Optimal treatment of complicated skin and skin structure infections

Anti-microbial photodynamic therapy: useful in the future?

Previous chapters in this volume have focused on fundamental principles and clinical applications of PDT. This chapter will attempt to outline emerging areas of research to identify some new applications that may become useful in the future in clinical practise. The worldwide rise in antibiotic resistance has driven research to the development of novel anti-microbial strategies. Cutaneous diseases caused by MRSA are ideally suited to treatment by anti-microbial photodynamic therapy for eradicating localized infections and for modulating wound healing due to the ability to deliver photosensitizer and light with topical application. The use of photosensitizer and light as an anti-microbial agent against periodontal microbial biofilms should also represent an attractive method of eliminating oral bacteria. Suitable light sources, laser light and non-coherent light will be briefly covered. This chapter will focus on some aspects of anti-microbial photodynamic therapy that appear to be promising for dermatological indications and inactivation of pathogenic bacteria within the oral cavity.

Antimicrobial activity of a novel peptide deformylase inhibitor, LBM415, tested against respiratory tract and cutaneous infection pathogens: a global surveillance report (2003-2004)

OBJECTIVES

To evaluate the spectrum of activity and potency of LBM415, the first of the peptide deformylase inhibitor (PDFI) class to be developed for treatment of community-acquired respiratory tract infections and uncomplicated skin and soft tissue infections (uSSTI), against a large, contemporary international collection of targeted pathogens collected during 2003-2004.

METHODS

A total of 21,636 isolates were tested by reference broth microdilution methods as part of a longitudinal international antimicrobial resistance surveillance study. Characteristics of the organism collection included resistance to oxacillin among 35.0% of Staphylococcus aureus and 76.0% of coagulase-negative staphylococci (CoNS); resistance to penicillin (MIC > or = 2 mg/L) among 18.0% of Streptococcus pneumoniae; vancomycin resistance among 20.0% of Enterococcus spp. and ampicillin resistance among 22.0% of Haemophilus influenzae.

RESULTS

LBM415 displayed potent activity against staphylococci, streptococci, Enterococcus faecium and Moraxella catarrhalis, with > or = 99.0% of strains being inhibited at < or = 4 mg/L; 97.0% of Enterococcus faecalis isolates and 92.0% of H. influenzae isolates were also inhibited at this concentration. Seventy-seven percent of Burkholderia cepacia and 82.0% of Stenotrophomonas maltophilia were inhibited at < or = 8 mg/L. No differences in LBM415 activity against S. aureus, CoNS, S. pneumoniae, Enterococcus spp. and H. influenzae were detected for subsets susceptible or resistant to antimicrobials such as oxacillin, penicillin, ampicillin, macrolides, vancomycin and fluoroquinolones. While regional differences were apparent with some comparator agents, sensitivity to LBM415 did not vary significantly among strains from the various geographic areas sampled. One isolate of S. aureus displayed high-level resistance to LBM415 owing to multiple sequence changes in resistance phenotype genes (defB and fmt), despite the absence of the compound in clinical practice. This isolate remained susceptible to all other antimicrobials tested except for penicillin.

CONCLUSIONS

With few differences detected among strains from various geographic regions, the first PDFI class agent to enter clinical development has consistently demonstrated a broad spectrum of activity against commonly isolated pathogens associated with uncomplicated respiratory and cutaneous infections. These compounds represent a significant therapeutic advance owing to their novel mechanism of action and antibacterial spectrum, including activity against resistant organisms, should pharmacokinetic and pharmacodynamic parameters support their continued development. Given the detection of a pre-existing PDFI-resistant isolate of S. aureus as demonstrated here, surveillance for resistance among the PDFI-targeted pathogens following introduction of this class of agent into clinical usage will be an important component of future studies.

Treatment of intra-abdominal and skin and soft tissue infections: The role of the glycylcyclines

The need for new, effective agents to treat multidrug-resistant infections continues to grow as more and more bacteria develop resistance that may result in clinical therapeutic failure. This is particularly true for common surgical infections, such as complicated intra-abdominal infections, which frequently involve multiple pathogens, making therapy with a broad-spectrum antibiotic an important treatment intervention, and also for complicated skin infections, which often involve methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). With treatment options limited, it has become critical to identify antibiotics with novel mechanisms of activity. Several new drugs have emerged as possible therapeutic alternatives: linezolid, quinupristin-dalfopristin and most recently daptomycin have all been FDA-approved for the treatment of skin and skin structure infections. This review examines the potential role of a new class of investigational agents, the glycylcyclines, also recently FDA-approved and currently under review for European licensing, in the treatment of complicated skin infections and intra-abdominal infections. Tigecycline, the first of the glycylcyclines, has shown excellent activity in Phase III studies of these infections, achieving clinical success rates ranging from 70% to 91%. Furthermore, it has a good safety profile, suggesting it will be a clinical useful addition to current therapeutic options for the treatment of complicated skin infections and intra-abdominal infections.

