Efficacy of dalbavancin against methicillin-resistant Staphylococcus aureus in the rat granuloma pouch infection model

Acute Bacterial Skin and Skin-Structure Infections, efficacy of Dalbavancin: a systematic review and meta-analysis

OBJECTIVES

To know the efficacy of different doses of dalbavancin in acute bacterial skin and skin-structure infections (ABSSSIs) and versus other antibiotics.

METHODS

We performed a systematic review of dalbavancin efficacy for ABSSSIs. We selected 10 clinical trials from MEDLINE and Cochrane databases for qualitative review. Of these, five trials compared one or two doses of dalbavancin versus other antibiotics such as vancomycin or linezolid.

RESULTS

Treatment outcomes with other antibiotics were not significantly different versus two doses of dalbavancin (OR 1.13; 95% CI 0.75-1.71; p = 0.55) or single dose dalbavancin (OR 0.98; 95% CI 0.19-5.17; p = 0.98). One dose versus two doses of dalbavancin did not show significant differences in any of the treatment groups. In contrast, the global microbiological assessment results indicated a favorable outcome for two doses of dalbavancin compared to the single dose of dalbavancin (OR 2.96; 95% CI 1.19-7.39; p = 0.02) in both methicillin-resistant and methicillin-susceptible Staphylococcus aureus.

CONCLUSION

Either single dose or two dose dalbavancin treatment is as clinically effective as other antibiotics such as vancomycin and linezolid for the treatment of ABSSSIs.Abbreviations ABSSI: acute bacterial skin and skin-structure infection; AUC: area under the concentration-time curve; CE: clinical evaluable; CI: confidence interval; EOT: end of treatment; ITT: intention-to-treat; LOS: length of stay; MIC: minimum inhibitory concentration; MIC₉₀: minimum concentration to inhibit growth of 90% of isolates; MR: methicillin resistant; MRSA: methicillin-resistant Staphylococcus aureus; MS: methicillin susceptible; MSSA: methicillin-susceptible Staphylococcus aureus; OPAT: Outpatient Parenteral Antimicrobial Therapy; OR: odds ratio; PI: penicillin intermediate; PR: penicillin resistant; PS penicillin susceptible; SIRS: systemic inflammatory response syndrome; SSTI: skin and soft tissue infection; TOC: test of cure; VR: vancomycin resistant; VS: vancomycin susceptible.

Animal Models for Drug Development for MRSA

One of the foremost challenges of drug discovery in any therapeutic area is that of solidifying the correlation between in vitro activity and clinical efficacy. Between these is the confirmation that affecting a particular target in vivo will lead to a therapeutic benefit. In antibacterial drug discovery, there is a key advantage from the start, since the targets are bacteria-therefore, it is simple to ascertain in vitro whether a drug has the desired effect, i.e., bacterial cell inhibition or killing, and to understand the mechanism by which that occurs. The downstream criteria, whether a compound reaches the infection site and achieves appropriately high levels to affect bacterial viability, can be evaluated in animal models of infection. In this way animal models of infection can be a highly valuable and predictive bridge between in vitro drug discovery and early clinical evaluation.The Gram-positive pathogen Staphylococcus aureus causes a wide variety of infections in humans (Archer, Clin Infect Dis 26:1179-1181, 1998), and has been said to be able to infect every tissue type. Fortunately, over the years a great deal of effort has been expended toward developing infection models in rodents using this organism, with good success. This chapter describes the advantages, setups, and outcome measurements of the rodent models most used in drug discovery for S. aureus. Mouse models will be the focus of this chapter, as they are the most economical and thus most commonly used, but a rat infection model is included as well.

Efficacy of Dalbavancin and Telavancin in the Treatment of Acute Bacterial Skin and Skin Structure Infections

Objectives

Two glycopeptide analogues, such as dalbavancin and telavancin, with improved pharmacokinetic/pharmacodynamic parameters have been developed. These two glycopeptide analogues are approved by Food and Drug Administration (FDA) for treatment of various Gram-positive bacterial skin infections.

Materials and methods

We have conducted an open labelled prospective randomized study to compare the efficacy of these two drugs. A total of 200 patients diagnosed with acute bacterial skin and skin structure infections (ABSSSI) were recruited for the study. They were randomized to receive either a single dose of dalbavancin 1500 mg i.v (Group I) or telavancin 10 mg/kg intravenously (i.v.) every 24 hours for six days (Group II). The skin infection rating score (SIRS) was calculated on Day 0 for all patients at the time of diagnosis. Signs and symptoms of the lesions were assessed based on the following factors: blistering, exudate/pus, erythema/inflammation and itching/pain. Each factor was classified as one of the following: absent - 0, minimal - 1, moderate - 2 and severe - 3.

