daptomycin is effective in the treatment of experimental...

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Daptomycin Is Effective in the Treatment of Experimental Endocarditis Due to

Methicillin-Resistant and Glycopeptide-Intermediate Staphylococcus aureus

Francesc Marco,1 Cristina García de la Mària,

1 Yolanda Armero,

1 Eurídice Amat,

1 Dolors

Soy,2 Asunción Moreno,

3 Ana del Río,

3 Manel Almela,

1 Carlos A. Mestres,

4 José M.

Gatell,3 María Teresa Jiménez de Anta,

1 José M. Miró,

3* for the Hospital Clinic

Experimental Endocarditis Study Group†

1Microbiology Service, Hospital Clínic, Institut d’Investigacions Biomèdiques August Pi-

Sunyer, University of Barcelona School of Medicine, Barcelona, Catalunya, Spain

2 Pharmacy Service, Hospital Clínic, Institut d’Investigacions Biomèdiques August Pi-

Sunyer, University of Barcelona School of Medicine, Barcelona, Catalunya, Spain

3 Infectious Diseases Service, Hospital Clínic, Institut d’Investigacions Biomèdiques

August Pi-Sunyer, University of Barcelona School of Medicine, Barcelona, Catalunya,

Spain

4Cardiovascular Institute, Institut d’Investigacions Biomèdiques August Pi-Sunyer,

University of Barcelona School of Medicine, Barcelona, Catalunya, Spain

†Members of the Hospital Clinic Endocarditis Study Group, Hospital Clínic-IDIBAPS,

University of Barcelona School of Medicine, Barcelona, Spain: Miró JM, Moreno A, del

Río A, Gatell JM (Infectious Diseases Service); Marco F, García de la Mària C, Armero

Y, Almela M, Jiménez de Anta MT (Microbiology Service), Mestres CA, Cartañá R,

Ninot S, Pomar JL, Azqueta M, Sitges M, Paré JC, Sanz G (Cardiovascular Institute),

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Copyright © 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.Antimicrob. Agents Chemother. doi:10.1128/AAC.00510-07 AAC Accepts, published online ahead of print on 21 April 2008

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Pérez N, Ramírez J, Ribalta T (Pathology Department), Brunet M (Toxicology Service),

Soy D (Pharmacy Service), and de Lazzari E (UASP).

*Corresponding author:

Jose M. Miró

Infectious Diseases Service

Hospital Clinic Universitari

Villarroel 170

08036-Barcelona

Spain

Phone: 34-93-2275586

Fax: 34-93-4514438

E-mail: [email protected]

Presented in part at the Interscience Conference on Antimicrobial Agents and

Chemotherapy (ICAAC), held December 16-19, 2005, in Washington, DC, USA.

Abstract number B-2002.

Suggested running head: Daptomycin for MRSA/GISA Experimental Endocarditis

Conflicts of interest: None of the authors have any potential conflicts of interest with

this study.

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Abstract

Daptomycin is a lipopeptide antibiotic with potent in vitro activity against gram-positive cocci,

including S. aureus. This study evaluated in vitro and in vivo efficacy of daptomycin against 2

methicillin-resistant clinical S. aureus (MRSA) isolates: MRSA 277 (vancomycin MIC 2

µg/ml) and GISA ATCC 700788 (vancomycin MIC 8 µg/ml). Time-kill experiments

demonstrated that daptomycin was bactericidal in vitro against these 2 strains. The in vivo

activity of daptomycin (6 mg/kg q 24 h) was evaluated using a rabbit model of infective

endocarditis and compared with high-dose (HD, 1 g i.v. q 6 h) and recommended-dose (RD, 1

g i.v. q 12 h) vancomycin regimens for 48 hours and an untreated control group. Daptomycin

was significantly more effective than vancomycin-RD in reducing the density of bacteria in the

vegetations for the MRSA (0 [0-1.5] vs. 2 [0-5.6] log CFU/g veg; P = 0.02) and GISA (2 [0-2]

vs. 6.6 [2.0-6.9] log CFU/g veg; P < 0.01) strains studied. In addition, daptomycin sterilized

more vegetations than vancomycin-RD against MRSA (13/18 [72%] vs. 7/20 [35%]; P = 0.02)

and both vancomycin regimens against GISA (12/19 [63%] vs. 4/20 [20%]; P < 0.01). No

statistical difference between vancomycin-HD and vancomycin-RD for MRSA treatment was

noted. These results support the use of daptomycin for treatment of aortic valve endocarditis

caused by GISA and MRSA.

