Moxifloxacin provides prophylaxis against bacterial growth

Beaumont, TX-Moxifloxacin (Vigamox, Alcon Laboratories) appears to be superior to gatifloxacin (Zymar, Allergan) in preventing the growth of endophthalmitis-causing bacteria in preoperative samples of aqueous fluid, according to Asad Abbas, MD, director of ophthalmology, Southeast Texas Medical Associates, Beaumont, TX.

Beaumont, TX-Moxifloxacin (Vigamox, Alcon Laboratories) appears to be superior to gatifloxacin (Zymar, Allergan) in preventing the growth of endophthalmitis-causing bacteria in preoperative samples of aqueous fluid, according to Asad Abbas, MD, director of ophthalmology, Southeast Texas Medical Associates, Beaumont, TX.

"Cataract surgery is the most commonly performed procedure in the United States, and the most devastating complication of cataract surgery is endophthalmitis," Dr. Abbas said. The incidence of this complication has been on the rise due to the increased resistance of pathogenic bacteria and the decreasing effectiveness of third-generation fluoroquinolones against organisms that cause endophthalmitis, he said, adding, "By 2001, all the isolates that caused endophthalmitis were resistant to the third-generation fluoroquinolones."

As a result of this trend, the fourth-generation fluoroquinolones gatifloxacin and moxifloxacin became commercially available, and they provided enhanced protection against the isolates resistant to the previous generation of fluoroquinolones, Dr. Abbas said.

Data indicate that both moxifloxacin and gatifloxacin achieve levels of penetration in the aqueous "that far exceed the minimum inhibitory concentration (MIC) 90 levels of the ocular isolates that cause endophthalmitis," Dr. Abbas said. Another study found that the administration of the two antibiotics results in the complete sterilization of the aqueous fluid at the time of cataract surgery. The antibiotics, however, do not eradicate the flora present on the ocular surface, and so clinical cases of endophthalmitis continue to occur.

Keeping in mind that aqueous inoculation from external fluid might be an etiology in post-cataract surgery endophthalmitis, Dr. Abbas and George F. Hyman, MD, FACS, conducted a randomized, double-blind pilot study in which they evaluated the efficacy of the fourth-generation fluoroquinolones in suppressing bacterial growth in intraoperative aqueous fluid samples from cataract patients randomly assigned to receive moxifloxacin or gatifloxacin for preoperative prophylaxis. The study was an in vitro experiment comparing the antibacterial effectiveness of the two different fourth-generation fluoroquinolones in the setting of a simulated intraoperative contamination (with an endophthalmitis-causing isolate of Staphylococcus epidermidis) of aqueous fluid obtained from patients during routine phacoemulsification cataract extraction and IOL implantation surgery.

The trial included 20 consecutive patients scheduled to undergo conventional cataract surgery; 10 patients were treated with moxifloxacin, and 10 patients were treated with gatifloxacin. Ten samples of balanced saline solution served as controls.

One drop of antibiotic was administered four times daily beginning the day before surgery, then four drops were administered at 15-minute intervals for 1 hour before surgery.

The procedure involved the removal of a preoperative sample of aqueous fluid from the anterior chamber, and a postoperative sample at the completion of the surgery. In the microbiology laboratory, 0.1 ml of the aqueous fluid was mixed with 0.01 ml of an endophthalmitis-causing strain of S epidermidis at a concentration of 107 CCU. The samples were incubated on culture plates and were examined for bacteria growth at 24, 48, and 72 hours.

Results

"Compared with the control group, both antibiotics were significantly efficacious," Dr. Abbas said.

In the samples taken preoperatively from patients treated with moxifloxacin, 90% showed no bacterial growth, compared with 40% of the samples taken preoperatively from patients treated with gatifloxacin. Though not statistically significant, the data showed a trend that moxifloxacin was more active in suppressing bacterial growth than gatifloxacin in an instance of simulated aqueous fluid contamination.

The results of this study compared favorably with other studies that showed higher penetration into the aqueous fluid and lower MIC levels of moxifloxacin compared with gatifloxacin.

"However, in the postoperative samples, both antibiotic groups were found to be ineffective in suppressing bacterial growth. This might have been because of the washout effect of the procedure," Dr. Abbas said.