JAC Advance Access originally published online on April 21, 2007
Journal of Antimicrobial Chemotherapy 2007 60(1):159-161; doi:10.1093/jac/dkm116
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In vitro and in vivo antibacterial evaluation of DRF 8417, a new oxazolidinone
Anti-infective Group, Discovery Research, Dr Reddy's Laboratories Ltd, Miyapur, Hyderabad 500 049, India
* Corresponding author. Tel: +91-40-2304-5439, ext. 260; Fax: +91-40-2304-5438; E-mail: sreenivaskandepu{at}drreddys.com
Received 10 December 2006; returned 8 February 2007; revised 22 March 2007; accepted 27 March 2007
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Abstract |
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Objectives and methods: DRF 8417, a novel oxazolidinone, has been evaluated against Gram-positive and fastidious Gram-negative bacteria. In vitro activity of DRF 8417 was determined by broth microdilution method and in vivo efficacy studies were carried out in different murine systemic infection models.
Results: DRF 8417 exhibited potent activity against Gram-positive pathogens with MIC50 and MIC90 values ranging from 0.06 to 1 mg/L. MICs against Haemophilus influenzae and Moraxella catarrhalis were one to two dilutions lower than those of linezolid. The in vivo efficacy, by oral route, in different susceptible and resistant Gram-positive systemic bacterial infection models ranged from 2.0 to 2.9 mg/kg.
Conclusions: These studies displayed the excellent in vitro and in vivo activity of DRF 8417 against Gram-positive pathogens and lower MICs when compared with linezolid against H. influenzae and M. catarrhalis.
Keywords: clinical isolates , systemic infection models , linezolid
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Introduction |
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Antibiotic resistance is a major problem in hospitals as well as in community settings. Gram-positive pathogens such as Staphylococcus aureus, Enterococcus faecalis, Enterococcus faecium and Streptococcus pneumoniae are becoming resistant to most of the existing antibiotics.1 With the steady emergence and spread of antibiotic-resistant bacterial pathogens, treatment is no longer an easy task. The introduction of linezolid has given hope to treat these infections effectively, but already resistance has been reported.2 There is clearly an unmet medical need to develop more potent and new classes of antibiotics to treat these resistant bacterial infections. In an effort to address this issue, we developed DRF 8417, a novel and potent oxazolidinone molecule. Herein, we describe the in vitro and in vivo profile of DRF 8417 when compared with linezolid and a few other standard antibiotics, against a panel of Gram-positive and fastidious Gram-negative microbes.
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Materials and methods |
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Bacterial strains
All the standard bacterial strains were procured from ATCC. Clinical bacterial isolates were collected from different medical centres across India during 2002–04 and were maintained in Dr Reddy's culture collection (DRCC). Identification of each culture was performed by conventional methods.3
DRF 8417 (S)-{2-oxo-3-[4-(2-oxo-oxazolidin-1-yl)-phenyl]-oxazolidin-5-ylmethyl}-thiocarbamic acid O-methyl ester (US 7030148) was synthesized in-house. Linezolid was synthesized according to the method described previously.4 All other antibiotics were obtained from commercial sources.
In vitro susceptibility testing
In vitro activity of DRF 8417 and standard antibiotics was determined by broth microdilution method, following CLSI (formerly NCCLS) guidelines.5 DRF 8417 was dissolved in dimethyl sulphoxide and all other compounds were prepared as described previously.6 Quality control strains of S. aureus ATCC 29213, E. faecalis ATCC 29212, S. pneumoniae ATCC 49619 and Haemophilus influenzae ATCC 49247 were incorporated in the susceptibility testing.
All procedures were approved by the Institutional Animal Ethics Committee. For efficacy studies, inbred specific-pathogen-free male and female Swiss albino mice of 4–6 weeks old were used.
The systemic infection models were standardized according to the method described previously.7 The infecting inoculum (0.5 mL) was adjusted to yield approximately 100 times the LD50 and injected intraperitoneally. To enhance the bacterial virulence, 5% mucin (Difco Laboratories, USA) was used except for enterococcal infection where 7.5% was used. For infection with methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA), the final concentration of inoculum was 
108 cfu/mL. For infections with vancomycin-resistant E. faecalis and penicillin-intermediate-resistant S. pneumoniae, the inoculum was 109 and 106 cfu/mL, respectively.
DRF 8417 and linezolid were formulated in sterile Tween and carboxy methyl cellulose. Other antibiotics were formulated following the manufacturer's directions. Vancomycin was administered subcutaneously and all other antibiotics by oral route for 1 day at 1 and 5 h post-infection. For S. pneumoniae, the treatment was continued for 2 days. Three dosage levels of antibiotic using serial 2-fold dilutions were employed to determine the 50% effective dose (ED50). A treatment group of six mice was used for each antibiotic dose level. Death in each treated and untreated group was monitored daily for 5 days, or in the case of S. pneumoniae for 7 days, and the ED50 calculated by Probit analysis.8 Respective drug and formulation control groups were incorporated in the study.