Results

Clinically successful treatment was defined as complete resolution of clinically meaningful signs and symptoms of infection, including SIRS score of 0. The outcome measure was the percentage of patients with SIRS score of 0 on day 7 (clinical success). The third most common diagnosis at baseline was impetigo (13% in both groups). Patients who received dalbavancin had a higher clinical success rate than those receiving telavancin.

Conclusion

Findings of the present study show that single i.v dose of dalbavancin is better than telavancin repeated doses in treatment of ABSSSI.

Dalbavancin: A New Option for the Treatment of Gram-Positive Infections

Objective:

To review the pharmacology, microbiology, chemistry, in vitro susceptibility, pharmacokinetics, clinical efficacy, safety, tolerability, dosage, and administration of dalbavancin, a new semisynthetic lipoglycopeptide.

Data Sources:

A MEDLINE search, restricted to the English language, was conducted from 1966 through January 2006. Supplementary sources included program abstracts from the Interscience Conference on Antimicrobial Agents and Chemotherapy, American Society of Microbiology, and the Infectious Diseases Society of America from 2000 to 2005 and information available from the manufacturer's Web site.

Study Selection and Data Extraction:

In vitro and preclinical studies, as well as Phase I, II, and III clinical trials, were evaluated to summarize the microbiology, pharmacology, clinical efficacy, and safety of dalbavancin. All published trials and abstracts citing dalbavancin were selected.

Data Synthesis:

Dalbavancin, a novel lipoglycopeptide, has a mechanism of action similar to that of other glycopeptides. It has in vitro activity against a variety of gram-positive organisms, but no activity against gram-negative or vancomycin-resistant enterococci that possess VanA gene. Due to its prolonged half-life (6–10 days), dalbavancin can be administered intravenously once weekly. In Phase II and III clinical trials, dalbavancin was effective and well tolerated for the treatment of skin and soft-tissue infections, catheter-related bloodstream infections, and skin and skin-structure infections. To date, adverse events are mild and limited; the most common include pyrexia, headache, nausea, oral candidiasis, diarrhea, and constipation.

Conclusions:

Dalbavancin appears to be a promising antimicrobial agent for the treatment of gram-positive infections. A new drug application was filed with the Food and Drug Administration (FDA) in December 2004. The FDA issued an approvable letter in 2005 for dalbavancin. If approved, dalbavancin is expected to be launched in the first quarter of 2006.

Dalbavancin for the treatment of acute bacterial skin and skin structure infections

INTRODUCTION

Acute bacterial skin and skin structure infections (ABSSSI) have increased in incidence and severity. The involvement of resistant organisms, particularly methicillin-resistant Staphylococcus aureus, presents additional challenges. The lipoglycopeptide dalbavancin has a prolonged half-life, high protein binding, and excellent tissue levels which led to its development as a once-weekly treatment for ABSSSI. In the pivotal DISCOVER 1 and DISCOVER 2 trials, dalbavancin proved non-inferior to vancomycin followed by linezolid when used sequentially for ABSSSI, forming the basis for its recent approval in the US and Europe for ABSSSI.

AREAS COVERED

A literature search of published pharmacologic and clinical data was conducted to review the chemistry, pharmacodynamics, and pharmacokinetics of dalbavancin. We also discuss its development process, highlighting efficacy and safety data from pertinent clinical trials and the role it could play in the current clinical landscape.

EXPERT OPINION

DISCOVER 1 and DISCOVER 2 demonstrated dalbavancin's non-inferiority to vancomycin followed by linezolid for ABSSSI and confirmed its safety and tolerability. They were among the first trials to use new, early primary efficacy endpoints, and dalbavancin was among the first agents designated a Qualified Infectious Disease Product for expedited review. Dalbavancin may prove to be a valuable option for ABSSSI patients in whom conventional therapy is limited.

Animal models in drug development for MRSA

One of the foremost challenges of drug discovery in any therapeutic area is that of solidifying the correlation between in vitro activity and clinical efficacy. Between these is the confirmation that affecting a particular target in vivo will lead to a therapeutic benefit. In antibacterial drug discovery, there is a key advantage from the start, since the targets are bacteria-therefore, it is simple to ascertain in vitro whether a drug has the desired effect, i.e., bacterial cell inhibition or killing, and to understand the mechanism by which that occurs. The downstream criteria, whether a compound reaches the infection site and achieves appropriately high levels to affect bacterial viability, can be evaluated in animal models of infection. In this way animal models of infection can be a highly valuable and predictive bridge between in vitro drug discovery and early clinical evaluation.The Gram-positive pathogen Staphylococcus aureus causes a wide variety of infections in humans (Archer, Clin Infect Dis 26:1179-1181, 1998) and has been said to be able to infect every tissue type. Fortunately, over the years a great deal of effort has been expended toward developing infection models in rodents using this organism, with good success. This chapter will describe the advantages, methods, and outcome measurements of the rodent models most used in drug discovery for S. aureus. Mouse models will be the focus of this chapter, as they are the most economical and thus most commonly used, but a rat infection model is included as well.

