Understanding factors associated with de novo daptomycin-nonsusceptible Enterococcus (DNSE) infections will aid in better understanding the mechanisms of daptomycin nonsusceptibility. We conducted a case-control study to compare patients with DNSE infections who were daptomycin treatment naïve (n = 9) and those with DNSE infections who had exposure to daptomycin (n = 13). Less frequent exposure to antimicrobials, increased susceptibility to nitrofurantoin and gentamicin, and shorter duration of hospitalization were associated with de novo DNSE infection, suggesting a potential community reservoir.
Daptomycin efficacy against clinical isolates of Enterococcus faecalis, Enterococcus faecium, and a lab-derived daptomycin-resistant isolate of E. faecalis was investigated in a mouse model of renal infection. The daptomycin MICs against these enterococci ranged from 0.5 to 50 μg/ml. The objective of this study was to determine the relationship between the MICs of drugs against E. faecalis and E. faecium and the level of daptomycin exposure needed to evaluate the drug's efficacy. Correlating the required therapeutic exposures of mice with the exposures achieved clinically allowed us to project enterococcal breakpoint values. Mice pretreated with carrageenan were infected intravenously with 3 × 108 to 4 × 108 CFU of E. faecalis or E. faecium. Daptomycin (5 to 50 mg of drug/kg of body weight) or saline control was administered 4 h postinfection and continued once daily for 2 days (three total doses). On day 4, infected kidneys were harvested, homogenized, and dilution plated. Efficacy was defined as a ≥2-log10 (99%) reduction in bacterial burden in infected kidneys. At clinically relevant dosages and exposures (area under the curve, 400 to 600 μg · hr/ml), daptomycin demonstrated similar and marked efficacy against all clinical enterococcal isolates tested. Daptomycin achieved efficacy with comparable doses against both vancomycin-sensitive (MIC, ≤4 μg/ml) and -resistant enterococcal strains tested. Efficacy was also established against the lab-derived daptomycin-resistant E. faecalis isolate. In this murine renal infection model, clinically relevant exposures of daptomycin were effective against E. faecalis and E. faecium strains for which MICs were ≤8 μg/ml. These murine efficacy data for daptomycin, along with surveillance data and human pharmacokinetic exposures achieved, suggest a breakpoint concentration value of ≤8 μg/ml (susceptible) and ≥16 μg/ml (resistant) for daptomycin against E. faecium and E. faecalis.
Potential emergence of enterococcal daptomycin nonsusceptibility among patients with no prior exposure to daptomycin poses clinical and public health challenges. We found that development of infections with daptomycin-nonsusceptible enterococci in these patients could be associated with sporadic emergence and clonal spread.
Daptomycin; bacteria; enteric infections; Enterococcus; drug resistance; nonsusceptibility; antimicrobial resistance
Daptomycin MICs for enterococci are typically 1- to 2-fold higher than those for Staphylococcus aureus, and there is an imminent need to establish the optimal dose for appropriate treatment of enterococcal infections. We investigated the bactericidal activity of daptomycin at various dose exposures compared to that of linezolid against vancomycin-resistant enterococcus (VRE) in an in vitro pharmacokinetic/pharmacodynamic model utilizing simulated endocardial vegetations over 96 h. Daptomycin at doses of 6, 8, 10, and 12 mg/kg of body weight/day and linezolid at a dose of 600 mg every 12 h were evaluated against two clinical vancomycin-resistant Enterococcus faecium strains (EFm11499 and 09-184D1051), one of which was linezolid resistant (09-184D1051), and one clinical vancomycin-resistant Enterococcus faecalis strain (EFs11496). Daptomycin MICs were 4, 2, and 0.5 μg/ml for EFm11499, 09-184D1051, and EFs11496, respectively. Bactericidal activity, defined as a ≥3 log10 CFU/g reduction from the initial colony count, was demonstrated against all three isolates with all doses of daptomycin; however, bactericidal activity was not sustained with the daptomycin 6- and 8-mg/kg/day regimens. Linezolid was bacteriostatic against EFm11499 and displayed no appreciable activity against 09-184D1051 or EFs11496. Concentration-dependent killing was displayed with more sustained reduction in colony count (3.58 to 6.46 and 5.89 to 6.56 log10 CFU/g) at 96 h for the simulated regimen of daptomycin at doses of 10 and 12 mg/kg/day, respectively (P ≤ 0.012). No E. faecium mutants with reduced susceptibility were recovered at any dosage regimen; however, the E. faecalis strain developed reduced daptomycin susceptibility with daptomycin at 6, 8, and 10 but not at 12 mg/kg/day. Daptomycin displayed a dose-dependent response against three VRE isolates, with high-dose daptomycin producing sustained bactericidal activity. Further research is warranted.
