Abstract
Daptomycin is an antibacterial agent with activity against Gram-positive organisms and is a reliable option for the treatment of invasive Gram-positive infections. Daptomycin has been approved for the treatment of complicated skin and skin-structure infections and bacteremia including right-sided endocarditis. In methicillin-resistant
Introduction
Vancomycin is considered the agent of choice for the treatment of resistant Gram-positive cocci, including methicillin-resistant
Daptomycin is the first-in-class cyclic lipopeptide antibiotic that is active against various Gram-positive bacteria and was approved for the treatment of complicated skin and soft tissue infections (cSSTIs) and for the treatment of right-sided infective endocarditis (RIE) due to
Mechanism of Action of Daptomycin
Although the mechanism of action of daptomycin is not well understood, it seems to act through insertion into the cytoplasmic membrane of Gram-positive cells.6,7 Daptomycin interacts with the membrane leading to disruption of the functional structure with membrane leakage, release of ions, and cell death.7,8 Gram-negative organisms are not affected because of a lack of permeability of the external membrane.
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The emergence of daptomycin resistance in gram positive organisms such as
Antimicrobial Activity of Daptomycin
Daptomycin is active against Gram-positive bacteria. Its spectrum includes staphylococci, streptococci including
Pharmacokinetics of Daptomycin can Determine Its Efficacy
Studies performed with a dosage of 6 mg/kg showed that daptomycin has linear pharmacokinetics, becoming nonlinear at higher dosages.
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The efficacy of daptomycin is best correlated with the Cmax or AUC24: MIC of the bacterial strain.6,7 Daptomycin is excreted in the urine (53%–59% at 24 h) with minimal hepatic metabolization,
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and metabolites seem to be inactive and nontoxic.
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Because of its renal excretion, dosage must be adjusted in patients with renal malfunction,6,15 but not in hepatic failure.
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The half-life is 8–9 h, which allows daily administration,
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and the volume of distribution is around 0.1 l/kg, which corresponds with a predominantly extracellular distribution and high protein binding (90%–94%).6,7,15 Protein binding diminishes the activity of the drug in vitro.
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Daptomycin also has a high postantibiotic effect, which ranges between 1.7 and 6 h.6,15 Daptomycin is bactericidal for
Efficacy of Daptomycin against Gram Positive Organisms
The efficacy of daptomycin to treat infections caused by gram positive pathogens was recently studied in a large cohort in which daptomycin was used in Europe and Argentina to treat a variety of Gram-positive infections in a severely ill patient population with multiple co-morbidities, who were commonly infected with drug-resistant pathogens [MRSA, coagulase-negative staphylococci (CoNS) and vancomycin-resistant enterococci (VRE)], and almost half of whom were aged ≥65 years. 18 Daptomycin demonstrated a favorable safety and tolerability profile 18 and low overall rates of clinical failure similar to the early results from the CORE database in the USA,19–22 despite its use in this severely ill population, frequently as second-line or salvage therapy.
Unlike glycopeptides, daptomycin has proven similar efficacy against both MRSA and Methicillin-sensitive
There is emerging evidence that daptomycin is being used to treat infections caused by other Gram-positive species that are of increasing importance in hospital and outpatient practice,27–30 particularly in orthopaedic-related and endovascular infections where other long-term treatment options may be limited. This is also reflected in published treatment guidelines where daptomycin is recommended as first alternative to vancomycin when the vancomycin MIC is no longer associated with a significant chance of clinical success. 1 The efficacy of daptomycin as treatment option for specific infections such as complicated skin and soft tissue infections, bacteremia, endocarditis and orthopedic infections is reviewed separately.
