Telavancin In Vitro Activity against a Collection of Methicillin-Resistant Staphylococcus aureus Isolates,Including Resistant Subsets,from the United States

Telavancin had MIC₅₀, MIC₉₀, and MIC₁₀₀ values of 0.03, 0.06, and 0.12 μg/ml, respectively, against methicillin-susceptible Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and non-multidrug-resistant (non-MDR) and MDR subsets. MRSA with elevated MIC values for vancomycin (2 to 4 μg/ml) or daptomycin (1 to 2 μg/ml) had telavancin MIC₅₀ (0.06 μg/ml) values 2-fold higher than those of isolates with lower MIC results (MIC₅₀, 0.03 μg/ml). However, telavancin had MIC₉₀ and MIC₁₀₀ results of 0.06 and 0.12 μg/ml (100% susceptible), respectively, regardless of the MRSA subset.     

Baseline Activity of Telavancin against Gram-Positive Clinical Isolates Responsible for Documented Infections in U.S. Hospitals (2011-2012) as Determined by the Revised Susceptibility Testing Method

Telavancin had MIC₅₀ and MIC₉₀ values of 0.03 and 0.06 μg/ml (100.0% susceptible), respectively, against methicillin-resistant and -susceptible Staphylococcus aureus. Telavancin was active against vancomycin-susceptible Enterococcus faecalis (MIC_50/90, 0.12/0.12 μg/ml; 100% susceptible) and Enterococcus faecium (MIC_50/90, 0.03/0.06 μg/ml), while higher MIC values were obtained against vancomycin-resistant E. faecium (MIC_50/90, 1/2 μg/ml) and E. faecalis (MIC_50/90, >2/>2 μg/ml). Streptococci showed telavancin modal MIC results of ≤0.015 μg/ml, except against Streptococcus agalactiae (i.e., 0.03 μg/ml). This study reestablishes the telavancin spectrum of activity against isolates recovered from the United States (2011-2012) using the revised broth microdilution method.     

In Vitro Pharmacodynamics of Human Simulated Exposures of Telavancin against Methicillin-Susceptible and -Resistant Staphylococcus aureus with and without Prior Vancomycin Exposure

Telavancin is a lipoglycopeptide with potent activity against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA). The activity of telavancin against MRSA and MSSA after prior vancomycin exposure was studied in an in vitro pharmacodynamic model. Two clinical MRSA and two MSSA isolates, all with vancomycin MICs of 2 μg/ml, were subjected to humanized free drug exposures of vancomycin at 1 g every 12 h (q12h) for 96 h, telavancin at 750 mg q24h for 96 h, and vancomycin at 1 g q12h for 72 h followed by telavancin at 750 mg q24h for 48 h (120 h total). The microbiological responses were measured by changes from 0 h in log₁₀ CFU/ml at the end of experiments and area under the bacterial killing and regrowth curves over 96 h (AUBC₀₋₉₆). The control isolates grew to 8.8 ± 0.3 log₁₀ CFU/ml. Initially, all regimens caused −4.5 ± 0.9 reductions in log₁₀ CFU/ml by 48 h followed by slight regrowth over the following 48 to 72 h. After 96 h, vancomycin and telavancin achieved −3.7 ± 0.9 and −3.8 ± 0.8 log₁₀ CFU/ml changes from baseline, respectively (P = 0.74). Sequential exposure to telavancin after vancomycin did not result in additional CFU reductions or increases, with ultimate log₁₀ CFU/ml reductions of −4.3 ± 1.1 at 96 h and −4.2 ± 1.3 at 120 h (P > 0.05 for all comparisons at 96 h). The AUBC_0–96 was significantly smaller for the regimen of telavancin for 96 h than for the regimens of vancomycin for 96 h and vancomycin followed by telavancin (P ≤ 0.04). No resistance was observed throughout the experiment. Against these MRSA and MSSA isolates with vancomycin MICs of 2 μg/ml, telavancin was comparable with vancomycin and its activity was unaffected by prior vancomycin exposure.     

Efficacy of Telavancin in a rabbit model of aortic valve endocarditis due to methicillin-resistant Staphylococcus aureus or vancomycin-intermediate Staphylococcus aureus

The activities of telavancin and vancomycin were compared in vitro and in the rabbit model of aortic valve endocarditis against a methicillin-resistant Staphylococcus aureus strain, COL, and a vancomycin-intermediate S. aureus (VISA) strain, HIP 5836. Telavancin was bactericidal in time-kill studies at a concentration of 5 microg/ml against both COL and HIP5836. Vancomycin was bacteriostatic at 5 microg/ml and bactericidal at 10 microg/ml against COL and was bacteriostatic at 10 microg/ml against VISA strain HIP 5836. Compared to untreated controls, a twice-daily regimen of 30 mg/kg of telavancin reduced mean aortic valve vegetation titers of the COL strain by 4.7 log(10) CFU/g after 4 days of therapy and sterilized 6/11 vegetations compared to 3.4 log(10) CFU/g with 3/10 vegetations sterilized for a regimen of twice-daily vancomycin, 30 mg/kg; these differences were not statistically significant. Telavancin was significantly more effective than vancomycin in the VISA model, producing a 5.5 log(10) CFU/g reduction versus no reduction in CFU with vancomycin. In experiments comparing 2-day regimens of telavancin at 30 mg/kg and 50 mg/kg twice daily, organisms were rapidly eliminated from vegetations, but the effect was not different between the two doses. These results suggest that telavancin may be an effective treatment for endocarditis and other serious staphylococcal infections accompanied by bacteremia, including infections caused by staphylococci not susceptible to vancomycin.     