Dalbavancin, a long-acting lipoglycopeptide for the treatment of multidrug-resistant Gram-positive bacteria

Dalbavancin is a new lipoglycopeptide antibiotic in late-stage clinical development as a once-weekly treatment for serious infections including skin and skin structure infections. Its in vitro potency is greater than that of vancomycin, with a MIC(90) of 0.06 mg/l for Staphylococcus aureus and coagulase-negative staphylococci (irrespective of oxacillin susceptibility), 0.06-0.12 mg/l for vancomycin-susceptible Enterococcus spp. and 0.003 mg/l or less for Streptococcus pneumoniae or beta-hemolytic streptococci. Dalbavancin has dual routes of elimination. The results of Phase II/III studies show clinical efficiency in complicated skin and skin structure infection. During clinical trials, dalbavancin was as effective as linezolid or vancomycin in the treatment of patients with complicated skin and skin structure infection, including those with methicillin-resistant S. aureus. An additional Phase II study demonstrated efficacy in catheter-related bacteremia. Other preliminary in vitro and in vivo data have identified putative interest of dalbavancin in endocarditis, osteitis, diabetic foot, respiratory tract or joint infection.

Perturbation of Staphylococcus aureus gene expression by the enoyl-acyl carrier protein reductase inhibitor AFN-1252

This study examines the alteration in Staphylococcus aureus gene expression following treatment with the type 2 fatty acid synthesis inhibitor AFN-1252. An Affymetrix array study showed that AFN-1252 rapidly increased the expression of fatty acid synthetic genes and repressed the expression of virulence genes controlled by the SaeRS 2-component regulator in exponentially growing cells. AFN-1252 did not alter virulence mRNA levels in a saeR deletion strain or in strain Newman expressing a constitutively active SaeS kinase. AFN-1252 caused a more pronounced increase in fabH mRNA levels in cells entering stationary phase, whereas the depression of virulence factor transcription was attenuated. The effect of AFN-1252 on gene expression in vivo was determined using a mouse subcutaneous granuloma infection model. AFN-1252 was therapeutically effective, and the exposure (area under the concentration-time curve from 0 to 48 h [AUC(0-48)]) of AFN-1252 in the pouch fluid was comparable to the plasma levels in orally dosed animals. The inhibition of fatty acid biosynthesis by AFN-1252 in the infected pouches was signified by the substantial and sustained increase in fabH mRNA levels in pouch-associated bacteria, whereas depression of virulence factor mRNA levels in the AFN-1252-treated pouch bacteria was not as evident as it was in exponentially growing cells in vitro. The trends in fabH and virulence factor gene expression in the animal were similar to those in slower-growing bacteria in vitro. These data indicate that the effects of AFN-1252 on virulence factor gene expression depend on the physiological state of the bacteria.

Natural product disaccharide engineering through tandem glycosyltransferase catalysis reversibility and neoglycosylation

A two-step strategy for disaccharide modulation using vancomycin as a model is reported. The strategy relies upon a glycosyltransferase-catalyzed 'reverse' reaction to enable the facile attachment of an alkoxyamine-bearing sugar to the vancomycin core. Neoglycosylation of the corresponding aglycon led to a novel set of vancomycin 1,6-disaccharide variants. While the in vitro antibacterial properties of corresponding vancomycin 1,6-disaccharide analogs were equipotent to the parent antibiotic, the chemoenzymatic method presented is expected to be broadly applicable.

Dalbavancin in the treatment of complicated skin and soft-tissue infections: a review

Increasing rates of antimicrobial resistance among strains of Streptococcus, Staphylococcus, and Enterococcus spp. have been widely documented. At least 50% of nosocomial Staphylococcus aureus infections in intensive care units in the US and UK are due methicillin-resistant S. aureus (MRSA). Drug resistance is not confined to hospitals, and community-acquired MRSA (CA-MRSA) strains are now common causes of complicated skin and soft-tissue infections (cSSTIs) in many regions. Dalbavancin is a novel parenterally administered semisynthetic lipoglycopeptide similar to the naturally produced glycopeptides vancomycin and teicoplanin. Dalbavancin features a multifaceted mechanism of action that inhibits bacterial cell wall formation by two different mechanisms that enhances its activity against a wide range of gram-positive bacteria including staphylococci, streptococci, enterococci, and some anaerobes. Additionally, dalbavancin possesses unique pharmacokinetic properties, the most significant of which is a long terminal half-life that allows for once weekly dosing. This attribute may prove to yield clinical and cost benefit. Overall, clinical trials indicate that dalbavancin is a safe, well-tolerated, and effective antimicrobial agent. In the largest investigation evaluating dalbavancin for the treatment of cSSTIs, it appeared to be as effective as linezolid. Dalbavancin, which is expected to receive FDA approval in 2008, appears to be a promising new antimicrobial agent for the treatment of cSSTIs.

