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Intraoperative Antibiotics and Bacterial Contamination of the Anterior Chamber

Dear Editor, We read with great interest the recent article by Sobaci and colleagues (Sobaci G., Tuncer K, Tas A, et al. “The effect of intraoperative antibiotics in irrigating solutions on aqueous humor contamination and endophthalmitis after phacoemulsification surgery.” Eur J Ophthalmol 2003; 13: 773-8). The authors demonstrated that the rate of aqueous humor contamination was significantly decreased when the irrigating solution contained antibiotics throughout the surgery. However, the authors tested a concentration of antibiotics (20 mg/ml vancomycin and 8 mg/ml gentamicin), which is 1000 times higher than the concentration clinically recommended in irrigating solutions (20 μg/ml vancomycin and 8 μg/ml gentamicin) (1); this factor might have distorted the results and should have been discussed. The efficiency of vancomycin in this study, which contrasts with reports inthe literature as the authors noted, is therefore easily explained. Intracameral vancomycin used in irrigating liquids shows a postoperative half-life of less than 2 hours (2, 3). Therefore, with a classical 20 μg/ml vancomycin solution, its concentration becomes theoretically inferior to the minimal inhibitory concentration (MIC) after 4 to 6 hours (4) (the estimated MIC for most bacteria responsible for postoperative endophthalmitis is about 2 4 μg/ml (3). However, vancomycin antibacterial activity is slow, time-dependent, and is reported to begin in vitro only after 6 hours, becoming complete after 24 to 48 hours (5). With a concentration such as 20 mg/ml, vancomycin should remain in the anterior chamber long enough to develop any bactericidal effect. But, on the other hand, a potential retinal toxicity has to be taken into account, since vancomycin in concentrations above 10 μg/ml significantly increases the risk of cystoid macular edema and visual loss (4, 6). Furthermore, such high concentrations might change pH and osmolality of aqueous humor, and therefore might be toxic for endothelial cells (7). It would therefore be noteworthy for the authors to report long term visual function, endothelial and macular status of their patients. Due to the above mentioned arguments, we cannot follow the conclusion of the authors to use such fortified antibiotic concentrations daily practice in until supplementary data and studies on efficacy, safety and toxicity of this protocol are available.