In vitro efficacy of an ophthalmic drug combination against corneal pathogens of horses.
OBJECTIVE
To evaluate the in vitro efficacy of an ophthalmic drug combination against common corneal pathogens of horses.


METHODS
Representative isolates of 3 bacterial and 2 fungal corneal pathogens of horses.


METHODS
Pathogens were subjected to minimum inhibitory concentration (MIC) testing of a drug combination that consisted of equal volumes of natamycin 3.33%, tobramycin 0.3%, cefazolin 5.5%, and equine serum. Proteinase inhibitory activity of the drug combination was assessed by use of a fluorescence microplate assay with gelatin and collagen I as substrates. The MICs of the drug combination were compared with those for each of the component medications and antiproteinase activity of the drug combination was compared with that of serum by use of paired t tests and a 2-way ANOVA, respectively.


RESULTS
The drug combination was at least as effective as each medication separately for inhibiting microbial growth of all pathogens tested and was significantly more effective against B-hemolytic Streptococcus spp, Aspergillus spp, and Fusarium spp than the relevant medications separately. Serum and the drug combination both had significant antigelatinase activity, and serum had significant anticollagenase activity. Antiproteinase activity of serum was a concentration-dependent event, which enabled serum to achieve significantly greater activity than the drug combination after 3.5 and 4 hours of incubation [corrected] for the gelatin and collagen I assays, respectively.


CONCLUSIONS
Drug combinations have the attractive potential of minimizing the time, stress, and fatigue associated with topical treatment regimens consisting of multiple drugs used separately for horses with keratitis.
Scotty
Nicole C
NC
University of Florida Veterinary Medical Center, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32608, USA.
Brooks
Dennis E
DE
Schuman Rose
Crystal D
CD
D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000494:pharmacology; D000935:Antifungal Agents / Q000008:administration & dosage* / Q000494:pharmacology; D001230:Aspergillus / Q000187:drug effects*; D001419:Bacteria / Q000187:drug effects*; D001424:Bacterial Infections / Q000382:microbiology / Q000662:veterinary; D002437:Cefazolin / Q000008:administration & dosage / Q000494:pharmacology; D003316:Corneal Diseases / Q000382:microbiology / Q000662:veterinary; D004338:Drug Combinations; D005670:Fusarium / Q000187:drug effects*; D006734:Horse Diseases / Q000382:microbiology*; D006736:Horses; D008826:Microbial Sensitivity Tests; D009181:Mycoses / Q000382:microbiology / Q000662:veterinary; D010866:Natamycin / Q000008:administration & dosage / Q000494:pharmacology; D011480:Protease Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D011550:Pseudomonas aeruginosa / Q000187:drug effects; D013211:Staphylococcus aureus / Q000187:drug effects; D013291:Streptococcus / Q000187:drug effects; D014031:Tobramycin / Q000008:administration & dosage / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D000935:Antifungal Agents; D004338:Drug Combinations; D011480:Protease Inhibitors; D010866:Natamycin; D002437:Cefazolin; D014031:Tobramycin