Initial clinical trials with daptomycin (2 mg/kg per day) were prematurely suspended because of unexplained treatment failures in patients with bacteremia who were treated with daptomycin, despite in vitro data indicating that the gram-positive cocci causing the infection were susceptible to daptomycin. One explanation for these clinical failures may relate to the relatively high degree of daptomycin protein binding (94%). To evaluate the impact of protein on daptomycin activity, a two-chamber in vitro pharmacodynamic model was used to study and compare the interaction between Staphylococcus aureus (clinical isolate) and either daptomycin or vancomycin, each in the presence and absence of physiologic human albumin concentrations. Low-dose (2 mg/kg) daptomycin, high-dose (6 mg/kg) daptomycin, and 10 mg of vancomycin per kg beta-phase elimination serum-concentration-versus-time curves were simulated by using this in vitro pharmacodynamic model. The bacterial kill rates by all three regimens were decreased in the presence of albumin (P less than 0.0002). The average times required for a 99% kill of the initial S. aureus inocula (approximately 5 x 10(7) CFU/ml) without albumin were 0.81 (low-dose daptomycin), 0.33 (high-dose daptomycin), and 6.18 (vancomycin) h. The average times required for a 99% kill of S. aureus with albumin were 7.66 (low-dose daptomycin), 0.95 (high-dose daptomycin), and 10.52 (vancomycin) h. These data demonstrate that, depending on the concentration of daptomycin, the presence of albumin can profoundly diminish the bactericidal activity of daptomycin.
To describe the patient populations and infections being treated with daptomycin, as well as the efficacy and safety outcomes.
Patients and methods
Data from the European Cubicin Outcomes Registry and Experience (EU-CORESM), retrospectively collected at 118 institutions between January 2006 and August 2008, were analysed.
Daptomycin treatment was documented in 1127 patients with diverse infections, including complicated skin and soft tissue infections (33%), bacteraemia (22%), endocarditis (12%) and osteomyelitis (6%). It was used empirically, before microbiological results became available, in 53% of patients. Staphylococcus aureus was the most common pathogen (34%), with 52% of isolates resistant to methicillin; coagulase-negative staphylococci and enterococci were also frequent, with 22% of Enterococcus faecium isolates resistant to vancomycin. Daptomycin was used as first-line therapy in 302 (27%) patients. When used second line, the most common reasons for discontinuation of previous antibiotic were treatment failure and toxicity or intolerance. The use of concomitant antibiotics was reported in 65% of patients. Most frequent doses were 6 mg/kg (47%) and 4 mg/kg (32%). The median duration of daptomycin therapy was 10 days (range 1–246 days) in the inpatient setting and 13 days (range 2–189 days) in the outpatient setting. The overall clinical success rate was 79%, with a clinical failure rate of <10% for all infection types. Low failure rates were observed in first- and second-line therapy (6% and 8%, respectively). Daptomycin demonstrated a favourable safety and tolerability profile regardless of treatment duration.
Daptomycin has a relevant role in the treatment of Gram-positive infections.
cyclic lipopeptide; Gram-positive infections; registry
Daptomycin is a lipopeptide antibiotic with activity against several important gram-positive bacterial pathogens, including drug-resistant staphylococci and enterococci. Because the mechanism of action of daptomycin is calcium-dependent depolarization of the cell membrane, susceptibility testing requires medium supplemented with a physiological level of calcium. This study assessed two Food and Drug Administration-cleared commercial test devices for determination of daptomycin MICs, Etest and JustOne. A collection of 220 selected isolates, including Staphylococcus aureus, coagulase-negative staphylococci, Enterococcus faecalis, E. faecium, E. avium, E. durans, E. casseliflavus, and E. gallinarum, were tested by both methods. Included in the collection were 22 S. aureus and 14 Enterococcus sp. isolates that were recovered from patients and were nonsusceptible on the basis of the daptomycin MICs. As the reference method for comparison, all isolates were tested by the Clinical and Laboratory Standards Institute broth microdilution method incorporating cation-adjusted Mueller-Hinton broth with 50 μg/ml calcium. Daptomycin MICs agreed, within 1 twofold dilution, for 97% of the isolates by Etest and for 100% by JustOne. However, daptomycin MICs determined by Etest were 1 dilution lower than the reference MICs for 65% of the Enterococcus sp. isolates tested. This resulted in 28.5% very major (VM) errors (4/14) with enterococci (all E. faecium) but none (0/22) with staphylococci. Use of JustOne yielded MICs that were 1 dilution lower than the reference MICs for 69% of the staphylococci and 25% of the enterococci. This resulted in 13.6% VM errors (3/22) with staphylococci and 14.3% VM errors (2/14) with enterococci. The manufacturer-recommended JustOne inoculum preparation resulted in mean colony counts of only 5 × 104 to 1 × 105 CFU/ml in the wells of the strip. Increasing the inoculum to 3 × 105 to 4 × 105 CFU/ml eliminated two of five VM errors upon retesting. No major interpretive errors occurred with either device. In summary, daptomycin MICs generated by the Etest or JustOne method generally agreed within 1 dilution of the reference daptomycin MICs. However, both devices produced slightly lower MICs that resulted in some VM errors.
