Viability of Equine Chondrocytes After Exposure to Mepivacaine and Ropivacaine In Vitro

Chondrocyte health is altered when exposed to local anesthetics, raising concerns as to the long-term effects of local anesthetics intra-articularly for diagnosis and analgesia. To investigate the drug with the lowest toxic potential, the effect of ropivacaine and mepivacaine on chondrocytes was evaluated. Articular cartilage from normal metacarpophalangeal joints of five equine cadaver specimens was used to establish chondrocyte cultures. Following seven days, chondrocytes were exposed to standard culture medium (DMEM), ropivacaine 7.5 mg/ml (ROP7.5), ropivacaine 10 mg/ml (ROP10), mepivacaine 20 mg/ml (MEP20), mepivacaine 30 mg/ml (MEP 30), and 0.9% saline solution (SAL). Chondrocyte viability was evaluated by trypan blue exclusion, MTT, and flow cytometry via cellular staining with propidium iodide. No differences were observed between treatments following trypan blue exclusion assay. A difference was observed between DMEM and all other treatment groups (P < .0001) with a significant viability drop using the MTT assay. Mepivacaine 20 mg/ml and MEP30 exposure between showed greatest decrease in cellular viability compared to SAL, ROP7.5, and ROP10 (P < .0001). Cellular viability decreased as measured by flow cytometry in all groups compared to DMEM and ROP7.5 (P < .02). Interestingly, the trypan blue, MTT, and flow cytometry assays yielded different results. Although there was no difference using trypan blue, MTT demonstrated that ropivacaine-treated cells had lower viability than DMEM, and cytometry found that ROP7.5 did not differ from DMEM. Results in vitro suggest that short-term exposure to ropivacaine may result in less chondrotoxicity than mepivacaine. In vivo studies are warranted investigating long-term effects of local anesthetics on equine articular cartilage.

Epidural analgesia with morphine or buprenorphine in ponies with lipopolysaccharide (LPS)-induced carpal synovitis

This study evaluated the analgesia effects of the epidural administration of 0.1 mg/kg bodyweight (BW) of morphine or 5 μg/kg BW of buprenorphine in ponies with radiocarpal joint synovitis. Six ponies were submitted to 3 epidural treatments: the control group (C) received 0.15 mL/kg BW of a 0.9% sodium chloride (NaCl) solution; group M was administered 0.1 mg/kg BW of morphine; and group B was administered 5 μg/kg BW of buprenorphine, both diluted in 0.9% NaCl to a total volume of 0.15 mL/kg BW administered epidurally at 10 s/mL. The synovitis model was induced by injecting 0.5 ng of lipopolysaccharide (LPS) in the left or right radiocarpal joint. An epidural catheter was later introduced in the lumbosacral space and advanced up to the thoracolumbar level. The treatment started 6 h after synovitis induction. Lameness, maximum angle of carpal flexion, heart rate, systolic arterial pressure, respiratory rate, temperature, and intestinal motility were evaluated before LPS injection (baseline), 6 h after LPS injection (time 0), and 0.5, 1, 2, 4, 6, 8, 10, 12, 16, 20, and 24 h after treatments. Although the model of synovitis produced clear clinical signs of inflammation, the lameness scores in group C were different from the baseline for only up to 12 h. Both morphine and buprenorphine showed a reduction in the degree of lameness starting at 0.5 and 6 h, respectively. Reduced intestinal motility was observed at 0.5 h in group M and at 0.5 to 1 h in group B. Epidural morphine was a more effective analgesic that lasted for more than 12 h and without side effects. It was concluded that morphine would be a valuable analgesic option to alleviate joint pain in the thoracic limbs in ponies.