HISTOPATHOLOGY AFTER REPEATED INTRATHECAL INJECTIONS OF PRESERVATIVE-FREE KETAMINE IN THE RABBIT - A LIGHT AND ELECTRON-MICROSCOPIC EXAMINATION

Epidural and spinal administration of ketamine has been used in humans . Single-dose studies have shown that preservative-free ketamine lacks neurotoxic effects, but there are no studies after repeated administr ations. The aim of this study was to examine the effects of daily admi nistration of preservative-free ketamine. Fourteen New Zealand albino rabbits were assigned to two groups receiving either intrathecal prese rvative-free ketamine 5 mg, 0.5 mt 1% solution (eight rabbits) or sali ne 0.5 mt (six rabbits) once a day for 14 consecutive days. The rabbit s had a total subcutaneous implanted intrathecal catheter, which was i ntroduced during general anesthesia. On Day 15 the rabbits were anesth etized and in vivo fixated by transcardial perfusion with Tyrode's sol ution followed by a mixture of 2% glutaraldehyde and 1% formaldehyde i n a 0.1 mol/L phosphate buffer. A segment 5 cm on each side of the cat heter tip was removed and kept in a cold solution of the fixative. Lig ht microscopic, electron microscopic, and morphometric examinations sh owed no differences between the spinal cords from the rabbits injected with ketamine versus saline. Intrathecal ketamine produced motor impa irment for a period of 15 min. We conclude that repeated intrathecal a dministration of preservative-free ketamine confirms the lack of neuro toxicity from single-dose studies.