Vancomycin assay performance in patients with acute renal failure

Objective: Fluorescence polarization immunoassays (FPIA) have been reported to overestimate vancomycin serum concentrations compared to high-performance liquid chromatography (HPLC) or enzyme multiplied immunoassay technique (EMIT) in patients with chronic renal disease. The assay manufacturer has modified the FPIA to remedy this overestimation. The purpose of this study was to compare the assay performance of two FPIAs to EMIT in acute renal failure patients receiving vancomycin and continuous venovenous hemofiltration.¶Design: Open-label trial.¶Setting: Intensive care unit in a university affiliated hospital.¶Patients and participants: 15 serum and ultrafiltrate samples were obtained from 14 critically ill patients (mean ± SD; 57 ± 12 years; 8 males/6 females).¶Measurements and results: Vancomycin concentrations were determined by a polyclonal FPIA (pFPIA) performed on the TDx system, a monoclonal FPIA (mFPIA) performed on the AxSYM system and EMIT. The coefficient of variation for all assays was < 5 %. The mean difference ± SD_d between mFPIA vs EMIT and pFPIA vs EMIT assays in serum were: –0.08 ± 1.55 and 1.24 ± 2.11 mg/l, respectively. The limits of agreement between the mFPIA vs EMIT and pFPIA vs EMIT assays in serum were: –3.18 to 3.03 and –2.99 to 5.46 mg/l, respectively.¶Conclusions: Our data demonstrate that the manufacturer's changes to the pFPIA have reduced overestimation. The mFPIA appears to be an acceptable assay for measuring vancomycin serum concentrations in acute renal failure patients and does not significantly overestimate these concentrations.     

In Vivo Assessment of SMT19969 in a Hamster Model of Clostridium difficile Infection

SMT19969 [2,2′-bis(4-pyridyl)3H,3′-H 5,5-bibenzimidazole] is a novel narrow-spectrum nonabsorbable antibiotic currently in development for the treatment of Clostridium difficile infection. The comparative activities of SMT19969 and vancomycin against nonepidemic and epidemic strains of C. difficile were studied in an established hamster model. Against nonepidemic (VA11) strains, the survival rates of SMT19969-treated animals ranged from 80% to 95%. Vancomycin exhibited 100% protection during treatment, with relapse observed starting on day 9 and 50% survival at day 20. At 50 mg/kg of body weight, SMT19969 administered orally once daily for 5 days provided full protection of treated animals on the dosing days and through day 12 against epidemic strains. Vancomycin also protected during the dosing interval, but apparent relapse occurred earlier, starting on day 11. SMT19969 exhibited excellent in vitro activity, with MICs of 0.25 μg/ml for all isolates. The MICs for vancomycin were 2- to 4-fold higher at ≤0.5 to 1 μg/ml. All plasma sample concentrations of SMT19969 were below the limit of quantification (25 ng/ml) at all time points, consistent with the reported lack of bioavailability of the compound. Cecal concentrations were significantly above the MIC (ranging from 96 μg/ml to 172 μg/ml).     

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 log₁₀ 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.Over the course of the last 15 years, methicillin resistance among Staphylococcus aureus strains has increased steadily. Recent surveys report methicillin-resistant S. aureus (MRSA) rates of upwards of 50% for hospitalized patients with staphylococcal infections and upwards of 60% for patients in intensive care units (27). Considering that S. aureus accounts for 20 to 30% of hospital-acquired pneumonia cases, MRSA is a clinically important pathogen to consider in empirically choosing a regimen to treat pneumonia (22, 33).Vancomycin has long been regarded as the drug of choice for the treatment of MRSA infections. Current practice guidelines for the treatment of health care-associated pneumonia recommend vancomycin as a first-line therapy (2). Despite its being a first-line recommendation, studies evaluating the clinical success of vancomycin treatment in patients with MRSA pneumonia have observed failure in 45% to 77% of patients (15, 24). One possible explanation could be the recently reported vancomycin MIC creep detected among S. aureus strains (32). Over the last decade, an increase in vancomycin MICs has been noted by some centers, despite values staying within the Clinical and Laboratory Standards Institute (CLSI)-defined susceptibility range of ≤2 μg/ml (6). Among selected patients with MRSA bacteremia treated with vancomycin, Sakoulas and colleagues found significantly more treatment failures for patients infected with isolates possessing vancomycin MICs of 1 to 2 μg/ml (90.5%) than for those infected with isolates with vancomycin MICs of ≤0.5 μg/ml (44.4%) (31).In addition to MIC creep, another explanation for vancomycin failures is the increasing appearance of vancomycin-intermediate S. aureus (VISA) and heterogeneous vancomycin-intermediate S. aureus (hVISA) strains (3). The simultaneous increases in frequency of these isolates are expected, as hVISA isolates are thought to be the strains immediately preceding VISA in its evolution (12). The parent strains of hVISA have vancomycin MICs ranging from 1 to 4 μg/ml. However, when these strains are subjected to increasing concentrations of vancomycin, a subpopulation of resistant clones develops, with MICs of at least 8 μg/ml (21).Clinically, poor outcomes have been reported for both VISA and hVISA infections treated with vancomycin (21). In one study, hVISA-infected bacteremia patients were shown to have a significantly longer length of hospital stay, to have a greater proportion of high-bacterial-load infections, and to more commonly fail vancomycin therapy than those with vancomycin-susceptible MRSA infections (5). For this reason, it is necessary to characterize other treatment options not only for MRSA but also for the increasingly prevalent hVISA and VISA isolates.The recently approved lipoglycopeptide telavancin is the newest option for the treatment of resistant S. aureus. In vitro studies of telavancin demonstrated potent activity against a number of Gram-positive organisms, including MRSA, hVISA, and VISA (7, 8, 18). A murine lung infection model of human simulated exposures of telavancin and vancomycin showed an increased efficacy of telavancin against a single MRSA isolate (28). Similar results were noted against an hVISA and 2 VISA isolates in a murine bacteremia model (10). The present study was designed to merge these two findings by comparing the efficacies of human simulated exposures to telavancin and vancomycin against a number of MRSA isolates, including hVISA and VISA isolates, in a murine lung infection model.(These data were presented in part at the 49th Interscience Conference on Antimicrobial Agents and Chemotherapy.)     

