Comparative evaluation of daptomycin (LY146032) and vancomycin in the treatment of experimental methicillin-resistant Staphylococcus aureus osteomyelitis in rabbits

Comparing the efficacy of different antibiotic regimens on osteomyelitis: A network meta-analysis of animal studies

Background

Despite the surge in the number of antibiotics used to treat preclinical osteomyelitis (OM), their efficacy remains inadequately assessed.

Objective

To establish network comparisons on the efficacy of antibiotic regimens on OM in animal studies.

Methods

PubMed, Embase, Web of Science, and The Cochrane Library were searched from inception to March 2022 for relevant articles. Odds ratios (ORs) were generated for dichotomous variants, and the standard mean difference (SMD) was calculated for constant variables. The predominant outcomes were the effective rate of sterility, also known as sterility rates, as well as the bacterial counts at the end of the experiments and antibiotic concentrations in serum or bone. All the network meta-analyses were performed using STATA MP 16.0. This study was registered in the International Prospective Register of Systematic Reviews (PROSPERO; no. CRD42022316544).

Results

A total of 28 eligible studies with 1,488 animals were included for data analysis, including 13 antibiotic regimens. Regarding the effective rate of sterility, glycopeptides (GLY), linezolid (LIN), rifampicin (RIF)+β-Lactam, and β-Lactam showed significant efficacy compared with placebo (OR ranging from 0.01 to 0.08). For radiological grade, only RIF+GLY (SMD: −5.92, 95%CI: −11.65 to −0.19) showed significant efficacy compared with placebo. As for reducing bacteria count, fosfomycin (FOS), tigecycline (TIG), GLY, LIN, RIF, RIF+β-Lactam, RIF+GLY, aminoglycosides (AMI), and clindamycin (CLI) showed significant efficacy compared with placebo (SMD ranging from −6.32 to −2.62). Moreover, the bone concentrations of GLY were higher 1 h after administration and the higher blood concentrations were higher after 1 h and 4 h compared with the other antibiotics.

Conclusion

Multiple antibiotic regimens showed significant efficacy in animals with OM, including increasing effective rates of sterility, reducing bacterial counts, and lowering radiological scores. Among them, RIF+GLY was the most promising treatment regimen owing to its optimal efficacy. Based on the preclinical studies included in our meta-analysis, head-to-head clinical randomized controlled trials are required to confirm these findings in humans.

Unexpected synergistic and antagonistic antibiotic activity against Staphylococcus biofilms

Objectives

To evaluate putative anti-staphylococcal biofilm antibiotic combinations used in the management of periprosthetic joint infections (PJIs).

Methods

Using the dissolvable bead biofilm assay, the minimum biofilm eradication concentration (MBEC) was determined for the most commonly used antimicrobial agents and combination regimens against staphylococcal PJIs. The established fractional inhibitory concentration (FIC) index was modified to create the fractional biofilm eradication concentration (FBEC) index to evaluate synergism or antagonism between antibiotics.

Results

Only gentamicin (MBEC 64 mg/L) and daptomycin (MBEC 64 mg/L) were observed to be effective antistaphylococcal agents at clinically achievable concentrations. Supplementation of gentamicin with daptomycin, vancomycin or ciprofloxacin resulted in a similar or lower MBEC than gentamicin alone (FBEC index 0.25-2). Conversely, when rifampicin, clindamycin or linezolid was added to gentamicin, there was an increase in the MBEC of gentamicin relative to its use as a monotherapy (FBEC index 8-32).

Conclusions

This study found that gentamicin and daptomycin were the only effective single-agent antibiotics against established Staphylococcus biofilms. Interestingly the addition of a bacteriostatic antibiotic was found to antagonize the ability of gentamicin to eradicate Staphylococcus biofilms.

18-Fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography scan for monitoring the therapeutic response in experimental Staphylococcus aureus foreign-body osteomyelitis

Background

18-Fluoro-2-deoxy-d-glucose positron emission tomography combined with computed tomography (¹⁸F-FDG PET/CT) scan is useful for diagnosis of osteoarticular infections. Whether ¹⁸F-FDG PET/CT scanning may be used for therapeutic monitoring is not clear. The objective of this study was to develop ¹⁸F-FDG PET/CT scanning for monitoring therapeutic response to antimicrobials in experimental Staphylococcus aureus osteomyelitis.

Methods

A total of 22 rabbits were studied. In 20 animals, the right tibia was inoculated intraoperatively with S. aureus. Two control animals were inoculated with normal saline. A needle was placed in the tibia as a foreign body. Infection was allowed to develop for 21 days when ¹⁸F-FDG PET/CT was performed, the needle was removed, and bone specimens were cultured to confirm infection. Antimicrobial therapy with daptomycin was initiated in all successfully infected animals for 1, 3, or 6 weeks. Following completion of treatment, a second ¹⁸F-FDG PET/CT was performed, animals were euthanized, and infected tibias were harvested for quantitative cultures and histology. A positive scan was defined as ¹⁸F-FDG signal activity greater in the infected tibia than that of the contralateral non-infected control tibia. Therapeutic response was measured by the change of ¹⁸F-FDG signal activity in the infected tibia.

Results

All successfully infected animals (n = 14), with microbiologically and/or histologically confirmed osteomyelitis, had positive ¹⁸F-FDG PET/CT scans, while the two control animals had negative scans despite the presence of the foreign body [mean maximum standardized uptake value (SUVmax) (±SD) values 2.96 (±0.80) vs. 1 (±1.10), respectively, P = 0.04]. In the 14 successfully infected animals, the mean SUVmax was significantly higher in the infected compared to the uninfected tibia (P < 0.0001). A SUVmax of 1.4, when used as a cutoff for infection, yielded a diagnostic accuracy of 93 %. At the end of treatment, successfully treated animals and saline controls had a negative ¹⁸F-FDG PET/CT scan (n = 4), while animals with persistent infection despite treatment (n = 12) had a positive ¹⁸F-FDG PET/CT scan (SUVmax 1.0–3.0) (p < 0.001). SUVmax values were significantly reduced after 42 days of treatment from 3.15 ± 0.5 (day 7) to 1.71 ± 0.37 (day 42) (p = 0.05).

Conclusions

¹⁸F-FDG PET/CT scan is a sensitive and specific tool in therapeutic monitoring of experimental foreign-body osteomyelitis.

