Efficacy of vancomycin and daptomycin against Staphylococcus aureus isolates collected over 29 years

Synthesis and characterisation of phenanthroline-oxazine ligands and their Ag(I), Mn(II) and Cu(II) complexes and their evaluation as antibacterial agents

A series of phenanthroline-oxazine ligands were formed by a cyclisation reaction between L-tyrosine amino acid esters and 1,10-phenanthroline-5,6-dione (phendione). The methyl derivative of the phenanthroline-oxazine ligand 1 was complexed with Ag(I), Mn(II) and Cu(II) to form [Ag(1)₂]ClO₄, [Mn(1)₃](ClO₄)₂ and [Cu(1)₃](ClO₄)₂. The activity of these metal complexes was tested against the bacteria Escherichia coli and Staphylococcus aureus. Each of the metal complexes was more active than 1 against S. aureus and the Mn(II) and Cu(II) complexes also showed greater activity than 1 towards E. coli. The effect of increasing the length of the alkyl moiety on the phenanthroline-oxazine ligands and their corresponding tris homoleptic Cu(II) complexes was investigated. In all cases both the ligands and their complexes were more active against Gram-positive S. aureus than against Gram-negative E. coli. Differences in the lipophilicity of the ligands and their corresponding Cu(II) complexes did alter the antibacterial activity, with the hexyl and octyl derivatives and their complexes showing the greatest activity and comparing well with clinically used antibiotics. The most active Cu(II) complexes and their respective ligands were also active against Methicillin-resistant S. aureus (MRSA). In vivo toxicity studies, conducted using the Galleria mellonella model, showed that all of the compounds were well tolerated by the insect larvae.

When antibiotics fail: a clinical and microbiological perspective on antibiotic tolerance and persistence of Staphylococcus aureus

Staphylococcus aureus is a major human pathogen causing a vast array of infections with significant mortality. Its versatile physiology enables it to adapt to various environments. Specific physiological changes are thought to underlie the frequent failure of antimicrobial therapy despite susceptibility in standard microbiological assays. Bacteria capable of surviving high antibiotic concentrations despite having a genetically susceptible background are described as 'antibiotic tolerant'. In this review, we put current knowledge on environmental triggers and molecular mechanisms of increased antibiotic survival of S. aureus into its clinical context. We discuss animal and clinical evidence of its significance and outline strategies to overcome infections with antibiotic-tolerant S. aureus.

Tunable antibiotic delivery from gellan hydrogels

Hydrogels are used extensively in wound management. Many wounds are highly susceptible to infection and hydrogels can provide localized antibacterial delivery to treat and prevent this infection. There are several key considerations in designing antibacterial hydrogels for wound therapy, including preserving activity of encapsulated antibacterial agents, controlling drug release timescales and concentrations, and having the ability to conform to various wound configurations. In this work, we have used gellan, a U.S. Food and Drug Administration approved food additive, to develop antibiotic loaded hydrogels focusing on these criteria. These hydrogels were formed to exhibit a range of mechanical properties, which were investigated using oscillatory rheology. We denoted hydrogels formed using 1% w/v gellan and 1 mM CaCl₂"ointment" hydrogels and those formed using 4% w/v gellan and 7 mM CaCl₂"sheet" hydrogels. Vancomycin, a broad-spectrum antibiotic against Gram-positive bacteria, was encapsulated in these hydrogels both directly and/or in graphitized carbon black nanoparticles (CNPs). We found that vancomycin released from both sheet and ointment hydrogels at therapeutically effective concentrations over 9 days with CNPs and 6 days without CNPs. Applying the Ritger-Peppas and Peppas-Sahlin semi-empirical drug release models to sheet hydrogels, we determined that Fickian diffusion dominates release while case II relaxation also has a small contribution. The sheet hydrogels exhibited a larger overall release of the drug (83.6 ± 1.6% compared to 67.0 ± 2.6% for ointments), which was attributed to the larger swelling resulting from osmotic pressure differences between the hydrogel formulations and the release buffer. We also suggest that final drug release amounts are influenced by intermolecular interactions between vancomycin and gellan, which were observed via quartz crystal microbalance with dissipation monitoring. Lastly, we examined the potential for future in vivo translation. We demonstrated in vitro growth inhibition of Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus in the presence of these hydrogels, demonstrating that vancomycin activity is preserved upon encapsulation. We also showed that these hydrogels are non-toxic to important wound healing cells including fibroblasts and mesenchymal stem cells.

