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Comparison of In vitro efficacy of linezolid and vancomycin against methicillin resistant Staphylococcus aureus (MRSA)

Comparison of In vitro efficacy of linezolid and vancomycin against methicillin resistant Staphylococcus aureus (MRSA). Dr Fatima Kaleem. Introduction.

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Comparison of In vitro efficacy of linezolid and vancomycin against methicillin resistant Staphylococcus aureus (MRSA)

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  1. Comparison of In vitro efficacy of linezolid and vancomycin against methicillin resistant Staphylococcus aureus (MRSA) Dr Fatima Kaleem

  2. Introduction • Staphylococcus aureus is a facultatively anaerobic Gram-positive coccus. It is a major pathogen associated with serious community and hospital-acquired infections. Methicillin resistant. • Staphylococcus aureus (MRSA) is a strain of Staphylococcus aureus that is resistant to all beta-lactams, including penicillins, cephalosporins and the carbapenems.

  3. Contt… • Methicillin-resistant Staphylococcus aureus (MRSA) was reported as a major nosocomial pathogen in the 1960s, and since then incidence of infections caused by this organism has continued to rise.

  4. Contt… • Resistance to all the available antibiotics against Staphylococcus has been reported with the notable exception of vancomycin. • It was feared after the emergence of vancomycin resistant enterococci that this resistance might also spread to staphylococci and it became true, when low-level vancomycin resistance in Staphylococcusaureus was reported in 1996

  5. Assadullah, S et al., 2003, Sonavane, A, 2007, Mehdinejad, M et al., 2008, Horieh, S et al., 2005.

  6. Vancomycin has a narrow spectrum of activity, restricted mostly against Gram-positive bacteria, and is potentially the drug of choice for the treatment of methicillin resistant Staphyloccus aureus. • This agent, however, requires intravenous administration, and occasionally patients experience unacceptable side effects. • Linezolid, a member of the new oxazolidinone class of antibiotics, has shown very good activity against methicillin resistant Staphyloccus aureus, has excellent oral bioavailability and is much inexpensive as compared to vancomycin.

  7. Aims and Objectives • Keeping in view the wide spread use of vancomycin and its pending emerging resistance, we planned to compare the in vitro activities of vancomycin with linezolid.

  8. Study design • Descriptive cross sectional study

  9. Study Duration • This study was carried over a period of Six months (1st July09 - 31st Dec 09)

  10. Study Place • Microbiology Department, National University of Sciences and Technology, Army Medical College, Rawalpindi, Pakistan.

  11. Materials and Methods • Clinical specimens sent for culture and sensitivity to our department were inoculated on appropriate culture media and incubated at 37oC for 24 hours. • Staphylococcus aureus was identified by recommended methods like Gram staining characteristics, morphology, catalase and coagulase tests. • Methicillin resistance was tested by modified Kirby-Bauer disk diffusion technique according to Clinical and Laboratory Standards Institutes (CLSI) guidelines. • First an inoculum was prepared according to 0.5 McFarland turbidity standards (106 cfu/ml). • After inoculating the isolates onto the Muller Hinton agar, E-strips of vancomycin and linezolid were applied over it and incubated along with controls for 18-24 hours at 37oC aerobically. The MIC results were interpreted according to criteria set by Clinical and Laboratory Standards Institute (CLSI).

  12. Control strains Methicillin resistant Staphylococcus aureus ATCC 33591 and methicillin sensitive Staphylococcus aureus (MSSA) ATCC 25923 were used as control strains.

  13. Results • Among a total of 50 MRSA isolates all were sensitive to both the drugs used but vancomycin showed comaparatively higher MICS than linezolid. The MIC 50 and MIC 90 of both were calculated and compared using SPSS 17.

  14. Fig 1: Graph showing comparison of MIC 50 and MIC 90 of vancomycin and linezolid. X axis shows drugs and Y axis shows MIC in ug/ml.

  15. Most of the MRSA isolates were isolated from pus samples followed by nasobronchial lavage and urine. Table 3:

  16. Discussion • A study carried out in USA in year 2005 indicated that intravenous or oral linezolid was well tolerated and superior to vancomycin in treating patients with MRSA-infected surgical-site infections.1 • Our results are also comparable with a study carried out in Iran in year 2009 which indicated that vancomycin and linezolid have similar activity against MRSA.2 • A study carried out in University of Health Sciences Lahore 2009 also concluded that linezolid has excellent activity against methicillin resistant staphylococci including multidrug resistant strains.3 • A study carried out in Japan 2007 indicated that linezolid was as effectiveas vancomycin for the treatment of patients with pneumonia and sepsis caused by MRSA and may be more effective thanvancomycin in achieving microbiological eradication.4

  17. CONCLUSION: • Vancomycin has been the treatment of choice for MRSA infections. This agent, however, requires intravenous (IV) administration, and occasionally patients experience unacceptable side effects. • Linezolid, a member of the new oxazolidinone class of antibiotics, is highly active in vitro against MRSA and has excellent oral bioavailability. • Cumulative data indicate that linezolid and vancomycin have similar efficacy against MRSA infections.

  18. Recommendations: Linezolid'soral dosing option may allow earlier discharge of hospitalized patients thus reducing bed occupancy, over head charges and is a cost effective option from patient’s point of view. It is recommended so as to prevent the emergence of Vancomycin resistant Strains of MRSA.

  19. References 1. John W , Haytham M.A. , Kamal M.F. and Robert N. Linezolid eradicates MRSA better than vancomycin from surgical-site infections. The American Journal of Surgery 2004; 188(6): 760-6 2. Aghazadeh M, Rahbar M, Monnavar MK, Moghadam FS. Sensitivity pattern of methicillin resistant and methicillin sensitive Staphylococcus aureus isolates, against several antibiotics including tigecycline in Iran: A hospital based study. Pak J Med Sci 2009;25(3): 443-6 • Hannan A, Muhammad A, Muhammad U, Tahir N, Sidrah S, Arshad M. In vitro activity of linezolid against clinical isolates of methicillin resistant Staphylococcus. J Ayub Med Coll Abbottabad 2009;21(1) 106_9 4. Kohno S, Yamaguchi K, Aikawa N, Sumiyama Y, Odagiri S, Aoki N, Niki Y,Watanabe S, Furue M, et al.. Linezolid versus vancomycin for the treatment of infections caused by methicillin-resistant Staphylococcus aureus in Japan. JAC Advance Access published online on October 3, 2007 Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkm369

  20. THANK YOU Antibiotics will never be an effective alternative to good medical practice

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