Sequential intravenous/oral moxifloxacin versus intravenous piperacillin-tazobactam followed by oral amoxicillin-clavulanate for the treatment of complicated skin and skin structure infection

In this prospective, double-blind, multicentre trial, adult patients with complicated skin and skin structure infection (cSSSI) randomly received sequential intravenous (i.v.)/oral (p.o.) moxifloxacin (400 mg once a day) or a control regimen of i.v. piperacillin-tazobactam (3.0/0.375 g every 6 h) followed by p.o. amoxicillin-clavulanate (800 mg every 12 h), each for 7-14 days. Clinical cure rates at the test-of-cure visit (10-42 days post therapy) for the efficacy-valid population were 79% (143/180) for the moxifloxacin-treated group and 82% (153/187) for the control group (95% confidence interval, -12.04, 3.29). Bacteriological eradication rates for Staphylococcus aureus, the most prevalent organism, were 78% and 80%, respectively. The incidence of drug-related adverse events was similar for both groups (31% moxifloxacin, 30% control). Sequential i.v./p.o. moxifloxacin was as effective and well tolerated as i.v. piperacillin-tazobactam followed by p.o. amoxicillin-clavulanate in treating patients with cSSSI.

Antistaphylococcal activity of DX-619, a new des-F(6)-quinolone, compared to those of other agents

The in vitro activity of DX-619, a new des-F(6)-quinolone, was tested against staphylococci and compared to those of other antimicrobials. DX-619 had the lowest MIC ranges/MIC(50)s/MIC(90)s (microg/ml) against 131 Staphylococcus aureus strains (</=0.002 to 2.0/0.06/0.5) and 128 coagulase-negative staphylococci (0.004 to 0.25/0.016/0.125). Among strains tested, 76 S. aureus strains and 51 coagulase-negative staphylococci were resistant to ciprofloxacin. DX-619 had the lowest MIC(50)/MIC(90) values against 127 quinolone-resistant staphylococci (0.125/0.5), followed by sitafloxacin (0.5/4), moxifloxacin (2/8), gatifloxacin (4/16), levofloxacin (16/>32), and ciprofloxacin (>32/>32). Raised quinolone MICs were associated with mutations in GyrA (S84L) and single or double mutations in GrlA (S80F or Y; E84K, G, or V) in all S. aureus strains tested. A recent vancomycin-resistant S. aureus (VRSA) strain (Hershey) was resistant to available quinolones and was inhibited by DX-619 at 0.25 microg/ml and sitafloxacin at 1.0 microg/ml. Vancomycin (except VRSA), linezolid, ranbezolid, tigecycline, and quinupristin-dalfopristin were active against all strains, and teicoplanin was active against S. aureus but less active against coagulase-negative staphylococci. DX-619 produced resistant mutants with MICs of 1 to >32 microg/ml after <50 days of selection compared to 16 to >32 microg/ml for ciprofloxacin, sitafloxacin, moxifloxacin, and gatifloxacin. DX-619 and sitafloxacin were also more active than other tested drugs against selected mutants and had the lowest mutation frequencies in single-step resistance selection. DX-619 and sitafloxacin were bactericidal against six quinolone-resistant (including the VRSA) and seven quinolone-susceptible strains tested, whereas gatifloxacin, moxifloxacin, levofloxacin, and ciprofloxacin were bactericidal against 11, 10, 7, and 5 strains at 4x MIC after 24 h, respectively. DX-619 was also bactericidal against one other VRSA strain, five vancomycin-intermediate S. aureus strains, and four vancomycin-intermediate coagulase-negative staphylococci. Linezolid, ranbezolid, and tigecycline were bacteriostatic and quinupristin-dalfopristin, teicoplanin, and vancomycin were bactericidal against two, eight, and nine strains, and daptomycin and oritavancin were rapidly bactericidal against all strains, including the VRSA. DX-619 has potent in vitro activity against staphylococci, including methicillin-, ciprofloxacin-, and vancomycin-resistant strains.

Antimicrobial Management of Complicated Skin and Skin Structure Infections in the Era of Emerging Resistance

BACKGROUND

Complicated skin and skin structure infections (cSSSIs) are among the most common infections treated in the hospital setting. The mainstays of treatment continue to be antimicrobial therapy combined with appropriate surgical intervention. Due to increasing resistance among pathogens commonly implicated in cSSSIs, the objectives of this review were to describe the potential pathogens causing skin infections, the implications of resistance to currently used drug therapy, and the role of new antibiotics with activity for pathogens causing cSSSIs.