Word count = 220

Keywords: experimental endocarditis, GISA, MRSA, Staphylococcus aureus,

vancomycin MIC 2 µg/ml, recommended-dose vancomycin, high-dose vancomycin,

daptomycin.

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Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) strains are a common cause of

severe community-acquired and healthcare-associated infections, causing over one

quarter of all S. aureus infective endocarditis (IE) cases (15). When treating IE caused by

MRSA, vancomycin may exhibit slow bactericidal activity and diffuse poorly into

bacterial vegetations (26, 33). Over the years, vancomycin use has been associated with

treatment failures in patients with IE and bacteremia, even in instances where patients’

MRSA isolates remained in the susceptible minimum inhibitory concentration (MIC)

range (16, 22). Furthermore, recent studies showed a vancomycin MIC shift from MRSA

with a vancomycin MIC of < 0.5 µg/ml to strains with MIC values of 1 or 2 µg/ml (21,

35). Sakoulas and colleagues found that clinical success correlated with vancomycin MIC

values: vancomycin treatment failure for MRSA bacteremia was significantly more likely

when the vancomycin MIC was 1-2 µg/ml compared with < 0.5 µg/ml (32). Two other

studies showed similar results (21, 34). Moreover, the emergence of glycopeptide-

intermediate S. aureus (GISA) and heterogeneous GISA (hGISA) (in addition to

vancomycin-resistant S. aureus [VRSA]) strains has mandated the development of

alternatives to vancomycin for the clinical care of drug-resistant S. aureus infections (1,

11, 36, 37).

Daptomycin is a cyclic lipopeptide antibiotic with rapid bactericidal activity against most

antibiotic-resistant gram-positive pathogens in vitro, including GISA and MRSA strains

(7, 17). It is approved by the FDA and EMEA for the treatment of complicated skin and

skin-structure infections and bacteremia, including those involving right-sided IE caused

by MSSA and MRSA (9). A randomized clinical study (14) found that daptomycin is not

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inferior to standard therapy for S. aureus bacteremia and right-sided IE. Against MRSA,

44% of daptomycin-treated patients had a successful clinical outcome, compared with

32% of patients receiving vancomycin (14).

Compared with MRSA data, there are far fewer data available regarding the activity of

daptomycin against S. aureus with reduced susceptibility to glycopeptides (GISA)

including vancomycin. The objective of this study was to compare daptomycin with 2

vancomycin regimens (using the recommended dose [RD] or a high dose [HD] of

vancomycin) in an experimental model of aortic valve endocarditis in rabbits infected

with MRSA or GISA using a humanized pharmacokinetics model.

Materials and Methods

Bacterial isolates. The MRSA 277 strain used in the study described here was isolated

from a patient with bacteremia at Hospital Clínic Universitari in Barcelona, while the

GISA strain was isolated from a patient in the United States (30) and is currently

included in the American Type Culture Collection of strains (ATCC 700788). Both

strains were stored at -80ºC in skim milk.

Antibiotics. Daptomycin powder was supplied by Cubist Pharmaceuticals (Lexington,

MA, USA). Vancomycin, gentamicin, and rifampin were purchased from Sigma (St.

Louis, MO, USA).

Susceptibility testing. Gentamicin, rifampin, and vancomycin MICs and minimal

bactericidal concentrations (MBCs) were determined using the microdilution method in

liquid media cation-adjusted Mueller-Hinton broth (Oxoid, Hampshire, England),

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according to the procedures of the Clinical and Laboratory Standards Institute (CLSI;

formerly National Committee for Clinical Laboratory Standards [NCCLS]) (29).

Daptomycin susceptibility testing was in Mueller-Hinton broth adjusted to 50 µg/ml of

calcium per standard methodology. S. aureus ATCC 29213 was used as the test control

strain.

Time-kill studies. All time-kill curves were performed in duplicate according to CLSI

criteria. An inoculum of 105 colony-forming units (CFU)/ml was used. Bactericidal

activity was defined as at least a 3-log reduction in CFU at 24 hours in comparison with

the initial inoculum. Viability counts were performed at 0, 4, and 24 hours (13).

