Serum bactericidal activities of high-dose daptomycin with and without coadministration of gentamicin against isolates of Staphylococcus aureus and Enterococcus species

A Methylazanediyl Bisacetamide Derivative Sensitizes Staphylococcus aureus Persisters to a Combination of Gentamicin And Daptomycin

Infections caused by Staphylococcus aureus, notably methicillin-resistant S. aureus (MRSA), pose treatment challenges due to its ability to tolerate antibiotics and develop antibiotic resistance. The former, a mechanism independent of genetic changes, allows bacteria to withstand antibiotics by altering metabolic processes. Here, a potent methylazanediyl bisacetamide derivative, MB6, is described, which selectively targets MRSA membranes over mammalian membranes without observable resistance development. Although MB6 is effective against growing MRSA cells, its antimicrobial activity against MRSA persisters is limited. Nevertheless, MB6 significantly potentiates the bactericidal activity of gentamicin against MRSA persisters by facilitating gentamicin uptake. In addition, MB6 in combination with daptomycin exhibits enhanced anti-persister activity through mutual reinforcement of their membrane-disrupting activities. Crucially, the "triple" combination of MB6, gentamicin, and daptomycin exhibits a marked enhancement in the killing of MRSA persisters compared to individual components or any double combinations. These findings underscore the potential of MB6 to function as a potent and selective membrane-active antimicrobial adjuvant to enhance the efficacy of existing antibiotics against persister cells. The molecular mechanisms of MB6 elucidated in this study provide valuable insights for designing anti-persister adjuvants and for developing new antimicrobial combination strategies to overcome the current limitations of antibiotic treatments.

Combination Therapy of Chloramphenicol and Daptomycin for the Treatment of Infective Endocarditis Secondary to Multidrug Resistant Enterococcus faecium

A 38-years-old female with an aortic valve replacement presented to an outside hospital (OSH) with fevers and malaise. Blood cultures revealed VRE which was resistant to linezolid, resistant to ampicillin, non-susceptible to daptomycin (MIC of 8 mcg/mL), and exhibited susceptibility to gentamicin. The patient was therefore initiated on intravenous (IV) daptomycin 6 mg/kg q24h and gentamicin IV 1 mg/kg q8h. However, after 14 days of therapy with daptomycin and gentamicin, the patient was transferred to our institution for the management of cardiogenic shock and hypoxemic respiratory failure. Given the concern for treatment failure, her antimicrobial regimen was changed to IV chloramphenicol 12.5 mg/kg every 6 hours with IV daptomycin 10 mg/kg every 48 hours given an estimated creatinine clearance of 30 mL/minutes. In vitro susceptibilities for chloramphenicol were performed which confirmed susceptibility. A transesophageal echocardiogram revealed a possible abscess at the left coronary cusp and aortic valve dehiscence. The patient underwent aortic valve replacement with aortic root reconstruction. The aortic valve culture grew VRE susceptible to linezolid but resistant to ampicillin and doxycycline. The patient was deemed clinically cured after 42 days of combination therapy with daptomycin and chloramphenicol. After 6 years of follow-up, the patient has not had a recurrent VRE infection. To our knowledge, this is the first case of endocarditis secondary to VRE that was successfully managed with the combination of daptomycin and chloramphenicol.

Should High-dose Daptomycin be an Alternative Treatment Regimen for Enterococcal Endocarditis?

INTRODUCTION

Previous series on the use of daptomycin in enterococcal infective endocarditis (EIE) have shown various outcomes, including higher mortality rates. We analyzed the effectiveness of high-dose daptomycin for the treatment of EIE.

METHODS

We performed a prospective study from 2010 to 2018 in a referral center in patients with native (NVE) and prosthetic valve endocarditis (PVE) due to Enterococcus spp. The standard high-dose daptomycin at our institution is 10-12 mg/kg/day (CLCr > 30 ml/min). We compared the efficacy of a daptomycin-based regimen (DBR) versus daptomycin-sparing regimen (DSR) and daptomycin monotherapy versus combination therapy. Primary endpoints of the study were evaluation of risk factors associated with 30-day mortality and failure at end of therapy.