METHODS

Relevant information from the primary literature and review articles were identified through a MEDLINE search of the medical literature (1980 to the present) using the terms abscess, wound infection, skin and skin structure infection, antibiotics, resistance, quinupristin- dalfopristin, linezolid, daptomycin, tigecycline, oritavancin, and dalbavancin. Meeting posters and slides were identified from the Interscience Conference of Antimicrobial Agents and Chemotherapy (1998-2004) for supplemental data.

RESULTS

The most commonly implicated pathogens in cSSSIs include gram-positive bacteria, specifically Staphylococcus aureus. Gram-negative and mixed organisms are additionally encountered in serious cSSSI. Antimicrobial resistance among both gram-positive and gramnegative bacteria has increased significantly during the last decade, with methicillin resistance among S. aureus approaching 60% in hospitals and becoming more frequent in the community as well. As a result, resistance is the driving factor for treatment failure and rising costs for infection management. Few antimicrobial agents are available currently to treat resistant bacteria in cSSSIs; vancomycin is currently the drug of choice against resistant grampositive cocci; however, resistance to this agent has appeared in enterococci and S. aureus. Several new antibiotics such as linezolid and daptomycin are now available for the management of cSSSIs. Other agents such as tigecycline are under investigation and should be available soon to increase treatment options for cSSSIs caused by resistant bacteria.

CONCLUSIONS

Although the resistance of cSSSI pathogens is problematic, new antibiotics with broad-spectrum activity against resistant gram-positive and gram-negative bacteria are promising for the management of severe cSSSIs.

Clinical trial results with linezolid, an oxazolidinone, in the treatment of soft tissue and postoperative gram-positive infections

BACKGROUND

Infectious complications encountered after major surgery include operative site infections and nosocomial pneumonia. Recent infection surveillance programs have identified the increasing pathogenic role of gram-positive bacteria in these infections and the high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in the United States and abroad. Surgical site infections and nosocomial pneumonia, often serious infections, are associated with adverse clinical outcomes including bacteremia and its resultant complications, as well as the socioeconomic consequences of excess hospitalization and discharge to nursing care.

METHODS

The essential triad for management of postoperative soft tissue infection consists of thorough appraisal of the infection site for reintervention, culture of drainage or infected tissue, and prompt initiation of empiric antimicrobial therapy designed to cover the most probable causative pathogens. Broad-spectrum antimicrobial regimens are often necessary for empiric therapy of skin and soft tissue infections or nosocomial pneumonia; however, regimens should be tailored to the most effective and clinically appropriate agent based on results of susceptibility testing.

RESULTS

Results of the clinical trial experience with the first United States Food and Drug Administration (FDA)-approved antimicrobial in the new class of oxazolidinones, linezolid, are reviewed.

CONCLUSION

In randomized, controlled trials, linezolid 600 mg twice daily (intravenously or orally) provided effective antimicrobial therapy for gram-positive soft tissue infections, including MRSA, and nosocomial pneumonia in which S. aureus was a causative pathogen.

Linezolid versus vancomycin in treatment of complicated skin and soft tissue infections

Skin and soft tissue infections (SSTIs) are a common cause of morbidity in both the community and the hospital. An SSTI is classified as complicated if the infection has spread to the deeper soft tissues, if surgical intervention is necessary, or if the patient has a comorbid condition hindering treatment response (e.g., diabetes mellitus or human immunodeficiency virus). The purpose of this study was to compare linezolid to vancomycin in the treatment of suspected or proven methicillin-resistant gram-positive complicated SSTIs (CSSTIs) requiring hospitalization. This was a randomized, open-label, comparator-controlled, multicenter, multinational study that included patients with suspected or proven methicillin-resistant Staphylococcus aureus (MRSA) infections that involved substantial areas of skin or deeper soft tissues, such as cellulitis, abscesses, infected ulcers, or burns (<10% of total body surface area). Patients were randomized (1:1) to receive linezolid (600 mg) every 12 h either intravenously (i.v.) or orally or vancomycin (1 g) every 12 h i.v. In the intent-to-treat population, 92.2% and 88.5% of patients treated with linezolid and vancomycin, respectively, were clinically cured at the test-of-cure (TOC) visit (P=0.057). Linezolid outcomes (124/140 patients or 88.6%) were superior to vancomycin outcomes (97/145 patients or 66.9%) at the TOC visit for patients with MRSA infections (P<0.001). Drug-related adverse events were reported in similar numbers in both the linezolid and the vancomycin arms of the trial. The results of this study demonstrate that linezolid therapy is well tolerated, equivalent to vancomycin in treating CSSTIs, and superior to vancomycin in the treatment of CSSTIs due to MRSA.

