing four distant regions (median distance of 1,500 km) of the United States. In all, 944 animals were sampled in the summer of 2008. C. difficile was isolated from 1.8% (17 of 944) of cattle, with median fecal shedding concentration of 2.2 log CFU/g (range = 1.6 to 4.8, 95% confidence interval = 1.6, 4.3). Toxigenic C. difficile isolates were recovered from only four (0.4%) cattle. One of these isolates was emerging PCR ribotype 078/toxinotype V. The remaining toxigenic isolates were toxinotype 0, one of which was an isolate with resistance to linezolid, clindamycin, and moxifloxacin (by the E-test). All isolates were susceptible to vancomycin, metronidazole, and tigecycline, but the MICs against linezolid were as high as the highest reported values for human-derived isolates. The source of the linezolid-clindamycin-moxifloxacin resistance in a toxigenic C. difficile isolate from cattle is uncertain. However, since the use of these three antimicrobial agents in cattle is not allowed in North America, it is possible that resistance originated from an environmental source, from other species where those antimicrobial agents are used, or transferred from other intestinal bacteria. This study confirms that commercial cattle can carry epidemiologically relevant C. difficile strains at the time of harvest, but the prevalence at the time they enter the food chain is low.

Comparison of ceftaroline fosamil, daptomycin and tigecycline in an experimental rabbit endocarditis model caused by methicillin-susceptible, methicillin-resistant and glycopeptide-intermediate Staphylococcus aureus

OBJECTIVES

The aim of this study was to compare the in vivo activities of the new antistaphylococcal drugs ceftaroline fosamil, daptomycin and tigecycline at projected human therapeutic doses against methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA) and glycopeptide-intermediate S. aureus (GISA) strains in a rabbit model of endocarditis.

METHODS

The efficacy of therapeutic regimens in our model was evaluated following 4 days of treatment by determining colony counts of infected vegetations. Emergence of resistant variants during therapy was assessed.

RESULTS

Using this model of infective endocarditis, ceftaroline fosamil and daptomycin demonstrated high bactericidal in vivo activity (reduction of >5 log(10) cfu/g of vegetation) after a 4 day treatment against MSSA, MRSA and GISA strains. Both drugs were more efficacious than tigecycline, which showed moderate activity but failed to exhibit a bactericidal effect. Ceftaroline was superior to daptomycin in terms of sterilization of the vegetations. Emergence of resistant variants during daptomycin therapy was observed in two animals (one in the MSSA group and one in the MRSA group) but was not observed in ceftaroline- or tigecycline-treated animals.

CONCLUSIONS

The novel β-lactam agent ceftaroline fosamil was the most active bactericidal drug in this model and is a promising therapeutic option for the treatment of severe S. aureus infections, including those caused by MRSA and GISA strains.

Potential role of tigecycline in the treatment of community-acquired bacterial pneumonia

Tigecycline is a member of the glycylcycline class of antimicrobials, which is structurally similar to the tetracycline class. It demonstrates potent in vitro activity against causative pathogens that are most frequently isolated in patients with community-acquired bacterial pneumonia (CABP), including (but not limited to) Streptococcus pneumoniae (both penicillin-sensitive and -resistant strains), Haemophilus influenzae and Moraxella catarrhalis (including β-lactamase-producing strains), Klebsiella pneumoniae, and ‘atypical organisms’ (namely Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila). Comparative randomized clinical trials to date performed in hospitalized patients receiving tigecycline 100 mg intravenous (IV) × 1 and then 50 mg IV twice daily thereafter have demonstrated efficacy and safety comparable to the comparator agent. Major adverse effects were primarily gastrointestinal in nature. Tigecycline represents a parenteral monotherapy option in hospitalized patients with CABP (especially in patients unable to receive respiratory fluoroquinolones). However, alternate and/or additional therapies should be considered in patients with more severe forms of CABP in light of recent data of increased mortality in patients receiving tigecycline for other types of severe infection.