Complicated skin and soft tissue infections (cSSTIs)
Skin and soft-tissue infections caused by Gram-positive cocci range from a simple cellulitis to life-threatening necrotizing fasciitis. Intravenous daptomycin was approved by the Food and Drug Administration (FDA) in 2003 for the treatment of patients with complicated skin and skin-structure infections (cSSIs), including those infected with MRSA. 31 Two randomized trials compared daptomycin at a dose of 4 mg/kg daily to penicillinase-resistant penicillins or vancomycin for the treatment of cSSIs. 31 Among 902 evaluated patients, the clinical efficacy of daptomycin was 83.4%, compared with 84.2% for the comparator group and daptomycin required a shorter duration of administration. 31
In a retrospective analysis of the Cubicin Outcomes Registry and Experience (CORE) 2004 database, 522 patients with skin and skin-structure infections (SSIs) were evaluated. 19 Of these, 64% had cSSIs. 19 Surgical site infections were most common, followed by wound, abscess and diabetic foot infections. Among the subset of patients with cSSIs, the reported clinical outcome was cure in 53%, improvement in 43% and failure in 4%. 19 Daptomycin was also successful in 9 of 10 patients with necrotizing infections. 19 The median dose of daptomycin was 4 mg/kg daily and median treatment duration was 12 days. 19 Daptomycin at a dose of 4 mg/kg was compared with vancomycin and was found to have similar success rate for the treatment of cellulitis and erysipelas, 32 although short-duration, high-dose (10 mg/kg for 4 days) daptomycin for cSSIs was inferior to vancomycin in another study. 33 Another study examined daptomycin efficacy in 53 adult patients with cSSTIs at risk for MRSA infection compared with a matched retrospective cohort of 212 patients treated with vancomycin. The proportions of patients with clinical improvement or resolution of their infections on days three and five were 90% vs. 70% and 98% vs. 81% in the daptomycin and vancomycin groups, respectively. 34
In a separate analysis of a subset of 133 patients with diabetic foot infections, clinical success rates were comparable (66% for the daptomycin arm vs. 70% in the comparator arm). 35 Even with a standard 4 mg/kg regimen, daptomycin allowed for earlier patient discharge than vancomycin in one study of SSTIs, reducing infection costs from $7552 per patient to $5027. 34 According to a recent meta-analysis additional research seems warranted for use of daptomycin in MRSA-confirmed cSSTIs, as adequate sample sizes were not available to draw meaningful conclusions. 36
Another multi-center study demonstrated that intravenous daptomycin is safe, well tolerated, and effective in treating superficial and deep incisional SSI caused by gram-positive microorganisms, including MRSA. 37 Daptomycin therapy provided overall clinical success in more than 90% of patients, including 100% of patients with superficial SSI. The microbiologic response rate was high. 37 Baseline infection pathogens were eradicated in 84% of patients with superficial incisional SSI and in approximately 50% of those with deep SSI. 37 Importantly, all isolates tested–-including MRSA–-were susceptible to daptomycin, and isolates persisting after one course of daptomycin treatment remained susceptible to the drug. 37 Daptomycin was effective in eradicating 100% of superficial SSI and 67% of deep SSI caused by MRSA. 37 The overall clinical success rate of 92% for daptomycin in treating SSI 37 was similar to the clinical success rate of 84% for patients with infected wounds seen in previous studies.19,31 In addition, the results of this multi-center study were similar to those recently reported in a post marketing analysis of the use of daptomycin in the treatment of SSI, in which the overall clinical success rate at the end of therapy in 231 patients was 94%; 98% of patients with a superficial SSI and 89% of patients with a deep SSI achieved clinical success. 38 The differential outcomes in superficial and deep SSI suggest that wound classification should be considered a stratification variable in future studies of antibacterial treatment of SSI. 37
Bacteremia and endocarditis S. aureus bacteremia and endocarditis
Daptomycin was noninferior to standard treatment in a randomized trial that compared daptomycin at a dose of 6 mg/kg daily to either vancomycin or an anti-staphylococcal penicillin, both with initial low-dose gentamicin for the treatment of
In a separate analysis of the subset of patients with MRSA bacteremia or right-sided endocarditis, daptomycin was successful in a higher proportion of patients (44.4% vs. 32.6%) compared to vancomycin/ gentamicin, but the difference did not reach statistical significance.
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In the setting of pulmonary emboli complicating
Daptomycin may be used in the setting of MRSA bacteremia and endocarditis when the vancomycin MIC is ≥2 μg/ml because of the high incidence of therapeutic failure in these cases.8,20 Daptomycin may be considered as an option for empiric therapy in
An ongoing clinical trial compares daptomycin at 10 mg/kg daily with vancomycin dosed to achieve levels of 15–20 μg/ml for the treatment of MRSA bacteremia (clinical trials.gov NCT00695903).
