In vivo assessments of microneedle arrays and iontophoresis of pilocarpine in human palmar sweating.

Emotional stress-induced sweating in glabrous skin of the palm and sole, which can be excessive in some individuals (hyperhidrosis), can negatively impact quality of life. Understanding the mechanisms underlying this response can lead to potential treatments. Transdermal iontophoresis is a method to administer ionized sudorific agents to sweat glands within the dermis. However, due to the reduced permeability of pharmacological agents in thicker skin such as the palms, this technique has been shown to be less effective when applied in thicker skin. Thus, we assessed the effectiveness of pre-treating palmar skin with microneedles to create micropores on the stratum corneum of the palm to enhance the iontophoretic delivery of pilocarpine to modulate sweat production. On three separate sessions, we applied microneedles (0.78 cm2, 190 needles with a length of 875 μm) to palm and forearm skin sites. Upon removal of the microneedles, we assessed the number of perforations colored by gentian violet in the forearm only (Protocol 1, n = 20), skin barrier function indexed by transepidermal water loss (TEWL) (Protocol 2, n = 21), and sweating induced by the iontophoretic application of 1% pilocarpine (Protocol 3, n = 43). Briefly, we measured 1) ∼172 dyed spots on forearm skin, 2) an increase of ∼300% and ∼ 900% in TEWL on palm and forearm skin, respectively; and 3) a 2-fold increase in sweating on the palm only following the application of the microneedles. Notably, the microneedle array failed to enhance pilocarpine delivery at either the palm or forearm skin sites. We showed the application of a microneedle array enhanced skin permeability and sweat production on the palm without a concomitant increase in pilocarpine delivery. Therefore, this methodology could be employed to advance our understanding of the causes and treatments of medical conditions such as hyperhidrosis.