ABSTRACT
Objective:To evaluate the efficacy of bupivacaine pamoate for sciatic nerve block in rats.Methods:Forty-eight SPF healthy male Sprague-Dawley rats, weighing 300-400 g, were divided into 6 groups using a random number table method: bupivacaine pamoate vehicle group (group VE), bupivacaine HCl group (group BH), liposomal bupivacaine group (group BL), low-dose bupivacaine pamoate group (group HL), moderate-dose bupivacaine pamoate group (group HM) and high-dose bupivacaine pamoate group (group HH), with 8 animals in each group.In VE, BH, BL, HL, HM and HH groups, bupivacaine pamoate vehicle 0.4 ml, bupivacaine HCl solution 0.4 ml, liposomal bupivacaine suspension 0.4 ml, and 1, 3 and 10 mg/ml bupivacaine pamoate suspension 0.4 ml were injected around the left sciatic nerve, respectively.The thermal paw withdrawal latency were measured before administration (T 0) and at 0.5, 1.5, 3, 5, 8, 12, 16, 24 and 48 h after injection (T 1-9). The percentage of maximum possible effect (MPE) of thermal paw withdrawal latency was calculated, and motor function score was simultaneously performed to evaluate the efficacy of sensory and motor block.Five and three rats in each group were sacrificed at 2 and 7 days after administration (T 9, 10), respectively, and the sciatic nerve at the injection site and the surrounding muscle tissues were harvested for microscopic examination (with a light microscope) after Luxol fast blue and HE staining.Nerve damage and inflammatory responses were assessed and scored to evaluate neurotoxicity. Results:Compared with group VE, the MPE was significantly increased at T 1-4 in group HL, at T 1-8 in group HM and at T 1-8 in group HH, the motor function scores were decreased at T 1-4 in group HL, at T 1-5 in group HM and at T 1-7 in group HH ( P<0.05), and no significant change was found in inflammatory response scores for the sciatic nerve and surrounding muscles at each time point in HL, HM and HH groups ( P>0.05). Compared with group BH, the MPE was significantly increased at T 3-8, motor function scores were decreased at T 3-5, and inflammatory response scores for the muscles around the sciatic nerve were decreased at T 9 in group HM ( P<0.05). Compared with group BL, the MPE was significantly increased at T 3-7, motor function scores were decreased at T 4, 5, and inflammatory response scores for the sciatic nerve and surrounding muscles were decreased at T 9 in group HM ( P<0.05). The nerve damage score was 0 in the six groups. Conclusion:Bupivacaine pamoate can block the sciatic nerve of rats, the duration of block is prolonged with the increase in the concentration, and the duration of motor block is not longer than that of sensory block; compared with the same concentration and equal volume of bupivacaine HCl and liposomal bupivacaine, bupivacaine pamoate produces longer duration of sciatic nerve block and less neurotoxicity.