Chitosan coating to enhance the therapeutic efficacy of calcium sulfate-based antibiotic therapy in the treatment of chronic osteomyelitis

We demonstrate that coating calcium sulfate with deacetylated chitosan enhances the elution profile of daptomycin by prolonging the period during which high concentrations of antibiotic are released. Coatings reduced initial bolus release of daptomycin by a factor of 10 to approximately 1000 µg/ml, and levels remained above 100 µg/ml for up to 10 days. Chitosan-coated and uncoated calcium sulfate implants with and without 15% daptomycin were evaluated in an experimental model of staphylococcal osteomyelitis through bacteriology scores, radiology, histopathology, and Gram staining. Significant reduction in bacteriology scores was observed for implants containing daptomycin and coated with chitosan compared with all the other groups. We confirm that the use of chitosan-coated calcium sulfate beads for local antibiotic delivery can be correlated with an improved therapeutic outcome following surgical debridement in the treatment of chronic osteomyelitis.

Periprosthetic joint infections: clinical and bench research

Prosthetic joint infection is a devastating complication with high morbidity and substantial cost. The incidence is low but probably underestimated. Despite a significant basic and clinical research in this field, many questions concerning the definition of prosthetic infection as well the diagnosis and the management of these infections remained unanswered. We review the current literature about the new diagnostic methods, the management and the prevention of prosthetic joint infections.

Randomized controlled trial of the safety and efficacy of Daptomycin versus standard-of-care therapy for management of patients with osteomyelitis associated with prosthetic devices undergoing two-stage revision arthroplasty

The prevalence of Staphylococcus aureus causing prosthetic joint infection (PJI) supports investigation of higher doses of daptomycin in the management of PJI. This was a prospective, randomized controlled trial studying safety and efficacy of daptomycin (6 and 8 mg/kg of body weight) compared with standard-of-care therapy for PJI. This open-label study randomized 75 patients undergoing 2-stage revision arthroplasty to daptomycin at 6 or 8 mg/kg or a comparator (vancomycin, teicoplanin, or semisynthetic penicillin). After prosthesis removal, patients received 6 weeks of antibiotic treatment and a 2- to 6-week antibiotic-free period before implantation of a new prosthesis. Test of cure (TOC) was within 1 to 2 weeks after reimplantation. The primary objective was evaluation of creatine phosphokinase (CPK) levels. Secondary objectives were clinical efficacy and microbiological assessments. Of 73 CPK safety population patients, CPK elevation of >500 U/liter occurred in 4 of 25 (16.0%) (daptomycin, 6 mg/kg) and 5 of 23 (21.7%) (daptomycin, 8 mg/kg) daptomycin-treated patients and 2 of 25 (8.0%) comparator patients. Adverse-event rates were similar among daptomycin and comparator groups. Among modified intent-to-treat patients at TOC, clinical success rates were 14 of 24 (58.3%) for 6 mg/kg daptomycin, 14 of 23 (60.9%) for 8 mg/kg daptomycin, and 8 of 21 (38.1%) for the comparator. Overall microbiological success at TOC was 12 of 24 (50.0%) for 6 mg/kg daptomycin, 12 of 23 (52.2%) for 8 mg/kg daptomycin, and 8 of 21 (38.1%) for comparator patients. In conclusion, daptomycin at 6 and 8 mg/kg given for up to 6 weeks was safe and appeared to be effective in managing staphylococcal PJI using a 2-stage revision arthroplasty technique in a total of 49 patients.

Daptomycin compared to vancomycin for the treatment of osteomyelitis: a single-center, retrospective cohort study

BACKGROUND

Osteomyelitis (OM) is a serious infection with high rates of recurrence. Vancomycin has been used for decades in the treatment of OM, but, despite adequate dosing, 30% to 50% of patients experience infection recurrence within 12 months. Daptomycin, a novel lipopetide antibiotic, is also active against resistant gram-positive organisms, but there is little published about its efficacy and tolerability in the treatment of OM.

OBJECTIVE

Our aim was to compare the recurrence rates of OM in patients treated with daptomycin or vancomycin.

METHODS

A retrospective cohort study of all patients at a VA Medical Center between January 1, 2003, and July 31, 2009, who received daptomycin for the treatment of OM was undertaken. Patients with a diagnosis of OM who received at least 2 weeks of daptomycin and had at least 1 follow-up visit within 6 months after completion of therapy were included. Each patient was matched with 2 controls treated with at least 2 weeks of vancomycin for OM. Matching criteria included previous OM, diabetes, peripheral vascular disease, hardware involvement, and surgical therapy. Patients were excluded from the evaluation if they received <14 days of therapy, had no follow-up in the 6 months after therapy was discontinued, had an absolute neutrophil count <500 cells/mm(3), or were receiving vancomycin and daptomycin concurrently. The primary outcome was recurrence of infection within 6 months after the discontinuation of therapy. Secondary outcomes included mean change in creatine phosphokinase (CPK), incident thrombocytopenia, and mean doses of antibiotics. The χ(2) test was used to compare rates of recurrence between groups.

RESULTS

Seventeen patients received at least 2 weeks of daptomycin for the treatment of OM and were matched to 34 vancomycin controls. Twenty-nine percent of patients receiving daptomycin had a recurrence of infection compared with 61.7% in the vancomycin group (P = 0.029). The mean change in CPK for the daptomycin group was +28.8 U/L. No thrombocytopenia developed in any patients receiving daptomycin compared with 2 (5.9%) patients in the vancomycin group.

CONCLUSIONS

In a limited number of cases, significantly fewer patients treated with daptomycin for OM had a recurrence of their infection. Daptomycin may be a tolerable and effective alternative to vancomycin for the treatment of OM.

Daptomycin: local application in implant-associated infection and complicated osteomyelitis

BACKGROUND

The rise of highly resistant bacteria creates a persistent urge to develop new antimicrobial agents. This paper investigates the application of the lipopeptide antibiotic daptomycin in infections involving the human bone.

METHODS

Compressive and tensile strength testing of daptomycin-laden PMMA was performed referring to the ISO 5833. The microstructure of the antibiotic-laden PMMA was evaluated by scanning electron microscopy. Intracellular activity of daptomycin was determined by a human osteoblast infection model. Elution kinetics of the antibiotic-laden bone cement was measured by using a continuous flow chamber setup.

RESULTS

There was no significant negative effect of adding 1.225% and 7.5% per weight of daptomycin to the PMMA. There was no significant difference in intracellular activity comparing gentamicin to daptomycin. Elution of daptomycin from PMMA showed within the first-hour initial peak values of 15-20 μg/mL.

