Efficacy, chondrotoxicity and plasma concentrations of tramadol following intra-articular administration in horses undergoing arthroscopy: preliminary findings

Intra-articular administration of analgesics is performed to ensure good perioperative pain management avoiding undesirable systemic effects. To evaluate the effect of intra-articular injection of tramadol on postoperative pain after arthroscopy in horses and to determine whether tramadol had a local effect. Before the in vivo study, an in vitro test was performed aiming to evaluate the viability of equine chondrocytes after exposure to various concentrations of tramadol. The concentration identified as most appropriate was used to treat the horses’ joints. Twelve horses affected by osteochondrosis were randomly assigned to two groups that were treated intra-articularly at the end of surgery with tramadol (4 mg/mL) and saline, respectively. At predetermined time-points a Composite Pain Scale was applied and blood samples were collected in order to define the extent of tramadol absorption into the systemic circulation. The Mann-Whitney test was used for statistical analysis. Serum of four out of six treated horses revealed traces of tramadol (range 10.6–19.3 ng/mL) sporadically between 0.5 and 4 hours post-treatment, while in the other two horses, no trace of drug was found. Findings suggested that any eventual effect was probably due to local action rather than systemic absorption. The pain scores obtained in tramadol-treated horses were lower between 1 and 6 hours post-administration, than those obtained in the control group, but the differences were not statistically significant. These preliminary results suggest that tramadol, at this concentration, is only mildly beneficial in the pain management of horses after arthroscopy.