Formulation, Characterization, and Evaluation of Benzocaine Phospholipid-Tagged Lipospheres for Topical Application

The objective of the present study is to incorporate and evaluate benzocaine in the lipid microstructured systems for its drug delivery and pharmacodynamic potential. Drug lipospheres were prepared to improve the local anesthetic performance using different combinations of lipids/oils (e.g., castor oil, arachis oil, and soyabean oil), with surfactant (lecithin) and cosurfactant (polyoxyethylene sorbitan monooleate). Following selection of suitable oil phase, surfactant, and cosurfactant, the composition of the lipospheres was optimized to obtain maximum drug loading and sustainability. The formulations were further evaluated for ex vivo drug permeation and retention behavior in mice skin. The optimum formulation with the highest skin permeation rate and retention consisted of benzocaine (0.1 g), soybean oil (25 g), lecithin (0.15 g), and Tween 80 (0.025 g) with aqueous: non-aqueous phase volume ratio as 5:1. The onset of anesthetic effect in rabbit cornea was found to be 6 min with lipospheres vis-à-vis 17 min and 13 min, observed with the classical emulsion system and plain drug solution, respectively. Analogously, the anesthetic effect lasted much longer for 53 min with lipospheres in comparison to 11 min and 18 min with classical emulsion and plain drug solution, respectively. Another study on human volunteers using pin-prick method also corroborated improved pharmacodynamic activity of lipospheres over classical conventional emulsion system. Accordingly, the in vivo results were quite in accordance with the ex vivo findings, as the lipospheres exhibited quicker onset of action and longer duration of anesthesia.