CONCLUSION

Daptomycin has a certain degree of activity in the intracellular environment of osteoblasts. Daptomycin admixed to PMMA remains bactericidal and does not significantly impair structural characteristics of the PMMA. The results of this paper suggest that daptomycin might be a potent alternative for treating osteomyelitis and implant-associated infection in trauma and orthopedic surgery caused by multiresistant strains.

Successful Treatment of Polymicrobial Calcaneal Osteomyelitis with Telavancin, Rifampin, and Meropenem

OBJECTIVE:

To report a case of multidrug-resistant osteomyelitis successfully treated with telavancin, rifampin, and meropenem.

CASE SUMMARY:

An 18-year-old male with spina bifida was treated primarily in the outpatient setting over the course of 133 days with multiple antimicrobials for a recurrent right calcaneal wound and osteomyelitis infection. Initial cultures were positive for methicillin-resistant Staphylococcus aureus and coagulase-negative Staphylococcus, which were treated with intravenous vancomycin 1 g every 12 hours, increased after 13 days to 1.5 g every 12 hours with addition of rifampin 300 mg twice daily, both of which were discontinued on day 22 due to leukopenia (white blood cell count 3.0 × 103/μL) and neutropenia (absolute neutrophil count 0.2 × 103/μL). Daptomycin 8 mg/kg/day was then initiated with rifampin 300 mg twice daily; treatment was discontinued after 49 days due to an elevated creatine kinase level of 1831 U/L (baseline 86). Intravenous meropenem 1 g every 8 hours was again initiated on day 83 following additional identification of quinolone-resistant Pseudomonas aeruginosa from the soft tissue of the right foot. Intravenous vancomycin 1 g every 12 hours was also restarted at this time for persistent coagulase-negative Staphylococcus and oral rifampin 300 mg twice daily was again added. Adverse events again required the discontinuation of vancomycin on day 91. The eventual drug therapy regimen consisted of telavancin 750 mg/day for 42 days, meropenem for 50 days, and oral rifampin for 50 days. At the end of treatment, the patient's right heel wound had almost completely closed. He was without recurrence or treatment-related adverse events at follow-up 1 year later.

DISCUSSION:

Antimicrobial selection for osteomyelitis infections presents a challenge to the clinician due to patient intolerance, increasing antimicrobial resistance, and variable antimicrobial penetration at the site of infection. To our knowledge, this is the first case report of the successful use of a regimen including telavancin for the treatment of a recurrent, coagulase-negative Staphylococcus osteomyelitis infection.

CONCLUSIONS:

In this complex case involving a polymicrobial infection of the right calcaneal bone and surrounding soft tissue, eventual drug therapy including telavancin, meropenem, and rifampin resulted in a successful clinical response.

Successful use of daptomycin in Panton-Valentine leucocidin positive Staphylococcus aureus paediatric osteomyelitis

INTRODUCTION

Efficacy of daptomycin has been recorded in adult Gram-positive bone and joint infections OAI (1) and daptomycin has been used as secondary or tertiary agent when primary agents have failed (1, 2) in the treatment of osteoarticular infections caused by Staphylococcus aureus.

PRESENTATION OF CASE

We report a 16-year-old schoolboy with Panton-Valentine Leucocidin (PVL) positive methicillin susceptible S. aureus osteomyelitis, who was refractory to 9days of recognised antimicrobial chemotherapy with progressive multifocal haematogenous spread. Subsequent addition of daptomycin promptly cleared the bacteraemia and arrested the disease process within 9days.

DISCUSSION

Although cases have been reported of daptomycin usage in children with invasive staphylococcus bacteraemia, endocarditis and OAI (2), we believe this to be the first case report describing the use of daptomycin in paediatric osteomyelitis caused by PVL positive S. aureus.

CONCLUSION

Repercussions of osteomyelitis, in particular those caused by PVL S. aureus, and evolving resistance patterns internationally, highlight the need for further evaluation of daptomycin in the paediatric arena. The response seen with the addition of Daptomycin in this case suggests possible reduction in hospital stay and number of surgical procedures when compared to other published series using conventional antibiotic regimens.

Ceftobiprole: First reported experience in osteomyelitis

A 74-year-old man with long-standing diabetes presented with advanced infection of the right forefoot associated with septic arthritis and osteomyelitis involving the second and third metatarsophalangeal joints. Polymicrobial infection, which included methicillin-resistant Staphylococcus aureus, was documented. First-line antibiotic therapy, which included vancomycin, was not tolerated. A durable cure was obtained following a six-week course of intravenous ceftobiprole medocaril combined with local surgery. The present report is the first to administer intravenous ceftobiprole medocaril to a patient with methicillin-resistant S aureus-associated septic arthritis and osteomyelitis.

Daptomycin, fosfomycin, or both for treatment of methicillin-resistant Staphylococcus aureus osteomyelitis in an experimental rat model

The in vivo activities of daptomycin, fosfomycin, and a combination of both antibiotics against a clinical isolate of methicillin-resistant Staphylococcus aureus (daptomycin MIC, 0.25 μg/ml; fosfomycin MIC, 0.5 μg/ml) were evaluated in a rat model of osteomyelitis. A total of 37 rats with experimental osteomyelitis were treated for 4 weeks with either 60 mg/kg of body weight of daptomycin subcutaneously once daily, 75 mg/kg fosfomycin intraperitoneally once daily, a combination of both drugs, or a saline placebo. After the completion of treatment, animals were euthanized, and the infected tibiae were processed for quantitative bacterial culture. Bone cultures were found to be positive for methicillin-resistant S. aureus in 9 of 9 (100%) animals of the placebo group, in 9 of 9 (100%) animals treated with daptomycin, in 1 of 10 (10%) fosfomycin-treated rats, and in 1 of 9 (22.2%) rats comprising the combination group. Results of bacterial counts in the bone samples were expressed as log(10) CFU/g of bone and analyzed by using the Mann-Whitney U test followed by Bonferroni's multiple-comparison test. Based on bacterial counts, treatment with daptomycin was significantly superior to placebo, although it remained inferior to treatment with fosfomycin. No synergistic or antagonistic effect was observed for the combination therapy. No development of resistance against daptomycin or fosfomycin was observed after the 4-week treatment period.