Efficacy of the new lantibiotic NAI-107 in experimental infections induced by multidrug-resistant Gram-positive pathogens

NAI-107 is a novel lantibiotic active against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), glycopeptide-intermediate S. aureus (GISA), and vancomycin-resistant enterococci (VRE). The aim of this study was to evaluate the in vivo efficacy of NAI-107 in animal models of severe infection. In acute lethal infections induced with a penicillin-intermediate Streptococcus pneumoniae strain in immunocompetent mice, or with MRSA, GISA, and VRE strains in neutropenic mice, the 50% effective dose (ED(50)) values of NAI-107 were comparable or lower than those of reference compounds, irrespective of the strain and immune status (0.51 to 14.2 mg/kg of body weight for intravenous [i.v.] NAI-107, 5.1 to 22.4 for oral linezolid, and 22.4 for subcutaneous [s.c.] vancomycin). In the granuloma pouch model induced in rats with a MRSA strain, intravenous NAI-107 showed a dose-proportional bactericidal activity that, at a single 40-mg/kg dose, compared with 2 20-mg/kg doses at a 12-h or 24-h interval, caused a 3-log(10)-CFU/ml reduction of viable MRSA in exudates that persisted for more than 72 h. Rat endocarditis was induced with a MRSA strain and treated for five consecutive days. In a first experiment, using 5, 10, or 20 mg/kg/day, and in a second experiment, when 10 mg/kg at 12-h intervals was compared to 20 mg/kg/day, intravenous NAI-107 was effective in reducing the bacterial load in heart vegetations in a dose-proportional manner. Trough plasma levels, as determined on days 2 and 5, were several times higher than the NAI-107 minimal bactericidal concentration (MBC). NAI-107 binding to rat and human serum ranges between 93% and 98.6%. The rapid bactericidal activity of NAI-107 observed in vitro was thus confirmed by the efficacy in several models of experimental infection induced by Gram-positive pathogens, supporting further investigation of the compound.

Surmounting antimicrobial resistance in the Millennium Superbug: Staphylococcus aureus

Staphylococcus aureus is the third most dreaded pathogen posing a severe threat due to its refractory behavior against the current armamentarium of antimicrobial drugs. This is attributed to the evolution of an array of resistance mechanisms responsible for morbidity and mortality globally. Local and international travel has resulted in the movement of drug resistant S. aureus clones from hospitals into communities and further into different geographical areas where they have been responsible for epidemic outbreaks. Thus, there is a dire necessity to refrain further cross movement of these multidrug resistant clones across the globe. The plausible alternative to prevent this situation is by thorough implementation of regulatory aspects of sanitation, formulary usage and development of new therapeutic interventions. Various strategies like exploring novel antibacterial targets, high throughput screening of microbes, combinatorial and synthetic chemistry, combinatorial biosynthesis and vaccine development are being extensively sought to overcome multidrug resistant chronic Staphylococcal infections. The majority of the antibacterial drugs are of microbial origin and are prone to being resisted. Anti-staphylococcal plant natural products that may provide a new alternative to overcome the refractory S.aureus under clinical settings have grossly been unnoticed. The present communication highlights the new chemical entities and therapeutic modalities that are entering the pharmaceutical market or are in the late stages of clinical evaluation to overcome multidrug resistant Staphylococcal infections. The review also explores the possibility of immunity and enzyme-based interventions as new therapeutic modalities and highlights the regulatory concerns on the prescription, usage and formulary development in the developed and developing world to keep the new chemical entities and therapeutic modalities viable to overcome antimicrobial resistance in S. aureus.

Activity of dalbavancin against Bacillus anthracis in vitro and in a mouse inhalation anthrax model

Bacillus anthracis, the causative agent of anthrax, can produce fatal disease when it is inhaled or ingested by humans. Dalbavancin, a novel, semisynthetic lipoglycopeptide, has potent activity, greater than that of vancomycin, against Gram-positive bacteria and a half-life in humans that supports once-weekly dosing. Dalbavancin demonstrated potent in vitro activity against B. anthracis (MIC range, < or =0.03 to 0.5 mg/liter; MIC(50) and MIC(90), 0.06 and 0.25 mg/liter, respectively), which led us to test its efficacy in a murine inhalation anthrax model. The peak concentrations of dalbavancin in mouse plasma after the administration of single intraperitoneal doses of 5 and 20 mg/kg of body weight were 15 and 71 mg/kg, respectively. At 20 mg/kg, the dalbavancin activity was detectable for 6 days after administration (terminal half-life, 53 h), indicating that long intervals between doses were feasible. The mice were challenged with 50 to 100 times the median lethal dose of the Ames strain of B. anthracis, an inoculum that kills untreated animals within 4 days. The efficacy of dalbavancin was 80 to 100%, as determined by the rate of survival at 42 days, when treatment was initiated 24 h postchallenge with regimens of 15 to 120 mg/kg every 36 h (q36h) or 30 to 240 mg/kg every 72 h (q72h). A regimen of ciprofloxacin known to protect 100% of animals was tested in parallel. Delayed dalbavancin treatment (beginning 36 or 48 h postchallenge) with 60 mg/kg q36h or 120 mg/kg q72h still provided 70 to 100% survival. The low MICs and long duration of efficacy in vivo suggest that dalbavancin may have potential as an alternative treatment or for the prophylaxis of B. anthracis infections.

