Age-related macular degeneration is the leading cause of blindness among over-65s in the western world, treatment of which often involves monthly injections of medication into the eye.
This treatment is also being studied for eye problems related to diabetes and retina vein occlusions, but for years many have question whether it could be more effective and carry less risks.
In order to prevent the most severe complication from intraocular injection, endophthalmitis, ophthalmologists regularly prescribe ophthalmic antibiotics after every injection
However, experts at Vanderbilt University School of Medicine, Nashville, Tennessee, have claimed that repeated exposure of ocular flora may lead to resistant bacterial strains and cultivate "superbugs" with multiple-drug resistance that could considerably affect the treatment of ocular infections.
Dr Stephen J Kim and Dr Hassanain S Toma, from the facility, carried out a study involving 24 patients who received intraocular injection in each eye and obtained cultures of the conjunctiva at baseline and after every injection for both treated and untreated eyes.
The patients were then randomised to one of four antibiotics and after each injection used only the antibiotic they were assigned, with the experts then testing the bacterial samples for susceptibility to 16 antibiotics, before analysing the bacterial DNA.
Injections were administered every four weeks for at least four consecutive months, and patients were followed for one year, with the specialists finding that repeated exposure to fluoroquinolone antibiotics was associated with coagulase-negative staphylococci (CNS), that demonstrated significantly increased rates of resistance to both older- and newer-generation fluoroquinolones.
Furthermore, repeated exposure to azithromycin was associated with CNS that demonstrated significantly increased resistance to macrolides and decreased resistance to both older- and newer-generation fluoroquinolones.
The authors noted that specimens of CNS from treated eyes demonstrated significant increases in multiple-drug resistance, with 81.8 per cent of CNS specimens appearing resistant to at least three antibiotics and 67.5 per cent appeared resistant to at least five.
"This finding has considerable implications because conjunctival flora are presumed to be the predominant source of postinjection endophthalmitis," the experts wrote in a recent issue of Archives of Ophthalmology, one of the JAMA/Archives journals.
"Our findings indicate the need for more judicious use of ophthalmic antibiotics after intraocular injection to reduce the potential emergence and spread of antimicrobial resistance."
by Emily Tait