Resolution of Staphylococcus aureus biofilm infection using vaccination and antibiotic treatment

Staphylococcus aureus infections, particularly those from methicillin-resistant strains (i.e., MRSA), are reaching epidemic proportions, with no effective vaccine available. The vast number and transient expression of virulence factors in the infectious course of this pathogen have made the discovery of protective antigens particularly difficult. In addition, the divergent planktonic and biofilm modes of growth with their accompanying proteomic changes also demonstrate significant hindrances to vaccine development. In this study, a multicomponent vaccine was evaluated for its ability to clear a staphylococcal biofilm infection. Antigens (glucosaminidase, an ABC transporter lipoprotein, a conserved hypothetical protein, and a conserved lipoprotein) were chosen since they were found in previous studies to have upregulated and sustained expression in a biofilm, both in vitro and in vivo. Antibodies against these antigens were first used in microscopy studies to localize their expression in in vitro biofilms. Each of the four antigens showed heterogeneous production in various locations within the complex biofilm community in the biofilm. Based upon these studies, the four antigens were delivered simultaneously as a quadrivalent vaccine in order to compensate for this varied production. In addition, antibiotic treatment was also administered to clear the remaining nonattached planktonic cells since the vaccine antigens may have been biofilm specific. The results demonstrated that when vaccination was coupled with vancomycin treatment in a biofilm model of chronic osteomyelitis in rabbits, clinical and radiographic signs of infection significantly reduced by 67 and 82%, respectively, compared to infected animals that were either treated with vancomycin or left untreated. In contrast, vaccination alone resulted in a modest, and nonsignificant, decrease in clinical (34% reduction) and radiographic signs (9% reduction) of infection, compared to nonvaccinated animal groups untreated or treated with vancomycin. Lastly, MRSA biofilm infections were significantly cleared in 87.5% of vaccinated and antibiotic-treated animals, while antibiotics or vaccine alone could not significantly clear infection compared to controls (55.6, 22.2, and 33.3% clearance rates, respectively). This approach to vaccine development may lead to the generation of vaccines against other pathogenic biofilm bacteria.

Efficacy of daptomycin combined with rifampicin for the treatment of experimental meticillin-resistant Staphylococcus aureus (MRSA) acute osteomyelitis

Daptomycin exhibits rapid bactericidal activity against Gram-positive organisms, including meticillin-resistant Staphylococcus aureus (MRSA). Daptomycin in combination with rifampicin needs to be assessed in bone infection. An MRSA acute osteomyelitis model was used. Daptomycin and vancomycin were compared, alone or in combination with rifampicin, over 4 days. Surviving bacteria were counted in bone, bone marrow and joint fluid. Vancomycin and daptomycin as single therapies were ineffective, but both combinations were significantly more effective than the corresponding monotherapy. Combination of daptomycin and rifampicin could prevent S. aureus from developing resistance. This combination could be a useful alternative to treat MRSA osteomyelitis at an early stage.

New therapeutic choices for infections caused by methicillin-resistant Staphylococcus aureus

In recent years, a marked increase in the incidence of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) has occurred in many countries. This review addresses the effectiveness and limitations of drugs classically used for the treatment of MRSA, e.g. vancomycin, and also newer anti-MRSA antimicrobials, e.g. second-generation glycolipopeptides, tigecycline, and beta-lactams.

Daptomycin in bone and joint infections: a review of the literature

INTRODUCTION

To review the pharmacology, pharmacokinetics, efficacy, and safety of daptomycin, a novel antibiotic for the treatment of bone and joint infections, a literature search of relevant articles was conducted.

MATERIALS AND METHODS

A PubMed/MEDLINE search (1990-April 2008) to identify relevant English-language literature was conducted. Search terms included bone and joint infection, osteomyelitis, daptomycin, and methicillin-resistant Staphylococcus aureus (MRSA). Additional articles were identified by reviewing the bibliographies of articles cited. Programs and abstracts from infectious disease meetings were searched, and prescribing information of antibiotics indicated for bone and joint infections consulted. All articles identified from data sources published in English were evaluated.

RESULTS

Caused primarily by Gram-positive pathogens such as S. aureus and, to a lesser extent, Enterococcus faecalis, bone and joint infections are difficult to treat successfully. Surgical intervention and prolonged courses of antibiotics are frequently required, and failure of first-line antibiotic therapy is common. The emergence of S. aureus strains with reduced susceptibility to vancomycin, the longstanding gold standard for bone and joint infections, has complicated the clinical scenario. Few randomized trials comparing the efficacy of different antibiotics for bone and joint infections exist. Daptomycin, a novel intravenous lipopeptide antibiotic, has shown potent in vitro activity against a broad spectrum of Gram-positive bacteria, including many resistant pathogens commonly associated with bone and joint infections such as MRSA and vancomycin-resistant E. faecalis. Early clinical investigation of daptomycin in bone and joint infections unresponsive to antibiotics, such as vancomycin, has found a cure rate of approximately 80%, with a low incidence of adverse events and drug resistance.

CONCLUSION

Further studies are warranted to determine if limited clinical evidence, described in individual case reports and a daptomycin-specific retrospective registry, suggests daptomycin is a promising option for patients with bone and joint infections such as MRSA osteomyelitis.

Daptomycin: The First Approved Lipopeptide Antimicrobial

OBJECTIVE

To review the literature concerning the first Food and Drug Administration-approved lipopeptide antimicrobial, daptomycin.

DATA SOURCES

A PUBMED search was conducted to identify pertinent English-language journal articles between 1985 and November 2003, and additional references were obtained from the bibliographies of these articles. Abstracts from the Interscience Conference on Antimicrobial Agents and Chemotherapy meetings from 1985 through 2003 also were reviewed.

STUDY SELECTION

All studies evaluating any aspect of daptomycin.

DATA SYNTHESIS

Daptomycin is a semisynthetic lipopeptide, the first such antimicrobial agent to reach the marketplace. Its mechanism of action differs from that of the related agent vancomycin in that much of its effect is not because of inhibition of peptidoglycan biosynthesis, but instead is a result of alterations in cell-membrane electrical charge and transport. It exhibits a broad spectrum of activity against gram-positive aerobes and anaerobes, including methicillin-, penicillin-, aminoglycoside-, and vancomycin-resistant strains. In subjects with normal renal function, the terminal disposition half-life is about 7 to 10 hours. It is principally eliminated as unchanged drug in the urine. Available clinical trial data demonstrate efficacy in complicated skin and skin-structure infections resulting from susceptible gram-positive pathogens, but not in pneumonia. The principal adverse event of concern, although rare, is myotoxicity, manifested by muscle pain and/or weakness and elevated serum creatine phosphokinase (CPK) concentrations. The approved dosage regimen is 4 mg/kg intravenously over 30 minutes once daily for 7 days to 14 days. Studies are underway evaluating doses of up to 8 mg/kg once daily.

