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

Synthesis, microbiological evaluation and structure activity relationship analysis of linezolid analogues with different C5-acylamino substituents

Antimicrobial resistance and lack of new antibiotics to treat multidrug-resistant (MDR) bacteria is a significant public health problem. There is a discovery void and the pipeline of new classes of antibiotics in clinical development is almost empty. Therefore, it is important to understand the structure activity relationships (SAR) of current chemical classes as that can help the drug discovery community in their efforts to develop new antibiotics by modifying existing antibiotic classes. We studied the SAR of the C5-acylaminomethyl moiety of the linezolid, an oxazolidinone antibiotic, by synthesizing 25 compounds containing various aromatic, heteroaromatic and aliphatic substitutions. Our findings suggest that this position is highly important for the function of this antibiotic class, since only smaller non-polar fragments are tolerated at this position while larger and polar ones lead to a decrease in activity compared to linezolid. Our findings have led us to construct a structure activity relationship, around the C5-acylaminomethyl moiety of linezolid, that provides valuable insight into the function of the oxazolidinone class of antibiotics.

Synergistic Antimicrobial Effects of Silver/Transition-metal Combinatorial Treatments

Due to the emergence of multi-drug resistant strains, development of novel antibiotics has become a critical issue. One promising approach is the use of transition metals, since they exhibit rapid and significant toxicity, at low concentrations, in prokaryotic cells. Nevertheless, one main drawback of transition metals is their toxicity in eukaryotic cells. Here, we show that the barriers to use them as therapeutic agents could be mitigated by combining them with silver. We demonstrate that synergism of combinatorial treatments (Silver/transition metals, including Zn, Co, Cd, Ni, and Cu) increases up to 8-fold their antimicrobial effect, when compared to their individual effects, against E. coli and B. subtilis. We find that most combinatorial treatments exhibit synergistic antimicrobial effects at low/non-toxic concentrations to human keratinocyte cells, blast and melanoma rat cell lines. Moreover, we show that silver/(Cu, Ni, and Zn) increase prokaryotic cell permeability at sub-inhibitory concentrations, demonstrating this to be a possible mechanism of the synergistic behavior. Together, these results suggest that these combinatorial treatments will play an important role in the future development of antimicrobial agents and treatments against infections. In specific, the cytotoxicity experiments show that the combinations have great potential in the treatment of topical infections.

The efficacy and safety of arbekacin and vancomycin for the treatment in skin and soft tissue MRSA infection: preliminary study

Background

Methicillin-resistant Staphylococcus aureus (MRSA) has become a one of the most important causes of nosocomial infections, and use of vancomycin for the treatment of MRSA infection has increased. Unfortunately, vancomycin-resistant enterococcus have been reported, as well as vancomycin-resistant S. aureus. Arbekacin is an antibacterial agent and belongs to the aminoglycoside family of antibiotics. It was introduced to treat MRSA infection. We studied the clinical and bacteriological efficacy and safety of arbekacin compared to vancomycin in the treatment of infections caused by MRSA.

Materials and Methods

This was a retrospective case-control study of patients who were admitted to tertiary Hospital from January 1st, 2009 to December 31st, 2010, and received the antibiotics arbekacin or vancomycin. All the skin and soft tissue MRSA infected patients who received arbekacin or vancomycin were enrolled during the study period. The bacteriological efficacy response (BER) was classified with improved and failure. The improved BER was defined as no growth of MRSA, where failure was defined as growth of MRSA, culture at the end of therapy or during treatment. Clinical efficacy response (CER) was classified as improved and failure. Improved CER was defined as resolution or reduction of the majority of signs and symptoms related to the original infection. Failure was defined as no resolution and no reduction of majority of the signs and symptoms, or worsening of one or more signs and symptoms, or new symptoms or signs associated with the original infection or a new infection.

