Factors Affecting Precipitation of Vancomycin and Ceftazidime on Intravitreal Injection

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Abstract
Purpose: The aim of this study was to investigate the factors that affect the precipitation of vancomycin and ceftazidime which are currently used in intravitreal injections for infectious endophthalmitis. Methods: The minimum concentration required for precipitation of the 2 antibiotics was estimated by 2-fold dilution. In addition, the amount of the precipitate that formed was measured at 4, 3, 2, and 1 mL volumes, temperatures (37°C or 4°C), and in different medias (balanced salt solution plus and normal saline). Results: When 2-fold serial dilutions of vancomycin and ceftazidime were mixed, precipitates started forming at a concentration of 12.5 mg/mL for ceftazidime and 10 mg/mL for vancomycin. The precipitation of vancomycin and ceftazidime increased at lower temperatures (4°C) and lower media volumes (1 mL). However, using a micropipette with a complete mixed media and an antibiotic (vancomycin or ceftazidime) prevented the formation of a precipitate when the other antibiotic was added. Conclusion: The formation of a precipitate associated with intravitreal injections was correlated with the diffusion rate of the antibiotics in the media. Precipitation increased at lower temperatures, lower media volumes, and at higher antibiotic concentrations.

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