Antimicrobial Activity of Ceftaroline Tested against Staphylococci with Reduced Susceptibility to Linezolid,Daptomycin, or Vancomycin from U.S. Hospitals, 2008 to 2011

Vancomycin, linezolid, and daptomycin are very active against staphylococci, but isolates with decreased susceptibility to these antimicrobial agents are isolated sporadically. A total of 19,350 Staphylococcus aureus isolates (51% methicillin resistant [MRSA]) and 3,270 coagulase-negative staphylococci (CoNS) were collected consecutively from 82 U.S. medical centers from January 2008 to December 2011 and tested for susceptibility against ceftaroline and comparator agents by the reference broth microdilution method. Among S. aureus strains, 14 isolates (0.07%) exhibited decreased susceptibility to linezolid (MIC, ≥8 μg/ml), 18 (0.09%) to daptomycin (MIC, ≥2 μg/ml), and 369 (1.9%) to vancomycin (MIC, ≥2 μg/ml; 368 isolates at 2 μg/ml and 1 at 4 μg/ml). Fifty-one (1.6%) CoNS were linezolid resistant (MIC, ≥8 μg/ml), and four (0.12%) were daptomycin nonsusceptible (MIC, ≥2 μg/ml). Ceftaroline was very active against S. aureus overall (MIC_50/90, 0.5/1 μg/ml; 98.5% susceptible), including MRSA (MIC_50/90, 0.5/1 μg/ml; 97.2% susceptible). All daptomycin-nonsusceptible and 85.7% of linezolid-resistant S. aureus isolates were susceptible to ceftaroline. Against S. aureus isolates with a vancomycin MIC of ≥2 μg/ml, 91.9, 96.2, and 98.9% were susceptible to ceftaroline, daptomycin, and linezolid, respectively. CoNS strains were susceptible to ceftaroline (MIC_50/90, 0.25/0.5 μg/ml; 99.1% inhibited at ≤1 μg/ml), including methicillin-resistant (MIC_50/90, 0.25/0.5 μg/ml), linezolid-resistant (MIC_50/90, 0.5/0.5 μg/ml), and daptomycin-nonsusceptible (4 isolates; MIC range, 0.03 to 0.12 μg/ml) strains. In conclusion, ceftaroline demonstrated potent in vitro activity against staphylococci with reduced susceptibility to linezolid, daptomycin, or vancomycin, and it may represent a valuable treatment option for infections caused by these multidrug-resistant staphylococci.     

In Vitro Activity of Rifampin Alone and in Combination with Nafcillin and Vancomycin Against Pathogenic Strains of Staphylococcus aureus

Twenty strains of Staphylococcus aureus isolated from patients with endocarditis were examined in vitro for susceptibility to rifampin, nafcillin, and vancomycin and to combinations of rifampin with nafcillin or vancomycin. Minimum bactericidal concentrations of rifampin ranged from 0.0031 to 0.0125 μg/ml, of nafcillin ranged from 0.078 to 0.312 μg/ml, and of vancomycin ranged from 0.312 to 1.25 μg/ml. The combination of rifampin with nafcillin was synergistic for 12 strains; the combination of rifampin plus vancomycin was synergistic for 5 of the isolates.     

Study of the in vitro activities of rifaximin and comparator agents against 536 anaerobic intestinal bacteria from the perspective of potential utility in pathology involving bowel flora

Rifaximin, ampicillin-sulbactam, neomycin, nitazoxanide, teicoplanin, and vancomycin were tested against 536 strains of anaerobic bacteria. The overall MIC of rifaximin at which 50% of strains were inhibited was 0.25 μg/ml. Ninety percent of the strains tested were inhibited by 256 μg/ml of rifaximin or less, an activity equivalent to those of teicoplanin and vancomycin but less than those of nitazoxanide and ampicillin-sulbactam.     

Effects of telavancin on coagulation test results

Background: The lipoglycopeptide antibiotic, telavancin, may interfere with some laboratory coagulation tests including prothrombin time (PT) and activated partial thromboplastin time (aPTT). Objective: To evaluate the effects of telavancin on PT and aPTT assays in common use. Methods: Pooled normal human plasma was spiked with telavancin 10, 20, 100 or 200 μg/ml (equivalent to trough, 2 × trough, peak and 2 × peak clinical plasma concentrations, respectively) or diluent control (0.9% sodium chloride). Samples were analysed using 16 PT reagents and seven aPTT reagents. Results: Telavancin 200 μg/ml (corresponding to 2 × peak clinical plasma concentration), produced significant PT prolongation (> 9% difference vs. diluent control) with all the 16 PT reagents (range 12% to > 600%). At lower telavancin concentrations, PT prolongation was dose‐dependent and varied among reagents, but appeared greatest with preparations containing recombinant tissue factor. With telavancin 10 μg/ml (equivalent to trough), PT prolongation was 10% with HemosIL^® PT‐Fibrinogen Recombinant, while ranging from 5% to –1% with all other reagents. Significant (> 34% difference vs. baseline) and dose‐dependent aPTT prolongation was observed with all the seven reagents in samples spiked with telavancin 100 or 200 μg/ml (range 65–142% at 200 μg/ml). aPTT reagents containing a silica activator appeared to be more sensitive to telavancin interference. Telavancin 10 μg/ml was not associated with increased aPTT with any of the reagents tested. Conclusions: Telavancin has the potential to prolong both PT and aPTT in vitro. It is recommended that samples for PT or aPTT be obtained just prior to a telavancin dose (trough).     

