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Los Angeles-The rates of infection after cataract surgery can be reduced by a meticulous approach to controlling the microbes on the ocular surface and in the eye. The use of fourth-generation fluoroquinolones can better control the microorganisms that have grown resistant to previous generations of the drugs.
Wound architecture seems to be an enormously important factor since incisions that are square or nearly square in their surface architecture do not leak as readily as those that are rectangular, which facilitates controlling the microbial entrance into the eye postoperatively, according to Samuel Masket, MD. This is in keeping with the earlier work of Ernest who demonstrated this concept with human cadaver eyes.
"The obvious way to reduce infection after cataract surgery is to decrease the opportunity for microbes to enter the eye," said Dr. Masket, clinical professor of ophthalmology, Jules Stein Eye Institute, David Geffen School of Medicine, Los Angeles, and in private clinical practice in Los Angeles. "To accomplish this, there needs to be a four-pronged approach.
"Third, the incision must be constructed and managed appropriately to avoid chances for chamber contamination after surgery," Dr. Masket continued. "Finally, we need to destroy microbes that may enter the chamber at the close of surgery or in the early postoperative period."
The evidence in the literature is very clear about the symbiosis of povidone iodine and antibiotic drugs, Dr. Masket said.
"We know that povidone iodine kills most microorganisms very rapidly and that 5% is well tolerated in the conjunctival cul-de-sac and 10% on the skin," Dr. Masket said. He also noted the rarity of patient systemic allergy to topically applied iodine resulting in anaphylaxis, making this approach available to most patients.
In addition, it is beneficial to reduce the microorganism population on the surface before preparing the patient for surgery; this is where topical antibiotics are effective, he said.
"Because of high tolerance and broad spectrum, the fluoroquinolones have long been the preferred agent preoperatively," Dr. Masket said. "However, in 2000 the microorganisms that cause endophthalmitis began to show substantial resistance to the second- and third-generation fluoroquinolones."
It was at this point that the fourth-generation fluoroquinolones, moxifloxacin (Vigamox, Alcon Laboratories) and gatifloxacin (Zymar, Allergan), became available in 2004. In addition to increased antimicrobial efficacy, they help prevent the development of resistance by microorganisms, in part as the result of the 8-methoxy side chain.
"Both gatifloxacin and moxifloxacin were reported to exhibit much lower minimum inhibitory concentrations to 93 endophthalmitis isolates in real cases, as reported by Mather and colleagues in the American Journal of Ophthalmology in 2002," he said. "Eighteen of the 93 isolates had been refractory to treatment with the previous generation of fluoroquinolones but not to the fourth generation.
"Prophylaxis seems best with the fourth generation of these drugs. I no longer employ second and third generations in my practice," he said.
The use of intracameral antibiotics has been controversial until recently, according to Dr. Masket. He referred to preliminary results from a European Society of Cataract and Refractive Surgeons study that pointed to a five-fold reduction in the rates of endophthalmitis in patients treated with intracameral cefuroxime (Zinacef, GlaxoSmithKline) at the end of the surgery.
"This information is interesting and may change our standard of care," he said.
Dr. Masket also described a survey he conducted among members of the American Society of Cataract and Refractive Surgery regarding use of intracameral antibiotics. Intracameral vancomycin (Vancocin, Eli Lilly) was reportedly used by 18% of respondents in about 104,000 eyes.