Dalbavancin

Dalbavancin is a semisynthetic glycopeptide antibacterial agent that is active against Gram-positive bacteria associated with complicated skin and skin structure infections (cSSSIs). It is administered as a two-dose regimen intravenously infused over 30 minutes once weekly. The efficacy of dalbavancin (1000 mg on day 1 and 500 mg on day 8) has been examined in two randomized controlled trials in adults with cSSSIs. In each study, the primary efficacy measure was clinical success at the test-of-cure or follow-up visit in clinically evaluable patients. In a randomized, controlled, double-blind, multinational, phase III trial, dalbavancin was noninferior to linezolid, with clinical success rates of 88.9% and 91.2%. In a randomized, open-label, multicentre, phase II trial, clinical success rates were 94% with dalbavancin and 76% with comparator antibacterials. Dalbavancin was generally well tolerated by adult patients with cSSSIs, with most adverse events being of mild or moderate severity.

Efficacies of ceftobiprole medocaril and comparators in a rabbit model of osteomyelitis due to methicillin-resistant Staphylococcus aureus

The pharmacokinetics and distribution into bone tissue of ceftobiprole in uninfected New Zealand White rabbits were determined after subcutaneous administration of the prodrug ceftobiprole medocaril. Serum exposure (maximum concentration of the drug in serum, trough concentration, area under the concentration-time curve) to ceftobiprole at 20 and 80 mg/kg was dose proportional, and there was no accumulation of ceftobiprole following repeated (every 6 h [q6h]) injections of the antibiotic. Ceftobiprole titers in the tibial matrix and marrow were 3.2 +/- 1.3 microg/g and 11.2 +/- 6.5 microg/g, respectively, in uninfected animals treated with 20 mg/kg of the antibiotic and 13.4 +/- 7.3 microg/g and 66.3 +/- 43.2 microg/g, respectively, in uninfected animals treated with 80 mg/kg of the antibiotic. No differences in ceftobiprole titers were observed between right and left tibiae for either bone matrix or marrow. The efficacies of 4 weeks of treatment with ceftobiprole (40 mg/kg administered subcutaneously [s.c.] q6h), vancomycin (30 mg/kg administered s.c. q12h), or linezolid (60 mg/kg administered orally q8h) were compared, using a rabbit model of methicillin-resistant Staphylococcus aureus tibial osteomyelitis. After treatment with ceftobiprole, the bacterial titers in all infected left tibiae from evaluable rabbits were below the level of detection, whereas only 73% of infected left tibiae from vancomycin- or linezolid-treated animals had bacterial titers below the level of detection; the mean titers of ceftobiprole were 3 to 5 times higher in infected left tibiae than in uninfected right tibiae. These results indicate that ceftobiprole provided effective parenteral treatment of osteomyelitis in this rabbit model.

Dalbavancin: a novel antimicrobial

The increasing incidence of serious infections because of Gram-positive pathogens and the rising cost in parenteral administration of antimicrobials has inspired the development of a novel antibiotic. Dalbavancin is the first once a week antibiotic with activity against a broad range of Gram-positive pathogens. A large multicentre, pivotal, Phase III clinical trial, which included 854 patients with complicated skin and skin structure infections, compared 1-2 doses of dalbavancin vs. linezolid. The results demonstrated non-inferiority and a comparable safety profile. With its unique pharmacokinetic profile, ease of use and excellent safety profile, dalbavancin should provide a valuable addition to the armamentarium used to treat infections because of Gram-positive cocci.

Review of dalbavancin, a novel semisynthetic lipoglycopeptide

Dalbavancin is a semisynthetic lipoglycopeptide that is derived from teicoplanin with an extended half-life that enables once-weekly dosing. It has potent in vitro activity against most gram-positive organisms, with lower minimum inhibitory concentration values than vancomycin and other investigational lipoglycopeptides. Dalbavancin is active against multi-drug-resistant pathogens such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci, except for strains exhibiting vanA resistance. Several Phase II and III trials have established similar efficacy and safety of dalbavancin with comparator agents in the treatment of complicated skin and skin structure infections and in catheter-related bloodstream infections. Dalbavancin may serve as an appealing alternative agent in the treatment of gram-positive infections, especially with its convenient once-weekly regimen.