Susceptibility of Streptococcus mutans to Antimicrobial Agents

Fifty strains of Streptococcus mutans, including defined strains and clinical isolates, were tested for susceptibility to 20 different antimicrobial agents. Minimal inhibitory concentrations were determined by a liquid microtiter procedure. Antibiotics that were most effective in concentrations below 0.1 μg/ml included penicillin, ampicillin, erythromycin, cephalothin, and methicillin. Antibiotics effective in concentrations between 0.1 μg and 10 μg/ml included rifampin, lincomycin, thiostrepton, spiromycin, vancomycin, streptolydigan, novobiocin, tetracycline, chloramphenicol, spectinomycin, and gentamicin. Antibiotics effective at higher concentrations ranging from 10 μg/ml to 400 μg/ml included the aminoglycosides kanamycin, neomycin, streptomycin, and kasugamycin. Although most antibiotics exhibited inhibitory effects in a narrow range of concentrations, antibiotics such as tetracycline, thiostrepton, and spiromycin had a 1,000-fold range from the lowest to highest concentrations required for growth inhibition.     

Comparative Efficacies of Telavancin and Vancomycin in Preventing Device-Associated Colonization and Infection by Staphylococcus aureus in Rabbits

Telavancin is an investigational lipoglycopeptide antibiotic that is active against gram-positive pathogens. In an in vivo rabbit model, subtherapeutic (15-mg/kg) and therapeutic (30- or 45-mg/kg) doses of telavancin were demonstrated to be noninferior and superior to vancomycin (20 mg/kg), respectively, for preventing subcutaneous implant colonization and infection by Staphylococcus aureus.Estimated annual infection rates in the United States associated with the most commonly used medical devices range from 3% to 8% for central venous catheters, 10% to 30% for bladder catheters, and 5% to 10% for fracture fixation devices (2). Since more than 37 million of these devices are inserted annually, device-associated infections affect millions of patients and, as such, are a major medical and economic issue (2).Telavancin is an investigational lipoglycopeptide, with activity against clinically relevant gram-positive pathogens, including Staphylococcus aureus (8, 9, 15), which is one of the most important bacterial species implicated in the pathogenesis of device-related infections (2). In clinical trials, telavancin has been shown to be efficacious for the treatment of complicated skin and skin structure infections (17-19) as well as hospital-acquired pneumonia (14). The present study provides preclinical evidence that telavancin may also be more efficacious for the prevention of device colonization and infection by gram-positive pathogens than vancomycin. We used vancomycin rather than a β-lactam antibiotic as a control prophylactic agent for the following three reasons. (i) Vancomycin is currently the most commonly used agent for perioperative systemic prophylaxis when inserting surgical implants, regardless of the patient''s status of methicillin-resistant Staphylococcus aureus colonization. (ii) Vancomycin has been reported to be superior to some β-lactam antibiotics in preventing certain postoperative infections. For instance, in a randomized, double-blinded trial by Maki and colleagues, the preoperative prophylactic use of vancomycin in patients embarking on cardiac and vascular operations was more protective against infection than the use of cefazolin or cefamandole. As a result, the authors suggested the use of vancomycin as an antibiotic prophylaxis in prosthetic valve replacement and prosthetic vascular graft implantation to reduce the risk of implant infection (12). (iii) Although both vancomycin and β-lactam antibiotics share with telavancin a rather similar mechanism of action (inhibition of cell wall synthesis), it was important to determine if the two structurally related glycopeptide compounds, vancomycin and telavancin, indeed differ in their efficacies.This study was conducted with prior approval from the appropriate Institutional Animal Care and Use Committee (IACUC). Modifications to a previously described rabbit model of subcutaneous implant colonization and infection by S. aureus were used in these studies (3, 4, 6). In a similar rabbit model that compared vancomycin to dalbavancin, a compound closely related to telavancin, we demonstrated a statistically insignificant trend for lower rates of device colonization in the dalbavancin group than in the vancomycin group. Telavancin was obtained from Theravance, Inc. (South San Francisco, CA), vancomycin from Hospira (Lake Forest, IL), and water with 5% dextrose (D5W) from IVX Animal Health (St. Joseph, MO). In vitro bacterial susceptibility to telavancin and vancomycin was tested, in triplicate, by standard macrodilution (1). We used specific-pathogen-free, 4- to 7-month-old female New Zealand White rabbits, with a body mass of 3 to 4 kg each (Myrtle''s Rabbitry, Thomson Station, TN). Anesthesia was induced by intramuscular injection of xylazine at 6 mg/kg and acepromazine at 2 mg/kg and maintained via inhalation of 0.5% to 2% isoflurane for the duration of the surgery.Anesthetized animals were randomly assigned to one of five treatment groups (nine rabbits each) and injected, intravenously, over a period of ∼2 min, with a single dose of sterile D5W (control), vancomycin (20 mg/kg), or one of three doses of telavancin (15, 30, or 45 mg/kg). Based on previously reported efficacy and exposure data for rabbits (11), this telavancin dose range of 15 to 45 mg/kg for rabbits corresponds to 50% to 150% of the human area under the concentration-time curve-equivalent dose (HED) of 10 mg/kg (10), which is also the recommended human clinical dose (18). The vancomycin dose used in this study was similar to those used in prior rabbit studies, including this particular model (3). Following a surgical procedure described previously (3), six 2-cm-long segments of seven French triple-lumen polyurethane vascular catheters were implanted subcutaneously in the back of each animal, for a total of 54 devices per nine rabbits in each group. The implanted devices were inoculated on the surface directly with 10⁵ CFU (50-μl total inoculum in Trypticase soy broth) using strain P1 of S. aureus, a methicillin-sensitive S. aureus (MSSA) clinical isolate associated with device-related infections that has been used by us and others for studies of medical device colonization (3, 6). The mean MIC and minimal bactericidal concentration of the MSSA P1 strain used in this study were 0.25 μg/ml and 1 μg/ml for telavancin, respectively, and 1 μg/ml and 8 μg/ml for vancomycin, respectively. Surgical wounds were closed, and the animals were observed closely in the operating room until they achieved sternal recumbency. The analgesic/anti-inflammatory agent ketoprofen (3 mg/kg) was given intramuscularly to each rabbit immediately following surgery and as needed thereafter. The animals were monitored daily for signs of pain, distress, erythema, local infection, and sepsis.One week postsurgery, all rabbits were anesthetized and humanely sacrificed. Implanted catheter segments were recovered in a sterile fashion and cultured based on a previously described sonication technique (13, 16). Swab cultures were collected from the soft tissues adjacent to the implantation site or wound drainage, while blood samples were collected by cardiac puncture. The surgical site swabs as well as the blood samples were cultured using standard techniques (4, 5).Device colonization was defined as growth of the inoculated S. aureus strain from the sonication culture of the explanted device. Device-related infection was defined as any growth of the inoculated strain from both the sonication culture of the explanted device and the swab culture of any soft tissue collection or wound site discharge. Explanted devices were sonicated in 2 ml of normal saline, and 200 μl of the sonicate and subsequent dilutions were cultured. As a result, the detectability limit was 10 CFU.The sample size was determined based on our previous experience with this animal model, which showed a 19% reduction in the rate of infection when using dalbavancin rather than vancomycin (3). In this study, we sought a similar magnitude of reduction (19%) in the frequency of infection when using telavancin compared to vancomycin with a power of 80% and a type I error of 5%. Frequencies of device colonization and local device-related infections in the five treatment groups were compared using a two-tailed Fisher''s exact test at an alpha level of 0.05 (Stata statistical software, version 8.2; StataCorp, College Station, TX).The mean MIC and minimal bactericidal concentration of the MSSA P1 strain used in this study were 0.25 μg/ml and 1 μg/ml for telavancin, respectively, and 1 μg/ml and 8 μg/ml for vancomycin, respectively. Blood cultures derived from all groups were sterile, indicating the absence of device-related bacteremia. The frequencies of device colonization and device-associated infection by the inoculated S. aureus strain were significantly higher in the control group than in each of the four treatment groups (Table ​(Table1).1). Preoperative systemic administration of telavancin reduced the rates of S. aureus device colonization and device-associated infection in a dose-related fashion. A subtherapeutic dose of telavancin (15 mg/kg), representing a HED of 4.8 mg/kg, was noninferior to vancomycin at 20 mg/kg in preventing device colonization and device-related infections. Single therapeutic doses of telavancin (30 mg/kg or 45 mg/kg), representing HEDs of 9.6 and 14.4 mg/kg, respectively, were superior to vancomycin (20 mg/kg) at preventing device colonization and device-related infections (Table ​(Table11).

