DEVELOPMENT OF LIPID NANOCAPSULES CONTAINING BENZOCAINE AND EUGENOL FOR TOPICAL DENTAL APPLICATION

Benzocaine (BZC), one of the earliest local anesthetic agents is synthesized trough Fischer esterification of para-aminobenzoic acid (PABA), in ethanol. Due to the lack of a terminal amino group (which is present in other local anesthetics) BZC remains neutral at pH > 3 and exhibits low water solubility, what restricts its use to topical applications. BZC is extensively used for mucosal antinociception in dental procedures. However, BZC-associated systemic toxicity arises from methemoglobin formation by PABA, leading to functional anemia and tissue hypoxia. Eugenol (EUG) is another lipophilic agent widely used in dentistry for its anesthetic and bioactive properties. Our strategy was to develop a lipid-based drug delivery system (DDS), capable of co-encapsulating BZC and EUG to prolong buccal anesthesia and reduce BZC-associated toxicity. Lipid nanocapsules (LNC), consisting of oily core surrounded by surfactant layer and prepared by the phase-inversion technique (Heurtault et al, 2002), was chosen as the DDS. The relatively high content of non-ionic surfactants produces low-sized nanocapsules (< 100 nm), suitable for skin permeation / topical applications. Formulation of LNC containing 0.5% BZC and 1.0% EUG was prepared by Design of experiments (DoE), by changing the composition and proportion of triglycerides and surfactants toward nanoparticles of small size, low polydispersity (PDI) and Zeta potentials (ZP) far from zero, as measured by DLS, electrophoretic mobility. To date, the optimized (LNC_BZC-EUG) formulation has achieved 6 months of shelf-stability, with particles of 91.30 +/- 0.95 nm, PDI = 0.053 +/- 0.017, ZP = -12.4 +/- 3.41 mV and high drug encapsulation efficiency (99.8% for BZC and 99.7% for EUG, as measured by HPLC). Preliminary in vitro essays, over 3T3 fibroblast cells in culture revealed that encapsulation did not decrease the intrinsic cytotoxicity of BZC, probably because of the toxicity imposed by the high levels of surfactants in the LNC. The IC₅₀ values varied from 3.70 mM (free BZC) to 0.21 mM (LNC_BZC) and 0.60 mM (LNC_BZC-EUG) since eugenol has also exhibited some toxicity: IC₅₀ = 1.09 mM (free EUG) and 0.54 mM (LNC_EUG). Further characterization experiments using diffraction techniques (SANS and SAXS) are underway to analyze the internal organization of the LNC particles.