Efficacy of telavancin in a murine model of pneumonia induced by methicillin-susceptible Staphylococcus aureus

Crisaborole efficacy in murine models of skin inflammation and Staphylococcus aureus infection

Phosphodiesterase 4 (PDE4) is highly expressed in keratinocytes and immune cells and promotes pro-inflammatory responses upon activation. The activity of PDE4 has been attributed to various inflammatory conditions, leading to the development and approval of PDE4 inhibitors as host-directed therapeutics in humans. For example, the topical PDE4 inhibitor, crisaborole, is approved for the treatment of mild-to-moderate atopic dermatitis and has shown efficacy in patients with psoriasis. However, the role of crisaborole in regulating the immunopathogenesis of inflammatory skin diseases and infection is not entirely known. Therefore, we evaluated the effects of crisaborole in multiple mouse models, including psoriasis-like dermatitis, AD-like skin inflammation with and without filaggrin mutations, and Staphylococcus aureus skin infection. We discovered that crisaborole dampens myeloid cells and itch in the skin during psoriasis-like dermatitis. Furthermore, crisaborole was effective in reducing skin inflammation in the context of filaggrin deficiency. Importantly, crisaborole reduced S. aureus skin colonization during AD-like skin inflammation. However, crisaborole was not efficacious in treating S. aureus skin infections, even as adjunctive therapy to antibiotics. Taken together, we found that crisaborole reduced itch during psoriasis-like dermatitis and decreased S. aureus skin colonization upon AD-like skin inflammation, which act as additional mechanisms by which crisaborole dampens the immunopathogenesis in mouse models of inflammatory skin diseases. Further examination is warranted to translate these preclinical findings to human disease.

The Novel Oxazolidinone TBI-223 Is Effective in Three Preclinical Mouse Models of Methicillin-Resistant Staphylococcus aureus Infection

Staphylococcus aureus is an important cause of various infections in humans, including bacteremia, skin and soft tissue infections, and infections associated with implanted medical devices. The emergence of hospital- and community-acquired methicillin-resistant Staphylococcus aureus (MRSA) underscores the urgent and unmet need to develop novel, safe, and effective antibiotics against these multidrug-resistant clinical isolates. Oxazolidinone antibiotics such as linezolid have excellent oral bioavailability and provide coverage against MRSA infections. However, their widespread and long-term use is often limited by adverse effects, especially myelosuppression. TBI-223 is a novel oxazolidinone with potentially reduced myelosuppression, compared to linezolid, but its efficacy against MRSA infections is unknown. Therefore, the preclinical efficacy of TBI-223 (80 and 160 mg/kg twice daily) was compared with that of linezolid (40 and 80 mg/kg twice daily) and sham treatment in mouse models of MRSA bacteremia, skin wound infection, and orthopedic-implant-associated infection. The dosage was selected based on mouse pharmacokinetic analysis of both linezolid and TBI-223, as well as measurement of the MICs. In all three models, TBI-223 and linezolid had comparable dose-dependent efficacies in reducing bacterial burden and disease severity, compared with sham-treated control mice. Taken together, these findings indicate that TBI-223 represents a novel oxazolidinone antibiotic that may provide an additional option against MRSA infections. Future studies in larger animal models and clinical trials are warranted to translate these findings to humans. IMPORTANCE Staphylococcus aureus is the predominant cause of bloodstream, skin, and bone infections in humans. Resistance to commonly used antibiotics is a growing concern, making it more difficult to treat staphylococcal infections. Use of the oxazolidinone antibiotic linezolid against resistant strains is hindered by high rates of adverse reactions during prolonged therapy. Here, a new oxazolidinone named TBI-223 was tested against S. aureus in three mouse models of infection, i.e., bloodstream infection, skin infection, and bone infection. We found that TBI-223 was as effective as linezolid in these three models. Previous data suggest that TBI-223 has a better safety profile than linezolid. Taken together, these findings indicate that this new agent may provide an additional option against MRSA infections. Future studies in larger animal models and clinical trials are warranted to translate these findings to humans.

Efficacy of Telavancin in Comparison to Linezolid in a Porcine Model of Severe Methicillin-Resistant Staphylococcus aureus Pneumonia