Systematic review and meta-analysis of the effectiveness and safety of tigecycline for treatment of infectious disease

The aim of this study was to compare the efficacy and safety of tigecycline, a newly developed glycylcycline antibiotic, with those of empirical antibiotic regimens which have been reported to possess good efficacy for complicated skin and skin structure infections (cSSSIs), complicated intra-abdominal infections (cIAIs), community-acquired pneumonia (CAP), and other infections caused by methicillin-resistant Staphylococcus aureus (MRSA) or vancomycin-resistant Enterococcus (VRE). A meta-analysis of randomized controlled trials (RCTs) identified in PubMed, the Cochrane Library, and Embase was performed. Eight RCTs involving 4,651 patients were included in the meta-analysis. Compared with therapy with empirical antibiotic regimens, tigecycline monotherapy was associated with similar clinical treatment success rates (for the clinically evaluable [CE] population, odds ratio [OR] = 0.92, 95% confidence interval [CI] = 0.76 to 1.12, P = 0.42; for the clinical modified intent-to-treat [c-mITT] population, OR = 0.86, 95% CI = 0.74 to 1.01, P = 0.06) and similar microbiological treatment success rates (for the microbiologically evaluable [ME] population, OR = 0.86, 95% CI = 0.69 to 1.07, P = 0.19). The incidence of adverse events in the tigecycline group was significantly higher than that in the other therapy groups with a statistical margin (for the modified intent-to-treat [mITT] population, OR = 1.33, 95% CI = 1.17 to 1.52, P < 0.0001), especially in the digestive system (mITT population, OR = 2.41, 95% CI = 1.67 to 3.46, P < 0.00001). No difference regarding all-cause mortality and drug-related mortality between tigecycline and the other regimens was found, although numerically higher mortality was found in the tigecycline group. This meta-analysis provides evidence that tigecycline monotherapy may be used as effectively as the comparison therapy for cSSSI, cIAIs, CAP, and infections caused by MRSA/VRE. However, because of the high risk of mortality, AEs, and emergence of resistant isolates, prudence with the clinical use of tigecycline monotherapy in infections is required.

A review of tigecycline--the first glycylcycline

The dawn of a troubling post-antibiotic era likely is on the horizon, fuelled by a rise in bacterial resistance to existing antibiotic therapy alongside a waning pipeline of novel antibacterial agents. Tigecycline, a new glycylcycline with an expanded broad spectrum of in vitro activity, was recently approved for the treatment of complicated skin and soft tissue infections (cSSTIs) and complicated intra-abdominal infections (cIAIs). This review will examine how tigecycline evades the common mechanisms of antibiotic resistance, the metabolism and pharmacokinetics of tigecycline, and its spectrum of in vitro activity. The results of randomized clinical trials for the treatment of cSSTIs and cIAIs with tigecycline are also described, as is the patient safety and tolerability observed during these studies. Tigecycline monotherapy has been shown to be as effective as its comparators and, against a backdrop of rising bacterial resistance, the role for tigecycline in monotherapy of infections from Gram-positive, Gram-negative and anaerobic bacteria is a meaningful development.

Tigecycline in combination with other antimicrobials: a review of in vitro, animal and case report studies

Tigecycline has been investigated in combination with other antibacterials against a wide range of susceptible and multiresistant Gram-positive and Gram-negative bacteria. Combinations have been analysed in vitro, in animal models and in human case reports. In vitro, tigecycline combined with other antimicrobials produces primarily an indifferent response (neither synergy nor antagonism). Nevertheless, synergy occurred when tigecycline was combined with rifampicin against 64-100% of Enterococcus spp., Streptococcus pneumoniae, Enterobacter spp. and Brucella melitensis isolates. Combinations of tigecycline with amikacin also showed synergy for 40-100% of Enterobacter spp., Klebsiella pneumoniae, Proteus spp. and Stenotrophomonas maltophilia isolates. Moreover, bactericidal synergisms occurred with tigecycline plus amikacin against problematic Acinetobacter baumannii and Proteus vulgaris, and with colistin against K. pneumoniae. Data from animal experiments and case reports, although limited, displayed consistent beneficial activity of tigecycline in combination with other antibacterials against multiresistant organisms, including vancomycin against penicillin-resistant S. pneumoniae in experimental meningitis, gentamicin against Pseudomonas aeruginosa in experimental pneumonia, daptomycin against Enterococcus faecium endocarditis, and colistin against K. pneumoniae bacteraemia and P. aeruginosa osteomyelitis. Antagonism was extremely rare in vitro and was not reported in vivo. Thus, tigecycline may be combined with a second antimicrobial as part of a combination regimen.