Photodynamic effects of novel XF porphyrin derivatives on prokaryotic and eukaryotic cells

The worldwide rise in the rates of antibiotic resistance of bacteria underlines the need for alternative antibacterial agents. A promising approach to the killing of gram-positive antibiotic-resistant bacteria of the skin uses light in combination with a photosensitizer to induce a phototoxic reaction. Different concentrations (0 to 100 microM) of porphyrin-based photosensitizers (CTP1, XF70, and XF73) and different incubation times (5 min, 1 h, and 4 h) were used to determine phototoxicity against two methicillin-resistant Staphylococcus aureus strains, one methicillin-sensitive S. aureus strain, one methicillin-resistant Staphylococcus epidermidis strain, one Escherichia coli strain, and human keratinocytes and fibroblasts. Incubation with 0.005 microM XF70 or XF73, followed by illumination, yielded a 3-log10 (> or = 99.9%) decrease in the viable cell numbers of all staphylococcal strains, indicating that the XF drugs have high degrees of potency against gram-positive bacteria and also that the activities of these novel drugs are independent of the antibiotic resistance pattern of the staphylococci examined. CTP1 was less potent against the staphylococci under the same conditions. At 0.005 microM, XF70 and XF73 demonstrated no toxicity toward fibroblasts or keratinocytes. No inactivation of E. coli was detected at this concentration. XF73 was confirmed to act via a reactive oxygen species from the results of studies with sodium azide (a quencher of singlet oxygen), which reduced the killing of both eukaryotic and prokaryotic cells. When a quencher of superoxide anion and the hydroxyl radical was used, cell killing was not inhibited. These results demonstrate that the porphyrin-based photosensitizers had concentration-dependent differences in their efficacies of killing of methicillin-resistant staphylococcal strains via reactive oxygen species without harming eukaryotic cells at the same concentrations.

A new approach for treatment of deep skin infections by an ethosomal antibiotic preparation: an in vivo study

OBJECTIVES

Dermal and subdermal bacterial infections, caused mainly by Staphylococcus aureus, are currently treated by systemic antibiotics. The aim of the present study was to investigate a new approach to treat deep skin and soft tissue bacterial infections by dermal application of erythromycin in an ethosomal carrier.

METHODS

A model for deep dermal S. aureus infection in mice was developed. The efficiency of ethosomal erythromycin applied to the skin-infected site was compared with intraperitoneal erythromycin administration and with local application of hydroethanolic erythromycin solution. The parameters evaluated were the development of dermal wound, histological sections and bacterial count of the infected tissue.

RESULTS

The in vivo experiments demonstrated a very efficient healing of S. aureus-induced deep dermal infections when the mice were treated with ethosomal erythromycin. Bacterial counts and histological evaluation of the skin treated with ethosomal antibiotic revealed no bacterial growth and normal skin structure. On the contrary, no subdermal healing was observed in infected animals treated with topical hydroethanolic erythromycin solution. In this group, animals developed deep dermal abscesses and the dermal structures were destroyed where S. aureus colonies were present. Bacterial counts of the infected tissues were 1.06 x 10(7) and 0.27 x 10(7) cfu/g of tissue, respectively, on days 7 and 10.

CONCLUSIONS

Therapy with ethosomal erythromycin applied to the skin of S. aureus-infected mice was as effective as systemically administered erythromycin, suggesting a new possibility to treat deep dermal infections by local application of antibiotic in ethosomal carrier.

Daptomycin: a cyclic lipopeptide antimicrobial agent

Objectives:

The aims of this article were: to summarize the pharmacology, pharmacokinetics, and efficacy ofdaptomycin; to explore its safety profile; and to discuss its current and potential roles as an antimicrobial therapy.

Methods:

A literature search was conducted using the MEDLINE (1966–August 2004) and InternationalPharmaceutical Abstracts (1970–August 2004) databases with the search terms daptomycin, LY146032, and lipopeptide antibiotics. Abstracts of the Interscience Conference on Antimicrobial Agents and Chemotherapy and documents submitted to the US Food and Drug Administration were also reviewed.