Study animals. An experimental aortic valve endocarditis was induced in New Zealand

White rabbits (body weight, 2 kg), which were obtained from San Bernardo Farm

(Pamplona, Spain). The animals were housed in the animal facilities of Facultad de

Medicina, Universidad de Barcelona, which is equipped with automatic air exchange

with a high-efficiency particulate air (HEPA) filter and a circadian light cycle. They were

nourished ad libitum.

Human pharmacokinetics simulation studies. Antibiotics were administered using a

computer-controlled infusion pump system, designed to reproduce human serum

pharmacokinetics in rabbits after an intravenous (i.v.) infusion. Animal drug doses were

chosen to simulate the pharmacokinetic profile of daptomycin (6 mg/kg i.v. q 24 h) (4,

10, 11) and vancomycin (30 mg/kg i.v. divided into 2 doses; for an adult of 70 kg, 1 g i.v.

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q 12 h) in humans. These are the current recommended doses to treat S. aureus

endocarditis (2, 14). In addition, vancomycin-HD was also tested in order to achieve the

proposed optimal pharmacokinetic/pharmacodynamic (PK/PD) index of AUC/MIC > 350

(28) for the treatment of serious infections due to MRSA. For this vancomycin-HD

treatment, the animals received 60 mg/kg i.v. vancomycin divided into 4 doses

(equivalent to 1 g i.v. q 6 h, for a 70-kg adult). Assuming an MIC for MRSA of 2 µg/ml,

this dose would simulate the human PK profile necessary for the aforementioned PK/PD

ratio.

To determine the concentrations of daptomycin and vancomycin in serum samples in 5

healthy rabbits, blood was drawn from a carotid catheter at different times after a single

i.v. injection of the antibiotic. Rabbits received 25 mg/kg of vancomycin and 15 mg/kg of

daptomycin. Daptomycin concentrations in plasma were assayed by the disk-plate

bioassay method (12) with Micrococcus luteus (ATCC 9341) as the bioassay

microorganism and Mueller-Hinton agar as the growth medium. The sensitivity of

daptomycin bioassay was 0.5 µg/ml. Vancomycin concentrations were assayed at the

Centre de Diagnòstic Biomèdic, Hospital Clínic, Barcelona. The concentration was

measured by immunoturbidimetric test, boosted by latex method (ADVIA Chemistry

System, Bayer Health Care LLC, Leverkusen, Germany). The limit of detection of the

procedure was 0.8 µg/ml. The range was from 0.8 to 72.9 µg/ml, and the inter- and intra-

assay coefficient of variation was from 2.2% to 2.7%, evaluated for 3 levels of

concentrations: 10.9, 39.3, and 73.1 µg/ml.

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In order to ensure that rabbits were dosed appropriately in the experimental IE model, it

was necessary to first obtain the pharmacokinetic parameters of daptomycin and

vancomycin in healthy, uninfected rabbits. Different pharmacokinetic parameters were

estimated on the basis of an open 2-compartment model in order to compare the

pharmacokinetics in rabbits, the human-adapted model, and humans (19, 20) as

previously described (27).

An infusion pump system was set up to deliver antibiotics intravenously into rabbits at

previously calculated flow rates to simulate the human kinetics of 6 mg/kg daptomycin

daily (n = 5); 1 g vancomycin every 12 hours (n = 5); or 1 g vancomycin every 6 hours (n

= 4). To determine the antibiotic concentrations in rabbits’ serum, 1 ml of blood was

sampled at different times after the start of drug infusion.

Endocarditis model. Experimental aortic valve infective endocarditis was induced

according to the method described by Garrison and Freedman (18). A catheter was

inserted through the right carotid artery into the left ventricle, and the catheter for the

antibiotic administration was placed into the inferior vena cava through the jugular vein,

as previously described (27).

The infusion pump delivered 2 ml/hour of 0.9% saline solution until the beginning of

antimicrobial administration. Twenty-four hours after placement of the intracardiac

catheter, all animals were infected via the marginal ear vein with 1 ml of saline solution

containing 7 × 105

CFU/ml of the MRSA strain or 8 × 105 CFU/ml of the GISA strain.