Daptomycin, a new cyclic lipopeptide, was recently approved for the treatment of infections by gram-positive organisms, including infections with methicillin-resistant Staphylococcus aureus (MRSA). A patient infected with infected with MRSA developed resistance to daptomycin after prolonged exposure, which resulted in clinical failure. Clinicians should be aware of the possibility of daptomycin resistance and should consider routine testing for daptomycin susceptibility.
We examined sequential methicillin-susceptible Staphylococcus aureus isolates from a patient with mitral valve endocarditis recovered during persistent bacteremia on standard therapy and relapse after treatment with daptomycin. An isolate obtained after 5 days of antimicrobial therapy, but before exposure to daptomycin, showed subtle physiological changes in response to daptomycin, with significant regrowth in the daptomycin killing assay compared to the treatment-naive strain. Once daptomycin was started, the population became more heterogeneous and tested as nonsusceptible. These organisms were examined in a simulated-vegetation in vitro pharmacodynamic model, which confirmed progressive decreases in killing with daptomycin concentrations that simulate those attained in humans with 6-mg/kg of body weight daily dosing. Early surgical intervention or combination therapy or both might have prevented the loss of daptomycin susceptibility.
Daptomycin is a rapidly bactericidal agent with broad coverage against Gram-positive organisms, including Staphylococcus aureus, the most frequent cause of osteomyelitis. The objective of this study was to describe the clinical outcome of patients with non-hardware associated osteomyelitis, and the safety profile of daptomycin in the treatment of these infections.
All patients with osteomyelitis, excluding concurrent orthopedic foreign body infections, treated with daptomycin and identified between 2007–2008 in a retrospective, multicenter, observational registry, were included. Investigators assessed patient outcome (cured, improved, failed, non-evaluable) at the end of daptomycin therapy. Patients with a successful outcome at the end of daptomycin therapy were reassessed in 2009. All patients were included in the safety analysis; evaluable patients were included in the efficacy analysis. Data was assessed using descriptive statistics. A Kaplan Meier analysis was used to assess time to clinical failure.
Two-hundred and nine osteomyelitis patients successfully completed daptomycin therapy in 2007–2008, 71 of which (34%) had a follow-up visit in 2009 and had an evaluable clinical outcome. The median (min, max) daptomycin dose and duration were 6 mg/kg (4, 10) and 42 days (1, 88), respectively. Of the 52 patients with a documented pathogen, S. aureus was the most common (42%); primarily methicillin-resistant S. aureus. All patients were included in the safety analysis; evaluable patients were included in the efficacy analysis. Clinical resolution was reported in 94% (CI - 86.2%, 98.44%) of patients. A Kaplan Meier analysis of time to clinical failure showed that approximately 85% (CI – 64%, 95%) of patients had a continued successful outcome at the time of re-evaluation. Eighteen patients (25%) in the safety population experienced an adverse event; 13 patients (18%) had an adverse event that was possibly-related to daptomycin treatment.
Daptomycin appears to be an effective therapeutic choice with an acceptable safety profile in the management of osteomyelitis that does not involve hardware.
Daptomycin is a lipopeptide with bactericidal activity that acts on the cell membrane of enterococci and is often used off-label to treat patients infected with vancomycin-resistant enterococci. However, the emergence of resistance to daptomycin during therapy threatens its usefulness.
We performed whole-genome sequencing and characterization of the cell envelope of a clinical pair of vancomycin-resistant Enterococcus faecalis isolates from the blood of a patient with fatal bacteremia; one isolate (S613) was from blood drawn before treatment and the other isolate (R712) was from blood drawn after treatment with daptomycin. The minimal inhibitory concentrations (MICs) of these two isolates were 1 and 12 μg per milliliter, respectively. Gene replacements were made to exchange the alleles found in isolate S613 with those in isolate R712.
