Sustained Tear Film Exposure After Parenteral Cefovecin Administration in Dogs: Pharmacokinetics and Relevance to Canine Bacterial Keratitis

Objective: To characterize the tear film pharmacokinetics of parenterally administered cefovecin (Convenia) and compare tear concentrations with the minimum inhibitory concentrations (MICs) of common ocular pathogens. Animals Studied: Six healthy research-bred Beagles. Procedures: Dogs received a single subcutaneous injection of cefovecin (8 mg/kg) after inducing blood-tear barrier disruption through histamine-mediated conjunctivitis. Tear fluid was collected using Schirmer strips at multiple time points up to 336 h and analyzed via liquid chromatography–mass spectrometry. Tear concentrations from both eyes were averaged for analysis. MIC values were determined for Staphylococcus pseudintermedius, Streptococcus canis, and Pseudomonas aeruginosa (n = 10 isolates per species). Results: In a pilot experiment (n = 1 dog), tear cefovecin concentrations were 1.5 to 430-fold higher in the conjunctivitis eye than in the control eye at all but one time point. Across all dogs, tear concentrations ranged from 68 to 73 035 ng/mL and remained detectable throughout the 336-h study. Mean ± SD pharmacokinetic parameters were: C_max 27.23 ± 27.74 μg/mL, T_max 61 ± 83 h, AUC 2734 ± 2563 μg/mL·h, and t_1/2 64 ± 46 h. Tear concentrations exceeded the MIC₉₀ for Streptococcus (0.64 μg/mL) for 336 h and exceeded the MIC₉₀ for some Staphylococcus (10.2 μg/mL) between 48 and 120 h, but remained below the MIC₉₀ for Pseudomonas. Conclusions: Parenteral cefovecin achieved sustained tear concentrations sufficient to inhibit some susceptible Streptococcus and Staphylococcus isolates in vitro for clinically relevant time windows. While these findings support further investigation of cefovecin as an adjunctive therapy in selected cases, they do not justify empiric systemic antimicrobial use. Larger pharmacokinetic and clinical studies are warranted to validate these findings.