Intravitreal antibiotics foundation for endophthalmitis cases

Chicago-Empiric intravitreal therapy remains the mainstay for initial management of most cases of endophthalmitis while the roles of pars plana vitrectomy and treatment with systemic antibiotics are more variable, said Dennis P. Han, MD, at the annual meeting of the American Academy of Ophthalmology.

Dr. Han, professor of ophthalmology, Medical College of Wisconsin, Milwaukee, reviewed the etiology of endophthalmitis and evidence and recommendations for the use of various treatment alternatives.

Results from the Endophthalmitis Vitrectomy Study (EVS) show that the most common cause in acute postoperative cases is coagulase-negative Staphylococcus, which was isolated in about 70% of culture-positive cases, while gram-negative organisms were isolated in only about 6% of cases and fungi were found even less commonly. However, in eyes with post-traumatic endophthalmitis, fungi are present in up to 15% of cases, and a fungal cause may be found in more than 50% of endogenous cases.

"More recently, however, due to concerns about aminoglycoside retinal toxicity, amikacin is being used less frequently than ceftazidime," Dr. Han said.

When a fungal pathogen is suspected, intravitreal amphotericin B (5 µg) has been standard treatment, although intravitreal voriconazole (Vfend, Roerig) 100 µg has emerged as a potential alternative when the infection is due to organisms resistant to amphotericin B.

"Use of this newer azole antifungal may increase because of a presumed lower risk for retinal toxicity compared with amphotericin," Dr. Han said.

Findings from the EVS regarding the role of vitrectomy and intravenous antibiotics continue to have relevance for the management of postoperative endophthalmitis. In that study, immediate vitrectomy in patients with postoperative infections was of no benefit when presenting visual acuity was hand motion or better, whereas in patients with light perception only acuity, vitrectomy doubled the rate of achieving visual acuity of 20/100 or better and halved the risk of a 20/200 or worse outcome.

A case for vitrectomy

In addition, the EVS data showed a strong trend suggesting that patients with diabetes may benefit from vitrectomy, even if their baseline acuity was hand motion or better.

Based on those results, patients with acute postoperative endophthalmitis and light perception only acuity should get vitrectomy and it should be considered for diabetics, Dr. Han said.

Regarding systemic antibiotics, the EVS found no benefit from adding intravenous ceftazidine and amikacin to intravitreal antibiotics.

"Keep in mind, however, that these findings in the EVS may not apply to patients with bleb-related, post-traumatic, or endogenous endophthalmitis due to differences in microbial etiology," Dr. Han said. "For these types of infections, we consider vitrectomy if the presentation is moderate to severe, such as in eyes with vitreous inflammation severe enough to obscure the retinal vessels.

"In addition, systemic antibiotics may also have a role as an adjunct to intravitreal antimicrobial therapy in patients with bleb- or trauma-related endophthalmitis, as definitive therapy for endogenous or fungal endophthalmitis, and perhaps as prophylaxis after penetrating trauma," Dr. Han said.

The fourth-generation fluoroquinolones, moxifloxacin 0.5% (Vigamox, Alcon Laboratories) and gatifloxacin 0.3% (Zymar, Allergan), became available after the EVS, and while they are promising adjuncts, their exact roles in endophthalmitis management are yet to be defined. The fourth-generation quinolones offer many desirable characteristics, including broad-spectrum activity, ability to achieve therapeutic intraocular levels for most pathogens when administered orally, and low toxicity when administered into the vitreous.

However, a few studies have also reported significant rates of coagulase-negative staphylococci resistance to moxifloxacin and gatifloxacin. Therefore, they should not be used as sole agents for empiric therapy of established postoperative endophthalmitis, Dr. Han stated.

While highly feared, emergence of vancomycin-resistant gram-positive organisms has been rarely reported in the endophthalmitis literature. In such cases, linezolid (Zyvox, Pfizer) may become the treatment of choice.

"Both systemic and intravitreal dosing of linezolid have been evaluated experimentally, and this may become important in our armamentarium in the future," Dr. Han said.