Comparison of ceftaroline fosamil, daptomycin and tigecycline
in an experimental rabbit endocarditis model caused
by methicillin-susceptible, methicillin-resistant
and glycopeptide-intermediate Staphylococcus aureus
Ce ´dric Jacqueline1*, Gilles Amador1, Eric Batard1, Virginie Le Mabecque1, Anne-Franc ¸oise Mie `geville1,
Donald Biek2, Jocelyne Caillon1and Gilles Potel1
1Universite ´ de Nantes, Nantes Atlantique Universite ´s, The ´rapeutiques Cliniques et Expe ´rimentales des Infections, EA3826, F-44000
Nantes, France;2Cerexa, Inc., 2100 Franklin St, Oakland, CA 94612, USA
*Corresponding author. Tel: +33-240-41-2854; Fax: +33-240-41-2854; E-mail: firstname.lastname@example.org
Received 13 December 2010; returned 2 January 2011; revised 10 January 2011; accepted 11 January 2011
Objectives: The aim of this study was to compare the in vivo activities of the new antistaphylococcal drugs
ceftaroline fosamil, daptomycin and tigecycline at projected human therapeutic doses against methicillin-
susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA) and glycopeptide-intermediate
S. aureus (GISA) strains in a rabbit model of endocarditis.
Methods: The efficacy of therapeutic regimens in our model was evaluated following 4 days of treatment by
determining colony counts of infected vegetations. Emergence of resistant variants during therapy was
Results: Using this model of infective endocarditis, ceftaroline fosamil and daptomycin demonstrated high
bactericidal in vivo activity (reduction of .5 log10cfu/g of vegetation) after a 4 day treatment against
MSSA, MRSA and GISA strains. Both drugs were more efficacious than tigecycline, which showed moderate
activity but failed to exhibit a bactericidal effect. Ceftaroline was superior to daptomycin in terms of steriliza-
tion of the vegetations. Emergence of resistant variants during daptomycin therapy was observed in two
animals (one in the MSSA group and one in the MRSA group) but was not observed in ceftaroline- or tigecy-
Conclusions: The novel b-lactam agent ceftaroline fosamil was the most active bactericidal drug in this
model and is a promising therapeutic option for the treatment of severe S. aureus infections, including
those caused by MRSA and GISA strains.
Keywords: antistaphylococcal drugs, cephalosporins, MRSA
Infective endocarditis is a severe disease associated with high
morbidity and mortality rates. Staphylococcus aureus is the most
common cause of endocarditis worldwide and methicillin-
susceptible S. aureus (MSSA) isolates are found in up to two-thirds
of cases.1b-Lactam agents are the standard therapy for MSSA
endocarditis, but currently available b-lactams are generally inef-
fective against methicillin-resistant S. aureus (MRSA) strains. High
rates of clinical failure have been reported with vancomycin
therapy forMRSA endocarditis,2
glycopeptide-intermediate S. aureus (GISA) strains highlights the
urgent need for new therapeutic options for treatment of infec-
tions by isolates not susceptible to methicillin and glycopeptides.
Among the new options, tigecycline is the first member of a
new class of broad-spectrum antibacterials, the glycylcyclines,
which have been specifically developed to overcome the two
major mechanisms of tetracycline resistance.3Daptomycin is a
cyclic lipopeptide antimicrobial agent with in vitro activity
against S. aureus, including MRSA strains. Daptomycin is a poten-
tial alternative to vancomycin for the treatment of severe MRSA
infections, with benefits such as once-daily dosing, the lack of
need for monitoring serum concentrations and FDA approval
for the treatment of right-sided endocarditis.4
fosamil, recently approved by the FDA for use in treating
community-acquired bacterial pneumonia, is a novel broad-
spectrum cephalosporin prodrug that is rapidly converted to
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J Antimicrob Chemother
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Journal of Antimicrobial Chemotherapy Advance Access published January 31, 2011
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the microbiologically active drug, ceftaroline, in plasma following
parenteral administration. Ceftaroline demonstrates bactericidal
time-dependent killing activity. In contrast to other classic and
new antistaphylococcal drugs, ceftaroline exhibits antibacterial
activity against common Gram-negative pathogens, which
could allow clinicians to avoid the use of combination therapy
for empirical treatment of certain infections.
