Pre-clinical evaluation of new dibucaine formulations for preventive analgesia.

We have previously developed ammonium sulphate gradient loaded liposomes to encapsulate dibucaine. Thus, the purpose of this study was to evaluate the pre-clinical safety and effectiveness of this novel ionic liposomal formulation of dibucaine (DBC), as described in previous work. Effectiveness was evaluated in vivo on Wistar rats (n = 8) that received plain DBC or liposomal DBC (DBCLUV). Control empty liposomes (without DBC) or saline were also used as control. Sciatic nerve block was performed using the formulations or controls (0.4 mL). A hindpaw incision-based postoperative pain model was used to evaluate mechanical hypersensitivity with von Frey filaments. To verify antiinflamatory activity protein levels of TNF-α, IL-1β, substance P and CGRP were measured by ELISA in the hindpaw tissue after 1 and 6 hours of the incision. To corroborate drug safety, sciatic nerve Schwann cell cultures were treated with the aforementioned formulations and assessed for cell viability (MTT assay) and death (flow cytometry assay). Histopathology of the tissues surrounding the sciatic nerve region was also assessed 2 and 7 days after treatment. All animals presented post incisional hypersensitivity and DBCLUV showed longer analgesic effect (p < 0.001). DBCLUV reduced TNF-α and CGRP levels (p < 0.05). Histopathological evaluation showed greater inflammatory reaction after the administration of control liposomes when compared to DBC (p < 0.05). There was no difference in Schwann cell viability and death between plain and encapsulated DBC. DBCLUV was safe and enhanced anaesthesia duration due to slow release of dibucaine from ammonium sulphate gradient loaded liposomes.