Current guidelines recommend vancomycin and linezolid as first-line agents against methicillin-resistant Staphylococcus aureus (MRSA) nosocomial pneumonia. Telavancin is a potential new therapeutic alternative, specifically in monomicrobial MRSA pneumonia. This study compared the efficacies of telavancin versus linezolid in a porcine model of severe MRSA pneumonia. In 18 mechanically ventilated pigs (32.11 ± 1.18 kg), 75 ml of 10⁶ CFU/ml of MRSA was administered into each pulmonary lobe. After the onset of pneumonia, pigs were randomized into three groups: a control group, a group receiving 22.5 mg/kg of body weight every 24 h (q24h) of telavancin, and a group receiving 10 mg/kg q12h of linezolid intravenously. Tracheal aspirate and bronchoalveolar lavage (BAL) fluids were cultured every 24 h. After 48 h of treatment, tissue samples were collected from the ventral and dorsal sections of each lobe. Microbiological and histopathological analyses were performed. Lung tissue concentrations differed among the groups (P = 0.019), with the lowest MRSA lung burden in the telavancin group (P < 0.05 versus the control). MRSA was detected in 46.7%, 40.0%, and 21.7% of the lung tissue samples from the control, linezolid, and telavancin groups, respectively (P < 0.001). MRSA concentrations differed among the groups in tracheal aspirate fluid (P = 0.011) but not in BAL fluid. Furthermore, there was no increased risk of kidney injury during telavancin use. Thus, telavancin has higher bactericidal efficacy than linezolid during the first 48 h of treatment in a porcine model of severe MRSA pneumonia. However, studies are needed to confirm the benefits of telavancin in treating MRSA nosocomial pneumonia.

Efficacy of a Multimechanistic Monoclonal Antibody Combination against Staphylococcus aureus Surgical Site Infections in Mice

Surgical site infections (SSIs) are commonly caused by Staphylococcus aureus We report that a combination of three monoclonal antibodies (MEDI6389) that neutralize S. aureus alpha-toxin, clumping factor A, and four leukocidins (LukSF, LukED, HlgAB, and HlgCB) plus vancomycin had enhanced efficacy compared with control antibody plus vancomycin in two mouse models of S. aureus SSI. Therefore, monoclonal antibody-based neutralization of multiple S. aureus virulence factors may provide an adjunctive perioperative approach to combat S. aureus SSIs.

Oral-Only Linezolid-Rifampin Is Highly Effective Compared with Other Antibiotics for Periprosthetic Joint Infection: Study of a Mouse Model

BACKGROUND

The medical treatment of periprosthetic joint infection (PJI) involves prolonged systemic antibiotic courses, often with suboptimal clinical outcomes including increased morbidity and health-care costs. Oral and intravenous monotherapies and combination antibiotic regimens were evaluated in a mouse model of methicillin-resistant Staphylococcus aureus (MRSA) PJI.

METHODS

Oral linezolid with or without oral rifampin, intravenous vancomycin with oral rifampin, intravenous daptomycin or ceftaroline with or without oral rifampin, oral doxycycline, or sham treatment were administered at human-exposure doses for 6 weeks in a mouse model of PJI. Bacterial burden was assessed by in vivo bioluminescent imaging and ex vivo counting of colony-forming units (CFUs), and reactive bone changes were evaluated with radiographs and micro-computed tomography (μCT) imaging.

RESULTS

Oral-only linezolid-rifampin and all intravenous antibiotic-rifampin combinations resulted in no recoverable bacteria and minimized reactive bone changes. Although oral linezolid was the most effective monotherapy, all oral and intravenous antibiotic monotherapies failed to clear infection or prevent reactive bone changes.

CONCLUSIONS

Combination antibiotic-rifampin regimens, including oral-only linezolid-rifampin and the newer ceftaroline-rifampin combinations, were highly effective and more efficacious than monotherapies when used against a preclinical MRSA PJI.

CLINICAL RELEVANCE

This study provides important preclinical evidence to better optimize future antibiotic therapy against PJIs. In particular, the oral-only linezolid-rifampin option might reduce venous access complications and health-care costs.

Telavancin: a novel semisynthetic lipoglycopeptide agent to counter the challenge of resistant Gram-positive pathogens

