Lidocaine as eutectic forming drug for enhanced transdermal delivery of nonsteroidal anti-inflammatory drugs

Co-application of local anesthetics as lidocaine and nonsteroidal anti-inflammatory drugs (NSAIDs) can enhance local analgesia. Co-formulation of lidocaine with NSAIDs can modulate physicochemical properties like melting point which can affect transdermal delivery. The purpose was to probe lidocaine as eutectic forming drug for enhanced transdermal delivery of a series of NSAIDs with increasing melting points. NSAIDs included ketoprofen, flurbiprofen, aceclofenac, tenoxicam and meloxicam. Each drug was co-ground with lidocaine at increasing molar ratios. The products were characterized by thermal analysis and Fourier-transform infrared (FTIR). Saturated aqueous solutions containing excess of optimum NSAID/lidocaine were evaluated for transdermal delivery with reference to the corresponding saturated aqueous solution of each drug. Thermal analysis and FTIR suggested eutectic system formation. Drugs with lower melting points formed eutectic with smaller proportion of lidocaine. Ketoprofen, flurbiprofen and aceclofenac separated as oily liquid from the saturated aqueous solution of their mixtures with lidocaine. Eutectic mixtures of lidocaine with tenoxicam and meloxicam melted above 50 °C and separated from saturated aqueous solution as solid system. Eutexia increased the transdermal flux of NSAIDs. The extent of increase depended on the melting point of the developed system. The study introduced lidocaine as eutectic co-former for enhanced skin delivery of NSAIDs.