RESULTS

We collected 43 EIE cases; 29 were NVE (67.4%). Overall, 16 (37.2%) were treated with DBR, mainly with combination regimens (11, 68.7%), in the majority of cases in association with ß-lactam (7, 43.7%). The mean administered dose of daptomycin was 10.125 mg/kg/day (range 8-12 mg/kg/day). Overall, patients treated with DBR compared with patients treated with DSR had no higher mortality rates and/or failure at end of therapy (6.2% vs. 22. 2%; P 0.41 and MICs 0.25-2 mg/l, 6.2% vs. 3.7%; P 1.0). In the sub-group of patients with NVE and PVE treated with DBR and DSR, no difference was found regarding the primary endpoints on the single or combined use of daptomycin.

CONCLUSION

Our findings suggest that high-dose daptomycin might be used as an alternative treatment regimen in EIE.

Daptomycin

Daptomycin is a cyclic lipopeptide antibiotic used for the treatment of Gram-positive infections including complicated skin and skin structure infections, right-sided infective endocarditis, bacteraemia, meningitis, sepsis and urinary tract infections. Daptomycin has distinct mechanisms of action, disrupting multiple aspects of cell membrane function and inhibiting protein, DNA and RNA synthesis. Although daptomycin resistance in Gram-positive bacteria is uncommon, there are increasing reports of daptomycin resistance in Staphylococcus aureus, Enterococcus faecium and Enterococcus faecalis. Such resistance is seen largely in the context of prolonged treatment courses and infections with high bacterial burdens, but may occur in the absence of prior daptomycin exposure. Furthermore, use of inadequate treatment regimens, irregular drug supply and poor drug quality have also been recognized as other important risk factors for emergence of daptomycin-resistant strains. Antimicrobial susceptibility testing of Gram-positive bacteria, communication between clinicians and laboratories, establishment of internet-based reporting systems, development of better and more rapid diagnostic methods and continuous monitoring of drug resistance are urgent priorities.

A fully validated microbiological assay for daptomycin injection and comparison to HPLC method

abstract Daptomycin (DPT) was the first lipopeptide antibiotic available for commercialization. It is active against gram-positive bacteria, including resistant strains. This work aimed to develop and validate a turbidimetric microbiologic assay to determine daptomycin in an injectable form. A 3x3 design was employed, at concentrations of 1, 2 and 4.0 µg/mL. The microorganism test used was Staphylococcus aureus ATCC 6538p, and Antibiotic Medium 3 was used as the culture medium. Method validation demonstrated that the bioassay was linear (r=0.9995), precise (RSD=2.58%), accurate (recovery 100.48± 2.11%), and robust. Degradation kinetics was also performed in an alkaline medium, indicating that daptomycin degradation follows first order kinetics under these conditions. The analyses of degraded solutions showed that daptomycin degradation products do not possess bactericidal activity. The bioassay was compared to HPLC method that was previously developed and no significant difference was found between them (p>0.05). The method proved to be appropriate for daptomycin injection quality control.

Daptomycin-Nonsusceptible Staphylococcus aureus: The Role of Combination Therapy with Daptomycin and Gentamicin

Reduced susceptibility to daptomycin in Staphylococcus aureus has now been described, leading to clinical failures. Here we determined the impact of daptomycin and gentamicin combination therapy on bactericidal activity and resistance emergence using daptomycin-susceptible and -resistant isolates with mutations linked to previous daptomycin or vancomycin exposure. Enhanced killing of S. aureus was observed when gentamicin was combined with daptomycin, most commonly with daptomycin concentrations below the peak serum free-drug concentrations achieved with standard dosing. Synergy was seen with daptomycin-susceptible isolates and with isolates resistant to vancomycin and daptomycin. Combination therapy also prevented the emergence of resistance. Daptomycin and gentamicin combination therapy may provide the synergy required to prevent emergence of resistance when daptomycin levels are below peak serum concentrations as would be found in deep-seated, complicated infections.

