Effect of intravitreal triamcinolone acetonide on susceptibility to experimental bacterial endophthalmitis and subsequent response to treatment.

OBJECTIVES Recent reports of high endophthalmitis rates after intravitreal triamcinolone acetonide injection have raised concerns about the safety of this treatment. We sought to evaluate the effect of intravitreal triamcinolone injection on (1) the susceptibility to experimental bacterial endophthalmitis and (2) the subsequent therapeutic response to antibiotic treatment. DESIGN For the susceptibility study, the right eye of 40 New Zealand white rabbits received an intravitreal injection of a known quantity of Staphylococcus epidermidis organisms. Half of the eyes received a simultaneous intravitreal injection of triamcinolone acetonide, 4 mg. All eyes were examined daily for signs of endophthalmitis (photophobia, conjunctival injection, and vitritis) using standardized grading protocols (scaled from 0 to 4 with increasing severity). On day 7, vitreous cultures were obtained. For the therapeutic response study, the right eye of 12 rabbits received an intravitreal injection of S epidermidis organisms sensitive to vancomycin. Half of the eyes received a simultaneous intravitreal injection of triamcinolone acetonide, 4 mg. All 12 eyes received an intravitreal injection of vancomycin hydrochloride, 1 mg, on development of the first signs of endophthalmitis. All eyes were examined daily for 7 additional days. On day 7 after treatment, vitreous cultures were obtained. RESULTS In the susceptibility study, all 40 eyes developed signs of endophthalmitis. In eyes that received intravitreal bacteria plus triamcinolone, 17 (85%) of the 20 vitreous cultures were positive, whereas only 6 (30%) were positive in the 20 eyes receiving bacteria alone (P = .001). The vitritis was significantly increased in the bacteria plus triamcinolone group compared with the bacteria-only group (17 of 20 vs 7 of 20 with 4+ vitritis, respectively; P = .003). In the therapeutic response study, all 12 eyes developed clinical signs of endophthalmitis within 48 hours. All vitreous samples obtained 7 days after intravitreal vancomycin injection were culture negative. However, the severity of vitritis at the time of vitreous sampling was less in the eyes receiving triamcinolone plus bacteria compared with eyes receiving bacteria alone (0 of 6 vs 5 of 6 with 4+ vitritis, respectively; P = .02). CONCLUSIONS In eyes with experimentally induced bacterial endophthalmitis, the presence of intravitreal triamcinolone results in a higher culture-positive rate and a higher degree of inflammation, suggesting an impaired ocular immune response and greater susceptibility to infection. However, in eyes with experimentally induced bacterial endophthalmitis receiving early treatment with intravitreal antibiotics, triamcinolone appears to suppress the ocular inflammatory response without impairing the therapeutic effect. CLINICAL RELEVANCE These data suggest that caution must be exercised when combining intravitreal triamcinolone injection with intraocular surgery.