Characterization of drug particle delivery to ex vivo human skin by needle-free powder injection systems

摘要

The PowderJect~direct R needle-free injector delivers drugs in dry powder form into the skin by accelerating the particles to high velocity using pressurised helium gas (1). Relationship between particle size, pressure and bioavailability (2,3) as well as between dosage and plasma concentration were previously demonstrated (4). However, the barrier function of skin in this case has to be hypothetically regarded as different to the case of needle-free injection of liquids and even more different to application by transdermal diffusion. thus, for an better understanding of the relationship between drug application, skin structures and bioavailability, studies on excised human skin provide the most authentic conditions with respect to penetrability and mechanical resistance. For investigations of extent and depth of drug penetration a crystalline model compound was chosen, as it should easily be recovered from the biological material and previous pharmacokinetical studies on needle-free powder injection were mostly done with pure crystalline compounds (2,3). tape-stripping, as it is a common method to remove the stratum corneum, offers a first step towards characterisation of the barrier function of the particular skin layers. It is a simple way to demonstrate, whether or not an intact stratum corneum substantially affects the particle penetration.