Intrathecal pramoxine causes long-lasting spinal sensory and motor block in rats.

OBJECTIVES: The objective of this experiment was to investigate spinal anaesthetic effects of pramoxine and its comparison with bupivacaine, a long-lasting local anaesthetic.

METHODS: After intrathecal injection, three neurobehavioural assessments, which consisted of nociceptive, proprioceptive and motor block, were constructed in rats. The effects of bupivacaine and pramoxine (four doses of each drug) in a dose-related manner were conducted to obtain the ED50 (50% effective dose). Pramoxine potency and duration at provoking spinal nociceptive, proprioceptive and motor block were compared with those of bupivacaine.

KEY FINDINGS: We manifested that pramoxine provoked dose-relatedly spinal blockades of nociception, proprioception and motor function. Based on the ED50 , the rank potency at producing spinal nociceptive, proprioceptive and motor block was bupivacaine (0.90 (0.82-1.02), 1.00 (0.92-1.08) and 1.16 (1.02-1.34) μmol/kg) greater (P < 0.01 for the differences) than pramoxine (15.47 (14.04-17.05), 16.46 (15.06-17.99), and 17.77 (16.48-19.15) μmol/kg). The spinal block duration created by bupivacaine was not predominantly different (P > 0.05 for the differences) from that created by pramoxine at the equipotent doses (ED75 , ED50 and ED25 ).

CONCLUSIONS: Our preclinical experiment indicated that pramoxine elicited a dose-related spinal block, was less potent than bupivacaine and had a similar duration of spinal block compared with bupivacaine.