CONCLUSIONS

Daptomycin, the first lipopeptide antimicrobial to be marketed, exhibits activity against multiresistant gram-positive pathogens, including linezolid- and quinupristindalfopristin-resistant strains. As such, it is a potentially valuable agent to treat infections resulting from such pathogens. To preserve its utility, it should not be used indiscriminately for infections resulting from pathogens sensitive to other antimicrobials. It is probably best used with restricted access and used only for multiresistant gram-positive pathogens where alternative agents cannot be employed. If used, careful monitoring for the signs and symptoms of myotoxicity, including obtaining weekly serum CPK levels, is mandatory. In addition, bacterial sensitivities to this agent should be prospectively monitored by national antimicrobial surveillance programs like SENTRY, TRUST, and LIBRA.

Daptomycin-rifampin for a recurrent MRSA joint infection unresponsive to vancomycin-based therapy

A 54-y-old morbidly obese male presented with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia secondary to chronic right hip arthroplasty infection. Bacteremia persisted despite prolonged vancomycin-based therapy (MIC < or = 1 microg/ml) and prosthetic removal. Adding daptomycin-rifampin resolved bacteremia within 48 h; hip cultures remained negative post-discharge. This case describes alternative treatment for chronic MRSA infections.

Combination therapy with daptomycin, vancomycin, and rifampin for recurrent, severe bone and prosthetic joint infections involving methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) infections are commonly treated with vancomycin (VAN) or another glycopeptide antibiotic. However, when vancomycin fails or infections recur, there are few other therapeutic options. Presented here are 2 cases where a novel combination of daptomycin, vancomycin, and rifampin resolved recurrent MRSA bone and prosthetic joint functions.

Daptomycin eluted from calcium sulfate appears effective against Staphylococcus

The emergence of resistant strains of Gram-positive organisms in osteomyelitis creates treatment challenges. Daptomycin is an antibiotic that shows promise for treating some resistant strains of Gram-positive infections; however, it has not been widely used clinically for the treatment of osteomyelitis. We determined whether daptomycin eluted from calcium sulfate-a local delivery vehicle used for the treatment of osteomyelitis-retained activity against Gram-positive bacteria. Daptomycin was mixed with calcium sulfate hemihydrate, with both laboratory powder and a commercial kit, to form a hardened pellet. Daptomycin was eluted from calcium sulfate and retained its ability to inhibit bacterial growth of Staphylococcus aureus and Staphylococcus epidermidis for eluates gathered up to 28 days. Our preliminary data demonstrates sterilized pellets with daptomycin retained their ability to inhibit bacterial growth of certain strains of Gram-positive organisms.

Efficacies of ceftobiprole medocaril and comparators in a rabbit model of osteomyelitis due to methicillin-resistant Staphylococcus aureus

The pharmacokinetics and distribution into bone tissue of ceftobiprole in uninfected New Zealand White rabbits were determined after subcutaneous administration of the prodrug ceftobiprole medocaril. Serum exposure (maximum concentration of the drug in serum, trough concentration, area under the concentration-time curve) to ceftobiprole at 20 and 80 mg/kg was dose proportional, and there was no accumulation of ceftobiprole following repeated (every 6 h [q6h]) injections of the antibiotic. Ceftobiprole titers in the tibial matrix and marrow were 3.2 +/- 1.3 microg/g and 11.2 +/- 6.5 microg/g, respectively, in uninfected animals treated with 20 mg/kg of the antibiotic and 13.4 +/- 7.3 microg/g and 66.3 +/- 43.2 microg/g, respectively, in uninfected animals treated with 80 mg/kg of the antibiotic. No differences in ceftobiprole titers were observed between right and left tibiae for either bone matrix or marrow. The efficacies of 4 weeks of treatment with ceftobiprole (40 mg/kg administered subcutaneously [s.c.] q6h), vancomycin (30 mg/kg administered s.c. q12h), or linezolid (60 mg/kg administered orally q8h) were compared, using a rabbit model of methicillin-resistant Staphylococcus aureus tibial osteomyelitis. After treatment with ceftobiprole, the bacterial titers in all infected left tibiae from evaluable rabbits were below the level of detection, whereas only 73% of infected left tibiae from vancomycin- or linezolid-treated animals had bacterial titers below the level of detection; the mean titers of ceftobiprole were 3 to 5 times higher in infected left tibiae than in uninfected right tibiae. These results indicate that ceftobiprole provided effective parenteral treatment of osteomyelitis in this rabbit model.

Clinical experience with daptomycin for the treatment of patients with osteomyelitis

Data from a registry were analyzed to describe the clinical experience with daptomycin (Cubicin; Cubist Pharmaceuticals, Inc., Lexington, MA) for the treatment of patients with osteomyelitis. The Cubicin Outcomes Registry and Experience (CORE) 2004 database was used to identify patients treated for osteomyelitis. Posttherapy follow-up outcome assessments were collected for a subset of these patients. A total of 67 patients with osteomyelitis were clinically evaluable for outcome at the end of daptomycin therapy and had outcome assessed at a posttherapy visit. The median follow-up interval after the last dose of daptomycin was 76 days (range, 1 to 547 days). The median initial dose was 5.6 mg/kg (range, 3.2 to 7.5 mg/kg), and the median duration of therapy was 35 days (range, 3 to 546 days). Daptomycin was given concurrently with other antibiotics in 48% of cases. Methicillin-resistant Staphylococcus aureus was the most common pathogen (45%). Clinical outcomes at follow-up were cure, 42 (63%); improved, 13 (19%); failure, 7 (10%); and nonevaluable, 5 (7%). A total of 82% of patients with an orthopedic device (n = 17) were successfully treated, as were 88% of patients with concurrent bacteremia (n = 16). Failures were more likely if surgical debridement was not performed (24% vs. 5%; P = 0.045). The clinical success rate for patients treated with an initial daptomycin dose >4 mg/kg was significantly higher than for patients treated with an initial dose < or =4 mg/kg (88% vs. 65%; P = 0.013, chi2 test). Daptomycin had a 94% success rate when used alone with no follow-up antibiotics. The results indicate that daptomycin is being used in clinical practice to treat patients with osteomyelitis caused by gram-positive pathogens including MRSA. Prospective, controlled clinical trials of daptomycin are warranted that include rigorous data collection and long-term follow-up analysis.