In vivo pharmacodynamic activity of the glycopeptide dalbavancin

Dalbavancin is a lipoglycopeptide antibiotic with broad-spectrum activity against gram-positive cocci and a markedly prolonged serum elimination half-life. We used the neutropenic murine thigh and lung infection models to characterize the pharmacodynamics of dalbavancin. Single-dose pharmacokinetic studies demonstrated linear kinetics and a prolonged elimination half-life which ranged from 7.6 to 13.1 h over the dose range of 2.5 to 80 mg/kg of body weight. The level of protein binding in mouse serum was 98.4%. The time course of in vivo activity of dalbavancin over the same dose range was examined in neutropenic ICR Swiss mice infected with a strain of either Streptococcus pneumoniae or Staphylococcus aureus by using the thigh infection model. The burden of organisms for S. pneumoniae was markedly reduced over the initial 24 h of study, and organism regrowth was suppressed in a dose-dependent fashion for up to the entire 96 h of study following dalbavancin doses of 2.5 mg/kg or greater. Dalbavancin doses of 20 mg/kg or greater resulted in less killing of S. aureus but were still followed by a prolonged suppression of regrowth. Multiple-dosing-regimen studies with the same organisms were used to determined which of the pharmacodynamic indices (maximum concentration in serum [C(max)]/MIC, area under the concentration-versus-time curve [AUC]/MIC, or the duration of time that levels in serum exceed the MIC) best correlated with treatment efficacy. These studies used a dose range of 3.8 to 480 mg/kg/6 days fractionated into 2, 4, 6, or 12 doses over the 144-h dosing period. Nonlinear regression analysis was used to examine the data fit with each pharmacodynamic index. Dalbavancin administration by the use of large, widely spaced doses was the most efficacious for both organisms. Both the 24-h AUC/MIC and the C(max)/MIC parameters correlated well with the in vivo efficacy of treatment against S. pneumoniae and S. aureus (for 24-h AUC/MIC, R(2) = 78 and 77%, respectively; for C(max)/MIC, R(2) = 90 and 57%, respectively). The free-drug 24-h AUC/MICs required for a bacteriostatic effect were 17 +/- 7 for five S. pneumoniae isolates. A similar treatment endpoint for the treatment against five strains of S. aureus required a larger dalbavancin exposure, with a mean free-drug 24-h AUC/MIC of 265 +/- 143. Beta-lactam resistance did not affect the pharmacodynamic target. The dose-response curves were relatively steep for both species; thus, the pharmacodynamic target needed to achieve organism reductions of 1 or 2 log(10) in the mice were not appreciably larger (1.3- to 1.6-fold). Treatment was similarly efficacious in neutropenic mice and in the lung infection model. The dose-dependent efficacy and prolonged elimination half-life of dalbavancin support the widely spaced regimens used in clinical trials. The free-drug 24-h AUC/MIC targets identified in these studies should be helpful for discerning rational susceptibility breakpoints. The current MIC(90) for the target gram-positive organisms would fall within this value.

Bactericidal activity and resistance development profiling of dalbavancin

Dalbavancin, a semisynthetic lipoglycopeptide being developed for the treatment of skin and skin structure infections (SSSIs), has a half-life of 5 to 7 days in humans and offers promise for a convenient weekly dosing regimen. We studied the in vitro bactericidal activity of dalbavancin against target organisms, using the concentrations that are maintained in human blood with the proposed dosage regimen. Dalbavancin minimal bactericidal concentrations (MBCs) were<or=0.5 microg/ml for eight staphylococcal isolates; and for six of these strains, including one vancomycin-intermediate Staphylococcus aureus (VISA) isolate, the MBCs were equal to or within 1 doubling dilution of the MIC. Dalbavancin MICs for all three Streptococcus pyogenes strains were 0.008 microg/ml, as were the MBCs for two of the isolates. In time-kill studies conducted with a different set of seven strains (two methicillin-susceptible S. aureus isolates, three methicillin-resistant S. aureus isolates, one VISA isolate, and one S. pyogenes isolate), all strains exhibited a>or=3-log10 decrease in their viable counts when they were exposed to>or=1 microg/ml of dalbavancin for 24 h. Resistance development studies by both direct selection (resistance frequency, <10(-10)) and serial passage failed to produce stable mutants with decreased susceptibility to dalbavancin. These observations suggest that dalbavancin will be an effective choice for the management of patients with SSSIs.

Importance of the Structure of Vancomycin Binding Pocket in Designing Compounds Active Against Vancomycin-resistant Enterococci (VRE)

16-Membered meta, para-cyclophanes mimicking the vancomycin binding pocket (D-O-E ring) are designed and synthesized. The structural features of these biaryl ether containing macrocycles are: a) the deletion of the carboxyl group of vancomycin's central amino acid (amino acid D); b) the elongation of the N-terminal; c) the presence of lipidated aminoglucose at the D-ring. Cycloetherification by way of an intramolecular nucleophilic aromatic substitution reaction (S(N)Ar) is used as a key step for the construction of the macrocycle. Minimum inhibitory concentrations for all of the derivatives are measured using a standard microdilution assay. Compounds 2a-2c and 3a-3c displayed weak activities against resistant strain Enterococcus faecalis L560 and were inactive against Enterococcus faecium resistant strain L2215.

