Stability and antibacterial potency of ceftazidime and vancomycin eyedrops reconstituted in BSS® against Pseudomonas aeruginosa and Staphylococcus aureus

Purpose: We aimed to study the stability and the in vitro antibacterial potency of ceftazidime and vancomycin eyedrops against Pseudomonas aeruginosa and Staphylococcus aureus, respectively, under different storage temperatures and light conditions. Methods: Solutions of ceftazidime 50 mg ⁄ ml and vancomycin 50 mg ⁄ ml were prepared by reconstituting with balanced salt solution (BSS � ) and stored at 4 � C and at 24 � Cw ith and without exposure to light. The minimum bactericidal concentrations against P. aeruginosa and S. aureus were measured to evaluate the antimicrobial potency over a 4-week period. Changes in the pH values and physical characteristics of the solutions were recorded over the same period of time. Results: The antibacterial potency of ceftazidime decreased significantly from days 3 and 7 onwards at storage temperatures of 24 � C and 4 � C, respectively, but was not affected by light exposure. The pH value progressed from acidic to alkaline, peaking at day 3, in all solutions. The antibacterial potency of vancomycin remained stable during the 4-week period, but its pH showed a slight progression from acidic to less acidic, in all solutions.