Intracameral antibiotic prophylasix remains controversial

"The undertaking of this study is commendable, but it is the subject of an ongoing critique, and more research is needed. Surgeons who are currently using an intracameral antibiotic with good safety and success may continue, but for those who have not adopted the technique, it seems reasonable to wait," said Dr. Mah, assistant professor of ophthalmology and co-medical director of the Charles T. Campbell Eye Microbiology Laboratory at the University of Pittsburgh Medical Center.

Discussing the role of antibiotics and anti-infectives in cataract surgery prophylaxis, Dr. Mah noted that no agent has been approved in the United States for that indication because none has been investigated in a large-scale, prospective, randomized, masked clinical trial needed to demonstrate efficacy and safety.

Rate of endophthalmitis

Although a rate of 1 in 1,000 is frequently cited as the risk of endophthalmitis after cataract surgery, some studies indicate that it has been increasing in recent years. In the ESCRS trial, endophthalmitis occurred at a rate of about 1 in 400 to 500 eyes. Gram-positive organisms, and especially coagulase-negative staphylococci, are the most prominent pathogens in post-cataract surgery endophthalmitis, and the patient's flora is the source.

Topical antisepsis with povidone-iodine (Betadine 5%, Alcon Laboratories) is considered standard of care for reducing the external flora, and evidence exists that a topical antibiotic acts synergistically with povidone-iodine.

"Povidone-iodine is not 100% effective against all organisms. For example, povidone-iodine does not affect Serratia species, and so adjunctive antibiotic treatment is needed to eradicate that organism," Dr. Mah said.

Several other lines of surrogate evidence exist for the benefits of topical antibiotic use for endophthalmitis prophylaxis, including the experience in the pivotal trial investigating intravitreal injection with pegaptanib sodium (Macugen, Pfizer/[OSI] Eyetech) that showed a protocol change requiring more intensive antibiotic prophylaxis with topical levofloxacin 0.5% (Quixin, Vistakon Pharmaceuticals) was associated with a reduction in the endophthalmitis rate from 0.16% per injection to 0.03%. In addition, studies have been performed in rabbit models showing that topical treatment with one of the commercially available fourth-generation fluoroquinolones, moxifloxacin 0.5% (Vigamox, Alcon) or gatifloxacin 0.3% (Zymar, Allergan), reduced the development of experimentally induced endophthalmitis, Dr. Mah said.

Assuming that antibiotics have value for endophthalmitis prophylaxis, decisions about agent selection are guided in part by results of in vitro testing. Data from the University of Pittsburgh antibiotic anagram, which are updated semiannually, support the use of one of the fourth-generation fluoroquinolones because they offer the most potent activity against the broadest spectrum of target pathogens.

"Our published papers of the in vitro susceptibility of clinical isolates from patients with endophthalmitis, keratitis, and conjunctivitis also show moxifloxacin and gatifloxacin have lower minimum inhibitory concentration values compared with the older fluoroquinolones against gram-positive organisms and equivalent activity against gram-negative bacteria," Dr. Mah said.