Isolate R712 had in-frame deletions in three genes. Two genes encoded putative enzymes involved in phospholipid metabolism, GdpD (which denotes glycerophosphoryl diester phosphodiesterase) and Cls (which denotes cardiolipin synthetase), and one gene encoded a putative membrane protein, LiaF (which denotes lipid II cycle-interfering antibiotics protein but whose exact function is not known). LiaF is predicted to be a member of a three-component regulatory system (LiaFSR) involved in the stress-sensing response of the cell envelope to antibiotics. Replacement of the liaF allele of isolate S613 with the liaF allele from isolate R712 quadrupled the MIC of daptomycin, whereas replacement of the gdpD allele had no effect on MIC. Replacement of both the liaF and gdpD alleles of isolate S613 with the liaF and gdpD alleles of isolate R712 raised the daptomycin MIC for isolate S613 to 12 μg per milliliter. As compared with isolate S613, isolate R712 — the daptomycin-resistant isolate — had changes in the structure of the cell envelope and alterations in membrane permeability and membrane potential.
Mutations in genes encoding LiaF and a GdpD-family protein were necessary and sufficient for the development of resistance to daptomycin during the treatment of vancomycin-resistant enterococci. (Funded by the National Institute of Allergy and Infectious Diseases and the National Institutes of Health.)
Daptomycin is a cyclic lipopeptide with potent activity and broad spectrum against Gram-positive bacteria currently used for the treatment of complicated skin and skin structure infections and bacteremia, including right sided endocarditis. We evaluated the in vitro activity of this compound and selected comparator agents tested against clinical strains of staphylococci and enterococci collected in European medical centers in 2005.
A total of 4,640 strains from 23 medical centers located in 10 European countries, Turkey and Israel (SENTRY Program platform) were tested for susceptibility by reference broth microdilution methods according to Clinical and Laboratory Standards Institute guidelines and interpretative criteria. Mueller-Hinton broth was supplemented to 50 mg/L Ca++ for testing daptomycin. Results for oxacillin (methicillin)-resistant staphylococci and vancomycin-resistant enterococci were analyzed separately.
Oxacillin resistance rates among Staphylococcus aureus varied from 2.1% in Sweden to 42.5% in the United Kingdom (UK) and 54.7% in Ireland (29.1% overall), while vancomycin resistance rates varied from 0.0% in France, Sweden and Switzerland to 66.7% in the UK and 71.4% in Ireland among Enterococcus faecium (17.9% overall). All S. aureus strains were inhibited at daptomycin MIC of 1 mg/L (MIC50/90, 0.25/0.5 mg/L; 100.0% susceptible) and only one coagulase-negative staphylococci strain (0.1%) showed an elevated (>1 mg/L) daptomycin MIC value (4 mg/L). Among E. faecalis (MIC50/90, 0.5/1 mg/L; 100% susceptible) the highest daptomycin MIC value was 2 mg/L; while among E. faecium (MIC50/90, 2/4 mg/L; 100% susceptible) the highest MIC result was 4 mg/L.
Daptomycin showed excellent in vitro activity against staphylococci and enterococci collected in European medical centers in 2005 and resistance to oxacillin, vancomycin or quinupristin/dalfopristin did not compromise its activity overall against these pathogens. Based on these results and those of previous publications, daptomycin appears to be an excellent therapeutic option for serious infections caused by oxacillin-resistant staphylococci and vancomycin-resistant enterococci in Europe.
Antibiotic lock therapy (ALT) is an adjunctive procedure to prevent or treat central venous catheter infections, ensuing catheter-related bacteremia, and catheter-related metastatic infections. Daptomycin is a cyclic lipopeptide that is rapidly bactericidal against methicillin-susceptible and -resistant Staphylococcus aureus. The efficacies of daptomycin against central venous catheter biofilms, catheter-related bacteremia, and catheter-related metastatic infections were evaluated by adapting a previously reported central venous catheter biofilm model in rats. Combined daptomycin ALT and systemic dosing resulted in the clearance of an established in vivo S. aureus central venous catheter biofilm after just two daily ALT treatments (30 min with daptomycin at 5 mg/ml) with concurrent systemic daptomycin dosing (40 mg/kg of body weight/day subcutaneously [s.c.]; equivalent exposure of 6 mg/kg/day in people). Daptomycin ALT solutions formulated in either saline or lactated Ringer's solution were equally fast in eradicating established in vivo methicillin-resistant Staphylococcus epidermidis (MRSE) central venous catheter biofilms. However, the lactated Ringer's formulation was superior to that of saline in sustaining the bacterial clearance of treated central venous catheters (83% versus 50%). In MRSE-infected central venous catheter studies, 3 days of daptomycin or vancomycin ALT (18 h at 5 mg/ml) with systemic s.c. dosing (40 mg/kg/day daptomycin or 100 mg/kg/day vancomycin) was equally effective 1 week posttherapy in maintaining cleared central venous catheters (90% [n = 10] versus 100% [n = 8]). These results suggest that daptomycin ALT, along with systemic dosing, could be an effective treatment option for the prevention or eradication of staphylococcal central venous catheter biofilm infections, thereby reducing the occurrence of catheter-related bacteremia or catheter-related metastatic infections.
