• Jan H Vranken, Dirk Troost, Peter de Haan, Fritz A Pennings, Marinus H van der Vegt, Marcel G W Dijkgraaf, and Markus W Hollmann.
• Pain Relief Unit, Department of Anesthesiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. j.h.vranken@amc.uva.nl
• Anesthesiology. 2006 Oct 1; 105 (4): 813-8.

BackgroundKetamine and S(+)-ketamine have been advocated for neuraxial use in the management of postoperative pain and severe intractable pain syndromes unresponsive to opioid escalation. Although clinical experience has accumulated with S(+)-ketamine, safety data on toxicity in the central nervous system after neuraxial administration of S(+)-ketamine are conflicting. In this study, neurologic and toxicologic effects on the spinal cord from repeated daily intrathecal administration of commercially available, preservative-free S(+)-ketamine were evaluated against placebo in a randomized, blinded design.MethodsEighteen white New Zealand rabbits were assigned to two groups receiving either 0.5 ml intrathecal S(+)-ketamine, 0.5% solution (12 rabbits), or 0.5 ml saline (6 rabbits) once a day for 7 consecutive days. During general anesthesia, an intrathecal catheter was placed between the fifth and sixth spinous processes (lumbar). Neurologic (according to Tarlov criteria) and histopathologic assessments were performed after 7 days of treatment.ResultsPostmortem investigation of the spinal cord and nerve roots revealed histopathologic lesions suggestive of toxic damage in 11 rabbits, from the group of 12 animals receiving S(+)-ketamine. These results were significantly different compared with 5 control animals (no histologic changes observed). There was no significant difference in neurologic status between the two groups after 7 days of intrathecal treatment.ConclusionsThe authors conclude that repeated intrathecal administration of preservative-free S(+)-ketamine in a clinically relevant concentration and dosage has, considering the extent and severity of the lesions, a toxic effect on the central nervous system of rabbits.

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