PollenGuard - Crosslinked Polydimethylsiloxane Networks as Transdermal Vehicles for Loratadine: Formulation, Diffusion Kinetics and Structural Integrity

Seasonal pollen allergies affect nearly 30% of the population and are treated with oral antihistamines like loratadine, whose hepatic metabolism limits bioavailability to 40%. Transdermal delivery offers an alternative that increases systemic bioavailability. Here, loratadine-loaded patches were developed from crosslinked polydimethylsiloxane (PDMS) networks, synthesized via either platinum-catalyzed hydrosilylation (AD) or tin-catalyzed condensation (E). The former adds hydride across vinyl groups, while the latter condenses silanol with alkoxysilane groups releasing alcohol, yielding Si–C or Si–O–Si crosslinks. Sixteen formulations were prepared, varying the silicone matrix (Gumosil AD/E), co-solvent (PEG/PG), thickness (400/800 µm), and penetration enhancer presence. FTIR confirmed loratadine's integrity after crosslinking. Diffusion was assessed in vitro and ex vivo on porcine skin, where the standard addition method overcame matrix interference, revealing a release of 4.89 mg of loratadine over 15 h for the optimized 400 µm Gumosil E/PEG formulation. Fluorescence microscopy with Nile Red confirmed deep penetration to the subcutaneous layer.