Initial in vitro synergy studies were promising, but
Due to once-daily administration, daptomycin is an attractive option for the treatment of Gram-positive infections in the outpatient setting. In a survey of the agents used for the outpatient treatment of Gram-positive infections in the United States, vancomycin was the most commonly used antimicrobial (70%) followed by daptomycin (27%). 43 Among 949 daptomycin-treated patients registered with the CORE database, clinical success rates were higher (94.6%) for the outpatient parenteral antimicrobial therapy (OPAT) group versus 86.3% for the inpatient group. 44 In addition, in the endocarditis trial, clinical success rates were also high among patients who received daptomycin as outpatients (90% vs. 83% for standard therapy). 43 Better outcomes among OPAT patients were most likely because of patient selection for OPAT and thus additional studies should focus on clinical characteristics of patients who would be ideal candidates for daptomycin OPAT.
Enterococcus bacteremia
The use of daptomycin in the treatment of vancomycin-resistant enterococcal (VRE) bacteremia has only been evaluated in retrospective case series. Although daptomycin has not been approved for the treatment of vancomycin-resistant enterococcal bacteremia, available data suggest that it may be as effective as linezolid.
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A Phase III study comparing daptomycin with linezolid for the treatment of VRE bacteremia was terminated because of difficulty enrolling patients.
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In a recent retrospective study of 30 patients with bacteremia due to VRE who received a median daptomycin dose of 6 mg/kg microbiological cure rate was 80%, while clinical success was observed in 17 patients (59%).
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In a retrospective study in 98 adult patients, 68 of whom received linezolid and 30 of whom received daptomycin, daptomycin and linezolid were found to be equivalent in efficacy, although there was a non-significant trend towards a longer duration of bacteremia (3 vs. 2 days) and a higher mortality rate (26.7% vs. 20.6%) with daptomycin.
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Success rate was observed in 87% among the subset of patients with enterococcal bacteremia from the CORE registry, excluding those with endocarditis.
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In this study, a total of 159 patients with enterococcal bacteremia, were treated with daptomycin either as first-line therapy (17%) or after prior treatment with other antibiotic agents.
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The overall clinical success rate was 87%, with similar rates between patients infected with
Several reports have focused on the use of daptomycin for the treatment of enterococcal bacteremia in neutropenic patients. In a study of 34 allogeneic haematopoietic stem cell recipients, who developed bloodstream infections, 14 (41%) were due to VRE. 52 Ten of these patients received daptomycin, three of whom were reported as microbiological failures; however, the infecting strains remained susceptible to daptomycin in vitro in all three cases. 52 This observation, coupled with the fact that all 10 patients treated with daptomycin had also received linezolid or other antibiotics, highlights the inherent difficulty in interpreting microbiological outcomes. 52 In addition, the clinical picture was complicated by the presence of underlying conditions in these patients and the absence of a comparator group. 52 In an open-label trial four out of nine (44%) febrile neutropenic patients with bacteremia due to VRE who were treated with daptomycin achieved clinical and/or microbiological cure; two patients died within 3 days of commencement of treatment, indicating the severity of their illnesses.53,54 In a retrospective study of neutropenic cancer patients, 10 of whom received linezolid and 21 of whom received daptomycin, daptomycin and linezolid were found to be equivalent in efficacy in terms of clearance of blood cultures, relapse of infection and overall mortality. 28 More recently, treatment failure was observed in 13 of 31 bacteremic patients treated with daptomycin, 6 of which were due to relapses within 1 month of initiation of initial infection. 55
The Infectious Diseases Society of America 2009 guidelines recommend the use of daptomycin for the treatment of catheter-related bacteremia due to VRE or ampicillin-resistant enterococci in patients with or without dialysis. 1 However, no prospective trials are likely to define the role of daptomycin in this setting, because of the complicated clinical presentation and the presence of multiple co-morbidities in patients who develop enterococcal bacteremia.