Results:

Phase III study results suggest no difference in efficacy or tolerability between daptomycin 4 mg/kgIV QD and vancomycin or semisynthetic penicillins for complicated skin and skin-structure infections. Animal studies suggest daptomycin may be useful for the treatment of endocarditis. Daptomycin is not indicated for pneumonia, with poorer outcomes than conventional treatment It is available as an IV medication and exhibits 92% plasma protein binding in vitro. In healthy adult humans, daptomycin has a volume of distribution of 0.1 Ukg and a plasma elimination half-life of ∼9 hours, and is eliminated primarily by renal excretion (∼54%). In patients with reduced renal function, including those receiving hemodialysis and peritoneal dialysis, the dose interval should be 48 hours. No dosage adjustment appears to be necessary for mild to moderate hepatic impairment. The use of daptomycin in patients with severe hepatic impairment has not been assessed. The most commonly reported adverse events include constipation, nausea, injection-site reactions, headache, and diarrhea. Patients should also be monitored regularly for skeletal muscle toxicity.

Conclusions:

Daptomycin may be useful for complicated skin and skin-structure infections and gram-positive pathogens resistant to conventional antimicrobials. However, limited data are currently available for duration of treatment beyond 14 days and at doses >4 mg/kg QD.

Antistaphylococcal activity of dalbavancin, an experimental glycopeptide

Dalbavancin, tested against 146 staphylococci, was more potent than other drugs tested, with an MIC at which 50% of staphylococci were inhibited of 0.03 microg/ml and an MIC at which 90% of staphylococci were inhibited of 0.06 microg/ml by microdilution. For all strains, MICs of vancomycin, linezolid, ranbezolid, oritavancin, daptomycin, and quinupristin-dalfopristin were </=4.0 microg/ml. Dalbavancin was bactericidal at four times the MIC against all six strains tested.

Antistaphylococcal activity of CB-181963 (CAB-175), an experimental parenteral cephalosporin

Among 265 methicillin-susceptible and -resistant staphylococci, CB-181963 (CAB-175) had a 50% minimum inhibitory concentration of 2 microg/ml and a 90% minimum inhibitory concentration of 4 microg/ml. All strains except two vancomycin-resistant S. aureus and 5 vancomycin-intermediate S. aureus strains were also susceptible to vancomycin and teicoplanin, and all were susceptible to linezolid, ranbezolid, tigecycline, and quinupristin-dalfopristin. Most methicillin-resistant strains were levofloxacin resistant. CB-181963 was bactericidal against all six methicillin-resistant strains at four times the MIC after 24 h.

Antistaphylococcal activity of LBM415, a new peptide deformylase inhibitor, compared with those of other agents

The MICs of LBM415, a new peptide diformylase inhibitor, were </=0.06 to 4.0 microg/ml for 258 isolates of Staphylococcus aureus and coagulase-negative staphylococci. LBM415 MICs were similar irrespective of whether the strains were methicillin susceptible or resistant. All strains were also susceptible to vancomycin, linezolid, ranbezolid, daptomycin, oritavancin, and quinupristin-dalfopristin. LBM415 at the MIC was bacteriostatic after 24 h.

The Safety and Efficacy of Daptomycin for the Treatment of Complicated Skin and Skin-Structure Infections

Daptomycin is the first available agent from a new class of antibiotics, the cyclic lipopeptides, that has activity against a broad range of gram-positive pathogens, including organisms that are resistant to methicillin, vancomycin, and other currently available agents. Daptomycin (4 mg/kg intravenously [iv] every 24 h for 7-14 days) was compared with conventional antibiotics (penicillinase-resistant penicillins [4-12 g iv per day] or vancomycin [1 g iv every 12 h]) in 2 randomized, international trials involving 1092 patients with complicated skin and skin-structure infections. Among 902 clinically evaluable patients, clinical success rates were 83.4% and 84.2% for the daptomycin- and comparator-treated groups, respectively (95% confidence interval, -4.0 to 5.6). Among patients successfully treated with iv daptomycin, 63% required only 4-7 days of therapy, compared with 33% of comparator-treated patients (P<.0001). The frequency and distribution of adverse events were similar among both treatment groups. Overall, the safety and efficacy of daptomycin were comparable with conventional therapy.

Efficacy of ertapenem against methicillin-susceptible Staphylococcus aureus in complicated skin/skin structure infections: results of a double-blind clinical trial versus piperacillin-tazobactam

Staphylococcus aureus is the predominant pathogen in complicated skin/skin structure infections. In this analysis of a subgroup of data from a randomised, double-blind trial, the efficacy of ertapenem 1 g daily was compared with piperacillin-tazobactam 3.375 g Q6H for treatment of complicated skin/skin structure infections caused by methicillin-susceptible S. aureus (MSSA). Of the 529 treated patients in this trial, 185 (35.0%) had MSSA as a baseline pathogen. At the test of cure assessment 10-21 days post-therapy, 54 of 67 (80.6%) protocol evaluable patients in the ertapenem group and 55 of 68 (80.9%) in the piperacillin-tazobactam group were cured (odds ratio: 1.0 (95% confidence interval (CI): 0.4-2.4), P = 0.99). In both treatment groups, cure rates were higher in patients with monomicrobial than polymicrobial infections, but the difference was not significant. In this subgroup analysis of patients with MSSA complicated skin/skin structure infections, therapy with ertapenem 1 g daily was as effective as piperacillin-tazobactam 13.5 g divided in four daily doses.