Combination antibiotic therapy for the treatment of infective endocarditis due to enterococci

INTRODUCTION

Enterococci are common causes of infective endocarditis (IE) in both health care and community-based setting. Enterococcal IE requires bactericidal therapy for an optimal outcome. For decades, cell-wall-active antimicrobial agents (penicillins or vancomycin) in combination with aminoglycosides were the cornerstone of the treatment; however, the emergence of antibiotic resistance has significantly reduced the efficacy of these regimens.

MATERIALS AND METHODS

Data for this review were identified by searches of MEDLINE and references from relevant articles on antibiotic combination regimens for the treatment of enterococcal IE. Abstracts presented in scientific conferences were not searched for.

CONCLUSION

New effective and safe combination treatments, including double-β-lactam and daptomycin/β-lactam combination, are proving useful for the management of IE due to enterococci.

Real-World Treatment of Enterococcal Infections with Daptomycin: Insights from a Large European Registry (EU-CORE)

Introduction

Evolution of antibacterial resistance in pathogenic enterococcal strains poses a growing therapeutic challenge. Daptomycin, a cyclic lipopeptide, exhibits broad antibiotic activity against Gram-positive bacteria.

Methods

The European Cubicin^® Outcomes Registry and Experience, a multicenter, retrospective, non-interventional study, recorded clinical outcomes following daptomycin treatment.

Results

Overall, 472 patients (predominantly elderly Caucasian males) were treated for enterococcal infections. Of those, 72.7% received antibiotics prior to daptomycin treatment, whereas 77.1% received other antibiotics concomitantly. Failure of previous therapy, resistant or non-susceptible pathogen, and narrowing of antibiotic therapy were the main reasons for switching to daptomycin treatment. Nosocomial infections comprised 55.8% of the cohort. Bacteremia (29.9%), complicated skin and soft tissue infection (29.2%) and endocarditis (12.3%) were the most common primary infections. Clinical success was achieved in 77.1% of patients, with similar success rates across all primary infection categories. The overall clinical success rate was marginally higher (82.5% vs 74.6%, p = 0.09) with daptomycin use as first-line versus second-line therapy. Patients receiving higher doses of daptomycin exhibited the highest clinical success rates (85.7% for ≥8 mg/kg/day vs 75.8% for <8 mg/kg/day, p = 0.08). While 81 (17.2%) patients reported at least one adverse event (AE), only 11 (2.3%) and 3 (0.6%) had treatment-related AEs and serious AEs, respectively. Separate microbiologic findings from Leipzig University Hospital demonstrate small proportions of Enterococcus faecium isolates with daptomycin minimum inhibitory concentrations = 4 mg/L (4%) or ≥8 mg/L (0.8%), which are regarded as non-susceptible.

Conclusion

For enterococcal infections, daptomycin appears to be an effective and well-tolerated treatment option, exhibiting highest clinical success rates at higher doses.

Electronic supplementary material

The online version of this article (doi:10.1007/s40121-015-0072-z) contains supplementary material, which is available to authorized users.

Activity of daptomycin or linezolid in combination with rifampin or gentamicin against biofilm-forming Enterococcus faecalis or E. faecium in an in vitro pharmacodynamic model using simulated endocardial vegetations and an in vivo survival assay using Galleria mellonella larvae