The purpose of the present study was to assess and compare
the in vivo activity of ceftaroline fosamil with that of daptomycin
and tigecycline against three S. aureus strains (methicillin sus-
ceptible, methicillin resistant and glycopeptide intermediate) in
a rabbit model of aortic valve endocarditis with projected
human therapeutic doses.
Materials and methods
The animals used for this study were female New Zealand white rabbits
(weight, 2.2–2.5 kg) housed in individual cages with free access to food
and water. Animals were treated in accordance with institutional policies
and the guidelines stipulated by the animal welfare committee. The
Committee of Animal Ethics of the University of Nantes approved all
animal experimentation in this study.
We studied three S. aureus strains: MSSA, strain ATCC 29213; MRSA, strain
P9 (clinical strain isolated from blood cultures); and a methicillin-resistant
GISA strain (Mu50).
Clinical forms of daptomycin (Cubist Pharmaceuticals, Lexington, MA,
USA) and tigecycline (Wyeth, Paris, France) were used in this study. Cef-
taroline fosamil powder was provided by Forest Laboratories, Inc.
(New York, NY, USA). The drugs were prepared according to the manufac-
The MICs of ceftaroline, daptomycin and tigecycline for the three strains
were determined in cation-supplemented Mueller–Hinton (MH) broth by
the CLSI microdilution technique.5For daptomycin, the test medium
was supplemented with Ca2+to 50 mg/L according to the CLSI guide-
lines.6Overnight MH broth cultures were used to prepare inocula of
105cfu/mL. The MIC was defined as the lowest concentration of antimi-
crobial agent that prevented turbidity after 24 h of incubation at 378C.
The human pharmacokinetic profiles of ceftaroline and daptomycin were
simulated as previously described.7,8For tigecycline, the first step in the
pharmacokinetic studies consisted of investigating the parameters that
would allow simulation of the kinetics of tigecycline in human serum.
Blood samples were taken from three healthy rabbits at 0, 0.5, 0.75, 1,
1.25, 1.5, 2, 3, 4, 6, 8 and 24 h after administration of a 30 min infusion
of tigecycline (1 mg/kg) to determine spontaneous drug kinetics. The
pharmacokinetic data were analysed and compared with those for
humans.9Simulation was intended to provide pharmacokinetic par-
ameters close to those observed in healthy volunteers after adminis-
tration of tigecycline 50 mg twice daily. The infusion was delivered by a
computer-controlled pump that allowed the flow to be adjusted to a
profile mathematically defined in time.
Animal model (endocarditis)
The procedures used in the experimental endocarditis model were as pre-
viously described.10,11A catheter was placed into the left ventricle of
anaesthetized New Zealand white rabbits. Twenty-four hours later,
each animal was inoculated intravenously with 1 mL of a bacterial sol-
ution (adjusted to 108cfu/mL) with the MSSA, MRSA or GISA strain. Treat-
ment began 24 h after inoculation using a computer-controlled pump, as
described elsewhere.9The animals were euthanized by using an intrave-
nous bolus of thiopental at the beginning of the treatment period (con-
trols) or at the end of the 4 day regimen. Aortic valve vegetations were
excised, weighed, homogenized in 0.5 mL of saline buffer and used for
quantitative cultures on agar for 24 h at 378C. If there was no growth
of undiluted vegetation homogenates spread on agar plates after 48 h
of incubation at 378C, the sample was considered sterile and the lower
detection limit for the method was assigned (i.e. 1 cfu per 50 mL of
undiluted vegetation homogenate).
To evaluate whether ceftaroline, daptomycin or tigecycline treatment
could induce the selection of resistant variants, undiluted vegetation
homogenates were spread on agar plates containing the study drugs
at concentrations corresponding to four times the MIC (with adjustment
of calcium to 50 mg/mL for daptomycin testing). Bacterial counts were
determined after 48 h of incubation at 378C.