TABLE 1.

Rates of device colonization and device-related infection by S. aureus

A Reference Laboratory Experience of Clinically Achievable Voriconazole,Posaconazole, and Itraconazole Concentrations within the Bloodstream and Cerebral Spinal Fluid

Interest in antifungal therapeutic-drug monitoring has increased due to studies demonstrating associations between concentrations and outcomes. We reviewed the antifungal drug concentration database at our institution to gain a better understanding of achievable triazole drug levels. Antifungal concentrations were measured by high-performance liquid chromatography (HPLC), ultraperformance liquid chromatography and single-quadrupole mass spectrometry (UPLC/MS), or a bioassay. For this study, only confirmed human bloodstream (serum or plasma) and cerebral spinal fluid (CSF) concentrations of voriconazole, posaconazole, and itraconazole were analyzed. The largest numbers of bloodstream and CSF samples were found for voriconazole (14,370 and 173, respectively). Voriconazole bloodstream concentrations within the range of 1 to 5.5 μg/ml represented 50.6% of samples. Levels below the lower limit of quantification (0.2 μg/ml) were observed in 14.6% of samples, and 10.4% of samples had levels of ≥5.5 μg/ml. CSF voriconazole levels ranged from undetectable to 15.3 μg/ml and were <0.2 μg/ml in 11% of samples. Posaconazole bloodstream concentrations were ≥0.7 and ≥1.25 μg/ml in 41.6% and 18.9% of samples, respectively. Posaconazole was detected in only 4 of 22 CSF samples (undetectable to 0.56 μg/ml). Itraconazole levels, as measured by UPLC/MS, were ≥0.5 μg/ml in 43.3% and were undetectable in 33.9% of bloodstream samples. In contrast, when measured by a bioassay, itraconazole/hydroxyitraconazole bloodstream concentrations were ≥1.0 μg/ml in 72.9% of samples and were undetectable in 18% of samples. These results indicate that there is marked variability in bloodstream concentrations achieved with these three azoles. In addition, many levels within the bloodstream for each azole and for voriconazole and posaconazole in the CSF were undetectable or below thresholds associated with efficacy.     