Staphylococcus coagulase negative (CNS) bacteremia
In one study of CNS bacteremia, all strains were susceptible to daptomycin with a low level MIC and therefore the loss of vancomycin susceptibility did not influence daptomycin susceptibility. 56 These results showed a high efficacy of daptomycin for CNS, and this antibiotic could be useful for the treatment of primary bacteremia or catheter associated bacteremia in severe ill patients, while in patients with high risk to develop pneumonia linezolid should be used instead. 56
Enterococcus endocarditis
In an analysis of the CORE database, clinical success was reported in 10 of 14 patients with
Orthopedic infections
With regard to osteomyelitis and joint infections, Gram positive cocci largely predominate over other microbial pathogens and
In 67 evaluable patients with osteomyelitis from the CORE 2004 database with a median of 76 days of follow-up, clinical outcomes were reported as cure in 63%, improvement in 19% and failure in 10%. 22 Success rates were high (82%) among patients with an orthopedic device and in patients with concurrent bacteremia. 22 A caveat was that many patients underwent further surgery, with joint removal or debridement, which may have influenced outcome. Failures were more common if debridement was not performed. 22 The median dose of daptomycin in patients with osteomyelitis was 5.6 mg/kg, and it was given for a median duration of 35 days but when a dose > 6 mg/kg was used, the success rate was significantly higher (88 vs. 63%). 22 The most common organism was MRSA. 22
In another report from the same database, among 22 patients with septic arthritis without osteomyelitis, 41% were cured and 50% improved. 63 The median dose was 5 mg/kg and the median duration of therapy was 22 days. 63 Almost two-thirds of patients received another antibiotic in addition to daptomycin, with rifampin being the most common. The effectiveness of daptomycin in the treatment of prosthetic hip or knee joint infections is the subject of an ongoing clinical trial (clinical trials.gov NCT00428844). In addition, in a case series of 31 patients with orthopedic infections, 64 16 of whom had osteomyelitis, 87% were cured. In another series, all 10 patients with orthopedic infections were treated successfully. 65 In two retrospective studies, 22 patients with osteomyelitis and three subjects with septic joint infections were treated with daptomycin. 65 MRSA was the predominant pathogen in over 75% of patients. Daptomycin was used as salvage therapy, and its usual dose was 6 mg/kg/day. Clinical success rate was about 90%; follow up periods were one year or less.
Daptomycin has been used for the treatment of prosthetic joint infections in many cases.65–67 These studies included patients with implant-related infection usually caused by multidrug-resistant organisms such as MRSA or VRE and showed good activity in the treatment of infection, with percentage improvements of 60%–90% at the end of therapy.65–69 However, some reports include patients treated with doses of 6 mg/kg, which are probably low for these infections. In fact, in vivo experimental studies suggest that higher dosages are needed in such cases. 17
Owing to its thermostability, daptomycin can be incorporated into polymethylacrylate beads, where it shows similar release kinetics to vancomycin. 70 Such beads, containing daptomycin 7.5% by weight, gave local bone concentrations of up to 178 mg/g in a rat osteomyelitis model and maintained levels above 10 mg/g for over 10 days. 59 Daptomycin-containing beads have yet to be used in human orthopaedic infections, but their successful use was reported in four patients with lower-limb prosthetic vascular graft infections; vancomycin- and tobramycin-containing beads were used in other patients, but numbers were too small for meaningful comparison. 71 Bone and joint infections surely warrant wider investigation, given both their numbers and associated morbidity. 30
Pneumonia and lower respiratory tract infections
The currently available experimental and clinical data for mice72,73 and humans 74 suggest that daptomycin has little efficacy against Gram-positive bacterial infections of the lung, possibly due to interactions of the compound with pulmonary surfactant components, and is therefore currently not recommended for use for the monotherapy of pneumonia. 72
Other infections
A small number of publications documenting the use of daptomycin for the treatment of other infections have appeared recently in the literature. Lower urinary tract infections (UTIs), is a potential area of interest because ~50% of the daptomycin dose is excreted as unchanged drug in urine over 24 h following intravenous administration. 75 One open-label, single-blinded study compared daptomycin and ciprofloxacin for the treatment of adults with complicated UTIs caused by Gram-positive pathogens, the microbiological eradication rate was 81.8% for daptomycin and 78.3% for ciprofloxacin. 76 In a separate report, in all five hospitalized patients with UTIs due to multidrug-resistant VRE who were treated with daptomycin for 5 days, urine cultures 2 days after completion of therapy were negative, and follow-up 10–14 days after therapy revealed no recurrence of bacteriuria. 77
Daptomycin has also been used successfully in two patients receiving peritoneal dialysis for end-stage renal disease who developed peritonitis due to VRE.
