Ocular penetration of topical antibiotics: study on the penetration of chloramphenicol, tobramycin and netilmicin into the anterior chamber after topical administration

BACKGROUND: To compare penetration in the aqueous humour of topically applied antibiotics. DESIGN: Randomized prospective study, Department of Ophthalmology, University of Perugia, Italy. PARTICIPANTS: Patients undergoing phacoemulsification and intra-ocular lens implantation. METHODS: 122 patients were included: 14 received one drop of chloramphenicol (CAF) suspension; 12 one application of CAF gel; 11 one drop of netilmicin suspension; 13 one drop of tobramycin suspension; 37 repeated instillations of CAF suspension every 10 minutes for a total of four drops; and 35 repeated instillations of CAF gel every 10 minutes for a total of four drops. Samples were taken immediately before surgery from anterior chamber in order to determine antibiotic by means of HPLC. Samples were taken 45-190 minutes after the eye drops were instilled. MAIN OUTCOME MEASURES: intraocular penetration of CAF, netilmicin and tobramicyn. RESULTS: After a single administration, netilmicin and tobramycin were undectectable, whereas the CAF suspension reached a mean concentration of 0.23+0.21 μg/mL, and the CAF gel a mean concentration of 0.13+0.14 μg/mL. After repeated administrations, the mean concentrations of the CAF suspension and gel were respectively 0.60+0.26 μg/mL and 0.58+0.18 μg/mL. CONCLUSIONS: Tobramycin and netilmicin do not reach detectable concentrations, and so their use in the prophylaxis and treatment of post-operative infections does not seem to be rational. CAF after multiple administrations, reaches concentrations that are effective against Haemophilus influenzae and parainfluenzae, Legionella pneumophila, Moraxella catarrhalis, Neisseria meningitidis, Pasteurella multocida and Streptococcus pneumoniae. This means that CAF can be rationally used in the prophylaxis and the treatment of infections supported by sensitive germs.