Анотация: To compare the extent of inflammation and catabolic collagen response in the middle carpal joints (MCJs) of healthy horses following intra-articular injection of 2 PROCENT lidocaine, 2 PROCENT mepivacaine, lactated Ringer solution (LRS), or 0.1 PROCENT methyl parahydroxybenzoate. ANIMALS 17 adult horses. PROCEDURES In the first of 2 experiments, the left middle carpal joint (MCJ) of each of 12 horses was injected with 10 mL of 2 PROCENT lidocaine (n = 3), 2 PROCENT mepivacaine (3), or LRS (control; 6). After a 4-week washout period, the right MCJ of the horses that received lidocaine or mepivacaine was injected with 10 mL of LRS, and the right MCJ of horses that received LRS was injected with 10 mL of 2 PROCENT lidocaine (n = 3) or 2 PROCENT mepivacaine (3). In experiment 2, the left MCJ of each of 5 horses was injected with 10 mL of 0.1 PROCENT methyl parahydroxybenzoate. After a 48-hour washout period, the right MCJ of each horse was injected with 10 mL of LRS. Synovial fluid (SF) samples were aseptically collected before and at predetermined times after each injection. Synovial fluid WBC count, neutrophil percentage, and total protein, neutrophil myeloperoxidase, neutrophil elastase, and Coll2-1 concentrations were compared among treatments. RESULTS Both lidocaine and mepivacaine induced SF changes indicative of inflammation and a catabolic collagen response, but the magnitude of those changes was more pronounced for lidocaine. Methyl parahydroxybenzoate did not cause any SF changes indicative of inflammation. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that mepivacaine was safer than lidocaine for intra-articular injection in horses