Antimicrobial resistance in recent fecal enterococci from healthy volunteers and food handlers in Spain: genes and phenotypes

Susceptibility patterns to 15 different antibiotics and the presence of resistance genes were evaluated in recent fecal Enterococcus isolates recovered from 42 healthy volunteers (HV) and 43 food-handlers (FH). A total of 142 Enterococcus faecalis, 74 Enterococcus faecium, and 23 Enterococcus spp. with different antibiotic susceptibility patterns were studied. A higher percentage of resistance for moxifloxacin, erythromycin, glycopeptides and high-level resistance (HLR) to gentamicin were observed in the FH group. Ampicillin- or linezolid-resistant isolates were not recovered in any of the groups. The tet(M) gene was found in 96% and in 85% of tetracycline-resistant isolates from HV and FH, respectively. HLR-kanamycin was mediated by aph(3')-IIIa, or aac(6')-aph(2"), or both genes in all isolates from HV group and in 86% from FH group. The aac(6')-aph(2") gene was found in all HLR-gentamicin isolates. Ninety-one percent of HV and 71% of FH erythromycin-resistant isolates harbored the erm(B) gene (erythromycin MIC range of 8-128 microg/ml), whereas erm(A), erm(C), or mef(A) genes were not detected. Coexistence of erm(B), aph(3')-IIIa, and tet(M) genes was observed in 17% of the isolates of both groups. The HLR-gentamicin isolates presented unrelated PFGE patterns while 2 out of 3 vanA E. faecium isolates showed an indistinguishable SmaI-pulsed-field gel electrophoresis (PFGE) pattern. This study shows that despite 4 years of official banning of antibiotic growth promoters in animals, enterococci isolated from FH are more resistant than those from HV. This suggests the permanence of resistant clones or transferable resistance elements in farms and a possible exchange between food products and humans, or eventually the long-term permanence of certain clones in the FH intestinal tract.

Linezolid for the treatment of complicated skin and skin structure infections in children

BACKGROUND

Gram-positive pathogens are a major cause of complicated skin and skin structure infections (CSSSIs) in children. Many pathogens are developing decreased susceptibility to currently used antibiotics, increasing the need for new therapies. Linezolid is well-tolerated and effective in the treatment of these infections in adults.

OBJECTIVE

To evaluate the clinical efficacy and safety of iv/oral linezolid and iv vancomycin in children with Gram-positive CSSSIs.

METHODS

Hospitalized children <12 years of age were randomized (2:1 ratio) to receive either linezolid 10 mg/kg iv every 8 h (with the option to change treatment to oral linezolid suspension 10 mg/kg every 8 h) or iv vancomycin 10 to 15 mg/kg every 6 to 24 h (according to age). Clinical response, tolerance and safety were evaluated at follow-up. The results of a subset analysis of patients with CSSSIs are presented here.

RESULTS

One hundred twenty intent-to-treat patients (linezolid 80, vancomycin 40) with CSSSI were included in this analysis. Clinical cure rates for clinically evaluable patients with CSSSI did not differ between treatment groups (linezolid, 93.2% vs. vancomycin, 90.0%; P = 0.594). Significantly fewer linezolid-treated patients experienced drug-related adverse events than did vancomycin-treated patients (23% vs. 48%; P = 0.006). The percentages of patients with laboratory abnormalities, including selected hematologic parameters, were generally low and similar between the treatment groups.

CONCLUSIONS

Linezolid given iv or orally was well-tolerated and safe. It was as effective as vancomycin in treating children with Gram-positive CSSSIs.

Effect of linezolid versus vancomycin on length of hospital stay in patients with complicated skin and soft tissue infections caused by known or suspected methicillin-resistant staphylococci: results from a randomized clinical trial

BACKGROUND

Complicated skin and soft tissue infections are common surgical indications usually requiring patients to be hospitalized, and are often caused by gram-positive bacteria, including methicillin-resistant staphylococci such as MRSA. Vancomycin has been the standard treatment for methicillin-resistant staphylococcal infections in many countries, but its intravenous-only formulation for systemic infections often confines patients to the hospital for the treatment. Linezolid, a novel oxazolidinone antibiotic available in intravenous and 100% bioavailable oral forms, was shown in a randomized trial to be as efficacious as vancomycin for suspected or proven methicillin-resistant staphylococcal infections. To determine if oral linezolid can reduce length of hospital stay (LOS) when compared to vancomycin, we compared the LOS for the 230 complicated skin and soft tissue infection patients enrolled in this trial.