Enterococci are the third most frequent cause of infective endocarditis. A high-inoculum stationary-phase in vitro pharmacodynamic model with simulated endocardial vegetations was used to simulate the human pharmacokinetics of daptomycin at 6 or 10 mg/kg of body weight/day or linezolid at 600 mg every 12 h (q12h), alone or in combination with gentamicin at 1.3 mg/kg q12h or rifampin at 300 mg q8h or 900 mg q24h. Biofilm-forming, vancomycin-susceptible Enterococcus faecalis and vancomycin-resistant Enterococcus faecium (vancomycin-resistant enterococcus [VRE]) strains were tested. At 24, 48, and 72 h, all daptomycin-containing regimens demonstrated significantly more activity (decline in CFU/g) than any linezolid-containing regimen against biofilm-forming E. faecalis. The addition of gentamicin to daptomycin (at 6 or 10 mg/kg) in the first 24 h significantly improved bactericidal activity. In contrast, the addition of rifampin delayed the bactericidal activity of daptomycin against E. faecalis, and the addition of rifampin antagonized the activities of all regimens against VRE at 24 h. Also, against VRE, the addition of gentamicin to linezolid at 72 h improved activity and was bactericidal. Rifampin significantly antagonized the activity of linezolid against VRE at 72 h. In in vivo Galleria mellonella survival assays, linezolid and daptomycin improved survival. Daptomycin at 10 mg/kg improved survival significantly over that with linezolid against E. faecalis. The addition of gentamicin improved the efficacy of daptomycin against E. faecalis and those of linezolid and daptomycin against VRE. We conclude that in enterococcal infection models, daptomycin has more activity than linezolid alone. Against biofilm-forming E. faecalis, the addition of gentamicin in the first 24 h causes the most rapid decline in CFU/g. Of interest, the addition of rifampin decreased the activity of daptomycin against both E. faecalis and VRE.

Engaging Pharmacy Students, Residents, and Fellows in Antimicrobial Stewardship

Antimicrobial stewardship programs are mainly established by infectious diseases physicians and infectious diseases-trained clinical pharmacists with the goal of optimizing patients' outcomes while halting antimicrobial resistance, decreasing adverse events, and controlling health care cost. The role of the infectious diseases-trained clinical pharmacist in antimicrobial stewardship is well established; however, there are not enough formally trained pharmacists to assume the challenging responsibilities of the steward coordinator. The purpose of this article was to review the available literature and resources and propose a model to engage introductory pharmacy practice experience students, advanced pharmacy practice experience students, postgraduate year (PGY) 1 pharmacy residents, PGY2 infectious diseases pharmacy residents, and PGY2 or PGY3 infectious diseases pharmacy fellows in antimicrobial stewardship. Further studies are needed to assess and document the impact of pharmacy students and postgraduate trainees on antimicrobial stewardship programs.

Treatment considerations in vancomycin-resistant enterococcal bacteremia: daptomycin or linezolid? A review

BACKGROUND

Vancomycin resistant enterococcal bloodstream infections are an important cause of morbidity and mortality in hospitalized patients.

AIM OF THE REVIEW

A search of the literature was undertaken to determine the optimal antimicrobial therapy for the management of vancomycin resistant enterococcal bloodstream infections.

METHOD

MEDLINE, EMBASE, and the Cochrane Library (unrestricted to time or language) were searched for studies of vancomycin resistant enterococcal bloodstream infections in adults reporting outcomes of direct comparisons of linezolid versus daptomycin on November 26, 2012. Studies of basic science, reviews, commentaries, pharmacologic, epidemiologic, or pediatric studies, and those studies examining conditions other than enterococcal bacteremia, a single antimicrobial agent or other antimicrobials were excluded.

RESULTS

226 studies were screened for eligibility and yielded eight studies evaluating a total of 807 patients. Inter-rater agreement was 100 %. Qualitative evaluation of the studies was performed using the Newcastle-Ottawa scale. No randomized controlled trials were identified. All studies were retrospective cohorts and non-randomized. 458 (57 %) patients treated with linezolid and 349 (43 %) with daptomycin were analyzed. Variable comorbidities and severity of illness were described in the included studies and reported here for comparison.

CONCLUSION

The optimal treatment of vancomycin resistant enterococcal bloodstream infections is yet to be determined. Well-designed prospective studies are needed to lend more convincing evidence regarding choice of antimicrobial therapy for this important multidrug resistant organism.

Staphylococcus aureus biofilm formation and antibiotic susceptibility tests on polystyrene and metal surfaces

AIM

We compared the MBEC™-HTP assay plates made of polystyrene with metal discs composed of TMZF(®) and CrCo as substrates for biofilm formation.

