International Journal of Antimicrobial Agents 27 (2006) 557–560

Evaluation of dalbavancin in combination with nine antimicrobialagents to detect enhanced or antagonistic interactions

David M. Johnson a, Thomas R. Fritsche a,∗, Helio S. Sader a, Ronald N. Jones a,b

a JMI Laboratories, 345 Beaver Kreek Centre, Suite A, North Liberty, IA 52317, USAb Tufts University School of Medicine, Boston, MA, USA

Received 9 November 2005; accepted 19 December 2005

Abstract

Dalbavancin is a potent, once-weekly administered lipoglycopeptide that is active against a broad spectrum of Gram-positive species.Synergy studies were performed with dalbavancin and each of nine antimicrobial agents (90 tests in total) representing nine antimicrobialclasses using the broth microdilution checkerboard method to establish in vitro interactive categories. Antagonism was not observed betweendalbavancin and any of the antimicrobials tested. However, dalbavancin was synergistic or partially synergistic with oxacillin for staphylococci,if©

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ncluding methicillin-resistant strains, vancomycin-intermediate Staphylococcus aureus and enterococci, a significant finding that warrantsurther investigation to establish its potential clinical relevance.

2006 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.

eywords: Dalbavancin; Synergy; Lipoglycopeptide; Interaction studies

. Introduction

Staphylococcus, Enterococcus and Streptococcus spp. areajor causes both of community-acquired and nosocomial

nfections [1,2]. During the past decade, numerous stud-es have documented increasing rates of resistance amonghese Gram-positive species, including oxacillin resistancemong staphylococci, vancomycin resistance among ente-ococci, and penicillin and erythromycin resistance amongtreptococci [1,3–6]. Acquisition of additional resistanceechanisms and virulence factors by these pathogens have

esulted in the spread of multidrug-resistant clones that haveeen detected globally, thereby compromising empirical andirected therapies [1,3,7–10]. The increase in prevalence ofesistant organisms and the resulting increases in morbiditynd mortality have resulted in the need for development ofew antimicrobials with activity against these pathogens.

Dalbavancin (BI-397) is a semisynthetic glycopeptideerivative of the natural glycopeptide A40926 producedy 3,3-dimethylaminopropyl amide substitution on the pep-

∗

tide carboxyl group [3,9,11,12]. It is similar to other gly-copeptides in its mechanism of activity, binding to theterminal alanyl-d-alanine of nascent peptidoglycan chainsand thus interfering with bacterial cell wall biosynthesisand resulting in cell death [6,13]. Previous studies havedemonstrated the potent activity of dalbavancin againstaerobic and anaerobic Gram-positive organisms, includ-ing such clinically relevant strains as oxacillin-resistantstaphylococci, penicillin-resistant Streptococcus pneumo-niae and vancomycin-resistant enterococci (vanB pheno-types) [1,5,11].

Given the lack of published data on antimicrobial interac-tions with this agent, we established the in vitro interactivecategories (antagonism, synergy, etc.) of dalbavancin whencombined with representatives of nine other classes of antimi-crobial agents when testing staphylococci, enterococci andstreptococci, including resistant subsets.

2. Materials and methods

Corresponding author. Tel.: +1 319 665 3370; fax: +1 319 665 3371.E-mail address: thomas-fritsche@jmilabs.com (T.R. Fritsche).

The broth microdilution checkerboard titration method[14] using 96-well panels was utilised according to the

924-8579/$ – see front matter © 2006 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.oi:10.1016/j.ijantimicag.2005.12.015

558 D.M. Johnson et al. / International Journal of Antimicrobial Agents 27 (2006) 557–560

Clinical and Laboratory Standards Institute (formerly theNational Committee for Clinical Laboratory Standards) M7-A6 standard [15]. These panels were produced with dal-bavancin (Vicuron, King of Prussia, PA) and the pairedtest compounds at JMI Laboratories (North Liberty, IA).Cation-adjusted Mueller–Hinton broth (with 2–5% lysedhorse blood added for streptococci) was utilised as the testmedium. Polysorbate-80 (Sigma Chemical Co., St Louis,MO) was added to all wells (0.002% final concentration)containing dalbavancin, as recommended [3]. The antimicro-bials and dilutions tested were: oxacillin (0.004–64 mg/L)+ dalbavancin (0.016–8 mg/L); gentamicin (0.03–64 mg/L) + dalbavancin (0.016–8 mg/L); clindamycin (0.008–16 mg/L) + dalbavancin (0.016–8 mg/L); levofloxacin (0.06–64 mg/L) + dalbavancin (0.016–8 mg/L); rifampicin (0.008–8 mg/L) + dalbavancin (0.016–8 mg/L); vancomycin (0.06–64 mg/L) + dalbavancin (0.016–8 mg/L); quinupristin/dalfo-pristin (0.06–64 mg/L) + dalbavancin (0.016–8 mg/L); line-zolid (0.06–64 mg/L) + dalbavancin (0.016–8 mg/L); anddaptomycin (0.016–16 mg/L) + dalbavancin (0.016–8 mg/L).

