Ocular Pharmacokinetics of Topical Chloramphenicol in Dogs: Effects of Concentration and Vehicle Formulation

ABSTRACT This study compared tear film exposure and retention of four chloramphenicol ophthalmic formulations in dogs, evaluating the effects of drug concentration (0.2% to 5%) and vehicle type (solution vs. ointment). Eight healthy dogs were enrolled in a randomized paired‐eye crossover study consisting of two sessions with a 7‐day washout. Tear samples were collected via microcapillary tubes at intervals up to 480 min post‐instillation, and concentrations were quantified using UV–Vis spectrophotometry. Results showed that chloramphenicol exposure was significantly enhanced by higher concentrations and ointment vehicles. The 0.8% solution achieved a 2.2‐fold increase in AUC 0–480 over the 0.2% solution, while the 5% ointment provided a 3.0‐fold increase over the 1% ointment. Tear concentration at 480 min was superior for ointments, with the 5% formulation maintaining 88.7 ± 6.8 μg/mL, whereas both solutions fell below quantification limits by the end of the interval. Overall exposure did not differ significantly between the 0.8% solution and 1% ointment. In conclusion, chloramphenicol exposure on the ocular surface depends on both concentration and formulation. High‐concentration ointments maximize exposure and prolong retention, providing a pharmacokinetic framework for optimizing therapy in canine bacterial keratitis.