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Results |
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The structure of DRF 8417 and the comparative antimicrobial activity of DRF 8417 and other standard drugs are summarized in Table 1. DRF 8417 demonstrated potent antibacterial activity against Gram-positive strains. This molecule is four to eight times more active than linezolid, vancomycin and moxifloxacin against resistant strains of S. aureus. Against vancomycin-susceptible and -resistant strains of enterococci, DRF 8417 displayed two to four times improved activity when compared with other standard antibiotics. More significantly, the compound showed enhanced activity against S. pneumoniae when compared with linezolid and was equipotent to amoxicillin. Interestingly, MICs of DRF 8417 against H. influenzae and Moraxella catarrhalis were one to two dilutions lower than those of linezolid.
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In vivo efficacy of DRF 8417 was evaluated and the results are presented in Table 2. DRF 8417 showed better efficacy than linezolid and amoxicillin and equal efficacy to that of vancomycin, against the MSSA infection model. In the MRSA infection model, DRF 8417 displayed superior efficacy when compared with linezolid and vancomycin. Amoxicillin failed to show protection. In the S. pneumoniae model, DRF 8417 exhibited superior efficacy when compared with that of linezolid and moxifloxacin; amoxicillin showed the best efficacy. In the vancomycin-resistant E. faecalis sepsis model, efficacy of DRF 8417 was superior to that of linezolid and amoxicillin.
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Discussion |
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DRF 8417, a new oxazolidinone, has demonstrated significant in vitro activity against susceptible and resistant Gram-positive organisms.9,10 Its in vitro activity against H. influenzae and M. catarrhalis is slightly superior to that of linezolid. However, pharmacokinetic/pharmacodynamic (PK/PD) studies are necessary to confirm its efficacy against these pathogens. DRF 8417 possesses in vivo efficacy in different susceptible and resistant S. aureus, E. faecalis and S. pneumoniae infection models. The superior in vitro and in vivo activity displayed by DRF 8417 against Gram-positive pathogens indicates its potential as a candidate for future development. Further PK/PD investigations of this molecule are in progress.
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Transparency declarations |
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All authors are employees of Dr Reddy's Laboratories Ltd. K. S., J. I., R. R. and R. C. own stocks in the company.
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Acknowledgements |
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We express our thanks to C. Chandrasekhar for providing excellent technical assistance. Part of this work was presented at the Forty-second Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, USA, 2002 (Abstracts F-1327 and 1328). This is DRL publication no. 618.
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References |
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1 Tally FP, DeBruin MF. Development of daptomycin for Gram-positive infections. J Antimicrob Chemother (2000) 46:523–6.
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Jones RN, Moet GJ, Sader HS, et al. Potential utility of a peptide deformylase inhibitor (NVP PDF-713) against oxazolidinone-resistant or streptogramin-resistant Gram-positive organism isolates. J Antimicrob Chemother (2004) 53:804–7.
3 Collee JG, Miles RS. Tests for identification of bacteria. In: Mackie and McCartney Practical Medical Microbiology—Thirteenth Edition (1989) 141–60.
4 Brickner SJ, Hutchinson DK, Barbachyn MR, et al. Synthesis and antibacterial activity of U-100592 and U-100766, two oxazolidinone antibacterial agents for the potential treatment of multidrug-resistant Gram-positive bacterial infections. J Med Chem (1996) 39:673–9.[CrossRef][Web of Science][Medline]
5 National Committee for Clinical Laboratory Standards. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically-Fifth Edition: Approved Standard M7-A5 (2000) Villanova, PA, USA: NCCLS.
6 Andrews JM. Determination of minimum inhibitory concentrations. J Antimicrob Chemother (2001) 48(Suppl S1):5–16.[Abstract]
7 Cleeland R, Squires E. Evaluation of new antimicrobials in vitro and in experimental animal infections. In: Antibiotics in Laboratory Medicine—Lorian V, ed. (1991) Baltimore, MD: The Williams & Wilkins Co. 739–86.
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Litchfield JT, Wilcoxon F. A simplified method of evaluating dose–effect experiments. J Pharmacol Exp Ther (1949) 96:99–113.
9 Sarnaik HM, Chandrashekhar C, Amarnath PVS, et al. In vitro activity of DRF 8417, a novel oxazolidinone, against recent clinical staphylococcal isolates from India. In: Abstracts of the Forty-second Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, USA, 2002. Washington, DC, USA: American Society for Microbiology. Abstract F-1327, p. 214.
10 Chandrashekhar C, Sarnaik HM, Mamidi RNVS, et al. In vitro and in vivo activity of a novel oxazolidinone—DRF 8417. In: Abstracts of the Forty-second Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, USA (2002) Washington, DC, USA: American Society for Microbiology. Abstract F-1328, p. 214.
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