Patterns of post-operative slbconjuncttval antibiotic usage

Purpose Subconjunctival antibiotics are often administered poni-imperatively for prophylaxir against bacterial endophlhal nitis Within an instituted virnce amongst attending -vr -ar.s to b: based on subsp'tcia'ty A common propinvia.egimen is the combination of an ammoglycoside (gentan.icin) and a cephalosrjonn (cefazolinj favored for synergism and broad spectrum of coverage. However in vitro inaclivation of beta-lactani by aniinoglycosides is well documentée Unraveling of the beta-laclam ring by the methylamino group of ami nogly cos ides s a proposed mechanism Additionally betalactam drugs have been shown to inactivat ; ammoglycosides This study was conducted to assess the patterns of post-operative ; ubconjunctival antibiotic usage amongst our attending physicians Methods Data comprising subconjunctival drugs, drug, combinations and type of surgery was gathered from the char's of 104 consecutive intracular surgeries performed by eight full-time attending from May to July 1996 Chisquare analysis was done to test for statisical independence between the surgery and type of injection given Results. Subconjunc'ival injections of gentamicin and cefazohn were administered 35 6% of the time; cefazolit, 32.7% and vancomycin, 9 6% There was a 40% probability of combined gentamicin and cefazohn use after cataract procedures compared to 14.7% after retinal procedures. Retinal surgery patients had a 47% probability of receiving cefazolin alone compared to 34% for cataract patients Conclusions These results indicate the type of subconjunctival injection, used in our institution, is statistically dependent on the ype of surgery performed The use of cefazolin with gentamicin is the most common tost-operative regimen used Because drug inactivation might occur when administered simultaneously, we recommend further studies to delineate the extent of mutual inactiva ion of ammoglycosides and cepahalosporins in standard post-operative ophthalmic doses.