Intravitreal Injections and Endophthalmitis

Stephen J. Kim, MD

Disclosures

Int Ophthalmol Clin. 2015;55(2):1-10. 

In This Article

Ophthalmic Antibiotics

In contrast to povidone-iodine, antibiotic use is controversial. Prospective studies have consistently demonstrated that topically applied antibiotics administered 1 hour before significantly reduces conjunctival bacteria flora.[14,15] In addition, in vitro studies using fourth-generation fluoroquinolones demonstrate eradication of causative organisms of endophthalmitis in as little as 5 to 15 minutes. Topical application of moxifloxacin achieves MIC50 levels in the vitreous for causative organisms of endophthalmitis and may therefore assist in neutralizing bacteria inoculated into the vitreous at the time of injection; a potential clinical advantage over povidone-iodine which does not enter the eye.[16]

Despite rationale, a large observational study by the Diabetic Retinopathy Clinical Research Network did not observe a reduced rate of endophthalmitis in eyes treated with topical antibiotics.[17] In addition, the additive benefit of topical antibiotics to 5% povidone-iodine is uncertain as povidone-iodine is extremely effective as a single agent in rapidly sterilizing the conjunctival surface.[13] Furthermore, it is presumed that the vast majority of cases of endophthalmitis are due to direct inoculation of bacteria at the time of injection from contamination of the needle tip and not from subsequent entry through a wound track.[18] This latter mechanism is in contrast to cataract surgery where entry of surface bacteria may occur at a subsequent time point through a clear cornea incision.[19] Taken together, the rationale for and benefit of postinjection antibiotics is unproven.

Surveys performed in 2009 indicated that >80% of retina specialists used topical antibiotics either before and/or after IVT injections. More recent surveys, however, have suggested a steady decline in antibiotic use. A survey of members of the American Society of Retina Specialists in 2011 revealed that only 27% and 62% of responding members use preinjection and postinjection topical antibiotics, respectively. The reduced use of antibiotics may be explained by a lack of perceived effectiveness in preventing endophthalmitis, increasing awareness of antibiotic resistance, and lessoned fear of litigation.

The Antibiotic Resistance of Conjunctiva and Nasopharynx Evaluation (ARCANE) study provided the first direct evidence that short-term and repeated exposure of ocular flora to topical antibiotics selects for antibiotic-resistant strains of coagulase-negative staphylococci.[20] More alarming was the fact that these resistant coagulase-negative staphylococci also demonstrated coresistance to other commonly used classes of antibiotics.[21] At least 1 study has shown that resistant Staphylococcus epidermidis causes greater intraocular inflammation than susceptible ones and repeated antibiotic use promotes strains of S. epidermidis that have alterations in their biofilm, which facilitate avoidance of host defense mechanisms.[22] Furthermore, the ARCANE study demonstrated the potential for repeated topical antibiotic use to select for antibiotic-resistant strains among nasopharyngeal flora.[23] Approximately 40% of a standard 50 μL eye drop directly enters the highly vascular tear drainage apparatus and is absorbed by the nasopharyngeal mucosa. Although the ocular surface harbors bacteria that can cause systemic infection, its actual contribution to these infections is probably minor. In contrast, nasopharyngeal flora contributes too upper and lower respiratory infections. S. aureus and Streptococcus pneumonia colonize the nasopharynx of healthy individuals and are the most common cause of hospital-acquired and community-acquired pneumonia, respectively. Repeated exposure to subinhibitory concentrations of antibiotic over time may promote resistance.

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