Abstract
BackgroundOphthalmic antibiotic therapy in large animals is often used empirically because of the lack of pharmacokinetics studies. The purpose of the study was to determine the pharmacokinetics of topical tobramycin 0.3% ophthalmic solution in the tears of normal horses using an automated immunoassay analysis.ResultsThe mean tobramycin concentrations in the tears at 5, 10, 15, 30 minutes and 1, 2, 4, 6 hours after administration were 759 (±414), 489 (±237), 346 (±227), 147 (±264), 27.6 (±28.4), 14.8 (±66.6), 6.7 (±18.6), and 23.4 (±73.4) mg/L. Mean tobramycin concentration was maintained above the MIC90 for commonly isolated bacteria for 68.5 min.ConclusionA single dose of topical tobramycin resulted in therapeutic concentrations of tobramycin in the tears for 1 h after administration. Therapeutic levels of tobramycin remained in equine tears 6 times longer than was reported in rabbit tears.
Highlights
Ophthalmic antibiotic therapy in large animals is often used empirically because of the lack of pharmacokinetics studies
Extraction and Immunoassay A tobramycin immunoassay developed for use on human serum was adapted for use with tear fluid collected on Schirmer test strips
We showed that the mean tobramycin in the tear film reached the MIC90 of 16 mg/L after 68.5 minutes, indicating that therapeutic concentrations of the drug were maintained for over an hour, compared to the 10 minutes reported in the rabbit tears [10]
Summary
Ophthalmic antibiotic therapy in large animals is often used empirically because of the lack of pharmacokinetics studies. Their prominent eye profile and active nature likely predispose them to ocular trauma [1]. Primary corneal bacterial pathogens, such as Pseudomonas, can establish infection despite an intact corneal epithelium [1,2,3]. Bacteria most frequently cultured from the corneas of horses with ulcerative keratitis include Streptococcus equi subspecies zooepidemicus, Pseudomonas aeruginosa, and Staphylococcus spp. General recommendations are to use a broad-spectrum initial antimicrobial therapy for ulcerative keratitis, the antibiotic choice and frequency of administration are empirical and guided by the clinical examination and cytological evaluation of corneal swabs [1]. Therapy is modified based on bacterial and fungal culture and sensitivities, when they become available in the following days to weeks [1,6]
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