Towards a better mechanistic comprehension of drug permeation and absorption: Introducing the diffusion-partitioning interplay

The process of passive drug absorption from the gastrointestinal tract is still poorly understood and modelled. Additionally, rapidly evolving field pharmaceutics demands efficient, affordable reliable in vitro tools for predicting vivo performance. In this work, we combined established methods quantifying diffusivity (localized UV-spectroscopy) permeability (Permeapad® plate) order to gain a better understanding role unstirred water layers (UWLs) absorption. effect diffusion/permeability media composition viscosity on apparent permeation resistance (Rapp) model drugs caffeine (CAF) hydrocortisone (HC) were tested evaluated by varying type concentration viscosity-enhancing agent – glycerol or poly(ethylene glycol) (PEG) with different average molecular weights. For all types media, increased lead reduction but could not alone explain observed effect, which was attributed intermolecular polymer-drug interactions. both drugs, smaller hydrophilic agents (glycerol PEG 400) had larger influence than ones (PEG 3350 6000). results highlighted UWL as an additive barrier indicated that diffusion through rate-limiting step CAF’s permeation, whilst HC partition-driven process.