The determination of lidocaine and benzocaine in isopropyl myristate

Abstract

An in vitro membraneless drug release model utilizing an isopropyl myristate (ISM) sink as the acceptor phase has been used for the study of the release of lidocaine and benzocaine from aqueous Pluronic F-127 gels. The use of this system necessitated the development of a quantitative determination of lidocaine and benzocaine m isopropyl myristate solution. Extraction processes were developed to prepare the samples for the appropriate assay procedures: benzocaine by ultraviolet absorption spectrophotometry and lidocaine by gas chromatography. Direct assay of aqueous acid extracts of ISM sink solutions was not possible for benzocaine due to interfering UV absorbing substances. In the case of lidocaine, variable results were obtained from direct injections of the viscous ISM solutions into the GC column. In the latter case, however, direct assay was useful for the estimation of lidocaine concentrations, providing qualitative results for establishing appropriate concentrations necessary for a more complicated, but quantitative method based on a double extraction procedure.