Promazine and chlorpromazine for prolonged spinal anesthesia in rats

Though promazine and chlorpromazine elicited cutaneous anesthesia, no study of spinal anesthesia with chlorpromazine and promazine has been reported. This study was to examine whether chlorpromazine and promazine produce spinal anesthesia. Using a rat model via intrathecal injection, we tested spinal blockades of motor function and nociception by promazine, chlorpromazine or bupivacaine, and so were dose-response studies and durations. We demonstrated that chlorpromazine and promazine elicited dose-dependent spinal blockades in motor function and nociception. On the 50% effective dose (ED(50)) basis, the rank of potency of these drugs was bupivacaine>promazine>chlorpromazine (P<0.05 for the differences). On an equipotent basis (25% effective dose [ED(25)], ED(50), and ED(75)), the block duration caused by chlorpromazine or promazine was longer than that caused by the long-lasting local anesthetic bupivacaine (P<0.01 for the differences). Chlorpromazine and promazine, as well as bupivacaine, showed longer duration of sensory block than that of motor block. Our data reported that intrathecal promazine and chlorpromazine with a more sensory-selective action over motor blockade had less potent and longer-lasting spinal blockades when compared with bupivacaine.