Efficacy of Liposome-Encapsulated Mepivacaine for Infiltrative Anesthesia in Volunteers

Objectives: Liposomes have been used to prolong the analgesic effect and to decrease the toxic effects of several local anesthetics. Hence, the purpose of this blinded cross-over study was to evaluate the efficacy and the pain sensitivity evoked by commercial and liposome-encapsulated mepivacaine formulations. Methods: Thirty healthy volunteers received a buccal infiltration at the upper-right canine (1.8 mL) at four different sessions, of the following formulations: 2% mepivacaine with 1:100,000 epinephrine (MVC_2%EPI/ Mepiadre®), 3% mepivacaine (MVC_3%/MepiSV®), 2% and 3% liposome-encapsulated mepivacaine (MVC_2%LUV and MVC_3%LUV). Latency period (LP) and pulpal anesthesia (PA) were assessed by an electrical pulp tester and injection discomfort by a Visual Analogue Scale (VAS). Data were analyzed with Tukey-Kramer and Friedman tests (p<0.05). Results: No significant difference was found regarding LP (min) among the formulations (p>0.05). The mean values (±SD) for the duration of PA (min) were 49.33(±16.59), 24(±8.50), 22.33(±9.35) and 31.66(±11.79) for MVC_2%EPI, MVC_3%, MVC_2%LUV and MVC_3%LUV, respectively. PA was longer with MVC_2%EPI when compared with MVC_2%LUV, MVC_3%LUV and MVC_3% (p<0.05). However, the duration of PA was longer with MVC_3%LUV when compared with MVC_2%LUV and MVC_3% (p<0.05). MVC_2%LUV and MVC_3% showed no significant difference regarding PA (p>0.05). The VAS (cm) medians (min-max) were 3.15 (0.3–8.8), 1.65 (0.1–8.0), 1.90 (0–6.7), 1.60 (0–7.8), for MVC_2%EPI, MVC_3%, MVC_2%LUV and MVC_3%LUV, respectively.  MVC_3%LUV showed lower VAS median values than MVC_2%EPI (p<0.05), there were no significant differences among the others formulations. Conclusion: Liposome-encapsulated 3% mepivacaine showed longer PA when compared to the same concentration in the commercial formulation. In addition, MVC_2%LUV produced similar duration of anesthesia when compared with the 3% commercial formulation, despite of the 50% decrease in the concentration. Thus, the encapsulation of mepivacaine increased the duration of PA and reduced the injection discomfort caused by the vasoconstrictor-associated formulations. Supported by FAPESP (06/00121-9) and CNpQ.