METHODS AND RESULTS

Staphylococcus aureus was grown on polystyrene and on metal discs made of titanium and chrome-cobalt. Antibiotic susceptibility was assessed by examining the recovery of cells after antibiotic exposure and by measuring the biofilm inhibitory concentration (BIC). The minimal inhibitory concentration (MIC) was assessed with planktonic cells. Bacterial growth was examined by scanning electron microscopy. The antibiotic concentration for biofilm inhibition (BIC) was higher than the MIC for all antibiotics. Microscopic images showed the biofilm structure characterized by groups of cells covered by a film.

CONCLUSIONS

All models allowed biofilm formation and testing with several antibiotics in vitro. Gentamicin and rifampicin are the most effective inhibitors of Staph. aureus biofilm-related infections. We recommend MBEC™-HTP assay for rapid testing of multiple substances and TMZF(®) and CrCo discs for low-throughput testing of antibiotic susceptibility and for microscopic analysis.

SIGNIFICANCE AND IMPACT OF THE STUDY

In vitro assays can improve the understanding of biofilms and help developing methods to eliminate biofilms from implant surfaces. One advantage of the TMZF(®) and CrCo discs as biofilm in vitro assay is that these metals are commonly used for orthopaedic implants. These models are usable for future periprosthetic joint infection studies.

The safety and efficacy of linezolid and daptomycin as an additive in Optisol-GS against methicillin-resistant Staphylococcus aureus

PURPOSE

To evaluate the efficacy of adding either linezolid or daptomycin to Optisol-GS donor storage medium in reducing methicillin-resistant Staphylococcus aureus (MRSA) contamination of donor corneas.

METHODS

Optisol-GS was supplemented with either linezolid at 2×, 4×, or 10× minimum inhibitory concentration (MIC) or daptomycin and calcium at 5× or 50× MIC. Unsupplemented control groups were also used. Gentamicin-sensitive and gentamicin-resistant isolates of MRSA were added, and vials were refrigerated for 48 hours followed by sampling for viable colony counts immediately upon removal from refrigeration and after warming to room temperature for 3 hours. Safety studies of Optisol-GS supplemented with 50× MIC daptomycin and calcium were performed by evaluating the central corneal thickness and endothelial cell density of the donor cornea. Stability of daptomycin in Optisol-GS at storage was also tested.

RESULTS

No added benefit was observed with linezolid supplementation to Optisol-GS against gentamicin-sensitive MRSA, with reduction in viable colony counts by >90% in all groups. No benefit was observed with linezolid supplementation against gentamicin-resistant MRSA, with the majority of inocula remaining viable in all groups. Viable counts of gentamicin-sensitive MRSA and gentamicin-resistant MRSA were effectively reduced with both 5× MIC and 50× MIC daptomycin supplementation. 50× MIC daptomycin-supplemented Optisol-GS had no appreciable effect on the central corneal thickness or endothelial cell density of the donor cornea and was stable at storage for 14 days.

CONCLUSIONS

The addition of daptomycin to Optisol-GS significantly increases the anti-MRSA activity of the medium without any apparent negative effects on donor corneal tissue.

Cutaneous infections and infestations: new therapies

Directed and preventive therapies for cutaneous infectious disease and infestation continue to evolve, providing physicians with new options for care. Common infectious diseases (e.g., genital herpes, herpes zoster, and head lice) occur in the outpatient and inpatient setting. This review of the literature highlights new therapies, including those still in development, such as novel drugs and vaccines, all of which should help to decrease the frequency and severity of common infectious diseases of the skin and subcutaneous tissues.

Determination of daptomycin in human plasma by liquid chromatography-tandem mass spectrometry. Clinical application

BACKGROUND

Daptomycin is a recently developed cyclic lipopeptide antibiotic active against most Gram-positive pathogens including vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus. To optimize treatment efficacy and safety, especially in patients undergoing multiple drug regimens and/or co-morbidities, a specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the quantification of daptomycin in plasma.

METHODS

A C18 column was used for separation, with a mobile phase initially consisting of 0.1% formic acid, water, and acetonitrile (ACN) in a linear gradient from 20% to 70%. After protein precipitation with ACN, the clear upper layer was diluted in water:ACN (50:50, v/v) before injection. Detection was performed using an electrospray ionization technique. MS/MS transitions, monitored in the positive ion mode were m/z 811.1 → m/z 313.1 for daptomycin, and m/z 609.4 → m/z 194.9 for reserpine, used as internal standard.