Sustained local delivery of high-concentration vancomycin from a hybrid biodegradable, antibiotic-eluting, nanofiber-loaded endovascular prosthesis for treatment of mycotic aortic aneurysms

BACKGROUND

Endovascular repair for mycotic aortic aneurysm (MAA) is a less invasive alternative to open surgery, although the placement of a stent graft in an infected environment remains controversial. In this study, we developed hybrid biodegradable, vancomycin-eluting, nanofiber-loaded endovascular prostheses and evaluated antibiotic release from the endovascular prostheses both in vitro and in vivo.

METHODS

Poly(D,L)-lactide-co-glycolide and vancomycin were dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol. This solution was electrospun into nanofibrous tubes, which were mounted onto commercial vascular stents and endovascular aortic stent grafts. In vitro antibiotic release from the nanofibers was characterized using an elution method and high-performance liquid chromatography. Antibiotic release from the hybrid stent graft was analyzed in a three-dimensional-printed model of a circulating MAA. The in vivo drug release characteristics were examined by implanting the antibiotic-eluting stents in the abdominal aorta of New Zealand white rabbits (n = 15).

RESULTS

The in vitro study demonstrated that the biodegradable nanofibers and the nanofiber-loaded stent graft provided sustained release of high concentrations of vancomycin for up to 30 days. The in vivo study showed that the nanofiber-loaded stent exhibited excellent biocompatibility and released high concentrations of vancomycin into the local aortic wall for 8 weeks.

CONCLUSIONS

The proposed biodegradable vancomycin-eluting nanofibers significantly contribute to the achievement of local and sustainable delivery of antibiotics to the aneurysm sac and the aortic wall, and these nanofibers may have therapeutic applications for MAAs.

Pharmacokinetics and Tolerance of the Phage Endolysin-Based Candidate Drug SAL200 after a Single Intravenous Administration among Healthy Volunteers

This study was a phase 1, single-center, randomized, double-blind, placebo-controlled, single-dosing, and dose-escalating study of intravenous SAL200. It is a new candidate drug for the treatment of antibiotic-resistant staphylococcal infections based on a recombinant form of the phage endolysin SAL-1. The study evaluated the pharmacokinetics, pharmacodynamics, and tolerance among healthy male volunteers after the intravenous infusion of single ascending doses of SAL200 (0.1, 0.3, 1, 3, and 10 mg/kg of body weight). SAL200 was well tolerated, and no serious adverse events (AEs) were observed in this clinical study. Most AEs were mild, self-limiting, and transient. The AEs reported in more than three participants were fatigue, rigors, headache, and myalgia. No clinically significant values with respect to the findings of clinical chemistry, hematology, and coagulation analyses, urinalysis, vital signs, and physical examinations were observed, and no notable trends in our electrocardiogram (ECG) results for any tested dose were noticed. A greater-than-dose-proportional increase with regard to systemic exposure and the maximum serum concentration was observed when the SAL200 dose was increased from 0.1 mg/kg to 10 mg/kg. This investigation constitutes the first-in-human phase 1 study of an intravenously administered, phage endolysin-based drug. (This study has been registered at ClinicalTrials.gov under identifier NCT01855048 and at the Clinical Research Information Service [https://cris.nih.go.kr/cris/] under identifier KCT0000968.).

Relationship between vancomycin tolerance and clinical outcomes in Staphylococcus aureus bacteraemia

BACKGROUND

Previous data have demonstrated the clinical importance of vancomycin MIC values in Staphylococcus aureus bacteraemia (SAB); however, the impact of vancomycin tolerance (VT) is unknown.

OBJECTIVES

To compare the frequency of clinical failure between patients with VT and non-VT isolates in SAB.

METHODS

This was a retrospective cohort study of patients with SAB, excluding treatment <48 h or polymicrobial bacteraemia. The primary outcome was clinical failure (composite of 30 day mortality, non-resolving signs and symptoms, and 60 day recurrence). Vancomycin MIC and MBC were determined by broth microdilution. The association between VT (MBC/MIC ≥32) and clinical failure was evaluated by multivariable Poisson regression.

