Prolonged local anesthetic effect of bupivacaine liposomes in rats

The purpose of the present study was to develop a sustained release local a nesthetic formulation that would localize the local anesthetic drug at targ et sites and produce a prolonged sensory block by a single usual dose. Bupi vacaine aqueous solution was encapsulated in multilamellar vesicles (MLV) o f liposomes by mechanical shaking method. Wister rats (240 +/- 30 g body we ight) were given an injection of 0.2 mi liposomal bupivacaine (5 mg/ml), bu pivacaine solution (5 mg:ml) or blank liposome. The duration of sensory ana lgesia was quantified using the tail flick test, and compared among the thr ee preparations. Blank liposomes did not show any sensory block action. The duration of sensory block and the antinociceptive index (AI) in the rats t reated with liposomal bupivacaine were 447 +/- 19.6 min and 54 +/- 5%, resp ectively, 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 anesth esia as compared with bupivacaine solution. The results suggest that liposo mes are candidates for the formulation of ultra-long lasting local anesthet ics with enhanced effect in a single normal dose. (C) 1998 Elsevier Science B.V. All rights reserved.