The suppression of bacterial growth that persists after brief exposure to antimicrobial agents has been termed the postantibiotic effect (PAE). This pharmacodynamic interaction varies for each microorganism-antimicrobial agent combination. Daptomycin (LY146032) is a new lipopeptide antibiotic with activity against gram-positive organisms. We studied the in vitro bactericidal activities and PAEs of the following drugs: daptomycin compared with penicillin G and vancomycin, without and with gentamicin against Enterococcus faecalis strains; daptomycin compared with nafcillin and vancomycin against methicillin-susceptible Staphylococcus aureus strains; and daptomycin compared with vancomycin against methicillin-resistant S. aureus strains. Daptomycin, alone and when used in combination with gentamicin, exhibited greater bactericidal activity and in general produced a longer PAE than standard effective regimens against the organism strains studied.
Staphylococcus aureus bacteremia is a common disease with a high risk of mortality and complications. An increasing proportion of cases are methicillin-resistant S.aureus (MRSA), and methicillin-resistance is being observed from both community-acquired bacteremias and in healthcare-associated infections. The duration of bacteremia and transesophageal echocardiographic findings are useful in predicting the likelihood of complications including endocarditis. Therapy with vancomycin has been the mainstay in the treatment of MRSA bacteremias, but is associated with a long duration of bacteremia on therapy and relapses. Loss of susceptibility to vancomycin, due to thickened cell walls and through the acquisition of the vanA gene, has been described. Daptomycin is newly approved lipopeptide that is highly bactericidal against most strains of MRSA. In a randomized trial, daptomycin was demonstrated to be effective in the treatment of S. aureus bacteremia and right-sided endocarditis. However treatment failures associated with isolates with daptomycin non-susceptibility are reported, and there is a correlation between isolates with reduced vancomycin susceptibility and reduced daptomycin susceptibility. Daptomycin is a useful alternative to vancomycin in the therapy of MRSA bacteremia and endocarditis. However the appropriate role of daptomycin in optimizing therapy with MRSA bacteremia and endocarditis remains to be elucidated.
methicillin-resistant Staphylococcus aureus; bacteremia; endocarditis; daptomycin
The emergence of multidrug-resistant enterococci as a leading cause of hospital-acquired infection is an important public health concern. Little is known about the genetic mechanisms by which enterococci adapt to strong selective pressures, including the use of antibiotics. The lipopeptide antibiotic daptomycin is approved to treat Gram-positive bacterial infections, including those caused by enterococci. Since its introduction, resistance to daptomycin by strains of Enterococcus faecalis and Enterococcus faecium has been reported but is still rare. We evolved daptomycin-resistant strains of the multidrug-resistant E. faecalis strain V583. Based on the availability of a fully closed genome sequence for V583, we used whole-genome resequencing to identify the mutations that became fixed over short time scales (∼2 weeks) upon serial passage in the presence of daptomycin. By comparison of the genome sequences of the three adapted strains to that of parental V583, we identified seven candidate daptomycin resistance genes and three different mutational paths to daptomycin resistance in E. faecalis. Mutations in one of the seven candidate genes (EF0631), encoding a putative cardiolipin synthase, were found in each of the adapted E. faecalis V583 strains as well as in daptomycin-resistant E. faecalis and E. faecium clinical isolates. Alleles of EF0631 from daptomycin-resistant strains are dominant in trans and confer daptomycin resistance upon a susceptible host. These results demonstrate a mechanism of enterococcal daptomycin resistance that is genetically distinct from that occurring in staphylococci and indicate that enterococci possessing alternate EF0631 alleles are selected for during daptomycin therapy. However, our analysis of E. faecalis clinical isolates indicates that resistance pathways independent from mutant forms of EF0631 also exist.
In a prospective, randomized trial, daptomycin was non-inferior to standard therapy for Staphylococcus aureus bacteraemia and right-sided endocarditis. Since rates of infection due to methicillin-resistant S. aureus (MRSA) infection are increasing and treatment outcomes for bacteraemia caused by MRSA are generally worse than those observed with methicillin-susceptible S. aureus bacteraemia, clinical characteristics and treatment results in the trial’s pre-specified subset of patients with MRSA were analysed.
Clinical characteristics and outcomes of patients receiving daptomycin were compared with those receiving vancomycin plus low-dose gentamicin. Success was defined as clinical improvement with clearance of bacteraemia among patients who completed adequate therapy, received no potentially effective non-study antibiotics and had negative blood cultures 6 weeks after end of therapy.