RESULTS

Elution of daptomycin and reserpine occurred at 4.5 and 3.9 min, respectively. The method was validated over a range of concentrations from 1 mg/L to 120 mg/L. The assay met recommended acceptance criteria: coefficients of variation were <6.3% and <7.4%, and accuracies were between -5.9% and +11.2% and between -3.5% and +3.7%, for intra- and inter-day validations, respectively.

CONCLUSIONS

This method appears well-adapted to routine hospital practice for therapeutic drug monitoring of daptomycin considering its time of analysis, range of concentrations measured, precision and accuracy.

Limitations of antibiotic options for invasive infections caused by methicillin-resistant Staphylococcus aureus: is combination therapy the answer?

Invasive infections caused by methicillin-resistant Staphylococcus aureus (MRSA), particularly those involving persistent bacteraemia, necrotizing pneumonia, osteomyelitis and other deep-seated sites of infections, are associated with high mortality and are often difficult to treat. The response to treatment of severe MRSA infection with currently available antibiotics active against MRSA is often unsatisfactory, leading some physicians to resort to combination antibiotic therapy. Now, with the emergence of community-associated MRSA (CA-MRSA) clones that display enhanced virulence potentially related to up-regulated toxin production, the use of adjuvant protein synthesis-inhibiting antibiotics to reduce toxin production also has been advocated by some experts. In this review, we discuss the limitations of antibiotics currently available for the treatment of serious invasive MRSA infections and review the existing literature that examines the potential role of combination therapy in these infections.

Addition of gentamicin or rifampin does not enhance the effectiveness of daptomycin in treatment of experimental endocarditis due to methicillin-resistant Staphylococcus aureus

This study evaluated the activity of daptomycin combined with either gentamicin or rifampin against three methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates in vitro and one isolate in vivo against a representative strain (MRSA-572). Time-kill experiments showed that daptomycin was bactericidal against these strains at concentrations over the MIC. Daptomycin at sub-MIC concentrations plus gentamicin at 1x and 2x the MIC yielded synergy, while the addition of rifampin at 2 to 4 microg/ml resulted in indifference (two strains) or antagonism (one strain). The in vivo activity of daptomycin (6 mg/kg of body weight once a day) was evaluated +/- gentamicin (1 mg/kg intravenously [i.v.] every 8 h [q8h]) or rifampin (300 mg i.v. q8h) in a rabbit model of infective endocarditis by simulating human pharmacokinetics. Daptomycin plus gentamicin (median, 0 [interquartile range, 0 to 2] log10 CFU/g vegetation) was as effective as daptomycin alone (0 [0 to 2] log10 CFU/g vegetation) in reducing the density of bacteria in valve vegetations (P = 0.83), and both were more effective than daptomycin plus rifampin (3 [2 to 3.5] log10 CFU/g vegetation; P < 0.05) for the strain studied. In addition, daptomycin sterilized a ratio of vegetations that was similar to that of daptomycin plus gentamicin (10/15 [67%] versus 9/15 [60%]; P = 0.7), and both regimens did so more than daptomycin plus rifampin (3/15 [20%]; P = 0.01 and P = 0.02, respectively). No statistical difference was noted between daptomycin plus gentamicin and daptomycin alone for MRSA treatment. In the combination arm, all isolates from vegetations remained susceptible to daptomycin, gentamicin, and rifampin. Sixty-one percent of the isolates (8/13) acquired resistance to rifampin during monotherapy. In the daptomycin arm, resistance was detected in only one case, in which the daptomycin MIC rose to 2 microg/ml among the recovered bacteria. In conclusion, the addition of gentamicin or rifampin does not enhance the effectiveness of daptomycin in the treatment of experimental endocarditis due to MRSA.