Results

Totally, 122 patients (63/99 in arbekacin, 59/168 in vancomycin group) with skin and soft tissue infection who recieved arbekacin or vancomcyin at least 4 days were enrolled and analysed. The bacteriological efficacy response [improved, arbekacin vs vancomycin; 73.0% (46/63), 95% confidence interval (CI) 60.3 to 83.4% vs 83.1% (49/59), 95% CI 71.0 to 91.6%] and clinical efficacy response [improved, arbekacin vs vancomycin; 67.2% (41/61), 95% CI 52.0 to 76.7% vs 78.0% (46/59), 95% CI 65.3 to 87.7%] were similar between the two groups (P=0.264, 0.265). The complication rate was significantly higher in the vancomycin group [29/59(49.2%), 95% CI 35.9 to 62.5%] than arbekacin [10/63(15.9%), 95% CI 8.4 to 29.0%] (P<0.001).

Conclusions

Arbekacin could be considered as an alternative antibiotics for vancomycin in skin and soft tissue infection with MRSA. However, further prospective randomized trials are needed to confirm this finding.

Retrospective cohort chart review study of factors associated with the development of thrombocytopenia in adult Japanese patients who received intravenous linezolid therapy

BACKGROUND

Linezolid is an oxazolidinone antibiotic agent active against Gram-positive bacteria. It has been associated with hematologic adverse effects such as thrombocytopenia. Little is known about the mechanism underlying thrombocytopenia in patients who receive intravenous linezolid.

OBJECTIVE

The aim of the present study was to investigate the risk factors associated with the development of thrombocytopenia in adult Japanese patients who received intravenous linezolid therapy.

METHODS

This was a retrospective review of the medical charts of patients who were treated with linezolid 600 mg IV BID (q12h) between June 2006 and March 2008 at Gifu University Hospital in Gifu, Japan. Data were extracted from the electronic medical records obtained from a central database in the hospital. Thrombocytopenia was defined as a decrease in platelet count of > or = 25% and a final platelet count of <100 x 10(3)/mm3. Risk factors associated with thrombocytopenia in patients who received linezolid were identified via logistic regression analysis.

RESULTS

In total, 42 patients (31 men and 11 women; mean [SD] age, 59.6 [12.8] years [range, 33-85 years]) were included in the study. The mean duration of linezolid therapy was 13.6 (10.1) days, with a range of 3 to 48 days. Seven patients with renal insufficiency received hemodialysis before linezolid infusion. Thrombocytopenia occurred in 7 patients (16.7%). Among the 7 patients with renal insufficiency, 2 patients (28.6%) developed severe thrombocytopenia, requiring platelet transfusion. In univariate analysis, a high daily dose of > or = 22 mg/kg (odds ratio [OR] = 20.25; 95% CI, 2.115-193.9; P = 0.009), low baseline platelet count of <200 x 10(3)/mm3 (OR = 8.437; 95% CI, 1.367-52.06), and lowered creatinine clearance of <30 mL/min (OR = 6.444; 95% CI, 1.136-36.57) were significant factors for thrombocytopenia associated with linezolid therapy; however, in multivariate analysis, only daily dose (> or = 22 mg/kg) was a significant risk factor for thrombocytopenia associated with linezolid therapy.

CONCLUSIONS

The daily dose of > or = 22 mg/kg was a significant risk factor associated with thrombocytopenia in patients who received linezolid therapy. Prospective studies comparing the efficacy and safety profile of linezolid in patients receiving a conventional dose (600 mg q12h) and those receiving a weight-adjusted dose are needed to determine an adequate dose of linezolid, particularly in patients with renal insufficiency or low baseline platelet count.

