Antibiotic prophylaxis after IVT may be harmful

By Joanna Lyford, Senior medwireNews Reporter

Researchers are warning against routine antibiotic prophylaxis with intravitreal injection (IVT) after finding that the practice can increase the antibiotic resistance of ocular surface flora.

"This practice of administering IVT injections may be harmful because of an increase in the growth of resistant organisms on the ocular surface," write Peter Kertes (Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada) and co-authors in JAMA Ophthalmology.

Kertes et al conducted a prospective cohort study among 178 individuals who underwent IVT of ranibizumab for the treatment of age-related macular degeneration (AMD). Of these, 84 received repeated prophylactic topical antibiotics - specifically, topical moxifloxacin hydrochloride for 3 days after each monthly injection - while 94 did not.

The decision whether or not to give prophylactic antibiotics was not randomized and was based on the treating physicians' usual practice. The study's main outcome measure was resistance to moxifloxacin and ceftazidime in cultured isolates.

Kertes et al found that in the antibiotic group the minimum inhibitory concentration (MIC) increased from 1.04 µg/mL at baseline to 1.25 µg/mL at 3 months, the MIC for 50% of isolates increased from 0.64 to 1.00 µg/mL, and the MIC for 90% of isolates increased from 0.94 to 4.00 µg/mL.

In the no-antibiotic group, between baseline and 3 months there were no changes in the MIC or in the MIC for 50% and 90% of isolates.

The overall baseline culture-positive rate was 18.9%, and after adjusting for baseline values, the antibiotic group had a higher culture-positive rate at months 1, 2, and 3 compared with the no-antibiotic group.

Finally, subgroup analysis found that the presence or absence of diabetes mellitus did not influence either MIC or culture-positive rates.

While there were no adverse events in this study, the researchers remark that infectious endophthalmitis is a devastating complication that carries a high risk for morbidity and vision loss.

They write: "Because patients with neovascular AMD require an indefinite number of IVT injections, there is theoretically an increased risk of more virulent cases of endophthalmitis caused by more resistant strains of bacteria.

"As such, we believe that routine use of prophylactic antibiotics after IVT injection should be discouraged."

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