PROLONGATION OF SPINAL-ANESTHESIA WITH BUPIVACAINE-LOADED (DL-LACTIDE) MICROSPHERES

There is considerable interest in developing a sustained-release local anesthetic formulation to provide long-lasting anesthesia and to decr ease systemic toxicity. Bupivacaine (B), 10 mg, loaded in two differen t types of polylactide microspheres (PLA1 and PLA2) was evaluated afte r spinal injection and compared with plain bupivacaine (pB), 2 mg. Exp eriments were performed in six New Zealand rabbits. Duration of motor block was significantly prolonged for PLA1 compared to pB (177.5 +/- 7 9.5 min vs 44.6 +/- 18.0 min; P < 0.05), as well as for the recovery t ime (545.0 + 299.6 min vs 44.2 +/- 21.5 min; P < 0.05). The duration a nd recovery were not prolonged for PLA2. Systemic release of B after i ntrathecal injection was measured from blood samples by using high-per formance liquid chromatography. There was no significant difference in maximum B plasma concentration between pB and PLA1 (326 +/- 81 mg/mL vs 321 +/- 57 ng/mL). The time taken to reach the maximum plasma conce ntration (6.6 +/- 2.6 min vs 41.7 +/- 20.4 min; P < 0.05) was signific antly different. This study demonstrated that the use of bupivacaine-l oaded (DL-lactide) microspheres can prolong spinal motor block.