Tigecycline pharmacokinetic/pharmacodynamic update

This brief review summarizes recently published data on the pharmacokinetics and pharmacodynamics of tigecycline in man. Significant pharmacokinetic data are now available from the studies of infected patients, as is information on tissue distribution. Importantly, drug exposure-response relationships have been established for complicated skin and skin structure infections and intra-abdominal infection. These studies highlight the difficulties of undertaking pharmacodynamic studies in humans where account must be taken of both mixed pathogen infections and the potential impact of surgery. These data help to define the clinical role for tigecycline.

Evaluation of tigecycline penetration into colon wall tissue and epithelial lining fluid using a population pharmacokinetic model and Monte Carlo simulation

The objective of these analyses was to assess the penetration of tigecycline into colon wall tissue and epithelial lining fluid (ELF). The analyses included data from subjects without infection (phase 1) and patients with intra-abdominal infections (phase 2/3). Steady-state serum samples were collected from all subjects/patients (n = 577), while colon wall specimens (n = 23) and ELF specimens (n = 30) were obtained from subjects without infection. Tissue and serum data were simultaneously comodeled by using the BigNPAG program, and a four-compartment, open model with zero-order intravenous input and first-order elimination was employed. To examine the full range of tissue penetration and the associated probabilities of occurrence, a 9,999-subject Monte Carlo simulation was performed with two outputs, one for ELF penetration and one for colon wall tissue penetration. Data were well fit using models described above, with all r(2) values above 0.95. For subjects without infection, the median (5th and 95th percentiles) colon wall and ELF penetration ratios were 1.73 (0.160 and 199) and 1.15 (0.561 and 5.23), respectively. Simulation results predict that tissue penetration varies considerably and likely explain unexpected clinical outcomes for those patients infected with strains at margins of the MIC distribution.

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.

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.

Activity of tigecycline in the treatment of acute Burkholderia pseudomallei infection in a murine model

Burkholderia pseudomallei is the causative agent of melioidosis. Standard therapy includes ceftazidime alone or in combination with co-trimoxazole. Tigecycline, a novel agent, has displayed activity against B. pseudomallei. We evaluated the in vivo efficacy of tigecycline using a murine model of melioidosis. Mice were infected with either a high or low virulence B. pseudomallei isolate followed by administration of antibiotics alone or in combination (tigecycline, ceftazidime, tigecycline plus ceftazidime) for 7 days. Bacterial loads were assessed up to 7 days and survival was determined up to 7 days post infection. Tigecycline in combination with ceftazidime was the most effective and conferred the lowest mortality, suggesting the use of this new agent in B. pseudomallei infection.

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.

Tigecycline: The answer to beta-lactam and fluoroquinolone resistance?