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A separate case report also showed that intraperitoneal daptomycin (15 mg/kg once weekly) was successful in the treatment of continuous ambulatory peritoneal dialysis-related peritonitis due to vancomycin-resistant
Efficacy of High Dose Daptomycin
The current literature on a high-dose daptomycin treatment strategy suggests safety and tolerability, even when given for extended durations, along with improved in vitro efficacy.
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However, evidence in support of improved in vivo efficacy from randomised, prospective clinical trials in large populations is still lacking, but necessary. With the optimum dose of daptomycin still unknown, perhaps the most appropriate situations to utilise high-dose daptomycin are in difficult-to-treat infections such as endocarditis.
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A high dose regimen of daptomycin was studied in a prospective, multicentre, randomised, active-controlled study involving 100 patients.
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This study evaluated the efficacy and safety of daptomycin at 10 mg/kg/q24 h for 4 days compared with vancomycin 1 g i.v. every 12 h for up to 14 days. Despite a lack of statistical significance, lack of statistical power to detect difference between treatment groups, unblinded study investigators and imbalanced frequency of adjunctive surgical procedures this study raises efficacy concerns for a high dose daptomycin treatment regimen because of lower clinical success rates.
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The efficacy of daptomycin ≥ 8 mg/kg was also evaluated from data collected as part of the Cubicin® Outcomes Registry and Experience (CORE) database.
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Clinical success (clinical cure or improvement) was achieved in 66 (89%) of 74 patients. Notably, a significantly lower clinical success rate (8/12; 67%) was reported with endocarditis when judged against the other infections (
Safety of High Dose Daptomycin
Prior to optimization of the dosing interval to a once-daily regimen, daptomycin had been associated with reversible CPK elevation and skeletal muscle toxicity. 86 However, in clinical trials with once-daily dosing, daptomycin-associated CPK elevations were demonstrated in 7% of patients receiving the 6 mg/kg dose, only leading to discontinuation of daptomycin in 2.5% of patients, and did not occur in patients receiving the 4 mg/kg dose. 23 In agreement with these clinical trial findings, analysis of the EU-CORE database has shown that daptomycin therapy minimally impacts upon serum CPK concentrations as reflected in the low rates of related adverse effects and discontinuations. 18
A single-center, randomised, double-blinded, placebo-controlled phase 1 study involving 36 healthy volunteers, demonstrated the safety and tolerability of high-dose daptomycin in doses up to 12 mg/kg in healthy study participants over a 2-week period and provided support for further investigation of high-dose daptomycin especially in infections that are difficult to treat. The safety of a high dose regimen of daptomycin (10 mg/kg/q24 h for 4 days compared with vancomycin 1 g i.v. every 12 h for up to 14 days) was also studied in a prospective, multicentre, randomised, active-controlled study involving 100 patients. 33 Importantly, none of the adverse effects that patients in the daptomycin treatment arm experienced were deemed as serious and thus this study adds to the increasing evidence of the safety and tolerability of high-dose daptomycin as no serious adverse events were observed. 33
In a Phase III trial of daptomycin for the treatment of complicated skin and skin-structure infections (cSSIs), adverse effects were comparable in both groups. 9 The most common side effects were gastrointestinal disturbances, headache and injection-site reactions. Daptomycin has been shown to interact with thromboplastin reagents and cause a falsely elevated International Normalized Ratio, without clinical significance. 87
In a retrospective chart review of patients treated with high-dose daptomycin (>6 mg/kg/ dose) ≥14 days, 22 (36.1%) of 61 patients experienced mild adverse events (eg, diarrhea, nausea and arthralgia) that did not require daptomycin to be discontinued. 54 In the 47 patients who had any CPK analysis, a significant CPK elevation was observed in 3 patients (6.4%). The investigators concluded that high-dose daptomycin at a mean of 8 mg/kg/dose for a median duration of 25 days was well tolerated and that the incidence of significant serum CPK elevation was similar to those previously reported when shorter courses of treatment and/or lower doses of daptomycin were utilised. 54