Clinical experience with daptomycin treatment of foot or ankle osteomyelitis: a preliminary study

We retrospectively reviewed 25 patients with foot or ankle osteomyelitis reported to a registry who were treated with daptomycin. The patients' clinical experience was analyzed and described at a median dose of 6 mg/kg (range, 4-6.2 mg/kg) and a median duration of 38 days (range, 6-59 days). Twenty-three patients received daptomycin as secondary or tertiary therapy, primarily for not responding to their prior antibiotic therapy (n = 15). Concomitant antibiotics were given to 11 patients, mostly for Gram-negative and/or anaerobic coverage. Methicillin-resistant Staphylococcus aureus was the most common pathogen overall (15 of 25 patients). The median followup interval was 9 weeks (range, 0.5-77 weeks). Outcomes at the end of therapy were 16 patients' symptoms resolved, eight patients improved, and one patient did not respond to therapy; at followup, 19 patients' symptoms resolved, three patients improved, and three patients did not respond to therapy. Ongoing antibiotics were given to 52% of patients for a minimum of 8 days (median, 30 days; range, 8-232 days). Four patients with an implant (all removed) were successfully treated. Daptomycin appears promising for foot and ankle osteomyelitis caused by Gram-positive bacteria. Prospective, controlled clinical trials of daptomycin for osteomyelitis are warranted.

Experimental osteomyelitis: what have we learned from animal studies about the systemic treatment of osteomyelitis?

Clinical trials of systemic antibiotic treatment of osteomyelitis are difficult to perform for many reasons, such as low incidence rate of osteomyelitis, variety of anatomic locations, stage and etiologic agents. In this article, we reviewed the experimental studies on osteomyelitis available in the English medical literature since 1968, to ascertain their actual and potential impact on the treatment of human osteomyelitis. Major results are summarized and topics of major interest, such as reproducibility of animal models, predictive value of animal models, correlation of pharmacokinetics between different animals and humans, and the correlation of outcome between animal and clinical studies are discussed. Most of the reviewed animal models are reproducible and dependable. However, establishing the right dose regimen in animals appeared a critical factor, which might undermine the predictive value of the experimental study. Due to difficulties in comparing results of animal and human studies, the predictive value of animal studies about osteomyelitis is still unclear. However, animal models gave valuable information to the clinician for choosing the minimal duration of antibiotic treatment. Even though the use of antibiotic combinations was associated with better outcome in the majority of animal studies, such a finding seems to have limited impact on clinical practice.

Uncertain efficacy of daptomycin for prosthetic joint infections: a prospective case series

Daptomycin is an option for prosthetic joint infection (PJI) because it is bactericidal against gram-positive bacteria, including multiple-resistant isolates, and active against stationary-phase bacteria in biofilm present on implants. To evaluate its possible utility, we prospectively monitored 12 adults with gram-positive PJI who were not candidates for vancomycin. Pathogens included methicillin-resistant Staphylococcus aureus (n = 7), methicillin-resistant-coagulase-negative Staphylococci (n = 4), and methicillin-sensitive Staphylococcus aureus (n = 1). All patients completed a 6-week course of daptomycin 4 mg/kg/day. One died of an unrelated cause shortly after completing therapy. After a followup of 7 to 13 months, six patients had no clinical, laboratory, or radio-graphic signs of recurrence. One patient failed a first course and was subsequently treated with hardware removal and a second course with no recurrence. Five patients had culture-confirmed failure-all due to MRSA-including two during therapy despite hardware removal and three 1 to 10 months after completing daptomycin but with retained hardware. The efficacy of daptomycin 4 mg/kg/day is uncertain in patients with PJI, especially when hardware is retained. Further study is needed to determine why in vitro data did not predict clinical success and to ascertain any potential benefit from higher doses.

Emergence of a clinical daptomycin-resistant Staphylococcus aureus isolate during treatment of methicillin-resistant Staphylococcus aureus bacteremia and osteomyelitis

The emergence of a clinically daptomycin-resistant Staphylococcus aureus isolate occurred during treatment of methicillin-resistant S. aureus bacteremia and probable vertebral osteomyelitis. The breakthrough isolate was indistinguishable from pretreatment daptomycin-susceptible isolates by pulsed-field gel electrophoresis. Daptomycin nonsusceptibility was confirmed by MIC and time-kill curve analyses.

Daptomycin treatment of Staphylococcus aureus experimental chronic osteomyelitis

BACKGROUND

Infection due to methicillin-resistant Staphylococcus aureus (MRSA) is increasingly common in nosocomial and community settings. Daptomycin is a cyclic lipopeptide anti-infective with activity against MRSA, approved for treatment of complicated skin and skin structure infections. Daptomycin may be useful in systemic or local treatment of chronic osteomyelitis.

METHODS

We measured mechanical strength of daptomycin- and vancomycin-loaded polymethylmethacrylate (PMMA), assayed in vivo release of daptomycin and vancomycin from daptomycin- and vancomycin-loaded PMMA, respectively, and compared the efficacy of two systemic doses of daptomycin with that of vancomycin, each with or without the respective anti-infective loaded into PMMA, using a rat model of MRSA chronic osteomyelitis.

RESULTS

Neither tensile nor compressive strength of PMMA was impacted by impregnation with these antimicrobials at a concentration of 7.5% by weight. The peak concentrations of daptomycin and vancomycin in rat tibial bone surrounding a 7.5% daptomycin- and vancomycin-loaded 3 mm PMMA bead were 178 and 49 mg/L, respectively. In the treatment of experimental osteomyelitis, rats assigned to no treatment, daptomycin 50 mg/kg subcutaneously twice daily, daptomycin 60 mg/kg subcutaneously twice daily, and vancomycin 50 mg/kg intraperitoneally twice daily had 6.4, 4.1, 4.0 and 4.5 median log10 cfu/g of bone at the end of 21 days of therapy. All systemic anti-infectives studied were more active than was no treatment. Daptomycin- or vancomycin-loaded PMMA did not, however, exhibit microbiological efficacy alone or adjunctively, as assessed 21 days after implantation.

CONCLUSIONS

Daptomycin is released from PMMA in vivo at a rate similar to that of vancomycin. Systemic daptomycin is as active as vancomycin in a rat model of chronic MRSA experimental osteomyelitis.

Clinical progression of methicillin-resistant Staphylococcus aureus vertebral osteomyelitis associated with reduced susceptibility to daptomycin

Daptomycin, a novel cyclic lipopeptide antibiotic, exhibits rapid bactericidal activity in vitro against most clinically relevant gram-positive organisms, including drug-resistant pathogens. Herein we describe a patient in whom methicillin-resistant Staphylococcus aureus with reduced susceptibility to daptomycin was responsible for bacteremia and progressive vertebral osteomyelitis during daptomycin therapy.