Patients with serious bacterial infections such as intra-abdominal infections and complicated skin and soft tissue infections are often treated empirically because a delay in appropriate initial antimicrobial therapy has been shown to significantly increase morbidity and mortality. Furthermore, pathogens that have developed resistance to mainstay therapeutic options are increasing in prevalence making these infections a challenge for physicians. Treatment guidelines for surgical and intra-abdominal infections recommend selection of an agent or a combination of agents with activity to cover both Gram-positive, Gram-negative organisms and anaerobes. Recommended agents include second-generation cephalosporins with anaerobic coverage, beta-lactam/beta-lactamase inhibitor agents, fluoroquinolone/metronidazole combinations and carbapenems. However, the effectiveness of these agents has come into question as once susceptible organisms are now showing signs of resistance to such antimicrobial therapies. Alternative agents specifically designed to overcome mechanisms of microbial resistance have been sought. The result of that search has been the development of a new class of antimicrobials termed glycylcyclines. The first of these novel antibacterials is tigecycline, with a broad spectrum of activity that includes coverage against vancomycin-resistant enterococci, methicillin-resistant S. aureus, and many species of multidrug-resistant Gram-negative bacteria. Tigecycline also has activity against most penicillin-susceptible and resistant Gram-positive organisms. Clinical trial experience with tigecycline has shown it to be at least as effective as current recommended regimens for the treatment of intra-abdominal infections and complicated skin and soft tissue infections. This new agent thus holds promise as an alternative to the beta-lactams and fluoroquinolones for the initial empiric treatment of serious bacterial infections.

Hospital-acquired pneumonia in the 21st century: a review of existing treatment options and their impact on patient care

Hospital-acquired pneumonia is a common nosocomial infection, with significant morbidity and mortality, and represents a major therapeutic challenge to clinicians. The therapeutic approach must be patient-oriented and institution-specific. The specific risk factors of each patient, such as previous antibiotic exposure, underlying diseases, length of hospital stay and the local patterns of antimicrobial resistance, should guide physicians in their decision of the initial optimal empirical therapy. Delays in the initiation or inappropriate/inadequate initial therapy are related to increased mortality and worse outcomes. In responding patients, as soon as culture data are available, efforts should be made to change the initial broad spectrum antibiotic regimen to a more targeted one (de-escalation). The optimal duration of treatment is a matter of debate, but courses longer than 1 week are rarely justified.

Gram-negative bacterial pneumonia: aetiology and management

PURPOSE OF REVIEW

Recent articles of clinical and investigational interest on Gram-negative pneumonia, particularly hospital-acquired and ventilator-associated pneumonia, are reviewed.

RECENT FINDINGS

The high rate of respiratory infections due to Gram-negative bacteria in late-onset ventilator-associated pneumonia has been repeatedly documented. The predominant pathogens are Pseudomonas aeruginosa and Acinetobacter baumannii. On the other hand, the frequency of Gram-negative bacteria in community-acquired pneumonia and in early-onset ventilator-associated pneumonia is increasing. Patients with risk factors for infection with resistant pathogens should initially receive a combination therapy that covers a broad spectrum, and, as soon as the pathogen and the susceptibilities are available, treatment should be simplified to a more targeted one (with the possible exception of P. aeruginosa pneumonia). Adequate dosing is of great importance and the use of pharmacodynamic/pharmacokinetic principles when prescribing antibiotics increases effectiveness. The optimal duration of therapy remains unknown; several studies have supported the use of shorter courses of treatment. Alternative treatment approaches (e.g. vaccines) are under investigation.

SUMMARY

The increasing frequency of resistant Gram-negative bacteria and the shortage of newer antibiotics in the pipeline with activity against Gram-negative bacteria is of concern. Early effective antimicrobial treatment is a key for the resolution of infection and improved survival.

Antibiothérapie des états infectieux graves

Severe sepsis, which is related to a high mortality rate, requires a very specific antibiotic strategy, which must be adapted to each case. The appropriateness of empiric therapy is based on the delay before administration of the molecule, the bacterial resistance profile, and the kinetic and/or dynamic properties of the available antibiotics.

Stratégie antibiotique au cours du choc septique

Septic shock remains a true challenge to modern therapeutics. The quality and earliness of antibiotic administration are both fundamental elements. Treatment should be individually adapted to each patient. The pharmacokinetic indicators and predicted resistance of the bacteria targeted determine the choice of treatment, often empirical. Radical treatment of the source of infection, especially by surgery, should be combined with antibiotic treatment whenever possible.