Determining the Effect of Antibiotic Drop Prophylaxis on the Conjunctival Flora

Overview

Ranibizumab (Lucentis) is currently the best treatment for wet Age-Related Macular Degeneration (AMD). To work, the drug must be injected by means of an intravitreal injection (IVT) into the vitreous (jelly-like material) cavity in the back of the eye, repeatedly at intervals ranging from one to several months. Endophthalmitis is a rare but devastating infection of the eye that occurs in approximately 0.2% of patients after IVT injection. Many ophthalmologists ask patients to use antibiotic eye drops after IVT injection in the hope that this may reduce the risk of endophthalmitis. There is no proof that this happens and there is a possible risk that repeated exposure to the same antibiotic may cause antibiotic resistance organisms (bacteria) to develop over time. The investigators hypothesize that repeated exposure to antibiotic during the initial stages of treatment for AMD will result in a progressive shift in the conjunctival flora with an increasing number of antibiotic resistant organisms appearing over time. If this is demonstrated, changes to the prevailing treatment approach will be needed to reduce the long term risk of a patient developing antibiotic resistant endophthalmitis during treatment.

Intraocular injection of a VEGF inhibitor on a repeated basis has become the standard of care for the treatment of Age-Related Macular Degeneration (AMD) following pivotal studies which demonstrated that vision could be stabilized in 90% of treated patients. Most patients require injection, on average, every two months indefinitely. The incidence of intraocular infection (endophthalmitis) following intraocular injection is approximately 0.2%. Current injection protocols involve the use of topical poviodine prior to injection based on evidence that this significantly reduces the bacterial flora on the conjunctiva. Following injection there is often some reflux of vitreous fluid from the cavity of the eye into the subjunctival space. For this reason many Ophthalmologists have patients use topical antibiotics for 2-3 days post injection with the expectation that this may reduce the risk of infection as the eye is healing. Ta et al have demonstrated that following a 3 day course of topical antibiotic the incidence of resistant strains of bacteria in the conjunctival sac does not significantly increase (159 patients).There are no longitudinal studies which examine the effects of repeated short term antibiotic exposure on the conjunctival flora over time. This is a prospective, randomized, comparative study which will follow the conjunctival flora of patients undergoing induction treatment with a VEGF inhibitor for AMD. The incidence of resistant organisms in the group receiving antibiotics will be compared to that in a similar group who do not receive antibiotics. Following informed consent, patients will have a conjunctival swab taken by the treating Ophthalmologist after instillation of sterile topical anesthetic but before application of poviodine. The swabs will be cultured in thyoglycollate broth. Bacteria present and resistance to the antibiotic used will be identified. This process will be repeated each visit during the induction phase of treatment which consists of four sequential injections each a month apart. Patients in the antibiotic arm will be asked to use topical Moxifloxacin drops 4 times a day for 3 days following injection. The control group will not receive antibiotics.