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L. Nguyen, M.J. Gallardo, R.D. Glickman, F. Gonzalez; Evaluation of Antimicrobial Activity of Intravitreal Antibiotics After Prolonged Storage . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5551.
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Purpose: Intravitreal injection of antibiotics are often utilized method for treating suspected infectious endophthalmitis. Typical the antibiotics are prepared by a compounding pharmacy immediately before use. Product manufacture stipulate that the preparations should be not be used 24 hours after suspension.The purpose of this study is to evaluate the antimicrobial activity, sterility and pH of resuspended intravitreal antibiotic preparations of Amikacin, Vancomycin, and Ceftazidime following prolonged storage. Methods: Three different intravitreal antibiotics were studied including Amikacin (0.4mg/0.1 cc), Vancomycin (1mg/0.1cc), and Ceftazidime (2.25mg/0.1cc). Antibiotic suspensions were prepared by certified compounding pharmacist and stored in multiple tuberculin syringes–five syringes for each antibiotic. Antibiotic suspensions were assayed on days 1, 3, 7, 14, 21 and 28. For each day of analysis, one syringe for each antibiotic was assayed. Antimicrobial activity was conducted using a disc diffusion assay. Kirby–Bauer discs were inoculated with each antibiotic in 5, 10 and 15 µL aliquots and placed on separate blood agar plates containing lawns of Escherichia coli, Staphylococcus aureus, Bacillus cereus, or Pseudomonas aeruginosa. The sterility of the antibiotics was also analyzed by inoculating on enriched media to identify possible bacterial or fungal contamination. The pH was also analyzed on each day of analysis. Results: The disc diffusion assay revealed similar diameters of bacterial growth inhibition on several days of analysis. Higher aliquot amounts lead to greater zones of growth inhibition and was consistent for each antibiotic. Enriched growth media that was inoculated with antibiotic samples did not yield any bacterial or fungal growth. pH remained stable throughout analysis. Conclusions: Short term storage of intravitreal antibiotics, Amikacin, Vancomycin, and Ceftazidime does not appear to have an affect on their antimicrobial properties or pH. Also, there appears to be no evidence of bacterial or fungal contamination. Intravitreal antibiotics are typically suspended by hospital pharmacist for immediate intravitreal injection. This study provides evidence that short term storage of these prepared antibiotics at 5C does not reduce the antimicrobial activity.
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