MATERIALS AND METHODS

Patients received up to four weeks of linezolid (intravenous followed by optional oral) or vancomycin (intravenous only), followed by up to four weeks of observation. Unadjusted LOS was estimated using Kaplan-Meier survival functions, whereas the log-logistic survival analysis model was used to estimate the multivariate-adjusted LOS controlling for patient demographics and selected baseline clinical variables. Analysis was done on the intent-to-treat (n = 230) sample as well as on two subsamples of the clinically evaluable (n = 144) and surgical site infection (n = 114) patients.

RESULTS

The unadjusted Kaplan-Meier median LOS was five days shorter for the linezolid group than the vancomycin group in the intent-to-treat sample (9 vs. 14 days, p = 0.052). It was eight days shorter (8 vs. 16 days, p = 0.0025) in the clinically evaluable sample, but the difference in the surgical site infection sample was not significant (10 vs. 14 days; p = 0.29). The linezolid group's unadjusted mean LOS was 1.7, 5.3 and 0.8 days shorter in the intentto-treat, clinically evaluable, and surgical site infection samples, respectively. After adjusting for age, gender, race, geographic region, bacteremia, type of inpatient location, and number of concurrent medical conditions using the log-logistic model, between-treatment differences in the multivariate-adjusted median LOS decreased to 3, 6, and 3 days, whereas the differences in mean LOS increased to 3.1, 6.5 and 2.5 days for the intent-to-treat, clinically evaluable, and surgical site infection samples (p < 0.01, < 0.01, and < 0.10), respectively. When the between-treatment differences in LOS were expressed as odds ratio of hospital discharges, multivariate-adjustment increased the odds ratios in favor of linezolid for all the three samples.

CONCLUSION

Results from this randomized trial show that linezolid can significantly reduce LOS for patients with complicated skin and soft tissue infections from suspected or confirmed methicillin-resistant staphylococci.

Antipneumococcal and antistaphylococcal activities of ranbezolid (RBX 7644), a new oxazolidinone, compared to those of other agents

For 260 pneumococcal and 266 staphylococcal strains, ranbezolid MICs ranged from < or =0.06 to 4 micro g/ml. The MICs for pneumococci were similar irrespective of the strains' beta-lactam, macrolide, or quinolone susceptibilities, and ranbezolid MICs for coagulase-negative staphylococci were lower than those for Staphylococcus aureus. Ranbezolid was bacteriostatic against pneumococci. Ranbezolid MICs were similar to or lower than those of linezolid. Vancomycin and quinupristin-dalfopristin were also very active.

Macrolide-resistance genes in clinical isolates of Streptococcus pyogenes

Macrolide-resistance genes were investigated in 103 macrolide-resistant strains of Streptococcus pyogenes, isolated from children with pharyngotonsillitis. The presence of mef(A), erm(B), and erm(TR) genes was detected by PCR. mef(A) was found in 48 out of 103 (46.6%) strains, whereas erm(B) was detected in 43 isolates (41.7%). All mef(A) strains showed a typical M phenotype (resistance to 14- and 15-membered macrolides, and sensitivity to lincosamides and streptogramin B), whereas erm(B) strains had the MLSB phenotype (resistance to macrolides, lincosamides, and streptogramin B antibiotics). erm(TR) was found in 10 strains, always together with other resistance genes. In seven cases erm(TR) was associated with erm(B), and three cases with mef(A). In two isolates with the M phenotype (1.9%), it was not possible to detect the presence of any of the three macrolide resistance genes tested. Inducible resistance to macrolides was shown for 24 out of the 53 MLSB strains. Analysis of macrorestriction fragment patterns by pulsed-field gel electrophoresis showed that erythromycin-resistant S. pyogenes are polyclonal, however each phenotype, MLSB and M, formed essentially homogeneous groups.

Ertapenem once daily versus piperacillin-tazobactam 4 times per day for treatment of complicated skin and skin-structure infections in adults: results of a prospective, randomized, double-blind multicenter study

We conducted a prospective, randomized, double-blind trial comparing ertapenem (1 g once daily) with piperacillin-tazobactam (3.375 g every 6 h) as parenteral treatment for 540 adults with complicated skin and skin-structure infections. The most common diagnoses were skin or soft-tissue abscesses and lower-extremity infections associated with diabetes. The mean duration (+/- standard deviation) of therapy was 9.1+/-3.1 days for ertapenem and 9.8+/-3.3 days for piperacillin-tazobactam. At the assessment of primary efficacy end point, 10-21 days after treatment, 82.4% of those who received ertapenem and 84.4% of those who received piperacillin-tazobactam were cured. The difference in response rates, adjusting for the patients' assigned strata, was -2.0% (95% confidence interval, -10.2% to 6.2%), indicating that the response rates in the 2 treatment groups were equivalent. Cure rates for the 2 treatment groups were similar when compared by stratum, diagnosis, and severity of infection. The frequency and severity of drug-related adverse events were similar in the treatment groups.

