2-Adamantanamine produces prolonged spinal block in rats

We aimed to investigate the local anesthetic effect of 2-adamantanamine in spinal anesthesia. The dose–response curves were constructed after intrathecally injecting the rats with five doses of 2-adamantanamine and a common local anesthetic mepivacaine. The quality and duration of 2-adamantanamine at producing spinal nociceptive, proprioceptive and motor block were compared with that of mepivacaine. We revealed that 2-adamantanamine provoked spinal nociceptive, proprioceptive and motor block dose-dependently. On the 50% effective dose (ED₅₀) basis, the rank of potency was mepivacaine > 2-adamantanamine at producing spinal nociceptive, proprioceptive and motor block (p < 0.05 for the differences). 2-Adamantanamine, but not mepivacaine produced more nociceptive block than motor block (p < 0.05). At the equianesthetic doses (ED₇₅, ED₅₀, and ED₂₅), the nociceptive block duration caused by 2-adamantanamine was greater than that caused by mepivacaine (p < 0.01 for the differences). These preclinical data showed that 2-adamantanamine is less potent than mepivacaine, while 2-adamantanamine provokes greater duration of spinal nociceptive block than mepivacaine. Furthermore, 2-adamantanamine demonstrates a more nociceptive-selective action over motor block.