Twenty of the 45 (44.4%) daptomycin patients and 14 of the 43 (32.6%) vancomycin/gentamicin patients were successfully treated (difference 11.9%; confidence interval −8.3 to 32.1). Success rates for daptomycin versus vancomycin/gentamicin were 45% versus 27% in complicated bacteraemia, 60% versus 45% in uncomplicated bacteraemia and 50% versus 50% in right-sided MRSA endocarditis. Cure rates in patients with septic emboli and in patients who received pre-enrolment vancomycin were similar between treatment groups. However, in both treatment groups, success rates were lower in the elderly (≥75 years). Persisting or relapsing bacteraemia occurred in 27% of daptomycin and 21% of vancomycin/gentamicin patients; among these patients, MICs of ≥2 mg/L occurred in five daptomycin and four vancomycin/gentamicin patients. The clinical course of several patients may have been influenced by lack of surgical intervention.
Daptomycin was an effective alternative to vancomycin/gentamicin for MRSA bacteraemia or right-sided endocarditis.
MRSA; endovascular infections; bloodstream infections; combination therapy; clinical trial
This study identified optimal daptomycin dosing for patients receiving thrice-weekly hemodialysis (HD). Twelve adult patients on HD received daptomycin at 6 mg/kg of body weight intravenously (i.v.) one time; plasma and dialysate samples were collected over 3 days. A 2-compartment model with separate HD and non-HD clearance terms was fit to the data. A series of 9,999-subject Monte Carlo simulations (MCS) was performed to identify HD dosing schemes providing efficacy and toxicity profiles comparable to those obtained for MCS employing the daptomycin population pharmacokinetic (PK) model derived from patients in the Staphylococcus aureus bacteremia-infective endocarditis (SAB-IE) study. For efficacy, we selected the HD dosing scheme which generated an area-under-the-curve (AUC) exposure profile comparable to that for the SAB-IE population model. For toxicity, we selected HD dosing schemes that minimized trough concentrations of ≥24.3 mg/liter. Separate HD dosing schemes were developed for each FDA-approved regimen and for two weekly interdialytic periods (48 and 72 h). Administration of the same parent daptomycin dose intra-HD and post-HD resulted in AUC, maximum concentration of drug in serum (Cmax), and Cmin values most comparable to those for SAB-IE simulations for the 48-hour interdialytic period. In contrast, all candidate HD dosing schemes provided AUC48-72 values that were at least 50% lower than the SAB-IE AUC48-72 values. Increasing the parent dose by 50% provided more comparable AUC48-72 values while maintaining acceptable Cmin values. Administration of the daptomycin parent dose intra-HD or post-HD was optimal for the 48-h interdialytic period. For the 72-h interdialytic period, clinicians should consider increasing the dose by 50% to achieve more comparable AUC48-72 values.
Nosocomial infections caused by enterococci present a challenge for clinicians because treatment options are often limited due to the widespread occurrence of strains resistant to multiple antibiotics, including vancomycin. Daptomycin is a first-in-class cyclic lipopeptide that has proven efficacy for the treatment of Gram-positive infections. Although methicillin-resistant Staphylococcus aureus has been the most prominent target in the clinical development of daptomycin, this agent has demonstrated potent bactericidal activity in enterococcal infection models and has been used for the treatment of enterococcal infections in humans. In recent years, large-scale susceptibility studies have shown that daptomycin is active against >98% of enterococci tested, irrespective of their susceptibility to other antibacterial agents. This lack of cross-resistance reflects the fact that daptomycin has a mode of action distinct from those of other antibiotics, including glycopeptides. While there are limited data available from randomized controlled trials, extensive clinical experience with daptomycin in enterococcal infections (including bacteraemia, endocarditis, skin and soft tissue infections, bone and joint infections and urinary tract infections) has been reported. This growing body of evidence provides useful insights regarding the efficacy of daptomycin against enterococci in clinical settings.