Quinupristin/dalfopristin: a therapeutic review

BACKGROUND

The proliferation of multidrug-resistant gram-positive bacteria, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium (VREF), has created a pressing need for effective alternative antibiotics. Quinupristin/dalfopristin is a new combination streptogramin product with a selective spectrum of antibacterial activity, mainly against gram-positive aerobic bacteria. It has been assessed primarily in emergency-use protocols, in hospitalized patients with skin and skin-structure infections, and in patients with VREF bacteremia.

OBJECTIVES

The objectives of this review were to summarize important results of in vitro microbiologic studies; to provide information on relevant pharmacokinetic parameters, drug interactions, and Y-site compatibility; and to assess efficacy and safety data from clinical studies of quinupristin/dalfopristin.

METHODS

Articles included in this review were identified by a MEDLINE search of the literature published between 1966 and September 2000 using the terms Synercid, quinupristin, and dalfopristin. Additional articles were retrieved from the reference lists of articles identified in the MEDLINE search.

RESULTS

In vitro analysis of the spectrum of activity of quinupristin/dalfopristin has confirmed its relatively selective coverage of gram-positive aerobic bacteria. Both quinupristin and dalfopristin undergo hepatic metabolism and are extensively excreted in the feces. Combination quinupristin/dalfopristin inhibits the cytochrome P450 3A4 pathway, and caution is warranted with concomitant use of other medications eliminated via this pathway. In trials in patients with VREF infections, treatment success with quinupristin/dalfopristin varied depending on the site of infection, ranging from 51.9% in bacteremia of unknown origin to 88.9% in urinary tract infections. The results of comparative clinical trials suggest that quinupristin/dalfopristin has similar efficacy to that of commonly used antibiotics, including cefazolin, oxacillin, and vancomycin, in patients with skin and skin-structure infections or nosocomial pneumonia. The most frequently reported adverse effects with administration of quinupristin/dalfopristin were infusion-site inflammation, pain, and edema; other infusion-site reactions; and thrombophlebitis. Arthralgia, myalgia, nausea, diarrhea, vomiting, and rash occurred in 2.5% to 4.6% of patients and were the most frequently reported systemic adverse events.

CONCLUSIONS

Outcomes data from clinical trials indicate that quinupristin/dalfopristin has the potential to play an important role in the treatment of bacteremia, complicated skin and skin-structure infections, and nosocomial pneumonia caused by VREF. Issues of bacterial resistance to quinupristin/dalfopristin and other appropriate uses of this combination agent remain to be elucidated.

Randomized comparison of linezolid (PNU-100766) versus oxacillin-dicloxacillin for treatment of complicated skin and soft tissue infections

This randomized, double-blind, multicenter trial compared the efficacy and safety of linezolid, an oxazolidinone, with those of oxacillin-dicloxacillin in patients with complicated skin and soft tissue infections. A total of 826 hospitalized adult patients were randomized to receive linezolid (600 mg intravenously [i.v.]) every 12 h or oxacillin (2 g i.v.) every 6 h; following sufficient clinical improvement, patients were switched to the respective oral agents (linezolid [600 mg orally] every 12 h or dicloxacillin [500 mg orally] every 6 hours). Primary efficacy variables were clinical cure rates in both the intent-to-treat (ITT) population and clinically evaluable (CE) patients and microbiological success rate in microbiologically evaluable (ME) patients. Safety and tolerability were evaluated in the ITT population. Demographics and baseline characteristics were similar across treatment groups in the 819 ITT patients. In the ITT population, the clinical cure rates were 69.8 and 64.9% in the linezolid and oxacillin-dicloxacillin groups, respectively (P = 0.141; 95% confidence interval -1.58 to 11. 25). In 298 CE linezolid-treated patients, the clinical cure rate was 88.6%, compared with a cure rate of 85.8% in 302 CE patients who received oxacillin-dicloxacillin. In 143 ME linezolid-treated patients, the microbiological success rate was 88.1%, compared with a success rate of 86.1% in 151 ME patients who received oxacillin-dicloxacillin. Both agents were well tolerated; most adverse events were of mild-to-moderate intensity. No serious drug-related adverse events were reported in the linezolid group. These data support the use of linezolid for the treatment of adults with complicated skin and soft tissue infections.