Telavancin (TD-6424), a semisynthetic lipoglycopeptide vancomycin-derivative, is a novel antimicrobial agent developed by Theravance for overcoming resistant Gram-positive bacterial infections, specifically methicillin-resistant Staphylococcus aureus (MRSA). The US Food and Drug Administration (USFDA) had approved telavancin in 2009 for the treatment of complicated skin and skin structure infections (cSSSIs) caused by Gram-positive bacteria, including MRSA (S. aureus, Streptococcus agalactiae, Streptococcus pyogenes, Streptococcus anginosus group, or Enterococcus faecalis). Telavancin has two proposed mechanisms of action. In vitro, telavancin has a rapid, concentration-dependent bactericidal effect, due to disruption of cell membrane integrity. Telavancin has demonstrable in vitro activity against aerobic and anaerobic Gram-positive bacteria. Telavancin and vancomycin have similar spectra of activity. Gram-negative bacteria are usually non-susceptible to telavancin. Telavancin has been successfully tested in various animal models of bacteremia, endocarditis, meningitis, and pneumonia. Phase II Telavancin versus Standard Therapy for Treatment of Complicated Skin and Soft-Tissue Infections due to Gram-Positive Bacteria (FAST 1 and FAST 2) and phase III [Assessment of Telavancin in Complicated Skin and Skin Structure Infections 1 (ATLAS 1 and ATLAS 2)] clinical trials have been conducted for evaluating telavancin's efficacy and safety in cSSSIs. Phase III clinical trials have been carried out for evaluating telavancin's safety and efficacy in nosocomial pneumonia [Assessment of Telavancin for Treatment of Hospital acquired Pneumonia 1 and 2 (ATTAIN 1 and ATTAIN 2)]. A phase II randomized, double-blind, clinical trial has been carried out for evaluating telavancin's safety and efficacy in uncomplicated S. aureus bacteremia [Telavancin for Treatment of Uncomplicated S. aureus Bacteremia (ASSURE)]. Pacemaker lead-related infective endocarditis due to a vancomycin intermediate S. aureus (VISA) strain (non-daptomycin susceptible) was successfully treated with parenteral telavancin for 8 weeks. Telavancin extensively binds to serum albumin (~93%) and has a relatively small volume of distribution. Telavancin is not biotransformed by any cytochrome P450 microsomal enzymes and excreted mainly in the urine. Though well-tolerated, worrisome adverse effects, including renal dysfunction and QTc prolongation are of potential concern. Given its extensive binding to plasma proteins, long half-life, and a long post-antibiotic effect, it represents a promising addition to the therapeutic armamentarium in combating infections caused by resistant Gram-positive pathogens, namely, MRSA.

A review on cell wall synthesis inhibitors with an emphasis on glycopeptide antibiotics

Cell wall biosynthesis inhibitors (CBIs) have historically been one of the most effective classes of antibiotics. They are the most extensively used class of antibiotics and their importance is exemplified by the β-lactams and glycopeptide antibiotics. However, this class of antibiotics has not received impunity from resistance development. In the wake of this predicament, this review presents the progress of CBIs, especially glycopeptide derivatives as antibiotics to confront antibacterial resistance. The various strategies used for the development of CBIs, their clinical status and possible directions in which this field can evolve have also been discussed.

Polymeric nanofiber coating with tunable combinatorial antibiotic delivery prevents biofilm-associated infection in vivo

Bacterial biofilm formation is a major complication of implantable medical devices that results in therapeutically challenging chronic infections, especially in cases involving antibiotic-resistant bacteria. As an approach to prevent these infections, an electrospun composite coating comprised of poly(lactic-coglycolic acid) (PLGA) nanofibers embedded in a poly(ε-caprolactone) (PCL) film was developed to locally codeliver combinatorial antibiotics from the implant surface. The release of each antibiotic could be adjusted by loading each drug into the different polymers or by varying PLGA:PCL polymer ratios. In a mouse model of biofilm-associated orthopedic-implant infection, three different combinations of antibiotic-loaded coatings were highly effective in preventing infection of the bone/joint tissue and implant biofilm formation and were biocompatible with enhanced osseointegration. This nanofiber composite-coating technology could be used to tailor the delivery of combinatorial antimicrobial agents from various metallic implantable devices or prostheses to effectively decrease biofilm-associated infections in patients.

Comparative Efficacies of Tedizolid Phosphate, Linezolid, and Vancomycin in a Murine Model of Subcutaneous Catheter-Related Biofilm Infection Due to Methicillin-Susceptible and -Resistant Staphylococcus aureus

Tedizolid, a novel oxazolidinone, exhibits bacteriostatic activity through inhibition of protein synthesis. The efficacies of tedizolid, linezolid, and vancomycin were compared in a murine catheter-related biofilm infection caused by methicillin-susceptible and -resistant Staphylococcus aureus (MSSA and MRSA, respectively) strains engineered for bioluminescence. We observed significantly improved efficacy in terms of decreased S. aureus densities and bioluminescent signals in the tedizolid-treated group versus the linezolid- and vancomycin-treated groups in the model of infection caused by the MSSA and MRSA strains.