RESULTS

Of the 225 patients, 26.7% had VT isolates. VT was associated with clinical failure (48.0% overall) in unadjusted analysis [68.3% (n = 41/60) versus 40.6% (n = 67/165); P < 0.001] and this relationship persisted in multivariable analysis (adjusted risk ratio, 1.74; 95% CI, 1.36-2.24; P < 0.001). The association between VT and clinical failure was also consistent within strata of methicillin susceptibility [methicillin susceptible (n = 125, risk ratio, 1.67; 95% CI, 1.20-2.32; P = 0.002); methicillin resistant (n = 100, risk ratio, 1.69; 95% CI, 1.14-2.51; P = 0.010)]. Among methicillin-susceptible SAB cases treated with β-lactam therapy, VT remained associated with clinical failure (risk ratio, 1.77; 95% CI, 1.19-2.61; P = 0.004).

CONCLUSIONS

VT was associated with clinical failure in SAB, irrespective of methicillin susceptibility or definitive treatment. VT may decrease the effectiveness of cell-wall-active therapy or be a surrogate marker of some other pathogen-specific factor associated with poor outcomes. Future research should evaluate if bactericidal non-cell-wall-active agents improve outcomes in VT SAB.

Population Pharmacokinetics of Vancomycin in Postoperative Neurosurgical Patients and the Application in Dosing Recommendation

Our previous study indicates that cerebrospinal fluid (CSF) albumin level is a determinant of CSF vancomycin concentration for postoperative neurosurgical patients. We aimed to develop an improved vancomycin population pharmacokinetic model with incorporation of more covariates, and to provide dosing guidance for clinicians. Vancomycin was administered intravenously to 20 patients with external ventricular drains after neurosurgical operation. Blood and CSF were collected and vancomycin concentrations were measured by HPLC. A separate CSF compartment was considered, and was linked to the central compartment by a first-order process (Q_CSF). The clearance of the CSF compartment (Cl_CSF) was used to characterize vancomycin elimination from CSF through external ventricular drain. Nonlinear mixed-effects modeling approach was used to develop the model. The CSF albumin level (mg/dL) was the covariate influencing Q_CSF: Q_CSF=0.0049+0.000021×(CSF albumin-279). The effect of body weight (BW, kg) was significant on central volume (V_C): V_C=27.84+0.96×(BW-69). All parameters were estimated with an acceptable precision (relative standard error: RSE% < 30.26). The performance of the final model was acceptable with our previous dataset. A simple to use dosage regimen table was created to guide clinicians with vancomycin dosing. This model incorporates variables of both CSF albumin and BW, which offers improvements to the previous pharmacokinetics model.

Risk factors for mortality in patients with Staphylococcus aureus bloodstream infection

In this two year retrospective analysis, we evaluated the epidemiology and risk factors for mortality of Staphylococcus aureus bloodstream infection (SaBSI). Methicillin-susceptible S. aureus (MSSA) was isolated in 84 (44.2%) and methicillin-resistant S. aureus (MRSA) in 106 episodes (55.8%). The mortality rate after 21 days was 16.4%. At univariate analysis older age, no removal of central venous catheter (CVC), prosthetic heart valves, severe sepsis, septic shock and high APACHE II score were significantly associated with mortality, whereas treatment duration > 48 hours, appropriate targeted therapy and prolonged treatment duration were significantly associated with survival. At multivariate analysis, prosthetic valves, septic shock and fever 48 hours after the diagnosis were significantly related to mortality. In this study, the mortality was associated with clinical rather than microbiological factors.

Population Pharmacokinetics of Vancomycin in Postoperative Neurosurgical Patients

Neurosurgical procedures may damage the blood-brain barrier to allow more vancomycin distribution into the cerebrospinal fluid (CSF) from blood after intravenous administration. However, a large intersubject variability in CSF vancomycin concentration was observed. We aimed to develop a population pharmacokinetic model to guide vancomycin dosing in patients after neurosurgical operation. Blood and CSF samples were collected and determined from postoperative neurosurgical patients after vancomycin administration. A three-compartment (central, peripheral, and CSF) model was proposed to characterize the pharmacokinetics of vancomycin. A nonlinear mixed-effects modeling approach was applied to fit the blood and CSF data simultaneously. The covariate analysis found that the CSF albumin level was strongly associated with the clearance between central and CSF compartment. Visual predictive check indicated that the proposed population pharmacokinetic model agrees well with the observed vancomycin concentrations. Individualized vancomycin dosage regimens could be developed for postoperative neurosurgical patients with different CSF albumin levels through model simulations. The CSF albumin level is a determinant of CSF vancomycin concentration.