Activity of Telavancin against Staphylococci and Enterococci Determined by MIC and Resistance Selection Studies

This study used CLSI broth microdilution to test the activity of telavancin and comparator antimicrobial agents against 67 methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) isolates. Twenty-six vancomycin-intermediate S. aureus (VISA) strains were among the isolates tested; all strains were susceptible to telavancin at ≤1 μg/ml, whereas 12/26 (46%) of these isolates were nonsusceptible to daptomycin at the same concentration. All strains were susceptible to quinupristin-dalfopristin, while resistance was found to all other drugs tested. Telavancin demonstrated potent activity against all vancomycin-susceptible isolates as well as against heterogeneously VISA and VISA resistance phenotypes. In multistep resistance selection studies, telavancin yielded one stable mutant after 43 days in one MRSA strain out of the 10 MRSA strains tested with the MIC rising eightfold from 0.25 μg/ml (parent) to 2 μg/ml. MICs for this clone did not increase further when passages were continued for the maximum 50 days. In contrast, daptomycin selected stable resistant clones (MIC increase of >4×) after 14 to 35 days in 4 of 10 MRSA strains with MICs increasing from 1 to 2 μg/ml (parents) to 4 to 8 μg/ml (resistant clones). Sequencing analysis of daptomycin resistance determinants revealed point mutations in the mprF genes of all four stable daptomycin-resistant clones. Teicoplanin gave rise to resistant clones after 14 to 21 days in 2 of 10 MRSA strains with MICs rising from 1 to 2 μg/ml (parents) to 4 to 16 μg/ml (stable resistant clones). Linezolid selected stable resistant clones after 22 to 48 days in 2 of 10 MRSA strains with MICs rising from 2 to 4 μg/ml (parents) to 32 μg/ml (resistant clones). Vancomycin yielded no resistant clones in 10 MRSA strains tested; however, MICs increased two- to fourfold from 1 to 8 μg/ml to 2 to 16 μg/ml after 50 days. No cross-resistance was found with any clone/antimicrobial combination. The two enterococci developed resistance to daptomycin, and one developed resistance to linezolid. Single-step mutation frequencies for telavancin (<4.0 × 10⁻¹¹ to <2.9 × 10⁻¹⁰ at 2× MIC) were lower than the spontaneous mutation frequencies obtained with the comparators.Staphylococcus aureus is becoming increasingly resistant to antibiotics. Methicillin (meticillin)-resistant S. aureus (MRSA) strains are increasingly encountered all over the world and cannot be treated with existing ß-lactams. Additionally, the majority of hospital-acquired methicillin-resistant (and also some methicillin-susceptible) strains are resistant to all currently available quinolones. The situation has become more complicated by the appearance of heterogeneously vancomycin-intermediate S. aureus (hVISA) strains, vancomycin-intermediate S. aureus (VISA) strains, and recently nine reported vancomycin-resistant S. aureus (VRSA) strains (1). Two recent papers emphasize the recent spread of VISA strains in Turkey (47) and France (15), and a recent alert from the New York City Department of Health (11) has documented six cases of VISA infections in New York City, NY, between February and October 2007, which led to four fatalities. It seems clear that VISA phenotypes occur everywhere but that they are not being routinely detected due to lack of standardized methodology (1, 20). Recently, Rybak et al. (43) have indicated, with Etest macromethod and population analysis testing, that the incidence of hVISA strains has increased over the past 22 years to an overall incidence of 2.2%. Yusof et al. (55) have recently described the utility of the Etest macromethod using a double-sided vancomycin-teicoplanin Etest strip which accurately differentiates between hVISA and VISA strains. Utilization of the latter method will surely increase reports of the incidence of hVISA and VISA strains. As of this time, the pathogenicity of VRSA strains awaits confirmation.The situation has become further complicated by the appearance and rapid spread, especially in the United States, of community-acquired MRSA strains that are especially virulent, possibly by virtue of production of Panton-Valentine leukocidin (4, 10, 16, 28, 34, 37). Although these strains are currently more susceptible to antimicrobial agents than hospital-acquired strains are, this situation will surely change. Additionally, treatment of the community-acquired MRSA strains with glycopeptides will increase the selective pressure leading to nonsusceptibility to vancomycin and teicoplanin. Recently, we and others have documented clinical development of daptomycin resistance after daptomycin therapy (25), and not all VISA strains are daptomycin susceptible (1, 19, 25, 26). There is an urgent need for new agents to treat MRSA infections.Telavancin is an investigational lipoglycopeptide active (MICs of ≤1 μg/ml) against gram-positive organisms including MRSA (17, 18, 22, 29, 31, 38, 48). Barcia-Macay and coworkers (3) have reported telavancin MICs of 0.5 μg/ml against two strains of VISA and of 2 to 4 μg/ml against two strains of VRSA. Leuthner and coworkers in a study of 50 glycopeptide-nonsusceptible staphylococci and 3 VRSA strains showed telavancin to be potent against all 37 hVISA and VISA strains (13 coagulase-negative strains; resistance phenotypes not differentiated from one another) with MICs of <1 μg/ml, with higher MICs of 2 to 4 μg/ml against the 3 VRSA strains (33). The antibacterial mode of action of telavancin results from inhibition of bacterial cell wall synthesis and interference with the barrier function of the bacterial cell membrane (22). The mode of action of daptomycin also involves targeting the bacterial cell membrane to initiate antimicrobial activity (2, 24, 26). This fact is supported by the involvement of staphylococcal genes regulating cell membrane surface charge (e.g., mprF) (39) and fatty acid synthesis (e.g., yycG) (36) in the development of daptomycin nonsusceptibility.In an effort to expand the comparative activity of telavancin against MRSA strains of various resistance phenotypes, we have investigated the activity of telavancin against MRSA strains by determining the activities of telavancin and comparator agents against 67 vancomycin-susceptible and -nonsusceptible MRSA strains using broth microdilution and also by testing the potential of telavancin and the comparator agents vancomycin, teicoplanin, daptomycin, and linezolid to select for resistance in 10 MRSA strains as well as two strains of enterococci by single-step and multistep selection methodology. Additionally, we conducted molecular genetic studies to characterize the mechanism(s) of daptomycin resistance in isolated clones.(Part of this study was presented at the 48th Interscience Conference on Antimicrobial Agents and Chemotherapy and the 46th Annual Meeting of the Infectious Disease Society of America, a joint meeting held in Washington, DC, in 2008 [12].)     