Pharmacodynamic Profile of GSK2140944 against Methicillin-Resistant Staphylococcus aureus in a Murine Lung Infection Model

GSK2140944 is a novel bacterial type II topoisomerase inhibitor with in vitro activity against key causative respiratory pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). We described the pharmacodynamics of GSK2140944 against MRSA in the neutropenic murine lung infection model. MICs of GSK2140944 were determined by broth microdilution. Plasma and epithelial lining fluid (ELF) pharmacokinetics were evaluated to allow determination of pulmonary distribution. Six MRSA isolates were tested. GSK2140944 doses of 1.56 to 400 mg/kg of body weight every 6 h (q6h) were utilized. Efficacy as the change in log10 CFU at 24 h compared with 0 h controls and the area under the concentration-time curve for the free, unbound fraction of a drug (fAUC)/MIC required for various efficacy endpoints were determined. GSK2140944 MICs were 0.125 to 0.5 mg/liter against the six MRSA isolates. ELF penetration ratios ranged from 1.1 to 1.4. Observed maximal decreases were 1.1 to 3.1 log10 CFU in neutropenic mice. The mean fAUC/MIC ratios required for stasis and 1-log-unit decreases were 59.3 ± 34.6 and 148.4 ± 83.3, respectively. GSK2140944 displayed in vitro and in vivo activity against MRSA. The pharmacodynamic profile of GSK2140944, as determined, supports its further development as a potential treatment option for pulmonary infections, including those caused by MRSA.

A modified chronic infection model for testing treatment of Staphylococcus aureus biofilms on implants

Bacterial biofilms causing implant-associated osteomyelitis is a severe complication with limited antimicrobial therapy options. We designed an animal model, in which implant associated osteomyelitis arise from a Staphylococcus aureus biofilm on a tibia implant. Two bioluminescently engineered (luxA-E transformed), strains of S. aureus were utilized, Xen29 and Xen31. Biofilm formation was assessed with epifluorescence microscopy. Quantitative measurements were performed day 4, 6, 8, 11 and 15 post-surgery. Bacteria were extracted from the biofilm by sonication and the bacterial load quantified by culturing. Biofilm formation was evident from day 6 post-implantation. Mean bacterial load from implants was ∼1×10(4) CFU/implant, while mean bacterial load from infected tibias were 1×10(6) CFU/bone. Bioluminesence imaging revealed decreasing activity throughout the 15-day observation period, with signal intensity for both strains reaching that of the negative control by day 15 while there was no significant reduction in bacterial load. The model is suitable for testing antimicrobial treatment options for implant associated OM, as treatment efficacy on both biofilm and viable counts can be assessed.

The ATTAIN trials: efficacy and safety of telavancin compared with vancomycin for the treatment of hospital-acquired and ventilator-associated bacterial pneumonia

ABSTRACT: Hospital-acquired bacterial pneumonia (HABP) is the second most common nosocomial infection in the USA and the leading cause of mortality among hospital-acquired infections. An increasing proportion of HABP cases are the result of infection with methicillin-resistant Staphylococcus aureus (MRSA). Telavancin is a once-daily injectable, semisynthetic lipoglycopeptide antimicrobial with bactericidal activity against susceptible Gram-positive pathogens, including MRSA. The two methodologically identical Phase III ATTAIN studies demonstrated that telavancin was noninferior to vancomycin for the treatment of HABP, including ventilator-associated bacterial pneumonia, due to S. aureus (including methicillin-sensitive S. aureus and MRSA). Telavancin showed a similar safety profile to vancomycin, except that in patients with moderate-to-severe renal impairment, there was increased mortality, which warrants caution when using telavancin in this population. Now approved in the USA for the treatment of HABP, including ventilator-associated bacterial pneumonia, caused by susceptible isolates of S. aureus when other alternatives are not suitable, telavancin offers another therapeutic option.

Activity of Tigecycline in combination with Colistin, Meropenem, Rifampin, or Gentamicin against KPC-producing Enterobacteriaceae in a murine thigh infection model

Limited antimicrobials remain active for treating severe infections due to KPC-producing pathogens, and optimal regimens have not been established. In murine thigh infections caused by nine KPC-producing clinical strains of Enterobacteriaceae (meropenem MICs, 1 to 4 μg/ml), we evaluated the activities of tigecycline, colistin, meropenem, rifampin, and gentamicin in single and combination regimens lasting for 24 h and 48 h. Rifampin, tigecycline, and gentamicin were the most effective monotherapies, reducing significantly the CFU counts yielded from thighs infected by 88.9 to 100%, 77.8 to 88.9%, and 66.7 to 88.9% of strains, respectively; meropenem and colistin alone exhibited considerably lower performance (significant CFU reduction in 33.3% and 22.2 to 33.3% of the strains, respectively). The addition of rifampin or gentamicin to tigecycline produced synergistic effect in most strains, while antagonism was observed in 33.3 to 44.4% of the strains when colistin was added to tigecycline and in 44.4 to 55.5% of the strains for meropenem combination with tigecycline. Tigecycline combinations with gentamicin or with rifampin caused higher CFU reductions than did tigecycline plus colistin or plus meropenem with almost all strains. Furthermore, tigecycline plus gentamicin was significantly more effective than tigecycline plus colistin or tigecycline plus meropenem in 33.3 to 44.4% and 55.5 to 66.7% of the strains, respectively, while tigecycline plus rifampin significantly outperformed tigecycline plus colistin and tigecycline plus meropenem in 33.3% and 66.7 to 77.8% of the strains, respectively. Overall, our in vivo study showed that tigecycline plus rifampin or plus gentamicin is a robust regimen against soft tissue infections caused by KPC-producing strains. The combinations of tigecycline with colistin or meropenem should be considered with caution in clinical practice.

