NEW YORK (Reuters Health) – Despite changes in the flora responsible for microbial keratitis, second-generation fluoroquinolone monotherapy remains the empirical treatment of choice, researchers from the UK report in the July 18th online Ophthalmology.
“There is significant pressure, particularly from the pharmaceutical industry, to switch to fourth-generation fluoroquinolones as empirical therapy in microbial keratitis,” Dr. Zaid Shalchi from East Kent Hospitals University NHS Trust, Kent, UK told Reuters Health in an email. “In the UK at present, this is unlikely to be helpful and may in fact fail to treat a significant number of gram-negative infections.
Dr. Shalchi and colleagues investigated the scale of antibiotic resistance in microbial keratitis in East Kent from 1999 through 2008 in an effort to help guide antibiotic prescribing in the UK.
The study included 476 corneal scrapes from 440 patients. Culture was positive in 163 samples (34.2%), and bacterial keratitis accounted for 162 (94.2%) of the 172 organisms identified.
Most bacterial infections (99 isolates, 61.1%) were caused by gram-negative organisms, and there was a significant increase in the number of gram-negative isolates during the 10-year period, whereas the number of gram-positive organisms did not change significantly.
“Our finding that the majority of microbial keratitis is due to gram-negative infection is almost certainly a result of increased contact lens wear and contrasts with the majority of previous studies around the world where gram-positive infection was found to be most prevalent,” the investigators note.
Nearly three-quarters of gram-negative isolates were resistant to chloramphenicol (with sensitivity declining dramatically during the study period), and almost 95% were resistant to cefuroxime. Only a quarter of gram-positive isolates were resistant to cefuroxime, and they were also less likely to be resistant to chloramphenicol.
Only 8 of 143 isolates (5.6%) were resistant to ciprofloxacin, and all resistant isolates were Staphylococci, including 5 methicillin-resistant S. aureus (MRSA) strains. This represents 19.2% ciprofloxacin resistance among S. aureus isolates.
During the study period, there was no significant change in the proportion of ciprofloxacin-resistant organisms.
“In the UK, second-generation fluoroquinolones such as ciprofloxacin and ofloxacin can safely be used for the empirical treatment of microbial keratitis,” Dr. Shalchi said. “Increasing gram-negative resistance to chloramphenicol means that contact lens wearers should not be prescribed the antibiotic as prophylaxis of corneal infection.”
“Gram-negative corneal infection is highly related to the high and increasing incidence of contact lens wear in the UK,” Dr. Shalchi explained. “Meticulous hygiene is essential for all contact lens wearers. It is important that users avoid sleeping whilst wearing their lenses unless advised by a healthcare professional. Regular lens cleaning and avoidance of overwear are very important.”
The researchers add, “There is clearly a continued need to monitor isolate sensitivity closely for any increases in resistance, particularly in large walk-in eye casualty departments.”
Ophthalmology 18 July 2011.