Telavancin Demonstrates Activity against Methicillin-Resistant Staphylococcus aureus Isolates with Reduced Susceptibility to Vancomycin,Daptomycin, and Linezolid in Broth Microdilution MIC and One-Compartment Pharmacokinetic/Pharmacodynamic Models

Methicillin-resistant Staphylococcus aureus (MRSA) isolates have arisen with reduced susceptibility to several anti-MRSA agents. Telavancin (TLV), a novel anti-MRSA agent, retains low MICs against these organisms. Our objective was to determine the MICs for TLV, daptomycin (DAP), vancomycin (VAN), and linezolid (LZD) against daptomycin-nonsusceptible (DNS) S. aureus, vancomycin-intermediate S. aureus (VISA), heteroresistant VISA (hVISA), and linezolid-resistant (LZD^r) S. aureus. We also evaluated these agents against each phenotype in pharmacokinetic/pharmacodynamic (PK/PD) models. Seventy DNS, 100 VISA, 180 hVISA, and 25 LZD^r MRSA isolates were randomly selected from our library and tested to determine their MICs against TLV, DAP, VAN, and LZD via broth microdilution and a Trek panel. Four isolates were randomly selected for 168-h in vitro models to evaluate treatment with TLV at 10 mg/kg of body weight/day, DAP at 10 mg/kg/day, VAN at 1 g every 12 h (q12h), and LZD at 600 mg q12h. The MIC_50/90 for TLV, DAP, VAN, and LZD against 70 DNS S. aureus isolates were 0.06/0.125 μg/ml, 2/4 μg/ml, 1/2 μg/ml, and 2/2 μg/ml, respectively. Against 100 VISA isolates, the MIC_50/90 were 0.06/0.125 μg/ml, 1/1 μg/ml, 4/8 μg/ml, and 1/2 μg/ml, respectively. Against 170 hVISA isolates, the MIC_50/90 were 0.06/0.125 μg/ml, 0.5/1 μg/ml, 1/2 μg/ml, and 1/2 μg/ml, respectively. Against 25 LZD^r isolates, the MIC_50/90 were 0.03/0.06 μg/ml, 1/1 μg/ml, 2/2 μg/ml, and 8/8 μg/ml, respectively. The TLV MIC was >0.125 μg/ml for 10/365 (2.7%) isolates. In PK/PD models, TLV was universally bactericidal at 168 h and statistically superior to all antibiotics against DNS S. aureus strain R2334. These data further establish the potency of TLV against resistant MRSA. The model data demonstrate in vitro bactericidal activity of TLV against hVISA, VISA, DNS S. aureus, and LZD^r S. aureus strains. Further clinical research is warranted.     

Efficacy of telavancin in the treatment of experimental endocarditis due to glycopeptide-intermediate Staphylococcus aureus

The efficacy of telavancin, a novel lipoglycopeptide, was evaluated in experimental endocarditis in rabbits using two clinical isolates of glycopeptide-intermediate Staphylococcus aureus: ATCC 700788 and HIP 5836. Infected rabbits were treated for 2 days with telavancin (10 mg/kg of body weight once daily intravenously) or vancomycin (1 g twice daily intravenously), administered with a computer-controlled infusion pump system simulating human serum kinetics. Vegetations were harvested at 16 h postinoculation in the control group and at the end of treatment in the drug-treated group. For ATCC 700788, MICs and minimal bactericidal concentrations (MBCs), respectively, were 1 mg/liter and 4 mg/liter for telavancin and 8 mg/liter and 128 mg/liter for vancomycin. For HIP 5836, MICs and MBCs, respectively, were 4 mg/liter and 8 mg/liter for telavancin and 8 mg/liter and 128 mg/liter for vancomycin. Peak and trough levels were 90 microg/ml and 6 microg/ml, respectively, for telavancin and 46 microg/ml and 6 microg/ml, respectively, for vancomycin. In glycopeptide-intermediate S. aureus ATCC 700788, telavancin sterilized 6 of 16 vegetations (37%), whereas vancomycin sterilized 4 of 20 (20%) (P = 0.29) compared with 0 of 17 in the control group. In HIP 5836 experiments, telavancin and vancomycin sterilized 5 of 16 (31%) and 1 of 15 (7%) vegetations (P = 0.17), respectively, compared with none in the control group. Telavancin reduced vegetation titers by 2.0 and 2.3 logs greater than vancomycin for the ATCC 700788 (4.6 [2.0 to 5.8] versus 6.6 [2.0 to 6.9] log CFU/g vegetation; P = 0.05) and HIP 5836 (4.4 [2.0 to 7.4] versus 6.7 [4.5 to 8.7] log CFU/g vegetation; P = 0.09) strains, respectively; these differences did not reach statistical significance. All isolates from vegetations remained susceptible to telavancin after therapy. The results suggest that telavancin may be an effective treatment for endocarditis caused by glycopeptide-intermediate S. aureus.     

