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.