Prolonged local anesthetic effect of bupivacaine liposomes in rats

The purpose of the present study was to develop a sustained release local anesthetic formulation that would localize the local anesthetic drug at target sites and produce a prolonged sensory block by a single usual dose. Bupivacaine aqueous solution was encapsulated in multilamellar vesicles (MLV) of liposomes by mechanical shaking method. Wister rats (240 +/- 30 g body weight) were given an injection of 0.2 mi liposomal bupivacaine (5 mg/ml), bupivacaine solution (5 mg:ml) or blank liposome. The duration of sensory analgesia was quantified using the tail flick test, and compared among the three preparations. Blank liposomes did not show any sensory block action. The duration of sensory block and the antinociceptive index (AI) in the rats treated with liposomal bupivacaine were 447 +/- 19.6 min and 54 +/- 5%, respectively, and that in the rats treated with bupivacaine solution was 87 +/- 6.7 min and 30 +/- 8%, respectively. Liposomal bupivacaine significantly (p < 0.01) prolonged the duration and enhanced the intensity of local anesthesia as compared with bupivacaine solution. The results suggest that liposomes are candidates for the formulation of ultra-long lasting local anesthetics with enhanced effect in a single normal dose. (C) 1998 Elsevier Science B.V. All rights reserved.