The effect of liposome-encapsulated mepivacaine in biological tissues

Objectives: This study evaluated the effect on biological tissues induced by 2% mepivacaine with 1:100.000 epinephrine (MVC2%EPI, Mepiadre-DFL®), plain 3% mepivacaine (MVC3%, MepiSV-DFL®) and liposomal formulation (LUV) of 2% mepivacaine (MVCLUV). Methods: Two assays were carried out: the “paw oedema” test (POE) and the tissue reaction in the oral mucosa (TR). The anesthetic formulations and controls (positive= 1% carrageenan, negative 1= 0.9% NaCl; negative 2= 5mM LUV) were injected (0.1 mL) in 36 rats in the POE test. Oedema was quantified after 60, 120 and 180 min after administration by plethysmographic measurement (Ugo Basile 7140) of hindpaws. 90 animals were distributed into 5 groups in TR test: 1- needle puncture alone; 2- MVC2%EPI; 3- MVCLUV; 4- LUV and 5- MVC3%. The formulations were infiltrated (0.1 mL) in the first upper-right molar fornix. Samples were analyzed by histological techniques after 6 h, 24 h and 4 days of injections. Inflammatory infiltration was scored and analyzed by KrusKal–Wallis (Student-Newman-Keuls) test. POE was analyzed by ANOVA (Tukey-Kramer). Significance level was set at 5%. Results: POE showed that none of anesthetics/controls (0.11 to 0.01 mL) induced significant (p>0.05) oedema volume when compared to saline (0.06 to 0.11 mL) after 60, 120 and 180 min. Carrageenan induced higher (0.54 to 0.63 mL) oedema volumes (p<0.01) when compared to the anesthetics/controls. A low-intensity inflammatory reaction in the oral mucosa was found after the injection of liposome formulation in comparison to MVC2%EPI (p<0.05), but not with MVC3% (p>0.05) considering each period of time. Conclusion: We concluded that the liposome formulation of mepivacaine induced less inflammatory reaction in oral mucosa than the commercial formulation with epinephrine. Supported by CNPq and FAPESP (#2006/00121-9).