Design and Synthesis of Simple Macrocycles Active Against Vancomycin-ResistantEnterococci (VRE)

16-membered meta,para-cyclophanes mimicking the vancomycin binding pocket (D-O-E ring) were designed and synthesized. The structural key features of these biaryl ether containing macrocycles are (1) the presence of beta-amino-alpha-hydroxy acid or alpha,beta-diamino acid as the C-terminal component of the cyclopeptide and (2) the presence of a hydrophobic chain or lipidated aminoglucose at the appropriate position. Cycloetherification by an intramolecular nucleophilic aromatic substitution reaction (S(N)Ar) is used as the key step for the construction of the macrocycle. The atropselectivity of this ring-closure reaction is found to be sensitive to the peptide backbone and chemoselective cyclization (phenol versus primary amine) is achievable. Glycosylation of phenol was realized with freshly prepared 3,4,6-tri-O-acetyl-2-N-lauroyl-2-amino-2-deoxy-alpha-D-glucopyranosyl bromide under phase-transfer conditions. Minimum inhibitory concentrations for all of the derivatives are measured by using a standard microdilution assay, and potent bioactivities against both sensitive and resistant strains are found for some of these compounds (MIC (minimum inhibitory concentration) = 4 microg mL(-1) against VRE). From these preliminary SAR studies, it was anticipated that both the presence of a hydrophobic substituent and an appropriate structure of the macrocycle were required for this series of compounds to be active against VRE.

Dalbavancin: A Novel Lipoglycopeptide Antibacterial

Dalbavancin is a new lipoglycopeptide antibacterial possessing in vitro activity against a variety of gram-positive pathogens. Against methicillin-susceptible and methicillin-resistant Staphylococcus aureus, it has demonstrated favorable minimum inhibitory concentration ranges compared with those of currently available agents. Dalbavancin is highly protein bound (> 90%), which may contribute to its prolonged half-life of 149-300 hours. Because of this long half-life, once-weekly dosing strategies have been used in clinical trials. Efficacy and tolerability have been demonstrated in a wide variety of animal infection models. Clinical success and safety have been shown in phase II and III trials for skin and soft-tissue infections and a phase II trial for catheter-related bloodstream infections. In these trials with vancomycin, linezolid, and various beta-lactams as comparators, comparable results have been reported. The results of further phase III trials are anxiously awaited and will more clearly define the clinical role of this novel agent.

Microbiologic characterization of isolates from a dalbavancin clinical trial for catheter-related bloodstream infections

Dalbavancin, a new-generation semisynthetic lipoglycopeptide in phase 3 clinical development, has been documented to be more active than vancomycin or teicoplanin against Gram-positive bacteria, including multidrug-resistant strains, by in vitro testing and in animal models. The human pharmacokinetics of dalbavancin predicts efficacy at weekly dosing intervals. In a phase 2 open-label clinical trial, dalbavancin exhibited superiority when compared with vancomycin against catheter-related bloodstream infection (CR-BSI). The majority of pathogens identified in this study as in clinical practice were coagulase-negative staphylococci (CoNS), necessitating rigorous characterization of duplicate isolates to rule out contaminants and to validate cases for study evaluations. At follow-up for the intent-to-treat population, overall pathogen eradication was 92.3% for dalbavancin and 75.9% for vancomycin. We describe the details of organisms isolated, their epidemiologic/genetic characterization, susceptibility patterns against glycopeptides, and the eradication rates by organism group. In conclusion, dalbavancin was active against all isolated pathogens associated with CR-BSI (CoNS, Staphylococcus aureus and Enterococcus faecalis; all MIC results, < or = 0.25 microg/mL) and achieved significant (P < 0.05) clinical success when compared with vancomycin.

Randomized, Double-Blind Comparison of Once-Weekly Dalbavancin versus Twice-Daily Linezolid Therapy for the Treatment of Complicated Skin and Skin Structure Infections

BACKGROUND

Dalbavancin, a novel lipoglycopeptide with a pharmacokinetic profile that allows weekly dosing, is active against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). The efficacy of dalbavancin for treatment of skin and skin structure infections (SSSIs) was demonstrated in a phase 2 study.

METHODS

In a phase 3 noninferiority study, patients with complicated SSSIs, including infections known or suspected to involve MRSA, were randomized (ratio, 2 : 1) in a double-blind manner to receive dalbavancin (1000 mg given intravenously on day 1 and 500 mg given intravenously on day 8) or linezolid (600 mg given intravenously or intravenously/orally every 12 h for 14 days). Efficacy was assessed by determining clinical and microbiological responses at the end of therapy and at the test-of-cure visit. Relapses were identified by additional follow-up approximately 1 month later.

