Physicochemical studies of a novel two-phase melt system of benzocaine
Fields, Latosha Nicole
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Drug concentrations, thermodynamic activity, and solubility are significant factors in determining absorption of topical and transdermal drugs across the skin barrier. With the addition of melting point depression agents to some crystalline compounds, the solid states of drugs can spontaneously transform into an oily state at ambient room temperature. The high concentration of drug in the oil phase will enhance membrane transport of the drug. Benzocaine, a local anesthetic, is used as the model solid compound in the present study. Menthol is used to form a binary eutectic system with benzocaine. The highest concentration of benzocaine attainable in the oil at ambient temperature was 40% (w:w) with the presence of menthol at 60% (w:w). An aqueous solution of isopropyl alcohol (IPA) was used as a secondary agent for depressing the melting point of benzocaine. In a 20% aqueous IPA solution, benzocaine can be transformed into an oil at 25 o C, forming a two-phase melt system (TMS). This system contains two phases: a homogeneous oil phase and a homogeneous aqueous phase. Using menthol and aqueous IPA solution concurrently results in the melting point of benzocaine being further depressed and the highest benzocaine concentration approaching as much as 80% (w:w) of the oil phase, with this concentration of benzocaine being the highest in a liquid state at ambient temperature.