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B. K. Armstrong, S. Mehta, S. J. Kim, F. Recchia, L. L. Wayman, H. Toma, H. Yin, P. Sternberg; Long-Term Potency, Sterility, and Stability of Vancomycin, Ceftazidime, and Moxifloxacin for Intravitreal Use in the Treatment of Endophthalmitis. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6043.
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The intent of this study is to determine if vancomycin, ceftazidime, and moxifloxacin prepared for intravitreal use can be stored long-term while maintaining their potency, sterility, and stability. We hypothesize that long-term storage of frozen intravitreal antibiotics could provide a safe, quick, and cost-effective means to prevent treatment delay in endophthalmitis.
Vancomycin 1 mg/0.1 ml, ceftazidime 2 mg/0.1 ml, and moxifloxacin 160 µg/0.1 ml were prepared in compliance with national USP 797 standards. Antibiotic syringes were stored at 4, -20, and -80°C. Serial testing was performed at baseline, 1 week, 2 weeks, 1 month, 2 months, 3 months, and 6 months after preparation. Potency was tested using the Kirby-Bauer method, which consists of measuring zone of inhibition (ZOI) against Staphylococcus epidermidis (S. epidermidis), Staphylococcus aureus (S. aureus), and Pseudomonas aeruginosa (Pseudomonas). Sterility was tested by inoculating each antibiotic onto blood and Sabouraud agar plates and incubating at 37°C for 7 days. Concentration was tested using ultraviolet spectrophotometry. Osmolality and pH were tested using an osmometer and pH meter.
At 6 months, each antibiotic maintained 100% of its baseline potency against all organisms with 3 exceptions: 4°C ceftazidime against S. aureus (91%), 4°C vancomycin against S. epidermidis (95%), and all temperatures of moxifloxacin against Pseudomonas (ave. 94%). Moxifloxacin displayed the largest mean ZOI against S. epidermidis (43 mm) and S. aureus (40 mm), while ceftazidime showed the largest mean ZOI against Pseudomonas (38 mm). There was no growth on blood or Sabouraud agar plates from any antibiotic sample during the study with exception of one sample of moxifloxacin stored at 4°C, which grew out coagulase-negative staphylococcus at the 6-month timepoint only. All antibiotics maintained at least 73% of their baseline concentrations, regardless of storage temperature. Osmolality and pH remained steady for all antibiotics at all temperatures with no more than 10% variation from baseline at any time point.
Prepared antibiotics for intravitreal injection can be successfully stored for a period of at least 6 months. Such practice may prevent timely delays in the treatment of endophthalmitis.
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