Gram-positive bacteria; cyclic lipopeptide antibiotics; nosocomial infections; vancomycin resistance
Daptomycin is an investigational lipopeptide antibiotic active against gram-positive organisms. The mechanism of action is unique, resulting in interference with cell membrane transport. The bactericidal activity of daptomycin was evaluated against glycopeptide-intermediate susceptible Staphylococcus aureus (GISA), vancomycin-resistant Enterococcus faecium (VREF), and methicillin-resistant S. aureus (MRSA) in an in vitro infection model with simulated endocardial vegetations. Simulated regimens of daptomycin at 6 mg/kg/day (D6) and 10 mg/kg/day (D10) were utilized. MICs and MBCs for daptomycin were determined in the absence and in the presence of albumin with the following results (MIC/MBC): for GISA-992, 0.5/1.0 and 16/16; for VREF-590, 2.0/2.0 and 32/32; and for MRSA-494, 0.25/0.25 and 1.0/4.0 μg/ml, respectively. During the first 8 h daptomycin significantly reduced the inoculum for all organisms. Daptomycin at 6 mg/kg/day and 10 mg/kg/day had log10 CFU/g reductions of 5 and 6, 3.4 and 5, and 6.4 and 6.5 by 8 h for GISA-992, VREF-590, and MRSA-494, respectively. Against both GISA-992 and VREF-590, the D10 regimen achieved the limit of detection at 72 h, with D6 regimens showing slight regrowth. A concentration-dependent killing effect was noted to occur, with daptomycin demonstrating a more rapid and greater kill from the D10 versus the D6 regimen. The results of this study suggest that daptomycin demonstrates significant (P < 0.05) activity against gram-positive organisms in a simulated sequestered infection site.
To evaluate the molecular characteristics and antibiotic susceptibility in biofilm of vancomycin-resistant Enterococcus faecium (VREF) organisms that had caused catheter-related VREF bacteremia (VREF-CRB), we compared 22 isolates causing bacteremia obtained from patients with VREF-CRB with 30 isolates from control patients with gastrointestinal colonization by VREF. Using pulsed-field gel electrophoresis, we identified 17 unique strains among the 22 VREF-CRB isolates and 23 strains among the gastrointestinal isolates. The esp gene was detected in 53% (9 of 17) of the VREF-CRB and 61% (14 of 23) of the control strains (P = 0.6). VREF-CRB produced heavier biofilm colonization of silicone disks than did control organisms (P < 0.001). Daptomycin, minocycline, and quinupristin-dalfopristin were each independently more active than linezolid in reducing biofilm colonization by VREF-CRB (P < 0.01), with daptomycin being the most active, followed by minocycline. In conclusion, the esp gene in VREF is not associated with heavy biofilm colonization or catheter-related bacteremia. In biofilm, daptomycin and minocycline were the most active antibiotics against VREF, and linezolid was the least active.
Daptomycin is a novel cyclic lipopeptide that is approved by the U.S. Food and Drug Administration for the treatment of complicated skin and skin structure infections associated with Staphylococcus aureus and other gram-positive pathogens and also staphylococcal bacteremia, including right-sided endocarditis. The Clinical and Laboratory Standards Institute (CLSI) established “susceptible-only” interpretive criteria for broth microdilution (BMD) and disk diffusion (DD) testing of daptomycin in 2005. However, a series of S. aureus isolates have been recovered with daptomycin MICs in the nonsusceptible range (i.e., MICs of >1 μg/ml). The objective of this study was to determine the ability of the Etest and DD methods to differentiate daptomycin-susceptible from nonsusceptible isolates of S. aureus compared to the results of the CLSI BMD reference method. There was a good correlation between Etest MIC results and the results of BMD among laboratories (r = 0.86 to 0.88), with 95.3% of the Etest MICs within a ±1 log2 dilution of the BMD MIC result. A total of 92 of 102 (90.2%) non-daptomycin-susceptible isolates of S. aureus identified by BMD in two participating laboratories were also classified as nonsusceptible by Etest. However, the very major and major error rates reported by one of the participating laboratories were 13.5 and 4.0%, respectively, primarily due to the absence of an intermediate category. The DD method, however, did not reliably differentiate daptomycin-susceptible from non-daptomycin-susceptible isolates. In 2005, daptomycin disks were voluntarily removed from the market by Cubist Pharmaceuticals. The disk diffusion breakpoints were subsequently removed from the CLSI M100 standard in 2006.
