Percutaneous Absorption & Enhancers for Oil Formulation of Benzocaine by Melting Point Depression/Eutectic System

The search for a safe and effective topical anesthetic preparation for minor dermal procedures such as venipuncture, intravenous cannulation, vaccination, and circumcision has been partially successful with the introduction of a eutectic mixture of lidocaine and prilocaine (EMLA) in an emulsified topical cream. Direct emulsification of the active ingredients without prior dissolution provides the maximum thermodynamic activity in the external phase. Due to the low permeability through the stratum corneum (SC) and the necessity of high local drug concentration at the receptor site, topical anesthetic formulations are generally not effective in inducing local anesthesia through intact skin. The improved efficacy of EMLA, as compared to conventional topical formulations, can be attributed to the high drug concentration in the oil phase.

Emulsification of eutectic oils is a promising approach to improving both transdermal delivery drugs (TDD) and topical drugs (TD) of therapeutic agents. The candidacy of many therapeutic agents for topical administration is limited by the ability of the drugs to permeate the skin, in particular the rate-limiting barrier of the SC. In traditional methods of preparing anesthetic creams, the active ingredients simply are dissolved in inert pharmaceutical oils and then emulsified. Due to the limited solubility of drugs in these oils, such methods often result in low concentrations. In comparison, the melting point depression method allows the oil phase to contain primarily the melted drug itself.