Studies on the mechanism of telavancin decreased susceptibility in a laboratory-derived mutant

Telavancin is a novel semisynthetic lipoglycopeptide derivative of vancomycin with a dual mode of action. This study sought to understand the mechanisms of decreased telavancin susceptibility in a laboratory-derived Staphlococcus aureus mutant Tlv(DS)MED1952. There were extensive changes in the transcriptome of Tlv(DS)MED1952 compared to the susceptible parent strain MED1951. Genes upregulated included cofactor biosynthesis genes, cell wall-related genes, fatty acid biosynthesis genes, and stress genes. Downregulated genes included lysine operon biosynthesis genes and lrgB, which are induced by telavancin in susceptible strains, agr and kdpDE genes, various cell surface protein genes, phenol-soluble modulin genes, several protease genes, and genes involved in anaerobic metabolism. The decreased susceptibility mutant had somewhat thicker cell walls and a decreased autolytic activity that may be related to decreased proteolytic peptidoglycan hydrolase processing. Membrane fatty acid changes correlated with increased membrane fluidity were observed. It seems likely that there are multiple genetic changes associated with the development of decreased telavancin susceptibility. The Tlv(DS) mutant showed some similar features to vancomycin-intermediate S. aureus and decreased daptomycin susceptibility strains, but also exhibited its own unique features.

Virulence of Acinetobacter baumannii Exhibiting Phenotypic Heterogeneous Growth against Meropenem in a Murine Thigh Infection Model

Acinetobacter baumannii may exhibit phenotypic heterogeneous growth under exposure to antibiotics. We investigated the in vitro characteristics of A. baumannii isolates grown heterogeneously in the presence of meropenem and their virulence evaluated in experimental infections treated with meropenem. Five clinical A. baumannii isolates and the respective heterogeneously grown subpopulations were tested by agar dilution minimum inhibitory concentration (MIC) testing, pulsed field gel electrophoresis (PFGE), population analysis using meropenem and growth curves. The virulence of isolates and the therapeutic efficacy of three meropenem dosing schemes was evaluated in a neutropenic murine thigh infection model. The clinical isolates were meropenem-susceptible (MICs 1 to 4 mg/liter) and exhibited three distinct PFGE patterns. In all clinical isolates, population analysis yielded heterogeneously grown colonies. After seven subcultures in antibiotic-free media, resistant MIC levels were retained in two isolates (heteroresistant), while three isolates were reversed to susceptible MICs (persisters). Clinical isolates and heterogeneous subpopulations had similar growth rates. The heterogeneously grown A. baumannii subpopulations had reduced virulence, killing considerably fewer animals than the respective clinical isolates without treatment. The meropenem treatment outcome was similar in infections caused by the clinical and the heterogeneous isolates, irrespective to their MICs. In vitro meropenem exposure induces phenotypic heterogeneous growth in A. baumannii. Compared with the parental clinical isolates, the heterogeneously grown subpopulations exhibited lower virulence, killing fewer mice and responding equally to meropenem treatment, despite their higher MICs.

Efficacy of two novel 2,2'-bifurans to inhibit methicillin-resistant Staphylococcus aureus infection in male mice in comparison to vancomycin

The therapeutic efficacy of two novel bifurans and vancomycin in an animal model of a methicillin-resistant Staphylococcus aureus (MRSA) infection was compared. Adult male CF-1 mice (25-35 g) were intraperitoneally injected with 200 μL/mouse containing 10(7) cell-forming units of MRSA. After 16 hours, animals were treated with 110 mg/kg of vancomycin, or 5 mg/kg of mononitrile bifuran (1A) or monocationic bifuran (1B) and killed after 8 hours. Treatment with bifurans did not cause any toxicity. Treatment of MRSA-infected animals with bifurans resulted in significant reductions in the viable bacterial count in blood, liver, kidney, and spleen. Colonies recovered from livers and kidneys of mice injected with 1A or 1B lost the initial resistance pattern and became susceptible to methicillin and ciprofloxacin. MRSA elevated the serum urea level and activities of alanine aminotransferase and γ-glutamyl transpeptidase. MRSA also elevated the hepatic level of malondialdehyde, and serum levels of tumor necrosis factor and interleukin-6. MRSA also reduced the glutathione content and activities of catalase and glutathione S-transferase in liver. Similar to vancomycin, bifurans ameliorated most of the previous effects. Compound 1B was superior to 1A, and sometimes both provided better antistaphylococcal agents than vancomycin against MRSA pathogenesis. The present findings along with our previous studies support further evaluation of the efficacy of these bifurans in clinical studies.