We studied an ampicillin- and vancomycin-resistant Enterococcus faecium (VRE) isolate from a patient with endocarditis and bacteremia refractory to treatment with daptomycin (6 mg/kg of body weight) plus linezolid. Blood cultures cleared within 24 h of changing therapy to daptomycin (12 mg/kg) plus ampicillin. We examined the effects of ampicillin on daptomycin-induced growth inhibition and killing, surface charge, and susceptibility to several prototypical host defense cationic antimicrobial peptides. MICs and time-kill curves with daptomycin were assessed in the presence and absence of ampicillin. The impact of ampicillin on surface charge was assessed by flow cytometry and a poly-l-lysine binding assay. The effects of ampicillin preexposures upon VRE killing by five distinct cationic peptides of different structure, charge, origin, and mechanism of action were analyzed using the epidermal cathelicidin LL-37, thrombin-induced platelet microbicidal proteins (tPMPs), and a synthetic congener modeled after tPMP microbicidal domains (RP-1), human neutrophil peptide-1 (hNP-1), and polymyxin B (bacteria derived). Fluoroscein-Bodipy-labeled daptomycin was used to evaluate daptomycin binding to VRE membranes in the presence or absence of ampicillin. In media containing ampicillin (25 to 100 mg/liter), daptomycin MICs decreased from 1.0 to 0.38 mg/liter. Based on time-kill analysis and an in vitro pharmacodynamic model, ampicillin enhanced daptomycin activity against the study VRE from a bacteriostatic to a bactericidal profile. VRE grown in ampicillin (25 to 150 mg/liter) demonstrated an incremental reduction in its relative net positive surface charge. When grown in the presence (versus absence) of ampicillin (25 and 100 mg/liter), the VRE strain (i) was more susceptible to killing by LL-37, tPMPs, hNP-1, and RP-1 but not to polymyxin B and (ii) exhibited greater binding to Bodipy-labeled daptomycin. We conclude that ampicillin induces reductions in net positive bacterial surface charge of VRE, correlating with enhanced bactericidal effects of cationic calcium-daptomycin and a diverse range of other cationic peptides in vitro. While the mechanism(s) of such β-lactam-mediated shifts in surface charge remains to be defined, these finding suggest a potential for β-lactam-mediated enhancement of activity of both daptomycin and innate host defense peptides against antibiotic-resistant bacteria.
Increasingly frequent reports have described the in vivo loss of daptomycin susceptibility in association with clinical treatment failures. The mechanism(s) of daptomycin resistance is not well understood. We studied an isogenic set of Staphylococcus aureus isolates from the bloodstream of a daptomycin-treated patient with recalcitrant endocarditis in which serial strains exhibited decreasing susceptibility to daptomycin. Since daptomycin is a membrane-targeting lipopeptide, we compared a number of membrane parameters in the initial blood isolate (parental) with those in subsequent daptomycin-resistant strains obtained during treatment. In comparison to the parental strain, resistant isolates demonstrated (i) enhanced membrane fluidity, (ii) increased translocation of the positively charged phospholipid lysyl-phosphotidylglycerol to the outer membrane leaflet, (iii) increased net positive surface charge (P < 0.05 versus the parental strain), (iv) reduced susceptibility to daptomycin-induced depolarization, permeabilization, and autolysis (P < 0.05 versus the parental strain), (v) significantly lower surface binding of daptomycin (P < 0.05 versus the parental strain), and (vi) increased cross-resistance to the cationic antimicrobial host defense peptides human neutrophil peptide 1 (hNP-1) and thrombin-induced platelet microbicidal protein 1 (tPMP-1). These data link distinct changes in membrane structure and function with in vivo development of daptomycin resistance in S. aureus. Moreover, the cross-resistance to hNP-1 and tPMP-1 may also impact the capacity of these daptomycin-resistant organisms to be cleared from sites of infection, particularly endovascular foci.
Cell wall thickening is a common feature among daptomycin-resistant Staphylococcus aureus strains. However, the mechanism(s) leading to this phenotype is unknown. We examined a number of cell wall synthesis pathway parameters in an isogenic strain set of S. aureus bloodstream isolates obtained from a patient with recalcitrant endocarditis who failed daptomycin therapy, including the initial daptomycin-susceptible parental strain (strain 616) and two daptomycin-resistant strains (strains 701 and 703) isolated during daptomycin therapy. Transmission electron microscopy demonstrated significantly thicker cell walls in the daptomycin-resistant strains than in the daptomycin-susceptible strain, a finding which was compatible with significant differences in dry cell weight of strain 616 versus strains 701 to 703 (P < 0.05). Results of detailed analysis of cell wall muropeptide composition, the degree of peptide side chain cross-linkage, and the amount of the peptidoglycan precursor, UDP-MurNAc-pentapeptide, were similar in the daptomycin-susceptible and daptomycin-resistant isolates. In contrast, the daptomycin-resistant strains contained less O-acetylated peptidoglycan. Importantly, both daptomycin-resistant strains synthesized significantly more wall teichoic acid (WTA) than the parental strain (P < 0.001). Moreover, the proportion of d-alanylated WTA species was substantially higher in the daptomycin-resistant strains than in the daptomycin-susceptible parental strain (P < 0.05 in comparing strain 616 versus strain 701). The latter phenotypic findings correlated with (i) enhanced tagA and dltA gene expression, respectively, and (ii) an increase in surface positive charge observed in the daptomycin-resistant versus daptomycin-susceptible isolates. Collectively, these data suggest that increases in WTA synthesis and the degree of its d-alanylation may play a major role in the daptomycin-resistant phenotype in some S. aureus strains.