One ml of blood was obtained 16 hours after infection and immediately before the

initiation of antimicrobial therapy to confirm the bacteremia, which was interpreted to

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indicate IE. The infected rabbits were then randomized to the following treatment groups:

control with saline solution only (n = 20 for MRSA, n = 17 for GISA); daptomycin (n =

19 for MRSA, n = 19 for GISA); vancomycin-RD (n = 20 for MRSA, n = 23 for GISA);

and vancomycin-HD (n = 18 for MRSA, n = 22 for GISA). Eighteen hours after

inoculation with the MRSA/GISA, daptomycin and vancomycin treatments were

initiated; also at that time, control animals were sacrificed and vegetations quantitated for

bacterial CFUs. Antibiotics were administered via the computer-controlled infusion pump

system for 48 hours. After finishing the 48-hour treatment, animals were sacrificed after

an additional 6 half-lives of either daptomycin (48 hours) or vancomycin (6 hours) had

elapsed. This provided growing time for residual viable bacteria contained within the

endocardial vegetations.

Analysis of endocardial vegetations. After antibiotic treatment, rabbits were killed and

aortic valve vegetations were removed and processed as previously described (27).

The recovered bacteria were retested to measure daptomycin and vancomycin MICs for

comparison to pretreatment MIC values. The results were expressed as the number of

log10 CFUs of MRSA or GISA per gram of vegetation. The result was assigned a value of

2 if there was no growth on the quantitative plates but there was growth in the qualitative

culture (the rest of the homogenate in tryptic soy broth). The result was assigned a value

of zero, and the vegetation was considered sterile if there was no growth from the initial

quantitative culture or from the homogenates cultured for a week.

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Statistical analysis. The results were expressed as the median and the interquartile range

(IQR) interval of the number of log10 CFUs of MRSA or GISA per gram of vegetation.

The Mann-Whitney rank-sum test was used to compare the log10 CFU/g values between

the different treatment groups. The Fisher exact test was used to compare the rate of

sterilization of vegetations and assess whether there were differences between treatment

groups.

Results

Susceptibility testing. The MRSA strain was susceptible to vancomycin and daptomycin

(MIC, 2 µg/ml and 0.12 µg/ml; MBC, 2 µg/ml and 0.25 µg/ml, respectively) but resistant

to gentamicin and rifampin (MIC > 256 µg/ml for both), according to the CLSI standard

MIC breakpoints (29). The GISA strain was susceptible to daptomycin and gentamicin

(MIC, 0.5 µg/ml and 0.25 µg/ml; MBC, 1 µg/ml and 128 µg/ml, respectively), but

presented intermediate resistance to vancomycin (MIC, 8 µg/ml) and resistance to

rifampin (MIC > 256 µg/ml). The MBC/MIC ratio (14) for the GISA isolate (128/8)

indicated it was tolerant to vancomycin (23).

In vitro time-kill experiments. The in vitro activity of daptomycin and vancomycin for

MRSA 277 and GISA ATCC 700788 is presented in Fig. 1A-1B and Fig. 2A-2B,

respectively. At the concentrations tested (between 4 and 0.5 times the MIC), daptomycin

showed a bactericidal activity over the MIC for both strains, while vancomycin was

bacteriostatic.

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Pharmacokinetic studies. The pharmacokinetic parameters obtained from the human-

adapted model were similar to those in humans (3) (Table 1). The mean trough

concentration of daptomycin was well above the daptomycin MICs of both the MRSA

and GISA strains, and the mean trough concentration of vancomycin-RD and

vancomycin-HD exceeded the vancomycin MIC of MRSA (2 µg/ml). Vancomycin

studies were also performed in GISA strains for a negative control. The mean trough

concentration in the 38 treated rabbits (18 MRSA and 20 GISA) of the vancomycin-HD

arms was 20 µg/ml at 24 hours and 19 µg/ml at 48 hours. We do not have concentrations

from treated rabbits in the vancomycin-RD arm.

Treatment of established endocarditis. The relative effectiveness of the daptomycin

and vancomycin therapeutic regimens for the treatment of established endocarditis

(control, daptomycin, vancomycin-RD, and vancomycin-HD) is shown in Table 2. One

rabbit treated with daptomycin (from MRSA arm), 3 treated with vancomycin-RD (from

GISA arm), and 2 with vancomycin-HD (from GISA arm) died during the experiment

and were not included in the analyses.

