Transdermal Delivery
Drug administration through the intact skin into systemic circulation, typically via a patch or specialised formulation. The skin's stratum corneum is a major barrier to peptide absorption. Emerging technologies including microneedle patches and iontophoresis aim to overcome this challenge.
Technical Context
The stratum corneum presents the rate-limiting barrier — its brick-and-mortar structure (corneocytes in a lipid matrix) has permeability limited to small (<500 Da) lipophilic molecules. Since most peptides are large and hydrophilic, passive transdermal delivery is extremely inefficient. Active enhancement technologies include: microneedle arrays (painlessly pierce the stratum corneum, creating micro-channels for peptide diffusion — dissolving microneedles release peptide as they dissolve in dermal fluid), iontophoresis (electrical current drives charged peptide molecules through the skin), sonophoresis (ultrasound temporarily disrupts the stratum corneum), and chemical permeation enhancers. Several transdermal peptide delivery systems are in clinical development but none have reached widespread approval.