Memantine elicits spinal blockades of motor function, proprioception, and nociception in rats

Although memantine blocks sodium currents and produces local skin anesthesia, spinal anesthesia with memantine is unknown. The purpose of the study was to evaluate the local anesthetic effect of memantine in spinal anesthesia and its comparison with a widely used local anesthetic lidocaine. After intrathecally injecting the rats with five doses of each drug, the dose-response curves of memantine and lidocaine were constructed. The potencies of the drugs and durations of spinal anesthetic effects on motor function, proprioception, and nociception were compared with those of lidocaine. We showed that memantine produced dose-dependent spinal blockades in motor function, proprioception, and nociception. On a 50% effective dose (ED50 ) basis, the rank of potency was lidocaine greater than memantine (P < 0.05 for the differences). At the equipotent doses (ED25 , ED50 , ED75 ), the block duration produced by memantine was longer than that produced by lidocaine (P < 0.05 for the differences). Memantine, but not lidocaine, displayed more sensory/nociceptive block than motor block. The preclinical data demonstrated that memantine is less potent than lidocaine, whereas memantine produces longer duration of spinal anesthesia than lidocaine. Memantine shows a more sensory-selective action over motor blockade.