Purchase this article with an account.
W. Tangpagasit, D. Miller, S. Gonzalez, S. Murphy, T. P. O'Brien, E. C. Alfonso; In vitro Efficacy of Combination Therapy for Ocular Infections. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2668.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Combination therapy is often used to treat recalcitrant ocular infections. Few clinical and or in vitro studies are available to support the practice. Time-kill studies were used to evaluate in vitro efficacy and synergy of gentamicin, tobramycin, moxifloxacin and vancomycin alone and in various combinations against select isolates of MRSA (3), MRSE (3), MSSA (3), MSSE (3) and P. aeruginosa (2).
Ten 10 µl aliquots containing 106 cfu/ml of each isolate were distributed in to microtiter wells containing 200 µl of each drug at ½ and full commercial or dosing strengths for gentamicin-.3% (gm), tobramycin-.3% (tm), moxifloxacin-.5% (mxf) and vancomycin-5% (van). Combination challenges included: Van-mxf, van-gm and mfx-gm for the staphylococci and mxf-gm, mxf-tm and gm-tm for Pseudomonas aeruginosa. Sampling times were 0, 0.5, 2, 4, 8 and 24 hrs.
A three log reduction (99.9% kill) in cfu was observed within 30 minutes for 50% or less of the isolates at both full and half strength. For both gentamicin (6/12, 50%) and vancomycin (41.7%, 5/12). There was no significant difference between the 30 minute killings rates for methicillin sensitive (gm-66.7%, van-50%) vs methicillin resistant (gm-50%, van-50%) isolates. Gentamicin kill rate was at least 4X that of the vancomycin and moxifloxacin. Synergy was demonstrated for the combinations: mxf-gm for 50%, and mxf-van 66.7%. No antagonism was observed for either combination. No synergy was observed for any of the staphylococcal isolates with van-gm combination at either strength. Antagonism was observed for 1/3 of the isolates with this combination. A 4X to 12X increased killing rate was observed when moxifloxacin was combined with either gentamicin or tobramycin against P. aeruginosa.
Antibiotic combinations can provide in vitro synergy against common ocular pathogens. Moxifloxacin when combined with vancomycin for staphylococci and or an aminoglycoside for P. aeruginosa may provide enhanced killing, reduced antibiotic resistance and improved clinical outcomes.
This PDF is available to Subscribers Only