RESULTS

MRSA was identified in 51% of patients from whom a pathogen was isolated at baseline. Dalbavancin and linezolid demonstrated comparable clinical efficacy in the clinically evaluable population at the test-of-cure visit (88.9% and 91.2% success, respectively). The rate of clinical success at the end of therapy was >90% in both arms. Less than 1.0% of patients in either treatment arm experienced relapse after the test-of-cure visit. Both treatments yielded successful microbiological response in excess of 85% among microbiologically evaluable patients at end of therapy and at the test-of-cure visit for all pathogens combined, for all S. aureus strains, and for MRSA. Gastrointestinal symptoms were among the most common adverse events in both arms. A higher proportion of patients in the linezolid arm reported adverse events that were judged by the investigator to be probably/possibly related to treatment (dalbavancin arm, 25.4% of subjects; linezolid arm, 32.2% of subjects).

CONCLUSIONS

Two doses of dalbavancin (1000 mg given on day 1 followed by 500 mg given on day 8) were as well tolerated and as effective as linezolid given twice daily for 14 days for the treatment of patients with complicated SSSI, including those infected with MRSA.

Mechanisms of action of newer antibiotics for Gram-positive pathogens

Certain Gram-positive bacteria, including meticillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and quinolone-resistant Streptococcus pneumoniae have achieved the status of "superbugs", in that there are few or no antibiotics available for therapy against these pathogens. Only a few classes of novel antibiotics have been introduced in the past 40 years, and all since 1999, including the streptogramin combination quinupristin/dalfopristin (Synercid), the oxazolidinone linezolid, and the lipopeptide daptomycin. This review discusses the mechanisms of antibiotic action against Gram-positive pathogens, and resistance counter-mechanisms developed by Gram-positive bacteria, with emphasis on the newer agents.

Antimicrobial activity of dalbavancin tested against Gram-positive clinical isolates from Latin American medical centres

The activity of dalbavancin, a new semi-synthetic lipoglycopeptide antibiotic, was evaluated in comparison with other antibacterial agents against 1229 Gram-positive organisms collected from medical centres in Latin America. Dalbavancin was the most potent compound tested against isolates of Staphylococcus aureus (MIC(50), 0.06 mg/L) and coagulase-negative staphylococci (MIC(50), 0.03 mg/L), independently of methicillin susceptibility. Dalbavancin inhibited all Streptococcus pneumoniae isolates at </= 0.06 mg/L. Dalbavancin also demonstrated excellent activity against beta-haemolytic (MIC(50), </= 0.008 mg/L) and viridans group (MIC(50), 0.016 mg/L) streptococci. All vancomycin-susceptible Enterococcus spp. isolates were inhibited by dalbavancin at </= 0.25 mg/L, but some vancomycin-resistant Enterococcus spp. isolates were only inhibited by dalbavancin levels of >/= 8 mg/L. Dalbavancin exhibited excellent activity against isolates of Corynebacterium spp. and Listeria spp. Dalbavancin may provide an important therapeutic option for Gram-positive infections, excluding those caused by enterococci with VanA-type resistance.

Tolerability, pharmacokinetics, and serum bactericidal activity of intravenous dalbavancin in healthy volunteers

Fifty-two healthy adult male and female volunteers were enrolled in this double-blind study to determine the maximum tolerated dose, characterize the pharmacokinetics, and obtain serum bactericidal activity (SBA) data for intravenous dalbavancin. Subjects were assigned to single- or multiple-dose groups and randomized to receive dalbavancin or placebo intravenously over 30 min. Doses started at 140 mg in the single-dose group and with a 300-mg loading dose (LD), followed by six daily 30-mg maintenance doses (MDs), in the multiple-dose cohort and escalated to a 1120-mg single dose and a 1000-mg LD and 100-mg MD regimen. Plasma, urine, and skin blister fluid aspirate drug concentrations were measured, and pharmacokinetic parameters were determined via noncompartmental methods. SBA against methicillin-resistant Staphylococcus aureus (MRSA) was determined at several time points. Adverse events and changes from the baseline for laboratory data, electrocardiograms, audiologic assessments, physical examinations, and vital signs were assessed. Concentrations increased in proportion to the dose. Steady-state concentrations were achieved by day 3 with the 10:1 LD-MD regimen. The half-life averaged 181 h, and the mean volume of distribution and clearance were 9.75 liters and 0.0473 liters/h, respectively. Mean values were similar in all groups and in males and females. The portion of the dose excreted renally averaged 33.5%. Bactericidal activity was demonstrated in serum at 7 days in all subjects receiving single doses of >or=500 mg. All doses were well tolerated. Dose-limiting toxicity was not encountered. No changes in auditory or vestibular function occurred. The long half-life and maintenance of SBA against MRSA for 1 week suggest that weekly dosing may be feasible.