Evaluation of Nisin F in the Treatment of Subcutaneous Skin Infections, as Monitored by Using a Bioluminescent Strain of Staphylococcus aureus

The potential of nisin F as an antimicrobial agent in treating subcutaneous skin infections was tested in vivo by infecting C57BL/6 mice with a bioluminescent strain of Staphylococcus aureus (Xen 36). Strain Xen 36 has the luxABCDE operon located on a native plasmid. Mice were grouped into four groups: Infected with strain Xen 36 and treated with nisin F, infected with strain Xen 36 and treated with saline (placebo), not infected and treated with nisin (control) and not infected and not treated (control). The immune systems of the mice were suppressed with deksamethasone. Mice were treated with either nisin F or sterile physiological saline 24 and 48 h after infection with subcutaneously injected S. aureus Xen 36 (4 × 10(6) CFU). Histology and bioluminescent flux measurements revealed no significant difference between infected mice treated with nisin and saline, respectively. However, infected mice treated with nisin F had an increased number of polymorphonuclear cells when compared with infected mice treated with saline. Also, not infected mice treated with nisin F had an influx of polymorphonuclear cells. Nisin F is thus ineffective in combating deep dermal staphylococcal infections. The apparent immune modulation of nisin when subcutaneously injected has to be investigated.

Linezolid for the treatment of infections caused by Gram-positive pathogens in China

In this randomised, double-blind, comparator-controlled, multicentre study conducted in China, 142 hospitalised patients aged 18-75 years with pneumonia (n=80) or complicated skin and soft-tissue infection (cSSTI) (n=62) due to suspected or known Gram-positive pathogens were randomised (1:1) to receive either linezolid 600mg (n=71) or vancomycin 1g in patients aged < or =60 years or 0.75g in patients aged >60 years (n=71) intravenously every 12h. The duration of treatment was 10-21 days for patients with pneumonia and 7-21 days for patients with cSSTI. Clinical outcomes were assessed at end-of-treatment (EOT) visit and follow-up (FU) visit 7-28 days post therapy. Staphylococcus aureus was the most common pathogen at baseline and most of these isolates were resistant to meticillin. All isolates were susceptible to linezolid and vancomycin. For the evaluable patients, the effective treatment rate for linezolid was higher than that for vancomycin at EOT (86.9% (53/61) vs. 61.7% (37/60)) and at FU (83.1% (49/59) vs. 64.9% (37/57)). Pathogen eradication rates for the microbiologically evaluable patients at FU were 79.2% (42/53) for linezolid and 61.5% (32/52) for vancomycin. The incidence of drug-related adverse events (AEs) was 25.4% (18/71) for linezolid and 16.9% (12/71) for vancomycin. Four (5.6%) linezolid-treated and eight (11.3%) vancomycin-treated patients discontinued the study drug because of an AE. Linezolid was well tolerated and effective for the treatment of infections caused by Gram-positive pathogens, including meticillin-resistant S. aureus.

How complicated skin and soft tissue infections are treated in Italy: economic evaluation of inpatient intravenous antibiotic treatment in seven hospitals

OBJECTIVES

Complicated skin and soft tissue infections (cSSTIs) are a common cause of morbidity at hospital level. This study aimed to evaluate the costs and outcomes of inpatient intravenous antibiotic therapy for the treatment of cSSTI in seven Italian hospitals.

METHODS

A total of 307 patients were enrolled in a retrospective, multicentre, incidence-based, observational study. The target population consisted of hospitalised patients eligible to receive intravenous antibiotic therapy for cSSTI. Direct hospital costs were measured through a microcosting approach.

RESULTS

Failure of initial antibiotic therapy occurred in 23% of patients. Average antibiotic treatment lasted 12.2 days; the average full cost of admission totalled euro5,530. If the initial antibiotic regimen fails to eradicate the infectious organism, the length of stay extends for 7 days and costs increase by euro2,850 per patient. Nevertheless, when taking into account the lower intensity of care during the last days of treatment, savings reduce costs to euro671 per patient. These could be increased by euro74 for each hospital day avoided because of faster antibiotic action.

CONCLUSIONS

Efforts should be made to minimise the risk of selecting wrong antibiotics and to identify the quickest antibiotic in eradicating the infection.

A comparison of costs and hospital length of stay associated with intravenous/oral linezolid or intravenous vancomycin treatment of complicated skin and soft-tissue infections caused by suspected or confirmed methicillin-resistant Staphylococcus aureus in elderly US patients

OBJECTIVES

This study compared the costs and hospital length of stay (LOS) and duration of intravenous therapy associated with intravenous/oral linezolid or intravenous vancomycin treatment of complicated skin and soft-tissue infections (cSSTIs) caused by suspected or confirmed methicillin-resistant Staphylococcus aureus (MRSA) in elderly US patients.