Development of Daptomycin resistance in vivo in methicillin-resistant Staphylococcus aureus

Daptomycin is a new lipopeptide antibiotic that is rapidly bactericidal against Staphylococcus aureus. We report daptomycin resistance and treatment failure in 2 patients with osteomyelitis due to methicillin-resistant S. aureus. Disk diffusion susceptibility testing failed to detect resistance. Daptomycin at high concentration retained bactericidal activity against resistant isolates.

Daptomycin: a novel cyclic lipopeptide antimicrobial

PURPOSE

The development, activity, pharmacokinetics, pharmacodynamics, clinical efficacy, adverse effects, and dosage and administration of daptomycin are reviewed.

SUMMARY

Daptomycin, a novel cyclic lipopeptide antimicrobial, is bactericidal against a range of gram-positive bacteria, including many multiple-drug-resistant isolates. It has only minimal activity against anaerobic bacteria and no activity against gram-negative bacteria. Daptomycin exhibits linear pharmacokinetics, and the plasma concentration-versus-time relationship is best described by a two-compartment model with first-order elimination. The initial bactericidal activity is rapid, extensive, and concentration related. In clinical trials, daptomycin has shown efficacy in treating complicated skin and skin-structure infections (CSSSIs); the drug carries FDA-approved labeling for same. The adverse effects of daptomycin appear comparable to those of vancomycin and semisynthetic penicillins. The dosage for CSSSIs is 4 mg/kg by i.v. infusion every 24 hours.

CONCLUSION

Daptomycin is bactericidal against gram-positive organisms and offers an option in the treatment of CSSSIs.

Daptomycin: a cyclic lipopeptide antimicrobial agent

Objectives:

The aims of this article were: to summarize the pharmacology, pharmacokinetics, and efficacy ofdaptomycin; to explore its safety profile; and to discuss its current and potential roles as an antimicrobial therapy.

Methods:

A literature search was conducted using the MEDLINE (1966–August 2004) and InternationalPharmaceutical Abstracts (1970–August 2004) databases with the search terms daptomycin, LY146032, and lipopeptide antibiotics. Abstracts of the Interscience Conference on Antimicrobial Agents and Chemotherapy and documents submitted to the US Food and Drug Administration were also reviewed.

Results:

Phase III study results suggest no difference in efficacy or tolerability between daptomycin 4 mg/kgIV QD and vancomycin or semisynthetic penicillins for complicated skin and skin-structure infections. Animal studies suggest daptomycin may be useful for the treatment of endocarditis. Daptomycin is not indicated for pneumonia, with poorer outcomes than conventional treatment It is available as an IV medication and exhibits 92% plasma protein binding in vitro. In healthy adult humans, daptomycin has a volume of distribution of 0.1 Ukg and a plasma elimination half-life of ∼9 hours, and is eliminated primarily by renal excretion (∼54%). In patients with reduced renal function, including those receiving hemodialysis and peritoneal dialysis, the dose interval should be 48 hours. No dosage adjustment appears to be necessary for mild to moderate hepatic impairment. The use of daptomycin in patients with severe hepatic impairment has not been assessed. The most commonly reported adverse events include constipation, nausea, injection-site reactions, headache, and diarrhea. Patients should also be monitored regularly for skeletal muscle toxicity.

Conclusions:

Daptomycin may be useful for complicated skin and skin-structure infections and gram-positive pathogens resistant to conventional antimicrobials. However, limited data are currently available for duration of treatment beyond 14 days and at doses >4 mg/kg QD.

Daptomycin: a lipopeptide antibiotic for the treatment of serious Gram-positive infections

Infections caused by drug-resistant pathogens are on the rise. Daptomycin, a cyclic lipopeptide with activity against most Gram-positive pathogens, including vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus, is a newly US-FDA approved antimicrobial for complicated skin and skin structure infections (cSSSI). Daptomycin has a unique mechanism of action that results in destruction of the membrane potential. The rapid bactericidal activity of daptomycin makes it an attractive antibiotic for serious Gram-positive infections.

Daptomycin: a novel agent for Gram-positive infections

The alarming increase in the incidence of Gram-positive infections, including those caused by resistant bacteria, has sparked renewed interest in novel antibiotics. One such agent is daptomycin, a novel lipopeptide antibiotic with proven bactericidal activity in vitro against all clinically relevant Gram-positive bacteria. These include resistant pathogens, such as vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), glycopeptide intermediately susceptible Staphylococcus aureus (GISA), coagulase-negative staphylococci (CNS) and penicillin-resistant Streptococcus pneumoniae (PRSP), for which there are very few therapeutic alternatives. Daptomycin provides rapid, concentration-dependent killing and a relatively prolonged concentration-dependent post-antibiotic effect in vitro. Spontaneous acquisition of resistance to daptomycin occurs rarely. Daptomycin exhibits linear pharmacokinetics, minimal accumulation with once-daily dosing, and low plasma clearance and volume of distribution. Phase II clinical trials indicate that daptomycin at doses of 2 mg/kg q24 h and 3 mg/kg q12 h is efficacious against skin and soft tissue infections and bacteremia, respectively. In addition, results in endocarditis suggested potential efficacy with higher doses. On the basis of clinical trials to date, it appears that daptomycin has an excellent safety profile, with the incidence and nature of serious adverse events comparable to those observed with conventional therapy. Adverse events associated with other classes of antimicrobials (nephrotoxicity, local irritation, ototoxicity, hypersensitivity, and gastrointestinal effects) were uncommon with daptomycin. Minimal skeletal muscle toxicity was seen at only the highest dose tested (4 mg/kg q12 h), predicted by elevations in serum creatinine phosphokinase, and readily reversible upon discontinuation of treatment. There were no signs of toxicity in cardiac or smooth muscle. Phase II and III clinical trials are underway to evaluate daptomycin for the treatment of Gram-positive bacteremia and complicated skin and soft tissue infections, respectively. Daptomycin holds promise as a rapidly acting and highly effective antibiotic for Gram-positive infections.

Release of daptomycin from polymethylmethacrylate beads in a continuous flow chamber

Because daptomycin is active against Gram-positive cocci, it may be useful in the treatment and prevention of bone and joint infections when incorporated into polymethylmethacrylate (PMMA). The release kinetics of daptomycin from PMMA were studied in a continuous flow chamber designed to simulate in vivo conditions. Three-millimeter beads containing 2.5%, 7.5%, and 15.0% daptomycin (weight daptomycin per weight PMMA) were individually placed in a chamber with 1 mL Krebs Ringer buffer flowing at 1 mL/hour. The majority of daptomycin was released in the first 24 hours. The mean peak concentrations were 13.4, 62.3, and 146.7 microg/mL; the mean AUC0-infinity were 30, 272, and 1204 h x microg/mL; and the mean percentages of daptomycin released were 6%, 18%, and 42% for the beads containing 2.5%, 7.5%, and 15.0% daptomycin, respectively. Daptomycin is released from PMMA in a continuous flow chamber at a rate similar to that previously determined by our laboratory for vancomycin.