Further insights into the mode of action of the lipoglycopeptide telavancin through global gene expression studies

Telavancin is a novel semisynthetic lipoglycopeptide derivative of vancomycin with a decylaminoethyl side chain that is active against Gram-positive bacteria, including Staphylococcus aureus strains resistant to methicillin or vancomycin. A dual mechanism of action has been proposed for telavancin involving inhibition of peptidoglycan biosynthesis and membrane depolarization. Here we report the results of genome-wide transcriptional profiling of the response of S. aureus to telavancin using microarrays. Short (15-min) challenge of S. aureus with telavancin revealed strong expression of the cell wall stress stimulon, a characteristic response to inhibition of cell wall biosynthesis. In the transcriptome obtained after 60-min telavancin challenge, in addition to induction of the cell wall stress stimulon, there was induction of various genes, including lrgA and lrgB, lysine biosynthesis operon (dap) genes, vraD and vraE, and hlgC, that have been reported to be induced by known membrane-depolarizing and active agents, including carbonyl cyanide m-chlorophenylhydrazone, daptomycin, bacitracin, and other antimicrobial peptides These genes were either not induced or only weakly induced by the parent molecule vancomycin. We suggest that expression of these genes is a response of the cell to mitigate and detoxify such molecules and is diagnostic of a membrane-depolarizing or membrane-active molecule. The results indicate that telavancin causes early and significant induction of the cell wall stress stimulon due to strong inhibition of peptidoglycan biosynthesis, with evidence in support of membrane depolarization and membrane activity that is expressed after a longer duration of drug treatment.

Activity of oxacillin versus that of vancomycin against oxacillin-susceptible mecA-positive Staphylococcus aureus clinical isolates evaluated by population analyses, time-kill assays, and a murine thigh infection model

We compared the activity of dicloxacillin with that of vancomycin against 15 oxacillin-susceptible, methicillin-resistant Staphylococcus aureus (OS-MRSA) clinical isolates. By population analyses, we found that 6 OS-MRSA isolates were able to grow in the presence of up to 8 μg/ml dicloxacillin and 9 isolates were able to grow in 12 to >32 μg/ml dicloxacillin; all isolates grew in up to 2 μg/ml vancomycin. Both drugs exhibited similar bactericidal activities. In experimental infections, the therapeutic efficacy of dicloxacillin was significant (P < 0.05 versus untreated controls) in 10 OS-MRSA isolates and vancomycin was effective (P < 0.05) against 12 isolates; dicloxacillin had an efficacy that was comparable to that of vancomycin (P > 0.05) in 8 isolates. The favorable response to dicloxacillin treatment might suggest that antistaphylococcal penicillins could be used against OS-MRSA infections.

Telavancin: a lipoglycopeptide antimicrobial for the treatment of complicated skin and skin structure infections caused by gram-positive bacteria in adults

BACKGROUND

Telavancin, a lipoglycopeptide antibiotic, is a semisynthetic derivative of vancomycin. It was approved by the US Food and Drug Administration (FDA) in 2009 for the treatment of complicated skin and skin structure infections (cSSSIs) caused by gram-positive bacteria, including methicillin-resistant Staphylococcus aureus.

OBJECTIVE

This article summarizes the pharmacology, in vitro and in vivo activity, pharmacokinetic properties, and clinical efficacy and tolerability of telavancin.

METHODS

Relevant information was identified through a search of MEDLINE (1966-August 2010), Iowa Drug Information Service (1966-August 2010), International Pharmaceutical Abstracts (1970-August 2010), and Google Scholar using the terms telavancin, lipoglycopeptide, and TD-6424. Abstracts and posters from scientific meetings, as well as documents submitted by the manufacturer of telavancin to the FDA as part of the approval process, were consulted. In vivo and in vitro experimental and clinical studies and review articles that provided information on the activity, mechanism of action, pharmacologic and pharmacokinetic properties, clinical efficacy, and tolerability of telavancin were reviewed.

RESULTS

In vitro, telavancin has potent activity against S aureus, including methicillin-resistant strains; Streptococcus pneumoniae; and vancomycin-susceptible enterococci with MICs generally <1 μg/mL. Telavancin appears to have a dual mechanism of action, inhibiting cell wall formation and disrupting the cell membrane. In Phase III studies (ATLAS 1 and ATLAS 2), telavancin was found to be noninferior to vancomycin, with clinical cure rates of 88.3% and 87.1%, respectively, in clinically evaluable patients in the treatment of cSSSIs (difference, 1.2%; 95% CI, -2.1 to 4.6; P = NS). The effectiveness of telavancin in the treatment of hospital-acquired pneumonia was assessed in 2 Phase III studies (ATTAIN 1 and ATTAIN 2). Preliminary findings were that the effectiveness of telavancin was not significantly different from that of vancomycin, with cure rates of 82.7% and 80.9% in the clinically evaluable population, respectively (difference, 1.8%; 95% CI, -4.1 to 7.7; P = NS). The most commonly (>10%) reported adverse events included taste disturbances, nausea, headache, vomiting, foamy urine, constipation, and insomnia.