For each strain, animals were randomly assigned to either no
treatment (controls), ceftaroline fosamil mimicking the human dose of
10 mg/kg/12 h (600 mg twice daily), daptomycin mimicking the human
dose of 6 mg/kg once daily or tigecycline mimicking the human dose of
100 mg initially, followed by 50 mg twice daily.
Statistical analyses were performed with GraphPad Prismwv4.0 (Graph-
Pad Software, San Diego, CA, USA). For each strain studied, analysis of
variance was used to compare the effects between the different
groups, followed by Bonferroni’s test to compare treated groups two by
two. A P value of ≤0.05 was considered significant.
MICs for the MSSA, MRSA and GISA strains are shown in Table 1.
The three S. aureus strains were susceptible to ceftaroline, dapto-
mycin and tigecycline, with MICs ≤1 mg/L.
Table 1. MICs of ceftaroline, daptomycin and tigecycline for MSSA,
MRSA and GISA isolates
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Computer-controlled pharmacokinetic simulation
The mean peak concentration, area under the curve and
half-life after administration of a dose simulating a 50 mg
dose in humans were: 783.8+42.5 ng/mL; 4.9+0.4 mg h/mL;
and 12.5+0.6 h (ascompared
2.2+0.3 mg h/mL and 11.8+2.5 h in humans).12
Efficacy in endocarditis model
In vivo results after a 4 day treatment regimen are shown in
Table 2. For all strains, the ceftaroline fosamil regimen (600 mg
twice daily) demonstrated high bactericidal activity (defined as
≥3 log10reduction in bacterial titre over untreated controls at
thetimeofantibioticdosing) aftera4 daytreatment inthis exper-
imental endocarditis model, with reductions .5 log10cfu/gof veg-
etation. Daptomycin (6 mg/kg once daily) was also bactericidal
against the S. aureus strains tested in this study, but ceftaroline
was the only drug that achieved 100% sterilization of the infected
57% and 100% achieved with daptomycin for animals infected
with MSSA, MRSA and GISA strains, respectively).
Bacterial counts in aortic valve vegetations from rabbits
treated with tigecycline were significantly reduced for the three
strains compared with the controls; however, tigecycline failed
to exhibit bactericidal activity.
Agar plates containing ceftaroline or tigecycline at four times
the MIC showed no S. aureus colonies after plating undiluted veg-
etation homogenates and incubating for 48 h at 378C. Agar
plates containing daptomycin at four times the MIC showed
daptomycin-resistant mutants isolated from one animal of the
MSSA group and one animal of the MRSA group. Daptomycin
MICs were determined to be 2 mg/L for these resistant variants.
During recent years, new drugs active against S. aureus, including
methicillin-resistant strains, have reached the market (i.e. dapto-
mycin, tigecycline and telavancin) or, like ceftaroline, will be
available soon. The FDA has recently approved ceftaroline
fosamil for the treatment of community-acquired bacterial
pneumonia and for acute bacterial skin and skin structure infec-
tions (ABSSSI), including those caused by MRSA.13
Prescribing doctors should be able to use clinical trial data as
a major source of information for evidence-based medicine for
the treatment of infectious diseases.14However, the difficulty
in performing clinical trials in severe types of infection such as
endocarditis has resulted in a lack of clinical information for
many new antibiotics regarding use in treating severe infections.
Experimental animal models are one method used to assess the
in vivo activity of new antimicrobials in the treatment of severe
infections. In the present study, we used three resistant pheno-
types of S. aureus (MSSA, MRSA, GISA) in a head-to-head com-
parison of new therapeutic options for the treatment of severe
S. aureus infection.
Ceftaroline fosamil (simulated human dosing of 600 mg
twice daily) clearly demonstrated highly bactericidal activity
against MSSA, MRSA and GISA strains in this rabbit endocarditis
experimental model (reductions .5 log10cfu/g of vegetation).