Comparative activity of the new lipoglycopeptide telavancin in the presence and absence of serum against 50 glycopeptide non-susceptible staphylococci and three vancomycin-resistant Staphylococcus aureus

BACKGROUND: Telavancin, a new multifunctional lipoglycopeptide antibiotic, exhibits broad-spectrum Gram-positive activity against a variety of pathogens. We examined the effects of human serum and antimicrobial concentrations on the activity of telavancin against glycopeptide-intermediate staphylococcal species (GISS), heteroresistant GISS (hGISS) and three vancomycin-resistant Staphylococcus aureus (VRSA) compared with vancomycin, quinupristin/dalfopristin, linezolid and daptomycin. METHODS: MIC and MBCs were performed against all antimicrobials. Time-kill experiments were performed using two strains of GISS (Mu50; NJ992) and VRSA (VRSAMI; VRSAPA) at 1, 2, 4, 8, 16 and 32x MIC. Telavancin and daptomycin were evaluated in the presence and absence of serum. RESULTS: All GISS and hGISS were susceptible to the tested agents with telavancin and quinupristin/dalfopristin demonstrating the lowest MIC, followed by daptomycin, linezolid and vancomycin. Against VRSA, daptomycin and quinupristin/dalfopristin had the lowest MIC, followed by linezolid, telavancin and vancomycin. In the presence of serum, telavancin and daptomycin MICs increased 1- to 4-fold. Concentration-dependent activity was demonstrated by telavancin and daptomycin, in the presence and absence of serum. Telavancin and daptomycin were bactericidal against GISS and performed similarly in the presence of serum. Quinupristin/dalfopristin demonstrated bactericidal activity at clinically achievable concentrations, whereas linezolid was bacteriostatic. CONCLUSIONS: Telavancin demonstrated concentration-dependent bactericidal activity against GISS, hGISS and VRSA at concentrations equal to or above 4x MIC, which corresponds to therapeutic levels against GISS and clinically achieved concentrations against the VRSA. Similar to daptomycin, telavancin activity was diminished in the presence of serum but bactericidal activity was maintained. Further investigation with telavancin against GISS, hGISS and VRSA is warranted.     

In vitro activities of dalbavancin and nine comparator agents against anaerobic gram-positive species and corynebacteria

Dalbavancin is a novel semisynthetic glycopeptide with enhanced activity against gram-positive species. Its comparative in vitro activities and those of nine comparator agents, including daptomycin, vancomycin, linezolid, and quinupristin-dalfopristin, against 290 recent gram-positive clinical isolates strains, as determined by the NCCLS agar dilution method, were studied. The MICs of dalbavancin at which 90% of various isolates tested were inhibited were as follows: Actinomyces spp., 0.5 μg/ml; Clostridium clostridioforme, 8 μg/ml; C. difficile, 0.25 μg/ml; C. innocuum, 0.25 μg/ml; C. perfringens, 0.125 μg/ml; C. ramosum, 1 μg/ml; Eubacterium spp., 1 μg/ml; Lactobacillus spp., >32 μg/ml, Propionibacterium spp., 0.5 μg/ml; and Peptostreptococcus spp., 0.25 μg/ml. Dalbavancin was 1 to 3 dilutions more active than vancomycin against most strains. Dalbavancin exhibited excellent activity against gram-positive strains tested and warrants clinical evaluation.     

Susceptibilities of Penicillin- and Erythromycin-Susceptible and -Resistant Pneumococci to HMR 3647 (RU 66647), a New Ketolide, Compared with Susceptibilities to 17 Other Agents

Susceptibility of 230 penicillin- and erythromycin-susceptible and -resistant pneumococci to HMR 3647 (RU 66647), a new ketolide, was tested by agar dilution, and results were compared with those of erythromycin, azithromycin, clarithromycin, roxithromycin, rokitamycin, clindamycin, pristinamycin, ciprofloxacin, sparfloxacin, trimethoprim-sulfamethoxazole, doxycycline, chloramphenicol, cefuroxime, ceftriaxone, imipenem, and vancomycin. HMR 3647 was very active against all strains tested, with MICs at which 90% of the strains were inhibited (MIC₉₀s) of 0.03 μg/ml for erythromycin-susceptible strains (MICs, ≤0.25 μg/ml) and 0.25 μg/ml for erythromycin-resistant strains (MICs, ≥1.0 μg/ml). All other macrolides yielded MIC₉₀s of 0.03 to 0.25 and >64.0 μg/ml for erythromycin-susceptible and -resistant strains, respectively. The MICs of clindamycin for 51 of 100 (51%) erythromycin-resistant strains were ≤0.125 μg/ml. The MICs of pristinamycin for all strains were ≤1.0 μg/ml. The MIC₉₀s of ciprofloxacin and sparfloxacin were 4.0 and 0.5 μg/ml, respectively, and were unaffected by penicillin or erythromycin susceptibility. Vancomycin and imipenem inhibited all strains at ≤1.0 μg/ml. The MICs of cefuroxime and cefotaxime rose with those of penicillin G. The MICs of trimethoprim-sulfamethoxazole, doxycycline, and chloramphenicol were variable but were generally higher in penicillin- and erythromycin-resistant strains. HMR 3647 had the best kill kinetics of all macrolides tested against 11 erythromycin-susceptible and -resistant strains, with uniform bactericidal activity (99.9% killing) after 24 h at two times the MIC and 99% killing of all strains at two times the MIC after 12 h for all strains. Pristinamycin showed more rapid killing at 2 to 6 h, with 99.9% killing of 10 of 11 strains after 24 h at two times the MIC. Other macrolides showed significant activity, relative to the MIC, against erythromycin-susceptible strains only.