Daptomycin pharmacokinetics in adult oncology patients with neutropenic fever

Daptomycin is the first antibacterial agent of the cyclic lipopeptides with in vitro bactericidal activity against gram-positive organisms, including vancomycin-resistant enterococci, methicillin-resistant staphylococci, and glycopeptide-resistant Staphylococcus aureus. The pharmacokinetics of daptomycin were determined in 29 adult oncology patients with neutropenic fever. Serial blood samples were drawn at 0, 0.5, 1, 2, 4, 8, 12, and 24 h after the initial intravenous infusion of 6 mg/kg of body weight daptomycin. Daptomycin total and free plasma concentrations were determined by high-pressure liquid chromatography. Concentration-time data were analyzed by noncompartmental methods. The results (presented as means +/- standard deviations and ranges, unless indicated otherwise) were as follows: the maximum concentration of drug in plasma (C(max)) was 49.04 +/- 12.42 microg/ml (range, 21.54 to 75.20 microg/ml), the 24-h plasma concentration was 6.48 +/- 5.31 microg/ml (range, 1.48 to 29.26 microg/ml), the area under the concentration-time curve (AUC) from time zero to infinity was 521.37 +/- 523.53 microg.h/ml (range, 164.64 to 3155.11 microg.h/ml), the volume of distribution at steady state was 0.18 +/- 0.05 liters/kg (range, 0.13 to 0.36 liters/kg), the clearance was 15.04 +/- 6.09 ml/h/kg (range, 1.90 to 34.76 ml/h/kg), the half-life was 11.34 +/- 14.15 h (range, 5.17 to 83.92 h), the mean residence time was 15.67 +/- 20.66 h (range, 7.00 to 121.73 h), and the median time to C(max) was 0.6 h (range, 0.5 to 2.5 h). The fraction unbound in the plasma was 0.06 +/- 0.02. All patients achieved C(max)/MIC and AUC from time zero to 24 h (AUC(0-24))/MIC ratios for a bacteriostatic effect against Streptococcus pneumoniae. Twenty-seven patients (93%) achieved a C(max)/MIC ratio for a bacteriostatic effect against S. aureus, and 28 patients (97%) achieved an AUC(0-24)/MIC ratio for a bacteriostatic effect against S. aureus. Free plasma daptomycin concentrations were above the MIC for 50 to 100% of the dosing interval in 100% of patients for S. pneumoniae and 90% of patients for S. aureus. The median time to defervescence was 3 days from the start of daptomycin therapy. In summary, a 6-mg/kg intravenous infusion of daptomycin every 24 h was effective and well tolerated in neutropenic cancer patients.

Daptomycin in endocarditis and bacteraemia: a British perspective

Assessment of the place of daptomycin in the treatment of endocarditis and bacteraemia requires assimilation of data from one open-label randomized comparative clinical trial sized for equivalence, from registry data and from case reports. Selected relevant animal models and in vitro data are also considered in an effort to produce an integrated assessment of the current place of daptomycin in treatment. The evidence for the use of daptomycin is best in Staphylococcus aureus bacteraemia and endocarditis, but also includes some data on infections due to Enterococcus spp., especially if vancomycin-resistant. The emergence of resistance in a minority of patients on current dose regimens may mean that trials have to be repeated with higher doses, or the drug used in a combined therapy where rifampicin may be the best choice. In general, equivalence to comparator antibiotic regimens and a correlation for in vitro and in vivo findings have been demonstrated, but there are important gaps in the clinical data including a comparative equivalence trial in streptococcal and enterococcal endocarditis. Clinical benefit might be anticipated, but has not been proved, over aminoglycoside-containing regimens, and economic assessments are critical in the decision as to when and how daptomycin is deployed.