CONCLUSION

In clinical trials, the effectiveness of telavancin was not significantly different from that of vancomycin in the treatment of cSSSIs, and telavancin was generally well tolerated.

Telavancin Activity against gram-positive bacteria isolated from patients with skin and skin-structure infections

Telavancin is approved in the United States and Canada for the treatment of complicated skin and skin structure infections (cSSSI) in adults caused by susceptible Gram-positive organisms. The antimicrobial activity of telavancin and comparators was evaluated against 5,027 (2007-2008) Gram-positive bacteria responsible for SSSI in medical centers in Asia-Pacific, European, Latin American, and North American regions. Telavancin was active against Staphylococcus aureus (MIC₅₀(/)₉₀, 0.12/0.25 mg/l; 100.0% susceptible) and coagulase-negative staphylococci (MIC₅₀(/)₉₀, 0.12/0.25 mg/l). telavancin inhibited all Enterococcus faecalis, including four strains displaying a VanB phenotype, at ≤ 1 mg/L (MIC₅₀(/)₉₀, 0.25/0.5 mg/l), except for two isolates with a VanA phenotype (MIC, >2 mg/l). Vancomycin-susceptible and VanB vancomycin-resistant E. faecium were inhibited by telavancin at ≤ 0.25 mg/L, while this drug exhibited elevated MIC values (≥ 0.5 mg/l) against E. faecium of VanA phenotype (MIC₅₀(/)₉₀, 2/>2 mg/l). Telavancin was potent against β-haemolytic streptococci (MIC₅₀(/)₉₀, 0.03/0.12 mg/l; 100.0% susceptible) and viridans group streptococci (MIC₅₀(/)₉₀, 0.03/0.06 mg/l; 100.0% susceptible). These in vitro data document the activity of telavancin against contemporary Gram-positive isolates and support its clinical use for the treatment of cSSSI caused by the indicated pathogens.

An interspecies extrapolation of the pharmacokinetics of telavancin, a rapidly bactericidal, concentration-dependent antibiotic

Telavancin is an intravenous lipoglycopeptide antibiotic active against many Gram-positive pathogens via inhibition of bacterial cell wall synthesis and disruption of bacterial membrane function. Non-compartmental pharmacokinetic parameters of telavancin (clearance [Cl], steady-state volume of distribution [Vss], area under the concentration curve [AUC], and elimination half-life [t(1/2)]) were determined for five preclinical species (mice, rats, rabbits, dogs, and monkeys). Interspecies scaling was applied to predict the corresponding parameters in humans and compare retrospectively with observed values. Plasma concentrations of single doses of telavancin declined monoexponentially in all species with half-lives between 1.2 and 2.4 h. The pharmacokinetics of telavancin was demonstrated to be dose-proportional in rabbits and gender-independent in monkeys. Application of the simple allometric equation (Y = aW(b)) resulted in a good correlation between predicted and observed values of Vss in humans. Application of a modified allometric equation that includes brain weight (Cl × BW = aW(b)) resulted in a good correlation between predicted and observed values of Cl, AUC, and t(1/2) in humans. These data suggest that interspecies scaling may be useful to predict pharmacokinetic parameters of telavancin in humans.

Comparative efficacies of human simulated exposures of telavancin and vancomycin against methicillin-resistant Staphylococcus aureus with a range of vancomycin MICs in a murine pneumonia model