In the 2 strains of S. aureus tested, all control rabbits had infected aortic valve

vegetations with a high median bacterial titer per gram of vegetation (>9 log10 CFU).

Comparisons between treated groups revealed that after 48 hours of treatment,

daptomycin was significantly more effective than vancomycin-RD in sterilizing the

MRSA and GISA vegetations (P = 0.02 and P < 0.01, respectively). In comparison with

vancomycin-HD, daptomycin sterilized more vegetations in the MRSA group, but the

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differences did not reach statistical significance (P = 0.17), and compared to HD-

vancomycin, daptomycin was significantly more effective against the GISA isolates (P <

0.01). Daptomycin also reduced the median number of MRSA and GISA CFUs in the

vegetations of treated animals to a greater extent than both vancomycin regimens. These

differences were statistically significant for both strains in the vancomycin-RD arm

(MRSA, P = 0.02; GISA, P < 0.01) and against GISA in the vancomycin-HD arm (P =

0.02).

The vancomycin-HD was more active than the vancomycin-RD for the MRSA strain, but

there were no statistically significant differences either in the proportion of sterilized

vegetations (P = 0.35) or in the reduction of the density of the bacteria within the

vegetations (P = 0.13). In the GISA experimental endocarditis, vancomycin-HD showed

more activity than vancomycin-RD (P = 0.03), but the proportion of sterilized vegetations

was low and the same (20%) in both arms.

All the MRSA and GISA isolates from the endocardial vegetations had the same MIC of

the study strain after daptomycin, vancomycin-RD, and vancomycin-HD treatments.

Discussion

The in vitro susceptibility and time-kill results provided here indicate that daptomycin

has bactericidal activity against MRSA 277 and GISA ATCC 700788 strains, having

MIC/MBC values of 0.12/0.25 µg/ml and 0.5/1 µg/ml, respectively. This is consistent

with previous results in which daptomycin was found to be active against GISA isolates.

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Animal model experiments with daptomycin have been published previously in the peer-

reviewed literature for IE infections caused by enterococci (6, 25), as well as S. aureus

and MRSA (5, 31), but there are limited animal model data available with GISA IE

infections (24). The present study used a rabbit model simulating human-like

pharmacokinetics to investigate the efficacy of daptomycin in S. aureus aortic valve IE

caused by MRSA or GISA. Here daptomycin was significantly more effective in treating

GISA aortic IE than were both vancomycin regimens after 48 hours of treatment (P <

0.01). Daptomycin was also significantly more effective in treating MRSA aortic IE than

was vancomycin-RD (P < 0.01) but did not significantly differ from vancomycin-HD in

this regard. For both the MRSA and the GISA isolates studied, vancomycin-HD (60

mg/kg i.v. divided into 4 doses; for an adult of 70 kg, 1 g i.v. q 6 h) was not significantly

different from vancomycin-RD (30 mg/kg i.v. divided into 2 doses; for an adult of 70 kg,

1 g i.v. q 12 h) except for the reduction of bacteria within the vegetations in the GISA

animals (P = 0.03). In order to reach an optimal pharmacokinetic/pharmacodynamic

(PK/PD) index of AUC/MIC > 350 (28), we needed to simulate in rabbits a schedule of 1

g i.v. q 6 h. With this regimen, we obtained in the vancomycin-HD an AUC/MIC of 333,

and a mean steady-state trough serum concentrations of vancomycin close to 20 µg/ml in

the 38 treated rabbits. In humans, the efficacy of this vancomycin-HD regimen in treating

episodes of MRSA endocarditis with vancomycin MIC of 2 µg/ml isolates must be

counterbalanced with the increased risk of renal toxicity of this regimen (21).