In vivo microdialysis study of the penetration of daptomycin into soft tissues in diabetic versus healthy volunteers

Daptomycin is approved for the treatment of complicated skin and soft tissue infections, including diabetic wounds of the lower extremities, at a dose of 4 mg/kg of body weight once daily. For such localized tissue infections, drug concentrations in the interstitial space are an important determinant of successful therapy. In the diabetic population, peripheral arterial disease may limit antibiotic penetration into the target tissue. The objective of this study was to describe and compare the pharmacokinetic profiles of daptomycin in the interstitial fluid of soft tissues in diabetic and healthy volunteers by using in vivo microdialysis. Twelve subjects (six diabetic and six healthy) received a single 4-mg/kg dose of daptomycin intravenously. Samples of plasma and tissue were simultaneously collected over 24 h. Diabetic and healthy groups were matched in mean age (+/-10 years), gender ratio, mean weight (+/-10 kg), and creatinine clearance rate (+/-20 ml/min/1.73 m(2)). Pharmacokinetic parameters for plasma were similar between groups (P > 0.05). The mean peak drug concentrations +/- standard deviations in tissue were 4.3 +/- 3.3 microg/ml and 3.8 +/- 1.4 microg/ml for diabetic and healthy subjects, respectively. The degree of tissue penetration, defined as the ratio of the area under the free drug concentration-time curve for tissue to that for plasma, was 0.93 +/- 0.61 for diabetic subjects and 0.74 +/- 0.09 for healthy subjects (P = 0.46). Daptomycin at 4 mg/kg penetrated well into the soft tissue, reaching concentrations approximately 70 to 90% of those of the free drug in plasma. Moreover, these free, bioactive concentrations in tissue exceeded the MICs for staphylococci and streptococci over the 24-h dosing interval.

Bacteremia and endocarditis due to methicillin-resistant Staphylococcus aureus: the potential role of daptomycin

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.

In vitro effect of the presence of human albumin or human serum on the bactericidal activity of daptomycin against strains with the main resistance phenotypes in Gram-positives

OBJECTIVES

Bactericidal activity depends on antibiotic-bacteria couples, resistance phenotype and theoretically on protein binding. This work explores the influence of protein binding on the bactericidal activity of two antibiotics, daptomycin versus vancomycin, that exhibit, respectively, different C(max) (56 versus 25.5 mg/L), protein binding (91.7% versus 36.9%) and thus theoretical free-drug fractions (4.7 versus 16.1 mg/L).

METHODS

The effect of the presence of physiological concentrations of human albumin (4 g/dL) or human serum (90%) on the bactericidal activity of daptomycin was studied against Gram-positive isolates with troublesome resistance phenotypes [multidrug-resistant Streptococcus pneumoniae (MDRSP), methicillin-resistant Staphylococcus aureus (MRSA), heterogeneous vancomycin-intermediate MRSA (MRSA-hVI) and vancomycin-resistant Enterococcus faecium]. Killing curves (final inocula of approximately 10(7) cfu/mL) were performed using daptomycin and vancomycin concentrations similar to the C(max) obtained in serum.

RESULTS

Daptomycin was rapidly bactericidal (> or =3 log(10) initial inocula reduction) against S. pneumoniae and S. aureus, regardless of the strain tested or the presence of albumin or human serum (that slightly delayed bactericidal activity). Against vancomycin-susceptible or -resistant enterococci, daptomycin exhibited rapid bactericidal activity, delayed to 8 and 24 h, respectively, by human albumin. Vancomycin exhibited much slower bactericidal activity against MDRSP and methicillin-susceptible or -resistant S. aureus, but was never bactericidal against MRSA-hVI and vancomycin-susceptible or -resistant E. faecium.

CONCLUSIONS

Daptomycin exhibited rapid bactericidal activity against the strains of the three Gram-positive species tested, regardless of resistance phenotype or the presence of physiological concentrations of albumin.

Activity of daptomycin alone and in combination with rifampin and gentamicin against Staphylococcus aureus assessed by time-kill methodology

The synergistic effects of daptomycin plus gentamicin or rifampin were tested against 50 Staphylococcus aureus strains, with daptomycin MICs ranging between 0.25 and 8 microg/ml. Daptomycin sub-MICs combined with gentamicin concentrations lower than the MIC yielded synergy in 34 (68%) of the 50 strains. Daptomycin combined with rifampin yielded synergy in one vancomycin-intermediate S. aureus strain only, and virtually all synergy occurred between daptomycin and gentamicin.