Accelerating Topical Anaesthesia Using Microneedles

Background/Aims: Topical anaesthetics reduce pain during venous access procedures in children. However, clinical use is hindered by a significant anaesthetic onset time. Restricted diffusion of the topical anaesthetic through the stratum corneum barrier is the principal reason for the delayed onset. Microneedles can painlessly pierce the skin. This study evaluated microneedle pre-treatment of ex vivo human skin as a means to increase the rate of tetracaine permeation, in order to accelerate the onset of anaesthesia. Methods: Franz-type diffusion cells were used to determine permeation of a commercial tetracaine formulation, Ametop gel, through human skin epidermis. Microneedle-assisted permeation was compared to untreated epidermis. Upon completion of the permeation studies, the epidermal membranes were visually characterised. Results: At 30 min, 5.43 µg/cm 2 of tetracaine had permeated through the untreated membrane compared to 12.13 µg/cm 2 through the microneedle-treated membrane. Insertion of a hypodermic needle created a large single channel in the epidermis (approx. 4,250 μm 2 ) whilst the punctured surface area following microneedle treatments was estimated to be 75,000 μm 2 . Conclusion: Pre-treatment of skin with microneedles significantly enhances the permeation of tetracaine. Microneedles have the potential to more than halve the onset time for anaesthesia when applying Ametop gel.