Anesthetic Efficacy of Liposomal Articaine Formulation in Rats

Objective: This study evaluated the anesthetic efficacy of two liposomal formulations of articaine (3% and 4%) in rats. Methods: Infraorbital nerve block (IONB) and inferior alveolar nerve block (IANB) designs were used. For each experiment, 48 animals were divided into 6 groups (n=8), which received the injection of one of the following formulations, in the right side. Group 1: 4% articaine/1:100,000 epinephrine; Group 2: 4% liposomal articaine; Group 3: 3% liposomal articaine; Group 4: 4% articaine; Group 5: 3% articaine and Group 6: 4mM liposome. The left side received saline (control). For the IONB, 0.1mL of each formulation was injected near the infraorbital foramen. The duration of soft tissue anesthesia was evaluated by pinching the upper lip, every 5 minutes, until the first sign of aversive response. For the IANB, 0.2mL of the formulations was injected near the mandible foramen. Onset and duration of pulpal anesthesia were evaluated (electrical pulp tester). Data were submitted to ANOVA (alpha=5%). Results: Group 6 promoted no anesthesia. Soft tissue anesthesia of groups 1 (145.6±30min), 2 (128.1±37.1min) and 3 (123.8±34.4min) showed similar duration (p>0.05) which were longer (p<0.05) than groups 4 (68.8±25.2min) and 5 (61.25±22.5min). Group 1 (2.3±0.7min) showed the shortest onset of pulpal anesthesia and there was no difference among groups 2 (4.8±2.0min), 3 (5.0±1.9min), 4 (3.3±1.5min) and 5 (4.3±2.0min). Group 1 (38.8±7.9min) promoted longer duration of pulpal anesthesia followed by groups 2 (24.4±6.8min) and 3 (23.8±5.8min). Concerning duration of pulpal anesthesia, no difference was found between groups 2 and 3 and groups 4 (16.3±6.4min) and 5 (16.3±7.9min). Conclusion:Liposome encapsulation prolonged anesthetic effects of articaine when compared to plain solution. The epinephrine-containing solution showed longer pulpal anesthesia duration than liposomal formulations. Further studies must be performed in order to improve the anesthetic efficacy of liposomal 3% articaine formulation. Supported by FAPESP (#2006/00121-9).