Lidocaine permeation from a lidocaine NaCMC/gel microgel formulation in microneedle-pierced skin: vertical (depth averaged) and horizontal permeation profiles
To demonstrate rapid (~1 min) lidocaine delivery using 3M’s solid microstructured transdermal system (sMTS) for prolonged, local analgesic action. Polymeric microneedles were fabricated via injection molding and then dip-coated using an aqueous lidocaine formulation. The amount of lidocaine coated onto the microneedles was determined by high performance liquid chromatography (HPLC). To assess drug delivery and dermal pharmacokinetics, lidocaine-coated microneedles were inserted into domestic swine. Skin punch biopsies were collected and analyzed to determine lidocaine concentration in skin using HPLC-mass spectrometry (LC-MS). Commercial lidocaine/prilocaine EMLA (Eutectic Mixture of Local Anesthetic) cream was used as comparative control. Lidocaine dissolves rapidly off the microneedles and into skin such that the 1-min wear time achieves or exceeds lidocaine tissue levels needed to cause analgesia. This therapeutic threshold (100 ng/mg) was estimated by measuring the total amount of lidocaine and prilocaine in skin following a 1 h EMLA application. When co-formulated with 0.03 wt% vasoconstrictor-epinephrine, the concentration of lidocaine in tissue was maintained above 100 ng/mg for approximately 90 min. 3M’s sMTS can be used to provide rapid delivery of lidocaine for local analgesia up to 90 min.