Intrathecal amantadine for prolonged spinal blockade of sensory and motor functions in rats

We aimed to compare the hypothesized local anesthetic action of amantadine (1-adamantanamine) with that of the known local anesthetic mepivacaine. Motor, proprioceptive, and nociceptive functions were evaluated in rats after intrathecal administration. Amantadine elicited spinal anesthesia in a dose-related fashion and produced a better sensory-selective action over motor blockade (P < 0.01). On the 50% effective dose (ED50 ) basis, the rank of potency on spinal motor, proprioceptive, and nociceptive block was mepivacaine > amantadine (P < 0.01 for the differences). Amantadine (63.5 μmol/kg) and mepivacaine (7.1 μmol/kg) produced complete spinal block of motor function, proprioception, and nociception. On an equipotent basis (ED25 , ED50 , and ED75 ), the duration of amantadine was longer (P < 0.01) than that of mepivacaine on spinal motor, proprioceptive, and nociceptive block. Our preclinical data demonstrated that amantadine was less potent than mepivacaine at producing spinal anesthesia. The spinal block duration produced by amantadine was greater than that produced by mepivacaine. Both amantadine and mepivacaine produced a markedly nociceptive-specific blockade.