Organisms were selected to produce on-scale minimuminhibitory concentration (MIC) results to detect possibleadverse interactions (antagonism) occurring with combina-tion therapies. Strains included those species most com-monly isolated from skin and skin structure or catheter-related infections, including antimicrobial-resistant strainsacossdrS(cii

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s follows: oxacillin (methicillin)-susceptible Staphylococ-us aureus (MSSA; two strains including ATCC 29213);xacillin (methicillin)-resistant S. aureus (MRSA; twotrains); vancomycin-intermediate S. aureus (VISA; onetrain); oxacillin (methicillin)-resistant Staphylococcus epi-ermidis (MRSE; one strain); vancomycin-susceptible Ente-ococcus faecalis (VSE; two strains including ATCC 29212);. pneumoniae ATCC 49619; and Streptococcus pyogenesone strain). All isolates were tested once except for qualityontrol (QC) strains, which were included on each day of test-ng; repeat testing of QC isolates gave identical categoricalnterpretations.

Characterisation of antimicrobial interactions into cat-gories was defined as: antagonism = four-fold or greaterncrease in the MIC values of both agents; synergy = four-old or greater decrease in the MIC values of both agents;artial synergy = four-fold or greater decrease in the MICalue for one agent and a two-fold reduction in the MIC ofhe other; additive = two-fold decrease in MIC values of bothested agents; indifference = no decrease in the MIC valuesf either agent or only a two-fold decrease or increase inhe MIC of one agent; and indeterminate = results inconsis-ent with the described categories or results beyond the testedilution scales (generally lower).

. Results and discussion

The interaction results of dalbavancin combined withine comparator antimicrobial agents against the 10 selected

D.M. Johnson et al. / International Journal of Antimicrobial Agents 27 (2006) 557–560 559

Table 2Dalbavancin interaction categories with nine different agents representing distinctly different antimicrobial classes

Co-drug (no. of tests) Synergy Partial synergy Additive Indifferent Antagonism Indeterminate

Clindamycin (10) 0 4 1 5 0 0Daptomycin (10) 0 3 2 3 0 2Gentamicin (10) 0 6 3 1 0 0Levofloxacin (10) 0 3 2 5 0 0Linezolid (10) 0 1 1 8 0 0Oxacillin (10) 5 4 0 1 0 0Quinupristin/dalfopristin (10) 0 3 4 3 0 0Rifampicin (10) 0 1 4 3 0 2Vancomycin (10) 0 6 3 1 0 0

Total (90) 5 (5.6%) 31 (34.4%) 20 (22.2%) 30 (33.3%) 0 4 (4.4%)

Gram-positive isolates are summarised in Tables 1 and 2.The majority of the interaction results (90.0%) observedwere divided between three categories: partial syn-ergy (34.4%), indifference (33.3%) and additive effects(22.2%).

Synergy was present in 5.6% of testing events (all dal-bavancin with oxacillin), and only 4.4% of results werefound to be indeterminate (Table 2). Importantly, no antag-onistic interactions between dalbavancin and any of thetested antimicrobial agents were detected. The combina-tion of dalbavancin and oxacillin yielded the greatest num-ber of positive interactive results, demonstrating synergisticactivity against all three strains of oxacillin-resistant staphy-lococci and one VISA strain, and partial synergy againstthe three other clinical isolates (MSSA, VSE and S. pyo-genes). Only the combination of oxacillin and dalbavancindemonstrated synergistic activity against the most resis-tant isolate tested (VISA). After oxacillin, the combinationsof gentamicin + dalbavancin and vancomycin + dalbavancinwere equally effective, yielding partial synergy or addi-tive results against nine of the tested strains. The leastactive combination tested was linezolid + dalbavancin, whichdemonstrated indifferent activity against eight of the testedisolates; however, partial synergy and additive resultswere observed against the MRSE and VISA strains,respectively.

btEov(ailttoVa

lish potential clinical applications, including bactericidalinteractions.

References

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[

[

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In summary, no antagonistic interactions were detectedetween dalbavancin and any of the comparator agentsested in combination against 10 strains of staphylococci,. faecalis, S. pyogenes and S. pneumoniae. Synergy wasnly observed when oxacillin was combined with dalba-ancin and occurred against four strains of staphylococcithree oxacillin resistant, one vancomycin intermediate)nd one E. faecalis strain (ATCC 29212). Because of thencreasing global prevalence of oxacillin-resistant staphy-ococci [1] and the difficulties they present for therapeuticreatment of bloodstream and skin and soft tissue infec-ions [2,13], the favourable interactions observed betweenxacillin and dalbavancin, especially with MRSA andISA isolates, justifies further investigation against a larger

nd more diverse population of resistant strains to estab-

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[9] Streit JM, Fritsche TR, Sader HS, Jones RN. Worldwideassessment of dalbavancin activity and spectrum against over6,000 clinical isolates. Diagn Microbiol Infect Dis 2004;48:137–43.

10] Willems RJL, Top J, van Santen M, et al. Global spread ofvancomycin-resistant Enterococcus faecium from distinct nosocomialgenetic complex. Emerg Infect Dis 2005;11:821–8.

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560 D.M. Johnson et al. / International Journal of Antimicrobial Agents 27 (2006) 557–560

[13] Seltzer E, Dorr ME, Goldstein BP, et al. Once-weekly dalbavancinversus standard-of-care antimicrobial regimens for treatment of skinand soft tissue infections. Clin Infect Dis 2003;37:1298–303.

[14] Isenberg HD. Synergism testing: broth microdilution checkerboardand broth macrodilution methods. In: Clinical microbiology pro-

cedures handbook, Vol. 2. Washington, DC: American Society forMicrobiology; 2005. p. 5.12.1–23.

[15] National Committee for Clinical Laboratory Standards. Methods fordilution antimicrobial susceptibility tests for bacteria that grow aer-obically. Document M7-A6. Wayne, PA: NCCLS; 2003.