The effect of chronic toxicity of pethidine on the spinal cord: an experimental model in rabbits

The aim of this study was to evaluate the toxicity of chronic spinal analgesia with pethidine in a rabbit model. We introduced epidural catheters in twenty New Zealand white rabbits, divided into two groups, and we administered 0.5 mg/kg pethidine or the same volume of normal saline through the catheters, for three consecutive days. Throughout the experiment, the animals were evaluated in terms of neurological status using the Tarlov score. After the rabbit's euthanasia, 4 μm sections of spinal cord stained with Hematoxylin-Eosin were analyzed by a pathologist blinded to the study for neurohistopathological changes. The results were statistically analyzed with Prism 5 software for Windows. No significant differences were noticed between the two groups in as far as body temperature (p=0.295) and weight (p=0.139) were concerned. In the group of animals, which received epidural pethidine, nine rabbits showed histological changes suggestive for neurotoxicity at the lumbar level of the spinal cord. These findings were significantly different compared with the control group which received only saline (no microscopic lesions revealed; p=0.0006). When combining the data from both groups or using the pethidine group alone, there was a significant correlation between the presence of neurological injury (Tarlov score) and the presence of the histopathological lesions in the spinal cord (r=-0.709, p=0.0002 and r=-0.635, p=0.013, respectively). Based on our findings, the chronic epidural administration of pethidine in rabbits induces moderate to severe histological changes on the spinal cord, but further investigations are needed to make a definitive statement about the histological effect of pethidine on the neurological tissue.