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ARMOR study shows certain antibiotics still effective against stubborn bacterial infections
The majority of MRSA was shown be resistant to multiple antibiotics.
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The ongoing 5-year Antibiotic Resistance Monitoring in Ocular Microorganisms, or ARMOR, pathogen surveillance study has shown that a number of isolates’ resistance to common ophthalmic antibiotics remains constant and high; though, presently, certain antibiotics are still effective.
The Bausch + Lomb-sponsored study has been collecting isolates from known ocular infections from 25 sites around the U.S. for 4 years.
“We get 400 to 600 of these isolates each year, and we test them against the commercially available ocular antibiotics, including vancomycin,”
Calvin W. Roberts
According to Roberts, the study reported that 73% of methicillin-resistant Staphylococcus aureus (MRSA) are currently resistant to multiple antibiotics, and that 23% of all staphylococci have at least three resistances to ocular antibiotics.
“It’s really important for us, as clinicians, to be able to isolate the bugs, culture them, start patients on a very broad-acting antibiotic and then be able to check the resistance over time,” he said. “Fortunately, what we’re seeing is that the antibiotics we currently have available continue to be very effective against most of the bugs.
“However,” Roberts continued, “you have to keep in mind that those multiple resistant organisms, those MRSAs and those coagulase-negative staphylococci, continue to be a big problem and a very important issue not only in eye care, but all of medicine.”
Take-home message
“It’s good that we have a surveillance system that is monitoring, in real time, the developments and trends of these resistant organisms,” PCON Editorial Board member
Bruce E. Onofrey
The most important finding, according to Onofrey, is that the most common pathogen that causes acute bacterial eye disease in the adult population in the U.S., Staphylococcus, is developing greater resistances to drugs currently used to treat the infections it causes.
“That’s our greatest concern, because Staphylococcus epidermidis, or coagulase-negative Staphylococcus, is an opportunist, part of the normal flora of the eye, and it puts all patients who wear contact lenses or have LASIK surgery or have an ocular surface disease at risk for creating more resistant organisms,” he said.
Therefore, clinicians will want to practice habits that reduce the chances of developing more resistant strains of the pathogens, Onofrey said.
“It is important to be confident that you are treating a bacterial infection, not a viral, bacterial or allergic conjunctivitis,” he said. “When dealing with more serious conditions, such as keratitis, or postoperative patients, culturing and sensitivity testing may be necessary.”
Then, clinicians will want to prescribe the drug most effective against the worst organism that could possibly develop, for the most appropriate amount of time at the proper dosage, he said.
“Antibiotics should never be tapered,” Onofrey said. “It is important to realize that you kill susceptible bugs at the beginning of the infection and resistant ones at the end. You need to maintain a therapeutic level of drug throughout the treatment to eradicate the organisms completely.
“We also don’t want people to grab a bottle of antibiotic drops to use every time they get red eye,” he added. “We have to make sure we monitor those refills and treat in real time. We can’t allow the patient to use the drug chronically at low levels.”
ARMOR also showed that, although there has been a sharp increase in resistance to later-generation fluoroquinolones, some of the older drugs still retain their potency, according to PCON Editorial Board member
“The ARMOR data showed that besifloxacin is a very potent suppressor and killer of multiple gram-positive organisms,” Thomas said. “I think it would be very safe to say that we all, as a prescribing community, need to move away from the fourth-generation fluoroquinolones and go back to using the aminoglycosides, tobramycin and gentamicin, and embrace the chlorofluoroquinolone, besifloxacin.
Randall Thomas
“This past year, it received an extension approval for Pseudomonas aeruginosa, so it is indeed a broad-spectrum antibiotic,” he added. “The fact that it’s not used systemically, that it’s used exclusively topically, means there should be a good long period of time before it begins to suffer from resistance.”
Shortcomings
An area where the ARMOR study fell short is that it was an in vitro study, Thomas said.
“I wish we had some good in vivo studies with human subjects,” he said. “Besifloxacin had an equal MIC90 to vancomycin. The question is, can we extrapolate from it that, in vivo, Besivance [besifloxacin, Bausch + Lomb] would be clinically equivalent to vancomycin? Those are the kinds of studies that we do not have, but need to have so we can make sound clinical decisions, with the ultimate goal of improving patient care.” – by Daniel R. Morgan
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Disclosures: Onofrey has no relevant financial disclosures. Thomas is a consultant for Alcon, Bausch + Lomb and Merck. Roberts is chief medical officer for Bausch + Lomb.