Evaluation of induced and spontaneous contamination of ocular medications after first opening

In order to evaluate whether ophthalmic preparations can be safely used within 12 hours after first opening, four different sterile ocular medications,were opened and tested for spontaneous bacterial contamination after exposure to air. Samples (10ml) were collected from 5 containers of each ophthalmic preparation after 0, 2, 4, 8 and 24 hours. No viable microorganisms were found during and at the end of the evaluation time. In order to assess if the ocular bacterial population might contaminate the medications, about 105 microbial cells of different species (Staphylococcus aureus, S. epidermidis, S. haemolyticus, Streptococcus pneumoniae, S. pyogenes, Corynebacterium spp., Haemophilus influenzae, Moraxella catarrhalis, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumanii, and Candida albicans) were added to the containers and incubated at 35°C or at room temperature. Samples were collected and the number of viable microrganisms was estimated.The medicaments showed a bacteriostatic or bactericidal activity (<100 survivors after 24 h of exposure) against the majority of all relevant species, with the exception of E. coli, P. aeruginosa, and A. baumanii, which demonstrated to be able to grow in some of these ocular preparations.These data indicate that the risk of spontaneous contamination of the containers after first opening is low, and that all solutions do not offer a favourable substrate for the growth of the microrganisms showing in the great majority of the cases an antimicrobial activity. These results suggest that a safe usage of these ocular medications can be extended from the recommended 12 hours at least 24 hours after first opening.