Sustained release of vancomycin from novel biodegradable nanofiber-loaded vascular prosthetic grafts: in vitro and in vivo study

This study describes novel biodegradable, drug-eluting nanofiber-loaded vascular prosthetic grafts that provide local and sustained delivery of vancomycin to surrounding tissues. Biodegradable nanofibers were prepared by first dissolving poly(D,L)-lactide-co-glycolide and vancomycin in 1,1,1,3,3,3-hexafluoro-2-propanol. The solution was then electrospun into nanofibers onto the surface of vascular prostheses. The in vitro release rates of the pharmaceutical from the nanofiber-loaded prostheses was characterized using an elution method and a high-performance liquid chromatography assay. Experimental results indicated that the drug-eluting prosthetic grafts released high concentrations of vancomycin in vitro (well above the minimum inhibitory concentration) for more than 30 days. In addition, the in vivo release behavior of the drug-eluting grafts implanted in the subcutaneous pocket of rabbits was also documented. The drug-eluting grafts developed in this work have potential applications in assisting the treatment of vascular prosthesis infection and resisting reinfection when an infected graft is to be exchanged.

Brazilian experience in EU-CORE: daptomycin registry and treatment of serious Gram-positive infections

Objectives

To collect data about non-controlled prescribing use of daptomycin and its impact among Brazilian patients with serious Gram positive bacterial infection, as well as the efficacy and safety outcomes.

Materials and methods

This is a multi-center, retrospective, non-interventional registry (August 01, 2009 to June 30, 2011) to collect data on 120 patients (44 patients in the first year and 76 patients in the second year) who had received at least one dose of commercial daptomycin in Brazil for the treatment of serious Gram-positive bacterial infection.

Results

Right-sided endocarditis (15.8%), complicated skin and soft tissue infections (cSSTI)-wound (15.0%) and bacteremia-catheter-related (14.2%) were the most frequent primary infections; lung (21.7%) was the most common site for infection. Daptomycin was used empirically in 76 (63.3%) patients, and methicillin-resistant Staphylococcus aureus (MRSA) was the most common suspected pathogen (86.1%). 82.5% of the cultures were obtained prior to or shortly after initiation of daptomycin therapy. Staphylococcus spp. – coagulase negative, MRSA, and methicillin-susceptible S. aureus were the most frequently identified pathogens (23.8%, 23.8% and 12.5%, respectively). The most common daptomycin dose administered for bacteremia and cSSTI was 6 mg/kg (30.6%) and 4 mg/kg (51.7%), respectively. The median duration of inpatient daptomycin therapy was 14 days. Most patients (57.1%) did not receive daptomycin while in intensive care unit. Carbapenem (22.5%) was the most commonly used antibiotic concomitantly. The patients showed clinical improvement after two days (median) following the start of daptomycin therapy. The clinical success rate was 80.8% and the overall rate of treatment failure was 10.8%. The main reasons for daptomycin discontinuation were successful end of therapy (75.8%), switched therapy (11.7%), and treatment failure (4.2%). Daptomycin demonstrated a favorable safety and tolerability profile regardless of treatment duration.

Conclusions

Daptomycin had a relevant role in the treatment of Gram-positive infections in the clinical practice setting in Brazil.

Simultaneous quantification of antimicrobial agents for multidrug-resistant bacterial infections in human plasma by ultra-high-pressure liquid chromatography-tandem mass spectrometry

Antibiotic-resistant bacterial infection is one of the most serious clinical problems worldwide. Vancomycin, teicoplanin, daptomycin, and colistin are glycopeptide and lipopeptide antibiotics that are frequently used to treat multidrug-resistant bacterial infections. Therapeutic drug monitoring is recommended to ensure both safety and efficacy and to improve clinical outcomes. This study developed a fast, simple, and sensitive ultra-high-pressure liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for the simultaneous determination of the concentrations of these four drugs in human plasma. The sample preparation process includes a simple protein denaturation step using acetonitrile, followed by an 11-fold dilution with 0.1% formic acid. Eight target peaks for the four drugs can be analyzed within 3 min using a Kinetex™ 2.6 μm C18 column. The mass spectrometry parameters were optimized, and two transitions for each target peak were used for multiple reaction monitoring, which provided high sensitivity and specificity. The UHPLC-MS/MS method was validated over clinical concentration ranges. The intra-day and inter-day precisions for the ratio of the peak area of each analyte to the peak area of the internal standard were all below 12.7 and 14.7% relative standard deviations, respectively. The accuracy at low, medium, and high concentrations of the eight target peaks was between 89.3 and 110.7%. The standard curves for the analytes were linear and had coefficients of determination higher than 0.997. The limits of detection were all below 70 ng mL(-1). The use of this method to analyze patient plasma samples confirmed that it is effective for the therapeutic drug monitoring of these four drugs and can be used to improve the therapeutic efficacy and safety of treatment with antibiotics.

