In vitro dose-dependent effects of enrofloxacin on equine articular cartilage

Objective-To determine whether enrofloxacin has detrimental, dose-dependent effects on equine articular cartilage in vitro. Animals-Cartilage explants were developed from 6 healthy horses between 0 a nd 96 months old. Procedure-Patellar cartilage explants were incubated in 5 concentrations of enrofloxacin (2 mu/ml, 10 mu g/ml, 1.000 mu g/ml, 10,000 mu g/ml, and 50,0 00 mu g/ml) for 72 hours, Proteoglycan synthesis ((NaSO4)-S-35 incorporatio n for 24 hours), proteoglycan degradation ((NaSO4)-S-35 release for 72 hour s), endogenous proteoglycan content (dimethylmethiene blue assay), and tota l protein content were determined. Cartilage explants were evaluated by use of histomorphologic and histomorphometric techniques (toluidine blue stain ) for cytologic and matrix characteristics. Quantitative data were analyzed with a one-way ANOVA to compare results among various enrofloxacin concent ration groups and the control group. A general linear model was used to det ermine whether age had an effect. Result-Proteoglycan synthesis was excellent in control specimens and in spe cimens incubated in low concentrations of enrofloxacin (2 mu g/ml and 10 mu g/ml). High concentrations of enrofloxacin (> 1,000 mu g/ml) effectively e liminated proteoglycan synthesis regardless of horse age. Proteoglycan degr adation at low concentrations (2 mu g/ml and 10 mu g/ml) was not different than control. High concentrations of enrofloxacin (> 1,000 mu g/ml) caused significant degradation. Different concentrations of enrofloxacin did not a ffect endogenous proteoglycan. High concentrations of enrofloxacin were ass ociated with a significant increase in number of pyknotic nuclei. Conclusion-Concentrations of enrofloxacin that might be achieved following systemic administration did not suppress chondrocyte metabolism in vitro, H igh concentrations of enrofloxacin (> 1,000 mu g/ml) were toxic to chondroc ytes.