Liposomal formulations of prilocaine, lidocaine and mepivacaine prolong analgesic duration.

PURPOSE A laboratory investigation was undertaken to compare the in vivo antinociceptive effects of 2% liposomal formulations of prilocaine (PLC), lidocaine (LDC) and mepivacaine (MVC) compared to plain solutions of each of these three local anesthetics. METHODS Large unilamellar vesicles were prepared by extrusion (400 nm), at pH 7.4. The membrane/water partition coefficients were obtained from encapsulation efficiency values, after incorporation of each local anesthetic to the vesicles. The anesthetic effect of each liposomal formulation was compared to the respective local anesthetic solution in water, using the infraorbital nerve-blockade test, in rats. RESULTS The partition coefficients were: 57 for PLC, 114 for LDC and 93 for MVC. In vivo results showed that local anesthetic-free liposomes, used as control, had no analgesic effect. In contrast, the encapsulated formulations induced increased intensities of total anesthetic effect (35.3%, 26.1% and 57.1%) and time for recovery (percentage increases of 30%, 23.1% and 56%), respectively, for PLC, LDC and MVC when compared to the plain solutions (P < 0.01). CONCLUSIONS These results indicate that liposomes provide effective drug-delivery systems for intermediate-duration local anesthetics. Mepivacaine was affected to the greatest extent, while LDC benefited least from liposome encapsulation, possibly due to greater vasodilatory properties of LDC.