Novel biodegradable sandwich-structured nanofibrous drug-eluting membranes for repair of infected wounds: an in vitro and in vivo study

BACKGROUND

The purpose of this study was to develop novel sandwich-structured nanofibrous membranes to provide sustained-release delivery of vancomycin, gentamicin, and lidocaine for repair of infected wounds.

METHODS

To prepare the biodegradable membranes, poly(D, L)-lactide-co-glycolide (PLGA), collagen, and various pharmaceuticals, including vancomycin, gentamicin, and lidocaine, were first dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol. They were electrospun into sandwich-structured membranes with PLGA/collagen as the surface layers and PLGA/drugs as the core. An elution method and a high-pressure liquid chromatography assay were used to characterize in vivo and in vitro drug release from the membranes. In addition, repair of infected wounds in rats was studied. Histological examination of epithelialization and granulation at the wound site was also performed.

RESULTS

The biodegradable nanofibrous membranes released large amounts of vancomycin and gentamicin (well above the minimum inhibition concentration) and lidocaine in vivo for more than 3 weeks. A bacterial inhibition test was carried out to determine the relative activity of the antibiotics released. The bioactivity ranged from 40% to 100%. The nanofibrous membranes were functionally active in treating infected wounds, and were very effective as accelerators in early-stage wound healing.

CONCLUSION

Using the electrospinning technique, we will be able to manufacture biodegradable, biomimetic, nanofibrous, extracellular membranes for long-term delivery of various drugs.

Vancomycin tolerance in Gram-positive cocci

Vancomycin, a glycopeptide antimicrobial agent, represents the last line of defence against a wide range of multi-resistant Gram-positive pathogens such as enterococci, staphylococci and streptococci. However, vancomycin-resistant enterococci and staphylococci, along with vancomycin-tolerant clinical isolates, are compromising the therapeutic efficacy of vancomycin. It is conceivable that tolerance may emerge during prolonged vancomycin use. It has not been until recently, however, that the molecular basis of this tolerance began to be understood. Superoxide anions might be involved in the bactericidal activity of vancomycin in enterococci, and recent evidence suggests that the stringent response is partly responsible for vancomycin tolerance in Enterococcus faecalis. The mechanism of vancomycin tolerance in Staphylococcus aureus and Streptococcus pneumoniae is sometimes associated with a reduction of autolysin activity. Vancomycin tolerance in S. aureus and S. pneumoniae also appears to be somehow related with the two-component regulatory systems linked to cell envelope stress, although the precise molecular regulatory pathways remain poorly defined.

[Tolerance and heteroresistance in Gram-positive microorganisms]

During the last few years, insufficient efficacy of currently recommended antimicrobial agents has been observed, mainly in the case of glycopeptides, during the treatment of infections due to methicillin-resistant Staphylococcus aureus, even if these isolates show MIC values within the susceptible range. The phenomena associated with this observation are tolerance (a genetic event in which a bactericidal antibiotic fails to kill a bacterial population), persistence (a non-inherited and transient phenotypic phenomenon in which a bacterial subpopulation -0.1%-10%- survive lethal antimicrobial concentrations irrespective of the mechanisms of action) and heteroresistance (an epigenetic event in which less susceptible isogenic subpopulations are recovered when the entire population is challenged with concentrations exceeding MIC values). New antimicrobials, including daptomycin, are less affected by these phenomena and should be considered as the treatment of choice when these events are demonstrated or suspected.