These results confirm the data from a previous study with
two different MRSA strains,7and are consistent with results
obtained for the b-lactam ceftobiprole, as demonstrated by
Tattevin et al.15using a similar experimental model. Ceftaroline
achieved 100% sterilization of the vegetations infected by the
MSSA, MRSA or GISA strains, whereas daptomycin sterilized
62%, 57% and 100% of the vegetations, respectively. Tigecy-
cline exhibited 0% sterilization, as expected for a drug with a
bacteriostatic mode of action. Despite in vivo bactericidal
activity, the emergence of daptomycin-resistant variants after
only 4 days of therapy is a concern. This suggests the possible
need for combination therapy for daptomycin treatment of
S.aureusinfections. The6 mg/kg
regimen was not able to prevent the emergence of resistance
in two animals (one in the MSSA group and one in the MRSA
group). Moreover, the detection of these resistant variants
was correlated with a failure of daptomycin in treating the
infection in these particular rabbits. These data support the
use of daptomycin dosages exceeding 6 mg/kg to increase
bacterial killing and limit the risk of emergence of resistant
variants during daptomycin therapy. Case reports involving
daptomycin at doses up to 12 mg/kg have been described
and shown to be safe and well tolerated.16,17No resistant var-
iants were detected from vegetations during ceftaroline or
,2 log10cfu/g compared with the controls) against MRSA and
Table 2. Bacterial titres in vegetations after 4 days of treatment
Mean+SD log10cfu/g of vegetation (n)d
Ceftaroline (HE 10 mg/kg/12 h)
Daptomycin (HE 6 mg/kg/24 h)
Tigecycline (HE 50 mg/12 h)
HE, human equivalent.
aP,0.001 versus controls; Bonferroni’s test after analysis of variance.
bP,0.01 versus tigecycline; Bonferroni’s test after analysis of variance.
cP,0.05 versus controls; Bonferroni’s test after analysis of variance.
dn¼no. of sterile vegetations (below the limit of detection)/total no. of vegetations.
Efficacy of new antistaphylococcal drugs against S. aureus
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GISA strains in this model. This moderate activity could be
improved by the use of a partner drug in combination with tige-
cycline, but few studies have investigated the activity of combi-
nations with the glycylcycline antibiotic against MRSA strains.
Recently, it was observed that the addition of gentamicin signifi-
cantly improved the killing activity of tigecycline in biofilm-
forming S. aureus using an in vitro pharmacodynamic model.18
Studies conducted in both animals and humans have demon-
strated that tigecycline distributes widely into various tissues
and body fluids.19Nevertheless, peak serum concentrations do
not exceed 1 mg/L, which may limit its utility in the treatment
ofbacteraemia and endocarditis.20,21
dosage of tigecycline could be too low for the treatment of
severe infections and the assessment of higher doses in severe
experimental animals models could be useful.
Both ceftaroline fosamil and daptomycin demonstrated highly
bactericidal activity against MSSA, MRSA and GISA strains after
a 4 day treatment. These data support continued interest of
these new therapeutic options in the management of severe
MRSA infections. Nevertheless, the emergence of daptomycin
non-susceptible S. aureus during therapy strongly suggests the
need for considering combination therapy with other antibacter-
ial agents and for evaluating higher dosages.
These data support the novel cephalosporin ceftaroline as a
promising addition for the treatment of severe S. aureus infec-
tions, including those caused by MRSA and GISA strains.
A preliminary report of these results was presented at the Forty-ninth
Interscience Conference on Antimicrobial Agents and Chemotherapy,
San Francisco, CA, USA, 2009 (Abstract B-055).
This work was supported by a research grant from Forest Laboratories,
Inc. (New York, NY, USA) (to G. P.). Funding for editorial assistance was
provided by Forest Laboratories, Inc.
D. B. is an employee of Cerexa, Inc., a subsidiary of Forest Laboratories,
Inc. (New York, NY, USA), which is developing ceftaroline. D. B. holds
stock and options in Forest Laboratories, Inc. All other authors: none to
Scientific Therapeutics Information, Inc. (Springfield, NJ, USA) pro-
vided editorial assistance.
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