EyeWorld Asia-Pacific September 2016 Issue

67 EWAP PHARMACEUTICALS September 2016 cefuroxime may develop Enterobacter endophthalmitis, a bacterium not sensitive to cefuroxime. Dr. Arshinoff said that patients often end up going blind because Enterobacter is also not usually sensitive to the drugs used to routinely treat endophthalmitis. “The reason is the drugs we use to treat endophthalmitis are vancomycin and ceftazidime,” he said, adding that ceftazidime comes from the same class of drugs and both ceftazidime and vancomycin have similar mechanisms of action as cefuroxime. So if the bug is resistant to cefuroxime, there is a good chance that it’s also resistant to the usual treatment for endophthalmitis, Dr. Arshinoff explained. While the eye is immediately cultured, patients are put on routine endophthalmitis treatment before determining the exact cause. By the time more targeted medication can be used, it is usually too late with the highly aggressive Enterobacter bacterium. The same is not true with moxifloxacin. While the endophthalmitis fail rates for moxifloxacin and cefuroxime are pretty much equivalent, Dr. Arshinoff pointed out there is a distinction. The difference is that moxifloxacin works on DNA gyrase and topoisomerase, which is a completely dissimilar mechanism from the agents used to treat endophthalmitis, he said, adding that both vancomycin and ceftazidime work instead by inhibiting bacterial cell wall synthesis. “When you have drugs that work by a totally different action, the chances of having cross-resistance is much lower,” he said. As a result, if you are using moxifloxacin initially and this fails, when the patient is placed on traditional endophthalmitis treatment, he or she will get better rapidly. “If you use cefuroxime, almost all the failed cases go blind,” Dr. Arshinoff said. Possible complications While the antibiotics themselves can be used safely, Dr. Mah finds that there are two types of toxicity that practitioners need to be on the lookout for—toxic anterior segment syndrome (TASS) and long-term toxicity. “It would be evident right away if you have an episode of TASS,” Dr. Mah said. When it comes to long-term toxicity, however, there is no telling what may someday turn up. For example, Dr. Mah pointed out that the first reports with intracameral cefuroxime were made in 2001, with intracameral vancomycin being used in the 1990s. While there is some history, there is also the possibility that something will happen 30 or 40 years down the line that was not foreseen, Dr. Mah pointed out, citing the occurrence of HORV. Because this appears to be a very rare event that occurs several weeks later, it was probably not associated with the use of the agent initially, Dr. Mah noted. “Likewise, we may find down the road that there is an increased incidence of macular degeneration or glaucoma that we didn’t know about with intracameral antibiotics.” Dr. Arshinoff pointed out that there’s also an extremely rare chance of a reaction to Vigamox. He cited the recent case of a practitioner who used Vigamox for a vitrectomy, and the patient ended up with iris atrophy. While this was one rare case, some concern comes from high- dose systemic administration of moxifloxacin, which can lead to a syndrome of bilateral acute iris transillumination. He added that this, too, is rare and thought to be related to very high concentrations of the moxifloxacin transiting the iris or being in the vitreous but not in the anterior chamber. To help avoid endophthalmitis with these intracameral agents, Dr. Arshinoff recommended changing the volume injected. “Why does everyone inject 0.1 cc into the anterior chamber of the eye?” he asked, adding that it’s done this way because that’s what will fit in the small area of the vitreous when treating cases of endophthalmitis. “Why would we inject 0.1 cc into an anterior chamber when what we want to do is exchange the fluid in the anterior chamber or wash it out?” It would be easier to accurately inject 0.3 cc, with the concentration appropriately adjusted, he thinks. When it comes to the concentration, this may also need some rethinking. While Vigamox may work well for intracameral use right out of the bottle, rather than taking the risk of a problem from a high concentration, Dr. Arshinoff recommends diluting this in balanced salt solution so that you can be sure the solution is isotonic, pH balanced, and safe, and then injecting more of it. Overall, Dr. Arshinoff is convinced that American physicians will gradually begin using more intracameral drugs to prevent endophthalmitis. As physicians around the world get lower infection rates and American physicians lag behind, patients who do get endophthalmitis will ask why their physician didn’t use intracameral antibiotics to help stave this off, and some may even sue. EWAP References 1. Endophthalmitis Study Group, European Society of Cataract & Refractive Surgeons. Prophylaxis of postoperative endophthalmitis following cataract surgery: results of the ESCRS multicenter study and identification of risk factors. J Cataract Refract Surg . 2007;33:978–88. Editors’ note: Dr. Arshinoff has no financial interests related to his comments. Dr. Mah has financial interests with Alcon, Allergan (Dublin), Bausch + Lomb (Bridgewater, New Jersey), and PolyActiva (Melbourne, Australia). Contact information Arshinoff: ifix2is@gmail.com Mah: mah.francis@scrippshealth.org