Evaluation of the antimicrobial activity of lysostaphin-coated hernia repair meshes

Bacterial infections by antibiotic-resistant Staphylococcus aureus strains are among the most common postoperative complications in surgical hernia repair with synthetic mesh. Surface coating of medical devices/implants using antibacterial peptides and enzymes has recently emerged as a potentially effective method for preventing infections. The objective of this study was to evaluate the in vitro antimicrobial activity of hernia repair meshes coated by the antimicrobial enzyme lysostaphin at different initial concentrations. Lysostaphin was adsorbed on pieces of polypropylene (Ultrapro) mesh with binding yields of ∼10 to 40% at different coating concentrations of between 10 and 500 μg/ml. Leaching of enzyme from the surface of all the samples was studied in 2% (wt/vol) bovine serum albumin in phosphate-buffered saline buffer at 37°C, and it was found that less than 3% of adsorbed enzyme desorbed from the surface after 24 h of incubation. Studies of antibacterial activity against a cell suspension of S. aureus were performed using turbidity assay and demonstrated that the small amount of enzyme leaching from the mesh surface contributes to the lytic activity of the lysostaphin-coated samples. Colony counting data from the broth count (model for bacteria in wound fluid) and wash count (model for colonized bacteria) for the enzyme-coated samples showed significantly decreased numbers of CFU compared to uncoated samples (P < 0.05). A pilot in vivo study showed a dose-dependent efficacy of lysostaphin-coated meshes in a rat model of S. aureus infection. The antimicrobial activity of the lysostaphin-coated meshes suggests that such enzyme-leaching surfaces could be efficient at actively resisting initial bacterial adhesion and preventing subsequent colonization of hernia repair meshes.

Antibiotic Combinations with Daptomycin for Treatment of Staphylococcus aureus Infections

Daptomycin is a lipopeptide antibiotic with a unique mechanism of action on Gram-positive bacteria. It is approved for treatment of skin and soft-tissue infections with Gram-positive bacteria, bacteraemia and right-sided infective endocarditis caused by Staphylococcus aureus. Diminishing susceptibility of S. aureus to daptomycin during treatment of complicated infections and clinical failure have been described. Combinations of daptomycin with other antibiotics including gentamicin, rifampin, beta-lactams, trimethoprim/sulfamethoxazole (TMP-SMX), or clarithromycin present a new approach for therapy. In vitro and animal studies have shown that such combinations may, in some cases, be superior to daptomycin monotherapy. In this paper we focus on the antibiotic combinations for complicated S. aureus infections.

Prospective, open-label investigation of the pharmacokinetics of daptomycin during cardiopulmonary bypass surgery

As methicillin-resistant Staphylococcus aureus (MRSA) becomes more prevalent, vancomycin is becoming increasingly used as a prophylaxis against surgical-site infections for cardiothoracic surgeries. However, vancomycin administration can be challenging, and the pharmacokinetics of alternative antibiotics in this setting are poorly understood. The primary objective of this investigation was to describe the pharmacokinetics of daptomycin in patients undergoing coronary artery bypass graft surgery. We enrolled 15 patients undergoing coronary artery bypass surgery requiring cardiopulmonary bypass. Each subject was administered a single open-label dose of daptomycin (8 mg/kg of body weight) for surgical prophylaxis. Fourteen daptomycin plasma samples were collected. Safety outcomes between subjects who received daptomycin and 15 control subjects who received the standard-of-care antibiotic were compared. The mean maximal concentration of daptomycin (C(max)) was 84.4 ± 27.1 μg/ml; the mean daptomycin concentration during the cardiopulmonary bypass procedure was 33.2 ± 11.4 μg/ml and was 30.9 ± 12.7 μg/ml at sternum closure. Mean daptomycin concentrations at 12, 18, 24, and 48 h were 22.7 ± 9.7, 16.2 ± 8.2, 12.0 ± 4.7, and 3.5 ± 2.3 μg/ml, respectively. Mean daptomycin concentrations were consistently above the MIC at which 90% of the tested isolates are inhibited (MIC₉₀) for S. aureus and S. epidermidis during the cardiopulmonary bypass procedure. Daptomycin was not associated with surgical-site infections or differences in adverse events compared to findings for control subjects. We found that a single dose of daptomycin at 8 mg/kg was well tolerated and achieved adequate plasma concentrations against common pathogens associated with surgical-site infections after cardiothoracic surgery. Daptomycin may be considered an alternative surgical prophylaxis antibiotic for patients undergoing cardiothoracic bypass surgery who are unable to receive vancomycin.