Telavancin displays potent in vitro and in vivo activity against methicillin-resistant Staphylococcus aureus (MRSA), including strains with reduced susceptibility to vancomycin. We compared the efficacies of telavancin and vancomycin against MRSA strains with vancomycin MICs of ≥1 μg/ml in a neutropenic murine lung infection model. Thirteen clinical MRSA isolates (7 vancomycin-susceptible, 2 vancomycin-heteroresistant [hVISA], and 4 vancomycin-intermediate [VISA] isolates) were tested after 24 h, and 7 isolates (1 hVISA and 4 VISA isolates) were tested after 48 h of exposure. Mice were administered subcutaneous doses of telavancin at 40 mg/kg of body weight every 12 h (q12h) or of vancomycin at 110 mg/kg q12h; doses were designed to simulate the area under the concentration-time curve for the free, unbound fraction of drug (fAUC) observed for humans given telavancin at 10 mg/kg q24h or vancomycin at 1 g q12h. Efficacy was expressed as the 24- or 48-h change in lung bacterial density from pretreatment counts. At dose initiation, the mean bacterial load was 6.16 ± 0.26 log(10) CFU/ml, which increased by averages of 1.26 ± 0.55 and 1.74 ± 0.68 log in untreated mice after 24 and 48 h, respectively. At both time points, similar CFU reductions were noted for telavancin and vancomycin against MRSA, with vancomycin MICs of ≤2 μg/ml. Both drugs were similarly efficacious after 24 and 48 h of treatment against the hVISA strains tested. Against VISA isolates, telavancin reduced bacterial burdens significantly more than vancomycin for 1 of 4 isolates after 24 h and for 3 of 4 isolates after 48 h. These data support the potential utility of telavancin for the treatment of MRSA pneumonia caused by pathogens with reduced susceptibility to vancomycin.

Fluorescence microscopy demonstrates enhanced targeting of telavancin to the division septum of Staphylococcus aureus

The cellular binding patterns of fluorescent conjugates of telavancin and vancomycin were evaluated in Staphylococcus aureus by fluorescence microscopy and ratio imaging analysis. Telavancin showed enhanced binding at the division septum compared to vancomycin. This result is consistent with observations that telavancin binds with higher affinity to lipid II than to d-Ala-d-Ala residues in the cell wall, thus demonstrating the preferential binding of telavancin to the site of active cell wall biosynthesis.

Telavancin

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Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. For more information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The February 2010 monograph topics are on tranexamic acid tablets; human papillomavirus bivalent vaccine, recombinant; romidepsin, diclofenac sodium solution 1.5%; and ecallantide injection. The DUE is on vigabatrin.

Telavancin disrupts the functional integrity of the bacterial membrane through targeted interaction with the cell wall precursor lipid II

Telavancin is an investigational lipoglycopeptide antibiotic currently being developed for the treatment of serious infections caused by gram-positive bacteria. The bactericidal action of telavancin results from a mechanism that combines the inhibition of cell wall synthesis and the disruption of membrane barrier function. The purpose of the present study was to further elucidate the mechanism by which telavancin interacts with the bacterial membrane. A flow cytometry assay with the diethyloxacarbocyanine dye DiOC(2)(3) was used to probe the membrane potential of actively growing Staphylococcus aureus cultures. Telavancin caused pronounced membrane depolarization that was both time and concentration dependent. Membrane depolarization was demonstrated against a reference S. aureus strain as well as phenotypically diverse isolates expressing clinically important methicillin-resistant (MRSA), vancomycin-intermediate (VISA), and heterogeneous VISA (hVISA) phenotypes. The cell wall precursor lipid II was shown to play an essential role in telavancin-induced depolarization. This was demonstrated both in competition binding experiments with exogenous D-Ala-D-Ala-containing ligand and in experiments with cells expressing altered levels of lipid II. Finally, monitoring of the optical density of S. aureus cultures exposed to telavancin showed that cell lysis does not occur during the time course in which membrane depolarization and bactericidal activity are observed. Taken together, these data indicate that telavancin's membrane mechanism requires interaction with lipid II, a high-affinity target that mediates binding to the bacterial membrane. The targeted interaction with lipid II and the consequent disruption of both peptidoglycan synthesis and membrane barrier function provide a mechanistic basis for the improved antibacterial properties of telavancin relative to those of vancomycin.

In vitro activities of telavancin and vancomycin against biofilm-producing Staphylococcus aureus, S. epidermidis, and Enterococcus faecalis strains

We investigated the activities of telavancin and vancomycin against biofilm-producing Staphylococcus and Enterococcus strains. At clinically attainable concentrations, telavancin was active against bacteria embedded in biofilm (minimal biofilm eradication concentration [MBEC], 0.125 to 2 microg/ml) and inhibited biofilm formation at concentrations below the MIC. Vancomycin did not demonstrate the same activity (MBEC, > or =512 microg/ml) against Staphylococcus aureus and Enterococcus faecalis. Telavancin may have a unique role in biofilm-associated infections.

Current and novel antibiotics against resistant Gram-positive bacteria

The challenge posed by resistance among Gram-positive bacteria, epitomized by methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE) and vancomycin-intermediate and -resistant S. aureus (VISA and VRSA) is being met by a new generation of antimicrobials. This review focuses on the new β-lactams with activity against MRSA (ceftobiprole and ceftaroline) and on the new glycopeptides (oritavancin, dalbavancin, and telavancin). It will also consider the role of vancomycin in an era of existing alternatives such as linezolid, daptomycin and tigecycline. Finally, compounds in early development are described, such as iclaprim, friulimicin, and retapamulin, among others.