METHODS

Data were obtained from elderly (>or=65 years) US patients participating in a multinational randomized trial of hospitalized cSSTI patients treated with linezolid or vancomycin. Costs (hospital and total) from the provider perspective were estimated for intent-to-treat (ITT) patients (ie, all those receiving >or=1 dose) using national 2003 costs (ward, medication, intravenous administration). LOS for inpatient care, duration of intravenous linezolid and vancomycin therapy (ITT and MRSA groups), and cure rates were evaluated.

RESULTS

Of 717 enrolled subjects, 163 (23%) were elderly (87 linezolid, 76 vancomycin), with no significant differences in demographic characteristics between the linezolid and vancomycin groups. Mean hospitalization and total costs were lower with linezolid compared with vancomycin (hospitalization: US $4510 vs US $6478, P<0.001; total: US $6009 vs US $7329, P=0.03). Linezolid was associated with a 3.5-day reduction in LOS and a 9.5-day reduction in the duration of intravenous therapy compared with vancomycin in the ITT group (both, P<0.001). Cure rates were comparable between linezolid and vancomycin in both the ITT group (88.7% vs 81.4%, respectively) and the MRSA group (80.0% vs 71.4%). In multivariate analyses of the ITT group, linezolid patients were 57% less likely than vancomycin patients to have a LOS >7 days (odds ratio = 0.43; 95% CI, 0.21-0.87). Chronic renal failure, malnutrition, and a diagnosis of infected ulcer predicted an LOS >7 days.

CONCLUSIONS

In this analysis of data from elderly patients with cSSTI caused by suspected or confirmed MRSA, linezolid treatment was associated with reductions in the costs of care, LOS, and duration of intravenous treatment without affecting the clinical outcomes. Although the use of a subset of patients from a larger trial that did not focus on the elderly can be seen as a study limitation, the elderly represent an important population when evaluating health care resource use and costs.

Role of linezolid in the treatment of orthopedic infections

Gram-positive organisms, particularly staphylococci and streptococci, are responsible for the majority of bone and joint infections. The rising incidence of antimicrobial resistance among Staphylococcus aureus, coagulase-negative staphylococci and enterococci means that novel antibiotics with unique mechanisms of antimicrobial activity are needed, especially in orthopedic infections. Linezolid is the first of the oxazolidinones, a new class of antibacterial agents particularly effective against Gram-positive infections including methicillin- and vancomycin-resistant strains. With an excellent oral bioavailability and acceptable safety profile, linezolid offers a valuable alternative to more traditional therapies, such as glycopeptides. No large randomized trials have been published on its use in patients with orthopedic infections, but early results are encouraging. Reported adverse events, especially bone marrow suppression and optic neuropathy seen with prolonged administration, mean that treatment of such patients must be undertaken with careful follow-up of laboratory tests. Until now, little resistance has been reported.

Community-acquired methicillin-resistant Staphylococcus aureus

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

LEARNING OBJECTIVE

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

Efficacy of linezolid versus vancomycin in the treatment of methicillin-resistant Staphylococcus aureus discitis: a controlled animal model

STUDY DESIGN

A rabbit model was used to assess the efficacy of linezolid and vancomycin for the treatment of discitis due to methicillin-resistant Staphylococcus aureus (MRSA). Nontreated controls were used for comparison.

OBJECTIVE

The purpose of this study was to determine if there was a therapeutic difference between using linezolid and vancomycin in the treatment of MRSA discitis.

SUMMARY OF BACKGROUND DATA

Vancomycin is currently the gold standard treatment for medical management of MRSA discitis. Linezolid is a relatively new drug that has been approved for treatment of MRSA infections, but currently there is no research demonstrating its efficacy at treating infections of the disc space.