[Animal models of osteomyelitis]

Despite new approaches in biochemical testing, radiologic and nuclear medicine and advances in surgical techniques, the problem of diagnosis and therapy of acute and chronic osteitis has not been finally solved. Clinical research on osteitis is problematic as there are many variables influencing the inflammatory process and a wide spectrum in therapeutic options exists, hampering research under defined conditions. Consequently, there was an early need for animal models. In vivo experimental settings were established to gain reproducible and reliable results under standardized conditions on the pathogenesis and therapy of osteitis. In this article, an overview of the hitherto established experimental animal models and the results of osteitis research on these models is given.

Daptomycin

Daptomycin, the first in a class of agents known as lipopeptides, is a novel antimicrobial agent used for the treatment of gram-positive infections. The compound has a distinctive mechanism of action that exerts its bactericidal activity by disrupting plasma membrane function without penetrating into the cytoplasm. The agent has received much interest because of its activity against multidrug-resistant, gram-positive bacteria such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and glycopeptide-intermediate and -resistant S. aureus. Daptomycin demonstrates concentration-dependent killing and is eliminated primarily by glomerular filtration. It was approved in September 2003 for the treatment of complicated skin and soft tissue infections. It has a safety profile similar to other agents commonly administered to treat gram-positive infections. Daptomycin is a welcome addition to the antimicrobial armamentarium for the treatment of bacterial infections. Further clinical experience with this compound will help define its role in the treatment of resistant gram-positive organisms.

Slow-releasing potential of vancomycin-loaded porous hydroxyapatite blocks implanted into MRSA osteomyelitis

Although antibiotic-loaded hydroxyapatite blocks have been used for the treatment of chronic osteomyelitis, their long-term potential for releasing antibiotic into human bones is not well known. Five patients with chronic osteomyelitis due to methicillin-resistant Staphylococcus aureus (MRSA) infection were effectively treated with local implantation of vancomycin-loaded hydroxyapatite blocks. Blocks were removed during the following reconstructive surgeries when the releasing capability of the blocks, and the bacteriocidal activity of the remaining vancomycin in these blocks could be evaluated. Vancomycin was rapidly released within 1 month after implantation, and by 3 months 90% of vancomycin had leaked from the blocks. At 18 months vancomycin still remained in a bacteriocidal form in the hydroxyapatite blocks, though the blocks had no releasing potential or the eluted vancomycin had been changed to a different form. Vancomycin-loaded porous hydroxyapatite blocks would be useful for the treatment of chronic osteomyelitis or implant-associated osteomyelitis due to MRSA.

Efficacy of daptomycin in experimental endocarditis due to methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus is becoming increasingly prevalent as both a nosocomial and a community-acquired pathogen. Daptomycin, a lipopeptide antibiotic now in phase III clinical trials, is rapidly bactericidal in vitro against a range of gram-positive organisms, including methicillin-resistant S. aureus (MRSA). In this study, we compared the efficacy of daptomycin with that of vancomycin, each with or without rifampin, in a model of experimental aortic valve endocarditis due to MRSA. The infecting strain (MRSA strain 32) was susceptible to daptomycin (MIC = 1 micro g/ml), vancomycin (MIC = 0.5 micro g/ml), and rifampin (MIC = 0.5 micro g/ml). Daptomycin was administered at 25 or 40 mg/kg q24h (q24h) by subcutaneous injection in an attempt to simulate human doses of 4 and 6 mg/kg q24h, respectively. Vancomycin was given at 150 mg/kg q24h by continuous intravenous infusion. Rifampin was given at 25 mg/kg by intramuscular injection q24h. Treatment was started 6 h postinoculation and continued for 4.5 days. Outcome was assessed by counting the residual viable bacteria in vegetations. The mean peak daptomycin levels in serum at 2 h after subcutaneous administration of 25 and 40 mg/kg were 64 and 91 micro g/ml, respectively. Daptomycin was undetectable in serum at 24 h. The total exposure was comparable to that achieved clinically in humans receiving the drug. Bacterial counts (mean log(10) number of CFU per gram +/- the standard deviation) in untreated controls reached 10.6 +/- 0.8. In treated rats, bacterial counts were as follows: vancomycin, 7.1 +/- 2.5; daptomycin at 25 mg/kg, 5.5 +/- 1.7; daptomycin at 40 mg/kg, 4.2 +/- 1.5. The difference between daptomycin at 40 mg/kg and vancomycin at 150 mg/kg was statistically significant (P = 0.004). In the study of combination therapy, vegetation bacterial counts were as follows: daptomycin at 40 mg/kg, 4.6 +/- 1.6; rifampin, 3.6 +/- 1.3; vancomycin plus rifampin, 3.3 +/- 1.1; daptomycin plus rifampin, 2.9 +/- 0.8. The difference between daptomycin and daptomycin plus rifampin was statistically significant (P = 0.006). These results support the continued evaluation of daptomycin for serious MRSA infections, including infective endocarditis.

Experimental osteomyelitis treatment with antibiotic-impregnated hydroxyapatite

A calcium hydroxyapatite antibiotic implant was evaluated to determine its efficacy as an antibiotic delivery system in a localized osteomyelitis rabbit model. Localized rabbit tibial osteomyelitis was developed with an intramedullary injection of methicillin resistant Staphylococcus aureus. Infected rabbits were randomized and divided into eight groups depending on treatment with or without debridement, systemic antibiotics, antibiotic-impregnated polymethylmethacrylate beads, or calcium hydroxyapatite implants with and without antibiotic impregnation. All treatments began 2 weeks after infection. After 4 weeks of therapy, the involved bones were cultured for concentrations of Staphylococcus aureus per gram of bone. Rabbits (n = 11) that had calcium hydroxyapatite (impregnated with vancomycin) implanted into the dead space after the debridement surgery had an 81.8% infection clearance after treatment. Rabbits (n = 10) that had polymethylmethacrylate beads (impregnated with vancomycin) implanted into the dead space after debridement surgery had a 70% clearance rate. All other treatment modalities resulted in less than 50% clearance rates. Calcium hydroxyapatite may be an effective alternative to polymethylmethacrylate for providing local antibiotic therapy in cases of methicillin resistant Staphylococcus aureus osteomyelitis.