The safety of daptomycin ≥ 8 mg/kg was also evaluated from data collected as part of the Cubicin® Outcomes Registry and Experience (CORE) database. 83 One adverse event or abnormal laboratory result was reported in 28 (30%) of 94 patients, of which 6 (6.4%) of 94 patients had adverse events assessed as possibly related to treatment with daptomycin. Amongst the six patients who had possible daptomycin-related adverse events, three experienced CPK elevations. All CPK increases were assessed and deemed as non-serious. 83
In another retrospective study in patients with staphylococcal infections, comparing patients in the high-dose (>6 mg/kg/day) treatment group 84 versus patients in the standard-dose group, CPK was elevated in one patient (3.2%) treated with high-dose daptomycin to >1000 U/L demonstrating the safety and possible increased efficacy with high-dose daptomycin compared with standard-dose daptomycin. 84 Case reports provide further evidence in support of clinical benefit without increased toxicities when utilising a high-dose daptomycin treatment strategy.58,88–91
It is, however, important to keep in mind that the dosing interval in patients with severe renal impairment (CLCR < 30 mL/min) with or without dialysis should be adjusted to 48 h for both approved doses. 18 Concomitant administration of other antibiotic agents with daptomycin such aminoglycosides is common. Although aminoglycosides are typically associated with nephrotoxicity, the rate of renal toxicity with daptomycin combination regimens was very low (1%) overall and similar to that observed for daptomycin monotherapy (0.8%).18,23 In animal models, daptomycin has been shown to attenuate the nephrotoxicity induced by the administration of gentamicin leading to postulation that daptomycin may in fact have nephron-protective properties. 92
There are relatively few treatment options available for resistant Gram-positive infections that can be used for long treatment durations without an increased risk of adverse effects; eg, myelosuppression and peripheral neuropathy have been related to treatment duration with linezolid. 18 Daptomycin might, therefore, represent a useful option for the treatment of chronic complicated infections where extended duration of therapy is required, such as osteoarticular or endovascular infections.
In conclusion, toxicity is uncommon with daptomycin use. However, the incidence of muscular toxicity may increase in patients on HMG-CoA reductase inhibitors, in patients with renal failure, and in severely ill patients. Therefore, it is reasonable to discontinue these medications while a patient is receiving daptomycin and to monitor more closely for side effects in patients with renal failure and patients in critical condition.
Conclusion
Daptomycin is an antibacterial agent with activity against Gram-positive organisms and a role in the treatment of invasive Gram-positive infections when suboptimal response to vancomycin is expected. Daptomycin has been approved for the treatment of complicated skin and skin-structure infections and bacteremia including right-sided endocarditis. Little experience is available on the treatment of bone and joint infections, although initial data are encouraging. Daptomycin has rapid bactericidal activity that is associated with its unique mechanism of action on the cell membrane. It has favorable pharmacokinetic properties allowing once-daily dosing. Toxicity is rare with currently recommended dosing. With the rising antimicrobial resistance in Gram-positive infections, the use of daptomycin is expected to increase in the following years. However, as a consequence of its increased use, daptomycin resistance may emerge as a significant problem. The current data suggest that daptomycin has a relevant role in the therapeutic armamentarium of physicians for the treatment of Gram-positive infections.
Disclosures
Author(s) have provided signed confirmations to the publisher of their compliance with all applicable legal and ethical obligations in respect to declaration of conflicts of interest, funding, authorship and contributorship, and compliance with ethical requirements in respect to treatment of human and animal test subjects. If this article contains identifiable human subject(s) author(s) were required to supply signed patient consent prior to publication. Author(s) have confirmed that the published article is unique and not under consideration nor published by any other publication and that they have consent to reproduce any copyrighted material. The peer reviewers declared no conflicts of interest.