METHODS

Twenty-four rabbits were inoculated with MRSA at two adjacent lumbar disc spaces via an anterior retroperitoneal approach. Six rabbits were to receive only pain medication and to serve as controls. Ten rabbits were assigned to a 5-day course of intravenous vancomycin, and 8 were assigned to a 5-day course of intravenous linezolid. Disc spaces were sent for quantitative culture after the 5-day treatment course.

RESULTS

The mean culture growth for the disc spaces was not statistically different between the linezolid treated group and the nontreated controls. While vancomycin treatment did lead to lower bacterial loads when compared with controls, the reduction was not statistically significant. When bacterial counts for the vancomycin group and linezolid group were compared, vancomycin treatment resulted in less bacterial growth. This difference was statistically significant.

CONCLUSIONS

Linezolid is a clinically attractive alternative to vancomycin due to its mild side effect profile and oral bioavailability. However, in this MRSA discitis model with a short treatment course, vancomycin was superior to linezolid.

Early experience with linezolid for infections in orthopaedics

In infections following orthopaedic surgery, isolated staphylococci are reported to be methicillin resistant (MRSA) in up to 50% of cases. Linezolid, the first in a new class of antibiotics, has excellent efficacy against gram positive organisms that are resistant to other therapies and is 100% orally bioavailable. We report early results of its use for the treatment of resistant infections in orthopaedic practice. Infections were characterised according to the UK Nosocomial Infections National Surveillance Service classification of surgical infections as superficial, deep or organ/space. Osteomyelitis, joint sepsis and deep infection involving orthopaedic implants were included into the final category. Outcome was recorded as clinical, microbiological and blood parameter cure or fail. Over the 12-month study period, 54 patients received linezolid therapy, 41% of these had significant co-morbidity that might affect their ability to fight infection. Sixty-seven percent of infections were in association with implanted metal work. The majority of patients were treated with vancomycin for a short period before linezolid was used as oral 'switch' therapy for longer-term administration, allowing early discharge in all cases. MRSA was isolated in 87% of the patients treated. The mean length of linezolid therapy was 39 days (2-151). Clinical success was achieved in 90% of patients overall. Though there were no life-threatening complications, adverse event rates were significantly higher than those recorded in the literature, with 19% of patients needing to cease therapy. Linezolid offers an alternative to traditional treatments for resistant infections and can facilitate early discharge. Patients need to be monitored closely, particularly where long-term therapy is planned.

Linezolid reduces length of stay and duration of intravenous treatment compared with vancomycin for complicated skin and soft tissue infections due to suspected or proven methicillin-resistant Staphylococcus aureus (MRSA)

We compared the health outcomes in patients treated with linezolid or vancomycin for complicated skin and soft tissue infections (cSSTIs). This analysis is part of a randomised, open-label, multinational trial involving 1200 adult patients hospitalised with cSSTIs due to suspected or proven methicillin-resistant Staphylococcus aureus (MRSA). Subjects received linezolid 600 mg intravenous (i.v.) or oral, or vancomycin 1g i.v. every 12 h. A test-of-cure was assessed at 7 days post therapy. Compared with vancomycin, linezolid treatment was associated with significantly shorter length of stay (all P < 0.01), decreased i.v. antibiotic treatment duration (all P < 0.0001) and higher discharge rates (all P < 0.05). Thus, linezolid has the potential to reduce medical resource use for the treatment of cSSTIs.

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.

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.

New therapies and vaccines for bacterial meningitis

Acute bacterial meningitis remains an important cause of morbidity and mortality worldwide. There have recently been major advances in the prevention of the major causes of bacterial meningitis following improvements in vaccinology. The success of immunisation against Haemophilus influenzae type b infection is being mirrored with serogroup C conjugated meningococcal vaccine and pneumococcal conjugate vaccine. However, there remain major challenges, notably, serogroup B meningococcal infection and shifts in epidemiology caused by vaccine introduction. In addition, much of the world's population is unvaccinated. Therefore, improvements in management of acute bacterial meningitis are vital. In this review we attempt to summarise important advances in both prevention and treatment of acute bacterial meningitis.