The activity of daptomycin in our study is in partial agreement with 2 earlier studies. In a

rat model that did not use human-like pharmacokinetics, Voorn et al. (37) showed that

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daptomycin (5 mg/kg b.i.d.) was more effective than vancomycin (100 mg/kg b.i.d.) or

teicoplanin (15 mg/kg b.i.d.) to treat cloxacillin-tolerant or cloxacillin-nontolerant aortic

S. aureus endocarditis. In addition, Cha and Rybak (8) used an in vitro simulated

endocardial vegetations model, where daptomycin (6 mg/kg) achieved 99.9% kill of

GISA by 8 hours, while vancomycin was ineffective after the same period. In contrast,

Kaatz et al. demonstrated that daptomycin (8 mg/kg q 8h) and teicoplanin (12.5 and 40

mg/kg q 12h) were as efficacious as vancomycin (17.5 mg/kg q 6h) in reducing MRSA

found in rabbit endocardial vegetations after 4 days of treatment (24), but that study did

not use a human-like pharmacokinetic model. While the computer-controlled drug

infusion system used in the present study can simulate human drug pharmacokinetics and

is automated for technical ease, it has been only recently developed and, thus, confounds

interstudy comparisons using different vegetations models, animals, and different dosing

methods and frequencies. The other important limitation is bacterial strain heterogeneity.

Preclinical studies such as those presented here will continue to be important as

physicians look to optimize vancomycin dosage for MRSA endocarditis caused by

isolates with a vancomycin MIC = 2 µg/ml and to look for vancomycin alternatives to

treat MRSA endocardial infections, and potentially those caused by VRSA. There are

limited clinical data available on the use of other antibiotics in lieu of vancomycin for

MRSA IE. The recent clinical study with daptomycin published by Fowler et al.—the

largest study performed in patients with bacteremia and/or IE caused by S. aureus,

including isolates with methicillin resistance—demonstrated that daptomycin alone is

comparable to dual antibiotic therapy with semisynthetic penicillin or vancomycin plus

gentamicin in these infections (14). In this trial, the efficacy of daptomycin for right-

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sided endocarditis caused by MSSA or MRSA was good. However, for left-sided

endocarditis, its efficacy was as poor as current treatment options—antistaphylococcal

penicillin (nafcillin, oxacillin, flucloxacillin) or vancomycin—both with initial

gentamicin therapy. Furthermore, the MIC increase for daptomycin and vancomycin in

some patients with microbiological failure is a cause for concern. In our experimental

study, daptomycin was better than vancomycin-RD for the treatment of MRSA or GISA

IE and was also more effective than vancomycin-HD for the treatment of GISA IE. We

did not detect an increase in the MIC of the strains after 2 days of therapy. However, we

cannot rule out the possibility of the development of heteroresistance to vancomycin or

daptomycin, because population analyses were not performed on bacteria harvested from

vegetations.

In conclusion, in the rabbit experimental system used here, daptomycin was effective in

sterilizing GISA and MRSA aortic valve endocarditis vegetations, was more effective

than vancomycin-HD in treating MRSA experimental endocarditis, was more potent than

vancomycin-RD and vancomycin-HD in treating GISA experimental endocarditis, and

may provide a foundation for the use of daptomycin in treating left-sided MRSA/GISA

endocarditis in humans.

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Acknowledgments and Financial Disclosure/Conflict of Interest: This work was

supported in part by a medical school grant from Cubist Pharmaceuticals, Inc., 65

Hayden Avenue, Lexington, MA 02421 (USA); and a grant from the Ministerio de

Sanidad y Consumo, Instituto de Salud Carlos III Madrid (Spain), Spanish Network for

the Research in Infectious Diseases (REIPI RD06/0008), and CIBER CB 06/06/2008.

This work was also supported in part by Fondo de Investigaciones Sanitarias (FIS)

(Madrid, Spain) grants FIS 00/0475, FIS 02/0322, and FIS 05/0170. The authors also

thank Fundación Máximo Soriano Jiménez for technical support. Dr. J.M. Miró was a

recipient of a research grant from the Institut d’Investigacions Biomèdiques August Pi i

Sunyer (IDIBAPS) and the Conselleria de Salut de la Generalitat de Catalunya,

Barcelona (Spain).

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[[Figure legends]]

FIG. 1A. Results of time-kill experiments for MRSA 277 strain incubated with

daptomycin. Cell density (log 10 CFU/ml) was determined at indicated time points. CFU

= colony-forming unit; DAP = daptomycin.

FIG. 1B. Results of time-kill experiments for MRSA 277 strain incubated with

vancomycin. Cell density (log 10 CFU/ml) was determined at indicated time points. CFU

= colony-forming unit; VAN = vancomycin.

