Efficient sweat induction and pilocarpine delivery on the forearm but not the palm using coated microneedles in humans

• Pilocarpine-coated microneedles were developed for sweat induction in humans. • Efficacy was validated against iontophoresis on the forearm. • High test-retest reliability was confirmed on the forearm. • Effectiveness and reliability were reduced in thick skin regions like the palm. • A promising method to induce sweat for evaluating sweating function. The modulation of sweating via pharmacologic manipulation is widely employed in research, diagnostics, and therapeutics of the sweating response. However, its application requires a user-friendly drug delivery system that can be applied to various skin regions with varying permeability. In this study, we evaluated the effectiveness of a new pilocarpine-coated microneedle array for sweat induction on the forearm (non-glabrous, thin skin) and palm (glabrous, thick skin) in healthy young adults. The pilocarpine-coated microneedle arrays induced sweating on the forearm, which was highly consistent with responses observed using the iontophoretic application of pilocarpine. Further, it offered superior controlled delivery capabilities along with excellent reproducibility. However, its effectiveness was reduced on the palm, highlighting the possible roles of mechanical, anatomical, and physiological properties in microneedle-mediated drug delivery. Altogether, we show that pilocarpine-coated microneedle arrays is an effective method to induce sweating in thin, non-glabrous skin.