FIG. 2A. Results of time-kill experiments for GISA ATCC 700788 strain incubated with

daptomycin. Cell density (log 10 CFU/ml) was determined at indicated time points. CFU

= colony-forming unit; DAP = daptomycin.

FIG. 2B. Results of time-kill experiments for GISA ATCC 700788 strain incubated with

vancomycin. Cell density (log 10 CFU/ml) was determined at indicated time points. CFU

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Table 1. Pharmacokinetic and pharmacodynamic parameters

Vancomycin-RD Vancomycin-HD Daptomycin

Previously Reported Human

Values (Single Dose)

Dose 1 g i.v.a 6 mg/kg i.v.

b

Cmax/Cmin (µg/ml) 52/10 NA 86/15

K (h-1

) 0.15 a 0.07

b

T½ β (h) 4.8 a 9.5

b

AUC (µg⋅h/ml) 358.6 a NA 973.9

b

Protein binding 50% 92%

Animal Values (n = 5)

K (h-1

± SD) 0.53 ± 0.14 0.19 ± 0.01

T½ β (h ± SD) 1.3 ± 0.4 3.57 ± 0.19

AUC (µg⋅h/ml ± SD) 101 ± 16 665.7 ± 90 439.8 ± 132.4

Protein binding 65% 90%

Human-like Values (n = 5)

Cmax/Cmin (µg/ml) 46/6 50/15 86/15

K (h-1 ± SD) 0.18 ± 0.03 0.09 ± 0.01

T½ β (h ± SD) 3.8 ± 1.2 7.6 ± 1.3

AUC (µg⋅h/ml ± SD) 298.8 ± 18 665.7 ± 90.43 845.7± 207

Pharmacodynamic Data

AUC/MIC

MRSA 277 149.4c 332.8

c 7,047.5

d

GISA ATCC 700788 37.4e 83.2

e 1,691.4

f

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a Data from Blouin et al. Vancomycin pharmacokinetics in normal and morbidly obese

subjects. Antimicrob Agents Chemother. 1982;21(4):575-80. (4)

bCubist, data on file (11, 12) and data from Benvenuto M et al. (3).

cMIC277 vancomycin = 2 µg/ml;

dMIC277 daptomycin = 0.12 µg/ml;

eMIC700788

vancomycin = 8 µg/ml; fMIC700788 daptomycin = 0.5 µg/ml.

RD = Recommended dose; HD = High-dose; AUC = area under the curve; K =

elimination rate constant; SD = standard deviation; T1/2 = terminal half-life; NA = not

available.

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TABLE 2. Treatment of experimental endocarditis caused by MRSA 277 and ATCC

Treatment group Sterile vegetation, no./

total, no. (%)

Median (IQR)

(log10 CFU/g of

veg)

MRSA 277

Controla 0/20 (0) 9 (8.6–9.3)

Daptomycinb 13/18 (72)

c, g 0 (0–1.5)

d, i

Vancomycin-RDe 7/20 (35)

c, h 2 (0–5.6)

d, j

Vancomycin-HD f 9/18 (50)

g, h 1 (0-2)

i, j

GISA ATCC

700788

Controla 0/17 (0) 9.5 (8.3–9.8)

Daptomycinb 12/19 (63)

k, m 2 (0–2)

l, o

Vancomycin-RDe 4/20 (20)

k,n 6.6 (2–6.9)

l, p

Vancomycin-HDf 4/20 (20)

m,n 2.4 (2-4)

o, p

aThe control animals were sacrificed 18 hours after the infection was started.

bSimulating

6 mg/kg q 24 h i.v.; cP = 0.02;

dP = 0.02;

e vancomycin-RD (recommended dose)

simulating 1 g q 12 h i.v.; fvancomycin-HD (high dose) simulating 1 g q 6 h i.v.;

gP =

0.17; h

P = 0.35; iP = 0.19;

jP = 0.13;

kP < 0.01;

lP < 0.01;

mP < 0.01;

nP = 1.00;

oP = 0.02;

pP = 0.03.

CFU= colony-forming unit; GISA = glycopeptide-intermediate-resistant S. aureus; IQR=

interquartile range; MRSA= methicillin-resistant S. aureus; veg = vegetations.

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